2013/08/15 STP COL - FW: STP 3 & 4 Draft of Bulletin 2012 ... · STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 5 NRC Bulletin 2012-01 : Offsite power supply circuits

1

PMSTPCOL PEmails

From: Misenhimer, DavidSent: Thursday, August 15, 2013 5:13 PMTo: STPCOLSubject: FW: STP 3 & 4 Draft of Bulletin 2012-01 Presentation Scheduled for August 21, 2013Attachments: STP Bulletin 2012-01 Presentation 8-21-13 DRAFT C .pdf

From: Richard Bense [mailto:[email protected]] Sent: Wednesday, August 14, 2013 10:15 AM To: Misenhimer, David Subject: STP 3 & 4 Draft of Bulletin 2012-01 Presentation Scheduled for August 21, 2013 Dave, Attached is a draft of the presentation that STP 3 & 4 will make on August 21, 2013. This draft is for discussion during the Open Items call scheduled for August 14. Thanks

Dick Bense NINA Licensing Engineer [email protected] [email protected] 215-362-2552 (home office) 215-353-8857 (cell)

Hearing Identifier: SouthTexas34Public_EX Email Number: 3672 Mail Envelope Properties (9C2386A0C0BC584684916F7A0482B6CADEFA84CE12) Subject: FW: STP 3 & 4 Draft of Bulletin 2012-01 Presentation Scheduled for August 21, 2013 Sent Date: 8/15/2013 5:13:00 PM Received Date: 8/15/2013 5:13:07 PM From: Misenhimer, David Created By: [email protected] Recipients: "STPCOL" <[email protected]> Tracking Status: None Post Office: HQCLSTR02.nrc.gov Files Size Date & Time MESSAGE 667 8/15/2013 5:13:07 PM STP Bulletin 2012-01 Presentation 8-21-13 DRAFT C .pdf 1370253 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date: Recipients Received:

STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 1

South Texas Project Units 3 & 4Presentation on Single Phase EventNRC Bulletin 2012-01

AFTT

se Evese E


Attendees � Scott Head, Regulatory Affairs Manager, STP 3&4

� Bill Mookhoek, Licensing Supervisor, STP 3&4

� Steve Thomas, Engineering Manager, STP 3&4

� Evans Heacock, Electrical Engineering, STP 3&4

� Al Gutterman, Morgan, Lewis & Bockius LLP

� Richard Bense, Licensing, STP 3&4

DRAFT

anager, STanager

pervisor, STP 3&pervisor, STP 3

ng Manager, STManag

trical Engineerincal Engineer

rgan, Lewis & Brgan, Lewis & B

e, Licensing, STLicensing, ST


� Provide an overview of the STP 3 & 4 Electrical Distribution System

� Describe STP 3 & 4 response to NRC Bulletin 2012-01

� Describe STP Unit 2 Loss of Single Phase 2001 Event (LER 01-002, ML011200051)

� Discuss Forsmark 2013 Event

� Describe ETAP, Rev 12, Study for STP 3 & 4

� Summary and Questions

Agenda

DRAFT

& 4 & 4

nse to NRC Bullese to NRC Bull

oss of Single Phoss of Sing

2013 Event 2013 Even

P, Rev 12, StudP, Rev 12, Stu

and Questionsand Questi


� Demonstrate how a single-phase open circuit or high impedance ground fault on an off-site power circuit has no impact on STP 3 & 4 safety related functions.

� Describe how STP 3 & 4 ESF buses are protected from a single-phase open circuit or high impedance ground fault on an off-site power circuit.

� Describe how the STP 3 & 4 design will ensure that a single-phase open circuit or high impedance ground fault is detected in a timely manner.

Desired Outcomes:

DRAFT

circuit or higcircuit uit huit has no no impactim

buses are protecteses are mpedance ground mpedance gro

P P 3 & 3 & 4 design widesigh impedance grouh impedance gro


NRC Bulletin 2012-01 :

� Offsite power supply circuits were rendered inoperable by single-phase open circuit that was undetected by surveillances.

� Design of electric power system did not take into account possibility of loss of a single phase between the transmission network and the onsite power distribution system.

STP 3 & 4 is not susceptible to the issues described in Bulletin 2012-01

NRC Bulletin 2012-01: Design Vulnerability in Electric Power System

DRAFTre rendered rendered inoper

ndetected by ndetected by surve

system did not takm did not tase between the trase between th

ution systemution sys .

T

susceptible to the isusceptible

wer we


1. Describe how protection scheme for ESF buses (Class 1E) is designed to detect and automatically respond to a single-phase open circuit condition or high impedance ground fault condition on credited off-site power circuits.

