ML18092B478

Safety Evaluation for Mod of Second Level of Undervoltage Protection Sys.

ML18092B478
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Site:	Salem
Issue date:	03/23/1987
From:	Public Service Enterprise Group
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Text

Page PS~G 1 of 8 Date 3/23/87

-:Y' Public Service Electric and.Gas Company P.O. Box 236 Hancocks Bridge. New Jersey 08038 Nuclear Department TITLE: SAFETY EVALUATION FOR THE MODIFICATION OF THE SECOND LEVEL OF UhDbk\0L1AGE ~~0TbCllu~ ~k~TbM

1. 0 PURPOSE This Safety Evaluation supersedes the justification for continued operation Safety Evaluation S-C-El30-NSE-0458-l. It is being written to evaluate the modification of the Second Level of Undervoltage Protection System and the return to a normal electrical operating configuration with the Auxiliary Power Transformers in service.

2.0 SCOPE This Safety Evaluation is applicable to Salem Units No. 1 and No.

2.

3.0 REFERENCES

3.1 PSE&G Safety Evaluation S~C~El30-NSE-0458-l, Justification of Operation of Units 1 arid 2 with Limited 4KV Loads, dated September 6, 1986.

3.2 PSE&G Design Memorandum S-C-El30-CDM-0494-l, Second Level of Undervoltage Protection System, dated March 23, 1987.

3.3 Salem Nuclear Plant Voltage Study, Power Technologies Inc.

Report No. Rll-87, dated February 1987 3.4 Salem Generating Station, Technical Specifications Unit 1 3.5 Salem Generating Station, Technical Specifications Unit 2 3.6 Salem Generating Station, Updated Final Safety Analysis Report 3.7 Salem Nuclear Plant Undervoltage Study, Power Technologies Inc., Report No. R7-87 dated February 1987.

3.8 PSE&G Engineering Evaluation, S-C-El30-CEE-0162-0 Engineering Evaluation of Verification' and Validation of Power Technologies Inc. PSS/E Software Package and Salem Electrical Model, dated January 26, 1987j

• ise/mpm2

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-------4 EDD-7 FORM l REV 0 10SEPT81

Page 2 of 8 Date: 3/23/87 3.9 Letter from Manager - Salem Projects to General Manager -

Electric Production, Subject - Salem Nuclear Generating Station Unit~ No. 1 ahd 2 NRC Request for Additiorial Information Degraded Grid Voltage Protection (70%-90%), dated February 4, 19~0.

3.10 Letter dated October 10, 1979 from General Manager - Electric

~reduction to USNRC.

3.11 Letter dated January 19, 1981 from USNRC to PSE&G, Safety Evaluation Report - Salem Generating Station Unit 1 and 2 Degraded Grid Voltage Protection *for the Safety Related A-C Power System.

3.12 EG&G Report dated June 1981, Adequacy of Stati6n Electric Distr.ibution System Voltages, Salem Nuclear power Station Units 1 and 2, Docket No's. 50-272 and 50-311.

3.13 Letter dated March 22, 1987 fro~ J. D. Hebson to J~ T.

Boettger, Minimum Expected Steady State Grid Voltage Hope Creek Keeney Line out of Service.

4.0 BACKCI~OlmD On August 26, 1986 Salem Unit No. 2 separated its vital buses from the preferred offsite power source when the offsite source was within e~pect~d voltage limits. The initial investigation following the incident did not reveal any failed components or equipment. The investigation revealed that a transient voltage analysis had hot been performed on the plants since October 1979, and that plant loads had been modified by desigp changes since October 1979.

PSE&G Safety Evaluation S-C-El30-NSE-0458-l was writt~n to justify continued operation of the Salem Units based upon the USNRC approved October 1979 study. The Safety Evaluation also addressed the operation of the plants without utilizing the auxiliary power transformers. The preferred method of operation as described in the UFSAR utilizes the auxiliary power transformers to power the non~vital group buses.

In Janua~y 1987, a temporary power feed from the Hope Creek Generating Station Artificial Island Sub-Station was installed to remove approximately 6 MVA of load from each of the Salem Units electrical distribution systems. Three circulating water pumps from each Salem Unit are powered from this temporary power feed.

The reduction in the Salem electrical distribution system load is approximately eaual to the load which had been added to the system since October 1979 *

• se/mpm2 EDD-7 FO~M 1 REV 0 10SEPT81

Page 3 of 8 Date: 3/23/87 PSE&G has retained Power Technologies Inc. (PTI) to perform transient voltage profile studies of the Salem Station's electrical distribution system. PTI has modeled the Salem electrical distribution system utilizing th~ir PSS/E computer software package to predict transient and steady state voltages at the plant electrical buses. A test was performed on December 13, 1986 to verify and validate that the PTI model is capable of t,-red ict ing steady state .:.nu trans it1nt voltage values. Tli1::

comparison bf test results and computer model predictions as identified in Reference *3.8 has been found acceptable.

The PTI software package and Sale~ electrical model was also used to further investigate the August 26, 1986 event. The results presented in Reference 3.7 of the computer model's predictions.

indicate that after the non-vital group bus fast transfer on Unit No. 2 the voltage dipped below the second level of undervoltage protection system relays 91% trip setpoint. The voltage recovered to 95% as the motors came up to rated speed. The 95% final recovery voltage value is equal to the r~set value of the second level of undervoltage protection system relays. rhe recovery was not high enough to provide a positive reset of all of the undervoltage relays. The "A" vital bus transfer relay failed to reset and initiated a transfer of the "A" vital bus which subsequently led t6 multiple transfers of the "A" vital bus and finally separation of all of the Class lE vital buses from the preferred offsite power source *

• Due to the above findings, a thorough review of the Second Level of Undervoltage Protection System relaying and the capabilities of th~ Salem electrical distribution system was performed.

provided another voltage profile study, Reference 3.3, which indicates that the minimum recovery voltage on the 4160 volt vital PTI buses will be 92.9%. The study was performed with both auxiliary power transformers in service, the llA, 128, 13A, 21A, 228, and 23A circul~tors off loaded to the existing temporary power feed.

The study assumed a Loss of Coolant Accident (LOCA) on one unit and a controlled shutdown of the opposite unit when the 500KV grid was at its lowest expected value. Additionally no credit was taken in the study for voltage corrective actions by the automatic load tap changers on the station power transformers during the assumed LOCA or other bulk load shifts and the alignment of loads were selected to provide the worst case recovery voltage. Since the expected minimum recovery voltage will not exceed the Second Level of Undervoltage Protection System relays reset value, the 95% reset value is not acceptable. It should be noted that the 95% reset value for the relays had been selected by PSE&G as a means of' preventing multiple transfers of vital buses between station power transformers. Therefore, the Second Level of -

Undervoltage Protection System relaying must be redesigned *

• ~~~~----,-~~~~~~~~

se/mpm2 EDD-7 FORM 1 REV 0 10SEPT81

Page 4 of 8 Date: 3/23/8 7 The Salem Technical Specifications Reference 3.4 and 3.5 Section 3/4.3 Table 3.3-3 provide applicability information with respect to the sustained degraded grid protection. The redesign of the Second L~vel of Un~ervoltage Pr6tection System must not alter the protection described in the Technical Specification if the modification is to be performed in a timely manner.

In addition, the review revealed that the present Technical Specification setpoint and minimum allowable value do not provide adequate protection to preclude operating Class lE equipment at unacceptable degraded voltages. The electrical motors are the limiting components under steady state conditions and are designed to run continuously at 90% of nameplate voltage as identified in Reference 3.10. The >91% setpoint was found acceptable by the USNRC in Reference 3.Tl. However, the USNRC assumed that the Class lE 4KV motors were rated at 4000 volts and the 91% setpoint of the 4160 volt bus would provide 94.5% protection for 4000 volt rated motors. The 4~V Class lE motors are rated at 4160 volts.

The minimum allowable value >90% does not consider the voltage drop in cables from the 4KV switchgear to the motor terminals nor does it consider the accuracy of the potential transfcirmer which the undervoltage relay utilizes to monitor the bus voltage. A new setpoint of >91.6% has been selected and irnplementeq by a minor design change package. The new setpoint was determined in accordance with Regulatory Guide 1.105 and the calculations to reach this setpoint are shown in Reference 3.2. The new minimum

• allowable value >91% considers the voltage drop in the longest cable run and the potential transformer accuracy. Since the Technical Specificatio~ provides-th~se setpoints with a greater than sigri and the new setpoint is more conservative, the setpoints will be changed and controlled arlministratively until a license change is finalized.

The >91.6% setpoint provides adequate protection for the 480 and 230 volt Class lE equipment as well as the 4160 volt motors. The Class lE worst case 480 volt bus will be maintained at a voltage of 92.3% of 480 volts. Since the 480 volt motors are rated at 46.0 volts the setpoint of >91.6% will maintain the 480 volt bus at 96.3% of the 460 volt ~ated motors. Since the worst case voltage drop to these motors is 3.2%, the >91.6% setpoin~ ensures adequate voltage at the motor terminals. The c*1ass lE 230 volt motors are rated at 230 volts and the > 91.6% setpoint will maintain the worst case 230 volt bus at i voltage of 94%. Since the worst case voltage drop is 3.5% for the 230 volt motors, the ~91.6% setpoint ensures adequate voltage to these motors also.

Recently one of the ~00 KV power lines that connect Artificial Island to the Pennsylvania, Jersey, Maryland, 500KV network was damaged by a freighter in the Delaware River. The loss of this line has not altered the minimum expected grid voltage of 505Kv as documented in Reference 3.13 .

• se/mpm2 EDD-7 FORM 1 REV 0 10SEPT81

Page 5 of 8 Date: 3/23/87

• 5.0 DISCUSSION The redesign of the Second Level of Undervoltage Protection System has been outlined in Reference 3.2. The redesigned system eliminates vital bus transfers between station power transformers at 91 % voltage. There wi 11 be 3 .undervol tage re lays per vital bus. The existing vital bus sustained degraded voltage relay and its interface ~ith the Safeguards Emergency Contrbller will remain. This satisfies the Salem Technical Specifications applicability Table 3.3-3 and provides protection in a 2 out of 3 bus undervoltage intelligence. The existing relay and two additional undervoltage relays will also provide inputs to its respective vital bus Safeguards Emergency Controller which will provide a 2 out of 3 relay undervoltage intelligence to initiate separation of its vital bus from the offsite power source and provide diesel generator loading. The redesigned protective control circuits are shown in Attachments A through G. The setpoint for vital bus sustained degraded voltage relays will be

>91.6%, and the relay reset vaiue will be lowered to 92.6% which Ts less than the minimum expected recovery voltage to prevent separation from the offsite power source when it is within expected limits.

The degraded grid relay protection system provides protection for the vital Class lE motors and motor control contactors and ensures that adequate voltage is supplied in the event of a decaying preferred offsite power source. If the voltage at the vital buses decays below the sustained degraded voltage minimum allowable value of 91%, operation of the vital equipment wou~d be jeopardized and therefore separation of the vital bus from the preferred offsite power source at this minimum value must occur.

The USNRC Position 3 in Reference 3.12 states that loss of offsite power to either of the redundant Class lE distribution systems due to operation of voltage protection relays, must not occur when the offsit~ power source is within expectE*l voltage limits. Since the minimum recovery voltage is expected to be 92.9% rated bus voltage, separation *from the offsite source above this voltage is unacceptable. Therefore, separation from the offsite power source is allowed at Salem between the bus voltage of 91% and 92.9%.

Furthermore the relay reset value of 92.6% is acceptable and will prevent separation from the offsite source when it is within expected limits.

The redesigned Second Level of Undervoltage Protection System is designed in accordance with IEEE 279-1971, "Criteria for ~

Protective Systems for Nuclear Power Generating Stations". The modification does not introduce or increase the possibility of adverse physical impact to other safety related equipment because the new equipment and mountings will be seismically installed.

