PSNH Power Quality Information
Things you should know

• What is an Electrical System?
  
• What is “Utility Grade Power”?
  
• PSNH Service Voltage Requirements
  
• Types of Electrical Disturbances
  
• Emergency Preparedness for your Electronic Equipment
  
• Solutions to Common Problems
  
• Glossary of Utility System Terms
  

What is an Electrical System?
Electrical systems are similar to plumbing systems. The components of the system, the wires (plumbing pipe), the location of the transformers (pressure reducers), and the types, sizes, and locations of appliances, all interact and determine how well the system performs.

Just as a washing machine or dishwasher can cause the pressure at the shower to vary, wiring, transformers, and electrical equipment can interact and cause pressure variations (electrical disturbances).

Although the National Electrical Code (NEC) is generally used as the design guide for residential and business electrical installations, the code was designed primarily as a safety code, protecting human life and preventing fires. Building to Code, as is most often done, will not necessarily guarantee optimum performance, particularly of sensitive electronic equipment.

Two key tenets of good electrical design are “source” and “separation”.

Source involves maintaining constant voltage (pressure) at the equipment.  This is often done by placing the transformer (pressure reducer) as close as possible to the equipment to be served and ensuring the wiring (plumbing) is more than adequate for the flow.

Separation is about keeping equipment that causes electrical disturbances (motors, printers, and copiers) electrically separated from equipment sensitive to electrical disturbances (computers).

An often recounted, but true, example is that of the computer plugged into a wall outlet with a refrigerator plugged into the same circuit on the opposite wall. Every time the refrigerator motor operated it would cause a voltage disturbance causing the computer to stop functioning. By plugging the computer into a different outlet served by a different circuit, the problem is often cured.

What is “Utility Grade Power”?
How are water and electricity alike? They’re alike in how they are delivered and used by all of us. There are many similarities between the water you receive from your well and the water you purchase from the local water utility and the electricity purchased from PSNH. Water straight out of the tap meets many needs such as irrigating and bathing. For other uses, it may need to be conditioned in some way. Drinking water may be filtered. Water for laboratories may be distilled. Other uses may require heating, cooling, or chemical treatment.

In the same way, electricity straight from the utility "tap" may be adequate to power many of your needs such as lighting and most motorized equipment. For some uses, however, the electricity you purchase may need to be filtered or conditioned to adequately meet the requirements of the equipment. This is especially true for sophisticated or sensitive electronic equipment.

Standards defining the quality of utility grade power include the evenness of the average pressure (voltage), the regularity (frequency), and the reliability. PSNH follows requirements defined by the NH Public Utilities Commission in operating the utility system for voltage and frequency. These requirements are based on industry standards set by the American National Standards Institute.

PSNH Service Voltage Requirements
Like any electric utility power supply, the voltage on PSNH's system will vary throughout the day largely due to the variation in customer electricity use. Under normal conditions, PSNH's secondary voltage service levels are supplied in accordance with the NH Public Utilities Commission requirements. These requirements are based on industry standards set by the American National Standards Institute. The rules governing utility voltage standards do provide several exceptions to these voltage limits. These exceptions are conditions that:

• Arise from adverse weather conditions;
• Arise from the operation of customer’s equipment
• Arise from utility equipment failures;
• Arise from circuit switching equipment during emergencies;
• Are causes beyond the control of PSNH.

Even though PSNH endeavors to maintain constant voltage to your service point, your equipment must be prepared to expect occasional deviations outside the nominal ranges.

Types of Electrical Disturbances
Electrical disturbances, a form of distorted electrical power, come in many shapes and sizes. Electricity as it comes from the generator is smoothly flowing and shaped like successive waves cycling up and down 60 times per second. Distorted electricity can be caused by electrical equipment in your building or in neighboring buildings, as well as by events on the utility system.

