ML042960393

Draft Preliminary Root Cause of Failure Analysis 13.8kV Breaker Failures During Losss of Switchyard Event

ML042960393
Person / Time
Site:	Palo Verde
Issue date:	07/05/2004
From:	Arizona Public Service Co
To:	Office of Nuclear Reactor Regulation
References
FOIA/PA-2004-0307
Download: ML042960393 (10)

Text

DRAFT Preliminary Root Cause Of Failure Analysis 13.8kV Breaker Failures during Loss of Switchyard Event Event Date: 6/14/04 Revision 0, 7/05/04 Executive Summary Two out of twenty 13.8kV breakers that provide offsite power to the units failed to close on demand from the control room during the Loss of Offsite Power event on June 14, 2004. One of these breakers has been removed for root cause of failure testing. These tests indicate that the breaker could have failed by either hardened grease that caused binding of the breaker mechanical linkage or high contact resistance in a relay in the close circuitry. These breakers were repeatedly cycled during the event so the true root cause may never be known. The second breaker that failed is still in service awaiting an opportunity to remove it for testing.

A review of the failure history of these and similar breakers revealed that we have had, including these two failures, seven similar failures since 1988, three of which happened this year. Action was taken in 2000 that cut the PM frequency on these breakers in half. This is apparently not enough to prevent these failures. A modification is in progress to provide air conditioning for these outdoor switchgear that will reduce temperatures and hopefully extend grease life.

A review of the maintenance history for these and similar breakers shows that the maintenance has been performed on them in accordance with the existing PM program, although we are still in the final stages of adapting to the periodicity change that took place in 2000. We have only three spares of these large breakers, which may be partly to blame for the length of time required to accomplish this goal.

The final corrective actions for this condition have not been determined but will include the air conditioning currently scheduled for installation in the W05 window (winter of 2005), and may include use of an alternate grease, exercising the breakers more often, and periodic replacement of the circuit breaker anti-pump relay.

Background

On 6/14/04, while recovering offsite power to the three PVNGS units after a Loss of Offsite Power event, 13.8kV circuit breakers IENANS06K and 3ENANS05D failed to close on demand from the control room. Electrical Maintenance and Engineering were dispatched to investigate.

With maintenance personnel in attendance, and while repeating the attempts to close each of these breakers from the control room, a clicking sound could be heard from the breaker cubicles but the breakers would not close. The breakers were moved to the test position, cycled closed and open several times, racked into the operating position and closed normally to re-energize the system. Closure problems with IENANS06K delayed restoration of offsite power to the unit I Train B 4160V bus and problems with 3ENANS05D delayed restoration of offsite power to the unit 3 Train A 4160V bus. Although these breaker problems delayed restoration of offsite power to the affected busses by approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, both of the busses were powered from their respective EDGs during this period. Both of these breakers had been successfully manually tripped per procedure in response to the event.

Each unit's E-NAN-S05 and -S06 switchgear are located outdoors in the startup yard near the 525kV switchyard. These busses are cooled by ventilating fans that circulate filtered outside ambient air through them. Especially during the daylight hours of the summer months, these

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DRAFT Preliminary Root Cause Of Failure Analysis 13.8kV Breaker Failures during Loss of Switchyard Event switchgear are exposed to high temperature conditions that lead to drying out of the breaker lubricating grease. Although the ventilating air is filtered, dirt accumulation still occurs. This condition also applies to outdoor busses E-NAN-S03 and -S04, which are other intermediate 13.8kV busses that are also in the offsite power lineup to the class IE 4160V busses. All breakers in these busses operated properly during the event.

Because these breakers provide offsite power to the units, they cannot be cycled frequently and are typically cycled only every 18 months during refueling outages. This mechanically static condition exacerbates the effects of the high temperatures because the lubrication is never freed up through exercise.

