ML20127G565
| ML20127G565 | |
| Person / Time | |
|---|---|
| Site: | Shoreham File:Long Island Lighting Company icon.png |
| Issue date: | 01/25/1985 |
| From: | Wynne J LONG ISLAND LIGHTING CO. |
| To: | Eselgroth P NRC |
| Shared Package | |
| ML20127B461 | List: |
| References | |
| FOIA-85-190 NUDOCS 8506250483 | |
| Download: ML20127G565 (9) | |
Text
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January 25, 1985 TO:
P. Eselgroth
SUBJECT:
NRC Item 84-10-01 Loss of Offsite Power Attached is a copy of the incident report covering the April 14, Loss of Power Event.
It is felt that this report discusses all your concerns raised in NRC Report 84-10. Note that a typo error exists in the NRC report in that the correct breaker number is 103-2 not 108-2.
If you have any questions contact Gary Rhoads at ext. 3417.
4 f.7/ h (ose h G. W rne
. Compliance Engineer JGW/jp SR2-A43.700 8506250483 850415 PDR FOIA BELAIR85-190 PDR d.Q 8
January 21, 1985 W. E. Steiger, Jr.
Plant Manager
SUBJECT:
Incident Report - Loss of Power April 14, 1984 Attached please find a copy of the completed incident report for the subject occurrence.
Although I am transmitting this to you on this late date, the draft report has been complete for several months awaiting final comments from the various LILCO organizations.
Shortly af ter the incident, Mr. M. S. Pollock (VP Nuclear at that time) directed a Task Force be put together to investigate the incident and develop recommendations for action.
The Task Force consiste'd of members from Electrical Engineering, Electrical The Task Systems Operations, NED, Relay and Protection, S&W, and Plant Staff.
Force was chaired by the undersigned.
As the report indicates, the incident was investigated fully, preliminary investigatory reports were analyzed and all recommendations have been addressed, with concurrence of the Task Force.
Since that time, as you are aware, operating nuclear plants have had similar occurrences with diesel generators paralleled to offsite grids during systemDue disturbances resulting in loss of both the grid and the diesel generators.
to this, the NRC felt it necessary to generate a bulletin to discuss this subject.
Based on the implementation of the recommendations of this report and the changes to station procedures, I feel we have adequately addressed their concerns.
Should you have any questions regarding this matter I am available to discuss
.them with you.
E
. A. Scalice Operations Manager JAS/km Attachment SR2-NF
- Paga 1 l
Event: Loss of Offsite Power on April 14, 1984 and Apparent Inability of Emergency Diesel Generator 103 to close onto its Emergency Bus After this Loss of Offsite Power System Configuration:
Power distribution to the plant and within the plant on April 14, 1984 was as shown in Attachment 1.
It should be noted that this configuration and loading was unique in that the plant was still in the construction phase.
Therefore, loads were minimal and the alignment of these loads was not re-flective of an operating plant.
Emergency Diesel Generators 101 and 102 were locked out (i.e. out of service for repair), and the NSST was out of service (de-energized) to permit the installation of the mobile emergency diesel generators. Additionally, Diesel Generator 103 was being load tested and was therefore paralleled to emergency switchgear 103 and to the RSST. This testing configuration resulted in both the D/G supply breaker (103-8) and the RSST supply breaker (103-2) to bus 103 being closed. D/G 103 was mechanically load limited to 3500 kw for this test.
The RSST, in conjunction with D/G 103 were supplying all on site loads -
plant and construction because the NSST was out of service.
In plant loads included 4KV buses 1A, IB, 11, 12, 101, 102 and 103.
Cause: Bus differential relay trip at the Wildwood Substation (69KV). This caused the loss of the Wildwood Substation feed to the RSST at the Shoreham plant.
Possible Initiating Event:
Office of Engineering (Electrical Engineering) performed a review of the Wildwood Substation and discovered that a current transformer wire in a bus differential relay protection circuit was broken. After discussions with Westinghouse relative to this discovery and the protective relaying which operated, it was postulated that this broken wire could have caused actuation of a relay fault detector and subsequent operation of the differential circuit.
Sequence and Description of Events:
1.
time = 0 a) Bus differential _ relay trip at Wildwood causes the loss of the RSST at Shoreham, b) RSST supply to the 4160 volt busses 1A, IB,11,12,101,102 and 103 is lost. However since D/G 103 is running in the test mode and is paralleled to the RSST (i.e.103-2 and 103-8 are closed), D/G 103 attempts to pick up all loads.
a
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P'ge 2 a
c) D/G 103 voltage and speed drop. The resulting undervoltage and speed reduction causes the following.
