A A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Absorber: A material that readily absorbs photons to generate charge
carriers (free electrons or holes).
Absorbers: Dark-colored objects that soak up heat in solar collectors.
Absorption coefficient: The factor by which photons are absorbed as they
travel a unit distance through a material.
Acceptor: A dopant material, such as boron, which has fewer outer shell
electrons than required in an otherwise balanced crystal structure, providing a
hole, which can accept a free electron.
Accessible: (As applied to wiring methods) Capable
of being removed or exposed without damaging the building structure or finish,
or not permanently closed in by the structure or finish of the building.
Accessible: (as applied to equipment) Admitting
close approach: not guarded by locked doors, elevation, or other effective
means. (see Accessible, Readily)
Accessible, Readily: (Readily Accessible) Capable of
being reached quickly for operation, renewal, or inspections, without requiring
those to whom ready access is requisite to climb over or remove obstacles or to
resort to portable ladders, chairs, etc.
Actinide: an element with atomic number of
89 (actinium) or above.
Activation product: A radioactive isotope
of an element (e.g., in the steel of a reactor core) which has been created by
neutron bombardment.
Active solar heater: A solar water or space-heating system that moves heated
air or water using pumps or fans.
Affected employee: An employee whose job
requires him or her to operate or use a machine or equipment on which
servicing or maintenance is being performed under lockout or tagout, or
whose job requires him or her to work in an area in which such servicing or
maintenance is being performed.
![Air Circuit Breaker Air Circuit Breaker](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/air_circuit_thumb.jpg) |
Air Circuit Breakers: These are used to interrupt circuits while current flows
through them. Compressed air is used to quench the arc when the connection is broken.
|
Air mass: The ratio of the mass of atmosphere in the actual observer-sun path
to the mass that would exist if the observer was at sea level, at standard
barometric pressure, and the sun was directly overhead. Note: (sometimes called
air mass ratio).
Air mass 1.5 (AM1.5) standard reference spectrum: The solar spectral
irradiance distribution (diffuse and direct) incident at sea level on a
sun-facing 37-degree tilted surface. The atmospheric conditions for AM1.5 are: precipitable water vapor, 14.2 mm; total ozone, 3.4 mm; turbidity (base e,
lambda=0.5 mm), 0.27. [ASTM E 892, Table 2]
Alternating current: Electric current in which the direction of flow is
reversed at frequent intervals: usually 100 or 120 times per second (50 or 60
cycles per second or 50//60 Hz).
ALARA: As Low As Reasonably Achievable, economic and social factors being
taken into account. This is the optimization principle of radiation protection.
Alpha particle: A positively-charged particle from the nucleus of an atom,
emitted during radioactive decay. Alpha particles are helium nuclei, with 2
protons and 2 neutrons.
Alternative fuels: Solid fuels such as municipal solid waste (MSW),
refuse derived fuel (RDF), biomass, rubber tires, and other combustibles that are used
instead of fossil fuels (gas, oil, or coal) in a boiler to produce steam for the generation
of electrical energy.
Ambient Temperature: The temperature of the air,
water, or surrounding earth. Conductor ampacity is corrected for changes in
ambient temperature including temperatures below 86°F. The cooling effect can
increase the current carrying capacity of the conductor. (Review Section 310-10
of the Electrical Code for more understanding)
Ammeter: An electric meter used to measure current,
calibrated in amperes.
Ampacity: The current-carrying capacity of
conductors or equipment, expressed in amperes.
Ampere (A) or amp: The basic SI unit measuring the quantity of electricity.
The unit for the electric current; the flow of electrons. One amp is 1 coulomb
passing in one second. One amp is produced by an electric force of 1 volt acting
across a resistance of 1 ohm.
Ampere-hour (Ah): Quantity of electricity or measure of charge. (1 Ah = 3600
C [Coulomb])
Amorphous semiconductor: A non-crystalline semiconductor material that has no
long-range order.
Annual solar savings: The annual solar savings of a solar building is the
energy savings attributable to a solar feature relative to the energy
requirements of a non-solar building.
Anthropogenic: Referring to alterations in the environment due to the
presence or activities of humans.
Antireflection coating: A thin coating of a material, which reduces the light
reflection and increases light transmission, applied to a photovoltaic cell
surface.
Armored Cable: A cable provided with a
wrapping of metal, usually steel wires or tapes, primarily for the purpose of
mechanical protection.
Arc-over Voltage: The minimum voltage
required to cause an arc between electrodes separated by a gas or liquid
insulation.
Array: Any number of photovoltaic modules connected together to provide a
single electrical output. Arrays are often designed to produce significant
amounts of electricity.
Atom: A particle of matter which cannot be
broken up by chemical means. Atoms have a nucleus consisting of
positively-charged protons and uncharged neutrons of the same mass. The positive
charges on the protons are balanced by a number of negatively-charged electrons
in motion around the nucleus.
Attendant: An employee assigned to remain
immediately outside the entrance to an enclosed or other space to render
assistance as needed to employees inside the space.
Attenuation: (l) The ratio of the input to
output power levels in a network (transmission line) when it is excited by a
matched source and terminated in a matched load. (2) Power loss in an electrical
system.
Authorized employee: An employee who locks out
or tags out machines or equipment in order to perform servicing or
maintenance on that machine or equipment. An affected employee becomes an
authorized employee when that employee's duties include performing servicing
or maintenance covered under this section.
Automatic circuit re-closer: A self-controlled
device for interrupting and re-closing an alternating current circuit with a
predetermined sequence of opening and re-closing followed by resetting,
hold-closed, or lockout operation.
Autonomous system: A stand-alone Photovoltaic system that has no back-up generating
source. May or may not include storage batteries.
Availability: Describes the reliability of power plants. It refers to the
number of hours the turbines are available to produce power divided by the total
hours in a year.
Avoided cost: The minimum amount an electric utility is required to pay an
independent power producer, under the PURPA regulations of 1978, equal to the
costs the utility calculates it avoids in not having to produce that power
(usually substantially less than the retail price charged by the utility for
power it sells to customers).
B A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Background radiation: The naturally-occurring ionizing
radiation
which every person is exposed to, arising from the earth's crust (including
radon) and from cosmic radiation.
Balance of system: Represents all components and costs other than the
Photovoltaic modules. It includes design costs, land, site preparation, system installation,
support structures, power conditioning, operation and maintenance costs,
indirect storage, and related costs.
Band gap: In a semiconductor, the energy difference between the highest
valence band and the lowest conduction band.
Band gap energy (EG): The amount of energy (in electron volts) required to
free an outer shell electron from its orbit about the nucleus to a free state
and, thus, to promote it from the valence level to the conduction level.
Band-to-band Auger recombination: Recombination of an electron and a hole
occurring between bands of the same energy in which no magnetic radiation is
emitted.
Bare Conductor: A conductor not covered with insulating material.
Barricade: A physical obstruction such as
tapes, cones, or A-frame type wood or metal structures intended to provide a
warning about and to limit access to a hazardous area.
Barrier: A physical obstruction which is
intended to prevent contact with energized lines or equipment or to prevent
unauthorized access to a work area.
Barrier energy: The energy given up by an electron in penetrating the cell
barrier; a measure of the electrostatic potential of the barrier.
Barrier, fire: A continuous membrane, either vertical or horizontal, such as
a wall or floor assembly, that is designed and constructed with specified
fire resistance rating to limit the spread of fire and that will also
restrict the movement of smoke. Such barriers can have protected openings.
Base load: That part of electricity demand which is continuous, and
does not vary over a 24-hour period. Approximately equivalent to the minimum
daily load.
Base power: Power generated by a utility unit that operates at a very high
capacity factor.
Baseline performance value: Initial values of
short-circuit current, open-circuit voltage,
and current at maximum power measured by
the accredited laboratory and corrected to Standard Test Conditions, used to
validate the manufacturer's performance measurements provided with the
qualification modules per IEEE 1262.
![Batteries Batteries](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation_batteries_thumb.jpg) |
Batteries: These are used in the substation control house as a backup to power the
control systems in case of a power blackout. |
Battery energy storage: The three main applications for battery energy
storage systems include spinning reserve at generating stations, load leveling
at substations, and peak shaving on the customer side of the meter. Battery
storage has also been suggested for holding down air emissions at the power
plant by shifting the time of day of the emission or shifting the location of
emissions.
Bayonet Coupling: A quick coupling device for plug and receptacle connectors,
accomplished by rotation of a cam operating device designed to bring the
connector halves together.
Becquerel: The SI unit of intrinsic radioactivity in a material. One
Bq measures one disintegration per second and is thus the activity of a quantity
of radioactive material which averages one decay per second. (In practice, GBq
or TBq are the common units.)
Beryllium Copper (BeCu): A relatively expensive contact material with properties superior to
brass and phosphor bronze. It is recommended for contact applications
requiring repeated extraction and reinsertion because of its resistance to
fatigue at high operating temperatures.
Beta particle: A particle emitted from an atom during radioactive
decay. Beta particles may be either electrons (with negative charge) or
positrons.
BIPV
(Building-Integrated Photovoltaic): A term for the design and integration of
Photovoltaic into the building envelope, typically replacing conventional building materials.
This integration may be in vertical facades, replacing view glass, spandrel
glass, or other facade material; into semitransparent skylight systems; into
roofing systems, replacing traditional roofing materials; into shading
"eyebrows" over windows; or other building envelope systems.
Biological shield: A mass of absorbing material
(e.g., thick concrete
walls) placed around a reactor or radioactive material to reduce the radiation
(especially neutrons and gamma rays respectively) to a level safe for humans.
Blocking diode: A diode used to restrict or block reverse current from
flowing backward through a module. [UL 1703] Alternatively, diode connected in
series to a Photovoltaic string; it protects its modules from a reverse power flow and,
thus, against the risk of thermal destruction of solar cells.
Boiling water reactor (BWR): A common type of light water reactor (LWR),
where water is allowed to boil in the core thus generating steam directly in the
reactor vessel. (cf PWR)
Bonding Jumper: A bare or insulated conductor used
to ensure the required electrical conductivity between metal parts required to
be electrically connected. Frequently used from a bonding bushing to the service
equipment enclosure to provide a path around concentric knockouts in an
enclosure wall - also used to bond one raceway to another.
Boron (B): A chemical element, atomic number 5, semi-metallic in nature, used
as a dopant to make p-semiconductor layers.
Boule: A sausage-shaped synthetic single-crystal mass grown in a special
furnace, pulled and turned at a rate necessary to maintain the single-crystal
structure during growth.
Breakdown Voltage: The voltage at which an insulator or dielectric ruptures, or at
which ionization and conduction take place in a gas or vapor.
Breed: To form fissile nuclei, usually as a result of neutron capture,
possibly followed by radioactive decay.
Breeder reactor: see Fast Breeder Reactor and Fast Neutron Reactor.
British thermal unit (Btu): The amount of heat energy required to raise the
temperature of one pound of water from 60 degrees F to 61 degrees F at one
atmosphere pressure.
Burnable poison: A neutron absorber included in the fuel which
progressively disappears and compensates for the loss of reactivity as the fuel
is consumed. Gadolinium is commonly used.
Burnup: Measure of thermal energy released by nuclear fuel relative to
its mass, typically Gigawatt days per tonne (GWd/tU).
Bushing: An insulating structure, including a
through conductor or providing a passageway for such a conductor, with
provision for mounting on a barrier, conducting or otherwise, for the
purposes of insulating the conductor from the barrier and conducting current
from one side of the barrier to the other.
![Bus Support Insulator Bus Support Insulator](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/bus_support_thumb.jpg) |
Bus Support Insulators: These are porcelain or fiberglass insulators that serve to
isolate the bus bar switches and other support structures and to prevent leakage current from flowing through the structure. These
insulators are similar in function of other insulators used in substations and transmission poles and towers. |
Bypass diode: A diode connected across one or more solar cells in a
photovoltaic module such that the diode will conduct if the cell(s) become
reverse biased. [UL 1703] Alternatively, diode connected anti-parallel across a
part of the solar cells of a Photovoltaic module. It protects these solar cells from
thermal destruction in case of total or partial shading of individual solar
cells while other cells are exposed to full light.
C A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Cable: A conductor with insulation, or a
stranded conductor with or without insulation and other coverings
(single-conductor cable), or a combination of conductors insulated from one
another (multiple-conductor cable).
Cable Assembly: A cable with plugs or connectors on each end.
Cable sheath: A conductive protective covering
applied to cables. Note: A cable sheath may consist of multiple layers of
which one or more is conductive.
Cadmium (Cd): A chemical element, atomic number 48, used in making certain
types of solar cells and batteries.