One function of these breakers is to open (trip) to provide electrical protection during electrical disturbances. They properly tripped in response to procedurally directed operator actions. The second function of these breakers is to provide offsite power to the units. For this latter function, they must be closed. They are currently closed and are in the required position per the Technical Specifications.

Evaluation From a work history standpoint, breaker S/N 269A7243-020 was rebuilt on 01/01/2002 and installed in cubicle 1ENANS06K on 11/18/2002. Breaker 269A7245-023 was rebuilt on 11/04/2002 and installed in cubicle 3ENANS05D on 12/24/2002. Breaker IENANS06K was operated in the last unit 1 refueling outage during the clean/inspect PM for the switchgear conducted in the second week of April 2004.

The higher than expected failure rate, coupled with similar industry operating experience, was recognized several years ago. Procedure 32MT-9ZZ37 implements periodic overhaul of 13.8kV breakers. Originally, testing and overhaul of these breakers was scheduled to be completed every 4 refueling cycles for breakers that cannot be done online, or every 8 years for those that can be done online. In 2000, this schedule was cut in half. These breakers are now tested and overhauled every 2 cycles (3 years for offline) or 4 years for those that can be worked online.

PVNGS is nearly complete with the last breaker under the new PM schedule. The last breaker (3ENANS06A) was actually scheduled for replacement on the day of the event.

On 6/19/04, breaker 3ENANS05D was removed from service for an Equipment Root Cause of Failure Analysis (ERCFA). However, because of the repeated cycling of the breaker during the event, root cause of failure evidence was unavoidably tampered with and lost. This investigation was performed in accordance with the ERCFA Plan provided in Attachment A.

The clicking sound heard from the cubicles was at first believed to be indicative of the electrical circuitry of the breakers to be working properly, leaving only the mechanical linkage of the breakers as the cause of the failure. However, after closer review of the control circuit, there is an interposing relay 'CR' that receives the signal from the control room handswitch. This relay picks up and closes a contact that actually closes the breaker. Because the clicking heard could be coming from the CR relay by itself, or the combination of the CR relay and the close coil armature, the exact source of the click is indeterminate.

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DRAFT Preliminary Root Cause Of Failure Analysis 13.8kV Breaker Failures during Loss of Switchyard Event The following conditions were investigated or found that were potential contributors to the breaker's failure to close during initial attempts from the control room.

1) The control circuit secondary disconnect male disconnect stab at pin 8 had evidence of arding which was a potential poor contact for the close circuit. On June 23, the mating socket was retrieved from the 3ENANS05D cubicle. It had no evidence of arcing.

Therefore, this arcing does not appear to be a contributing factor.

2) The control circuit secondary disconnect male disconnect stab at pin 8 is positioned

-1/8" lower than adjacent stabs. Shop testing has demonstrated satisfactory performance due to approximately 1/2" wipe between the male stab and the socket. This does not appear to be a contributing factor.

3) Also on June 23, the proper operation of the CR relay in 3ENANS05D was tested. The relay tested satisfactorily. This does not appear to be a contributing factor.

4) The anti-pump relay circuit had high intermittent contact resistance that could have prevented breaker closure. However, even with high resistance, the breaker would close on demand in the shop. This is a potential contributor to the failure.

5) The as-found breaker Close function was tested. Satisfactory results were obtained for both the minimum operating voltage (-42Vdc vs. maximum allowed of 9OVdc) and the close timing tests (72ms vs. maximum allowed of 100ms). This result is inconclusive due to the preconditioning that took place while cycling the breaker on the day of the event.

6) The as-found breaker Trip function was tested. Unsatisfactory results were obtained for both the circuit minimum operating voltage (77Vdc vs. maximum allowed of 7OVdc) and trip timing (77ms vs. maximum of 55ms). This condition could have been worse on the day of the event because the cycling of the breaker on the day of the event likely improved this condition. This is indicative of a hardened grease condition.