2. Describe the operating configuration of the ESF buses (Class 1E) at power (normal operating condition).

NRC Bulletin 2012-01 requested information:

NRC Bulletin 2012-01: Design Vulnerability in Electric Power System

DRAFT

on n scheme for Escheme forned to detect aned to detect an

lele--phase open cphase opund fault conditiund fault cond

s.

FT

the operating cthe operating E) at power (nE) at power

ed informationd information

er Syster S


DG DG DG

CTG

UAT A UAT B UAT C RAT A RAT B

PG

PIP

Class 1EDIV. I DIV. II DIV. III

Main Gen

Main Transformer3 Single Phase

Breaker

Normal Alignment

Other Unit

345kV26kV13.8kV4.16kV

CTG 1 CTG 2

CTG 3

DRAFT

DRDRDRDRDD

FFFFFFFFTFTTTFTFTTTFTFTFTFTFT

AFAFAFAFFFA

D

AFAF

DRDDRARAFT

DRDRA

DRARA

DRDRD

TT

AFAFAFAF

T CT CATT RAT ARATRATRAT

AFAFFFAA

DRDRDDDRDRRARARARAR

FT

DDDDDD

FTFTFTFTFTFTFTFTFT

RA

Tal Alignmal Al

CT


� Four 13.8 kV Power Generation (PG) buses� Three, 4.16 kV non-Class 1E Plant

Investment Protection (PIP) buses� Three, 4.16 kV Class 1E Divisional buses � Designed with a Main Generator Breaker

which opens on trip of the generator or reactor�Allows for immediate backfeed of power without

need for either fast or slow bus transfer.

STP 3 & 4 Electrical Distribution System

DRAFT

neration (Pnerationlass 1E Planlass 1E Pla

on (PIP) bus (PIPClass 1E Divass 1E Di

h a Main Geh a Main ns on trip of ts on trip of

s for immedias for immedior either for either


STP 3 & 4 Electrical Distribution System cont’d

� Main and Unit Auxiliary Transformers normally feed two divisions of Class 1E ESF buses. �Also normally feed the PG buses and PIP

buses�Main Transformer connected wye high side

and delta low side�3 Unit Auxiliary Transformers connected

delta/wye

DRAFT

ransformransfoions of Clasions of Cla

the PG busesthe PG b

rmer connectermer connow sideow side

Auxiliary TransAuxiliary Transwye wye



� Two Reserve Auxiliary Transformers�Three winding, 345 kv/13.8 kV-4.16 kV�Both RATs are connected wye/wye with

resistance grounding on secondary�One RAT normally feeds the remaining

Class 1E bus�Class 1E bus is normally loaded

DRAFT

TransformeTransfokv/13.8 kVv/13.8 k -4.11

onnected wye/nnected wunding on secing on sec

normally feedsnormally feeE busus

s 1E bus is nos 1E bus is n


STP 3&4 345kV Switchyard

Unit 4Main

Transformer

Unit 4RAT A

Unit 4RAT B

Unit 3Main

TransformerUnit 3RAT A

Unit 3RAT B

345kVLine

345kVLine

345kVLine

345kVLine

345kVLine

345kVLine

DRAFT

DRAAFTT

AARARAFTFT

AFAFAA

TT

DR

T

AAFT

DD

A

DRD

Unit 4URAT AR

Unit 4nit 4RATRAT

STP 3&4 Presentation on NRC Bulletin 2012-01 12


� STP design does not use fast or slow bus transfers on loss of offsite power.

� On loss of Main/Unit Auxiliary or Reserve Auxiliary transformers, Class 1E buses transfer to the Emergency Diesel Generators

DRAFT

st or slow bst or sloe power.e pow

Auxiliary or Reliary ers, Class 1E s, Class 1E

Diesel GeneraDiesel Genera


� Undervoltage and Degraded detection � Uses 3 independent undervoltage relays� Primary side of PTs are connected phase-to-phase in

a delta configuration� Loss of single phase will cause two of the three

relays to trip� Actuation of undervoltage and degraded voltage

isolates the ESF bus and starts the EDG.