Research by the Electric Power Research Institute and others has confirmed 70 to 80 percent of the disturbances originate in the customer’s building or factory. These disturbances are caused by equipment interaction and are often exacerbated by wiring and grounding problems.

The remaining 20 to 30 percent of the electrical disturbances that affect equipment originate on the utility system. These disturbances are caused by a number of factors including weather (lightning, rain, or fog), tree or limb contacts, accidents (dig-ins, vehicles hitting poles), and utility equipment failure.

Electrical disturbances interact with the system in several ways. First, something must cause the electrical disturbance such as a large motor starting or a lightning strike. Next, the wiring network, which carries the disturbance to other equipment, may aggravate the disturbance. Finally, the disturbance reaches electronic equipment which reacts to the disturbance. Listed below are the most common types of disturbances, typical causes, and impacts.

Transients: Also known as surges or spikes, these are caused by lightning, appliances such as printers and copiers, as well as utility activities such as circuit breaker operation and switching. Transients of sufficient energy can upset computers, corrupt data, or even cause damage to power supplies and components.

Sag: A brief drop in the voltage (electrical pressure). Sags can be caused by equipment such as motor starting, and heaters in printers and copiers cycling, as well as utility events. Sags often cause lights to dim or flicker and computer equipment to lock up or lose memory.

Swell: A brief increase in the normal voltage level. Most swells are caused when a motor stops. Although not generally a problem, swells have been known to cause failure of marginal components in electronic equipment.

Over and Undervoltage: Longer-term increases or decreases in the normal voltage. These disturbances often indicate an overloaded transformer or circuit, or the misoperation of a voltage regulating device.

Momentary Outage: Also called a “momentary”.This type of  power outage is generally caused by utility protective equipment operation when trees, animals, vehicles, lightning or others contact the utility wires or striking the utility pole.

Harmonics: Harmonics are a regular distortion of the voltage waveform often caused by the power supplies of electronic equipment. Harmonics can cause overheating in transformers, building wiring, and motors.

Noise: Electro Magnetic Interference (EMI) is electrical interference caused by electric and magnetic fields emanating from electrical equipment, typically transformers or wiring. One impact often seen is a wavy computer screen.

Noise - Radio Frequency Interference (RFI) is electrical interference from equipment that radiates high frequency electrical energy such as TV/radio transmitters and cell phones. Interference can also be caused by arcing sources (switches) or switching power supplies such as those found in electronic ballasts and adjustable speed drives. This kind of noise often causes interference to control circuits.

Emergency Preparedness for Your Electronic Equipment

Emergencies can strike at any time. Many things can cause loss of electrical power or fluctuations in power that could damage your equipment. Before something happens, consider this - what equipment is critical to your home or business and what is the risk of not providing adequate protection?

Surge Suppression

What's the problem? All homes and businesses experience occasional power disturbances. The microprocessors and other sensitive circuitry in modern appliances and equipment make them easily damaged by power surges. Equipment can be ruined by one hit of lightning or little by little over time.

Where do surges come from? Most surges originate in your building and result from motorized or "noisy" equipment. Some surges originate outside your building and result from factors such as weather, animals, nearby buildings, traffic accidents or utility equipment operations. Surges can enter your business through power or phone lines or cable TV connections.

What's the solution? One solution is to plug your sensitive equipment into a surge suppressor. It's an inexpensive option for your valuable equipment. A surge suppressor diverts excessive electrical energy away from your equipment to an electrical "ground" where it disappears without doing any harm.

Surge Suppressor Features

Look for the following features when purchasing a plug-in surge suppressor:

• UL 1449 listing: Signifies the suppressor has been tested by Underwriter Laboratory's for safety.
• Peak surge current (or maximum transient current or maximum surge): Look for a minimum of 39,000 amps. The higher number the better.
• Clamping voltage: The best protection is 330 volts; higher levels offer less protection. Also, look for three modes of protection (often shown as L-N, L-G and N-G).
• Energy dissipation: Should be 420 joules or more. The higher number the better.
• Appropriate connectors:  Use one outlet for each piece of equipment and have room for AC adapters (transformers). If you are protecting a TV, VCR, telephone, fax or computer, get a surge suppressor with a TV cable connector and/or phone jacks.
• Indicators: They should have status or warning lights to indicate when the device is working (and not just on).
• Electrical noise protection: For EMI (electromagnetic interference) and RFI (radio-frequency interference).

