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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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 2
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 3
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 4
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 5
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 6
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 7
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 8
� 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 Presentation on NRC Bulletin 2012-01 August 21, 2013 9
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 10
STP 3 & 4 Electrical Distribution System cont’d
� 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 Presentation on NRC Bulletin 2012-01 August 21, 2013 11
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 3 & 4 Electrical Distribution System cont’d
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 13
� 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
STP 3 & 4 Electrical Distribution System cont’d
detectiondetecoltage relaysoltage relays
connected phasonnected phas
se will cause twowill cause tw
undervoltage anundervoltage ESF bus and sESF bus and s
Reference sectioReference se
STP 3&4 Presentation on NRC Bulletin 2012-01 14
STP 3 & 4 Electrical Distribution System cont’d
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 15
STP 3 & 4 Electrical Distribution System cont’d
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 16
STP 3 & 4 Electrical Distribution System cont’d
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 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 17
� 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 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 18
STP Unit 2 – Loss of Single Phase EventSTP 1 & 2 Switchyard
FT
PhPhyardyard
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 19
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 20
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:
Reference - “A Practical Guide for Detecting Single-Phasing on a Three-Phase Power System” by John Horak and Gerald F. Johnson (Basler)
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 21
Forsmark – Loss of Two Phases cont’d
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:
Reference - “A Practical Guide for Detecting Single-Phasing on a Three-Phase Power System” by John Horak and Gerald F. Johnson (Basler)
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 22
Forsmark – Loss of Two Phases cont’d
� 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 Presentation on NRC Bulletin 2012-01 August 21, 2013 23
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 Presentation on NRC Bulletin 2012-01 August 21, 2013 24
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 25
STP 3 & 4 ETAP Rev 12 Studies cont’d
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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 26
STP 3 & 4 ETAP Rev 12 Studies cont’d
� 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
STP 3&4 Presentation on NRC Bulletin 2012-01 August 21, 2013 27
Questions and Comments
DRAFT
mmentsmments