G. Ziegler. Digital Differential Protection

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G. Ziegler, 10/2005 page 9

Differential Protection Symposium

Belo HorizonteNovember 2005

∆I

∆I

L1

L2

L3

∆I

Y d 5

Transformer differential protection

Matching

transformer

G. Ziegler, 10/2005 page 10

Differential Protection Symposium

Belo HorizonteNovember 2005

Φ

w

1

w

2

u

1

u

2

i

1

i

2

i

1

i

2

i

1

i

2

u

1

u

2

P

1

P

2

S

1

S

2

i

1

i

2

Equivalent electrical circuit

Function principle

Designation of CT terminals

according to IEC 60044-1

Polarity marks

2211

wiwi

⋅

=

⋅

2

2

1

1

w

u

w

u

=

2

1

u

1

u

2

Current transformer:

Principle, transformation ratio, polarity

G. Ziegler, 10/2005 page 11

Differential Protection Symposium

Belo HorizonteNovember 2005

∆I

G

M

Grid

infeed

0

3

4

2 0

Load

Analogprotection 7SS10/11/13

7SS600 with digital measuring relay (∆I)

G M

Grid

infeed

Load

∆I Central Unit

Optic

fibres

BUBU

BU

BU

Digital protection 7SS52

BU: bay unit

Busbardifferential protection

G. Ziegler, 10/2005 page 12

Differential Protection Symposium

Belo HorizonteNovember 2005

I

1

I

2

DI

I

2

I

1

I

1

∆I

∆I

I

2

dedicated O.F.

up to about 35 km

O.F. or Microwave

PCM

MUX

PCM

MUX

Other

services

∆I

∆I

Line differential protection

50/60 Hz current comparison

through wire connection

Phasorwith digital communication

via OF, microwave or pilot wires

Other

services

G. Ziegler, 10/2005 page 13

Differential Protection Symposium

Belo HorizonteNovember 2005

∆I ∆I

R

S

R

S

U

1

U

2

∆U

I

1

I

2

G

Grid

Two wire (pilot wire) line differential protection

Voltage comparison principle

3

3

∆I

∆I

G. Ziegler, 10/2005 page 14

Differential Protection Symposium

Belo HorizonteNovember 2005

4

3

2

1

15

1

10

∆I

GF

= total false current

∆I

WF

= CT false current

∆I

AF

= Inaccurate adaptation (CT ratios, tap

changer)

∆I

WF

= Transformer magnetising current

r

e

l

a

y

c

h

a

r

a

c

t

e

r

i

s

t

i

c

I

D

/ I

n

I

∆

/ I

n

False differential currents during load or external faults

G. Ziegler, 10/2005 page 15

Differential Protection Symposium

Belo HorizonteNovember 2005

I

1

I

2

I

1

+ I

2

Percentage differential relay

stabilise

operate

Basic-

pick-up value (B)

B

S = I

1

+ I

2

A = I

1

− I

2

G. Ziegler, 10/2005 page 16

Differential Protection Symposium

Belo HorizonteNovember 2005

Relay characteristic

Fault characteristic

(single side infeed)

21

III +=Σ

21

II

ΔI

−

=

with digital relays:

21

III +=Σ

2121

IIkII −⋅>+

2

1

k

k

k =

Differential protection: analogmeasuring circuit

Rectifier bridge comparator with moving coil relay

protection

object

I

1

I

2

i

1

i

2

W

1

W

2

W

1

W

3

W

4

()

21

1

Re

1

IIk

Ik

s

−⋅=

⋅

()

21

2

2

IIk

Ik

Op

+⋅=

⋅

s

Ik

Re

1

⋅

Op

Ik ⋅

2

2

1

1

w

w

k =

4

3

2

w

w

k =

G. Ziegler, 10/2005 page 17

Differential Protection Symposium

Belo HorizonteNovember 2005

s

Ik

Re

⋅

Op

I

IΣ=+++=

n

I....

2

I

1

I

op

I

I

R

Σ=+++=

n

I....

2

I

1

I

es

I

Multi-end differential protection:

Analogmeasuring principle

1

2

n

G. Ziegler, 10/2005 page 18

Differential Protection Symposium

Belo HorizonteNovember 2005

relay characteristic

Ideal fault characteristic

2

I

1

I

Res

I +=

2

I

1

I

Op

I

−

=

G

G

∆Ι

F1

I

F2

I

Load

R

L

R

F

∆Ι

2000A

300A

G

δ

F

I

s

I ⋅= 2

Re

2

cos2

δ

⋅⋅=

F

I

Op

I

A 2000

Op

I =

A 2600

S

I =

internal

fault

Healthy

protection object

CT saturation

Optimised relay characteristic