03_100 percent stator earth fault protection (1)
DESCRIPTION
Generator stator earth faultTRANSCRIPT
Stator Earth Fault Protection
100 % Protection Range
Dr. 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
Copyright © Siemens Siemens. Innovation for generations.
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
Copyright © Siemens Siemens. Innovation for generations.
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%)
Copyright © Siemens Siemens. Innovation for generations.
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 Hz
RE
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
Copyright © Siemens Siemens. Innovation for generations.
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
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100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method – Numerical Measuring Technique
Replica:
isSEF
iSEF VSEF
20HzRE RBCE
RE = 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 CERE Yers =
1RE
+ j ωωωωCERE =
V2r + V2
i
Vr. Ir + Vi
. Ii
Re
Vr. Ir + Vi
. Ii
V2r + V2
i
Fourierfilter
(20Hz)
V20 = Vr + jVi
I20 = Ir + jIi
=
20
20
V
I
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100%-Stator-Earth-Fault Protection with 20-Hz-Injection Method – Relay Settings (secondary values)
Two Stages
Backupovercurrent
Supervision
Calibration
Primary fault resistances:
1 to 3 kΩΩΩΩ Trip stage
5 to 8 kΩΩΩΩ Alarm stage
Copyright © Siemens Siemens. Innovation for generations.
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
Copyright © Siemens Siemens. Innovation for generations.
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
Copyright © Siemens Siemens. Innovation for generations.
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% U0
calculated
90% U0
calculated
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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
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Real Practical FailuresExternal insulation test equipment failed
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Real Practical FailuresCalculated Secondary Fault Resistance
100 200 300 400 500 600 7000
50
100
150
200
Resistance
TripPickup
t in ms
R i
n O
hm
200
0
60
86
REmk
SES100Ausk
GAnrk
687.5100 k ta.
Pickup
Drop off
Copyright © Siemens Siemens. Innovation for generations.
Real Practical FailuresEarth Fault in the Cable of Static Frequency Converter
Starting of the generator with
static frequency converterSFC
G
Permanently pickup by 100%-stator earth fault protection
Copyright © Siemens Siemens. Innovation for generations.
Real Practical FailuresEarth Fault in the Cable of Static Frequency ConverterFault Record
Input
signalsof the100%
SEF
frequency appr. 1,7 Hz
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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
ResistanceTrip
Pickup
t in ms
R i
n O
hm
100
0
48
57REmk 10−
SES100Ausk
GAnr k
686.9599.92 k ta⋅
Drop off
Pickup