Earth FAult Protection_new

7/30/2019 Earth FAult Protection_new

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Siemens AG 2006

Earth Fault protection

Power Transmissionand Distribution


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Page 2 TLQ 2004 Distance Protection -Earth Fault Protection

Siemens AG 2006

Power Transmission and Distribution

7SA522

High Resistance Earth Fault Protection: Features

Earth (zero sequence) current protection, 4 stages 1 and 3 pole tripping with special phase selectors

3 definite-time stages

1 inverse-time stage: IEC, logarithmic inverse or ANSI characteristic

this stage can also be used as a 4th definite-time stage

Directional determination with 3V0 and/or Ipol of an earthed powertransformer

Directional determination with V2 and I2 (negative sequence)

Sensitive 3I0-measurement with a pick-up range: 0.005 A to 100 x In

Elimination of higher harmonics with special digital filters

Inrush-stabilisation with I0/100Hz

Teleprotection: Directional comparison, Blocking or Unblocking

Operation with weak infeed trip and echo

Instantaneous trip after switch-onto-fault


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Siemens AG 2006


Example: Single phase fault with infeed from 2 sides

IL1

IL2

IL3

IEZf


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Siemens AG 2006


Symmetrical Component representation: L1-E Fault

B

Pos.Seq.

I1A

Neg.Seq.

ZeroSeq.

I1BA

I2A

I2B

I0A

I0B

3 xR

Fault

U0A

U2A

U2B

U0B


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*)

I0P U0P U2P

I0L,

I2L

*) not needed for numerical relays,

U0P may also be internally calculated

Polarizing Options for Directional Earth Fault

Relays


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Directional Characteristic (U0 and IY)


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Siemens AG 2006


7SA522

High Resistance Earth Fault Protection: functional

diagram

Earth fault

direction

=

EF IE> Echo

3I0>>>EF>>> Trip

P

EFp Trip

Inrush-stabilisation

T(3I0/IN)

T

Tele-protection

T

SOTF

= &

&

3I0>>> Def. Time Stage

Inverse Time Stage

&

&

P

>EF>>> block

Direc. 3I0>>>

P Direc. 3I0p

>EFp block

P 3I0p

EF Fault Det.

>EF Trip rel.

3I0>> Def. Time Stage

3I0> Def. Time Stage

= Input signal(binary input)

P = Parameter = Output Signal(alarm, command)

P3146 AddTdelay



Siemens AG 2006


7SA522 - Directional earth fault protection: Settings

Settings of the stages:

Settings for direction:

General settings:



Siemens AG 2006


Principle of phase selection logic with U and I - Example

L1-E

UL1E < 0.6 UNOM

UL2E > 0.7 UNOM

UL3E > 0.7 UNOM

IL1E > 2 INOM

IL2E < 1.2 INOM

IL3E < 1.2 INOM

&

&

OR

Select

L1-E

with U / I

If selection with U / I is not successful (U too large or I too small)

then symmetrical component method is used



Siemens AG 2006


Phase Selection Logic - Sequence Components

L2-E

L3-E

L1-E

I2 = I0

I2 = a2*I0

I2 = a*I0

Angle differenceI2/I0

Faulty Phase

-60 .. 60 L1-E

60 .. 180 L3-E

180 .. 300 L2-E



Siemens AG 2006Power Transmission and Distribution

U0P or U2P may fall below critical value (approx. 1 V secondary) and limit

relay high resistance earth fault sensitivity

Zero or negative sequence sources to be available behind relay location

Minimum settings at least > 3 times VT and CT inaccuracies

Current setting above line unsymmetry (M0 = Z01/Z0 or M2 = Z21/Z1)

(series compensated lines require higher current setting due to

possibility of unsymmetrical gap flashover)

Separate current threshold setting for tele-protection : 3I0 to avoid false operation with CT

saturation

DEF protection, Critical application issues



Siemens AG 2006Power Transmission and Distribution

7SA522 - Earth fault protection

Directional comparison teleprotection scheme

rec.

transm.

A B

E/F.

frwd. TS

& trip

rec.

&1

E/F.

frwd.TS

&trip

transm&

1

*Three-terminal schemes are supported as well

TS

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Earth FAult Protection_new