Day 2 Part 3 Special Cases

Part 2 Distance Protection Special Cases Gustav Steynberg © Siemens AG 2008 Energy Sector

For the application of distance protection Special Conditions: 1.

Short lin lines/cables les

2.

Parallel lines

3.

Fault resistance

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© Siemens AG 2008 Energy Sector

Short Lines: SIR - Definition Definition SIR (S (Source Impedance Ratio) describes the ratio between the source impedance and the line li ne impedance! If ZL

G

E

VF

distance relay

SIR =

V f

=

Z S Z L E

1 + SIR

High SIR = Small loop voltage V F in case of a fault at the end of the line Note: SIR trip time curves are mostly m ostly related to zone 1, i.e. ZL = Z1

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SIR - Considerati Considerations ons about line line length and infeed infeed

The SIR gives some information about the power of infeed and the line length! SIR > 4 SIR < 4 and >0.5 .

short line* medium line* *

For a distance relay the short line (large SIR) is more critical than on a long line (small SIR)! *Classification according IEEE-Guide

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Short Lines: Definition of the shortest zone 1 setting The smallest reach setting of the underreaching Zone 1 will be determined with the minimum voltage measured for a fault at this zone boundary! If Z source

Z line

Vf

SIR =

G

Z S Z L

V f

=

E

1 + SIR

To ensure sufficient measuring accuracy a minimum voltage must be available for a fault at the boundary of the zone 1 setting. By definition of the loop impedances a 3ph fault will result in the smallest voltage: Vmin=minimum voltage for measured accuracy in stated tolerance (e.g. 5%)

The shortest line length (zone 1 setting) is i s therefore defined by V min and the SIR.

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Short Lines: Lines: Example Example - shortest shortest zone 1 setting setting With minimum short circuit level on the busbar = 4 GVA, GVA, what is the smallest possible zone 1 setting is Vmin = 0.5V secondary? If Z source

Z line

Vf

SIR =

400kV

2

Z source

=

SIRmax

=

U N

S 3 ph E

V min

=

−1 =

400 2 4000 400 3⋅2

=

40Ω

V min_prim

− 1 = 114

Z 1min =

=

Z S

V f

Z L 0.5 100

Z source SIRmax

⋅ 400kV =

=

40 114

=

E

1 + SIR

2kV

= 0.35Ω

The shortest line length (zone 1 setting) is 0.35 Ohm primary. For a typical line reactance of 0.3 Ohm/km this corresponds to a line length of just over 1km.

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Parallel lines: Influence on distance measurement d

Resultant positive and negative sequence current enclosed = ZERO 2.5

IA

2.5

Z line

3.0

G

Z0 mutual

3.0

3.5

3.5 7 0 . 8 1

B Z line

Resultant zero sequence current enclosed = 3I0

7 0 . 5 1

Resultant coupling between two lines is only with zero sequence 7 8 . 2 1

7 6 . 0 1

Coupling of the parallel feeders for zero sequence current influences the measured fault impedance with ground loops.

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Parallel lines: Influence on distance measurement

Z1

Influence of parallel line

IA Z line

100%

G

Z

Z0 mutual

l i n e

IB Z line

distance

The loop voltage measured by Z1 for a single phase to ground fault as shown:

U L −G

Z L −G = Z Line

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November 09

Z 0 M

= I L ⋅ Z Line − I E _ A ⋅ Z E − I E _ B ⋅

The measured loop impedance:

100%

3

Z 0 I E _ B ⋅ M 3 − I L − K 0 ⋅ I E _ A

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Parallel lines: Compensation with modified XE/XL

IA

Z1

Z line

G

Z0 mutual

IB Z line

For compensation, influence of the parallel by X0Mis considered:

K X 0

=

XE XL

K X 0 M

=

X 0 M

3 XL

The measured loop reactance with modified XE/XL=KX0’:

