ML18092B481

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Rev 0 to S-C-E130-CDM-0494-1, Second Level Undervoltage Protection Sys Redesign.
ML18092B481
Person / Time
Site: Salem  PSEG icon.png
Issue date: 03/23/1987
From:
Public Service Enterprise Group
To:
Shared Package
ML18092B474 List:
References
S-C-E130-CDM-04, S-C-E130-CDM-4, NUDOCS 8704010148
Download: ML18092B481 (19)
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Text

PS~G Page 1 of 6

    • S-C-El30-CDM-0494-l Date 3/23/87
  • Public Service Electric and Gas Company Nuclear Department P.O. Box 236 Hancocks Bridge, New Jersey 08038 TITLE: - SECO_ND LEVEL UNDERVOLTAGE PROTECTION s*YSTEM REDESIGN 1.0 PURPOSE This Design Memorandum i~ being written to document the requirements and design for-the modification of the~installed

'relaying to provide undervoltage protection for the Class lE electrical equipment. This document will supersede CDS-4 (refer to Reference 3.7).

2.0 SCOPE This Design Memorand~m applie~ to Salem Units No. 1 and 2. It will be used to modify the Second Level* Undervol tage Protection System (SLUVPS). The SLUVPS prevents the Class lE electrical equipment from operating below their minimum voltage ratings.

3~0 RE~ERENCES IEEE 279-1~71 "Crit~ria for Protective Systems for Nuclear 3.1 Power Genera~irig Stations".

3.2 CDS-1 "Design C~iteria for Independence and Separation of Safety Related Instrumentation, Controls and Protection Syst~ms". -

3.3 U.S.N.R.C. *1etter date~ July 30, 1979 to G~neral Mariager -

Electric Production. -

3~4 U.S.N~R~C. letter dated Ju~e 2, 1977 to General Manager.~

Electric Production.

3.5 Letter dated February 4, 1980 from Manager - Salem Projects to Geperal Manager - Electric Production.

3.6 Letter dated October 10, 1979 from General Manager -

Electric Production to U.S.N.R.C.

3.7 PSE&G Functional Specification CDS-4 dated July 14, 1980.

3.8 10CFR50 Appendix "A" General Desi~n Criterion 5 and General Design Criteribn 17.

EDD-7 FORM 1 REV*O 10SEPT81

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8704010148 870324 \

PDR ADOCK 05000272 S PDR 95-2 ! 68 11 OOM, 12-81

s-c~El30-CDM-0494-l Page 2 of 6 3.9 Date: 3/23/87 Letter dated February 4, 1987, NLR-I87038 from General Manager - Licensing and Reliability to General manager -

Engineering and Plant Better~ent, "Licensing Basis for the Salem. Generatihg Station Electrical Distribution System"~

3.10 Salem Nuclear Plant Voltage Study, 'PTI Report No. Rll-87, dat~d February 1987.

3.11 10CFR21 Report, Rochester Instrument Systems to U.S.N.R.C.

dated October 11, 1985.

3.12 Regulatory Guid~ 1.105, Instrument Setpoints.

3.13 Rochester Instrument Systems, Product Data Bulletin Number 2035 AC Protective Relay.

3.14 Salem Generating Station, TechniGal Specifications Unit 1.

.3. 15 Salem Generating Station, Technical Specifications 'unit 2

  • 3.16 Letter dated January 19, 1981 from USNRC to PSE&G, Safety Evaluation Report - Salem Generating Stations Units 1 & 2 Degraded. Grid V~ltage Protection for the Safety Related A-C Power System.
  • 4.0 DISCUSSION On August 11, 1983 and again on August 26, 1986, the Second level of Undervoltage Protection System (SLUVPSJ caused the class lE 4160 volt buses to separate from the preferred offsite ~ower

~ource when the offsite power source was within expected limits.

A review of the existing relay scheme indicates that the cause of separation is due to the reset values of the SLUVPS relays. - The relays ,reset at a voltage of 95% arid under the worst case accid~nt and minimum grid condition the recovery was ricit expected to exceed 92%.

The existing SLUVPS relay design.was based on a voltage profile.

study (Reference 3.6) ~hich indicated the minimum re~overy voltage was 92% under the worst c~se conditions of a degraded grid, a LOCA on one unit with a simultaneous trip of the othei unit. The Lic~nsing Department has reviewed the NRC regulations relative to the electrical distribution system in Reference 3.9 and has determined that the el~ctrical distribution system must be capable of stipplying -the electrical loads to support a worst case accident on one unit and a controlled shutdown of the other unit.