The modifications to existing equipment will be performed such that the seismic integrity of the equipment is maintained. The

• se/mpm2 EDD-7 FORM 1 REV 0 10SEPT81

Page 6 of 8 Date: 3/23/87 change does not introduce any new failure modes as a result of electrical interaction or interfaces. All of the electrical components used to provide the protective function are Class lE items. A failure mode analysis as shown in Attachment "H" has been performed without any adverse findings. Additionally, inadvertent operation of any one of the components in a channel will not cause the protection to initiate an action unless it i~

coincident with a Loss of Coolant Accident (LOCA) si~nal to t~e Safeguards Emergency Controller. This is due to the single bus undervoltage coincident with LOCA feature presently designed into the Safeguards Emerge~cy Cbntroller. This is similar to the present design and is therefore acceptable. Based on these analyses, the probability of occurrence or the consequences of an accident or malfunction of eq~ipm~nt important to safety is not increased as previously evaluated in the UFSAR.

Section 8.3.1.2 of the UFSAR d~scribes the normal operation of the 4160 volt system which is to switch the non-vital loads from the station power transformers to the auxiliary power transformer after the unit is at approximately 20% power. Section 8.3 of the UFSAR refers to analyses and tests which were performed to verify that the offsite power systems in combination with the onsite power ~ystems possess sufficien~ capacity and capability to automatically start and subsequently operate all safety loads within their voltage ratings for anticipated transients and accidents. The redesigned Second Level of Undervoltage Protection System and the PTI voltage profile study ~rovide assurance that the offsite power system possesses sufficient capacity and capability to automatically start and subsequently operate all safety loads within their voltage ratings for.anticipated transients and accidents. Additionally, the redesign of the Second Level of Undervoltage Protection System and PTI study support the use of the auxiliary power transformer in accordance with the preferred normal operation of the 4160 volt system described in the UFSAR. The Secohd Level of Undervoltage Protection System operation is also described in the UFSAR in Section 8.3.1.2. The existing description on Pages 8.3-4 and 8.3-5 will be replaced with the description shown in Attachment

I". Section 7.3~1.1.10 of the UFSAR describes diesel generator loading. Although the existing sustained degraded voltage protection is not presently provided in this section, it will be added. Refer to Attachment I for the required change. These changes to the UFSAR are descriptive changes and do not affect any analyses of Safety performed in the UFSAR. A revision to the UFSAR description will be included as part of the design change package.

The Technical Specification (T.S. 3/4.8.1.la) requires that two physically independent circuits between offsite and onsite Class lE distribution systems (vital buses) shall be operable. The se/mpm2 EDD-7 FORM 1 REV 0 lOSEPTSl

Page 7 of 8 Date: 3/23/8 7

• bases for the limiting condition of operation is that sufficient power be available to supply the safety-related equipment requi'red for the safe shuidown of the plant and the mitigation and control of accident conditions within the plant. The redesigned Second Level of Undervoltage Protection System insures that the offsite power system will be availabl~ to supply the Class lE disttib~tion system (vital buses) during worst case transient conditions includin~ the lo~est expected ~ri~ voltage anci th~retore does not decrease the margin of* safety.

6.0 RECOMMENDATIONS 6.1 Perform the modifications to the Second Le~el of Undervoltage Protection System as described herein and identified in Reference 3.2 *

. 6.2 Return both Unit No. l and Unit No. 2 auxiliary power transformers to service.

6.3 The circulators powered from the temporary power feed must stay on the temporary power feed until long term corrective actions to improve voltage recovery are implemented.

6.4 Although thi~ configuration-is actept~ble, a license change request should be submitted~ such that the Technical Specifications address a 2 out of 3 relay logic and not the 2 out of 3 bus logic. Following LCR approval the 2 out of 3 bus logic for sustained degraded voitage should be delet~d.

The proposed Technical Specjf ication changes are shown on Attachments "J" and "K".

7.0 CONCLUSION

S The safe operation of Salem Units No. 1 and No. 2 within th~

b6unds of the PTI study after the modif ic~tions outlined in

-Reference 3.2 is justified. Implementation of the modific~tion to the Second Level of Undervoltage Protection System and return of the auxiliary power transformers to service does not rr1ult in an unreviewed safety question.

• se/mpm2 EDD-7 FORM l REV 0 10SEPT81

Page 8 of 8 Date: 3/23/87 8.0 SIGNATURES Originator . Date Verifier Date o£it~~Head ~:+/-? Man~tfehPlant Engineering se/mpm2 EDD-7 FORM 1 REV 0 10SEPT81

