United States Nuclear Regulatory Commission - Protecting People and the Environment

INFORMATION NOTICE 93-85, Revision 1: Problems with X-Relays in DB- and DHP-Type Circuit Breakers Manufactured by Westinghouse

ACCESSION #: 9401130254                                                       

                                                                              

                              UNITED STATES                                   

                      NUCLEAR REGULATORY COMMISSION                           

                  OFFICE OF NUCLEAR REACTOR REGULATION                        

                       WASHINGTON , D.C. 20555-0001                             

                                                                               

                            January 20, 1994                                   

                                                                              

NRC INFORMATION NOTICE 93-85, REVISION 1:    PROBLEMS WITH X-RELAYS IN        

                                             DB- AND DHP-TYPE CIRCUIT         

                                             BREAKERS MANUFACTURED BY         

                                             WESTINGHOUSE                     

Addressees                                                                    

                                                                              

All holders of operating licenses or construction permits for nuclear         

power reactors.                                                               

                                                                              

Purpose                                                                        

                                                                              

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information      

notice revision to correct an error that identified a Westinghouse            

Electric Company (Westinghouse) DHP-type relay as a DHB-type relay in the     

original notice. This error occurred in the original information notice       

title, Purpose and the second paragraph of the Description of                 

Circumstances. As in the original, the purpose of this information notice     

is to alert addressees to the possible failure of the 52X-relay (X-relay)     

to reset in DB- and DHP-type Westinghouse breakers, thus preventing them      

from reclosing on demand. It is expected that recipients will review the      

information for applicability to their facilities and consider actions,       

as appropriate, to avoid similar problems. However, suggestions contained     

in this information notice are not NRC requirements; therefore, no            

specific action or written response is required.                              

                                                                              

Description of Circumstances                                                   

                                                                              

On June 27, 1993 , power to a motor control center was lost at the Haddam      

Neck nuclear power plant. Connecticut Yankee Atomic Power Company, the         

licensee, determined that the possible root cause for this event was a        

failure of the X-relay (anti-pump relay) to reset to the de-energized         

position in a Westinghouse DB-25 circuit breaker.                             

                                                                               

Previously, between July 1 and August 24, 1984 , the licensee reported         

five incidents in which one DB-25 and four DHP-250 breakers failed to         

close when required. All five of those failures were attributed to            

malfunctions of the X-relay. The licensee believed that dirt had caused       

the problem and instituted a program for cleaning the stationary and          

moving cores of the relay.                                                     

                                                                              

On June 11, 1991 , and on January 28, 1992 , Duke Power Company reported        

that, at the Oconee Nuclear Station, X-relays failed to reset and             

prevented the DB-25 breakers from closing in the Keowee hydroelectric         

generator field and field flashing circuitry. (The Keowee hydrostation        

supplies emergency power                                                       

                                                                              

                                                                              

                                                  IN 93-85, Revision 1         

                                                  January 20, 1994             

                                                  Page 2 of 3                 

                                                                              

to the Oconee station.) The licensee modified the anti-pump function with     

an electrical scheme that does not require the X-relay.                       

                                                                              

Discussion                                                                     

                                                                              

The X-relay is usually denoted by the symbol 52X in the electrical            

control circuit schematic diagram for the breaker. On receipt of a signal     

to close the breaker, the X-relay energizes and one set of its normally       

open contacts closes to enable momentary energizing of the breaker            

closing coil. After the breaker closes, the same set of X-relay contacts      

opens to deenergize the closing coil even though the X-relay remains          

energized by the close signal. If the close signal is still present after     

the breaker trips, the X-relay serves to inhibit repeated closure             

attempts until the close signal is removed. Thus, it provides anti-pump       

protection to the breaker by preventing repeated breaker closure attempts     

when a standing closure signal exists after a breaker trips.                   

                                                                              

The armature assembly of an X-relay (see Figure 1) fits inside a brass        

sleeve and is surrounded by the electromagnetic coil (different from the      

breaker closing coil) of the relay. When this coil is energized, the          

plunger (moving core) is drawn up towards the top cap piece (stationary       

core) of the assembly and the latch arm operates the relay contacts. In       

its uppermost position, an air gap is maintained between the                  

bullet-shaped top of the plunger and the cavity in the cap piece, with        

the shoulder of the plunger mating with the lip on the cap piece. When        

the coil is de-energized, the moving core is designed to fall, by             

gravity, into its lowest position. The failure of the moving core to fall     

to its lowest position is the possible failure mode of interest at Haddam     

Neck.                                                                          

                                                                              

Westinghouse and the licensee believe that residual magnetism associated      

with continuous energization of the relay or mechanical adherence between     

the two parts are probable causes for the plunger failing to fall.            