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November 09

U L −G

r I 0

=

= I L ⋅ X L − I E _ A ⋅ X E − I E _ B ⋅

I E _ B

X 0 M

3

K X 0 ' = K X 0 + K X 0 M ⋅ r I 0

I E _ A

I L ⋅ X L − I E _ A ⋅ X E − I E _ B ⋅ X L −G

=

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I L

' − K 0 ⋅ I E _ A

X 0 M

3

=

X Line © Siemens AG 2008 Energy Sector

Parallel lines: Compensation with measured IE of parallel line

Z1

IA Z line

G

Z0 mutual

IB Z line

The loop voltage measured by Z1 for a single phase to ground fault as shown:

The measure loop impedance with modified parallel line compensation:

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November 09

U L −G

Z L−G

Z 0 M

= I L ⋅ Z Line − I E _ A ⋅ Z E − I E _ B ⋅

3

Z 0 I L ⋅ Z Line − I E _ A ⋅ Z E − I E _ B ⋅ M 3 = I L − K 0 ⋅ I E _ A − K 0 M ⋅ I E _ B

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=

Z Line © Siemens AG 2008 Energy Sector

Distance measurement Fault loop formulas RL + j XL

I L1

Relay location

I L2 I L3

VL1 VL2 VL3 RE + j XE

I E

Phase-to-Earth Phase-to-Earth loop: V

= I ⋅ R +

V L1

X

− I ⋅ R +

X

= ( I L1 ⋅ R L − I E ⋅ R E ) + j ( I L1 ⋅ X L − I E ⋅ X E )

    R X V L1 = R L ⋅  I L1 − E ⋅ I E  + jX L  I L1 − E ⋅ I E  R X 

L





L



Line and earth impedance are measured

Phase-to-Phase Phase-to-Phase loop:

V L1− L 2

=

( R L + jX L ) ⋅ ( I L1 − I L 2 )

Only the Line impedance is measured Page 11

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(Ph-E-loop (Ph-E-loop)) - influence influence of fault resistance resistance with setting setting RE/RL and XE/XL XE/XL - Siemens Siemens method method Ι L

UPh-E

Ι E

XL

RL RF X

Ι K

XE

RE

U Ph - E = I L (R L + j X L ) - I E (R E + j X E )+ R F ⋅ I L

Im X Ph-E =

1 +

RPh-E = with IE = - IL Page 12

Ph − E

  I L  X E

November 09

ZL Ph-E

=

X L R

X L

U Ph − E  Re   I L  R E 1 + R L

RF 1+kE,R

= R L +

RF E , R 1 + k

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No measuring error in the X-direction © Siemens AG 2008 Energy Sector

(Ph-E-loop) (Ph-E-loop) - influence influence of fault resistance resistance with separation separation of fault fault and line resista resistance nce - Not Siemens Siemens method method Ι L

UPh-E

Ι E

XL

RL

XE

RF

RF X

Ι K

RE

U Ph - E = I L (R L + j X L ) - I E (R E + j X E )+ R F ⋅ I L

ZL Ph-E

X TypeC =

Im{U I } 1 + K x

=

X L

with IE = - IL

R

RTypeC = Re{U / I } − X TypeC / tan(ϕ L ) ⋅ K r Note difference in fault resitance coverage with same zone setting!

RTypeC = R L + RF

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(Ph-E-loop) (Ph-E-loop) - influence influence of fault resistance resistance with complex complex KO settin setting g - Not Siemen Siemens s method method Ι L

UPh-E

Ι E

XL

This method is not used by SIEMENS

RL Ι K

RF

XE

RE

RF 1+k0

X

∆X

U Ph - E = I L (Z L + Z E ) + R F ⋅ I L

assume

I L = - I E

ZL

ZPh-E

Z E U Ph - E R F Z L Z Ph - E = = Z L ⋅ + 1+ k0 1+ k0 I L − k0 ⋅ I E

1+

If k0 setting adapted to

Z E RF , then Z Ph - E = Z L + Z E Z L 1+ Z L

R

=

RF

Z L +

1+

Z E j(ϕ E -ϕ L) ⋅e Z L

Also an additional measuring error in the X-direction Page 14

November 09

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Day 2 Part 3 Special Cases

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