The as-found test history of these offsite breakers and other breakers in similar environments was reviewed and is presented in Attachment B. Failures to meet the acceptance criteria are highlighted in red. The data show that these breakers are three to four times more likely to fail the trip function acceptance criteria than the close function acceptance criteria. This is consistent with the findings for breaker 3ENANS05D presented above. The high failure rates indicate that the PM program effectiveness needs to be improved although it should be noted that the acceptance criteria are generic and failure to meet them does not necessarily indicate an inability of a specific breaker to perform its design function. For example, the timing of these breakers to close is not particularly relevant; it matters little whether the breaker closes in 70 milliseconds or 170 milliseconds in response to a manual operator action to close the breaker during restoration of the breaker lineups. Similarly, available DC bus voltage is not expected to drop below approximately 112Vdc even though jhe close function acceptance criterion is conservatively set at 9OVdc.

Two more activities are planned that will hopefully shed addition light on the cause of the failures of these breakers. During the week of 7/26/04, breaker 3ENANS06A will be replaced with an overhauled breaker. This breaker is the oldest breaker in service and was scheduled for replacement on the day of the event. The same tests as described above will be performed on it.

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DRAFT Preliminary Root Cause Of Failure Analysis 13.8kV Breaker Failures during Loss of Switchyard Event However, this breaker had a failure-to-close event in April 2004 and it was somewhat lubricated in the field. Therefore, the results may not be very revealing.

The second activity is the retrieval of breaker 1ENANS06K to perform the same battery of tests.

To remove this breaker from service requires that unit l's 'B' class lE 4160V buss be put on its alternate source of power. Procedural revisions are in process to direct this configuration and a spare breaker must be overhauled to support this. This breaker replacement is not yet scheduled.

Transportability The failure history of these breakers and all breakers like them was investigated and is presented in Attachment B. There have been seven failures since 1988 that are possibly related to these recent breaker failures, three of which happened this year. Before that, the last one was in 1998.

One of these seven involves degraded relay contacts. In addition, there is a significant amount of industry operating experience involving GE Magne-Blast circuit breakers and hardened grease causing mechanical binding. This condition is believed transportable to all Magne-Blast breakers located in outside or hot switchgear locations.

The maintenance history of all breakers affected by this transportability has been reviewed and is presented in Attachment C. Although we are in the final stages of adapting to the PM frequency revisions implemented in 2000, all breakers have had appropriate periodic maintenance performed.

Apparent Cause Because of the preconditioning that occurred during the event on the two breakers that failed, their root cause of failure may never be known. At this time, based on only the findings of the assessment of 3ENANS05D, the apparent cause of its failure to close is improper operation of the close latching mechanism either due to poor lubrication and contamination by dirt or due to high contact resistance of the anti-pump relay.

Corrective Actions Modification WO 2508436 was initiated in April 2002 to add air conditioning to the outdoor sNwitchgear to provide cooling and reduce dirt intrusion. This mod is scheduled for implementation per the 3-cycle plan in late 2005 or early 2006.

Other potential corrective actions that may come out of the final assessment of this condition include use of an alternate grease that is less susceptible to hardening, more frequent exercise of the breakers, and periodic replacement of the anti-pump relay.

Conclusion Continued use of these breakers is acceptable based on their ability to properly trip and the fact that they are in the desired position thus obviating the need to close them. Additional preventative maintenance actions may be instituted during the final evaluation of the associated CRDR 2716019.

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ATTACHMENT A Breaker 3ENANSOSD Failure To Close Equipment Root Cause of Failure Investigation Plan WO 2717143 POTENTIAL CAUSES:

1. Breaker problem - mechanical, alignment, close latch wipe & lubrication issue

REFERENCES:

1. 03-E-NAB-0001

2. 32MT-9ZZ33, Maintenance of Medium Voltage Circuit Breakers Type AM-13.8-1000

3. 32MT-9ZZ37, Overhaul of AM-13.8-1000 Magne-blast Circuit Breakers PLANT IMPACTS:

None - This investigation is being performed on Out-Of-Service equipment.

