Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9511290232
ABB
November 20, 1995 Page 1 of 3
Document Control Desk
US Nuclear Regulatory Commission
Washington, D.C. 20555
SUBJECT: ABB Relays Power Shield Units Type SS-13
Illinois Power, Docket Number 50-461
10CFR Part 21 Report
NOTIFICATION BY: ABB Power T&D Company
Protective Relay Division
7036 Snowdrift Road
Allentown, PA 18106
Harry A. Hinch
Quality Assurance
On October 11, 1995 ABB Power T&D Co. Inc., Allentown, PA. received a
copy of a letter from Illinois Power, Clinton Station, that was sent to
the NRC Document Control Desk, Docket Number 50-461 dated October 6,
1995. This letter was in regard to the two (2) Power Shield Trip Units,
Type SS-13 Part Number 609901-T012, serial numbers 45779 and 45778 that
Illinois Power reported had false tripped their VC and VX system circuit
breakers.
Serial number 45779 was returned to ABB on October 13, 1995 for failure
analysis. The manufacturing date of this relay was 1980. The suspect
relay was electrically tested and inspected by the QA and Repair
Department with the following results:
1. Upon initial electrical testing, the reported problem of serial
number 45779 was verified. The unit was found with an
intermittent output signal that would cause the circuit breaker
to false trip.
2. The above unit was disassembled and inspected and the following
problem was identified:
ABB Power T & D Company Inc.
Telephone: Distribution Relay Division fax: :
610-395-7333 7036 Snowdrift Road, Suite 2 610-395-1055
Allentown, PA 18106
November 20, 1995 Page 2 of 3
2a. A broken solder connection, 360 degree break, was found on
pin #1 of the printed circuit board edge connector located
on the control board. Pin #1 connects the anode of diode
D-205 to terminal # 3 which is connected to R-11 power
supply external load resistor. Opening this circuit will
cause the unit to trip. The edge connector is a Molex
right angle type 2145 with gold plated brass terminals.
Serial number 45778 was returned to ABB on October 20, 1995 for test and
failure analysis. The manufacturing date of this unit was also 1980.
This unit was also electrically tested and inspected by the QA and Repair
Department with the following results:
1. Upon initial electrical testing, serial number 45778 operated
normally on all functions. No malfunctions were identified.
2. The unit was disassembled and inspected. The following items
were identified:
2a. A broken solder connection, 360 degree break, was found on
pin #1 of the edge connector of the control board. (Same
location identified in S/N 45779).
2b. Pin #2 on the same edge connector showed some partial
signs of cracking, less than 360 degrees.
Harry Hinch the Allentown ABB Quality Supervisor, visited Illinois Power
Clifton Station on October 21, 1995 to train Illinois Power personnel in
disassembly, inspection, assembly and testing of the Power Shield Units
Type SS-13. During the inspection several more questionable solder
connections were found. These connections were desoldered, cleaned and
resoldered per ABB procedures by Illinois Power personnel.
ABB has sent several printed circuit boards with defective solder
connections to SAIC (Science Applications International Corp.) test lab
for failure analysis. The findings are that the solder fillets have
become embrittled through copper diffusion (time and temperature related
phenomena). This in itself is not enough to cause a failure, as
evidenced by the lack of failures from other solder joints on the board.
However, embrittled solder is prone to fatigue cracks brought on by
mechanical and thermal stress. Thermal stress was probably a minor
problem, as none of the other solder joints from this assembly showed any
signs of cracking. Normal mechanical stress associated with the
connector mating operation and copper diffusion probably caused the
majority of the cracks.
November 20, 1995
Page 3 of 3
ABB recommends that all Power Shield SS Trip Units prior to serial number
80,000 in service be inspected. This potentially defective solder
connection could be present on the female edge connector on any of the
printed circuit boards and/or the male connector on the base board.
Instructions for inspection of acceptable and non-acceptable solder
connections, and procedures for removing solder, cleaning and resoldering
of defective solder connections are provided in Attachment A to this
letter.
Relays manufactured after serial number 80,000 contain a technical
improvement, namely double sided pads and plated through printed circuit
board holes which greatly reduce the likelihood of solder connection
failures. ABB has not seen any failures of this type since changing the
design.