Uninterruptible Power Supply (UPS)

Many kinds of electronic equipment cannot tolerate even the slightest fluctuation in power. Tiny disturbances can cause microprocessors - the brains of the computers - to reset, and you to lose your work. Computers have to be re-booted and production lines restarted.

How does a UPS help? A UPS can help protect any electronic equipment by isolating it from electrical disturbances. It filters the incoming power and provides additional power, stored in batteries, when the electric power drops or disappears altogether. The UPS does this so quickly that the sensitive equipment doesn't detect a drop in power.

Three Most Common Types of UPS

• Standby UPS: Power is normally routed directly to the equipment. Only if the power drops below a certain threshold does the unit switch on and function in a back-up mode. It's the least expensive type of unit.
• Line Interactive: This UPS provides some voltage regulation but switches to back-up only when an extended voltage dip is detected.
• Online UPS: The UPS is always on and always conditioning power. Although more expensive, they tend to provide more protection than the Standby model.

UPS Features

• Adjustments: A threshold adjustment lets you adjust how the unit operates. The adjustment may help prevent a UPS from cycling on & off unnecessarily, reducing battery life.
• Communications: A communication link can be used to manage the orderly shutdown of connected equipment before batteries are exhausted, alarm a system operator, schedule maintenance or report other parameters.
• Capacity: The rating or size of a unit is determined by the electrical demand, in Volt-Amperes, of the equipment it's intended to serve, plus any equipment growth. Battery size is based on the run time desired.
• Technology Type: The design determines the distortion (quality) of output power produced. Since some equipment is very sensitive, make sure the unit you purchase meets the requirements of the equipment to be powered.
• Filtering and Protection: Additional circuitry will determine how effective the UPS protects your equipment from conditions other than loss of power. You also should understand how your unit will react to abnormal conditions such as depleted batteries, overheating or loss of communications. Some units may turn off power to your equipment or leave your equipment totally unprotected.

UPS Recommendations

• Minimal - If you want protection at minimal cost, purchase a Standby UPS with 10 to 15 minutes of back-up.
• Critical - If you have critical equipment in an electrical environment with motors and other heavy equipment, purchase an Online UPS with 15 to 30 minutes of back-up.
• If you have a computer server or other critical application equipment, purchase an Online UPS with four hours or more of back-up batteries. Or, consider less battery time in combination with a back-up generator to carry the equipment before batteries are depleted.

Solutions to Common Problems

Computers

• Computer monitors are very sensitive to magnetic interference. Magnetic interference is common with fans, large electrical circuits, circuit breaker panels, etc. Position video displays away from fans or circuit breaker panels. If the monitor appears wavy, move it and see if the problem persists.
• Computer monitors also interact with fluorescent lighting. The monitor will appear to flutter. The video monitor settings in the operating software (Windows) allow you to change the display modes to 60Hz, 70Hz, 72Hz, 75Hz, 85Hz. The 85Hz appears to work well with office lighting. Your computer vendor can help you change these settings.
• Does your computer restart without warning? While computers are fairly tolerant to voltage changes, they will restart if the voltage drops significantly. Put sensitive equipment on its own circuit breaker and protect sensitive equipment with Uninterruptible Power Supplies (UPSs) and Surge Suppressors.
• Computers and monitors can also be sensitive to strong radio interference. Do not place your computer or monitor near a strong signal source such as a radio transmitting antenna. Even the small Family Radio Service (FRS) radios popular today can cause interference. Cell phones have not been a problem to date.