INSTRUCTIONS:

Breaker 3ENANS05D failed to close from the control room on 6/14/04. Electrician at the switchgear distinctly heard the closing coil attempting to pick up when Operations tried to close the breaker. The breaker was racked down, placed in TEST position and successfully cycled twice. The breaker was then racked up and was satisfactorily closed from the control room. Due to the emergent condition of the plant at the time, neither detailed troubleshooting plan nor a follow-up plan was issued until now.

This plan entails troubleshooting, overhaul and maintenance of the breaker only. The transfer of power from the normal supply to the alternate supply is a normal Operations activity and will not be covered by this plan.

The breaker replacement and breaker alignment are normal maintenance actions and will not be covered under this plan.

1. Verify breaker S/N and transport the breaker to the shop.

2. Before any overhaul or maintenance is done on the breaker perform the following:

a. Visually inspect the breaker. Look for signs of excessive dust and dirt build up.

b. Visually inspect the closing and tripping linkages for any signs of binding or misalignment that could cause breaker failure to close or open.

c. Check that the close latch & roller and the trip latch & roller are rotating freely and no hardened lubricant is present on the surface.

d. Perform step 4.21 "Closing Latch Wipe" check per procedure 32MT-9ZZ33 then perform a main contact closing time test.

e. Perform a main contact opening time test.

f. Repeat step 2.d for spring release coil pickup voltage test.

g. Repeat step 2.e trip coil pickup voltage test.

h. Repeat steps 2.d thru 2.h a minimum of three times.

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ATTACHMENT A Breaker 3ENANSO5D Failure To Close Equipment Root Cause of Failure Investigation Plan WO 2717143

3. Perform breaker overhaul & maintenance per procedures 32MT-9ZZ33 & 32MT-9ZZ37.

Using clean rags wipe, bag & tag the lubricant from bearings.

4. Steps in this plan may be performed out of sequence at the discretion of the Maintenance Engineer. The engineer may add, delete, or modify steps to accomplish the troubleshooting task. All additions, deletions, or modifications will be recorded in the troubleshooting work order continuation sheet. The additional steps may require lifting and landing leads.

TEST EQUIPMENT:

No special test equipment is required for this ERCFA investigation. Required M&TE are contained in procedure 32MT-9ZZ33 & 32MT-9ZZ37.

RETEST Functionally test breaker per procedure 32MT-9ZZ33.

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ATTACHMENT B Offsite Power Breaker As-Found Condition Data BREAKER BREAKER BREAKER CLOSE COIL CLOSE TRIP COIL P/U TRIP TIME

(<70V) lLOCATION RATING BESINKE DATE lWORK MECH l DATA lP/U (<90V) VOLTAGE l (<91.3MS) TIME lVOLTAGE l (R<55TMS)E 1ENANS01A 3000A 269A7241-023 02108101 OH -2342067 AS FOUND .& 89 j.'3f>>96 79 1ENANS01A 3000A 269A7241-023 04/30104 I/A-2611727 ASFOUND '. 48 ' ;76 ' '5,62 68 1ENANS03A 1200A 269A7239-005 06/15/99 OH -877126 AS FOUND ',.z 59:Z 69'.1. - 62 -46.7 IENANS03A 1200A 269A7239-005 04/22/01 I/A-2331359 AS FOUND 55..' 'r 72.3 59 .42.8 1ENANS04A 1200A 269A7247-010 03/16199 OH - 870287 AS FOUND :C54 " 76 55.,' '77 747', ,,

1ENANS04A 1200A .269A7247-010 10/13/02 I/A -2484885 AS FOUND -K ,;>46 5 >99 9 *.52.2' 64.3 2ENANS01A 3000A 269A7236-020 11/03/00 I/A -225860 ASFOUND -43 77 .77....

