United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 76-05: Relay Failures - Westinghouse BFD Relays

                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 20555  

                                                  IE Bulletin No. 76-05 
                                                  DATE: April 2, 1976 
                                                  Page 1 of 3 

RELAY FAILURES - WESTINGHOUSE BFD RELAYS 

DESCRIPTION OF CIRCUMSTANCES: 

Three defective Westinghouse (W) type BFD relays were identified during 
recent testing of the Reactor Protection System at the H. B. Robinson Unit 2 
facility. One relay had an open circuit failure and the others had excessive 
opening times. The relays which failed were (W) type BFD with coil style 
503C428G21 rated for 125/130 volts dc (plus or minus 10%). These relays are 
normally energized from the 125 volt dc bus and, therefore, will be subject 
to 140 volts dc during battery charging operations. 

The relay manufacturer has determined that the three relay failures were 
caused by overheating of the relay coils. It was found that the overheating 
may result in coil insulation breakdown or melting of the coil solder 
joints, either of which may lead to an open circuit failure. Also, the 
overheating may result in deformation of the nylon coil sleeve in which the 
plunger travels, and this may adversely affect the relay opening time. 

The defective coil style 503C428G21 may be identified by its varnished cloth
outer cover. Manufacture of relays with these coils was discontinued in 
1973, and they have been superseded by coil style 1259C71G19. This later 
coil style may be identified by its molded outer form. Portions of a (W) 
service letter containing information about these relays is attached to this 
bulletin. Further instructions regarding this relay problem can be obtained 
from Westinghouse Nuclear Service Division, Pittsburgh, Pennsylvania 15230. 
.

                                                       IE Bulletin No. 76-05 
                                                       DATE: April 2, 1976 
                                                       Page 2 of 3  

ACTION TO BE TAKEN BY LICENSEES AND PERMIT HOLDERS 

For all power reactor facilities with an operating license or construction 
permit:  

1.   If you have received the attached (W) service letter, describe the 
     actions taken regarding corrective measures to resolve the relay 
     problem as discussed in the attached (W) service letter. 

2.   If you have not received the attached (W) service letter, describe the 
     actions planned if relays of the type and style described in the 
     attached (W) service letter are in use or planned for use in safety 
     related systems at your facility. 

3.   With regard to Item 2 of the attached (W) service letter, if the 
     opening time of any older style BFD relay exceeds 30 milliseconds, the 
     component should be modified or replaced promptly with a relay which is 
     more suitable for the application. 

4.   With regard to Item 3 of the attached (W) service letter, if the 
     temperature of the relay coil is found to exceed 212 degrees F during 
     operation, provided a means for reducing this temperature. In the 
     report submitted describe the means for maintaining steady state 
     temperature below 212 degrees F. 

Reports for facilities with operating licenses should be submitted within 30
days after receipt of this bulletin, and reports for facilities with 
construction permits should be submitted within 60 days after receipt of 
this bulletin. Your report should include the date when the above actions 
were or will be completed. 

Reports should be submitted to the Director of the NRC Regional Office and a 
copy should be forwarded to the NRC Office of Inspection and Enforcement, 
Division of Reactor Inspection Programs, Washington, D. C. 20555.  
.

                                                       IE Bulletin No. 76-05 
                                                       DATE: April 2, 1976 
                                                       Page 3 of 3 

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U.S.C 3512 from the U. S. General 
Accounting Office. (GAO Approval B-180255(R0072), expires 7/31/77) 

ATTACHMENT: 
Extract from Westinghouse service letter: 
     BFD RELAYS     
.

                                                       Attachment A  
                                                       IE Bulletin No.76-05 
                                                       DATE: April 2, 1976 
                                                       Page 1 of 2 

EXTRACT FROM WESTINGHOUSE SERVICE LETTER:  

BFD RELAYS  

During recent periodic testing at an operating nuclear power plant, three 
defective BFD (dc) relays were detected during testing of Reactor Protection
logic circuits. One relay coil had failed open and the other two 
demonstrated abnormally long drop-out times. These failures appeared to be 
due to overheating of the relay coils, resulting in coil insulation 
breakdown, or sufficient heat-induced deformation to adversely affect relay 
drop-out characteristics. 

The relays which failed are Westinghouse type BFD, (deleted), with style 
503C428G21 coils. These coils are visually identifiable by their varnished 
cloth cover outer layer (as opposed to molded coils). These control relays 
are used in dc application only. Type BF (ac) relays, and AR or ARD relays 
are not involved. 

Even though the relay coils are rated at 125-130 volts dc +- 10%, and 
suitable for application where occasional battery equalization charging 
condition of 140 volts appear on the dc bus, a design review has confirmed 
that the elevated temperature developed during elevated voltage operation is
sufficient to cause accelerated aging of the relay, and can result in coil 
degradation. 

Manufacture of these relays was discontinued in late 1973, and they were 
superseded by BFD style 5069A95, with style 1259C71G19 coils. These new 
coils are visually identifiable by the molded outer form. 
.

                                                       Attachment A  
                                                       IE Bulletin No.76-05 
                                                       DATE: April 2, 1976 
                                                       Page 2 of 2 

The new relay can be used to replace the old, with all operational 
characteristic being equal to, or better than the old. In addition the new 
coil, having a different class insulation should provide a higher level of 
reliability through less susceptibility to over-temperature degradation. The
new coils are dimensionally not suitable for mounting on the old relay. 
Therefore, replacement of the entire relay is required. Additional testing 
is being initiated to reaffirm a higher level of reliability of this new 
relay. 

In order for Westinghouse to complete our investigation of this matter and 
establish a final recommendation, all operating plants are requested to 
provide the following information as soon as possible. 

1.   Advise normal dc bus voltage; bus voltage during battery equalizing 
     charge; normal duration of equalizing charge; and normal frequency of 
     equalizing charge. 

2.   Conduct relay drop-out time measurements (in milliseconds) of all BFD 
     relays which provide reactor trip functions or safeguards initiation, 
     and which are energized during normal operation on the dc bus which is 
     subjected to battery equalizing potential. 

3.   Advise ambient temperatures of relay racks housing the relays in 
     question. 

4.   Testing of relay drop-out times should be repeated if equalizing 
     charging is required within the next 30 days. 

5.   Westinghouse recommends that equalizing charging on the dc bus should 
     not exceed 140 volts, and 24 hours duration. 
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