VITAL BUS PROTECTION RELAY LOGIC A1 BUS ~8~ ~B~

1

~~~___,A~~~~- ~~~~~A~~~~-

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70Y. 91.6% 91.6%

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70/. 91.6Y. 91.6/. 91.6/.

70/. 91.6/. 91.6/. 91.6Y. 91.6/.

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~3 ~3 ~3 1r 1r ,r A DIESEL 1 1 1 81 DIESEL C DIESEL 1 1 LOADING LOADING LOADING.

VB? ' I

1 A VITAL BUS UNDERVOLTAGE SENSING CIRCUIT 1

A 4160V. B VITAL ---1-------'1~-

BUS 1A c

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'A' Vil AL BUS SECOND LEVEL UNDERVOL TAGE PROTECTION 27-lA 70/. BLACKOUT RELAY 62X-PROTECT10N DEFEAT RELAY 27-lA/l. 27-'JA/2. 27-JA/3-UNDERVOLTAGE

+ RELAY, ROCHESTER PR-2035, DROPOUT q1,6Z PICKUP 92.6Z 2-1, 2-2, 2-.3 - TIME DELAY PICK-UP 62X TD-5. SETPOINT 13 SECONDS HFA-EXISTING U.V.AUX.RELAY (I) 27-lA 27-lA/1 27-lA/2 27-lA/3 LLJ

....... 2-1 2-2 2-3 cc TDC TDC TDC uW t-t- t-z co LLJ

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2-2 2-3 TDC TDC 800./\.

25W j_ j_ l_ J_ J_* .l_ 27X-1A/l 27X-1A/2 27X-1A/3 27X-JA/1 27X-JA/2 27X-JA/3 27X-1A1 T 27X-1A2 T 27X-1A3 T 27X-1A/l T 27X-1A/2 T 27X-1A/3 T . 4t 4t 4t "A" sEc *s* SEC *c* sEc "A".sEc "A" SEC "A" SEC *I OVERHEAD ANNUNCIATOR I REACTOR COOLANT PUMP START PERMISSIVE VBl I

• 1 8 VITAL 1

BUS UNDERVOLTAGE SENSING CIRCUIT A

4160V. B VITAL ---1-----.....--

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1 8 Vil AL BUS .SECOND LEVEL UNDERVOL TAGE PROTECTION 1

27-lB 70% BLACKOUT RELAY 62X-PROTECTION DEFEAT RELAY 27-lB/l. 27-18/2. 27-18/3-UNDERVOLTAGE

+ RELAY, ROCHESTER PR-2035, DROPOUT qi.Si!

PICKUP q2~6i!

2-1, 2-2, 2 TIME DELAY PICK-UP 62X @ TD-5, SETPOINT 13 SECONDS HFA-EXISTING U~V.AUX.RELAY (J) 27-18 27-18/1 27-18/2 27-18/3 LLJ

....... 2-1 2-2 2-3 a:

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27X-IB/2 27X-IB/3 27X-1B/1 27X-1B/2 27X-18/3 4t 4t 4t 27X-18/l 27X-1B/2 27X-18/3 VB2

'A' SEC 'C" SEC 1 81 SEC 1 81 SEC 1 8 1 SEC OVERHEAD ANNUNCIATOR I REACTOR COOLANT PUMP START PERMISSIVE

• c* VITAL BUS UNDERVOLTAGE SENSING CIRCUIT A

4160V.

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+ RELAY, ROCHESTER PR-2035, DROPOUT ql.6/.

PICKUP q2.6Y.

2-1, 2-2, 2 TlME DELAY PICK-UP 62X @ TD-5, SETPOINT 13 SECONDS HFA-EXlSTING U.V.AUX.RELAY (J) 27-lC 27-lC/l 27-lC/2 27-lC/3 LU

...... 2-1 2-2 2-3 a: TDC TDC TDC

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25W 27X-ICI f "A" SEC 27X-IC2 f 1

8 1 SEC 27X-IC3 f 1

C1

• SEC

. 27X-IC/I f 27X-IC/2 f 27X-IC/3*f "C" SEC 27X-IC/l 27X-lC/2 27X-JC/3

+t +t 4t OVERHEAD 27X-IC/1 27X-1C/2 27X-IC/:;

REACTOR COOLANT "C" SEC "C" SEC PUMP START ANNUNCIATOR PERMISSIVE V83

Attachment "H" FAILURE MODE ANALYSIS

• Fa ilur~

Undervoltage Relay Normal Operation With Degraded Grid 2 out of 3 logic will be made to load bus to diesel generator.

LOCA & Degraded Grid 2 out of 3 logic will be made to load bus to diesel generator.

Acce12table. .Acce12table Timing Relay Same as above Sarne as above Failure Undervoltage Sarne as above Same as above Auxiliary Relay Failure HFA Relay Same as above Sarne as above Failure*

Loss of Bus with failed Bus with failed battery 125 Volt battery system would system would maintain Battery maintain conn.ection to connection to grid.

grid. Buses without Buses without failed failed battery would battery would load to load to diesel. Sarne diesel. Same _as present as pr_esent design. design. Previously Previously Analyzed Analyzed Loss of Same as above Sarne as above 125 Volt DC Branch CKT Loss of Ca:ble Bus with failed cable Bus with failed cable f tom Bus to would maintain connected would maintain connected S.E.C. to grid. other buses to grid. Other buses would load to diesel. would load to diesel.

Two vital - buses would Two vital*buses would be available for safe be available for safe shutdown. Therefore shutdown. Therefore 12reviously analyzed. 12reviously ana.lyzed ~

62X Defeat* .. Alarm in control room

• Alarm in control room.

Relay Bus with failed 62X Bus with failed 62X relay would maintain relay would maintain connection to grid. connection to grid.

Other buses would load Other buses would load

• • tO diesel. Two Vital to diesel. Two Vital bus.es would be available buses would be available for safe shu.tdown. for safe shutdown.

Therefore ErE~viously The ref ore EreviouslJ::

analyzed. analJ::zed.

• Potential Transformer Potential Transformer Primary Fuse Same as undervoltage relay failure Same as undervoltage relay failure

.Same as undervoltage relay failure Same as undervoltage relay failure se-mpm2

• Attachment "t" UFSAR DESCRIPTIVE CHANGE Section 8.3.1.2 The Second Level of Undervoltage Protection System is comprised of three relays per vital bus which react instantaneously when the voltage at the vital bus drops below the setpoint of 91.6 percent of rated voltage. There is also an external timer with adjustable time delay.

The time delay of the Second Level of Undervoltage Protection Sysiem relays is 13 seconds.

Each timer operates an auxiliary relay, which provides an input to the undervoltage relays associated vital bus safeguard equipment controller. The safeguard equipment controller utilizes the three auxiliary relays inputs to provide a two out of three relay intelligence to separate the vital bus from the offsite power sou~ce and load it to its associated onsite diesel generator. One of these timers will also operate the vital buses 70% auxiliary relays (one fo~

each Safeguards Equipment Controller) to provide a 2 out of 3 bus undervoltage intelligence similar to the 70% Blackout protection.

Section 7.3.1.7.10 (Add) - Sustained Degraded Vital Bus Voltage (Degraded Grid)

The Safeguards controllers also receives 91.6 percent undervotlage signals from its vital bus through a 13 second time delay relay to provide a 2/3 logic intelligence to develrip a signal to separate its respective vital bus from the offsite power system and initiate it respective diesel~generator loading. The loading sequence is identical to that of a Blackout sequence.

Section 7.3.1.1.10.4 (Delete) - Bus undervoltage by itself will not directly cause any action to be t~ken in the sequencing of equipment

• se-rnprn2

Attachment "J" TECH SPEC. TABLE 3.3-4 Functional Unit Trip Setpoint Allowable Value

7. Undervoltage Vital Bus Present

a. Loss of Voltage > 70% of bus voltage > 65% of bus voltage

b. Sustained > 91% of bus voltage for > 90% of bus voltage for Degraded Voltage

< 13 seconds < 15 seconds

7. Undervoltage Vital Bus

a. Loss of Voltage > 70% of bus voltage > 65% of bus voltage

b. Sustained > 91.6% of bus voltage for > 91% of bus voltage for Degraded Voltage

<*13 seconds < 15 seconds rnpm2

Attachment "K" TABLE 3.3-3 Engineered Safety Features Actuation System Instrumentation Minimum Total No. Channels Channels Applicable Functional Unit of Channels to Trip Operable Modes Action

7. Undervoltage Vital Bus Existing

a. Loss of Voltage 3 2 3 1, 2, 3 14*

b. Sustained Degraded Voltage 3 2 3 1, 2' 3 14*

7. Undervoltage Vital Bus New

a. Loss of Voltage 3 2 1, 2' 3 14*

b. Sustained Degraded Voltage 3/bus 2/bus 2/bus 1, 2' 3 14*

se-mpm2

f'*

t) PS~G - S-C-El30-NSE-0458, REV. 1 Page Date 1 of 4 9/6/86 Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge. New Jersey 08038 Nuclear Department TITLE: JUSTIFICATION FOR OPERATION OF UNITS 1 AND 2 WITH LIMITED 4KV LOADS 1.0 PURPOSE This Safety Evaluation is being written to justify the continued safe.operation of Salem Unit No. 1 and Unit No. 2 following the reactor trip/safety injection and subsequent loss of offsite power indication which occurred on Salem Unit No. 2 on August 26, 1986.

2.0 SCOPE This Safety Evaluation is applicable to the operation of both Salem Unit No. 1 and Salem Unit No. 2.

3.0 REFERENCES

3.1 U.S. NRC letter "Adequacy of Station Electrical Distribution System Voltages at Salem Units 1 and 2" to F.

w. Schneider, dated October 21, 1981.

3.2 "Adequacy of Station Electric Distributioh System Voltages, Salem Nuclear Power Stati0n Units 1 and 2". Prepared for U.S. NRC by EG&G Idaho, Inc., June, 1981.

3.3 U.F.S.A.R., Section 3, Section 8, and Section 15. Rl 3.4 G.D.C. 17, Electric Power Systems.

3.5 Public Service Electric and Gas Company Drawings 203061 A8789 and 203062 A8789 *

. 4.0 DISCUSSION:

On August 26, 1986, Unit No. 2 experienced a reactor trip and safety injection followed shortly by a loss of offsite power to the 4KV Vital A, s,*& C electrical busses. Initially on the safety injection, all safeguards loads loaded simultaneously in accordance with the design. Subsequent to the safety injection an indication of loss of offsite power was received. The "A" and "C" vital bus loads sequenced onto the diesels as per desig~.

The "B" vital bus remained deenergized because the "B" diesel generator was tagged for maintenance. (Two vital 4160 volt buses se/SS 4 EDD-7 FORM 1 REV 0 10SEPT81 The Energy People \\'/,/

L\O\ D \

Page 2 of 4

,. , S-C-El30-NSE-0458 REV. 1 Date: 9/6/86 are required to provide minimum safeguards equipment). Upon investigation it was determined that equipment failures did not initiate the loss of offsite power event. The investigation revealed that a transient stability analysis had not been performed on the plant since June, 1981. Plant loads have been'modified on the basis of a static loading analysis only. The changes in plant loads may be found in Attachment No. 1. The June, 1981 transient stability analysis was performed by Public Service Electric and Gas (PSE&G). and supplied to the U.S. NRC in accordance with a request dated August 8, 1979. The U.S. NRC then submitted this study to their contractor EG&G, Idaho, Inc. for review. The U.S. NRC then supplied PSE&G with a Safety Evaluation Report which approved the Salem Unit No~ 1 and Unit No. 2 electric distribution system (Reference 3.2).

Section 8.3.1.2 of the UFSAR describes the normal operation of the 4160 volt system which is to switch the non-vital loads from the station power transformer to the auxiliary power transformer after the unit is at approximately 20% power.

Section 8.3 of the UFSAR refer to analysis and tests which were performed to verify that the offsite power systems in combination with the onsite power systems possess sufficient capacity and capability to automatically start and subsequently operate all safety loads within their voltage ratings for anticipated transients and accidents. The worst sustained undervoltage condition in the plant distribution system was found to occur with a severely degraded 500 KV off site system simultaneous with ~ concurrent LOCA on Unit No. 2 and Unit trip on Unit No. 1, or vice versa. (Reference 3.2) This undervoltage condition results from the automatic transfer of the group busses from the auxiliary power R transformers to the station power transformers and the 1 automatic start of the required vital bus loads. The reduction of loads to the June 1981 level will ensure that the worst case transient conditions will not affect the capability of the station power transformer to supply sufficient power to the safeguards equipment. Additionally, the worst case transient may be improved by eliminating the voltage transient caused by the group bus transfer.

The station power transformers have been shown by previous analysis (Reference 3.2) to have sufficient capacity and capability of assuring power to the 4160 volt group and vital busses under the most severe transient conditions as stated in the UFSAR. Based on these analyses the probability of occurrence or the consequences of an accident or malfunction of equipment important to safety is not increased as evaluated in the UFSAR. Furthermore, the possibility for an accident or malfunction of a different type than previously evaluated in the UFSAR is not created by the alteration of the normal operating configurations.

EDD-7 FORM l REV 0 10SEPT81

Page 3 of 4 S-C-El30-NSE-0458 REV. i Date: 9/6/86

• The Technical Specification (T.S. 3/4.8.l.la) requires that two physically independent circuits between offsite and onsite Class lE distribution systems (Vital Busses) shall be operable. The bases for the limiting condition of operation is that sufficient power be available to supply the safety-related equipment required for the safe shutdown of the R

1 plant and the mitigation and control of accident conditions within the plant. The station power transformers f~lf ill the function of connecting the offsite and onsite distribution systems as analyzed in the June 1981 study. By operating the non-vital station loads on the station power* transformers instead of the auxiliary power transformer, the margin of safety is not decreased and the operability of the vital buses is not compromised. This change in operating configuration reduces the transient loading on the station power transformers and therefore enhances the availability of the offsite power feeds to the vital busses. In addition the complete loss of offsite power is analyzed in Section 15.2.9 of the UFSAR and therefore the altered configuration is within the scope of the UFSAR.

5.0 RECOMMENDATIONS

Since a transient stability analysis has not been performed since June 1981, operation of the Salem Unit No. 1 and Unit No. 2 plants may only be continued when the plant loads are returned to within the values identified in the study and approved by the NRC. In addition, the plant loads will be supplied from the station powe~ transformers with the auxiliary power transformer group bus infeed breakers open.

This will further remove the potential transient load added to the station power transformers when a group bus transfers from the auxiliary power transformer. The reduced loads identified in Attachment II. will result in more conservative loads than that which were identified in the June 1981 study.