Cadmium telluride (CdTe): A polycrystalline thin-film photovoltaic material.
Calandria: (in a CANDU reactor) a cylindrical reactor vessel which
contains the heavy water moderator. It is penetrated from end to end by hundreds
of calandria tubes which accommodate the pressure tubes containing the fuel and
coolant.
CANDU: Canadian deuterium uranium reactor, moderated and (usually)
cooled by heavy water.
Capacitance: That property of a system of conductors and dielectrics that permits
the storage of electricity when potential difference exists between the
conductors. Its value is expressed as the ratio of quantity of electricity to
a potential difference. A capacitance value is always positive.
![Capacitor Bank Capacitor Bank](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/capacitor_bank_thumb.jpg) |
Capacitor Bank:
An array of capacitors connected into a circuit. Capacitors are used to control voltages supplied to the customer by
eliminating the voltage drop in the system caused by inductive reactive loads. |
Capacity factor: The amount of energy that the system produces at a
particular site as a percentage of the total amount that it would produce if it
operated at rated capacity during the entire year. For example, the capacity
factor for a wind farm ranges from 20% to 35%. Thirty-five percent is close to
the technology potential.
Cathodic protection: A method of preventing oxidation (rusting) of exposed
metal structures, such as bridges and pipelines, by imposing between the
structure and the ground a small electrical voltage that opposes the flow of
electrons and that is greater than the voltage present during oxidation.
Cell: The basic unit of a photovoltaic system.
Cell barrier: A very thin region of static electric charge along the
interface of the positive and negative layers in a photovoltaic cell. The
barrier inhibits the movement of electrons from one layer to the other, so that
higher-energy electrons from one side diffuse preferentially through it in one
direction, creating a current and thus a voltage across the cell. Also called
depletion zone, cell junction, or space charge.
Cell junction: The area of immediate contact between two layers (positive and
negative) of a photovoltaic cell. The junction lies at the center of the cell
barrier or depletion zone.
Central power: The generation of electricity in large power plants with
distribution through a network of transmission lines (grid) for sale to a number
of users. Opposite of distributed power.
Chain reaction: A reaction that stimulates its own repetition, in
particular where the neutrons originating from nuclear fission cause an ongoing
series of fission reactions.
Charge carrier: A free and mobile conduction electron or hole in a
semiconductor.
Chemical vapor deposition (CVD): A method of depositing thin semiconductor
films. With this method, a substrate is exposed to one or more vaporized
compounds, one or more of which contain desirable constituents. A chemical
reaction is initiated, at or near the substrate surface, to produce the desired
material that will condense on the substrate.
Chlorofluorocarbon: A family of chemicals composed primarily of carbon,
hydrogen, chlorine, and fluorine whose principal applications are that of
refrigerants and industrial cleansers and whose principal drawback is the
tendency to destroy the Earth's protective ozone layer.
Circuit: A conductor or system of conductors
through which an electric current is intended to flow.
![Circuit Switchers Circuit Switchers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/circuit_switchers_thumb.jpg) |
Circuit Switchers:
Circuit switchers a a set of switches for redirecting current in a substation.
Circuit switchers provide equipment protection for
transformers, lines, cables, and capacitor banks. They also are used to energize and deenergize capacitor banks and other circuits. |
Cladding: The metal tubes containing oxide fuel pellets in a reactor
core.
Clearance (between objects): The clear
distance between two objects measured surface to surface.
Clearance (for work): Authorization to perform
specified work or permission to enter a restricted area.
Cleavage of lateral epitaxial films for transfer (CLEFT): A process for
making inexpensive GaAs photovoltaic cells in which a thin film of GaAs is grown
atop a thick, single-crystal GaAs (or other suitable material) substrate and
then is cleaved from the substrate and incorporated into a cell, allowing the
substrate to be reused to grow more thin-film GaAs.
Closed Entry Contact: A female contact designed to prevent the entry of a pin or probing
device having a cross-sectional dimension (diameter) greater than the mating
pin.
Coal: A black, solid fossil fuel found in the Earth. Coal is often burned to
make electricity.
Coaxial Cable: A high-band width cable consisting of two concentric cylindrical
conductors with a common axis that is used for high-speed data communication
and video signals.
Cogeneration: The process in which fuel is used to produce heat for a
boiler-steam turbine or gas for a turbine. The turbine drives a generator that
produces electricity, with the excess heat used for process steam.
Combined collector: A photovoltaic device or module that provides useful heat
energy in addition to electricity.
Compact fluorescent lights: Lights that use a lot less energy than regular
light bulbs. We can use compact fluorescent lights for reading lights and
ceiling lights.
Component Lead: The solid or stranded wire or formed conductor that extends from a
component and serves as a readily formable mechanical or electrical connection
or both.
Compressed-air energy storage (CAES): CAES plants use off-peak electrical
energy to compress air into underground storage reservoirs for storage until
times of peak or intermediate electricity demand. Wind power offers a good
opportunity for charging CAES storage. The storage is typically underground in
natural aquifers, depleted oil or gas fields, mined salt caverns, or excavated
or natural rock caverns. To generate power, the compressed air is first heated
by gas burners, then passed through a turbine.
Concentrator: A Photovoltaic module that uses optical elements to increase the amount
of sunlight incident on a Photovoltaic cell.
Concentrating: arrays must track the sun and use only the direct sunlight
because the diffuse portion cannot be focused onto the Photovoltaic cells.
Concentrate: See Uranium oxide concentrate (U3O8).
Concentrator (module, array, or collector): An arrangement of photovoltaic
cells that includes a lens to concentrate sunlight onto small-area cells.
Concentrators can increase the power flux of sunlight hundreds of times.
Concentricity: In a wire or cable, the measurement of the location of the center of
the conductor with respect to the geometric center of the surrounding
insulation.
![Concrete Foundation Concrete Foundation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/concrete_foundation_thumb.jpg) |
Concrete Foundations:
A platform made of concrete that provides a solid stable support for large
equipment. Concrete foundations or pads are laid for all
large equipment, support structures, and control buildings in a substation. |
Conductance: The reciprocal of resistance. It is the ratio of current passing
through a material to the potential difference at its ends.
Conduction band; Conduction level: Energy level at which electrons are not
bound to (orbiting) a specific atomic nucleus but are free to wander among the
atoms. An energy band in which electrons can move freely in a solid, producing a
net transport of charge.
Conductivity: The ability of a material to conduct electric current. It is
expressed in terms of the current per unit of applied voltage. It is the
reciprocal of resistivity.
Conductor: A wire or combination of wires not insulated from one another,
suitable for carrying electric current.
![Conduits Conduits](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/duct_thumb.jpg) |
Conduits: Conduits are hollow tubes running from manhole to manhole in an
underground transmission or distribution system. |
Connection: That part of a circuit that has negligible impedance and that joins
components, devices, etc., together.
Connector: A device providing electrical connection/disconnections. It consists
of a mating plug and receptacle. Various types of connectors include DIP, card
edge, two-piece, hermaphroditic and wire-wrapping configurations. Multiple
contact connectors join two or more conductors with others in one mechanical
assembly.
Connector Discontinuity: An ohmic change in contact resistance.
Connector Insert: For connectors with metal shells, the insert holds contacts in
proper arrangement while electrically insulating them from each other and from
the shell.
Connector Shell: The case that encloses the connector insert and contact assembly.
Shells of mating connectors can protect projecting contacts and provide proper
alignment.
Constant-speed wind turbines: Turbines that operate at a constant rotor
revolutions per minute (RPM) and are optimized for energy capture at a given
rotor diameter at a particular speed in the wind power curve.
Contact, Female: A contact located in an insert or body in such a manner that the
mating contact is inserted into the unit. It is similar in function to a
socket contact.
Contact, Male: A contact located in an insert or body in such a manner that the
mating portion extends into the female contact. It is similar in function to a
pin contact.
Contact Plating: Plated-on metal applied to the base contact metal to provide the
required contact resistance and/or wear resistance.
Contact Resistance: Maximum permitted electrical resistance of pin and socket contacts
when assembled in a connector under typical service use.
Contact Retainer: A device either on the contact or in the insert to retain the
contact.
Contact Size: Defines the largest size wire that can be used with the specific
contact. By specification dimensioning, it also defines the diameter of the
engagement end of the pin.
Contact resistance: The resistance between metallic contacts and the
semiconductor.
Continuity: The state of being whole, unbroken.
Continuous Load: A load where the maximum current is
expected to continue for three hours or more. Rating of the branch circuit
protection device shall not be less tan 125% of the continuous load.
![Control House Control House](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation_control_house_thumb.jpg) |
Control House: The substation control house contains switchboard panels,
batteries, battery chargers, supervisory control, power-line carrier, meters, and relays. The control house provides all
weather protection and security for the control equipment. It is also called a doghouse. |
![Control Panels Control Panels](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/control_panel_thumb.jpg) |
Control Panels:
Control panels contain meters, control
switches and recorders located in the control building, also called a doghouse. These are used to control the substation
equipment, to send power from one circuit to another or to open or shut down circuits when needed. |
Control rods: Devices to absorb neutrons so that the chain reaction in
a reactor core may be slowed or stopped by inserting them further, or
accelerated by withdrawing them.
![Control Wires Control Wires](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/control_cables_thumb.jpg) |
Control Wires: Control wires are installed connecting the control house
control panels to all the equipment in the substation. A typical substation control house contains several thousand feet of conduit
and miles of control wire. |
Conversion: Chemical process turning U3O8 into
UF6 preparatory to enrichment.
Conversion efficiency (cell or module): The ratio of the electric energy
produced by a photovoltaic device (under one-sun conditions) to the energy from
sunlight incident upon the cell.
![Converter Stations Converter Stations](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/converter_thumb.jpg) |
Converter Stations: Converter stations are located at the terminals of a DC
transmission line. Converter stations change alternating current into direct current and invert direct current to alternating current. |
Coolant: The liquid or gas used to transfer heat from the reactor core
to the steam generators or directly to the turbines.
Copper indium diselenide (CuInSe2, or CIS): A polycrystalline
thin-film photovoltaic material (sometimes incorporating gallium (CIGS) and/or
sulfur).
Core: The central part of a nuclear reactor containing the fuel
elements and control devices.
![Coupling Capacitor Coupling Capacitor](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/primary_coupling_capacitor_thumb.jpg) |
Coupling Capacitors: Coupling capacitors are used to transmit
communication signals to transmission lines. Some are used to measure the voltage in transmission lines. |
Critical mass: The smallest mass of fissile material that will support
a self-sustaining chain reaction under specified conditions.
Criticality: Condition of being able to sustain a nuclear chain
reaction.
Current at maximum power (Imp): The current at which maximum power is
available from a module. [UL 1703]
![Current Transformers Current Transformers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/400kv_current_transformer_thumb.jpg) |
Current Transformers: Current transformers can be used to supply information
for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and
distribution circuits or for power transformers. |
Cycle life: Number of discharge-charge cycles that a battery can tolerate
under specified conditions before it fails to meet specified criteria as to
performance (e.g., capacity decreases to 80-percent of the nominal capacity).
Czochralski process: A method of growing large size, high quality
semiconductor crystal by slowly lifting a seed crystal from a molten bath of the
material under careful cooling conditions.
D A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Dangling bonds: A chemical bond associated with an atom on the surface layer
of a crystal. The bond does not join with another atom of the crystal, but
extends in the direction of exterior of the surface.
dc to DC converter: Electronic circuit to convert DC voltages (e.g.,
Photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum
power point tracker (MPPT).
Decay: Disintegration of atomic nuclei resulting in the emission of
alpha or beta particles (usually with gamma radiation). Also the exponential
decrease in radioactivity of a material as nuclear disintegrations take place
and more stable nuclei are formed.
Decommissioning: Removal of a facility (e.g., reactor) from service, also
the subsequent actions of safe storage, dismantling and making the site
available for unrestricted use.
De-energized: Free from any electrical
connection to a source of potential difference and from electric charge; not
having a potential different from that of the earth. Note: The term is used only with reference to
current-carrying parts, which are sometimes energized (alive).
Deep discharge: Discharging a battery to 20-percent or less of its full
charge.
Deflagration: Propagation of a combustion zone through a
fuel-oxidizer mixture at a rate that is less than the speed of sound in the
un-reacted medium and capable of producing a significant increase in
pressure.
Demand Factor: For an electrical system or feeder circuit, this is a ratio of the amount of connected
load (in kva or amperes) that will be operating at the same time to the total
amount of connected load on the circuit. An 80% demand factor, for instance,
indicates that only 80% of the connected load on a circuit will ever be
operating at the same time. Conductor capacity can be based on that amount of
load.