A more recent voltage profile study, Reference 3.10, has been performed by Power Technologies Incor'pora ted in accordance with the above licensing requirements. Section 3.2 of this study

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dm/mpml EDD-7 FORM 1 REV 0 : 10SEPT81

.. S-C-El30-CDM-0494-l Page 3 of 6 Date: 3/23/87

  • .. bu~es during the lowest expected 500KV grid voltage, a LOCA.on one unit and a contr6lled shutdown of the opposite unit. The study was done with both" Unit No. 1 *and No. 2 Auxiliary Power Transformers in service. The llA, 12~, 13A, 21A, 228, and 23A circul~tors were.offloaded to the presently installed temporary power source from the Hope Creek Island Sub Station and the #11,
  1. 12, #21 and.#22 Station. Power Transformers' Automatic Load Tap Changers adjusted to control at a miniinum voltage of 4300 volts.

Additionally, the plant buses were aligned to provide the worst case transie~t and worst case recovery voltages. The study indicates that the worst case recovery is caused by t~e transfer of group buses to the already LOCA loaded station power transformers on No. 2 Unit. The voltage recovers to 92.9% after all of the motors are up to speed in about 6 seconds. The voltage will remain at this value for about 30 seconds at which time the Atitomatic Load Tap Changer will operate to increa~e the electrical distribution system voltage. At the Salem Stations the electrical motors are the limiting component under steady-state coriditions as they are designed to run con~inuously at 90% of nameplate voltage as identified in Reference 3.6.

  • However, the present Technical Specification setpoint and minimum allowable value do not provide adequate protection to prevent the motors from being operated at voltages iess than 90% name~lat~

ratings. The pres~nt >91% s~tpoint was found acceptable by the USNRC in Reference 3.lI. The Class lE motor~ were assumed to be.

rated at 4000.volts and the 91% setpoint of the 4160 volt bus would provide 94.5% protection for 4000 volt rated mcitors. The

>90% minimum allowable valu~ did not consider the voltage drop due to cabling from the switchgear to the *far,:thest motor nor did

  • .it consider the accuracy of the potential transformers used for monitoring the switchgear voltage. Therefore, th$ minimum all6wable value will be incie~sed by .7~ to account for the worst case motor cable voltage drop and . 3% to account for the. accuracy

. \.: of the potential transformer. The new minimum allowable value will be >91%. The new setpoint selected in accordance with Referenc~ ~.12 con~iders the tolerances of the potential trans~ormer, relay and calibration uncertanties as shown in Attachment I. The new setpont will be >91.6%.

Since the SLUVPS function is to protect the Clas~ lE equipment during degraded grid conditions, separation from the off~ite power source must occur when the bus voltage is equal to or le$S than 91% of rated bus voltage. Additionally, it is not acceptable to separate from the offsite source when the grid voltage is within expected limits. Therefore, the reset of the degraded grid relays must be less th~n the minimum expected recovery voltage of 92.9%. The Rochester Instrument Systems (RIS) *PR-2035 undervoliag~ relay will aga~n be used for the SLUVPS r~desigr. The *relay was identified in a 10CFR21 re~ort (Reference 3.11). The report indicated that the relays did not

-*~~~~~~~~~~~~~

dm/m~ml EDD~7 FORM 1 REV 0 lOSEPT~l

I .

S-C-El30-CDM-0494-l Page 4 of 6

    • Date: 3/23/87 maintain the manufacturer's reset repeatability specification when calibrated to the minimum deadband s~ecification of .51 of range. In addition* to this, RIS found that the relays did not meet the _repeatability specification when calibrated at the low end of its operating range of 85 to -88 vol ts. RIS has corrected the identified deficiencies by redesign and by chan~ing the minimum deadband specification. RIS has supplied *psE~G with certif i~a r~~ldceru~nt r~layb for th~ ~re~~ntly inst~lled relays.

The replacement relays have a minimum adjustable deadband of

~l.0% of range. The installed relays will be changed out with the ceriif ied replacement relays supplied by RIS.