Lights

• Have you ever wondered why certain bulbs in your home just don’t last very long? Check their location carefully. Incandescent light bulbs are vulnerable to heat and vibration. If the bulb is enclosed and the heat cannot escape it likely will not last long. If the bulb is located under a hallway, in a stairwell, or near any surface that experiences vibration, it likely will not last long. Use compact fluorescent light bulbs in place of incandescent bulbs. They last longer, use less energy and are less sensitive to vibration and voltage flicker.
• Avoid inexpensive light dimmers. They are very sensitive to voltage dips causing lights to dim significantly with minor changes in voltage. Use electronic dimmers whenever possible.

Appliances

• Do your clocks frequently reset to the wrong time or blink and require a reset? While PSNH strives to “keep the lights on”, momentary interruptions do occur. They could be the result of an automobile accident or an animal or tree branch contacting the wires. Most clocks and some appliances manufactured in the last several years have battery backup systems. Check the backup battery at least twice a year.

Glossary of Utility System Terms

Alternating current (AC) - An electrical system in which voltage polarity and current flow alternates direction on a regular basis. Your home is an example of a system that is powered by AC.

Amp - A unit of electrical flow. In a water system flow might be expressed as gallons per minute.

Direct current (DC) - An electrical system in which current flows in one direction only. Batteries provide direct current.

Distribution System - This system of wires distributes electricity to neighborhoods and communities. The voltage on distribution lines ranges from 2,160 volts to 34,500 volts and is further stepped down with pole-top or pad-mounted transformers to a customer use level ranging from 120 to 480 volts. There are approximately 14,400 miles of distribution lines within the PSNH service territory.

Electric Meter - Electricity is provided to customers by wires, often called service drops, emerging from distribution transformers. These wires go into electric meters that measure the quantity of electricity used (measured in kilowatt-hours). The meter is typically located where the utility hands off the delivery of electricity to the customer. Generally the customer is responsible for purchasing and maintaining equipment past this point.

Flicker - A small change in line voltage, which causes a perceptible change in the intensity of electric lights.

Frequency - In an AC system, the value of voltage and current rise from zero to a maximum, falls to zero, increases to a maximum in the opposite direction, and falls back to zero again. This complete set of values is called a cycle. The number of complete cycles passed through in one second is called the frequency. The General Conference on Weights and Measures has adopted the name hertz (abbreviated Hz) as the unit of frequency. The common power frequency in North America is 60 Hz. In Europe and most of Africa and Asia it is 50 Hz. Airplanes typically use 400 Hz systems.

Generating Station - This is where electricity is produced. A generator is similar to a water pump. While a water pump creates water pressure causing water to flow, a generator produces electrical pressure to push electricity through the wires. Typically, this pressure is accomplished by converting a mechanical energy source to electrical energy (electricity). Examples of mechanical energy sources used at generating stations include steam under pressure that was heated by burning natural gas, coal, or nuclear fusion, or blades being turned by the power of the wind. This mechanical energy is then converted to electrical energy through a spinning shaft turning large magnets. Stationary coils of copper wire surround these rotating magnets. This rotating action causes electrons (packets of electrical energy) to move from atom to atom in the copper wire of the coils. This motion of electrons in the copper wire is electricity.

Harmonic - A whole multiple of the basic power frequency. On a 60 Hz system the 2nd harmonic is 120 Hz, the third harmonic is 180 Hz, and so forth.

Momentary Interruption - An interruption lasting no longer than 5 minutes.

Nominal Voltage - A nominal value assigned to a circuit or system for the purpose of designating its voltage class. Typical nominal customer service voltages are 120, 208, 240, 277, and 480. Larger facilities may be served at 4,160 or 12,000 volts.

Over Voltage - A long duration voltage variation at least 10 percent greater than the nominal voltage for a period of time greater than two minutes.