2.
t = 2 seconds a)
Undervoltage relays on 4160 volt buses IA, IB, 11, 12, 101, 102 and 103 alarm.
b)
Closed motor feeder breakers on buses 1A, IB, 11 and 12 trip open on an undervoltage.
3.
t = 7 seconds Bus programs for bus 101 and 102 sense a sustained undervoltage and trip incoming breakers 101-2 and 102-2 to buses 101 and 102. However, D/G 101 and 102 are locked out, so they did not auto start, Bus 103 breaker 103-2 did not trip open on undervoltage at this time because D/G 103 was running and breaker 103-8 was closed.
4.
t = 25 seconds The D/G 103 run relay (RI) senses that D/G 103 speed has been less than 400 RPM for more than 25 seconds. R1 relay therefore operates and trips breaker 103-8, isolating D/G 103 from its 4160 volt bus (bus 103).
(see discussion section item 1 for R1 relay) Once Breaker 103-8 has tripped, it removes the undervoltage block on the 103-2 breaker.
5.
t = 30 seconds The bus 103 program has sensed a sustained undervoltage on the 103 bus and therefore trips the RSST incoming breaker 103-2.
(see discussion section, item 2) 6.
The D/G 103 is now running isolated from its loads on bus 103 and these loads are now de-energized due to 103-8 tripping open.
7.
Speed and voltage for the unloaded D/G 103 return to normal.
1B. Attempts to reclose breaker 103-8 were unsuccessful because the D/G control logic (Run Relay RI) has locked out breaker 103-8 when it sensed that engine speed had dropped below 400 RPM for more than 25 seconds. This was equivalent to a " fail to start" event and therefore breaker 103-8 was locked out as called for in the logic design.
Discussion of Events:
1.
The main purpose of the Run Relay (R1) is to start the D/G auxiliaries, field flashing, and to monitor diesel speed for a " fail to start" condition upon diesel start up, or a failure to run condition after the diesel has been running.
In either condition, the diesel would have to run at less than 400 RPM for at least 25 seconds at which time the run relay (R1) resets and shuts down the D/G auxiliaries, field flash, and transmits a trip signal to the D/G output breaker (103-8).
Page 3 2.
There is some question as to whether breaker 103-2 auto tripped or whether the operator, syeing a trip on breakers 101-2 and 102-2, beat the auto trip on 103-2 by manually tripping it after the run relay tripped the 103-8 breaker.
The operator had 5 seconds from the trip of breaker 103-8 to manually trip 103-2 prior to the auto trip signal.
It should.be noted that in subsequent relay and circuit performance l
checks, the auto trip si nal functioned as designed; and therefore it 3
is immaterial that the operator may have beat the auto trip logic.
3.
Even though D/G 103 speed had recovered, the relay logic required that i
the R1 relay had to be reset to clear the lockout on breaker 103-8.
This could have been accomplished by placing the D/G start switch in the START position, which would have reset the R1 relay. Once reset, the 103-8 breaker could have been closed, and voltage restored to bus 103.
Recommendations and Actions Taken:
1.
"The diesel electrical protection could be enhanced by lowering the setting of the 67/50 directional overcurrent relay from its present setting of 200% of rated load to approximately 120% of rated load"
Response
A lowering of the relay operating level to 120% would increase the potential for nuisance trips of breaker 103-2 during diesel generator testing when the plant is in an operating condition. This would be due to the fact that during plant operation, more plant loads would be normally running (than were running on April 14) and the combination of a lower relay setting and higher loads would increase the probability that the starting of any large loads within the plant while the diesel generator is in test, could cause the lower relay setting to be exceeded thereby causing a relay trip. This action would have no effect on any safety related systems, as all safety and non-safety related buses would remain energized.
Only the diesel generator under test would be affected, as the breaker parelleling it to the system (breaker 103-1 or 2) would be tripped.
It was therefore concluded that there was no enhancement to be gained via this proposed modification.
l l
l l
- Page 4 2.
"There should be either interlocks in the circuit logic to reset the R1 relay after an underfrequency trip (low RPM) with the diesel generator still running, or the procedures should say to press the START (RUN) button on a trip of the generator breaker, which subsequently prevents the running diesel generator from being reclosed to its bus."
Response
This recommendation intended to state the following:
There should be either interlocks in the circuit logic to reset the R1 relay after an underfrequency trip (low RPM) with the diesel generator still running, or the procedures should state to place the DG Start Switch in the START position af ter a trip of the generator output breaker, which will remove the lock out on the diesel generator output breaker.