Dendrite: A slender threadlike spike of pure crystalline material, such as
silicon.
Dendritic web technique: A method for making sheets of polycrystalline
silicon in which silicon dendrites are slowly withdrawn from a melt of silicon
whereupon a web of silicon forms between the dendrites and solidifies as it
rises from the melt and cools.
Depletion zone: Same as cell barrier. The term derives from the fact that
this microscopically thin region is depleted of charge carriers (free electrons
and holes).
Depleted uranium: Uranium having less than the natural 0.7% U-235. As
a by-product of enrichment in the fuel cycle it generally has 0.25-0.30% U-235,
the rest being U-238. Can be blended with highly-enriched uranium (e.g., from
weapons) to make reactor fuel.
Designated employee (designated person): An
employee (or person) who is designated by the employer to perform specific
duties under the terms of this section and who is knowledgeable in the
construction and operation of the equipment and the hazards involved.
Detachment: The locating of a combustible particulate solid process in the
open air or in a separate building.
Deuterium: "Heavy hydrogen", a stable isotope having one proton and
one neutron in the nucleus. It occurs in nature as 1 atom to 6500 atoms of
normal hydrogen, (Hydrogen atoms contain one proton and no neutrons).
Diallyl Phthalate (DAP): A thermosetting plastic that offers outstanding dimensional
stability and resistance to most chemicals and chemical compounds. It is used
in the production of connector housings.
Dielectric: (l) Any insulating medium that intervenes between two conductors.
(2) A material that, having the property required to establish an electric
field, is recoverable in whole or in part as electric energy.
Dielectric Constant: That property of a dielectric that determines the electrostatic
energy stored per unit volume for a unit potential gradient. Permittivity is
the preferred term.
Dielectric Strength: The maximum voltage that a dielectric material can withstand, under
specified conditions, without rupturing. It is usually expressed as volts/unit
thickness. Also called Disruptive Gradient or Electric Strength.
Dielectric Withstanding Voltage: Maximum potential gradient that a dielectric material can withstand
without failure.
Diffuse insulation: Sunlight received indirectly as a result of scattering
due to clouds, fog, haze, dust, or other obstructions in the atmosphere.
Opposite of direct insulation.
Diffusion furnace: Furnace used to make junctions in semiconductors by
diffusing dopant atoms into the surface of the material.
Diffusion length: The mean distance a free electron or hole moves before
recombining with another hole or electron.
Direct current (dc): Electric current in which electrons flow in one
direction only. Opposite of alternating current.
Direct gain: In direct-gain buildings, sunlight directly enters the home
through the windows and is absorbed and stored in massive floors or walls. These
buildings are elongated in the east-west direction, and most of their windows
are on the south side. The area devoted to south windows varies throughout the
country. It could be as much as 20% of the floor area in sunny cold climates,
where advanced glazings or moveable insulation are recommended to prevent heat
loss at night. These buildings have high insulation levels and added thermal
mass for heat storage.
Direct insulation: Sunlight falling directly upon a collector. Opposite of
diffuse insulation.
Discharge rate: The rate, usually expressed in amperes or time, at which
electrical current is taken from the battery.
![Disconnect Switches Disconnect Switches](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/converter_thumb.jpg) |
Disconnect Switches: Disconnect switches or circuit breakers are
used to isolate equipment or to redirect current in a substation. |
Distributed power: Generic term for any power supply located near the point
where the power is used. Opposite of central power. See 'stand-alone'; 'remote
site.'
Distributed systems: Systems that are installed at or near the location where
the electricity is used, as opposed to central systems that supply electricity
to grids. A residential photovoltaic system is a distributed system.
![Distribution Bus Distribution Bus](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/distribution_bus_thumb.jpg) |
Distribution Bus: A distribution bus is a steel structure array of switches
used to route power out of a substation. |
![Distribution Feeder Circuits Distribution Feeder Circuits](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/distribution_main_thumb.jpg) |
Distribution Feeder Circuits: These are the connections between the
output terminals of a distribution substation and the input terminals of primary circuits. The distribution feeder circuit
conductors leave the substation from a circuit breaker or circuit recloser via underground cables, called substation exit cables. |
![Distribution Transformers Distribution Transformers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/distribution_transformer_thumb.jpg) |
Distribution Transformers: Distribution transformers reduce the voltage of the primary
circuit to the voltage required by customers.
|
DOD: 'Depth of Discharge,' from 100-percent state of charge (SOC), in a
battery or battery system.
Donor: An n-type dopant that puts an additional electron into an energy level
very near the conduction band; this electron is easily exited into the
conduction band where it increases the electrical conductivity over than of an
undoped semiconductor.
Donor level: The level that donates conduction electrons to the system.
Dopant: A chemical element (impurity) added in small amounts to an otherwise
pure semiconductor material to modify the electrical properties of the material.
An n-dopant introduces more electrons. A p-dopant creates electron vacancies
(holes).
Doping: The addition of dopants to a semiconductor.
![Duct Runs Duct Runs](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/duct_on_grade_thumb.jpg) |
Duct Runs: Ducts are hollow tubes running from manhole to manhole inside a
conduit in an underground system. They are of various sizes usually from 2 to 6 inches in diameter. |
Dustproof: Constructed or protected so that dust
will not interfere with its successful operation.
Dusttight: Constructed so that dust will not enter
the enclosing case under specified test conditions.
Duty, continuous: A service requirement that demands
operation at a substantially constant load for an indefinitely long time.
Duty, intermittent: A service requirement that
demands operation for alternate intervals of load and no load, load and rest, or
load, no load, and rest.
Duty, periodic: A type of intermittent duty in which
the load conditions regularly reoccur.
Duty, short time: A requirement of service that
demands operations at a substantially constant load for a short and definitely
specified time.
Duty, varying: A requirement of of service that
demands operation at loads, and for intervals of time, both of which may be
subject to wide variation.
E A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Edge-defined film-fed growth (EFG): A method for making sheets of
polycrystalline silicon in which molten silicon is drawn upward by capillary
action through a mold.
Elastomer: A material that at room temperature stretches under low stress to at
least twice its length and snaps back to original length upon release of
stress.
Electric circuit: Path followed by electrons from a power source (generator
or battery) through an external line (including devices that use the
electricity) and returning through another line to the source.
Electric current: A flow of electrons; electricity.
Electrical grid: An integrated system of electricity distribution, usually
covering a large area.
Electric line truck: A truck used to transport personnel, tools, and material for electric supply line work.
Electric Strength: The maximum potential gradient that a material can withstand without
rupture. Also called Dielectric Strength and Disruptive Gradient.
Electric supply: Conductors used to
transmit electric energy and their necessary supporting or containing
structures. Signal lines of more than 400 volts are always supply lines
within this section, and those of less than 400 volts are considered as
supply lines, if so run and operated throughout.
Electric supply equipment: Equipment that produces, modifies, regulates, controls, or safeguards a supply of electric
energy.
Electric utility: An organization responsible for the installation, operation, or maintenance of an electric supply
system.
Electrodeposition: Electrolytic process in which a metal is deposited at the
cathode from a solution of its ions.
Electrolyte: A liquid conductor of electricity.
Electron volt: An energy unit equal to the energy an electron acquires when
it passes through a potential difference of one volt; it is equal to 1.602 x 10-19 volt.
Element: A chemical substance that cannot be divided into simple
substances by chemical means; atomic species with same number of protons.
Emc: Electromagnetic compatibility.
Emi: Electromagnetic interference.
Enclosed space: A working space, such as a
manhole, vault, tunnel, or shaft, that has a limited means of egress or
entry, that is designed for periodic employee entry under normal operating
conditions, and that under normal conditions does not contain a hazardous
atmosphere, but that may contain a hazardous atmosphere under abnormal
conditions.
Note: Spaces that are enclosed but not designed for
employee entry under normal operating conditions are not considered to be
enclosed spaces for the purposes of this definition. Similarly, spaces that are
enclosed and that are expected to contain a hazardous atmosphere are not
considered to be enclosed spaces for the purposes of this definition. Such
spaces meet the definition of permit spaces in 1910.146, and
entry into them must be performed in accordance with that standard.
Energized (alive, live): Electrically
connected to a source of potential difference, or electrically charged so as
to have a potential significantly different from that of earth in the
vicinity.
Energy audit: A survey that shows how much energy you use in your house or
apartment. It will help you find ways to use less energy.
Energy contribution potential: Recombination occurring in the emitter region
of a photovoltaic cell.
Energy density: The ratio of energy available from a battery to its volume (Wh/1)
or mass (Wh/kg).
Energy isolating device: A physical device
that prevents the transmission or release of energy, including, but not
limited to, the following: a manually operated electric circuit breaker, a
disconnect switch, a manually operated switch, a slide gate, a slip blind, a
line valve, blocks, and any similar device with a visible indication of the
position of the device. (Push buttons, selector switches, and other
control-circuit-type devices are not energy isolating devices.)
Energy levels: The energy represented by an electron in the band model of a
substance.
Energy source: Any electrical, mechanical,
hydraulic, pneumatic, chemical, nuclear, thermal, or other energy source
that could cause injury to personnel.
Enriched uranium: Uranium in which the proportion of U-235 (to U-238)
has been increased above the natural 0.7%. Reactor-grade uranium is usually
enriched to about 3.5% U-235, weapons-grade uranium is more than 90% U-235.
Enrichment: Physical process of increasing the proportion of U-235 to
U-238.
Environment: All the natural and living things around us. The earth, air,
weather, plants, and animals all make up our environment.
Epitaxial growth: The growth of one crystal on the surface of another
crystal. The growth of the deposited crystal is oriented by the lattice
structure of the original crystal.
Equipotential zone: A zone of equal potential used to protect workers from hazardous step
and touch potentials.
Extrinsic semiconductor: The product of doping a pure semiconductor.
Explosionproof: Designed and constructed to
withstand and internal explosion without creating an external explosion or fire.
Exposed: Not isolated or guarded.
F A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Fast breeder reactor (FBR): A fast neutron reactor
configured
to produce more fissile material than it consumes, using fertile material
such as depleted uranium in a blanket around the core.
Fast neutron reactor: A reactor with little or no moderator and hence utilizing fast neutrons. It normally burns plutonium while producing fissile
isotopes in fertile material such as depleted uranium (or thorium).
Feeder: A circuit, such as conductors in conduit or
a busway run, which carries a large block of power from the service equipment to
a sub-feeder panel or a branch circuit panel or to some point at which the block
power is broken into smaller circuits.
Fermi level: Energy level at which the probability of finding an electron is
one-half. In a metal, the Fermi level is very near the top of the filled levels
in the partially filled valance band. In a semiconductor, the Fermi level is in
the band gap.
Fertile (of an isotope): Capable of becoming fissile, by capturing
neutrons, possibly followed by radioactive decay; e.g., U-238, Pu-240.
Fill factor: The ratio of a photovoltaic cell's actual power to its power if
both current and voltage were at their maxima. A key characteristic in
evaluating cell performance.
Fire Barrier Wall: A wall separating buildings or subdividing a building to prevent the spread of
fire and having a fire resistance rating and structural stability.
Fire loading: The amount of combustibles present in a given area, expressed in Btu/ft2
(kJ/m2).
Fire point: The lowest temperature at which a liquid in an open container will give off sufficient
vapors to burn once ignited. It generally is slightly above the flash point.
Fire protection rating: The time,
in minutes or hours, that materials and assemblies used as opening protection have
withstood a fire exposure as established in accordance with test procedures of NFPA 252,
Standard Methods of Fire Tests of Door Assemblies, and NFPA 257, Standard on
Fire Test for Window and Glass Block assemblies, as applicable.
Fissile (of an isotope): Capable of capturing a slow (thermal) neutron
and undergoing nuclear fission, e.g., U-235, U-233, Pu-239.
Fissionable (of an isotope): Capable of undergoing fission: If
fissile, by slow neutrons; if fertile, by fast neutrons.
Fission: The splitting of a heavy nucleus into two, accompanied by the
release of a relatively large amount of energy and usually one or more neutrons.
It may be spontaneous but usually is due to a nucleus absorbing a neutron and
thus becoming unstable.
Fission products: Daughter nuclei resulting either from the fission of
heavy elements such as uranium, or the radioactive decay of those primary
daughters. Usually highly radioactive.
Flammable liquid: Any liquid having a flash point below 100°F
(37.8°C) and having a vapor pressure not exceeding an absolute pressure of
40 psi (276 kPa) at 100°F (37.8°C).
Flat-plate photovoltaic module: An arrangement of photovoltaic cells mounted
on a rigid flat surface with the cells exposed freely to incoming sunlight.
