COOPER Power Systems

Advanced Protective Relaying Based on Rogowski Coil Current Sensors

Ljubomir A. Kojovic Martin T. BishopCooper Power System

Thomas A. Edison Technical CenterFranskville, Wisconsin, USA

COOPER Power Systems

IP’

90

Iron-Core Current Transformer Rogowski Coil

IPIS

IE

M

RB

IP

VB

I’P

IS

IE 0

RBVB

IS

Low ImpedanceBurden

High ImpedanceBurden

VB

Lm

Ip Air Core

RB

Ip

RB

Iron Core

COOPER Power Systems

Vo

lta

ge

Current

Operating point

Non-Gapped Iron-Core Current Transformer

Rogowski Coil

Linear Coupler

Increasing Air-Gap

No Air-Gap

Air

-Gap

1

Air-Gap 2

V-I Characteristics

COOPER Power Systems

Design Criteria

1. Relative Position of the Primary Conductor inside the Coil Loop

2. The Impact of Nearby Conductors (external electromagnetic fields)

COOPER Power Systems

Printed Circuit Board Rogowski Coil

Winding imprints

dt

di(t)M

dt

di(t)nStv )( 0

Relative Position of the Primary Conductor inside the Coil Loop

S

n

i(t)

m

RB

Air Core(non-saturable)

v(t)

COOPER Power Systems

v(t)

PCB1 PCB2

PCB2 wound

in opposite direction

to PCB1

i(t)

External Electromagnetic Fields Curre

nt

Voltage

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Interior Applications Exterior Applications

Parallel Conductors

Split-Core Type Rogowski Coil

Designs

COOPER Power Systems

Heavy Gauge Wires

Multi-Function Relay

PrimaryCurrent

2000/5 A, C800Current Transformer

10 c

m Terminal Blocks

Weight: 90 kg64 cm

30 cm

Printed Circuit Board Rogowski Coil

Multi-Function Relay

PrimaryCurrent

Width 2 cmWeight: 2 kg

30 cm

Shielded Cable and Connectors

Comparison to CTs

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SN1 SN2 SN3

RogowskiCoil

Fuse

CircuitBreaker

NetworkProtector

Spot Networks

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R

Bus

Network 2

Network 1

G

Load

Zone 1

Zone 2

Zone 3

Zone 4

Zone 5

Integrated Relay Protection Solutions

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R

Network 2

Network 1

G

Load

RC3

Zone 1RC1 RC2

Relay1

Relay2

Integrated Relay Protection Solutions

COOPER Power Systems

R

Network 2

Network 1

G

Load

RC1 RC2

Zone 2

Relay1 Relay2

Fiber OpticCable

EthernetSwitch

other IEDs

Integrated Relay Protection Solutions

COOPER Power Systems

Busbar Protection

SummingBlock

Relay

Rogowski Coils

Protected Busbar

Relay

Rogowski Coils

Protected Busbar

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Traveling Wave Based Protection

COOPER Power Systems

Traveling Wave Based Protection

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Field Experience with Differential Protection of Power Transformers Based on Rogowski Coil Current Sensors

Ljubomir A. Kojovic Martin T. BishopCooper Power System

Thomas A. Edison Technical CenterFranskville, Wisconsin, USA

COOPER Power Systems

PowerTransformer

Fault

RMSDifference

False differential current causes nuisance protection operation

RMS RMS

CT CT

Differential Protection of Power Transformers

COOPER Power Systems

Blocking Zone

Dif

fere

nti

al

Cu

rre

nt

Restraint Current

Operating Zone withCurrent Transformers

Expanded Operating Zone withRogowski Coils

Differential Protection of Power Transformers

COOPER Power Systems

Non Split-CoreRogowski Coil

Split-CoreRogowski Coil

Multifunction Relay

EAF

Water Cooled Leads50 kA – 100 kA

Tapposition

EAFTransformer

Differential Protection of EAF Transformers

COOPER Power Systems

AB

C34.5 kV

1000 V

“Water-Cooled” Conductors

EAF Transformer

EAF

Multi-functionRelayPrimary RCs

Secondary RCs

Tap Position

Shielded Cableswith Connectors

Differential Protection of EAF Transformers

COOPER Power Systems

EAF25 MVA

32 kV/395 V25 MVA

138 kV/32 kV25 MVA

FilterC

L

Current Measurement200/5 A

Rogowski Coils

Rogowski Coils

Multi-FunctionRelay

TapEAF

Transformer

Differential Protection of EAF Transformers

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0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

Time [minutes]

Cu

rren

t [k

A]

EAF C-Phase CurrentsRMS Values averaged per one second

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

80

90

100

Time [minutes]

Cu

rren

t [k

A]

EAF C-Phase CurrentsMin and Max Values averaged per one second

Max

Min

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0.12 0.14 0.16 0.18

-4000

-2000

0

2000

4000

Time [s]

Cu

rren

t [A

]

0 0.02 0.04 0.06 0.08

-4000

-2000

0

2000

4000

Time [s]

Cu

rren

t [A

]

COOPER Power Systems

0 0.02 0.04 0.06 0.08

A-Phase

-4000

-2000

0

2000

4000

Time [s]

Cu

rren

t [A

]

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Circuit Breaker OperatesCircuit Breaker Operates

Relay OperatesRelay Operates

Relay OperatesFault Inception

Circuit Breaker OperatesPrimary Currents

Circuit Breaker OperatesSecondary Currents

Circuit Breaker OperatesOperate Signals

Circuit Breaker OperatesRestraints Signals

Circuit Breaker OperatesTrip Signals

COOPER Power Systems