These Power Shield SS Trip Units were manufactured during a period when
corporate name changes occurred. The nameplate may show one of these
Company names: ITE, Gould, BBC Brown Boveri Electric Co., BBC Brown
Boveri, or ASEA BROWN BOVERI.
ABB will notify all end users who purchased this product.
Prepared by
Harry Hinch
QA Supervisor
Reviewed by
Jack Martin
Product Line Manager
Reviewed by
Cheryl Dahle
Manager, Total Quality
Reviewed by
Robert Smith
Allentown, Site Manager
ABB
10CFR Part 21 Report
Attachment A
November 20, 1995
Page 1 of 2
All Power Shield Trip Units type SS prior to serial number 80,000 should
be inspected for broken or cracked solder connections. Units above
serial number 80,000 contain a technical improvement namely double sided
pads and plated through printed circuit board holes which greatly reduce
the likelihood of solder connection failure. ABB has not seen any
failures of this type since changing the design. Inspection of units
above serial number 80,000 is not required.
Before disassembly, the unit must be de-engerized and removed from the
circuit breaker.
Disassembly:
1. Remove the four (4 ) screws on the Plexiglas cover. Remove cover.
2. Record the tap pin settings for each function so the unit can be
reset after rework is complete. Remove tap pins after recording
settings.
3. Remove terminal screws number 3 and 16. Detach external resistor
wires.
4. Remove the two (2) shoulder screws at the top of the front panel and
the two (2) screws at the bottom of the panel. Remove the front
panel. Carefully remove the two (2) round spacers located on the
face of the mounting blocks on each side of the terminal block.
Note: at times, spacers stick to the underside of the front panel.
5. Remove two (2) screws, one from the face of each mounting block.
Remove the circuit card assembly from the gray case.
6. Remove the four mounting screws from the top printed circuit board.
( Short Time and Ground card PCB, if the unit is equipped with these
functions). Remove board.
7. Remove the four (4) shoulder screws from the next printed circuit
board ( Long Time and Inst. PCB). Remove board.
8. Remove the four (4) shoulder screws from the next printed circuit
board ( Control Board PCB). Remove board.
9. Remove mother board from Transformer printed circuit board.
ABB Power T & D Company Inc.
Telephone: Distribution Relay Division fax: :
610-395-7333 7036 Snowdrift Road, Suite 2 610-395-1055
Allentown, PA 18106
10CFR Part 21 Report
Attachment A
November 20, 1995
Page 2 of 2
Inspection:
1. Inspect the solder connections on the female edge connector of each
printed circuit board and all the solder connections on the four (4)
male connectors mounted on the mother board. The Martin Marietta
soldering standards or photographs provided by ABB should be used
when inspecting these solder connections. Photographs identifying
the defective joints can be provided upon request. If any broken or
defective solder connections are found, they should be repaired by
qualified personnel familiar with electronic repair. ABB recommends
the following method be used:
1a. The defective solder connection must be completely desoldered
by using a good quality desoldering tool or solder wick. Care
must be used when desoldering the joint. Excessive heat will
cause the printed circuit pad to lift off the board.
1b. All flux residue and poly spray must be removed from the
connection area. ABB recommends that Micro Care MCC Pro Clean
be used.
1c. ABB recommends when resoldering the connection, a 60/40 rosin
core solder be used. The soldering iron temperature should be
700 to 800 degrees. Upon completion, the soldered connection
should be cleaned of all flux residue. Personnel resoldering
questionable connections should have electronic repair and
soldering skills and follow established ESD practices. When
resoldering the connection on the female edge connector, ABB
recommends that the rear mother board with male connectors is
inserted into the female connector during soldering.
Reassembly.
1. Upon completion of the inspection, repair, and cleaning of the
solder connections, proceed with the assembly in reverse order of
steps 1 to 9.
2. Hardware should be torqued 9 to 10 inch pounds. All required
lockwashers should be fully compressed.
Upon completion of the reassembly, the unit must be tested per
Instruction bulletin IB number 6.1.2.7-4 before being returned to
service.
*** END OF DOCUMENT ***