Flat-plate Photovoltaic: Refers to a
Photovoltaic array or module that consists of non-concentrating elements. Flat-plate arrays and modules use direct and diffuse
sunlight, but if the array is fixed in position, some portion of the direct
sunlight is lost because of oblique sun-angles in relation to the array.
Float charge: Float charge is the voltage required to counteract the
self-discharge of the battery at a certain temperature.
Float life: Number of years that a battery can keep its stated capacity when
it is kept at float charge (see float charge).
Float-zone process: A method of growing a large-size, high-quality crystal
whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As
the coils are slowly raised the molten interface beneath the coils becomes
single crystal.
Fossil fuel: A fuel based on carbon presumed to be originally from
living matter, e.g., coal, oil, gas. Burned with oxygen to yield energy,
used in a boiler to produce steam for the generation of electrical energy.
Fresnel lens: An optical device that focuses light like a magnifying glass;
concentric rings are faced at slightly different angles so that light falling on
any ring is focused to the same point. Fresnel lenses are flat rather than thick
in the center and can be stamped out in a mold.
![Frequency Changers Frequency Changers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/frequency_changer_thumb.jpg) |
Frequency Changers: A frequency changer is a motor-generator set that
changes power of an alternating current system from one frequency to one or more different frequencies, with or without a change
in the number of phases, or in voltage. |
Fuel: Any material that can be burned to make energy.
Fuel assembly: Structured collection of fuel rods or elements, the
unit of fuel in a reactor.
Fuel cell: A device that converts the energy of a fuel directly to
electricity and heat, without combustion. Because there is no combustion, fuel
cells give off few emissions; because there are no moving parts, fuel cells are
quiet.
Fuel fabrication: Making reactor fuel assemblies, usually from
sintered UO2 pellets which are inserted into zircalloy tubes,
comprising the fuel rods or elements.
G A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Gallium (Ga): A chemical element, atomic number 31, metallic in nature, used
in making certain kinds of solar cells and semiconductor devices.
Gallium arsenide (GaAs): A crystalline high-efficiency
semiconductor/photovoltaic material.
Gamma rays: High energy electro-magnetic radiation from the atomic
nucleus, virtually identical to X-rays.
Gassing current: Portion of charge current that goes into
electrolytic
production of hydrogen and oxygen from the electrolytic liquid. This current
increases with increasing voltage and temperature.
Gel-type battery: Lead-acid battery in which the electrolyte is composed of a
silica gel matrix.
Genetic mutation: Sudden change in the chromosomal DNA of an
individual gene. It may produce inherited changes in descendants. Mutation in
some organisms can be made more frequent by irradiation (though this has never
been demonstrated in humans).
Gigawatt (GW): One billion watts. One million kilowatts. One thousand
megawatts.
Glazings: Clear materials (such as glass or plastic) that allow sunlight to
pass into solar collectors and solar buildings, trapping heat inside.
Grain boundaries: The boundaries where crystallites in a polycrystalline
material meet.
Graphite: Crystalline carbon used in very pure form as a moderator,
principally in gas-cooled reactors, but also in Soviet-designed RBMK reactors.
Gray: The SI unit of absorbed radiation dose, one joule per kilogram
of tissue.
Greenhouse effect: The effect of the Earth's atmosphere, due to certain
gases, in trapping heat from the sun; the atmosphere acts like a greenhouse.
Greenhouse gases: Gases that trap the heat of the sun in the Earth's
atmosphere, producing the greenhouse effect; the two major greenhouse gases are
water vapor and carbon dioxide; lesser greenhouse gases include methane, ozone,
chlorofluorocarbons, and nitrogen oxides.
Grid-connected (Photovoltaic
system): A Photovoltaic system in which the Photovoltaic
array acts like a
central generating plant, supplying power to the grid.
Grid-interactive (Photovoltaic
system): See 'Grid-connected (Photovoltaic system).'
Ground: A large conducting body (such as the earth) used
as a common return for an electric circuit and as an arbitrary zero of
potential.
Grounded, effectively: Intentionally connected to
earth through a ground connection or connections of sufficiently low impedance
and having sufficient current-carrying capacity to prevent the buildup of
voltages that may result in undue hazards to connect equipment or to persons.
Grounded Conductor: A system or circuit conductor
that is intentionally grounded, usually gray or white in color.
Grounding Conductor: A conductor used to connect
metal equipment enclosures and/or the system grounded conductor to a grounding
electrode, such as the ground wire run to the water pipe at a service; also may
be a bare or insulated conductor used to ground motor frames, panel boxes, and
other metal equipment enclosures used throughout electrical systems. In most
conduit systems, the conduit is used as the ground conductor.
Grounding Equipment Conductor: The conductor used to
connect the noncurrent-carrying metal parts of equipment, raceways, and other
enclosures to the system grounded conductor, the grounding electrode conductor,
or both, of the circuit at the service equipment or at the source of a
separately derived system.
Grounding Electrode: The conductor used to connect
the grounding electrode to the equipment grounding conductor, to the grounded
conductor, or to both, of the circuit at the service equipment or at the source
of a separately derived system.
![Grounding Resistors Grounding Resistors](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/ngrounding_resister_thumb.jpg) |
Grounding Resistors: Grounding Resistors are designed to provide added
safety to industrial distribution systems by limiting ground fault current to reasonable levels. |
![Grounding Transformers Grounding Transformers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/neutral_grounding_transformer_thumb.jpg) |
Grounding Transformers: A grounding transformer intended primarily
to provide a neutral point for grounding purposes. |
Ground Fault Circuit Interrupter: A device intended
for the protection of personal that functions to de-energize a circuit or
portion thereof within an established period of time when a current to ground
exceeds some predetermined value that is less than required to operate the
overcurrent protection device of the supply circuit.
Ground Fault Protection of Equipment: A system
intended to provide protection of equipment from damaging line to ground fault
currents by operating to cause a disconnecting means to open all ungrounded
conductors of the faulted circuit. This protection is provided at current levels
less than those required to protect conductors from damage through the
operations of a supply circuit overcurrent device.
Guarded: Covered, fenced, enclosed, or
otherwise protected, by means of suitable covers or casings, barrier rails
or screens, mats, or platforms, designed to minimize the possibility, under
normal conditions, of approach or accidental contact by persons or
objects. Note: Wires which are insulated, but not otherwise
protected, are not considered as guarded.
H A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Half-life: The period required for half of the atoms of a particular
radioactive isotope to decay and become an isotope of another element.
Hazardous atmosphere: An atmosphere that
may expose employees to the risk of death, incapacitation, impairment of
ability to self-rescue (that is, escape unaided from an enclosed space),
injury, or acute illness from one or more of the following causes:
-
Flammable gas, vapor, or mist in excess of 10 percent of
its lower flammable limit (LFL);
- Airborne combustible dust at a concentration that meets or
exceeds its LFL; Note: This concentration may be approximated as a
condition in which the dust obscures vision at a distance of 5 feet (1.52 m)
or less.
- Atmospheric oxygen concentration below 19.5 percent or
above 23.5 percent;
- Atmospheric concentration of any substance for which a
dose or a permissible exposure limit is published and which could
result in employee exposure in excess of its dose or permissible exposure
limit;
- Note: An atmospheric concentration of any substance that
is not capable of causing death, incapacitation, impairment of ability to
self-rescue, injury, or acute illness due to its health effects is not
covered by this definition.
- Any other atmospheric condition that is immediately
dangerous to life or health.
-
Note: For air contaminants for which OSHA has not
determined a dose or permissible exposure limit, other sources of
information, such as Material Safety Data Sheets that comply with the Hazard
Communication Standard, 1910.1200, published information, and
internal documents can provide guidance in establishing acceptable
atmospheric conditions.
Heat pump: Like an air conditioner or refrigerator, a heat pump moves
heat from one location to another. In the cooling mode, heat pumps reduce
indoor temperatures in the summer by transferring heat to the ground. Unlike
an air conditioning unit, however, a heat pump's cycle is reversible. In
winter, a heat pump can extract heat from the ground and transfer it inside.
The energy value of the heat thus moved can be more than three times the
cost of the electricity required to perform the transfer process.
Heavy water: Water containing an elevated concentration of molecules
with deuterium ("heavy hydrogen") atoms.
Heavy water reactor (HWR): A reactor which uses heavy water as its
moderator, e.g., Canadian CANDU (pressurized HWR or PHWR).
Heterojunction: A region of electrical contact between two different
semiconductor materials.
High-level wastes: Extremely radioactive fission products and
transuranic elements (usually other than plutonium) in spent nuclear fuel. They
may be separated by reprocessing the spent fuel, or the spent fuel containing
them may be regarded as high-level waste.
Highly (or High)-enriched uranium (HEU): Uranium enriched to at least
20% U-235. (In weapons it is about 90% U-235.)
High-power tests: Tests in which fault currents, load currents, magnetizing currents, and line-dropping currents
are used to test equipment, either at the equipment's rated voltage or at
lower voltages.
![High Voltage Underground Cables High Voltage Underground Cables](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/high_voltage_cables_thumb.jpg) |
High Voltage
Underground Cables: High voltage cables
are designed to carry high voltage current and are constructed in many different
ways, but are usually shielded cables. They are made with a conductor, conductor-strand shielding, insulation, semi-conducting insulation
shielding, metallic insulation shielding, and a sheath. |
High voltage direct current (HVDC) converter station: A facility that
functions as an electrical rectifier (ac-dc) to control and transmit power
in a high voltage network. There are two types of HVDC valves: the mercury
arc valve and the present-day technology solid state thyristor valve. Both
types of valves present a fire risk due to high voltage equipment that
consists of oil-filled converter transformers, wall bushings, and capacitors
in addition to various polymeric components.
![High Voltage Fuses High Voltage Fuses](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/high_voltage_fuses_thumb.jpg) |
High Voltage Fuses: High voltage fuses are used to protect the electrical
system in a substation from power transformer faults. They are switched for maintenance and safety. |
High-voltage tests: Tests in which voltages of
approximately 1000 volts are used as a practical minimum and in which the
voltage source has sufficient energy to cause injury.
High wind: A wind of such velocity that the following hazards would be present:
- An employee would be exposed to being blown from elevated locations, or
- an employee or material handling equipment could lose control of material being handled, or
- an employee would be exposed to other hazards not controlled by the standard involved.
- Note: Winds exceeding 40 miles per hour (64.4 kilometers
per hour), or 30 miles per hour (48.3 kilometers per hour) if material
handling is involved, are normally considered as meeting this criteria
unless precautions are taken to protect employees from the hazardous effects
of the wind.
Hole: The vacancy where an electron would normally exist in a solid;
behaves like a positively charged particle.
Homojunction: The region between an n-layer and a p-layer in a single
material photovoltaic cell.
Hybrid system: A Photovoltaic system that includes other sources of electricity
generation, such as wind or diesel generators.
Hydrogenated amorphous silicon: Amorphous silicon with a small amount of
incorporated hydrogen. The hydrogen neutralizes dangling bonds in the amorphous
silicon, allowing charge carriers to flow more freely.
I A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Impedance: The total opposition that a circuit offers to the flow of
alternating current or any other varying current at a particular frequency.
Incident light: Light that shines onto the face of a solar cell or module.
Indium oxide: A wide band gap semiconductor that can be heavily doped with
tin to make a highly conductive, transparent thin film. Often used as a front
contact or one component of a heterojunction solar cell.
Inductive reactance: Electrical current produces heat and/or a
magnetic field (such as in the windings of a motor). We refer to the tendency
for current flow and changes in flow to be influenced by magnetic fields as
inductance. An AC circuit that contains only inductance, capacitance or a
combination of the two is defined by the total opposition to current flow
expressed in reactance. Inductance only affects current flow when the current is
changing. Inductance produces a self-induced voltage (called a counter emf) that
opposes changes in current. Obviously, the current changes constantly in an AC
circuit. Inductance in an AC circuit, therefore, causes a continual opposition.
This opposition to current flow is called inductive reactance.
Infrared radiation: Electromagnetic radiation whose wavelengths lie in the
range from 0.75 micrometer to 1000 micrometers.
Insertion Force: The effort, usually measured in ounces, required to engage mating
components.
Insulation: A material that offers high electric resistance making it suitable
for covering components, terminals and wires to prevent the possible future
contact of adjacent conductors resulting in a short circuit.
Insolation: Sunlight, direct or diffuse; from 'incident solar radiation.' Not
to be confused with insulation.
Insulation: Materials that prevent or slow down the movement of heat.