6.0 CONCLUSION

S:

The continued operation of Salem Units 1 & 2 is justified on the basis of the discussion above. Implementation of the above recommendations do not constitute an Unreviewed Safety Question since, a) it does not involve a modification, test or experiment associated with equipment important to safety, but rather the administrative operation of balance of plant equipment, b) it is based on the results of analysis for a modification of a type previously approved by the NRC (Ref.

3.1), c) it recommends the administrative control of operation of non-vital equipment that are not part of the basis for any Technical Specification (See attachment).

EDD-7 FORM 1 REV 0 10SEPT81

Page 4 of 4 S-C-El30-NSE-0458 REV. l Date: 9/6/86 7.0 VENDOR MANUAL IMPACT None 8.0 SIGNATURES Group Head Date Date a .!'l444Anam-/-m711 /'J.4- ~ w/tJ. ~

Manager - 1 Date 9h/&

Plant Engineering ss-lh9/5 se/SS4 EDD-7 FORM 1 REV 0 10SEPT81 I

ATTACHMENT I - Changes in Plant Loads UNIT NO. l 11 Station Power Transformer 12 Station Power Transformer Group 2000 KVA ( 2 ) Cond. Pumps 1000 KVA (1) Cond. Pump Busses 333 KVA Misc. Subs. 333 KVA M*isc. Subs.

Vital 833 KVA Misc. Subs. 833 KVA Misc. Subs.

Susses 3166 KVA Total 2166 KVA Total UNIT NO. 2 21 Station Power Transformer 22 Station Power Transformer Group 6000 KVA ( 3 ) Cond. Pumps 1000 KVA ( 1 ) Cond. Pump Busses *1000 KVA Non Rad Waste 333 KVA Misc. Subs.

333 KVA Misc. Subs.

Vital 833 KVA Misc. Subs. 833 KVA Misc. Subs.

Busses 8166 KVA Total 2166 KVA Total

• ATTACHMENT II Equipment to be out of service to obtain reduction of Station Power Transformer Loads UNIT NO. 1 11 Station Power Transformer 12 Station Power Transformer must reduce by 3166 KVA, any must reduce by 2166 KVA, any of the following may be removed of the following may be removed from service to total 3166 KVA. from service to total 2166 KVA.

11 Cond. Pump - 4000 KVA* . 13 Cond. Pump - 4000 KVA 12 Cond. Pump - 4000 KVA 12 Heater Drain Pump - 1000 KVA 11 Heater Drain Pump - 1000 KVA 13 Heater Drain Pump - 1000 KVA llA Circ. Water Pump - 2000 KVA llB Circ. Water Pump - 2000 KVA 12A Circ. Water 13A Circ. Water Pump - 2000 Pump - 2000 KVA KVA 12B Circ. Water 13B Circ. Water Pump - 2000 Pump - 2000 KVA KVA UNIT NO. 2 21 Station Power Transformer 22 Station Power Transformer must reduce by 8166 KVA, any must reduce by 2166 KVA, any

• of the following may be removed of the following may be removed from service to total 8166 KVA. from service to total 2166 KVA.

11 Cond. Pump - .4000 KVA** 23 Cond

• Pump - 4000 KVA 21 Cond. Pump - 4000 KVA 22 Heater Drain Pump - 1000 KVA KVA 22 Cond. Pump - 4000 KVA 23 Heater Drain Pump - 1000 21 Heater Drain Pump - 1000 KVA 21B Circ. Water Pump - 2000 KVA 21A Circ. Water Pump - 2000 KVA 22B Circ. Water *Pump - 2000 KVA 22A Circ. Water Pump - 2000 KVA 23B Circ. Water Pump - 2000 KVA 23A Circ. Water Pump - 2000 KVA

• Out of service presently

• • ~OTE: _Unit No. 1 equipment

SE/FD RECEIPT FORM TO: Manager - Nuclear Engineering Control

• PART A I Document title J\,\5\\£\cA=r\oN £OR opE\2..f\3'\0t\l OF Ll~\\5 i BN.h <)_ 'v\l\1\1 L\M\\E.i> 4KY Lo{\hs Document number s..c. . . E \30- NSE- 0 459 , R£V. 1..

Sponsor Assigned Status Code *.~-~5~6=---*- - - - - - - - - - - - - - -

Sponsor Signature /lltJ/.tvJIP-~ Date PART Bl The subject document has been received and concurrence with the NED Assigned Status Code cannot be made at this time, but will be made by (date). When a decision is made, a copy of this form with Part C completed will be sent to the Manager - Nuclear Engineering Control.

Salem Operati~ns Response Coordinator Date

• (Signature)

• PART C I The subject document has been received and:

D i. We concur implement (date) as with the NED ~ssigned Status Code of and will/did (circle one) the recomrnendation(s) b y - - - - - - - - -

described below.

D 2. We do not concur as explained below:

• Salem Operations Response Coordinator

• (signature)

GM8-EMP-010 Exhibit 2 Date

• See reverse side for explanation (Rev. 1) **Continue on attached sheet(s)

NED/50 14

ENG.IN E.EJUNG AND PLANr BE:IT!'llMCNI' r.EPAR'IMCNI' DESI~ VERIFICATICN R~

GM8-~06

• PART A SUBJEJ:T:

DISCIPLINE(S):

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I OOlli IBIS DESI~ O'.Nl'AIN ASSUMPI'IOOS REQUIRING INPUl' OOCUMENTS REV.

LATER a::.t-lFIRMATIOO? _ _ _YES ~00 SE. E: c; ( c.,"T \ 0 "-) 3 or ORIGINATOR (PRll'IT)~ 't:i~Vi t'\~O Ni)

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'ciRIGINA'IDR Is SIGlA'ruRE zl!'~?

S bf EI)' E.-J f\L.U. f\3\ o N PART B

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1 Assigned By: '}J<.LcX..w ~

J'.t*~~'-'- Vrh'~.

Verifier Assigned (Print) Date PART C METiiOD Of VERIFICATILN EXTENT OF VERIFICATILN fZl J:esign Review/[):)cument Review Q. Identical to Previously verified J:esiyn (Identify)

[] Alternate Calculation D Similar to Previously Verified r::esign (Identity) 0 Qualification Testim 0 New (no identical or similar desionl FOR ITEMS VERH'IED BY DESIGN REVIEW, GIECK BELOW, "YES," "NO," CR "N/A" IF t-1.JT APPLICABLE.

PROVIDE ADDITIONAL CDMMEm:S, IF NEEDED, IN PART E. SEE REVERSE SIDE FOR COMPLETE QUESTIUN.

YE.S 00 N/A YES NJ N/A DESIGN REVIEW QUESTIUNS RESR.lNSE DESIGN REVIEW QUESTICNS RESFQNSE

• 1.

2.

3.

4.

Jl.ppropriate design input?

Pdequacy of Assumptions?

QA Requirements?

Codes, standards, regulatory

/

/

,/

10. Material Canpatibility

11. Ma.int. Reqnts. Accessibility

12. IS! Requirements?

13. Radiation Protection?

,/-

/

,/;

/

/

requirements?  ;/ 14. Inclusion of Acceptance Criteria?

/

5. construction and UperatirYJ 15. Test Requirements EXperiences? / /

16. Handlirr;i, Stor1!1,Je, Cleani rr;i and

6. Design Interface Requirements? / Shippirr;i Requirements?

/

7. Appropriate J:esign Method? / 17. Identification Requirements? /

8. Reasonable ().ltput? / 18. Recore Preparation, Review

/

Approval and Retention /'

Cf. Proper*Canponent Application? ,/ Requirements?

PART D verifier attests to beirr;i independent of the design eftort identified in Part "A" ([):)cuments to be verified). Verifier further attests that all carrnents regardirr;i the design :2~~lC1)rf~)/~~ crhb(

effort have been resolved and that the docunent is verified. Verifier slgnature ~~~/

PART E (Use additional sheets if required)

Ve,fl..1 hc.,,*di Ci'-' is bo_r;e0-~r-i pr-e,'ho.~<-s vo /fc~j~* ~E.R5 US fDi.1_J ~tz_rJy ktJe.

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G-!8-EMP-006 Exhibit 1 (Rev. l NED/5 12*-13 Pa9* l of 2 R*v. l

PUBLIC SERVtr.E ELECTRIC AND GAS COMPANY

• • ENGINEERING AND CONSTRUCTION DEPARTMENT DATE:

RESPONSE DUE:

February 4, 1980 TO: F *. P. Librizzi General Manager - Electric Production

. FROM: D. J. Jagt Manager - Salem P~ojects

SUBJECT:

SALEM NUCLEAR GENERATING STATION UNITS NO. l AND 2 NRC REQUEST FOR ADDITIONAL INFORMATION DEGRADED GRID VOLTAGE PROTECTION (70%-90%)

To satisfy NRC concerns regarding postulated degraded grid voltage conditions at Salem, a second level of undervoltage protection is required. A meeting was held*with the NRC staff in October, 1979 to discuss the proposed design

• Since that time, additional questions have been received, the responses to which are attached.

Please submit to the NRC in the appropriate ~~Or{1&f .LICENSING MANAGER SALEM E. A LIDEN FEB 19 1980

!'VU!Ct'J

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• 0 .........

', COPiES 0 ...*... 0 *********

RB:jb .j CUE .... *.*.*.*.*.. FiLE ............... .

I - ***************

Attachments: A - FSAR Fig. 8.3.l B - 10/10/79 Letter - Adequacy of Station Electric Distribution System Voltages *

. Figure 1 - Protective Relay Characteristic Curves CC: R. R. Bast E. *A. Liden ./

F. A. Christiana

. G. w. Supplee HK19/l

• 1.

The onsite distribution system for each unit at Salem is arranged so that two vital buses are connected to one station power transformer and the third is connected to the other station power transformer (FSAR tigure 8.3.1).

The in-feed breakers for each vital bus from the two station power transformers are electrically interlocked

.to prevent paralleling both sources through a vital bus. The breakers also provide the means for transfer~

ring between sources in the event of an interruption of power from one source.

Undervoltage protection for each vital bus will be pro-vided by two protective relay groups. One group is de-signed to protect the vital buses if bps supply voltage falls below 70% of its rated value. This group is al~

ready installed and operable. The other group will be designed to protect the vital buses if bus supply volt-age falls below 91% of .its rated value.

Each undervoltage protection group is/will be comprised of two sets of relays:

A set for undervoltage transfer, and A set for generating "Blackout" signals.

The 91% group will be comprised of adjustable time delay relays. The protective relays will be connected to the electrical system in the same manner and location as the present undervoltage protection. The new design ~ssen tially duplicates the present protective scheme in all regards (Attachment A) with the following exception.

The 91% relays will be equipped with an administratively controlled loc.kout which will allow the control room op-erator to disarm the system during the start of any ~e actor coolant pump. This feature is required to fore-stall any unnecessary undervoltage signals due to the voltage transient caused by a reactor coolant pump start. The lack of this manual lockout feature would require that an extended ti~e delay (30 seconds) be used to actuate the 91% relays. The system will be armed by the control room operator upon completion of any RCP start, and will remain armed under all conditions other than a RCP start. The disarming and rearming of the system will.become an integral part of the RCP starting HK19/2

• procedures used at Salem and an alarm will be provided for the. disarmed condition. In addition to manual re-arming, a timer will be provided to automatically rearm tqe system in the event the control room operator neg-lects to do so after a RCP has been started.

The time delay of the 91_% undervol tage transfer rel'ays will be 10.5 seconds when the output of the station power transformers is below 91% of its rated value (Figure 1).

• The time delay of the 91% bus "blackout" relays will be 13 seconds when the voltage on the affected bus (or buses) is below 91% of rated value (Figure 1).

In the event the supply voltage to a 4 KV vital bus or buses falls below 91% of its rated voltage, the affected bus 'O:t buses. will be automatically transferred to the alternate source by the action of the vital bus transfer relay (XET-230, Fig. 1) and the 91% transfer relays af-ter a 10.5 second time delay *

• The following conditions must be met before a bus trans-fer may be accomplished at either low-voltage condition:

a. The bus differential or overload relays have not operated.

b* Voltage on the affected bus or buses is below 35%

(this permissive prevents transfe~ with excessive out-of-phase residual bus voltage) *

.c. The in-feed breaker of the normal supply is opened *.

d. The related diesel-generator circuit breaker is open.

e. The alternate source voltage is above 91%.

f. The SEC (Safeguards Equipment Control) bus under-voltage (blackout) relays have not operated.

For both groups (10% and 91%), the undervoltage and vital bus (XET-230) transfer relays allow the a.ffected bus or buses to be transferred to the remaining station power transformer before the bus blackout relays are tripped

• HK19/3

• -3'""'.

If the supply voltage to the vital buses fall~ below 70%

of rated voltage and a transfer is not accomplished, the 70% blackout relays will provide a signal to start the diesel-generators. If the supply voltage to the vital buses falls below 91% of rated voltage and a transfer is not accomplished, the 91% bus blackout relays will pro-vide a signal to start the diesel-generato~s.

Undervoltage signals generated by either set of blackout relays will be combined (through the use of buffer re-lays) in a 2/3 logic matrix per bus to develop a black-out loading signal for that bus. The buffer relays will be used on each vital bus undervoltage sensor to supply independent signals to each SEC unit to maintain inde-pendence among the three buses.

If the output voltage of a station power transformer supplying one vital bus falls to 70% of its rated value and the transfer mechanism fails, the 70% blackout relay for that bus will g~nerate a signal which results in a

• • 1/3 condition at each SEC controller. The Salem design is such that a loss of one vital bus is tolerable for all normal operating conditions; therefore, no automatic equipment actuation will take place for this cbndition.

This design will also apply to the new 91% protective relays. For a postulated LOCA, this criterion will not apply. A postulated LOCA concurrent with an undervolt-age condition on one vital bus is discussed in the re-sporise to question 5.

2. The proposed design will employ t'est switches which can be used in conjunction with any external equipment (var-iable power supply, etc.) necessary for proper calibra~

tion and testing.

Technical specifications similar to those for the exist-ing undervoltage protection will be generated upon the Staff's approval of the proposed design.

3. Since this design is a duplicate of the present under-voltage protection system (except for the administrative controls), it will meet the necessary criteria for pro-tection and control of Class lE equipment (IEEE 279-1971) *

• HK19/4 I"

• 4.

. If a LOCA concurrent with a voltage degradation which reduces the output of both station power transformers to between 90% and 70% of rated voltage is postulated, the SEC system will react only to the LOCA while the 91%

