Distance Protection  Power Swing 

Distance Protection Power Swing Gustav Steynberg

Power swing: Voltage diagram diagr am   LZS1

Two Machine Problem E1 ZL

  LZS2

E2 = E'2

E1

U A

E2 ZS1

  LZL

UB U'B

ZS2

UB

U A

U' A E'1



' 'L

  L

If the angle becomes too large, the system stability can be lost

Power swing locus and relay characteristic characteris tic in the impedance diagram E1 > E2

X

ZS2

B

E1 = E2

ZL '



 A ZLoad

E1 < E2 ZS1

load point R

Power swing  Apparent impedance impedance at at relay location location equal   E 1  E 2

Power swing locus  E 1



 E 1  E 2

E 2

Dynamic system stability, stability, equal area criterion criteri on U1

E1

U2

ZL

ZS2

ZS1 D

1

E2

E 1 P TP

ZL

=

P 0 PT

 A

C

1

6

D 2

2 2

D

1 3

0

0

1

90°

2

· sin  X T

5

3 3 4 B

· E 2

180°



D

Power swing locus in the impedance plane X ZS1

1

2 ZL 2

6

4 5

3 0

0 ZS1

Zload

R

Power swing detection: Classic Method (Not used in 7SA52 and 7SA6)

Classic power swing detection is restricted to slow swings The setting of Z may not be too large to avoid load encroachment (typ. 5 )

Z

During fast swings the time available (t) for detection of impedance vector  in the power swing zone is too short.

t = time for transition of Z from outer to inner zone

 Advanced  Advanced Power swing swing blocking technique techniques s (7SA513, 7SA522, 7SA6) Novel space vector based principle

•

Self-setting

Unstable swing X

•

Small Z (1 Ohm at In=5 A)

•

Z

Blocking up to high slip frequencies (7 Hz)

•

Recognition of all fault types during swing

•

Remains effective during single pole ARC open time (3-phase set-up)

•

R

Stable swing



dZ/dt measurement



Calculation of swing centre and plausibility check (+90O<  EB)

Example:

Slip frequency

i/kA 6

-90O

3 -3

500

Xm

t/ms

90O

u/kV 200

500

t/ms

180O

Relay

R 

Novel power swing detection provides secure operation with swing frequencies of up to 7 Hz iL1/A 0 -2

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

t/s

-4

iL2/A

0 -2

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

0, 2

0, 3

0, 4

0, 5

0, 6

0, 7

0, 8

0, 9

1, 0

1, 1

t/s

iL3/A 2

t/s

0 -2

uL1/V 0 -50

t/s

uL2/V 50 0 -50

t/s

uL3/V 50 0 -50

t/s

Power Swing >DisTel Rec.Ch1 Dis.T.SEND Dis. forward Dis. reverse Relay PICKUP Relay TRIP DisTRIP3p Z1Bmf  1, 2

1, 3

1, 4

1, 5

1, 6

t/s

Example: 400 kV 400 km f PS  2 Hz 3-pole fault

Fault detection during power swing

I1

I2

V1

Trip

The Power swing passes through the trip characteristic several times. Single phase fault is detected and cleared.

Three phase fault during Power Swing

I1

V1

V2

V3 Trip

Three phase fault during power swing is detected and cleared Fault inception while swing is inside trip characteristic