In situ leaching (ISL): The recovery by chemical leaching of minerals
from porous ore bodies without physical excavation. Also known as solution
mining.
In Sight From: (within sight from, within sight)
Where it is specified that one equipment shall be "in sight from",
"within sight from" or "within sight", etc. of another equipment, the specified
equipment is to be visible and not more that 50´ distant from
the other
Insulated: Separated from other conducting
surfaces by a dielectric (including air space) offering a high resistance to
the passage of current.
Note: When any object is said to be insulated, it is
understood to be insulated for the conditions to which it is normally
subjected. Otherwise, it is, within the purpose of this section, uninsulated.
Insulation (cable): That which is relied upon to insulate the conductor from other conductors or conducting parts or from
ground.
Interconnect: A conductor within a module or other means of connection
which provides an electrical interconnection between the solar cells. [UL
1703]
Interfacial Seal: Sealing of a two-piece, multiple contact connector over the whole
area of the interface to provide sealing around each contact.
Interrupter Rating: The highest current at rated
voltage that a device is intended to interrupt under standard test conditions.
Intrinsic semiconductor: An undoped semiconductor.
Inverters: Devices that convert DC electricity into AC electricity (single or
multiphase), either for stand-alone systems (not connected to the grid) or for
utility-interactive systems.
Ion: An atom that is electrically-charged because of loss or gain of
electrons.
Ionizing radiation: Radiation (including alpha particles) capable of
breaking chemical bonds, thus causing ionization of the matter through which it
passes and damage to living tissue.
Irradiate: Material subjected to ionizing radiation. Irradiated reactor
fuel and components have been subjected to neutron irradiation and hence become
radioactive themselves.
Isotope: An atomic form of an element having a particular number of
neutrons. Different isotopes of an element have the same number of protons but
different numbers of neutrons and hence different atomic mass, e.g.,. U-235, U-238.
Some isotopes are unstable and decay to form isotopes of other elements.
ISPRA guidelines: Guidelines for the assessment of
Photovoltaic Plants, published by
the Joint Research Centre of the Commission of the European Communities, Ispra,
Italy.
I-type semiconductor: Semiconductor material that is left intrinsic, or
undoped so that the concentration of charge carriers is characteristic of the
material itself rather than of added impurities.
I-V curve: A graphical presentation of the current versus the voltage from a
photovoltaic device as the load is increased from the short circuit (no load)
condition to the open circuit (maximum voltage) condition. The shape of the
curve characterized cell performance.
I-V data: The relationship between current and voltage of a photovoltaic
device in the power-producing quadrant, as a set of ordered pairs of current and
voltage readings in a table, or as a curve plotted in a suitable coordinate
system (e.g., Cartesian). [ASTM E 1036]
J A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Jacket: Outermost layer of insulating material of a cable or wire.
Junction: A region of transition between semiconductor layers, such as a p/n
junction, which goes from a region that has a high concentration of acceptors
(p-type) to one that has a high concentration of donors (n-type).
Junction box: A Photovoltaic generator junction box is an enclosure on the module where
Photovoltaic strings are electrically connected and where protection devices can be
located, if necessary.
Junction diode: A semiconductor device with a junction and a built-in
potential that passes current better in one direction than the other. All solar
cells are junction diodes.
K A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Kilowatt (kW): 1000 watts.
Kilowatt-hour (kWh): One thousand watts acting over a period of 1 hour. The
kWh is a unit of energy. 1 kWh=3600 kJ.
L A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Labeled: Items to which a label, trademark, or other
identifying mark of nationally recognized testing labs has been attached to identify the items as having been tested and meeting appropriate standards.
Lattice: The regular periodic arrangement of atoms or molecules in a crystal.
Light-induced defects: Defects, such as dangling bonds, induced in an
amorphous silicon semiconductor upon initial exposure to light.
![Lightning Arresters Lightning Arresters](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/lightning_arresters_thumb.jpg) |
Lightning Arresters: Lightning arresters are
devices for protecting many different
pieces of equipment such as, power poles and towers, power transformers, circuit breakers, bus structures, and steel superstructures,
from damage from lightning strikes. |
Light trapping: The trapping of light inside a semiconductor material by
refracting and reflecting the light at critical angles; trapped light will
travel further in the material, greatly increasing the probability of absorption
and hence of producing charge carriers.
Light water: Ordinary water (H20) as distinct from
heavy water.
Light water reactor (LWR): A common nuclear reactor cooled and usually
moderated by ordinary water.
Lines, Communication: The conductors
and their supporting or containing structures which are used for public or
private signal or communication service, and which operate at potentials not
exceeding 400 volts to ground or 750 volts between any two points of the
circuit, and the transmitted power of which does not exceed 150 watts. If
the lines are operating at less than 150 volts, no limit is placed on the
transmitted power of the system. Under certain conditions, communication
cables may include communication circuits exceeding these limitations where
such circuits are also used to supply power solely to communication
equipment.
Note: Telephone, telegraph, railroad signal, data, clock,
fire, police alarm, cable television, and other systems conforming to this
definition are included. Lines used for signaling purposes, but not included
under this definition, are considered as electric supply lines of the same
voltage.
Line-commutated inverter: An inverter that is tied to a power grid or
line. The commutation of power (conversion from DC to AC) is controlled by
the power line, so that, if there is a failure in the power grid, the Photovoltaic
system cannot feed power into the line.
Listed: Equipment or materials included in a list
published by an organization acceptable to the authority having jurisdiction and
concerned with product evaluation, that maintains periodic inspection of
production of listed equipment or materials, and whose listing states either
that the equipment or material meets appropriate designated standards or has
been tested and found suitable for use in specified manner.
Load: Anything in an electrical circuit that, when the circuit is turned on,
draws power from that circuit.
Location, damp: A location subject to moderate
amount of moisture such as some basements, barns, cold storage, warehouse and
the like.
Location, dry: A location not normally subject to
dampness or wetness: a location classified as dry may be temporarily subject to
dampness or wetness, as in case of a building under construction.
Location, wet: A location subject to saturation with
water or other liquids.
Low-enriched uranium: Uranium enriched to less than 20% U-235. (That
in power reactors is usually 3.5: 5.0% U-235.)
Lower Flammable Limit (LFL): The lowest
concentration of material that will propagate a flame from an ignition source
through a mixture of flammable gas or combustible dust dispersion with a gaseous
oxidizer.
M A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Majority carrier: Current carriers (either free electrons or holes) that
are in excess in a specific layer of a semiconductor material (electrons in
the n-layer, holes in the p-layer) of a cell.
![Manholes Manholes](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/manhole_cover_thumb.jpg) |
Manholes: A manhole is the opening in the underground duct system which houses
cables plices and which cablemen enter to pull in cable and to make splices and tests. Also called a splicing chamber or cable vault. |
Marginal cost: The cost of one additional unit within a group of like units.
Maximum power point (MPP): The point on the current-voltage (I-V) curve of a
module under illumination, where the product of current and voltage is maximum.
[UL 1703] For a typical silicon cell, this is at about 0.45 V.
Maximum power point tracker (MPPT): Means of a power conditioning unit that
automatically operates the Photovoltaic-generator at its MPP under all conditions.
Megaohm: A unit of electrical resistance equal to
one million ohms.
Megaohmmeter: An instrument for measuring extremely
high resistance.
Megawatt (MW): A unit of power, = 106 watts. MWe
refers to electric output from a generator, MWt to thermal output from a reactor
or heat source (e.g., the gross heat output of a reactor itself, typically three
times the MWe figure).
Megger: A test instrument for measuring the
insulation resistance of conductors and other electrical equipment;
specifically, a megaohm (million ohms) meter; this is a registered trade mark
of the James Biddle Co.
![Metal-clad Switchgear Metal-clad Switchgear](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/indoor_switchgear_thumb.jpg) |
Metal-clad Switchgear: An outdoor
metal-clad switchgear is a weatherproof housing for circuit breakers,
protective relays, meters, current transformers, potential transformers, bus
conductors, and other equipment. An indoor switchgear must be protected from
the environment and contains the same types of equipment as the outdoor
type. |
Metal fuels: Natural uranium metal as used in a gas-cooled reactor.
![Meters Meters](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation_meters_thumb.jpg) |
Meters: They are measuring devices and can be an indicating meter or a
recording meter. An indicating meter shows on a dial the quantity being measured. A recording meter makes a permanent record of
the quantity being measured, usually by tracing a line on a chart or graph. |
Micro: one millionth of a unit (e.g., microsievert is 10-6 Sv).
Microgroove: A small groove scribed into the surface of a cell which is
filled with metal for contacts.
![Microwave Microwave](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/microware_thumb.jpg) |
Microwave: Substations commonly use microwave communication equipment for
communication with local and regional electric power system control centers. This system allows for rapid communication and signaling
for controlling the routing of power. |
Milling: Process by which minerals are extracted from ore, usually at
the mine site.
Minority carrier: A current carrier, either an electron or a hole, that is in
the minority in a specific layer of a semiconductor material; the diffusion of
minority carriers under the action of the cell junction voltage is the current
in a photovoltaic device.
Minority carrier lifetime: The average time a minority carrier exists before
recombination.
Mixed oxide fuel (MOX): Reactor fuel which consists of both uranium
and plutonium oxides, usually about 5% Pu, which is the main fissile component.
Moderator: A material such as light or heavy water or graphite used in
a reactor to slow down fast neutrons by collision with lighter nuclei so as to
expedite further fission.
Module: See 'Photovoltaic Module.'
Monolithic: Fabricated as a single structure.
Multicrystalline: Material that is solidified at such as rate that many small
crystals (crystallites) form. The atoms within a single crystallite are
symmetrically arranged, whereas crystallites are jumbled together. These
numerous grain boundaries reduce the device efficiency. A material composed of
variously oriented, small individual crystals. (Sometimes referred to as
polycrystalline or semicrystalline).
Multijunction device: A photovoltaic device containing two or more cell
junctions, each of which is optimized for a particular part of the solar
spectrum, to achieve greater overall efficiency.
N A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Natural uranium: Uranium with an isotopic composition as found in
nature, containing 99.3% U-238, 0.7% U-235 and a trace of U-234. Can be used as
fuel in heavy water-moderated reactors.
Neutron: An uncharged elementary particle found in the nucleus of
every atom except hydrogen. Solitary mobile neutrons traveling at various
speeds originate from fission reactions. Slow (thermal) neutrons can in turn
readily cause fission in nuclei of "fissile" isotopes, e.g., U-235, Pu-239,
U-233; and fast neutrons can cause fission in nuclei of "fertile" isotopes such
as U-238, Pu-239. Sometimes atomic nuclei simply capture neutrons.
Noninductive Circuit: A circuit in which the
magnetic effect of the current flowing has been reduced by one several methods
to a minimum or to zero.
Nonlinear Load: A load where the wave shape of the
steady state current does not follow the wave shape of the applied voltage.
Nonrenewable fuels: Fuels that cannot be easily made or "renewed." We can use
up nonrenewable fuels. Oil, natural gas, and coal are nonrenewable fuels.
N-type semiconductor: A semiconductor produced by doping an intrinsic
semiconductor with an electron-donor impurity (e.g., phosphorous in silicon).
Nuclear energy: Energy that comes from splitting atoms of radioactive
materials, such as uranium.
Nuclear reactor: A device in which a nuclear fission chain reaction
occurs under controlled conditions so that the heat yield can be harnessed or
the neutron beams utilized. All commercial reactors are thermal reactors, using
a moderator to slow down the neutrons.
O A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
"O" RING: A doughnut-shaped ring of rubber used as a seal around the periphery
of the mating insulator interface of cylindrical connectors.
Ohm: The derived SI unit for electrical resistance
or impedance; one ohm equals one volt per ampere.
Ohmmeter: an instrument for measuring resistance in
ohms.
Oil: A black liquid fossil fuel found deep in the Earth. Gasoline and most
plastics are made from oil.
![Oil Circuit Breakers Oil Circuit Breakers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/oil_circuit_breaker_thumb.jpg) |
Oil Circuit Breakers: Oil circuit breakers are used to switch circuits and
equipment in and out of a system in a substation. They are oil filled to provide cooling and to prevent arcing when the switch is activated. |
One-axis tracking: A system capable of rotating about one axis.
Open-circuit voltage (Voc): The maximum possible voltage across a
photovoltaic cell or module; the voltage across the cell in sunlight when no
current is flowing.
Overcurrent: Any current in excess of the rated
current of equipment or the ampacity of a conductor. It may result from
overload, short circuit or ground fault.
Overload: Load greater than the load for which the
system or mechanism was intended. A fault, such as a short circuit or ground
fault, is not an overload.