transfer relays are timing out. The time for the relays to actuate will be 10.5 ~econds.

While the relays are timihg out, ~he SEC system will perform ~he following functions:

a. Start the diesel-generator units.

b. Lockout ~anual control of equipment circuit breakers until the required loads are connected to the vital buses.

c. Connect all required accident loads.

The diesel-generators are started automatically so as to

• be available in the event they are subsequently re-quired. They are not automatically conn.ected to the_ vi-

• • tal buses

• The ability of the safeguards motors to start and carry their designated loads under degraded voltage conditions is described in Attachment B. The safeguards motors are.

capable of withstanding degraqed voltage conditions for the times under consider~tion without suffering any thermal damage.

When the 91% transfer relays time out (10.5 seconds),

the transfer will .not take place because the station power transformer potential relays will not generate a permissive. Therefore, the 91% blackout. relays will be.

allowed to time out (in an additional 2.5 seconds), and

_a blackout signal will be generated.. When the blackout signal is generated, the SEC will automatically shift modes from that for a LOCA (Mode I) to that for a LOCA

• plus blackout (Mode III). The shift of modes will re-*

quire less time than the recognition and actioh required to combat only a blackout due to the "-ready" status of the diesel-generators. -

• HK19/5

• The above mentioned sequence of operations ~ill take place within the required time limits to successfully mitigate the consequences of a LOCA. A delay time of 15 seconds between the occurrence of the incident and the application of power t6 the first sequenced safeguards

~umps was assumed in the original LOCA analysis.

• Although regarded as extremely unlikely, it may be pos-tulated that one stati6n power transformer may suffer a voltage degradation which reduces its output voltage to bet~een 90% and 70% of its rated value while the output of the remaining station power transformer is reduced to just above 91% of rated voltage. Under these condi-.

tions, one s~t of 91% transfer relays will begin timing out while the other set "sees" no.abnormal conditions.

It may be possible to reduce the output *voltage of the "normal" transformer to below 91% of its rated value af-ter the transfer from the affected transformer takes place. Also, the output voltage of the initially af-fected transf armer may rise above 91 % of its rated value due to its partial unloading. These voltage changes will not amount to.more than.3% for each transformer

• consequently, the 91% transfer relays for the alternate transformer will begin timing out and would effect a subsequent transfer at the end of an additional 10.5 seconds. These conditions would result in a continual flip-flop condition causing intermittent power interrup-tions on the vital buses.

This action will be preverited by the installation of 91%

blackout relays which have a 95% reset setting. The 91%

blackout relays began timing out at the same time as the 91% transfer relays on the initially affected trans-former. Since their tim~ delay will be 2.5 seconds .

longer than that of the transfer relays, and if the transfer does not successfully raise* the bus volta~e above 95%, the bus relays will initiate separation of the bus from both transformers. The -reset setting of 95% on the transfer relays will also ensure tha.t the -

buses do not continually transfer from one ~ource to the

• other.

• The interlocks and permissives utilized in the transfer of buses are described in Item 1 *

• HK19/6

5. In the event a LOCA occurs concurrent with a voltage level on one vital bu~ below 90% and above 70% of rated voltage, th~ SEC response will be the same as that ex~

plained in Item 4 while the 91% transfer relays are tim-ing out. Once the relays have timed out, a transfer to the alternate source will take place.

If the transfer mechanism fail~, a blackout signal will be generated for the affected bus and the SEC will auto-matically shift from a Mode I (LOCA) to a Mode IV (LOCA plus one vital bus undervoltage) condition, whereby only the affected bus is connected to its diesel-generator.

The other two buses will remain connected to offsite power.

If a LOCA occurs concurrent with a degraded voltage con-dition on two of the three vital buses which reduces the bus voltages to between 90% and 70% of rated volta~e, the.SEC will react as explained in Item 4 while the 9li transfe~ relays are timing out. Once the relays time out, the buses will be transferred to their alternate source.

If the. transfer mechanism fails, a blackout sigrial will be generated and the SEC will automatically shift from a Mode I (LbCA) to a Mode !I1 (LOCA plus blackout) condi-tion, whereby all three vital buses will be shifted to diesel-generator power.

Fo.r both postulated conditions, the safeguards motors on the aff~cted bus or buses will be subjected to* degraded voltage conditions .for no more than 13 seconds. Their ability to start and mainta~n operation (or to withstand a postulated voltage degradation wh~ch prevents starting) during the period prior to bus tran~fer, and the accepta-bility of* the time delays involved are explained in Item 4. *

6. The characteristics of AC contactors and associated control fuses are described in Attachment S.

7. With regard to Staff's suggestions of utilizing only bus blackout relays in the proposed design (no attempted transfer), the following scenario is ~resented *

• HK19/7 .

• The existing diesel starting and sequence loading logic is located in the Safeguards Equipment Control (SEC) sys-tem assotiated ~ith ~ach bµs. The plant _design is predi-cated on each SEC performing the master decision making and resultant actions associated with bus loading. To make use of this existing logic with the design sug-gested, would require paralleling the existing bus under-voltage inputs and the proposed secondary bu~ under-vol tage relays.

Assuming an* initial system configuration of two buses being supplied from one.station power transformer (as-sume #11) and the remaining bus powered by #12 SPT, a degraded voltage condition on #11 SPT side, coupled with a single failure within the bus voltage monitoring logic, could result in the following condition:

Bus "A" operating ~{th degraded voltage due to failure in monitoring logic.

Bu~ "B" operating with degraded vqltage due to lack of required coincident logic in SEC (failure cascaded from

-failure in Bus "A" circuits)

• Bus "C" operating at.normal voltage supplied from #12

• _ SPT.

The above scenario assumed that no condition exists which would generate a Safety Injection (SI) signal. If an SI signal were to exist during this occurrence, the following system configuration would result:

Bus "A" could attempt to block load all ESF loads during a degraded v*oltage situation. This would most l~kely result in a further bus voltage degradation to below 70%

and cause the-diesel to start and commence sequential loading via the SEC.

Bus "B" would follow the sequence of events described in Item 5 for a postulated LOCA concurrent with a voltage degradation on one vital bus.

Bus "C" would ."block *load" the ESF loads on the normal supply from the #12 SPT.

The sequence described for the case of "No SI Signal" is unacceptable. _The proposed design which includes an at-:-

tempted transfer, p~ecludes ~hat sequence of events and ensures that_ at least two buses are_ capable of supplying the needed equipment.

HK19/8

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• ATTACHMENT B

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• Public Service R. R. eAST/{.b Electric and Gas s-;.;r---------i a ac .

Company oc*i 12 197J 0 RM o~n 0 JJI( O"'Gw:

Director of N*uclear Reactor Regulation D WDD 0 FAC o.s. Nuclear Regulatory Commission 0 PRHL 0 Washington, DC 20555 Attention: Mr. William Gammill, Acting ~ssistant Director for Operating Reactors Projects Division of Operating Reactors Gentlenen:

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTI::1 VOLTAGES - SALEM GENERATING STf\TION UHITS NOS. 1 AND 2 We have performed the analysis on the Salem Generating Station Units Nos. 1 and 2 electric power system in accordance with NRC letter, Ad~quacy of St~tion Electric Distributitin System Voltages dated .August 8, 1979 and its enclosures-.

• The analysis de~onstrates that the offsite power system and the onsite distribution system is of sufficierit capacity and capa-bility to automatically start as well as operate all safety loads within their voltage ratings for all anticipated transients and accidents.

Satisfactory results were obtained as a result of the original design considerations. The Salem Generating Station was designed such that the resulting voltage profile was within component voltage -limitations, being +5% of transformer secondary voltage and -1oi of motor nameplate voltage*under steady-state conditions.

The system was also designed. such that the inrush current associ-ated with the start of a 6000 horsepower, 4.0 kV motor would not cause the bus voltages to drop below 80\. All motors are de-signed to accelerate their driven equipment with at least 80\

motor nameplate voltage applied to its terminals. This was acco~plished by optimum selection of transformer impedances,

• • iacerporation of no-load taps on all power and unit *ubstation transformers, and a + lOt automatic l_oad tap changer on all the 13.8/4.16 station p~er transformers. All meter atarters have a quaranteed drop out voltage of 70t. All *tarters vere bought with 300 V1' control pm.'er transformers, regardlesa of NEMA si:z:e,

~o minimize voltage drop_ at the contactor coil. Purther, con-sideration was given to cable size and length to limit voltage drop in a fee~er *

.. pir. of Hue. a.actor .. qulation .10-10-79

'l'be analyai* *bowed the wor*e *u*tained undar-voltaqe condition im.po*ed upon ~ 4i*tribution *Y*tam ooourred with a severely de-9raded SOOkV off*ite *y*tam *imultaneoua with a concurrent LOCA on Unit 2 and Unit t.rip on Unit 1 (or vie* ver*a). 'l'hi* under- #

TOltage condition re*ult* frum the automatic tran*fer of the vroup bu*** from th* auxiliary po¥9r t.ran*f oner* to tha *tation power t.ran*former and the automatic *tart of the required Tit.al bu* load*. ~or thi* condition the lowest YOltaqe* at the C.16

---

~-

• ... I

.. .~:; ..

. *.*r.,

kV, 460V and 230V load* ware .917, .923 and .91 per anit ra-apectively. '1'ha above analysi* indicate* that the ~it.a 41*-

t.ribution sy*tem and it* oomponants will operate within oomponent TOltaqe limitations. The motor* are the limitin9 component under ataady-atate ~ndition* a* they are deaiqnad to run continuoualy at .t per unit nameplate voltage.

Transient volta9e 4rop* due to the *tarting cf motor* were analyzed at each volta9e level with no adverse effects. 'l'hi* analyaia assumed the pJ;e11tart voltaqe*to bo*that oorra*pondin9 t.o the degraded 500 kV eystem and the load in parallel with the motor being *tarted equal to the maximum continuous rating of the t.ran*f ormar to which it i* connected le** the running load of the mot.or bain9 startetl. Purthar, the impedance ot the parallel load va* oonaervativaly a*sumed t.o ~ecrea*a aa tho wquare of the bu.

~1t.a9e to analytically compenaate for the additional currant d.ravn by induction motor* upon decrease in YOltaqe. 'l'he minimum

• - tran*ient voltage* obtained on the *.16 tv, C60V and 230V level*

were .86, .86 and .78 per unit, respectively for a duration of approximately 5 aeconds. 'J'heae transient* are within motor and *.

JnOtor *t.a.rt:-er design aa?a.bilities, the_reby having no a~verae affect on syat.eru operation. 'l'be re*ult* of this analysis were aaed to reexamine under-volta9e protective *ettings and aatabliah that no *purioua *eparation.s of the *afety bu*e* from offaite power would occur.

• The 5 kV power cablea t.hat OOMect t.he 13.8/4.16 kV station power*.

transformer* to the group and vital buae1 are the load limiting component in t.he di*tribution *yatem. The *ixt.een hour ratinq of the cable i* utilised for the load that results from the oonc:ur-rent LOCA Unit 2 and Unit trip on Unit 1. There 111 aufficient ma.rgin between t.hG cable ratinq.and the rel!lultant load to allov for implementation of exi*tinq atation prooedu;-e* used during ~*

event* analyzed and thu., avoid overloading. .,.

A.9 f.i\~icated in t.he NRC letter of Auqust. 8 1 1979, ta*t* had been previoualy run t.o correlate calculations with field condition*.

With Salem Unit* 1 and 2 and th* 500 kV *y*tem in an axi*tin9 mode corresponding ~o a 9iven loadinq of -~ plant distribution

• yatem, aelect.e~ *Y*tem para.meter* vere 1DOnitored over a 24-hour period. An analyai* waa then performe~ using the actual load and 500 kV *Y*tem voltaqe to obtain a calculated voltaqe profile and compare to actual mea*urementa. The calculation* and field .

J:Deasureroent* correlated within vary reasonable accuracy, thua

. -* .oir. of Bue. Raaot.or Regulation

_,_ *10-10-79

• *ub*.t.antiating our uaumptiona and. the *tho4 of calculation *

• 'l'h* naulta are viven in Attaohmant 1. Further, a teat on a oold

'000 horaepover, 4.0 kV reactor coolant pump motor w.. oond.uct.ed.

'1'he bu* voltage dropped. 15' upon *tart of thi* mot.or. 110 ad.verae effect* ware obaerved. on other operating equipment. 'l'b.e nault*

of thi* t.aat *ub*tantiate t.ha original-plant d**i9ft buia.

!'he electric power ayatam wa* reviewed to determine if t.hare are any event* or eond.ition* vhich could result in the aimult&ne0\19.

or*~onaequential loaa of required circuit* *to the offaite network that would violate GDC-17. No potential axiat* ~or violation of GJ>C-17.

