United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9603270295


28 February, 1996

Vern Hodge

Mail Stop 0-11A1
Washington, DC 20555

Reference:     Report No. 10CFR21-0073

Subject:       Reportable defect with NEI voltage regulator voltage
               adjust potentiometer

Dear Mr. Hodge:

MKW Power Systems' report 10CFR21-0073 is attached which addresses a
10CFR21 reportable defect with the voltage adjust potentiometer used on
the NEI Peebles (Portec) voltage regulators.  This was brought to our
attention by FP&L - Turkey Point and we immediately began an
investigation to determine the impact on other users of the same/similar
equipment.  Our investigation was completed on 2/26/96.

Yours very truly,


Michael Nuding
General Manager - Quality Assurance



    Post Office Box 1928 o Rocky Mount, North Carolina 27802-1928 o
                         Phone: (919) 977-2720
                TWX: (510) 929-0725 o FAX: (919) 446-3830


                                        Report No. 10CFR21-0073
                                        FEBRUARY 27, 1996

                      10CFR21 REPORTING OF DEFECTS
                           AND NON-COMPLIANCE

COMPONENT:     Chicago Telephone Supply (CTS), p/n 115R251A Voltage
               Adjust Potentiometer

SYSTEM:        Diesel Generator control systems with NEI Peebles (Portec)
               Voltage Regulators

CONCLUSION:    Defect is Reportable in Accordance with 10CFR21

PREPARED BY:                                      DATE:
               Donald D. Galeazzi
               Engineering Manager

REVIEWED BY:                                      DATE:
               Michael Nuding
               General Manager, Quality Assurance

     Post Office Box 1928 o Rocky Mount, North Carolina 27802-1928 o
                          Phone: (919) 977-2720
                TWX: (510) 929-0725 o FAX: (919) 446-3830

                                             REPORT NO. 10CFR21-0073
                                             PAGE: 1 OF 5


MKW Power Systems witnessed repair and testing of a voltage regulator for
FP&L Turkey Point at NEI Peebles on 2/10/96 and 2/11/96.  NEI
manufactured many of the voltage regulators utilized in MKW's safety
related diesel generators.  Voltage instability was observed and was
determined to be caused by foreign material on the stationary wiper
portion of the R4 voltage adjust potentiometer.  The potentiometer is 250
ohm, 2w, manufactured by Chicago Telephone Supply (CTS), p/n 115R251A and
had been used by NEI for over twenty years for this application.  Because
of availability problems, NEI replaced the CTS potentiometer with Maury
Instrument Corporation p/n 50-M123-251 in 8/94).  This is an enclosed
precision wirewound potentiometer, 250 ohm, 1.5w, with a shaft locking
nut.  According to NEI, applied burden is 0.06w.  When compared to the
CTS component, the Maury is an upgrade in quality and appears to be less
susceptible to contamination on the wiper surface.  The FP&L regulator
had the R4 potentiometer replaced with the Maury part while at NEI and
the voltage instability was corrected.

The purpose of the R4 potentiometer is to adjust generator voltage to
rated value after installation of the remote voltage adjust motor
operated potentiometer.  This is normally a one-time adjustment which
occurs during initial installation/startup of the EDG and is applicable
to the automatic and manual (if used) voltage regulators.

MKW has been supplying NEI voltage regulators for safety related EDG
control systems since 1972.  This incident and one prior in 1994 (FP&L
EDG 4A and 4B respectively) are the only reported problems of this type;
therefore, it is difficult to interpret this occurrence as a defect.  In
addition, because R4 is normally a one-time adjustment, any foreign
material which develops/accumulates on the wiper surface will not affect
voltage regulator operation because it will not interfere with the wiper
surface to wiper arm interface.  It is recognized that this could cause
problems if field adjustment of R4 is required; therefore, MKW Power
Systems will notify all customers with NEI voltage regulators about this
potential condition.


Chicago Telephone Supply (CTS), p/n 115R251A (NEI p/n 01068).