1ENANS05A 3000A 269A7236-020 01/08/04 OH - 2627363 AS FOUND i2&'49 - 75 .. ' - 68.,.. 3 1ENANS02A 3000A 288A3669-001 10/16/96 I/A -762929 AS FOUND 5,z 698 47.4 ...... 1.8 59.z<-'.'73 7 2A,  :;;',;-'65'- '63.5:

1ENANS05B 3000A 288A3669-001 11/08/99 OH -901601 AS FOUND I ENANS06F 3000A 269A7235-020 04/02/98 I/A- 825861 AS FOUND .48;5 '276;8'.  :

Y 58- 54'8 1ENANS06F 3000A 269A7235-020 08109/01 OH -2376564 AS FOUND *S .s -,66' ,Ž,, , 78,7t;~j, .i 64.1 .'-. ..

2ENANS 05B3000A 2 06/19197 69A7241-021 I/A -771152 AS FOUND =-"-63, 1,:;,., 78il1.K'j; 66', .,i , ... :' i ,489.

1ENANS06H 3000A 269A7241-021 10/03/01 OH - 2376574 ASFOUND <'85 s.<' 98;8

• 94 97.-4 1ENANS06K 3000A 269A7236-024 10/14/96 OH - 738065 AS FOUND >. , .;86.1r .. '. . 62

'49'.-;,' 55.5 1ENANS06K 3000A 269A7236-024 10/20/99 I/A -881711 ASFOUND '- ,<67 ' -" 87.4. 60"- - 5 3ENANS02A 3000A 269A7243-020 10/22/98 I/A -839490 ASFOUND ., 51s 1 0 ... . 73 64.7 47.4 1ENANS06K '3000A 269A7243-020 01/01/02 OH- 2414276 ASFOUND " 44KK' .-. '.76.5. .;--:;57

.......'51'7i 2ENANS03A 1200A 269A7238-007 5/23/00 OH - 923521 ASFOUND 6130.>1 r',..- -'79""'66.6 6..

2ENANS03A 1200A 269A7238-007 10/31/03 I/A 2565528 ASFOUND , 63A4- 7.;70K>-i,69 57 2ENANS04A 1200A 288A3669-004 4/18/99 I/A-864222 ASFOUND i42'.-i;

.. '  ; ,'73-,y 82.3 .  ! 60.2' 1ENANS02J 1200A 288A3669-004 4/26/02 OH -2489845 ASFOUND ., 38 '- - - -,71.9 90 97.7,.

1ENANS01 H 1200A 288A3669-005 2/9/99 I/A- 862454 AS FOUND ' f 52 -.. 65;6 -53 63 2:

2ENANS04A 1200A 288A3669-005 2/25/02 OH AS FOUND -72414095

.. '46.'71.7^ . - -:. .72 . , - 80.7 2ENANS05B 3000A 269A7235-021 03/17/98 I/A -825861 ASFOUND ., 58 ' ,37.4- -'51

.-- 48.3 2ENANS05B 3000A 269A7235-021 06/21/01 OH - 2365410 ASFOUND 36 . ' 75.3 ', 66 72.3 1ENANS06K 3000A 269A7236-024 10/20/99 I/A-881711 AS FOUND ... 67 ,, 874-. 60 , ,,52.2 .

2ENANS05D 3000A 269A7236-024 01/07/03 OH - 2552118 ASFOUND 58 82.3 , 76 56.8'-

2ENANS06A 3000A 269A7233-021 03/03/97 I/A-769115 ASFOUND 65.3

,34 57 41 3.