Reference section FSAR section 8.3.1.1.7


detectiondetecoltage relaysoltage relays

connected phasonnected phas

se will cause twowill cause tw

undervoltage anundervoltage ESF bus and sESF bus and s

Reference sectioReference se



� Main Transformer backfeed� The wye/delta connection recreates the lost phase in

the delta connected secondary� The transformer MVA rating is about 15 times greater

than the load needed � STP Unit 2 experienced a single phase event on high

side of Main Transformers in 2001� Generator tripped, safety loads operated without issue

DRAFTrecreates the lorecreates the l

ondaryndaryA rating is aboutA rating is a

ed erienced a singlerienced a singl

Transformers in Transformersor tripped, safety lopped, safety lo



� Reserve Auxiliary Transformer� Three winding, shell wye/wye low impedance

grounded on secondary windings� Is affected by a single-phase open circuit � Degraded voltage scheme will detect the condition

DRAFT

mermerwye low impedanwye low impeda

windingswindingsee--phase open cphase ope

scheme will deeme will de



Wye-G/Wye-G, 5 Legged Shell Form Xfmr, opened phase, some Ph-N loading

B phase lost (middle phase) (voltages in per unit)

VAN 1.00 �0 VAB 1.00 �30 DVR Does not trip

VBN ~0 VBC 0.578 �-120 DVR Tripped

VCN 1.00 �120 VCA 0.578 �180 DVR TrippedC phase lost (outside phase)

VAN 1.00 �0 VAB 1.00 �30 DVR Does not trip

VBN 1.00 �-120 VBC 0.578 �-120 DVR Tripped

VCN ~0 VCA 0.578 �180 DVR Tripped

Reserve Auxiliary Transformer expected secondary voltages

Reference - “A Practical Guide for Detecting Single-Phasing on a Three-Phase Power System” by John Horak and Gerald F. Johnson (Basler)

DDDDDDDRRDRDDRRDRDRARARARARARARAF

RAFT

AFT

AFFFFT

AFFTFT

AF

RARA

DRDRD

FT

D

opened phase, s

n per unit)

.00

578 120

CA 0.578 �

hase

VAB 20 BC 0

T

oo

CA

cted seconcted se


� STP 1 & 2 switchyard and distribution are similar to STP 3 & 4

� STP Unit 2 experienced single phase event on high side of Wye/Delta connected Main Transformers in 2001:

(LER 01-002, ML011200051).

� Switchyard breakers Y600 and Y610 were opened to remove the "Skyline" feed disconnect link.

� After disconnect link removed, breakers Y600 and Y610 were closed. However, C phase pole of breaker Y600 remained opened (indicated fully closed).

� When breaker Y590 was opened, STP Unit 2 experienced loss of single phase.

� Control Room received electrical panel alarms, three operating Circ. Water Pumps tripped and a reactor trip was manually initiated.

� All actuated safety equipment operated as required. � This event demonstrated that voltages are recreated on loss of a single phase

on main transformer.

STP Unit 2 – Loss of Single Phase Event

DRAFT

are similarare si

se event on highse event on hsformers sformers in 20012001

Y610 were opened were o

oved, breakers Y600breakers Y600e of breaker Y600 ree of breaker Y6

5900 was opened, STwas opened, ST

oom received electricoom received electrpped and a reactopped and a reacto

safety equipsafety equiprated rated

PhPh


STP Unit 2 – Loss of Single Phase EventSTP 1 & 2 Switchyard

FT

PhPhyardyard


� In 2013, plant was in an outage utilizing a feed from the 400 kV offsite power source

� The feed was tripped accidentally and two phases opened and the third phase stayed closed

� Onsite emergency diesel generators did not start automatically since induced voltage on the open phases was higher than the undervoltage relay settings

� Loss of two phases at STP would actuate loss of voltage trip to initiate EDG start.

Forsmark – Loss of Two Phases

DRAFT

age utilizinage utower sourceower source

accidentally accidentad the third phathe third p

gency gency diesel gdieselally y since indusince indu

was higher thwas higher

o phao pha

ss


Forsmark – Loss of Two Phases cont’d

Wye-G/Wye-G, 5 Legged Shell Form Xfmr, opened phase, some Ph-N loading

Loss of A and C Phases (Voltages in per unit)

VAN ~0 VAB 0.578 �60 DVR Tripped

VBN 1.00 �0 VBC 0.578 �-120 DVR Tripped

VCN ~0 VCA 0 DVR TrippedLoss of B and C Phases

VAN 1.00 �0 VAB 0.578 �0 DVR Tripped

VBN ~0 VBC 0 DVR Tripped

VCN ~0 VCA 0.578 �180 DVR Tripped

STP Reserve Auxiliary Transformer expected secondary voltages after loss of two phases:


DD

FT

AFT

AAFF

RARARARA

DRA

DRDRRDRDRDDRDRRAR

FAFT

AFARARA

DRDRD

FTFTFT

D

mr, opened phase,

r unit)