If you ahould have any queationa, pleaae do not beaitate to contact ua.

Very truly youra,

-rP u?¥p~

Frank P. Libz'i{zi General Manager -

"11'\.. Ar11 1A *

&act.ric Production GLS .l hll

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CC Gen'l Mgr. - Engg~

Proj. Licensing Mgr. - Salem Asst. Gen'l. Solicitor Mgr. - Nuc. Opera.

Mgr. - Plant Maint.

Mgr. - Salem SQAE - Salem EPD-OAE P *. A. M0eller N. R. Philipp

.Attachment

SALEM GENERATING STATION, UNIT 2 VOLTAGE PROFILE PIELD MEASUREMI:NTS VS,. CALCUI>.TIONS 00 kV Bus

.3 kV Bus

~o. 11

ta.

• P..*r.

so. 21 u Stae Pwr.

J 4200 Measured 4i56 ca~culated I 4 kV Bus 4160/4BOV 465-470 Measured LOad Lumped 4 kV 470 Calculatec Running Load 19.27 Mn 460V B-..:.s

,160/2 Lumpe 460V Lead Running 580 ICVA

• ~TT 1\ en MEt-..,.

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Response to NRC Letter ld:g~acy of Station Electric Distribution System Voltage - Dated August 8, 1979 35-239 Measured 239.1 Calculat.T

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• Public Service Electric and Gas Company October 10, 1979 Director of Nuclear Reactor Requlation u.s. Nuclear Regulatory Commission Washington, DC 20555 Attentionz Mr. William Gammill, Acting Assistant Director for Operating Reactors Projects Division of Operating Reactors Gentlemen:

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES - SALEM GENERATING STATION UNITS NOS. l AND 2 We have performed the analysis on the Salem Generating Station Units Nos. 1 and 2 electric power *ystem in accordance with NRC letter, Adequacy of Station Electric Distribution System Voltages dated August B, 1979 and its enclosures *

• The analysis demonstrates that the offsite power system and the onsite distribution *y*tem i* of sufficient capacity and capa-bility to automatically start as well as operate all safety loads within their voltage ratings for all anticipated transients and accidents.

Satisfactory results were obtained' as a result of the original design considerations. The Salem Generating Station was desi~ed such that the resulting voltage profile was within component voltage limitations, being +5\ of transformer aecondary voltage and -10% of motor nameplate voltage under steady-state conditions.

The system was a~so designed auch that the inrush current associ-ated with the atart of a 6000 horsepower, 4.0 kV motor would not cause the bus voltages to drop below 80%. All motors are de-aigned to accelerate their driven equipment with at least 80%

motor nameplate voltage applied to its terminals. This was accomplished by optimum selection of transformer impedances, incorporation of no-load tap* on all power and unit substation transformers, and a + 10\ automatic load tap changer on all the 13.8/4.16 station poWer transformers. All motor atarters have a guaranteed drop out voltage of 70%. All *tartars were bought with 300 VA control power transformers, regardless of NEMA size, to minimize voltage drop at the contactor coil. Further, con-sideration was given to cable size and length to limit voltage drop in a feeder

• 95 :.33C '*'.Xl*.* . --

Dir. Of Bue . . .actor a.CJUlation 10-10-79

'l'ba analysis ahowed the vorH aU9tained andar-YDltaqe oondition imposed upon the c!iatribution sy*tem ooourred with a aeverely d*-

9raded 500kV off *ita ayst. . aillultaneoua with a oonourrent LOCA on Unit 2 anc! unit uip on tJnit 1 (or vice versa). Thia andar-

"WOltaqe condition re*ulta froa the automatic uanafar of the vroup buae* from th* auxiliary power uansforln9r* t:o the atation power tranaformar ~ the autcmatic *tart of the required vital bu9 loada. Jlor ~* oon41tion the low'a*t voltage* at i:ha 4.16 kV, 460V and 230V loads . .re .117, .t23 and .91 per unit re-mpectively. '1'ba above analy*is in41cates that the onaite 41*-

uibution 8)'atem anc! it* oomponants will operata within component voltaqe limitations. The motor* are the limiting component under ataady-atate conditions aa they are 4ea1gned to run oontinuoualy at .t per unit nameplate voltage.

Transient voltage c!ropa c!ue to the *tarting of 11Dtor11 were analysed at each voltage level with no adv.rn effeata. Thia analy*is assumed the prestart voltage to be that oorraspondinq to the daqraded 500 kV aystem and the load in parallel with th9 motor being *tarted equal to t:he maximum continuous rating of the .

transformer to which it i* oonnected l*** the running load of the motor being *tarted. Further, the impedance of the parallel load waa conservatively assumed to decrease aa the aquare of the bua voltage to analytically compensate fo~ the additional current c!ravn by induct.i<<m llOt.o!:'* upon decreus -in YOlt~qe. The minimum uanaiant volt.ages obtained on tb8 '*16 kV, 460V and 230V level*

• were .86, .16 and .78 per unit, respectively for a duration of approximately 5 seconds. 'l'heae tr~*ient* are within motor and motor *tarter design capabilitiea, thereby havinq no adverse effect on syatem operation. '1'he re*ult* of this analysis were used to reexamtne under-volta99 protective **ttinga and **tabliah that no apuriows aeparationa of the safety busea from off*ite paver would occur.

The 5 JtV power cable* that oonnect the 13.8/4.16 kV station power tran*former* to the vroup and vital buae* are the load limiting component in t:he diatribution syatem. The aixt.een hour rating of the cable i* utilised for the load that results from the concur-rent LOCA Unit 2 and Unit trip on Unit 1. '!'here la aufficient margin between the cable ratin9 and the resultant load to allow for implementation of exiating *tation procedure* ued t!urinq the event* analyzed and thus, avoid overloading.

As indicated in the NRC letter of AuqwJt 8, 1979, test* had been previoualy run t.o correlate oaloulations with field oonditiona.

With Salam Unit* 1 and 2 and the 500 kV .Y*tem in an exiatinq mode oorreapondinq t.o a 9iven loading of .the plant distribution aystem, aelected system parameters were monitored over a 24-hour period. An analysis was than performed u*ing the actual load and 500 JtV *Y*tem volt.age to obtain a calculated voltage profile and compare to actual measurement*. The calculation* and field measurement* correlated within very reasonable accuracy, thus

Dir. of Nuc. Reactor Requlation ' 10-10-79

• *ub*tantiating our uaumption* and the method of calculation.

The re*ulta are given in Attachment 1. rurt.her, a t**t on a cold 6000 horsepower, 4.0 kV reactor coolant pump motor vu conducted.

The bua voltage dropped 15* upon *tart of thi* motor. No adver**

effect* were ob*erved on other operating equipment. '!'be re*ult*

of thia teat *ub*tantiate the original plant deai90 baaia.

'l'he electria power aystem wa* reviewed to determine if there are any event* or condition* which could re*ult in the simultaneoua or consequential lo** of required circuit* to the off *ite network that would violate GDC-17. No potential *xi*t* for violation of GDC-17.

If you ahould have any queationa, plea** do not heaitate to contact ua.

Very truly youra,

-;::PU~~~

Frank P. Libd/si General* Manager -

Electric Production

,_...---- ----- -______ , -----~--~*~---"" ..;::::..-.r11:;-----~-- -----

SALEM GENERATING STATION, UNIT 2 VOLTAGE PROFILE

• FIELD MEASUREMENTS VS. CALCULATIONS 500 kV BUS 13 kV BUS 4200 Measured I

i No. 11 Sta. Pwr.

No. 21 Sta. Pwr.

\J. J

'---4_1_s_6_ca..~cula ted I 4 kV Bus 4160/480V 465-470 Measured LO ad Lumped 4 kV 470 calculated Running Load 19.27 MVA 460V BUS 160/24 Lumpe 460V LOad Running 580 KVA 35-239 Measure~

• A'M'ACHMENT 1 239.l calculat!

To Response to NRC Letter 1d:q.lacy of Station Electric Distribution System Voltage - Dated August 8, 1979

,. UNITED STATES 'ii--(* 'L NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 January 19, 1981 lbcket No. 50-272 Mr. F. W. Schneider, Vice President Production Public Service Electric and Gas Company 80 Park Plaza lSA Newark, New Jersey 07101

Dear Mr. Schneider:

By letters dated June 2, 1977 and July 3Q, 1979 we advised you of our review of ons ite emergency power systems to assess the susceptibility of safety related electrical equipment to sustained degraded voltage conditions. We requested that you compare the design of the emergency power systems at Salem Unit No. 1 with the staff positions. You re-.

sponded to our requests for information by means of your letters dated*

August 1, 1977, September 13, 1979, and March 3, 1980. Representatives*

of our staffs also held a meeting on this subject on Octob.er 25, 1979. * -

The design modifications that you propose to achieve an acceptable level of protection against degraded grid voltage have been reviewed and approved. Our Safety Evaluation is enclosed. I request that you submit, for staff review, the Technical Specifications that are needed to im-plement these modifications. Your submittal should be made within 45 days of receipt of this letter.

1. 1

Enclosure:

Safety Evaluation cc:

See next page MAHAGER*NUCLEAR UCENSING UCENSIN8 AN .HVIADNMEHT E. H NOTED ***

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• ........ *:-_.., ~ *:** ...........:-_* ..

....... *.* ._._... .fl*********.*-****

• • • • • • • • • • • .*-~

DUE *.***** " FIL! *********

• Mr. F. W. Schneider Public Service Electric and Gas Company cc: Mark J. Wetterhahn. Esquire Conner, Moore and Corber Mr. R. A. Uderf tz General Manager, Nuclear Suite 1050 Production 1747 Pennsylvania Avenue. NW Public Service Electric and Washington. D. C. 20006 Gas Company 80 Park Plaza 15A Richard Fryling. Jr ** Esquire Newark., New Jersey 07101 Assistant General Solicitor Pub 11 c Service Electric and Gas Company Mr. J. T. Boettger 80 Park Place General Manager, Quality Newark, New Jersey 07101 Assurance I&E Public Service Electric and Gene Fisher. Bureau of Chief Gas Company Bureau of Radiation Protection 80 Park Plaza 380 Scotch Road Newark, New Jersey 07101 Trenton, New Jersey 08628 Mr. R~ L. *Mittl, General Manager Licensing anrl Environment Public Service Electric and Gas Company

• • 80 Park Plaza 17C Newark, New Jersey 07101 Mr. Henry J. Midura, Manager Salem Nuclear Generating Station Public Service Electric and Gas Company P. O. Box 168 Han~ocks Bridge, New 'Jersey 08038 Salem Free Library 112 West Broadway Salem, New Jersey 08079 Mr. Edwin A. Liden, Manager Nuclear Licensing Leif J. Norrholm, Resident Inspector Li cens f ng and *Environment Dept.

Salem Nuclear Generating Station Public Service Electric and Gas U. s. Nuclear Regulatory Commission . Company Drawer I SO Park Plaza 160 Hancocks Bridge, New Jersey 08038 Newark, New Jersey 07101 ...

Peter A. Moelle~

Nuclear Licensing Engineer Public Service Electric and Gas Company 80.Park Plaza - 15A .*

Newark, New Jersey 07101

Enclosure SAFETY. EVALUATION REPORT .

SALEM GENERATING STATION UNIT NOS. 1 AND 2 DOCKET NOS. 50-272 AND 50-311 DEGRADED GRID VOLTAGE PROTECTION FOR THE SAFETY RELATED A-C POWER SYSTEM

1.0 INTRODUCTION

Operating experience has shown that adverse effects on the safety _related power system and safety-related equipment and loads can be caused by sustained low or high grid voltage cond_ition. We therefore requested the Public Service Electric and Gas {PSE&G)to assess the susceptibility of the safety-related electric system at the Salem Generating Station to sustained voltage degradation of the offsite sources and to address three Staff pqsitions.

After comparing the current design to the Staff Positions, PSE&G was required to either propose modifications to satisfy the positions and criteria or furnish an analysis to substantia~e that the existing facility design has equivalent capabilities.

By letters dated August 1, 1977 and March 3, 1980, PSE&G proposed certain design modifications to satisfy Staff Positions and criteria .. These modifications con-sist of the installation of a second-level undervoltage protection system for the safety-related equipment. We have also required that the setpoints~ sur-veillance requirements, test requirements and allowable limits be included by PSE&G in the Salem Unit 1 Technical Specifications (position number 3).

Proposed pl ant Techl'l'ical Specifications that. address the*se requirements and reflect the proposed design modifications have not been submitted by the licensee. for our approval *

~*-r.. *-**-.**-** - - - * - - -.,. - - - - - - -. . . - - * - *

• 2.0 DESIGN BASIS CRITERIA The design basis criteria that were applied in determining the acceptability of the system modifications to protect the safety-related equipment from a sustained degradation of the offsite grid are:

(1) General Design Crherion 17(GDC17), "Electrical Power*Systems, 11 of Appendix A, "General Design Criteria for .Nuclear Power Plants, 11 of l 0 CFR 50.

(2) IEEE Standard 279-1971. "Protection Systems for Nuclear Power Ge~erating Stations."

(3) Staff Positions as detailed in a letter sent to the licensee,

• (4) dated June 2, 1977

• IEEE Standard 308-1974. "Cl ass 1 E Power Systems for Nuclear Power Generating Stations."

(5) ANSI Standard C84.1-1977, "Voltage Ratings for Electrical Power Systems and Equipment (60Hz). 11 3.0 DISCUSSION This section provides a brief description of the onsite distribution system, the existing undervoltage protection available to the Salem Generating Station and a description of~the licensee's proposed modifications for the second-level undervoltage protection *

• • ---.:*--***---:--.*.*** **- ~ *- - .** .. *:**--*-**- .. ~- .. **-*-

• 3.1 OnSite Distribution System The onsite distribution is arranged so that two 4.16 kv vital buses are connected to one Station Power Transformer and the third is connected to the other Station Power Transformer. The in-feed breakers for each vital bus from the two station power transformers are electrically interlocked to pre-vent paralleling both sources through a vital bus. The breakers also provide the means for transferring between sources in the event of an interruption of power from one source (power transformer).