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.. I ATTACHMENT B Offsite Power Breaker As-Found Condition Data BRAE BEKR BEKRCLOSE COIL CLOSE TRIP COIL PIU TRPIM LOCATKIEORN BRATINEGR BREANKER DATE WORK MECH DATA PIU VOLTAGE TIME VOLTAGE T(R<5PTMSE LOATONRAIN SN(<90V) (<91.3MS) (<70V) <M) 2ENANS06A 3000A 269A7233-021 07/26/00 OH - 234021 ASFOUND '> 45>} i ' 53" 46.8:'

2ENANS03B 3000A 269A7240-020 03/01/95 OH - 690499 ASFOUND -J ' 684 ". ~ 77rA>" 58.9- -- 61.4 2ENANS03B 3000A 269A7240-020 10/09/97 I/A-798178 ASFOUND ;u 89;c 8795'. -? 58 45.7 2ENANS06C 3000A 269A7240-020 01/16/01 OH - 2342065 ASFOUND 99:7;' . 75 60.9986 3ENANS03A 1200A 269A7239-009 3/17/00 OH - 907785 ASFOUND ' 33.5X ','>7V.9s' t - '; 59 5,:' -- ;--46.6 3ENANS03A 1200A 269A7239-009 4(20/03 I/A-2508462 ASFOUND A>'2 21 ' o ' -70.9-;r' 41.2 70.3;o, 3ENANS04A 1200A 269A7239-003 6/30/98 OH - 836718 ASFOUND f:.`;_,' 43 ' 64 *. "51.8' 3ENANS04A 1200A 269A7239-003 10/16/01 I/A -2366316 ASFOUND ' -41 , 69A - - 47. . 46.4 3ENANS03B 3000A 269A7244-021 03/12/97 I/A-769115 ASFOUND >'58 62- -43.8- '-

3ENANS05B 3000A 269A7244-021 06/13/00 OH - 922359 ASFOUND ':."KŽ'59 2'. 75.2 ;; , 7817 ' 67 1 ENANS05D 3000A 269A7236-023 04/30/95 I/A - 701115 ASFOUND 491 ' .2 - .88.3 """ 90.9 - ' 76.3`9 3ENANS05D 3000A 269A7236-023 01/20/99 OH - 863842 ASFOUND _ 101W' , 100

,1 -- r. 98...- .. .146 1ENANS04B 3000A 269A7245-023 03/15/99 OH - 864571 ASFOUND 96" > 87.4 8T'4  ; 99 -' - 93.

3ENANS05D 3000A 269A7245-023 10/24/02 OH- 2552116 ASFOUND r 59 "i 85.6 < ' ;74 >99 3ENANS06A 3000A 269A7245-021 10/03/95 OH - 724618 ASFOUND 54 77 4A  ; 49 "7 747.5 57' 3ENANS06A 3000A 269A7245-021 06/16/00 I/A-917631 ASFOUND o . >90- '.'i., >1O0-^.. 48 .51 3ENANS06C 3000A 269A7245-022 10/26/92 I/A- 549856 ASFOUND -; 77.3t. -.. < 7Q  ; 62.2. ' 41.5 3ENANS06C 3000A 269A7245-022 11/03/95 OH - 724620 AS FOUND ..- wii, 47 i73.3 r 6 5 58.2'...

3ENANS06C 3000A 269A7245-022 11/29/99 I/A- 889441 AS FOUND l ::79,' f <'75.5

-,Q ,- <71.

3ENANS05D 3000A 269A7245-022 02/20/04 OH - 2627369 ASFOUND 88- 81 84 . ... .

• 76 8

ATTACHMENT C Offsite Power Circuit Breaker Failures Cause: Degraded Lubrication and Dust Location Failure Date Corrective Action Corrective Action Document IENANS05A No remote/local elect open/trip 7/6/1988 EER 88-NA-021 To maintain PMs IENANS05A No remote/local elect open/trip 3/5/1989 EER 89-NA-012 GE - 2 yr CB lube cycle 1ENANS05D No remote elect open/trip 10/7/1998 CRDR 1-8-0494 Revised PM - cycle bkrs 3ENANS06A No remote elect close 4/21/2004 CRDR 2700714 PM revision under evaluation Cause: To be Determined Location Failure Date Corrective Action Corrective Action Document IENANS06K No remote elect close 6/14/2004 CRDR 2716019 Under evaluation 3ENANS05D No remote elect close 6/14/2004 CRDR 2716019 Under evaluation Cause: Degraded Contacts (oxidation and carbon)