Oxide fuels: Enriched or natural uranium in the form of the oxide UO2,
used in many types of reactor.
P A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Packing factor: The ratio of array area to actual land area or building
envelope area, for a system; or, the ratio of total Photovoltaic cell area to the total
module area, for a module.
Panelboard: A single panel or group of panel units
designed for assembly in the form of a single panel: includes buses and may come
with or without switches and/or automatic overcurrent protective devices for the
control of light, heat, or power circuits of individual as well as aggregate
capacity. It is designed to be placed in a cabinet or cutout box that is in or
against a wall or partition and is accessible only from the front.
Parallel connection: A way of joining two or more electricity-producing
devices (i.e., Photovoltaic cells or modules) by connecting positive leads together and
negative leads together; such a configuration increases the current.
Passivation: A chemical reaction that eliminates the detrimental effect of
electrically reactive atoms on a photovoltaic cell's surface.
Passive solar home: A house that uses a room or another part of the building
as a solar collector.
Peak load; Peak demand: The maximum load, or usage, of electrical power
occurring in a given period of time, typically a day.
Peak power: Power generated by a utility unit that operates at a very low
capacity factor; generally used to meet short-lived and variable high demand
periods.
Peak watts (Wp): See 'Photovoltaic peak watt.'
Phosphorous (P): A chemical element, atomic number 15, used as a dopant in
making n-semiconductor layers.
Photocurrent: An electric current induced by radiant energy.
Photoelectrochemical cell: A special kind of photovoltaic cell in which the
electricity produced is used immediately within the cell to produce a useful
chemical product, such as hydrogen. The product material is continuously
withdrawn from the cell for direct use as a fuel or as an ingredient in making
other chemicals, or it may be stored and used subsequently.
Photon: A particle of light that acts as an individual unit of energy.
Photovoltaic (Photovoltaic): Pertaining to the direct conversion of light into
electricity.
Photovoltaic (Photovoltaic) array: An interconnected system of
Photovoltaic modules that function
as a single electricity-producing unit. The modules are assembled as a discrete
structure, with common support or mounting. In smaller systems, an array can
consist of a single module.
Photovoltaic (Photovoltaic) cell: The smallest semiconductor element within a
Photovoltaic module
to perform the immediate conversion of light into electrical energy (dc voltage
and current).
Photovoltaic (Photovoltaic) conversion efficiency: The ratio of the electric power
produced by a photovoltaic device to the power of the sunlight incident on the
device.
Photovoltaic (Photovoltaic) device: A device that converts light directly into DC
electricity.
Photovoltaic (Photovoltaic) efficiency: The ratio of electric power produced by a cell
at any instant to the power of the sunlight striking the cell.
Photovoltaic (Photovoltaic) generator: The total of all
Photovoltaic strings of a Photovoltaic power supply
system, which are electrically interconnected.
Photovoltaic (Photovoltaic) module: The smallest environmentally protected, essentially
planar assembly of solar cells and ancillary parts, such as interconnections,
terminals, [and protective devices such as diodes] intended to generate DC power
under unconcentrated sunlight. The structural (load carrying) member of a module
can either be the top layer (superstrate) or the back layer (substrate). [UL
1703]
Photovoltaic (Photovoltaic) panel: often used interchangeably with
Photovoltaic module
(especially in one-module systems), but more accurately used to refer to a
physically connected collection of modules (i.e., a laminate string of modules
used to achieve a required voltage and current).
Photovoltaic (Photovoltaic) peak watt: Maximum "rated" output of a cell, module, or
system. Typical rating conditions are 0.645 watts per square inch (1000 watts
per square meter) of sunlight, 68 degrees F (20 degrees C) ambient air
temperature and 6.2 x 10-3 mi/s (1 m/s) wind speed.
Photovoltaic (Photovoltaic) system: A complete set of components for converting
sunlight into electricity by the photovoltaic process, including the array and
balance of system components.
Photovoltaic-thermal (Photovoltaic/T) system: A photovoltaic system that, in addition
to converting sunlight into electricity, collects the residual heat energy and
delivers both heat and electricity in usable form. Also called a total energy
system.
Physical vapor deposition: A method of depositing thin semiconductor films.
With this method, physical processes, such as thermal evaporation or bombardment
of ions, are used to deposit elemental semiconductor material on a substrate.
Plenum: Chamber or space forming a part of an air
conditioning system
Plutonium: A transuranic element, formed in a nuclear reactor by
neutron capture. It has several isotopes, some of which are fissile and some of
which undergo spontaneous fission, releasing neutrons. Weapons-grade plutonium
is produced in special reactors to give >90% Pu-239, reactor-grade plutonium
contains about 30% non-fissile isotopes. About one third of the energy in a
light water reactor comes from the fission of Pu-239, and this is the main
isotope of value recovered from reprocessing spent fuel.
P-i-n: A semiconductor device structure that layers an intrinsic
semiconductor between a p-type semiconductor and an n-type semiconductor; this
structure is most often used with amorphous silicon devices.
P/n: A semiconductor device structure in which the junction is formed between
a p-type layer and an n-type layer.
Point-contact cell: A high efficiency silicon concentrator cell that employs
light trapping techniques and point-diffused contacts on the rear surface for
current collection.
Polycrystalline: See 'Multicrystalline.'
![Potential Transformers Potential Transformers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/potential_transformer_thumb.jpg) |
Potential Transformers: Potential transformers are required to provide
accurate voltages for meters used for billing industrial customers or utility companies. |
![Potheads Potheads](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/3conductor_pothead_thumb.jpg) |
Potheads: A type of insulator with a bell or pot-like
shape used to connect underground electrical cables to overhead lines. It serves to separate the bunched-up conductors from one
another in the cable to the much wider separation in the overhead line. It also seals the cable end from the weather. |
Power conditioning equipment: Electrical equipment, or power electronics,
used to convert power from a photovoltaic array into a form suitable for
subsequent use. A collective term for inverter, converter, battery charge
regulator, and blocking diode.
Power density: The ratio of the power available from a battery to its mass
(W/kg) or volume (W/l).
Power factor: The ratio of the average power and the apparent volt-amperes.
![Power Generation Plants Power Generation Plants](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/nuclear_powerplant_thumb.jpg) |
Power Generation Plants: A facility designed to produce electric energy from another form of
energy, such as fossil fuel, nuclear, hydroelectric, geothermal, solar thermal, and wind.
|
![Power Line Carrier Power Line Carrier](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/electronic_powerline_thumb.jpg) |
Power Line Carrier: A device for producing radio-frequency power for
transmission on power lines. |
![Power Transformers Power Transformers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/transformer2_thumb.jpg) |
Power Transformers: Transformers raise or lower the voltage as needed to
serve the transmission or distribution circuits. |
Pressurized water reactor (PWR): The most common type of light water
reactor (LWR), it uses water at very high pressure in a primary circuit and
steam is formed in a secondary circuit.
![Primary Circuits Primary Circuits](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/3phase_thumb.jpg) |
Primary Circuits: These are the distribution circuits that carry power from substations to local load areas.
They are also called express feeders or distribution main feeders. The distribution feeder bay routes power from the substation to the
distribution primary feeder circuits. |
Projected area: The net south-facing glazing area projected on a vertical plane.
![Protective Equipment Protective Equipment](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/lightning_arrester_thumb.jpg) |
Protective Equipment:
Equipment in a distribution system such as protective relays, cutout switches,
disconnect switches, lightning arresters, and fuses. These all work in concert to open circuits whenever a short circuit, lightning
strikes or other disruptive event occurs. |
P-type semiconductor: A semiconductor in which holes carry the current;
produced by doping an intrinsic semiconductor with an electron acceptor impurity
(e.g., boron in silicon).
Pulse-width-modulated (pwm) wave inverter (PWM): PWM inverters are the most
expensive, but produce a high quality of output signal at minimum current
harmonics. The output voltage is very close to sinusoidal.
Photovoltaic: Abbreviation for photovoltaic(s).
Q A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Quad: A measure of energy equal to one trillion Btus; an energy equivalent to
approximately 172 million barrels of oil.
Qualified employee (qualified person): One
knowledgeable in the construction and operation of the electric power
generation, transmission, and distribution equipment involved, along with
the associated hazards.
Note 1: An employee must have the training required by 1910.269 in order to be considered a qualified
employee.
Note 2: Except as provided in 1910.260,
an employee who is undergoing on-the-job training and who, in the course of
such training, has demonstrated an ability to perform duties safely at his
or her level of training and who is under the direct supervision of a
qualified person is considered to be a qualified person for the performance
of those duties.
Qualification test (Photovoltaic): A procedure applied to a selected set of
Photovoltaic modules
involving the application of defined electrical, mechanical, or thermal stress
in a prescribed manner and amount. Test results are subject to a list of defined
requirements.
Quick Disconnect: A type of connector shell that permits rapid locking and unlocking
of two connector halves.
Quick Disconnect Coupling: A design feature, apparent in the quick disconnect connector; it
permits relatively rapid joining and separation.
R A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Radiation: The emission and propagation of energy by means of
electromagnetic waves or particles.
Radioactive waste: Radioactive materials left over from making nuclear energy.
Radioactive waste can harm people and the environment if it is not stored
safely.
Radioactivity: The spontaneous decay of an unstable atomic nucleus,
giving rise to the emission of radiation.
Radionuclide: A radioactive isotope of an element.
Radiotoxicity: The adverse health effect of a radionuclide due to its
radioactivity.
Radium: A radioactive decay product of uranium often found in uranium
ore. It has several radioactive isotopes. Radium-226 decays to radon-222.
Radon (Rn): A heavy radioactive gas given off by rocks containing
radium (or thorium). Rn-222 is the main isotope.
Radon daughters: Short-lived decay products of radon-222 (Po-218,
Pb-214, Bi-214, Po-214).
Rainproof: So constructed, projected, or treated as
to prevent rain from interfering with the successful operation of the apparatus
under specified test conditions.
Raintight: So constructed or protected that exposure
to a beating rain will not result in the entrance of water.
Rated Voltage: The maximum voltage at which an electric component can operate for
extended periods without undue degradation or safety hazard.
Recombination: The action of a free electron falling back into a hole.
Recombination processes are either radiative, where the energy of
recombination results in the emission of a photon, or non-radiative, where the
energy of recombination is given to a second electron which then relaxes back
to its original energy by emitting phonons. Recombination can take place in
the bulk of the semiconductor, at the surfaces, in the junction region, at
defects, or between interfaces.
![Rectifier Rectifier](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/power_rectifier_thumb.jpg) |
Rectifiers: A rectifier is a device used to convert alternating current to direct current. |
Recycling: A way to reuse materials instead of just throwing them away.
![](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/recycle_tn.jpg) |
Recycle mark: A design of three arrows that make up a circle. This mark
tells you that you can recycle the product. It can also mean that the material
is made from recycled materials.
|
![Relays Relays](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation_meters2_thumb.jpg) |
Relays: A relay is a low-powered device used to activate a high-powered
device. Relays are used to trigger circuit breakers and other switches in substations and transmission and distribution systems. |
Remote systems: Systems off of the utility grid.
Renewable fuels: Fuels that can be easily made or "renewed." We can never
use up renewable fuels. Types of renewable fuels are solar, wind, and
hydropower energy.
RES: Acronym for the Residential Experiment Stations.
Reserve capacity: The amount of generating capacity a central power system
must maintain to meet peak loads.
Resistive voltage drop: The voltage developed across a cell by the current
flow through the resistance of the cell.
Reactor pressure vessel: The main steel vessel containing the reactor
fuel, moderator and coolant under pressure.
Repository: A permanent disposal place for radioactive wastes.
Reprocessing: Chemical treatment of spent reactor fuel to separate
uranium and plutonium from the small quantity of fission product, waste products
and transuranic elements, leaving a much reduced quantity of high-level waste.
Ribbon: A thin sheet of crystalline or
multi-crystalline material, such as
silicon, produced in a continuous process by withdrawal from a molten bath of
the parent material.
![Riser Riser](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/riser_thumb.jpg) |
Riser: A riser is a power line pole that connects an overhead system to an
underground system. A riser has a conduit from the ground up the pole where potheads are used to connect to the overhead lines. |
S A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Satellite power system (SPS): Concept for providing large amounts of
electricity for use on the Earth from one or more satellites in geosynchronous
Earth orbit. A very large array of solar cells on each satellite would provide
electricity, which would be converted to microwave energy and beamed to a
receiving antenna on the ground. There, it would be reconverted into electricity
and distributed the same as any other centrally generated power, through a grid.