3.2 Existing Undervoltage Protection (First Level: Loss of Power)

The present design uses undervoltage relays to sense the loss of offsite power.

These relays monitor the 4160 V vital buses. When the voltage on these buses

• drops below 70% of its ra~ed voltage, the undervoltage relays drop out. The drop-out action of the relays isolates the buses from the offsite sources, starts the emergency diesel generator, initiates load shedding, and permits closure of the "diesel generator breakers *

. 3.3 Modification We required the licensee to comply with the three positions in o~r letter dated June 2, 1977, by documen~ing their modified design and committing to install a second level of undervoltage protection on the emergency buses *.

By letters dated August 1, 1977 and March 3, 1980, the licensee proposed the

~

install at ion of a second level undervol tage protection scheme in response to Staff Position 1. This scheme is in addition to the first level under-voltage protection scheme described in section 3.2 above. The second level*

• • undervoltage protection scheme will be comprised of two sets of relays:

set for und~rvoltage "transfer" and a set for generating "bladout" signals.

a

• The second level undervoltage protection relays will react instantaneously when the voltage drops below the setpoint of 91% of rated voltage. There will also be an external time~ with adjustable time delay._ The_ time delay of the second level undervoltage "transferu relay -will be 10.5 seconds when the output of the station power transfonners is below 91% of the rated voltage.

The second level undervoltage "blackout~ relays will consist of three under-voltage relays per unitg one relay for each of the three 4160 V vital buses and the time delay of the "blackout" relays will be 13 seconds when the voltage on the affected bus (or buses) is below 91% of the rated voltage. Tne_ output from the time in each bus will energize three auxiliary relays. One auxiliary relay output from each bus will be combined in a two-out-of-three matrix with its redundant counterpart from the other two buses. One of the three two-out-of-three matrices thus formed is assigned to each emergency bus. The output fr_om the two-out-of-three matrices signifies that an undervoltage condition ha*s occ..urred on at least two buses. This intelligence is input to each of the three independent safeguards equipment controllers which will act to disconnect the offsite power source from the emergency buses.

When an undervoltage condition at a 4160 V vital bus (or buses} persists below

• 91% of the rated voltage for at least 10.5 seconds, the affected bus (or buses) will be automatical~ly transferred to the alternate source by the action of the vital bus "transfer" relay. The vital bus "transfer" relays allow the affected b_us (or buses) to b~ transferred to the remaining station power transfonner be-

• fore the bus "blackout" relays are actuated. If the supply voltage to the vital buses .fall~ below 91 % of the rated voltage and a transfer is not accomplished,

• the second level "blackout" relays will provide a signal to start the diesel generators.

4.0 EVALUATION 4.1 Position 1 - Second Level of Undervol tage Protection The first position of the June 2, 1977 letter required that a second level of undervoltage protection for the onsite power system be provided. The letter also went on to identify certain criteria that the undervoltage protection must meet. Each criterion *has been evaluated against the licensee's proposal and is addressed below.

(1) The licensee's proposed setpoint of 91% of 4160 V rated system voltage is 94.5% of 4000V the motor rated voltage. This setpoint

• reflected down to the 480V buses will be greater than 90% of the motor rated voltage of 460 V. As the motors are the most limit-ing equipment in the system, this setpoint is acceptable. .

(2) The proposed time delay will not be beyond the thennal capability of the safety-related equipment. The setpoint is within voltage r.anges recoTTJnended by ANSI C84.1-1973 for sustained operation.

(3) The licensee's proposed time delay i~ long enough to override any short inconsequential grid disturbances. Further, we have reviewed the licensee's analysis and agree with the licensee's finding *that

~

any voltage dips caused from the starting of large motors will not trip the offsite source *

• (4) The proposed modification incorporates a two out of three coincidence logic scheme to preclude spurious trips of the offsite sources and thereby, satisfies the criterion.

(5) The licensee has stated in his proposals that the modifications are designed to meet the necessary requirements of IEEE Standard 279-1971.

The 1icensee has proposed that the second level undervoltage protection relaying scheme be administratively bypassed during the start of any reactor coolant pump (RCP). The inrush current associated with the start of a 6000 horsepower RCP motor would cause the 4 .kv vital bus voltage to drop below the 91 % setpoint

• for about 25 seconds, which would needlessly actuate the protection scheme

• The manual bypass of the undervoltage protection scheme on the vital buses will be reset by the control room operator upon completion of any RCP start and an alarm in the control room will be provided for the bypassed status. In addition to manual reinstatement by the control room operator, a timer of two minutes will be provided to automatically reset the andervoltage protection system. This bypass scheme is in accordance with our requirements and is acceptable.

4.2 Position 2 - Interaction of Load Shed Feature The design complies* with our position that requires automatic prevention of load shedding of the emergency buses once the onsite sources are supplying

- --*---------- - ---- . - - - -------- - . _... --::.--~- --- -- --- -- --- ,...---- -

~ .

• power to all sequenced loads on the emergency buses.

does not include the capability of having the load shedding feature to be However, the design automatically reinstated if the diesel generator incoming breakers are tripped. The Safeguard Equipment C:Ontrol System that governs the load shedding and sequencing operation provides indication in the control room of whether the load shedding feature has been reinstated: This feature in each diesel generator is manually r~instated from the ~ontrol room. The provisions of the design to have reinstatement indication and control of the load shedding feature available to the operator in the control room will minimize_ administrative procedural errors from interfering with the avail-ability of emergency power. Therefore, we conclude that the manual reinstate-ment of the load shedding feature is acceptable *

5.0 CONCLUSION

Based on the infonnation provided by PSE&G, it has been detennined that the proposed modifications comply with positions 1 and 2, and have met all of the staff's requirements and design basis criteria. The modifications, when implemented, will protect the safety related equipment from a sustained degraded voltage condition of the offsite power source. Therefore, we conclude that the licensee's proposed design modifications are acceptabl~.

The 1icensee indicated that the Technical Specifications will be modi fi~d.

upon our approval of the above' design modifications. We will issue a separate safety evaluation of the proposed Technical Specifications upon receipt and eva 1ua tion *

• ---*--**-:-- **--*-*-------".--*- -~ ....

- a- .

6.0 REFERENCES

1. Librizzi to Lear, letter dated April 25, 1977 ./

2. Librizzi to Lear, letter dated August 1, 1977

3. Librizzi to Gammill, letter dated October lO, 1979 /'

4. Librizzi to Schwencer, letter dated March 3, 1980

---

-------------- ---- --- ------- - ------~-.----- - - - -- -----~"- ---:-:-----*-:-*-;-~ --~-.,--,--~------ -~,-~*-,,--- -~~- --~ -------

T EGG-EA-5380 June 1981 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, SALEM NUCLEAR POWER STATION UNITS 1 AND 2, DOCKET NOS. 50-272 AND 50-311 D. A. Weber U.S. Department of Energy Idaho Operations Office

• Idaho National Engineering Laboratory This is an informal report Intended for use as a preliminary or working document Prepared for the U. S. Nuc1ear Regulatory ColTITlission

• - Under DOE Contract No. DE-AC07-76ID01570 FIN No. A6429 n

~~ EGC.G Idaho

4

. ~"~ EGC..G ldallo. Inc.

FORM EG&G*398

. . . . . 11*79)

INTERIM REPORT Accession N o . - - - - - - -

Report No. EGG-EA-5380 Contract Program or Project

Title:

Selected Operating Reactors Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System. Voltages, Salem Nuclear Power Station Units l and 2, Docket Nos. 50-272 and 50-311 Type of Document:*

Technical Evaluation Report Author(s):

D. A. Weber Date of Document:

June 1981

.esponslbl.e NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing This document was prepared primarily for preliminary or internal use. It has not received full review and approval. Since there may be substantive changes, this document should not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No

• DE*AC07*79 I 001570 NRC Fl N No* ...;.A.;.;:;6...;.;42::.:9;.__ _

• INTERIM REPORT

0322J ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES SALEM NUCLEAR POWER STATION UNITS 1 AND 2 Docket Nos. 50-272 and 50-311 June 1981

0. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

TAC No. 13009

AaSTRACT The Nuclear Regulatory Coli'l'llission has required all licensees to analyze~

the electric power system at each nuclear station. This review is to deter-mine if the onsite distribution system in conjunction with the offsite power

.sources has sufficient capacity and capability to automatically start and op*erate all required safety *loads within the equipment voltage ratings.

This iechnical Evaluation Report reviews the submittals for the Salem Nuc-lear Power Station.

The offsite power sources, in conjunction with the onsite distribution system, have be~n shown to have sufficient capacity and capability to continuously operate all required safety related loads, within the equip-

• ment rated voltage limits, in the event of either an anticipated transient or an accident condition. However, a sustained degraded* grid may result in spurious separation of class lE buses from the offsite source wnen one 500/13.SkV*Station Power Transformer is supplying all loads of both units.

FOREWORD 1n1l re~ort is supplied as part* cif the ~selected Operating Reactor Issues Program (III)" being conducted for the U.S. Regulatory Corrmission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by

G&G Iaano, Inc., Reliability and Statistics 3rancn.

ihe U.S. Nuclear Regulatory c*orr:nission funded the wcrx under tlie authorization, 61.R 20 19 01 16, FIN No. A6429 *

• i1

CONTENTS

• l .O 2 .0

3. 0 INTRODUCTION DESIGN BASIS CRITERIA *****..*****.************.*.*.******.*...*..*

SYSTEM DESCRIPTION * . * * * * * * * * * . * * . * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

• 4.0 ANALYSIS DESCRIPTION..............................................

2 2

4.1 Analysis Conditions *.*..*.* ~ *.*.**.. ; ....****.. ~............. 2 4.2 Analysis Result*s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3 Analysis Verification .... .....*......... ......... ..... ....... 4 5 .0 EVALUATION * * * * * . * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * . * . * *

• 4

6. 0 CONCLUSIONS * . . . . . * * * * * * . . * . . * * * * * . * . . . * * * * * * * * *.* * * * * * * * * * . * . * * * * .

• 7

7.0 REFERENCES

........................................................ 8 FIGURE

1. Salem Nuclear Power St~tion Units l and 2 electrical single-line diagram showing circuit breaker alignment for normal ope rat i ans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 TABLES

• 1.

2.

Class lE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages Comparison of Analyzed Voltages with the Undervoltage Relay Setpoints ........*.*...*........*.*........

........................ 5 6

• iii

• 1.0 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES INTRODUCTION SALEM NUCLEAR POWER STATION UNITS 1 AND 2 An event at the Arkansas Nuclear One station on September 16, 1978 is described in NRC IE Infonnation Notice No. 79-04. As a result of this event, station confonnance to General Design Criteria (GDC) 17 is being questioned at all nucle~r power stations. The NRC, in the generic letter of August 8, 1979, "Adequacy of Station Electric Distribution Systems Volt-ages," l required each licensee to confirm, by analysis, the adequacy of the voltage at the class lE loads. This letter included 13 specific guide-1ines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the class* lE loads.

Public Service Electric and Gas Company (PSE&G) responded to the NRC letter on March 3, 1980.3. This submittal~ submittals of October 10, 1979,2 September 24, 1980,4 June 16, 1981,j the NRC letter of January 19, 1981,6 and the Final Safety Analysis Report (FSAR) complete the information reviewed for this report.

Based on the information supplied by PSE&G, this report addresses the capacity and capability of the onsite distribution system of the Salem Nuclear Power Station, in conjunction with the offsite power system, to

• maintain the voltage for the required tlass lE eq~ipment within acceptable limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the class lE equipment are derived from the following:

1. General Design Criterion 17 (GDC 17), "Electrical Power Systems,* of Appendix A, "General Design Criteria for 11 Nuclear Power Plants," of 10 CFR 50.

2. General Design Criterion 5 ,(GDC 5), *isharing of Struc-tures, Systems, and Components," of Appendix A, General 11 Design Criteria for Nuclear Power Plants," of 10 CFR 50.