Location Failure Date Corrective Action Corrective Action Document IENANSO5B No remote elect close 10/27/1992 CRDR 1-2-0543 Maint Proc revision Cause: Trip Coil Mcchanism Binding (coil misalignment and dust)

Location Failure Date Corrective Action Corrective Action Document 2ENANS05D No remote elect open/trip 10/22/1992 CRDR 2-2-0325 Maint Proc revision

_ _ _Cause: Circuit Breaker Not Racked Up Completely Location Failure Date Corrective Action Corrective Action Document 2ENANS06A No remote elect close 11/16/1998 CRDR 2-8-0290 Operator training 9

ATTACHMENT D Offsite Power Circuit Breaker Maintenance History l Overhaul Installation Breaker ID Status Work Order Work Order Comments Date Date IENANSOSA AC WO 2627363 WO 2611671 SIN 269A7236-020

____________ ~~2/4/04 4/29/04 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

IENANS05B NC 009016014 WO 00896473 SIN 288A3669-001 scheduled for OH, WO 2586992, 12/14/04 W12/14/99 4/2/00 1ENANS05D NO 58646 W /12503 SIN 269A7241-020 5/6/03 6/16/03 IENANS03A AC WO 2627373 WO 2611670 SIN 269A7242-009 4/23/04 4/29/04 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

1ENANS06F NO WO 2376564 WO 2372704 SN 269A7235-020 8/9/01 8/14/01 IENANS06H NC WOI2376574 12/17/01 SIN269A7241-021 8/9/01 12/17/01 IENANS06K AC WO 2414276 WO 2484968 SIN 269A7243-020

______ 1/1/02 11/18/02 __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

1ENANS04A AC WO 00870287 WO 00881785 SIN 269A7247-010 - Last breaker inspection and adjustment 10/26/99 10/26/99 completed under WO 2484885 on 10/20/02 2ENANS05B NO W02365410 WO 2372930 SIN 269A7235-021 6/21/01 8/2/01 2ENANS05D NC WO 2552118 W02391131 SIN 269A7236-024 1/7/03 1/16/03 2ENANS03A 2_NANS03A_

AC AC WO5/23/00 00923521 WO10/24/00 00926621 SS/297307 269A7238-007 2ENANS06A NO WO 234021 WO 232447 SIN 269A7233-021 8/4/00 8/18/00 2ENANS06C NC WO 2342065 WO 2321950 S/N 269A7240-020 1/24/01 1/29/01 2ENANS04A AC WO 2414095 WO 2389492 SIN 288A3669-005

____________ ~2/25/02 4/2/02__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

3ENANS05B NO WO 2489843 WO 2427319 SIN 269A7240-021

_______4/23/02 7/2/02 S/N 269A7245-022 Note: Failed breaker S/N 269A7245-023 WO 2627369 WO 2716870 was removed under WO 2716870 and replaced with newly 3ENANS05D NC overhauled breaker S/N 269A7245-022 on 6/19/04. Breaker -

4/1/04 6/19/04 023 was overhauled under WO 2552116 on 11/04/02 and installed in 3ENANS05D under WO 2454572 on 12/24/02.

WO 00907785 WO 00905830 S/N 269A7239-009 - Last breaker inspection and adjustment 3ENANS03A AC 3/20/00 4/18/00 completed under WO 2508462 4/20/03 3ENANS06A NO WO 00720396 WO 00724618 S/N 269A7245-021 - scheduled for OH, U'O 2391149, 11/3/95 11/3/95 6114/04. Replacement reschedule required due to 3-unit trip.

3ENANS06C NC 3W12t03 2/13t04 S/N 256A9814-001 3ENANS04A AC WO 00836718 WO 00838168 StN 269A7239-003

_____________ ~6/30/98 10/10/98 __________________________

AC = Always closed NC = Normally closed NO = Normally open 10