-1- By Chang C.K.

원자력발전소 우선전력계통 지락보호 개선방안 Improvement of the Ground Fault Protection for the Preferred Power

Supply Line of Nuclear Power Plants

장 중 구 KEPCO International Nuclear Graduate School Home Page : www.kings.ac.kr E-mail : ckchang@kings.ac.kr

2016.08

-2- By Chang C.K.

Fig.1 Aux. Power System Configuration

NC

TO 345KV SWYD

GCB

NC

X Y Y Y X X X Y

H H

SAT UAT

H

NC NC NC

NC

D/G D/G

AAC

D/G CLASS

1E(DIV.A) CLASS

1E(DIV.B)

NC NC NC

NC

TO 345KV SWYD

H

SAT UAT

NO NO

NO NO NO NO

NO NO NO NO

1. Conceptual Diagram of Korean Standard Nuclear Power Plant

APR 1400

Class 1E 4.16kV Bus :

2Buses/Division

N-1E 4.16kV Bus :

Permanent Non Safety 분리

AAC SWGR 와 접속

Class 1E D/G :

2 Units/Division

[참조] APR1400 DCD Tier-2

-3- By Chang C.K.

2. Typical Protection Scheme for Large Generator and Transformers

Fig.2 Relay Diagram for Main Generator GE G60 Relay SLD

-4- By Chang C.K.

3. Example of Main Generator Protection by Digital Relays

Fig.3 Digital Protective Relays for Main Generator (2 out of 2 Scheme)

* Not hard-wired logic(Flex Logic)

-5- By Chang C.K.

4. Ground Protection Scheme for Main Generator

1) Stator Ground Fault Protection (59N)

발전기 중성점 근처(5% 이내)에서 지락시 지락전류 매우 작아서 검출불가

Fig.4 stator Ground Fault Protection Relay (59N)

-6- By Chang C.K.

2) 3rd Harmonic Ground Protection (27TN)

발전기 정상운전시 발전기에서 제3고조파 발생

발전기 중성점 근처에서 지락발생시 지락지점에서

제3고조파 전압 “0”에 가까워짐

따라서 제3고조파가 사라지면 지락고장으로 간주할

수있음

Fig.5 Third Harmonic Fault Protection Relay (27TN)

-7- By Chang C.K.

3) 100% Stator Ground Fault Protection (59N and 27TN)

Fig.6 Third Harmonic and Undervoltage Protection Scheme (59N or 27TN+59)

-8- By Chang C.K.

Fig. 7 100% Stator Ground Fault (59N/27TN)

-9- By Chang C.K.

4) Subharmonic Injection Type(64S)

Fig.8 Sub-harmonic Fault Protection Relay (64S)

Subharmonic injection typically at 20Hz

Coupling filter low pass or notch tuned

for subharmonic frequency

Measurement inputs tuned to respond to

subharmonic frequency

GCB (Generator Circuit Breaker) Open시

IPB는 비 접지 상태가 됨과 아울러 지락보호 범위에서 제외됨

-10- By Chang C.K.

Fig.9 Stator Ground Faults : High Impedance Element Coverage

-11- By Chang C.K.

3. Design Vulnerability of Ground Protection System in NPPs

MT

Generator

SAT-A UAT-A

IPB

GIB

CV cable

765kV

SWYD 154kV

SWYD

UAT-B SAT-B

Div. A Div. B

PPS #1 PPS #2

G

M M

4.16kV 13.8kV 13.8kV 4.16kV

I I

Fig.10 APR 1400 Main Power System Ground Fault Protection Scheme

∆

∆ ∆

Y

Y Y Y Y

∆ Y

Y Y

Y

System Grounding

- MT 1ry : Solidly grounded

- MT 2dry : No grounded

- UAT Primary : No grounded

- UAT 2dry : Resistance Grounded

- Generator : Impedance Grounded

IPB Ground Fault Relay 59GB

27G, 59G & 59GS 발전기 지락보호

GCB

-12- By Chang C.K.

Fig.11 APR 1400 Main Power System Ground Fault Protection Scheme(II)

MT

UAT-A

IPB

UAT-B

G

∆

∆ ∆

Y

Y Y Y Y

Y

59 GB

Y

MT

UAT-A

IPB

UAT-B

G

∆

∆ ∆

Y

Y Y Y Y

Y

64S

Y

Now After Change

27G, 59G & 59GS

27G, 59G & 59GS

20Hz

Subharmonic

Injection Type

Ground Fault

Relay

Over Voltage

Relay

4. Recommended Ground Protection System for NPPs

-13- By Chang C.K.

5. Conclusions

59N : Stator Ground Overvoltage Relay (95%)

27TN : Third harmonic Ground Fault Protection (Supplementary for 59N)

59GB : Isolated Bus Ground Fault Protection

64S : Subharmonic Frequency Injection Type Ground Fault Relay(추가)

- Replace 59GB

- Improve the performance of ground fault detection when high impedance

ground fault is occurred.

- Install at the IPB instead of generator neutral. For the protection of the IPB

when the GCB is opened also.

[Note] The operating condition for the function is the ratio between the 20 Hz

auxiliary voltage and the current in the auxiliary current transformer, which is

interpreted to be the resistance value. In the event of an earth fault in the stator

winding, the resistance value decreases, and operates the function.