3. General Design Criterion 13 (GDC 13), "Instrumentation and Control," of Appendix A, General Design Criteria 11 for Nuclear Power Plants, of 10 CFR 50.

11

4. IEEE Standard 308-1974, Class lE Power Systems for 11 Nuclear Power Generating Stations."

5. Staff positions as detailed in i letter sent to the licensee, dated August 8, 1979 .

• 6. ANSI CS4.1-1977, "Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."

Six review positions have been established from the NRC analysis guide-1 inesl and the above-listed documents. These positions are stated in Section 5.0.

• 3.0 SYSTEM DESCRIPTION Figure l of this report is a simplified sketch of the Units 1 and 2 single-line diagram showing the cir~it breaker positions (opened or

• closed) for normal full-power operation.

The class lE distribution system consists of three independent lE buses for each unit supplied from the 500/13kV Station Power Transformers

{SPTs) 1 and 2 via the 13/4kV S?Ts 11 and 12 for Unit 1, and 21 and 22 for

.' Unit 2. The 13/4kV SPTs have automatic load tap changers. During normal full-power operation, two of the three lE buses of one unit are supplied

• / ) .*

~,-*

from one 500/13kV S?T and the third lE bus from :~e other 500/13kV SPT.

The four non-~E buses of each unit are supplied from their respective unit Auxiliary Power Transformers (APTs). Should a uni; trip, the non-lE buses will automatically transfer from the APT source to the SPT source.

If one of the S00/13kV SPTs is out of service, the 13kV ring ~us could I .(. ..: _

• be closed and. the remaining S?T could supply all lE buses of both units

• Each of the lE instrument buses are supplied through static inverters from AC/OC~supplies and have an alternate emergency supply through an auto-transfer switch.

I wJ'.* .'L I

4.0 ANALYSIS DESCRIPTION 4.1 t~at th~

Analysis Conditions. PS&G has determined by load flow.studies maximum expectea orfsite grid voltage is 530kV (106~) a~d the minimum 4891c.V (97.8%).

?S~~G has analyzed each offsite sourc! to both units, including cne SGG/13k.V S?T supp1ying all loads of both units, to det2r.nine tne lE equip-ment terminal vo1taces. The *111orst case ciass 1E ec:uipment terminal volt- I ages occur under the following conditions:

1.

The maximum voltage occur~ ~nen the 500kV grid is at l

its maximum expected value with :ninimumstation loads.

2. The minimUJ!I voltage *occurs wnen the 500kV grid is at "--*-

its minimum expected value, one 500/131c.V transfor:ner n supplying both units, a simultaneous trip of Unit 1 and ~

a LOCA in Unit 2. , '

3. The minimum transient voltage occur~ with the start of a ~.,GOO hp reactor coolant pump (RC?) under cond'itions*

described in 2 above.

2

J

/'ii'

• I-,,.* 500 (V 8\.15 SECT IC~ I NO I STA PWR.

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• J,1~*4 '.? I ~ '.~G-0-rrn~

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~_J CUP5 I u SI' z5,.v4

. 1z SP z~ .,...~

BCV 'Pl' Z5KV 9Pf' IJOO "'"A llCO WVA 75"' "? 7!1*,.z

• Figure 1. Salem Nuclear Power Station Units 1 and 2 electrical single-line diagram showing circuit breaker aligoment for normal operations .

......_ ,**- 3

• 4.2 Analysis Result. Table 1 shows the projected worst case class lE equipment terminal voltages under conditions of 1, 2, and 3 above. Table 2 shows a comparison of the analyzed voltages with the undervoltage relay setpoint.

PSE&G letter of June 16, 19815 provided an analysis of a single transformer supplying both units under minimum offsite grid conditions of 489kV {97.8%) which results in* a 4160V bus voltage of 3670V (88.24%).

However, the analysis was very conservative and does not give credit for operation of the automatic load tap changers {ALTC), which changes 5/8%

every 30 seconds, resulting in a 3.l.5% improvement in voltage over a

• three-minute period. The values* in Table 1 and 2 give credit for the ALTCs since the grid is not expected to suddenly drop to ene exact value of 489kV (97.8~). -If the grid should decay at a rate which exceeas the operation of the ALTCs then the second level undervoltage relays (or loss-of-voltage relays) will separate the lE loads from the offsite source. The lE loads

• • . would then be re-energized by the on~ite power systems.

4.3 Analv~is Verification. PSE&G's submittal of March 3, 1980,3 included test~procedures and data to verify their analysis. Actual load data, obtained over a 24-hour period, ~as used as a basis.to calculate a voltage profile. This profile was then compared with the actual measure~

ments. The results showed an error of 1~ or less at the 4kV and 450V levels

-* and a maximum error of 1.7: at the 230V level ably Transformer and bus loadings were sufficiently high to obtain reason-accu~~te data.

5 .O

• EVALUATION The results of the test verify the analysis.

Six review positions have been established from the NRC analysis guide-.

linesl and the documents*listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee submittals and are based on PSE&G's analysis of one transfor.:ier supplying both units.

?osition 1--With the minimum expected offsite grid voltage and maximum load conaition, each offsite sour:e and distribution system connection combination must be capable of starting and of ccntinucusly operating all class lE equipment within the equipment volta;e ratings.

WitN the exception of the starting voltage of a 230V motor, ?SE&G's analy5is, as reflected in Tabl! 1, shows that terminal voltages will not go below the continuous ratings of 1E motors and the pick~p and ooer~ting ratings of the motor starters during the worst-case steady-state minimum-voltage conditions. #Table l shows the 230V motor terminal starting voltage to b~ 1.15~ below the minimum start rating of the motor. However, the low voltage condition is not expected to occur* due to PSE~*s very conservative ana1ysis. Therefore tnis position is satisfied.

• Position 2--With the maximum expec:ed offsite ;rid voltage and minimwn load cona1t1on, each offsite source and distribution system connec~ion

TABLE 1

• CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES

(% of nominal voltage)

Maximum Minimum Anal,Z'.zed Eguiement Condit ion Rated Anal,Z'.zed Rated Stead,Z'. State Transient a 4000V Motors Start 80 86.35 Operate 110 106 86.5b 9.1. 5 460V Motors Start 80 86.85 Operate 110 106 86.sb 92 230V Motors Start 80 78.ssc Operate 110 106 86.5b 90.75 430V Starters Pickup 85 88.45 Dropout 70 88.45 Operate 110 107 90 93.6 230V Starters Pickup 85 87.35 Dropout 70 87.35 Operate 110 107 90 95. 75 '

Other Equipmentd

a. Transient value due to the start of a non lE 6000 H.P. Reactor Coolant Pump, except where noted.

b. Al1 lE motors have a service factor of 1. 15.7

c. Transient due to the start of the largest 230V motor.

d. The minimum and maximum values of lE equipment below 230V (battery chargers, inverters, etc.) were not specifically provided. However, in their analysis of the onsite distribution system PSE&G state that all safety loads will o~erate within their voltage rating (letter of October ~1979 in Appen-d ix I. Giving credit for the automatic load tap changers on the 13/4kV.

Station Power Transformer, failure of lE equipmented below the 2~0V level is not expected .

• 5

• TABLE 2 COMPARISON OF ANALYZED VOLTAGES WITH THE UNOERVOLTAGE RELAY SETPOINTS

(% of nominal v61tage)

Minimum Analyzed Relay Setcointsa

.-l;ocat ion/Relays Voltaae Time Voltage Time 4160V Vital Buses Oei-~d Grid iransfer relays 92 cent. 91 10.5 sec B1ac~cut relaysb S2 cent. 91 13 sec Less of Voltage relays 86.9 25 secc 70 inst.

a. aased on infer.nation in Reference 6 .

. Relays will operate when an undervoltage condition exists on at least

• J of the three vital buses for 13 seconds*an9 will act to disconnect the offsite power source from the emergency buses.o

c. ihe value is due to t~e start of a non lE 6000 hp RCP motor. The sec-ond level undervolt~ge scheme will be administratively bypassed during the start of the mctor.o Transient times for the start of other motors will be less tnan 10 seconds *.

I

. I ccmbinaticn must be capable of continuously operating the required class lE equipment without exceeding the equipment voltage ratings.

?S~&G has shown, by analysis, that the voltage ratings of the class lE

~quipment will nc~ be exceeded for the conditions analyzed.

?osttion 3--Loss of offsite power to either of the redundant class lE

[I distrioution systems due to operation of voltage protection ralays, must not occ~r when the offsite power source is within expected voltag_e limits.

~RC, 6SS'nas indicated,~in a separate report,5 that the requirements of tnis po'Sition are satisfied when both SPTs 1 and 2 are supp1ying both Units 1 and 2 based on PS~&G's analy'Sis-of March 3, 1980.l However,--as-noted in Table 2, this oosition is not met when one S?T (1 or 2) is supply-ing both units ~s tne analyzed voltage t92~} is very close to the second-ve l undervoltage reJay setpoint (91%). ihe NRC OSS report did not provide

~ctpoint tolerances. Also, as noted in Section 4.2, spurious tripping mav occ~r if the offsite grid degrades to its minimum ana1ay:ed *...alue at a wnich exce~ds the operation of the AC'iC's.

• me

-)

Position 4--The NRC letterl requires that test results verify the accuracy of the voltage analyses supplied

• PSE&G has shown that the calculations accurately represent the lE buses and loads.

Position 5--No event or condition should result in the simultaneous or consequential loss of both required circuits from the offsite power network to the onsite distribution system (GDC 17).

PSE&G has analyzed the onsite connections to the offsite power grid, and determined that no potential exists for simultaneous or consequential loss of both circuits from the offsite grid.

Position 6--As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate starting and operating voltage for all required class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

Salem Nuclear Power Station is the site of two nuclear units. The six lE buses of both units are normally shared between two offsite 500/13.SkV station power transformers (SPTs). The FSAR, Section 8.3. 1, indicates that, if one of the SPTs is out of service, the 13kV ring bus can be closed and the remaining SPT can supply both units. PSE&G's analysis for this conditions indicates that one SPT is capable of supplying the loads of both units giving credit for operation of the ALTC's. Therefore, this position is satisfied (see.position 1) .

6.0 CONCLUSION

S The voltage analysis submitted by PSG&E for the Salem Nuclear Generat-ing Station were evaluated in Section 5.0 of this report. It was found that:

l. Voltages within the operating limits of the class lE equipment are supplied for all projected combinations of plant load and normal offsite power grid conditions; including an accident in one unit and the safe shutdown of the other unit with power to both units supplied from one offsite transformer giving credit for operation of the ALTC's.

2. The test used to verify the analysis shows the analysis to be an accurate repres~ntation of the worst case conditions analyzed.

3. PSE&G has determined that no potential for either a simultanous or consequential loss of both offsite power sources exists.

4. Loss of offsite power to class lE buses, due to spurious operation of voltage protection relays, will not occur with the offsite grid voltage within its expected limits

• 7

TO: R. R. Bast J. T. Boettger FROM:

SUS?fllllt!

INTRODUCTION A transmission network simulation analysis using the PSAP digital computer power flow program was performed to redetermine the minimum expected steady state grid voltage at the Salem and Hope Creek 500-kV buses taking into account the long duration outage of the Hope Creek-Keeney 500-kV line *

• RESULTS The results of the power flow analysis indicate that the minimum expected steady state grid voltage at the Salem and Hope Creek 500-kV buses during the long duration outage of the Hope Creek-Keeney 500-kV circuit is unchanged from the previously reported value of 1.01 per unit on a 500-kV base. This minimum expected. steady state grid voltage corresponds to a multiple overlapping outage of major generation and transmission facilities supplying the interconnected systems in southern New Jersey.

DISCUSSION The following are the significant characteristics of the base, or starting point, system model used in the analysis:

Hope Creek-Keeney 500-kV line out of service; No generation in service at Artificial Island; Oyster Creek Generating Station out of service; Peak load conditions; Imports into New Jersey totalling 6400 MW; Total PSE&G system load is 7650 MW; Total PSE&G internal generation is 4258 MW *

• The Energy People 95-200 I 1-:00M: 8*85

In order to depress the grid voltage at .Artificial Island to 1.01 per unit, it was necessary to subject the base system model to the additional stress of a triple overlapping outage involving critical transmission paths into southern New Jersey.

Specifically, the following three 230-kV circuits at or in the immediate vicinity of the transmission interface between southern New Jersey and Pennsylvania were outaged:

Chichester - Mickleton; Richmond - Waneeta; Croydon - Burling"t:on.

This triple overlapping outage results in a large portion of the southern New.Jersey demand requirements being supplied from the PJM 500-kV grid at Branchburg via the following 180 mile long 500-kV transmission path:

eastward from Branchburg to Deans, then southward from Deans to Salem, then northward from Salem/Hope Creek to New Freedom and, finally, down the New Freedom 500/230-kV autotransformers into the underlying system.

• d* b: JL~ cf*

C J. G. Gill

s. A. Mallard JDH:mkl