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Rotor-Earth-Fault
Protection
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Power Transmission and Distribution
Power Automation
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Generator Protection
Rotor-Earth-Fault Protection
Presenter: Dr. Hans-Joachim Herrmann
PTD PA13
Phone +49 911 433 8266
E-Mail: [email protected]
Power Automation
2
Power Transmission and Distribution
Requirement for Rotor Earth Fault Protection
Power Automation
Progress. It‘s that simple.
+
Rotor
Excitation
system
Earth fault in the rotor
Stator
RE

CE
in case of an earth fault, only small currents flow due to the galvanical isolation
Problem:
Double earth faults and interturn faults as a consequence of an earth fault cause:
• magnetical unbalance (unbalanced forces; violent vibration)
• high currents at the fault location
 Destruction of the Rotor (Generator)
Task: Detection an earth fault already when it starts to build up
Power Automation
3
Power Transmission and Distribution
Protection Principle
Power Automation
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+
Excitation
system
Coupling
Unit
Measuring
Voltage
Source
„Earthing brush “
Principles:
- Incoupling of an AC voltage (50 Hz or 60 Hz)
- Measuring of the earth fault current
- Measuring of the earth fault resistance
Higher
Sensitivity
- Incoupling of low frequency square wave voltage
Power Automation
4
Power Transmission and Distribution
Earth Current Criterion
Principle (50 Hz/60Hz - Voltage Injection)
Power Automation
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Connection
on the earthing
brush
L1 L2 L3
>40V
105 4F
IE
IE,Distr.
IE,Fault
If disturbance influence from the excitation is to large
Pick-up limit:
IE,Fault > IE,Dist...
0,75H
Coordinated
resonant circuit to fN
Protection
Power Automation
5
Power Transmission and Distribution
Earth Current Measurement
Connection
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Connection on the
phase to phase
voltage
AC Voltage
Source
appr. 42V or
65V
Err.
-
100 V - 125 V AC
105
+
7UM6
4A1
1A3
1A1
2B1
4B1
1B3
1B1
7XR61
3PP1336
Also IEE2
at 7UM62
is
possible
J7
J8
IEE1
105
External resistors
at excitation voltages
> 150 V (circulating current >0,2A)
Documentation for Coupling Device in the Internet
www.siprotec.com
Power Automation
6
Power Transmission and Distribution
Gain Characteristic of the R, C, L-Circuit
Power Automation
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Z( 50 )  169.65
Z( 60 )  69.531
Filterverhalten Bandpaß
2000
Impedanz in Ohm
1500
Z( f )
1000
500
0
0
50
100
150
200
250
300
f
Frequenz in Hz
I 
I 
U
ZCoupling  R f
45 V
 27mA
170  1,5 k
Imax approx. 300 mA
Power Automation
7
Power Transmission and Distribution
Earth Current Criterion
Protection Settings
Power Automation
Progress. It‘s that simple.
Measuring circuit supervision
Protection with two stages:
I 
I 
U
ZCoupling  R f
ZCouplingl(50Hz) = 400
45 V
 23mA
400  1,5 k
ZCouplingl(60Hz) = 335
Imax ca. 100 mA
(voltage source decreases a little bit )
Note: Coupling impedance only with R and C
Finally setting during commissioning
Power Automation
8
Power Transmission and Distribution
Earth Current Criterion
Logic
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Power Automation
9
Power Transmission and Distribution
Calculation of the Fault Resistance RE
(50Hz/60Hz- Voltage Injection)
Power Automation
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L1 L2 L3
100V
RV
RE
CE
u
Digital
protection
(7UM62)
calculation
of RE
CK
L1)
RV
42V
i
CK
1) Recommended
at static excitation
with inject harmonics
(3rd harm.; 6th harm.)
Power Automation
10
Power Transmission and Distribution
Calculation Formula of the Fault Resistance RE
Power Automation
Progress. It‘s that simple.
Model:
X*K
R*V
Zers
(1)
(3)
XE
ZMess
RE
2
2