In addition to the excessive reset value of the relays, a prbblem of transferring back and forth between Station Power Transformers occurred during the August* 26, 1986 event. Ifi the original SLUVPS design the time ~elay .settings and relay reset value~ were selected in an attempt to prevent the back and forth tr~nsferring between Station Power Transformers. The 91% transfer reLays and the 91% vit~l bus* relays were selected for time coordination and the res~t values of the relays were also selected at 95% to prevent the "f 1 ip-f lopping" phenomenon. (Refer to Reference 3. 5)

The original SL0VPS design required an attempted transfer from one station-power transformer to the other to provide adequate protection for the single failure criterion.-. Normal vital bus alignment is to have two vital buses on one station power transformer and the remaining vital bus on the other station power transformer. Referefice 3.5 provides a description of events which would be unacceptable if the station power transformer c~rrying the two vital buses had a degraded voltage condition with only a.single 90% bus protection relay installed.

Since the Safeguard~ Emergency Controller provides th~ 2 out of 3-logic and is operated by the bus protection relays, single failure of one of thes~ 90% protection relays could allow 2 of the 3 buses- to be operated at a degraded voltage value ana, there~ore, the attempted transfer of the vital bus was required.

The Salem Technical Specifications, Reference 3.14 and 3.15, Section 3/4.3~ Table 3.3-3 are presently written for the existing protection scheme as shown on Attachment "J". Therefore, to provide a timely redesign, the existing protection scheme described in the Techrtical Specification must be left intact to preclude a Technical Specification change. This_may be accomplished by not altering the present sustained undervoltage protection relay interface with the Safeguaids Emergency Controller and orily alterina the transfer scheme which was installed to prevent a ~ingie failure from p~oviding adequate protection. *

  • In order to positively preverit the possibility of "flip-flopping"

- the vital buses between Station Po~er Transformers, the existing 91% transfer sche~e outlined in CDS-4 (Reference 3.7) must be abandoned. Since the transfer scheme was installed to provide dm/mpml EDD-7 FORM 1 REV 0 10SEPT81

. i .

S-C-El30~CDM-0494-l Page 5 of 6 Pate: 3/23/87 protection for the single failure criterion, an alternate method to provide this protection is required. This will be accomplished by rewiring the PR-2035 undervoltage transfer r~lays to the vital bus potential transformers to provide (3) 91%

undervoltage relays per vital bus. The t~ree undervoltage relays

~ill be wired to the two existing bus potential transf6rmer secondaries *. For example (1) undervoltage relay will be wired from ~A to ~b, '1nuther relay will be wirea fro111 ~b to ./JC and the third relay will be wired from ~C to ~A. The u.v. protection relays will not be fused. The relay connection to the potential transformer secondaries through. the existing knife switches is required to allow calibration and testing of the system. In addition to the existing 90% vital bus protection relay Safeguards Emergency Controller interface, each of (3) vital bus undervoltage relays will send an undervoltage signal to its Safeguards Emergency Controller (SEC) via the existing tim~rs and an auxiliary reJay. (Refer to Attachments "A" through "G".) *The SEC will then make the decision based on 2 out of 3 logic to separate its bus from the offsite power source and load*it to its diesel generator along with the pre~ent 2 out of 3 bus undervol tage logic. ,

The control power for the relaying will be supplied by its vital bus respective 125 volt D.C. battery system. The existing overhead annunciator bus undervoltage alarm will be operated when any one of the vital bus SLUVPS relays operate. Relay contacts I

  • from the three Urtdervoltage Auxiliary relays will be wired in series and provide an input to the existing undervoltage overhead*

annunciator window.

The bus voltage is expected to dro~ below the r~lay setpoint during group bus bulk load shifts *. Therefore, the existing 13 second time delay to allow the volta~~ t6 recover is necessary prior to any automatic action by the SLUVPS. This time delay was justified and provided to the U.S.N.R.C. in neference 3.5.*

Since the r~lays are also expected to operate and time out when starting Reactor Coolant Pumps, the existing blocking feature provided by r~lay 62X to allow for the starting of these pumps' will remairi. A* control console lamp is illuminated providing the control room operator indication that the pr0tection has been sutcessfully bypassed ahd that it is safe to start a Reactor Cool~nt Pump without operating the SLUVPS. The existing design uses contacts from the time delay relay to provide the lamp indication. In the new design cont~cts from the auxiliary undervoltage relays will be used. In addition an audible alarm will be installed to notify the operator that the protection has b~en defeated. This is required to alert the operator since possible malfunctions in the bypass circuitry could defeat the SLUVPS *

