United States Nuclear Regulatory Commission - Protecting People and the Environment


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 ***



Page Last Reviewed/Updated Thursday, March 29, 2012