0.578 �6

.578 �-120

VCA

VAB

T

ss

BC

VCA

xpected xpec



Wye-G/Delta, Transformer, B and C phases opened

Primary Voltages

VAN 1.00 �0 VAB 0.867 �0

VBN ~0.5 �180 VBC ~0

VCN ~0.5 �180 VCA 0.867 �180

Secondary Voltages

VAN 0.866 �0 VAB 0.500 �0 DVR Tripped

VBN 0 VBC 0.500 �0 DVR Tripped

VCN 0.866 �180 VCA 1.00 �180 DVR Does not trip

STP Main Transformer expected secondary voltages after loss of two phases:


DD

AFT

AFT

RARAFF

RARARRARA

DRA

DRDRRDRDRDDRDRRAR

FAFT

AF

RARARA

DRDRD

FT

aseas

FT

D

ses opene

0.867 �0

C

VCA 7 �

VA

BC

VC

ondary onda vo



� The loss of two phases on an offsite circuit at STP 3 & 4 will be detectable by the bus degraded voltage relaying for both the Main and Reserve Auxiliary Transformers

DRAFT

aseas

n an offsite cirn an offsite cctable by the able by

elaying for botaying for by Transformery Transformer


STP 3 & 4 ETAP Rev 12 Studies

� ETAP Studies on loss of phase on the Reserve Auxiliary Transformer and Main Transformer

� Model is the same as single line shown earlier� Studies included

� 5 legged Shell form, wye/wye-wye transformer for the RAT with low resistance ground on secondary neutral connection

� 3 x 1 Shell form, wye/delta transformer for the Main Transformer

DRAFT

ase on the se on Main TransfoMain Tran

single line shongle lin

orm, wye/wyeorm, wye/wye-wwresistance grouresistance g

hell form, wye/dhell form, wyeformerform


STP 3 & 4 ETAP Rev 12 Studies cont’d

ETAP Study results for Reserve Auxiliary Transformer expected secondary voltages

Wye-G/Wye-low impedance, 5 Legged Shell Form Xfmr, A phase lostHigh Side Low Side

Light loading (Voltages in per unit)

VAN 1.00 �0 VAB 0.869 �6 DVR TrippedVBN ~0 VBC 0.599 �-91 DVR Tripped

VCN 1.00 �120 VCA 0.995 �150 DVR Does not tripDesign Loading

VAN 1.00 �0 VAB 0. 875 �1 DVR Tripped

VBN ~0 VBC 0. 555 �-101 DVR Tripped

VCN 1.00 �120 VCA 0. 936 �145 DVR Does not tripDDDDDDDDRRDRDRDRAFT

AFTFT

AF

RARARARA

DDRARA

DRAFT

AFT

AFARARAFT

liary Tranliary T

DRDRDD

FThell Form A p

)

0.869 �6VBC 0 �-VCA 0 995

AB

VBC



ETAP Study results for Main Transformer expected secondary voltages

Wye-G/Delta, 3 x 1 Shell Form Transformer, A phase lostHigh Side Low Side

Light loading (Voltages in per unit)

VAN 1.00 �0 VAB 1.01 �-30 DVR Does not tripVBN ~0 VBC 1.00 �-150 DVR Does not trip

VCN 1.00 �120 VCA .999 �90 DVR Does not tripDesign Loading

VAN 1.00 �0 VAB 0.998 �-33 DVR Does not tripVBN ~0 VBC 0.994 �-154 DVR Does not trip

VCN 1.00 �120 VCA 0.978 �86 DVR Does not tripDDD

AFT

AFF

RAF

RARARARA

DDRARA

DRDDDDDDRAFAFT

AF

RARARA

DRDD

FTFT

ormer expeormer e

D

FTmer, A pha

B 1 �-3VBC 1.00 �-1VCA

AB

VB



� Reserve Auxiliary Transformer� Studies show that an undervoltage will occur on either a

lightly loaded or a heavily loaded bus for 5 legged shell transformer

� Transformer construction/configuration matters� Voltage will be low enough to be detected by the bus

degraded voltage relays (DVR)� Two out of three DVR logic will actuate

� Main Transformer� On loss of single phase on high side of transformer,

secondary voltages is recreated on secondary� Transformers have capacity to produce adequate voltages

with the design loadDRAFT

tage will occur otage will occoaded bus for 5 leoaded bus for 5 l

tion/configurationon/configuraw enough to be deugh to be de

ge relays (DVR)ge relays (DVhree DVR logic wree DVR logic w

formerformerss of single phasss of single phas

ary voltagesary voltageers haers ha


Questions and Comments

DRAFT

mmentsmments

Documents

2013/08/15 STP COL - FW: STP 3 & 4 Draft of Bulletin 2012 ... · STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 5 NRC Bulletin 2012-01 : Offsite power supply circuits