day 2 part 3 special cases

HV Power Seminar Nov 2009 1

Part 2

Energy Sector© Siemens AG 2008

Distance ProtectionSpecial Cases

Gustav Steynberg


For the application of distance protection

Special Conditions:

1. Short lines/cables

2. Parallel lines

3. Fault resistance

Energy SectorEnergy Automation© Siemens AG 2008

November 09


G VF

ZL

E

If

SIR (Source Impedance Ratio) describes the ratio between the source impedance and the line impedance!

L

S

Z

ZSIR =

Short Lines: SIR - Definition


November 09

distance relay

High SIR = Small loop voltage V Fin case of a fault at the end of the line

SIR

EV f +

=1

Note: SIR trip time curves are mostly related to zone 1, i.e. ZL = Z1


The SIR gives some information about the power of infeed and the line length!

SIR > 4 short line*SIR < 4 and >0.5 medium line*SIR < 0.5 long line*

SIR - Considerations about line length and infeed


November 09

SIR < 0.5 long line*

For a distance relay the short line (large SIR) is more critical than on a long line (small SIR)!

*Classification according IEEE-Guide


The smallest reach setting of the underreaching Zone 1 will be determined with the minimum voltage measured for a fault at this zone boundary!

L

S

Z

ZSIR =

SIR

EV f +

=1

Short Lines: Definition of the shortest zone 1 setti ng

Z source

G

Z line

Vf

If


November 09

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 therefore defined by Vmin and the SIR.


With minimum short circuit level on the busbar = 4 GVA, what is the smallest possible zone 1 setting is Vmin = 0.5V secondary?

L

S

Z

ZSIR =

SIR

EV f +

=1

Short Lines: Example - shortest zone 1 setting

Z source

400kV

Z line

Vf

If


November 09

Ω=== 404000

4002

3

2

sourceph

N

S

UZ kVkVV 2400

100

5.0min_prim =⋅=

114123

4001

minmax =−

⋅=−=

V

ESIR

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.

Ω=== 35.0114

401

maxmin SIR

ZZ source


Parallel lines: Influence on distance measurement

G

Z line

IA

I

Z0 mutual 3.5

3.0

2.5

3.5

3.0

2.5

18.0

7

dResultant positive and negative sequence current enclosed = ZERO


November 09

Z lineIB

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

15.0

7

10.6

7

12.8

7

18.0

7

Resultant coupling between two lines is only with zero sequence

Resultant zero sequence current enclosed = 3I0


Parallel lines: Influence on distance measurement

Z line

G

Z line

IA

IB

Z0 mutual

Z1

Z line

100%

100%

Influence of parallel line


November 09

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

3

0__

MBEEAELineLGL

ZIZIZIU ⋅−⋅−⋅=−

The measured loop impedance:

AEL

MBE

LineGL IKI

ZI

ZZ_

_

030

⋅−

⋅−=−

distance 100%


Parallel lines: Compensation with modified XE/XL

Z line

G

Z line

IA

IB

Z0 mutual

Z1


November 09

3

0__

MBEEAELLGL

XIXIXIU ⋅−⋅−⋅=−

XL

XEK X =0 XL

XK M

MX 3

00 =

For compensation, influence of the parallel by X0Mis considered:

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

AEL

MBEEAELL

GL XIKI

XIXIXI

X =⋅−

⋅−⋅−⋅=−

_'

__

030

0000 ' IMXXX rKKK ⋅+=AE

BEI I

Ir

_

_0 =


Parallel lines: Compensation with measured IE of parallel line

Z line

G

Z line

IA

IB

Z0 mutual

Z1


November 09

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

The measure loop impedance with modified parallel line compensation:

LineBEAEL

MBEEAELineL

GL ZIMKIKI

ZIZIZI

Z =⋅−⋅−

⋅−⋅−⋅=−

__

__

0030

3

0__

MBEEAELineLGL

ZIZIZIU ⋅−⋅−⋅=−


Phase-to-Earth loop:

Distance measurement Fault loop formulas

RL + j XLIL1

RE + j XE

VL1 VL2 VL3

IL2IL3

IE

Relay location

( ) ( )+⋅−+⋅= EEELLLL jXRIjXRIV 11


November 09

Phase-to-Phase loop: ( ) ( )2121 LLLLLL IIjXRV −⋅+=−

Line and earth impedance are measured

Only the Line impedance is measured

( ) ( )

⋅−+

⋅−⋅=

⋅−⋅+⋅−⋅=+⋅−+⋅=

EL

ELLE

L

ELLL

EELLEELLL

EEELLLL

IX

XIjXI

R

RIRV

XIXIjRIRIV

jXRIjXRIV

111

111

11

)()(


(Ph-E-loop) - influence of fault resistance with set ting RE/RL and XE/XL - Siemens method

UPh-E

XL

ΙL RL

RF

XE

ΙE RE

ΙKX

ZL

Z

RF

1+kE,R

( ) ( ) LFEEELLLE-Ph III R +X j + R - X j + R = U ⋅U


November 09

R

ZPh-E

with I E = - IL

RE

FL

L

E

L

EPh

Ph-E + k

RR

R

R +

I

U

R,11

Re

+

−

=

=

L

L

E

L

EPh

Ph-E X

X

X +

I

U

X =

=

−

1

Im

No measuring errorin the X-direction


(Ph-E-loop) - influence of fault resistance with sep aration of fault and line resistance - Not Siemens method

UPh-E

XL

ΙL RL

RF

XE

ΙE RE

ΙK

( ) ( ) LFEEELLLE-Ph III R +X j + R - X j + R = U ⋅

X

ZL

Z

RF


November 09

with I E = - ILL

xTypeC X

K

IUX =

+=

1

Im

FLTypeC

rLTypeCTypeC

RRR

KXIUR

+=

⋅−= )tan(//Re ϕNote difference in fault resitance coverage with same zone setting!

R

ZPh-E


UPh-E

XL

ΙL RL

RF

XE

ΙE RE

ΙK

( ) E-L assume LFELLE-Ph IIII =⋅ R + Z + Z = U

This method is not used by SIEMENS

(Ph-E-loop) - influence of fault resistance with com plex KO setting - Not Siemens method

X

∆X

ZL ZPh-E

RF

1+k0


November 09

k0R

k0ZZ

Zk0

UZ

+ 1 +

+ 1

+ 1 =

FL

E

LEL

E-PhE-Ph ⋅=

⋅− II

)-Ej(

L

E

FL

L

E

FLE-Ph

L

E

Le1

R

1

R then , to adapted setting If

ϕϕ⋅++=

++=

ZZ

Z

ZZ

ZZZZ

k0

Also an additional measuring error in the X-direction

R

day 2 part 3 special cases

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