100 percent stator earth fault protection siemens

Stator Earth Fault Protection100 % Protection RangeDr. Hans-Joachim Herrmann

Power Transmission and Distribution

Copyright Siemens Siemens. Innovation for generations.

Content

Basics of stator earth fault protection Fault locations Disturbances from the high voltage side

100%-stator-earth-fault protection with 20-Hz-injection method Basic idea Practical design Numerical measuring technique Frequency operating range

Design of the protection schemes

Examples of real practical failures


Basics of Stator Earth Fault ProtectionFault Location

Region of earth faults Earth fault locations in the stator

U0

Low displacement voltage at earth faults close to the star point


Basics of Stator Earth Fault ProtectionDisturbances from the High Voltage Side

An additional load resistor limits the disturbance influence The design of the load resistor determines the protective range

(80% or 90 % or 95%)


100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method Goal and Basic Idea

Goal

Protection principle should cover 100 % protection range

Different measuring principles

20 HzRE

max.200 V

I

Basic idea

With injection of a 20-Hz-voltage into the star point a e.m.f. is available in case of an earth fault


100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method Practical Design

The protection measures the injected 20-Hz-voltage and current

Two connectionsare possible


100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method Numerical Measuring Technique

Replica:isSEF

iSEF VSEF

20HzRE RBCERE = Fault resistance

CE = Ground capacitance in stator circuit

VSEF

iSEF

1) Filtering

3) Impedance replica of fault 4) Calculation of fault resistor from 2) and 3)

2) Calculation of the real part

Yers CE RE Yers =1

RE+ j CE RE =

V2r + V2iVr . Ir + Vi . Ii

ReVr . Ir + Vi . Ii

V2r + V2i

Fourierfilter(20Hz)

V20 = Vr + jViI20 = Ir + jIi

=

20

20VI


100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method Relay Settings (secondary values)

Two StagesBackupovercurrentSupervision

Calibration

Primary fault resistances:1 to 3 k Trip stage5 to 8 k Alarm stage


100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method Frequency Operating Range

Stand still Rated frequency

Protection uses a frequency tracking for all protection functions 20-Hz-generator is activated before starting the generator Due to disturbances from zero sequence system during starting (e.q. static

frequency converter) or braking of the generator an internal blocking avoids an overfunction of the injection method

100%-Stator earth fault protection with 20 Hz injection

0Hz 10Hz 40Hz 70Hz

90% Stator earth fault protection with displacement voltage

50Hz


Design of the Protection SchemesApplication used in Three Gorges

100% stator earth fault protection

90% stator earth fault protection

Option:90% stator earth fault protection with calculated U0


Design of the Protection SchemesRedundancy of 100%-Stator Earth Fault Protection

Neutral

transformer

7UM62

UL

UE

IEE1

7UM62

UL

UE

IEE1

Group1 Group2

100% SEF-2

100% SEF-1

90% U0calculated

90% U0calculated


CommissioningPrimary Tests on a Generator (stand still and running)

The secondary signals are very small

The capacitivecurrent is visible.This disturbance current will be eliminated by the algorithm.

Phase to groundvoltage

Displacementvoltage

Ground current


Real Practical FailuresExternal insulation test equipment failed


Real Practical FailuresCalculated Secondary Fault Resistance

100 200 300 400 500 600 7000

50

100

150

200

ResistanceTripPickup

t in ms

R

i

n

O

h

m

200

0

60

86

REmk

SES100Ausk

GAnrk

687.5100 k ta.

Pickup

Drop off


Real Practical FailuresEarth Fault in the Cable of Static Frequency Converter

Starting of the generator withstatic frequency converterSFC

G

Permanently pickup by 100%-stator earth fault protection


Real Practical FailuresEarth Fault in the Cable of Static Frequency ConverterFault Record

Inputsignalsof the100%SEF

frequency appr. 1,7 Hz


Real Practical FailuresEarth Fault in the Cable of Static Frequency Converter Calculated Secondary Fault Resistance

0 100 200 300 400 500 600 7000

20

40

60

80

100

ResistanceTripPickup

t in ms

R

i

n

O

h

m

100

0

48

57REmk 10

SES100Ausk

GAnr k

686.9599.92 k ta

Drop off

Pickup

100 percent stator earth fault protection siemens

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