Pad-Mounted Distribution Transformer - This is the version of a distribution transformer which sits on the ground. Usually green and rectangular in appearance, this transformer is fed from underground lines.

Pole-Top Distribution Transformers -: These are the cylindrical gray cans you see mounted on utility poles. They will usually be found alone or in-groups of three depending on whether they serve a single-phase service (typical home or small business) or three-phase service (typical large business or industrial use). These transformers step-down the voltage on the distribution system to a level that can be utilized directly by customers.

Pole-Top Fuses -Fuses, similar to those found in some electrical equipment in your home, disconnect the electrical connection if a short circuit occurs. The fuse must be replaced after the problem has been located and corrected to restore service. Fuses are generally found at branches in the distribution system or ahead of transformers.

Power Factor - The ratio between Watts and Volt-Amperes. This ratio is generally expressed as a decimal fraction. A power factor of 1.00 is unity.

Recloser - This box, found on distribution utility poles, acts as a smart circuit breaker. It can determine if a short circuit occurs ahead or behind it. If the problem is behind the recloser it disconnects service. It can be programmed to try to reconnect after a short time period. This action may cause "blinks" on the line but can drastically reduce the length of the outage. Often short circuits on overhead distribution lines are caused by conditions that will disappear given a little time. Things like animal contacts or tree branches in the line. Many times the recloser can automatically re-energize the line after a very brief time. If the short circuit remains, the recloser will trip and lockout. At that point a service person must be dispatched to locate and repair the problem.

Short Circuit - An unwanted leak in the electrical system. Breakers or fuses act as safety devices to stop the flow should a short circuit occur.

Sustained Outage - Those interruptions lasting more than 5 minutes.

Substations - These sites contain specialized equipment to reduce or step-down transmission line voltage. Typically, the voltage is stepped down and is connected to a system of wires called the distribution system described above. Substations also contain large circuit breakers to stop the flow of electricity to transmission and distribution lines should the system develop a short-circuit (an electrical leak).

Switches -: Are used to easily reconfigure the electrical feeds on a distribution system should repairs or maintenance be needed. By reconfiguring the circuit, the number of customers without power can often be minimized.

Transient - A very brief excursion from nominal voltage with durations of a microsecond (millionths of a second) to several hundred microseconds.

Transmission System - The electricity produced at generating stations is connected to a system of wires called the transmission system. This interconnected "spider web" of wires carries electricity across cities, counties, states, and even countries through sets of three wires. The transmission system can carry electricity vast distances because it is done at very high voltages (up to 345,000 Volts). Because of this "high pressure" the wires of transmission lines must be suspended high in the air on very large steel structures or poles to keep it from "leaking away".

Under Voltage - A long duration voltage variation at least 10 percent below the normal (nominal) voltage for a period of time greater than two minutes.

Resistance - The opposition offered by a material to the flow of a steady electrical current.

Volt - A unit of electrical pressure. In a water system pressure might be expressed as pounds per square inch. The voltage found in most homes is 120 and 240 volts. Businesses will typically utilize voltage at 120 and 208, or 277 and 480 volts.

Voltage Sag - A decrease of 10 to 90% in the voltage for durations of one-half cycle to 1 minute.

Voltage Swell - A temporary increase in the value of voltage of more than 10% at the power frequency, for durations from one-half cycle to 1 minute.

Volt-Ampere (VA) - The product of volts times amps. A kilovolt-ampere (kVA) is equal to one thousand volt-amperes. VA is also known as apparent power.

Watt (W) - A unit of power equal to the product of the value of current of one ampere flowing in phase with the pressure of one volt. In a water system a comparable measure might be gallons per hour. A kilowatt is a thousand watts. W is also known as real (or true) power.

Watt-Hour (Wh) - A unit of energy equal to the power of one watt for one hour. In a water system a comparable measure might be gallons. A kilowatt-hour is a thousand watt-hours.