Station Procedure SP 23.307.01 for the Emergency Diesel Generators has been revised to instruct the operators as to the function of the R1 relay and the need to reset it under certain conditions.
3.
"The process computer should be modified to have a high speed storage device that will store all contact changes in their correct sequence.
This storage should be able to print the alarms at a later time for review. This recommendation was based upon the fact that the computer print out of alarms did not in some instances, reflect the actual sequence of events."
Response
A review of the process computer and the associated sequence of events log and recorder shows that this feature does exist. The sequence of events log provides for storage of 128 sequenced events, and the selection of plant alarms to be stored by this means has been based upon a review of each alarm with respect to its affect on the safety of the plant. A review of the alarms allocated to the sequence of events recorder, vs.
the alarms in questions for this. event has confirmed that those alarms currently transmitted to the sequence of events recorder are of the higher priority (relative to their safety function).
In spite of the lack of definite sequencing of the events / alarms reviewed for this event, it did not adversely impact the investigation when the record of events was reviewed in conjunction with other plant design documents. Therefore, no actions were taken with respect to this recommendation.
4.
"A test should be performed at the earliest possible time, to verify all
' trip functions of the 103-2 breaker are operable and that the breaker can be tripped when the bus programming logic is actuated."
Response
This confirmatory test was satisfactorily performed under SPF27.304.01-3 on April 27, 1984. This test verified that all control and relay circuits were wired correctly and that they correctly operated the equipment as designed.
,'Paga 5 5.
"An engineering evaluation should be performed to determine whether the directional relay setpoints for the RSST, NSST supply breakers and over-current protection on the Diesel Generator supply breaker are satisfactory.
Should these be determined to be acceptable, a logic modification should be considered, which would allow the emergency bus to remain energized given a similar occurrence.
Such a protective action would prevent a repeat of the scenario described in this report and maintain power to the i
emergency bus. This modification should also be considered for emergency buses 101 and 102."
4
Response
An evaluation was performed relative to the setting of the directional relaying (67/50 relays) associated with the NSST and RSST supply breakers.
This is discussed in item 1 of this section. Additionally, a cautionary note (4.13) has been added to SP 23.307.01 for bus loading during diesel generator testing relative to the 67/50 relay setpoint.
A review was performed of the diesel generator logic, including an evaluation of the R1 run relay. As discussed in item 2 of this section, operator instructions have been modified to alert the operator of the need to reset this relay should a similar situation arise in the future.
The review showed that the R1 relay functioned properly and provided backup to the directional relays.
It was therefore concluded that the existing relaying should remain as is.
6.
"The existing operating procedures requiring the tripping of all normal four (4) KV supply breakers shall be revised so that one (1) supply breaker remains closed. This will assure that control room personnel have indication as soon as power has been restored."
Response
Station Procedure SP 29.015.02, " Loss of All AC Power Emergency Procedure" 4
has been revised to provide for the closure of one incoming breaker to one of the normal 4160 volt buses (bus 1A,1B,11 or 12). This will pro-j vide the operator with immediate indication of restored offsite power.
7.
" Existing telephone communication procedures between control room personnel and system operations personnel shall be reviewed to assure the most efficient methods are being utilized."
Response
A review of communications available between the site (control room) and the LILCO System Operator (ES0) has shown that both normal and dedicated telephone lines were available and operable.
Initial contact was made by the control room to the ESO via the dedicated lines.
The radio link between the Control Room and the ESO was out of service at the time of i
this event due to repairs being performed to the inverter power supply which provides power to the radio system during a loss of AC power.
1 It should be noted that this item is unrelated to the event.
- .,., ;Eage 6 8.
" Protective relaying for off-normal electrical configurations shall be reviewed in operator training."
Response
This recommendation again referred to the function of the diesel generator R1 relay and the need to reset by placing the Start Switch in the START position to clear the lockout on breaker 103-8, thereby permitting it to close and permit the diesel generator to be connected to this emergency bus. A discussion of the R1 relay is included in requalification training, as well as a cautionary note in SP 23.307.01.
9.
"Any information resulting from the above recommendations shall be incorporated in operator training."
Response
Actions taken per these recommendations and any other significant revisions to SP's are covered in the normal qualification program for licensed operators.
==
Conclusion:==
A review of the equipment operations and circuits which operated indicates that all electrical protection devices and circuits functioned as intended and designed.
No further changes are required except those as noted above.
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