  • dm/mpml EDD-7 FORM 1 REV 0 10SEPT81

I -

S-C-El30-CDM-0494-l Page 6 of 6 Date: 3/23/8 7 The. redesign of the SLUVPS relaying must meet or exceed the*

  • design criteria identified in Reference 3.7. The criteria which were included were conformance to IEEE-279 and the single failu~e criterion, conformance to seismic I requirements, and provisions fot testing the system. The redesigned system was analyzed in accordance with the single failure criterion, and the results are tabulated in Attachment H. The redesighed system as outlined above wiil not alt~r the testab{lity of the system, although th~

procedure for t~sting the ~ystem mtisi be revised. * *

5. 0. Action The Engineering and Plant Betterment Design Division, Instruments and Controls and Electrical will provide the Operational Design Change Notices _(ODCN'S). The Engineering and Plant Betterment, Plant Engineering, Instruments and Con_trols and Electrical group will organize and be responsible for the design change package issue.

6.0 schedule The desigh change is an emergency. The OCR numbers ~re 1EC2271 and 2EC2271. The design group should complete their portion of the design change package by 2/25/87. The design change package must be ~eady for issue by 2/27/87.

  • 7.0 8.0 Funding Authoriz~tion The design change will be funded by o account .~umbers are E530.020, T00622.

S igna tu res*

& M.

  • _The authorization and 3/i.~/2> 7 Date
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1 _______________________________________E_D_o__

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VITAL BUS PROTECTION RELAY LOGIC A BUS , ~B~ ~B~

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~3 ~3 ~3 A DIESEL 1 1 8 DJESEL 1 1 1 1 C DJESEL LOADING LOADING LOADING VB? ~*

1 A VITAL BUS UNDERVOLTAGE SENSING CIRCUIT 1

A 4160V.

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1 A Vil AL BUS SECOND LEVEL UNDERVOL TAGE PROTECTION 1

27-IA 70Z BLACKOUT RELAY 62X-PROTECTION DEFEAT RELAY 27-IA/l, 27-lA/2. 27-lA/3-UNDERVOLTAGE

+ RELAY, ROCHESTER PR-2035, DROPOUT 91.SZ PICKUP 92.6Z 2-1, 2-2, 2 TIME DELAY PICK-UP 62X @ TD-5, SETPOINT 13 SECONDS HFA-EXJSTING

,. U.V.AUX.RELAY (J) 27-lA 27-lA/1 27-lA/2 27-lA/3 UJ

....... 2-1 2-2 2-3 0:

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27X-IA3 "C" SEC 27X-IA/I 27X-IA/2 "A" SEC 27X-IA/3 "A" SEC * "A" SEC 27X-IA/l 27X-IA/2 27X-IA/3 4t +t 4t OVERHEAD I

27X-1A/l 27X-1A/2 27X-1A/3 REACTOR COOLANT PUMP START ANNUNCIATOR PERMISSIVE

1 8 VITAL BUS UNDERVOLTAGE SENSING CIRCUIT 1

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

27-18 70/. BLACKOUT RELAY 62X-PROTECT10N DEFEAT RELAY 27-18/l. 27-lB/2. 27-18/3-UNDERVOL TAGE

+ RELAY, ROCHESTER PR-2035, DROPOUT 91.6/.

PICKUP 92.6Y.

2-1. 2-2, 2 TlME 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 UJ

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~t +t +t OVERHEAD REACTOR COOLANT 1

A1 SEC 1 C1 SEC - 1 81 SEC c 1

81 SEC 1 81 SEC PUMP START ANNUNCIATOR PERMISSIVE Ii i

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1 C VITAL BUS UNDERVOLTAGE SENSING CIRCUIT 1

4160V.

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  • c*~TAL BUS SECOND LEVEL UNDERVOLTAGE PROTECT~N 27~1C 70/. BLACKOUT RELAY 62X-PROTECTION DEFEAT RELAY 27-IC/l. 27.-lC/2. 27-IC/3-UNOERVOLTAGE

+ RELAY, ROCHESTER PR-2035, DROPOUT <U.61.