                                             REPORT NO. 10CFR21-0073
                                             PAGE: 2 OF 5



Duke Power - Oconee                #72-13000-100
FP&L - St. Lucie #2                #72-05000-100       #72-05100-100
FP&L - Turkey Point                #72-13000-100       #72-13200-100
Grand Gulf                         #72-03200-100       #72-03100-100
Knolls Atomic - Kesselring         #72-05000-100       #72-05100-100
Portland G.E.  - Trogan            #72-00101-100
PP&L Susquehanna                   #72-08300-100       #72-08400-100
SMUD                               #72-05000-100       #72-05100-100
TVA Watts Bar                      #72-06204-100       #72-05100-100
TVA Watts Bar/Sequoyah             #72-06204-100       #72-05100-100
Wisconsin Elec - Pt Beach          #72-05000-100       #72-05100-100


Almaraz - Spain                    #72-05000-100       #72-05100-100
CNV/G.E. - Spain                   #72-05000-100       #72-05100-100
Cofrentes/G.E. - Spain             #72-05000-100       #72-05100-100
Korea Elec - Kori II               #72-05000-100       #72-05100-100
KRSKO - Slovenia                   #72-05000-100
Kuo Sheng/G.E.                     #72-05000-100       #72-05100-100
Laguna Verde (HPCS)                #72-01200-201S      #72-01200-101
Laguna Verde - Units 1&2           #72-05000-100       #72-05100-100
Phillippines                       #72-05000-100       #72-05100-100
Zorita - Spain                     #72-05000-100       #72-05100-100


Microscopic examination of the potentiometer showed foreign material on
the surface and edge of the stationary slip-ring under the wiper arm
collar.  The material on the edge was translucent/white-ish and appeared
to be a lubricant.  The material on the surface was blackish with some
white flakes.  It is postulated that the lubricate accumulated
contaminants and/or dried on the surface.  The total amount of foreign
material is very small.

                                             REPORT NO. 10CFR21-0073
                                             PAGE: 3 OF 5


1)   FP&L is in the process of updating their voltage regulators with the
     Maury potentiometer.  Other users should be aware of this possible
     problem and monitor their EDG output voltage for unstable output
     during routine testing.  Replacement of the potentiometer is
     dependent upon monitoring/testing.  Immediate response to this
     notification does not appear to be necessary as the majority of the
     in-service voltage regulators have been operating without incident
     for approximately 15-20 years.

2)   The potentiometer is soldered to a circuit board within the voltage
     regulator assembly; therefore, field modification is not
     recommended.  For replacement of the potentiometer, it is
     recommended that the regulator be returned to NEI (either directly
     or through MKW Power Systems) where proper testing can be performed
     before the regulator is returned to the customer.  Contact MKW Parts
     Department for assistance.

     If a regulator is to upgraded, we would also recommend replacement
     of the R5 (stability) potentiometer which is the same type as the R4
     potentiometer except it is 100 ohms.  This is strictly optional, no
     voltage regulator operability problems exist with the R5
     potentiometer.  The R5 potentiometer is CTS p/n 115R101A (NEI p/n
     01070) and its replacement is Maury p/n 50-M123-101.

                                             REPORT NO. 10CFR21-0073
                                             PAGE: 4 OF 5

                                EXHIBIT 1
                            (1 page attached)

                           NEI DRAWING A-01068

                             Figure omitted.

                                             REPORT NO. 10CFR21-0073
                                             PAGE: 5 OF 5

                                EXHIBIT 2
                            (1 page attached)

                            "R4" REPLACEMENT
                           MAURY #50-M-123-251

Figure 50-M123 "WIREWOUND MIL-TRIMMER" omitted.

Rugged instrumentation trimmer potentiometer with shaft locking nut meets
MIL-R-12934C.  Extensively used in critical military aircraft
applications where small size and reliability are essential.  1.5 Watts
at 85 degree C; special 0.5 Watt at 150 degree C.


Page Last Reviewed/Updated Wednesday, February 12, 2020