Westinghouse is testing a design enhancement that uses a brass spacer         

between the moving and stationary cores to create a controlled air gap.       

Westinghouse plans to issue a Nuclear Safety Advisory Letter to notify        

users of this problem. The licensee is evaluating a design modification       

for the X-relay function in the motor control center.                         

                                                                              

                                                                              

                                                  IN 93-85, Revision 1        

                                                   January 20, 1994             

                                                  Page 3 of 3                 

                                                                              

This information notice requires no specific action or written response.      

If you have any questions about the information in this notice, please        

contact one of the technical contacts listed below or the appropriate         

office of Nuclear Reactor Regulation (NRR) project manager.                   

                                                                              

                                                                              

                              Brian K. Grimes, Director                       

                              Division of Operating Reactor Support           

                              Office of Nuclear Reactor Regulation            

                                                                               

Technical contacts: Kamalakar Naidu, NRR                                      

                    (301) 504-2980                                            

                                                                               

                    Frederick H. Burrows, NRR                                 

                    (301) 504-2901                                            

                                                                              

Attachments:                                                                  

1.   Figure 1, X-Relay Magnetic Core                                          

2.   List of Recently Issued NRC Information Notices                          

                                                                               

                                                                              

                                                  Attachment 1                

                                                  IN 93-85, Rev. 1            

                                                  January 20, 1994             

                                                  Page 1 of 1                 

                                                                               

Figure 1 "X-relay Magnetic Core" omitted.                                     

                                                                              

                                                                               

                                                  Attachment 2                

                                                  IN 93-85, Rev. 1            

                                                  January 20, 1994              

                                                  Page 1 of 1                 

                                                                              

                         LIST OF RECENTLY ISSUED                              

                         NRC INFORMATION NOTICES                              

                                                                              

Information                        Date of                                    

Notice No.    Subject              Issuance  Issued to                        

                                                                              

94-05   Potential Failure of       01/19/94   All holders of OLs or CPs        

        Steam Generator Tubes                for pressurized water            

        with Kinetically Welded              reactors (PWRs).                 

        Sleeves                                                               

                                                                               

94-04   Digital Integrated         01/14/94   All NRC licensees except         

        Circuit Sockets with                 licensed operators.              

        Intermittent Contact                                                   

                                                                              

94-03   Deficiencies Identified    01/11/94   All holders of OLs or CPs        

        during Service Water System          for nuclear power reactors.      

        Operational Performance                                               

        Inspections                                                           

                                                                              

94-02   Inoperability of General   01/07/94   All holders of OLs or CPs        

        Electric Magne-Blast                 for nuclear power reactors.      

        Breaker Because of Mis-                                               

        alignment of Close-Latch                                              

        Spring                                                                

                                                                              

94-01   Turbine Blade Failures     01/07/94   All holders of OLs or CPs        

        Caused by Torsional                  for nuclear power reactors.      

        Excitation from Electrical                                            

        System Disturbance                                                     

                                                                              

93-101  Jet Pump Hold-Down Beam    12/17/93   All holders of OLs or CPs        

        Failure                              for boiling-water reactors.      

                                                                              

93-100  Reporting Requirements     12/22/93   All U.S. Nuclear Regulatory      

        for Bankruptcy                       Commission licensees.             

                                                                              

91-29,  Potential Deficiencies     12/22/93   All holders of OLs or CPs        

Supp. 2 Found During Electrical              for nuclear power reactors.      

        Distribution System                                                   

        Functional Inspections                                                

                                                                              

93-99   Undervoltage Relay and     12/21/93   All holders of OLs and CPs       

        Thermal Overload Setpoint            for nuclear power reactors.      

        Problems                                                              

                                                                               

OL = Operating License                                                        

CP = Construction Permit                                                      

                                                                               

                                                                              

*** END OF DOCUMENT ***                                                                               

                                                                              

                                                                              

 

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