PICKUP q2.6/. .

  • 2-1, 2-2, 2 TIME DELAY PICK-UP 62X TD-5, SETPOINT 13 SECONDS HFA-EXISTING U.V.AUX.RELAY (I) 27-lC 27-lC/1 27-lC/2 27-lC/3 L1J

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25W 25W 27X-ICI f f f27X-IC2 27X-IC3 27X-IC/1 f f f 27X-IC/2 27X-1C/3 27X-IC/l 27X-1C/2 27X-1C/3 4t 4t 4t 27X-1C/l 27X-1C/2 27X-1C/::;

REACTOR COOLANT "A" SEC 1 81 SEC "C" SEC *c* SEC 1 C1 SEC "C" SEC' OVERHEAD .PUMP START ANNUNCIATOR PERMISSIVE *

  • VB3

Attachment "H" FAILURE MODE ANALYSIS .

Normal Operation

    • Relay Failure Undervoltage 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 w il,l

  • be made to load bus to diesel generator.

AcceEtable AcceEtable Timing Relay Same as above Same as above Failure

~ndervoltage Same as above Saine as above Auxiliary Relay Failure HFA Relay Sarne as above Same as .above Failure Loss of Bus with failed Bus with failed battery 125 Volt battery system would system would maintain Battery maintain connection 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 present design. design. Previousl:t:

Previousl:t: Arial:t:zed Analyzed

  • Loss of 125 Volt DC Branch CKT Loss of Cable f rorn Bus to Sarne as above Bus with failed cable woul<;l maintain connected

.Sarne as a);)ove Bus with failed cable 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. The ref ore shutdown. Therefore ereviousl:l anal:t:zed. 12reviously analyzed.

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 buses would be *available buses would be available for safe shutdown. for safe shutdown.

Therefore 12reviously Therefore 12reviously analyzed. anai:t:zed.

Po.tential Same as undervoltage Sarne as undervoltage Transformer relay ..failure relay failure Potential Same as undervoltage Same as undervoltage Transformer r*elay failure relay failure Primary Fuse drn/rnprnl

Attachment "I" SETPOINT CALCULATIONS Potential Transformer Accuracy +.3%

Relay Repeatability =*1% of range_ , +.13%

Relay Temperature influence +.5% - 20°C to 60°C +.63%

Calibration uncertainty =-5% of setpoint +.45%

Relay deadband <1% of range - use .8% of range 1%

Setpoint >90.7+ .J(.3)2 + (.13 + .63)2 + (.45)2 Setpoint > 90.7 + .* 9

12. 91.6% .,
    • Relay Reset = 91. 6% + 1% = .B NOTES:. 1. Tolerances used in square root of the sum of the squares are*

on the 4160 volt base across the 35:1 potential transformer.

2. A setpoint of 91% was assumed to calculate the tolerance for calibration uncertainties.
3. The entire temperature influence accuracy was used for*

conservatism. The relay will not see this type of temperature range when installed.

4. The range of the relay is 85 volts to 150 volts.

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

7. Undervoltage Vital Bus I' Existing
a. Loss of Voltage 3 2 3 1,2,3 14*
b. Sustained Degraded Voltage. 3 2 3 1,2,3 14*

mpml/8

SALEM GENERATING STATION ELECTRiCAL DISTRIBUTION SYSTEM IMPROVEMENT STUDY Goal: Assure a Safe and Reliable Electrical Distribution System at Salem Generating Station Objectives:

1) Develop a comprehensive Design Basis including:

a) Design Documents b) Calculaticins c) Procedures d) NRG Licensing Issues

2) Analyze System Deficiencies/Weaknesses
3) Develop Feasibility Studies for System Improvement Options

DESIGN ITEMS A. Data Collection B. Short Circuit

c. Coordination D. Relay & Transfer Scheme E. Sizing (Equipment)

F. Voltage Profile G. Motor Starting H. Cable & Raceway Criteria I. Coordinate with New REG's J. Maintainability K. Reliability/Availability L. Summary & Recommendations

SYSTEMS

1. 25 kV (GEN)
2. 13.8/4.16 kV
3. 480/230/208 v
4. 115 VAC (Vital )
5. 125 VDC (Vital)
6. 28 VDC (Vital)
7. 250 VDC
8. Penetrations
9. Diesel Generator
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