Saturation Temperature: The boiling point of a liquid, or the
temperature at which the liquid vapor pressure is equal to the total local
pressure. The saturation temperature for water at atmospheric pressure is
212°F (100°C).
Schottky barrier: A cell barrier established as the interface between a
semiconductor, such as silicon, and a sheet of metal.
Scribing: The cutting of a grid pattern of grooves in a semiconductor
material, generally for the purpose of making interconnections.
Seasonal energy-efficiency ratio (SEER): The ratio of the total seasonal
cooling requirement (measured in Btu) to the total seasonal watt-hours (Wh) of energy used,
expressed in terms of Btu/Wh. (The SEER rating equals 3.413 times the seasonal
COP.)
![Secondaries Secondaries](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/secondary2underground_thumb.jpg) |
Secondaries: These are the conductors originating at the
low-voltage secondary winding of a distribution transformer. |
Segregation: The interposing of a fire and explosion-resistant
barrier between the combustible particulate solid process and other
operations.
Semiconductor: Any material that has a limited capacity for conducting an
electric current. Certain semiconductors, including silicon, gallium arsenide,
copper indium diselenide, and cadmium telluride, are uniquely suited to the
photovoltaic conversion process.
Self discharge: The rate at which a battery, without a load, will lose its
charge.
Separation: The interposing of distance between the combustible
particulate solid process and other operations that are in the same room.
Separately Derived System: A premises wiring system
whose power is derived from a battery, a solar photovoltaic system, or from a
generator, transformer, or converter windings, and that has no direct electrical
connection, including solidly connected grounded circuit conductor, to supply
conductors originating in another system.
Separative Work Unit (SWU): This is a complex unit which is a function
of the amount of uranium processed and the degree to which it is enriched, i.e.,
the extent of increase in the concentration of the U-235 isotope relative to the
remainder. The unit is strictly: Kilogram Separative Work Unit, and it measures
the quantity of Separative work (indicative of energy used in enrichment) when
feed and product quantities are expressed in kilograms, e.g., to produce one kilogram of uranium enriched to 3.5% U-235 requires 4.3
SWU if the plant is operated at a tails assay 0.30%, or 4.8 SWU if the tails
assay is 0.25% (thereby requiring only 7.0 kg instead of 7.8 kg of natural U
feed). About 100-120,000 SWU is required to enrich the annual fuel loading for a
typical 1000 MWe light water reactor. Enrichment costs are related to electrical
energy used. The gaseous diffusion process consumes some 2400 kWh per SWU, while
gas centrifuge plants require only about 60 kWh/SWU.
Series connection: A way of joining circuits by connecting positive
leads to negative leads; such a configuration increases the voltage.
Series regulator: Type of battery charge regulator where the charging current
is controlled by a switch connected in series with the Photovoltaic module or array.
Series resistance: Parasitic resistance to current flow in a cell due to
mechanisms such as resistance from the bulk of the semiconductor material,
metallic contacts, and interconnections.
Service Drop: Run of cables from the power company's
aerial power lines to the point of connection to a customer's premises.
Service Conductors: The supply conductors that
extend from the street main or transformers to the service equipment of the
premises being supplied.
Service Entrance Conductors: (Overhead) The service
conductors between the terminals of the service equipment and a point usually
outside the building, clear of building walls, where they are joined by tap or splice to
the service drop.
Service Entrance Conductors: (Underground) The
service conductors between the terminals of the service equipment and the point
of connection to the service lateral.
Service Equipment: The necessary equipment, usually
consisting of a circuit breaker or switch and fuses and their accessories,
located near the point entrance of supply conductors to a building and intended
to constitute the main control and cutoff means for the supply to the building.
Service Lateral: The underground service conductors
between the street main, including any risers at a pole or other structure or
from transformers, and the first point of connection to the service-entrance
conductors in a terminal box, meter, or other enclosure with adequate space,
inside or outside the building wall. Where there is no terminal box, meter, or
other enclosure with adequate space, the point of connection is the entrance
point of the service conductors into the building.
Service Point: The point of connection between the
facilities of the serving utility and the premises wiring.
![Services Services](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/distribution_system_thumb.jpg) |
Services: The wires extending from the secondaries or
distribution transformer to a customer's location are called a service. A service can be above or below ground. |
![SF6 Circuit Breakers SF6 Circuit Breakers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/sf6_circuit_breaker_thumb.jpg) |
SF6 Circuit Breakers: These operate to switch electric circuits and
equipment in and out of the system. These circuit breakers are filled with compressed sulfur-hexafluoride gas which acts
to open and close the switch contacts. |
Shield: Device surrounding that portion of a connector that is used for
attaching wires or cables to shield against electromagnetic interference,
and/or protect connector wires or cable from mechanical damage.
Shelf life of batteries: The length of time, under specified conditions, that
a battery can be stored so that it keeps its guaranteed capacity.
Short-circuit current (Isc): The current flowing freely from a photovoltaic
cell through an external circuit that has no load or resistance; the maximum
current possible.
![Shunt Reactor Shunt Reactor](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/shunt_reactors_thumb.jpg) |
Shunt Reactors: These are used in an extra high-voltage substation to neutralize
inductive reactance in long EHV transmission lines. |
Shunt regulator: Type of a battery charge regulator where the charging
current is controlled by a switch connected in parallel with the Photovoltaic generator.
Overcharging of the battery is prevented by shorting the Photovoltaic generator.
Siemens process: A commercial method of making purified silicon.
Silicon (Si): A chemical element, atomic number 14,
semi-metallic in nature,
dark gray, an excellent semiconductor material. A common constituent of sand and
quartz (as the oxide). Crystallizes in face-centered cubic lattice like a
diamond. The most common semiconductor material used in making photovoltaic
devices.
Sine wave inverter: An inverter that produces utility-quality, sine wave
power forms.
Single-crystal material: A material that is composed of a single crystal or a
few large crystals.
Sievert (Sv): Unit indicating the biological damage caused by
radiation. One Joule of beta or gamma radiation absorbed per kilogram of tissue
has 1 Sv of biological effect; 1 J/kg of alpha radiation has 20 Sv effect and 1
J/kg of neutrons has 10 Sv effect.
Spent fuel: Fuel assemblies removed from a reactor after
use.
Stable: Incapable of spontaneous radioactive decay.
Solar cell: See 'Photovoltaic cell.'
Solar constant: The strength of sunlight; 1353 watts per square meter in
space and about 1000 watts per square meter at sea level at the equator at solar
noon.
Solar energy: Energy from the sun. The heat that builds up in your car when
it is parked in the sun is an example of solar energy.
Solar-grade silicon: Intermediate-grade silicon used in the manufacture of
solar cells. Less expensive than electronic-grade silicon.
Solar noon: That moment of the day that divides the daylight hours for that
day exactly in half. To determine solar noon, calculate the length of the day
from the time of sunset and sunrise and divide by two.
Solar spectrum: The total distribution of electromagnetic radiation emanating
from the sun.
Solar thermal electric: Method of producing electricity from solar energy by
using focused sunlight to heat a working fluid, which in turn drives a
turbogenerator.
Spinning reserve: Utility generating capacity on-line and running at low
power in excess of actual load.
Split-spectrum cell: A compound photovoltaic device in which sunlight is
first divided into spectral regions by optical means. Each region is then
directed to a different photovoltaic cell optimized for converting that portion
of the spectrum into electricity. Such a device achieves significantly greater
overall conversion of incident sunlight into electricity. See 'mulitjunction
device.'
Sputtering: A physical vapor deposition process where high-energy ions are
used to bombard elemental sources of semiconductor material, which eject vapors
of atoms that are then deposited in thin layers on a substrate.
Square wave inverter: The inverter consists of a DC source, four switches,
and the load. The switches are power semiconductors that can carry a large
current and withstand a high voltage rating. The switches are turned on and off
at a correct sequence, at a certain frequency. The square wave inverter is the
simplest and the least expensive to purchase, but it produces the lowest quality
of power.
Staebler-Wronski effect: The tendency of amorphous silicon photovoltaic
devices to lose efficiency upon initial exposure to light; named for Dr. David
Staebler and Dr. Christopher Wronski; work performed at RCA.
Standardized: For a lockout or tagout
device to be standardized they must all be similar in at least one of the
following ways: color, shape, size. Additionally, in the case of tagout
devices, print and format should also be similar.
Stand-alone (Photovoltaic
system): An autonomous or hybrid photovoltaic system not
connected to a grid. May or may not have storage, but most stand-alone systems
require batteries or some other form of storage.
Stand-off mounting: Technique for mounting a photovoltaic
array on a sloped roof, which
involves mounting the modules a short distance above the pitched roof and
tilting them to the optimum angle.
Standard reporting conditions (SRC): A fixed set of conditions (including
meteorological) to which the electrical performance data of a photovoltaic
module are translated from the set of actual test conditions. [ASTM E 1036]
Standard test conditions (STC): Conditions under which a module is typically
tested in a laboratory: (1) Irradiance intensity of 1000 W/square meter (0.645
watts per square inch), AM1.5 solar reference spectrum, and (3) a cell (module)
temperature of 25 degrees C, plus or minus 2 degrees C (77 degrees F, plus or
minus 3.6 degrees F). [IEC 1215]
State of charge (SOC): The available capacity remaining in the battery,
expressed as a percentage of the rated capacity.
![Steel Superstructures Steel Superstructures](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/circuit_breakers_thumb.jpg) |
Steel Superstructures: Steel superstructures are used to support equipment,
lines, and switches in substations as well as transmission and distribution line towers and poles. |
Step bolt: A bolt or rung attached at intervals along a structural member and used for foot placement during
climbing or standing.
Step Potential: The voltage between the feet of a person standing near an energized grounded object. It is equal to the
difference in voltage, given by the voltage distribution curve, between two points at different distances from the "electrode". A
person could be at risk of injury during a fault simply by standing near the grounding point.
Substrate: The physical material upon which a photovoltaic cell is made.
![Substation Substation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation2_thumb.jpg) |
Substations: A high-voltage electric system facility. It is used to switch generators, equipment,
and circuits or lines in and out of a system. It also is used to change AC voltages from one level to another,
and/or change alternating current to direct current or direct current to alternating current. |
![Step-up Transmission Substation Step-up Transmission Substation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/transmission_substation_thumb.jpg) |
Step-up Transmission Substation: Receives electric power from a nearby generating facility and uses a large power
transformer to increase the voltage for transmission to distant locations. |
![Step-down Transmission Substation Step-down Transmission Substation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/transformer2_thumb.jpg) |
Step-down Transmission Substation: These substations are located at switching points in an electrical grid. They
connect different parts of a grid and are a source for subtransmission lines. |
![Distribution Substation Distribution Substation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/distribution_substation_thumb.jpg) |
Distribution Substation: These are located near to the end-users. Distribution substation transformers change the subtransmission voltage to lower
levels for use by end-users. |
![Underground Distribution Substation Underground Distribution Substation](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/underground_dist_thumb.jpg) |
Underground Distribution Substation: These are also located near to the end-users. Distribution substation transformers
change the subtransmission voltage to lower levels for use by end-users. |
Sulfation: A condition that afflicts unused and discharged batteries; large
crystals of lead sulfate grow on the plate, instead of the usual tiny crystals,
making the battery extremely difficult to recharge.
Sunspace: A room that faces south, or a small structure attached to the south
side of a house.
Sun tempering: A sun-tempered building is elongated in the east-west
direction, with the majority of the windows on the south side. The area of the
windows is generally limited to about 7% of the total floor area. A sun-tempered
design has no added thermal mass beyond what is already in the framing, wall
board, and so on. Insulation levels are generally high.
Superconducting magnetic energy storage (SMES): SMES technology uses the
superconducting characteristics of low-temperature materials to produce intense
magnetic fields to store energy. SMES has been proposed as a storage option to
support large-scale use of photovoltaics and wind as a means to smooth out
fluctuations in power generation.
Superconductivity: The pairing of electrons in certain materials when cooled
below a critical temperature, causing the material to lose all resistance to
electricity flow. Superconductors can carry electric current without any energy
losses.
Superstrate: The covering on the sun side of a photovoltaic
module, providing
protection for the photovoltaic materials from impact and environmental degradation while
allowing maximum transmission of the appropriate wavelengths of the solar
spectrum.
