United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 76-02: Relay Coil Failures - GE Type HFA, HGA, HKA, HMA Relays

                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D. C. 20555
                                                            IEB 76-02 
                                                            3/12/76  
                                                            2 pages 

Inspection and Enforcement Bulletin (IEB) 
Number 76-02, March 12, 1976 

RELAY COIL FAILURES - GE TYPE HFA, HGA, HKA, HMA RELAYS 

DESCRIPTION OF CIRCUMSTANCES: 

A failure of a General Electric (GE) model 12 HFA 5lA42H Relay occurred 
recently in a safety related circuit at the Turkey Point facility. The relay
failed during reactor safeguards systems testing. Earlier failures of a 
similar nature involving GE type HGA relays were reported from Florida Power
and Light Company in 1973. 

The relay manufacturer has determined that open circuit coil failures of the
relay windings had been caused by corrosion. Halogens from a class of nylon 
coil spools (or bobbins) plus humid conditions were attributed as the 
fundamental causes of the corrosion and resulting coil failure. 

The relays identified by the manufacturer which may have this nylon spool 
include HFA, HGA, HKA, HKA relay types, made by GE prior to 1969, and they 
may be identified by a white, nylon coil spool. Portions of a GE service 
letter containing information about these relays are attached to this 
bulletin. Further instructions regarding repair procedures can be obtained 
from the GE Service Engineering Department, Philadelphia. 

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 GE service letter, describe what 
     action you have taken regarding replacement of the older style nylon 
     coil bobbins with the recommended Lexan type bobbins in the types of 
     relays identified in the enclosed GE letter. 

2.   If you have not received the attached GE service letter, describe what 
     action you plan to take if relays of the type and vintage described in 
     the enclosed GE letter are in use or planned for use in safety related 
     systems. 
.

                                                                 IEB 76-02 
                                                                 3/12/76 
                                                                 page 2 

      ACTION TO BE TAKEN BY LICENSEES AND PERMIT HOLDERS (continued) 

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 also 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.  

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U.S.C. 3152 from the U. S. General 
Accounting Office. (GAO Approval B-180255(R0072), expires 7/31/77) 

ATTACHMENT: 
     Extract from General Electric Service Letter: 
     HFA, HGA, HKA, HKA RELAYS 
     NYLON COIL BOBBINS 
.

IE Bulletin Number 76-02                                    IEB 76-02 
ATTACHMENT A                                                Att. A  
                                                            2 pages 

EXTRACT FROM GENERAL ELECTRIC SERVICE LETTER (retyped for transmission) 

HFA, HGA, HKA, HMA RELAYS NYLON COIL BOBBINS 

     In 1954, a program was initiated to improve the mechanical and 
electrical properties of paper based spools used for HFA, HGA, HKA and HMA 
relay coils. Heat stabilized nylon was selected for the spool material 
because its temperature characteristics made it well suited for Class A 
coils, and the material provided the desired improvement in electrical and 
mechanical properties. Manufacturing of HMA relays with the nylon spools 
started in 1955. After three years of successful experience, the change to 
nylon spools was implemented in HFA, HGA, and HKA relays in 1958. 

     In the mid 60's, a few failures of HKA coils utilizing the nylon spools
for DC applications were reported. As a result of these failures, an 
investigation was undertaken to determine the cause of the failures. It was 
found from this investigation that the heat stabilizing element of the nylon
coil spool contained halogen ions which could be released over a period of 
time. When combined with moisture, the halogen ions form hydrocloric acid 
and copper salts which could cause the eventual open circuit failure of the 
coils. 

     The most significant contributing factor in the reported failures is 
high humidity. Other contributing factors are the small wire size used in 
HMA relays and in DC relays, and the release of halogen ions is accelerated 
by DC potential. Relay coils which are continuously energized are not 
subject to this phenomenon because the coil temperature is maintained 
considerably above ambient, thus minimizing the probability of moisture 
getting into the coil. 
.

                                                            IEB 76-02 
                                                            Att. A  
                                                            page 2 

     After the Spool material was changed to nylon in 1955-58, a new 
material, Lexan, became available. Lexan has the desired chemical, 
mechanical and electrical characteristics for use in spools. The change to 
the use of Lexan for Spools was started in 1964 and completed in 1968. The 
first relay changed was the HMA followed by the HGA and HFA. Black was 
chosen for the color of Lexan spools to make them distinguishable from the 
nylon. 

     Since the initial report of open circuited HMA coils, the failures of 
auxiliary relays has been very limited. However, recently one customer 
reported an accumulation of open circuit failures of a significant number of
HGA relays with nylon spools which were used in X-Y closing circuits of 
breakers. As a result of this recent report and in keeping with our 
procedure of informing you of potential problems, we are bringing this 
matter to your attention, even though the overall rate of failure continues 
to be extremely low. 

     (Paragraph deleted) 

     If you have applications of HFA, HGA, HKA, and HMA relays in areas of 
high humidity, intermittent operation, DC power, and with white nylon 
spools, you may wish to consider replacing the coils or relays. 

     (Paragraph deleted)  
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