TLQ2 - February 2003 Power Swing 1

Distance Protection

Power Swing

Gustav Steynberg

TLQ2 - February 2003 Power Swing 2

Power swing: Voltage diagram

LZS1

LZL

LZS2

E2 = E'2E1UA UB

U'B

U'A

'L L

' E'1

E1 E2ZS1 ZS2ZL

UAUB

Two Machine Problem

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

TLQ2 - February 2003 Power Swing 3

Power swing locus and relay characteristic in the impedance diagram

E1 = E2

E1 > E2

E1 < E2

X

R

ZS2

B

ZL

A

ZS1

ZLoad

' load point

TLQ2 - February 2003 Power Swing 4

Power swing Apparent impedance at relay location

21 EE

21 EE

21 EE

equal

Power swing locus

TLQ2 - February 2003 Power Swing 5

Dynamic system stability, equal area criterion

ZS1

U1E1

U2E2ZS2

ZL

ZL

D PTP = · sinE1 · E2

XT

1

D

2

D

3

D

A

C

1

3

2

1

2

30

4

5

6

0

1

20 90° 180°

PT

P

B

TLQ2 - February 2003 Power Swing 6

56

1

34

X

RZload

ZS1

ZS1

ZL2

2

0

0

Power swing locus in the impedance plane

TLQ2 - February 2003 Power Swing 7

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 largeto avoid load encroachment (typ. 5 )

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

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

TLQ2 - February 2003 Power Swing 8

Advanced Power swing blocking techniques (7SA513, 7SA522, 7SA6)

•Novel space vector based principle

•Self-setting

•Small Z (1 Ohm at In=5 A)

•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)

dZ/dt measurement

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

Stable swing

Unstable swing

ZX

R

TLQ2 - February 2003 Power Swing 9

Power Swing detection: New method

dR

dX

(k-n)

(k-n)

dR(k)dX (k)

Power swingX

R

Fault entry

Fault impedance

Loadimpedance

Transition from load to fault is fast

Power swing transition is slow

Continuos monitoring of the impedance trajectory

Monitoring of trajectory continuity Monitoring of trajectory velocity

Evaluation of trajectory ellipse

TLQ2 - February 2003 Power Swing 10

Example:

i/kA

t/ms500

u/kV

t/ms500

200

-3

6

3

R

A ZA a Zl b ZB B~ ~ ~ ~ ~

Evaluation of the power swing process

Power swing locus(EA>EB)

-90O

180O

0O

90OXm

Slip frequency

EBEA

Relay

Relay

TLQ2 - February 2003 Power Swing 11

Novel power swing detection provides secure operation with swing frequencies of up to 7 Hz

t/s0,2 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 1,6iL1/A-4-20

t/s0,2 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 1,6iL2/A-20

t/s0,2 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 1,6iL3/A-202

t/s0,2 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 1,6uL1/V-500

t/s0,2 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 1,6uL2/V-50050

t/s0,2 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 1,6uL3/V-50050

t/s0,2 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 1,6DisTRIP3p Z1BmfRelay TRIPRelay PICKUPDis. reverseDis. forwardDis.T.SEND>DisTel Rec.Ch1Power Swing

Example:400 kV400 kmfPS 2 Hz3-pole fault

TLQ2 - February 2003 Power Swing 12

Fault detection during power swing

I1

I2

V1

Trip

The Power swing passes throughthe trip characteristic several times.

Single phase fault is detected andcleared.

TLQ2 - February 2003 Power Swing 13

Three phase fault during Power Swing

Three phase fault during power swingis detected and cleared

Fault inception while swing is insidetrip characteristic

I1

V1

V2

V3

Trip