![Supervisory Contorl Supervisory Contorl](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/supervisory_control_thumb.jpg) |
Supervisory Control: Supervisory control refers to equipment that allows for
remote control of a substation's functions from a system control center or other point of control. |
![Suspension Insulators Suspension Insulators](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/suspension_insulator_thumb.jpg) |
Suspension Insulators: An insulator type usually made of porcelain that
can be stacked in a string and hangs from a cross arm on a tower or pole and supports the line conductor. |
![Switches Switches](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/fused_cutout_thumb.jpg) |
Switches: Distribution systems have switches installed at strategic
locations to redirect power flows for load balancing or sectionalizing. |
Switchboard: A large single panel, frame, or
assembly of panels having switches, overcurrent, and other protective devices,
buses, and usually instruments mounted on the face or back or both. Switchboards
are generally accessible from the rear and from the front and are not intended
to be installed in cabinets.
Switch, general use: A switch intended for use in
general distribution and branch circuits. It is rated in amperes and is capable
of interrupting its rated voltage.
Switch, general-use snap: A type of general-use
switch so constructed that it can be installed in flush device boxes or on
outlet covers, or otherwise used in conjunction with wiring systems recognized
by the National Electric Code.
Switch, isolating: A switch intended for isolating
an electrical circuit from the source of power. It has no interrupting rating
and is intended to be operated only after the circuit has been opened by some
other means.
Switch, knife: A switch in which the circuit is
closed by a moving blade engaging contact clips.
Switch, motor-circuit: A switch, rated in
horsepower, capable of interrupting the maximum operating overload current of a
motor of the same horsepower rating as the switch at the rated voltage.
Switch, transfer: A transfer switch is an automatic
or non-automatic device for transferring one or more load conductor connections
from one power source to another.
Switch-Leg: That part of a circuit run from a
lighting outlet box where a luminaire or lampholder is installed down to an
outlet box that contains the wall switch that turns the light or other load on
or off: it is a control leg of the branch circuit.
![Synchronous Condensers Synchronous Condensers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/synchronous_condenser_thumb.jpg) |
Synchronous Condensers: A synchronous condenser is a synchronous machine
running without mechanical load and supplying or absorbing reactive power to or from a power system. Also called a synchronous
capacitor, synchronous compensator or rotating machinery. |
System operator: A qualified person designated to operate the system or its parts.
T A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Tails: Depleted uranium, with about 0.3% U-235.
Tailings: Ground rock remaining after particular ore minerals
(e.g.,
uranium oxides) are extracted.
Thermal electric: Electric energy derived from heat energy, usually by
heating a working fluid, which drives a turbogenerator. See 'solar thermal
electric.'
Thermal mass: Materials that store heat within a sunspace or solar collector.
Thermal reactor: A reactor in which the fission chain reaction is
sustained primarily by slow neutrons, and hence requiring a moderator (as
distinct from Fast Neutron Reactor).
Thermal Shock: Thermal shock is the effect of heat or cold applied at such a rate
that non-uniform thermal expansion or contraction occur within a given
material or combination of materials. In connectors, the effect can cause
inserts and other insulation materials to pull away from metal parts.
Thermal storage walls (masonry or water): A thermal storage wall is a
south-facing wall that is glazed on the outside. Solar heat strikes the glazing
and is absorbed into the wall, which conducts the heat into the room over time.
The walls are at least 8 in thick. Generally, the thicker the wall, the less the
indoor temperature fluctuates.
Thermophotovoltaic (TPV) device: A device that converts secondary thermal
radiation, re-emitted by an absorber or heat source, into electricity; The
device is designed for maximum efficiency at the wavelength of the secondary
radiation.
Thick-crystalline materials: Semiconductor material, typically measuring from
200-400 microns thick, that is cut from ingots or ribbons.
Thin film: A layer of semiconductor material, such as copper indium
diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few
microns or less in thickness, used to make photovoltaic cells.
III-V (three-five) materials: Elemental
materials that occupy groups III and V of the Periodic Table of the Elements.
Tin oxide: A wide band-gap semiconductor similar to indium oxide; used in
heterojunction solar cells or to make a transparent conductive film, called NESA
glass when deposited on glass.
Touch potential: The voltage between the energized object and the feet of a person in contact with the object. It is equal to
the difference in voltage between the object and a point some distance away. It should be noted that the
touch potential could be nearly the full voltage across the grounded object if that object is grounded at a point remote from the place where
the person is in contact with it. For example, a crane that was grounded to the system neutral and that contacted an energized line would
expose any person in contact with the crane or its uninsulated load line to a touch potential nearly equal to the full fault voltage.
Total energy system: See 'photovoltaic-thermal system.'
Total harmonic distortion (thd): The measure of closeness in shape between a
waveform and its fundamental component.
Total internal reflection: The trapping of light by refraction and reflection
at critical angles inside a semiconductor device so that it cannot escape the
device and must eventually be absorbed by the semiconductor.
Tracking Photovoltaic array: Photovoltaic array that follows the path of the sun to maximize the
solar radiation incident on the Photovoltaic surface. The two most common orientations are
(1) one axis where the array tracks the sun east to west and (2) two-axis
tracking where the array points directly at the sun at all times. Tracking
arrays use both the direct and diffuse sunlight. Two-axis tracking arrays
capture the maximum possible daily energy.
Transformer: Converts the generator's low-voltage electricity to higher
voltage levels for transmission to the load center, such as a city or factory.
![Transformer - Underground Transformer - Underground](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/transformer_thumb.jpg) |
Transformer - Underground: An underground transformer is essentially
the same as an aboveground transformer, but is constructed for the particular needs of underground installation. |
![Transformer Vault Transformer Vault](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/underground_vault_thumb.gif) |
Transformer Vault: A transformer vault is an underground structure or room
in which power transformers, network protectors, voltage regulators, circuit breakers, meters, etc. are housed. |
![Transmission Bus Transmission Bus](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/transmission_bus_thumb.jpg) |
Transmission Bus: Transmission buses are steel structure arrays of switches
used to route power in a substation. |
Transmission lines: Transmit high-voltage electricity from
the generation source or substation to another substation in the electric distribution system.
![](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/oh_dcline_thumb.jpg) |
Overhead Transmission Lines: Overhead AC transmission lines share one characteristic;
they carry 3-phase current. The voltages vary according to the particular grid system they belong to. Transmission voltages
vary from 69 kv up to 765 kv. |
![](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/substation2_thumb.jpg) |
Subtransmission Lines: These lines carry voltages reduced from the major
transmission line system, usually 69 kv. |
![](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/und_trans01_thumb.jpg) |
Underground Transmission Lines: These lines are becoming more common, especially in highly populated area. They may be
buried with no protection, or placed in conduit, trenches, or tunnels. |
Transmutation: Changing atoms of one element into those of another by
neutron bombardment, causing neutron capture.
Transuranic element: A very heavy element formed artificially by
neutron capture and possibly subsequent beta decay(s). Has a higher atomic
number than uranium (92). All are radioactive. Neptunium, plutonium, americium
and curium are the best-known.
Trickle charge: A charge at a low rate, balancing through self-discharge
losses, to maintain a cell or battery in a fully charged condition.
Tunneling: Quantum mechanical concept whereby an electron is found on the
opposite side of an insulating barrier without having passed through or around
the barrier.
Two-axis tracking: A system capable of rotating independently about two axes
(e.g., vertical and horizontal).
U A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Ultraviolet: Electromagnetic radiation in the wavelength range of 4 to 400
nanometers.
Uranium (U): A mildly radioactive element with two isotopes which are
fissile (U-235 and U-233) and two which are fertile (U-238 and U-234). Uranium
is the basic fuel of nuclear energy.
Uranium hexafluoride (UF6): A compound of uranium which is
a gas above 56oC and is thus a suitable form in which to enrich the
uranium.
Uranium oxide concentrate (U3O8): The mixture of
uranium oxides produced after milling uranium ore from a mine. Sometimes loosely
called yellowcake. It is khaki in colour and is usually represented by the
empirical formula U3O8. Uranium is sold in this form.
Utility-interactive inverter: An inverter that can function only when tied to
the utility grid, and uses the prevailing line-voltage frequency on the utility
line as a control parameter to ensure that the Photovoltaic system's output is fully
synchronized with the utility power.
V A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Vac: Volts ac
Vacuum evaporation: The deposition of thin films of semiconductor
material by the evaporation of elemental sources in a vacuum.
Vdc: Volts DC
Vmp: Voltage at maximum power
Voc: Open-circuit voltage
![Vacuum Circuit Breakers Vacuum Circuit Breakers](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/vacuum_circuit_thumb.jpg) |
Vacuum Circuit Breakers: A vacuum circuit breaker utilizes a vacuum to
extinguish arcing when the circuit breaker is opened and to act as a dielectric to insulate the contacts after the arc is interrupted. |
Vacuum evaporation: Method of depositing thin coatings of a substance by
heating it in a vacuum system.
Vacuum zero: The energy of an electron at rest in empty space; used as a
reference level in energy band diagrams.
Valence band: The highest energy band in a semiconductor that can be filled
with electrons.
Valence state; Valence level energy, bound state: Energy content of an
electron in orbit about an atomic nucleus.
Vault: An enclosure, above or below ground,
which personnel may enter and which is used for the purpose of installing,
operating, or maintaining equipment or cable.
Vented vault: A vault that has provision for
air changes using exhaust flue stacks and low level air intakes operating on
differentials of pressure and temperature providing for airflow which
precludes a hazardous atmosphere from developing.
Vertical multijunction cell
(VMJ) : A compound cell made of different
semiconductor materials in layers, one above the other. Sunlight entering the
top passes through successive cell barriers, each of which converts a separate
portion of the spectrum into electricity, thus achieving greater total
conversion efficiency of the incident light. Also called a multiple junction
cell. See 'multijunction device'; 'split-spectrum cell.'
Vitrification: The incorporation of high-level wastes into
borosilicate glass, to make up about 14% of it by mass. It is designed to
immobilise radionuclides in an insoluble matrix ready for disposal.
Volt (V): A unit of measure of the force, or 'push,' given the electrons in
an electric circuit. One volt produces one ampere of current when acting on a
resistance of one ohm.
Voltage: The effective (rms) potential
difference between any two conductors or between a conductor and ground.
Voltages are expressed in nominal values unless otherwise indicated. The
nominal voltage of a system or circuit is the value assigned to a system or
circuit of a given voltage class for the purpose of convenient designation.
The operating voltage of the system may vary above or below this value.
Voltage at maximum power (Vmp): The voltage at which maximum power is
available from a module.
Voltage Drop: The loss of voltage between the input
to a device and the output from a device due to the internal impedance or
resistance of the device. In all electrical systems, the conductors should be
sized so that the voltage drop never exceeds 3% for power, heating, and lighting
loads or combinations of these. Furthermore, the maximum total voltage drop for
conductors for feeders and branch circuits combined should never exceed 5%.
W A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Wafer: A thin sheet of semiconductor material made by mechanically sawing it
from a single-crystal or multi-crystal ingot or casting.
Waste: Refers to radioactive wastes. High-level waste (HLW) is highly radioactive material arising from nuclear
fission. It can be recovered from reprocessing spent fuel, though some countries
regard spent fuel itself as HLW. It requires very careful handling, storage and
disposal. Low-level waste (LLW) is mildly radioactive material usually disposed of
by incineration and burial.
Watertight: So constructed that water/moisture will
not enter the enclosure under specified test conditions.
Watt (W): The unit of electric power, or amount of work (J), done in a unit
of time. One ampere of current flowing at a potential of one volt produces one
watt of power.
Watt-hour (Wh): See 'Kilowatt-hour.'
Waveform: The shape of the curve graphically representing the change in the
ac signal voltage and current amplitude, with respect to time.
![](https://webarchive.library.unt.edu/web/20090312162945im_/http://www.osha.gov/SLTC/etools/electric_power/images/sign_danger_thumb.gif) |
Warning Signs: Display signs warning unqualified persons to 'keep out' at entrances to rooms
and spaces where hazards of high voltage are present. |
Weatherproof: So constructed or protected that
exposure to the weather will not interfere with successful operation.
Window: A wide band gap material chosen for its transparency to light.
Generally used as the top layer of a photovoltaic device, the window allows
almost all of the light to reach the semiconductor layers beneath.
Winston concentrator: A trough-type parabolic collector with one-axis
tracking, developed by Roland Winston.
Work function: The energy difference between the Fermi level and vacuum zero.
The minimum amount of energy it takes to remove an electron from a substance
into the vacuum.
Y A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Yellowcake: Ammonium diuranate, the penultimate uranium compound in U3O8
production, but the form in which mine product was sold until about 1970. See
also Uranium oxide concentrate.
Z A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | Y | Z
Zircaloy: Zirconium alloy used as a tube to contain uranium oxide fuel
pellets in a reactor fuel assembly.
Zone refining: Method of purifying solid rods by means of melting narrow
zones through the rods. These zones are slowly moved from one end of the rod to
the other, sweeping out the impurities.
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