RE X E
RE
X E 

Z ers  R * V 
 j - X *K 2

2
2

RE  X E 2 
RE  X E

R  XE
R,  E
2
RE  X E
2
2
Z
(2) Z Mess  Re Z  j I m Z
 RE Z - R * V
R  XE
X ,  E2
 I m Z - X *K
2
RE  X E
2
(4)
- I m Z - X *K   R Z - R *
X ,2
RE  ,  R, 
V
e
R
Re Z - R * V
2
combining (3) and (4):
Note: RV* and XK* are measured during commissioning
Power Automation
11
Power Transmission and Distribution
Earth Fault Resistance Calculation
Logic
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Power Automation
12
Power Transmission and Distribution
Earth Fault Resistance Calculation
Settings
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Measured during commissioning
Measuring circuit supervision
Measured current can be influenced by disturbances
Correction during primary test,
(in most case the alarm stage is concerned)
Power Automation
13
Power Transmission and Distribution
Injection of Square Wave Voltage with Low Frequency
Basic Diagram
Power Automation
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Typical frequency:
1 - 3 Hz
7XR6004
RV
Controlling device
(7XT71)
IE
RV
+
UH
Excitation
-
CE
Ucontrol
RE
RM
RE
RV
UH
RM
CE
Fault resistance
Coupling resistor
Auxiliary supply (  50V)
Measuring shunt resistor
Rotor capacitance
Umeas.
Digital
Protection
(7UM62)
Measuring
transducer
Power Automation
14
Power Transmission and Distribution
Injection of Square Wave Voltage
Connection Diagram (7UM62)
Power Automation
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Connection on the
phase to phase
voltage
7UM62
120 V
100 V
110 V
7
7XT71
+
40 k
9
11
27
27
25
Exc. 7XR6004
Control voltage
17
-
40 k
15
Measuring voltage
K13 +
K14
TD1
K15 +
TD2
K16
25
Power Automation
15
Power Transmission and Distribution
Injection of Square Wave Voltage with Low Frequency
Basic Principle
Power Automation
Progress. It‘s that simple.
50V
Equivalent circuit:
UH
RV
2
CE
t
- 50V
UH
RE
UM
RM
iE
RV
 20k
2
RM  375 
U H   50V
UM
1,88V
  RV  CE
2
UM  0
RE  
t
UM  RM  iE
- 1,88V
RE  5k
UM
0,75V
UM ~
1
RE
t
- 0,75V
Power Automation
16
Power Transmission and Distribution
Sources of Error and Error Compensation
Power Automation
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Influence of field voltage and earth fault location
b) Jumps in the field voltage
a) Earth fault location
a change in the field voltage takes
to jumps in the dc-voltage shifting
Shifting of measuring voltage with
a positive or negative dc voltage
UM
UM
Udc
UM1
UM2
Udc1
UM1
UM2
UM3
Udc = dc voltage shifting
U1 = |UM1 - UM2|
 U2 = |UM2 - UM3|
Solution:
Calculation of the difference voltage
 U = |UM1 - UM2|
Solution:
Block of measuring
at jumps (e.g. U1 = U2)
UM4
Udc2
 U3 = |UM3 - UM4|
Power Automation
17
Power Transmission and Distribution
Calculation Formulas
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CE RE
RV
2
UH
RM
UM
Voltage divider:
RV
 RE  RM
UH
2

UM
RM
U

R
RE   H - 1 RM - V
2
 UM 
Algorithm
Filtering:
UM
U1
1 N
1 N
U 1   u1,i ; U 2   u2,i
N i 1
N i 1
U2
UM :  U : 
U1 - U 2
2
Continuity supervision:
Validity requirement
UIK  UIK 1
1 8
otherwise U   Uk
8 k 1
Amplitude-log frequency curve: fA = 800 Hz; N = 64
1
G(f)0.1
0.01
0.001
0
30 60 90 120 150 180210240 270 300
f in Hz
Power Automation
18
Power Transmission and Distribution
Logic Diagram Rotor Earth Fault Protection (1-3Hz)
Power Automation
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Power Automation
19
Power Transmission and Distribution
Rotor Earth Fault Protection (1-3Hz)
Setting Values
Power Automation
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Measuring circuit supervision
Advanced parameter
only visible in DIGSI
If the integrated test function is used,
pick-up value of test resistor
Power Automation
20
Power Transmission and Distribution
Connection of the Rotor Earth Fault Protection
Power Automation
Progress. It‘s that simple.
EM
G
RW
RE
(50/60 Hz)
4µF
CE
(1 - 3 Hz)
40k
a) rotating diodes
L+
EX-T
UG
RW
L-
b) separate Exciter
(static excitation)
(50/60 Hz)
4µF
RE
40k
(1 - 3 Hz)
CE
Power Automation
21
Power Transmission and Distribution
Generator with Rotating Excitation
Fault Free Condition (Square Wave Principle)
Power Automation
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Chance of charge of
rotor earth capacitance
Disturbances by the
excitation generator
Power Automation
22
Power Transmission and Distribution
Generator with Rotating Excitation
Test Condition with a Fault Resistor
Power Automation
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Fault resistor is inverse proportional to the difference voltage
Power Automation
23
Power Transmission and Distribution
Parallel Operation of Rotor Earth Fault Protections
Power Automation
Progress. It‘s that simple.
50 Hz principle
1- 3 Hz principle
RV;40k
CK;4µF RK;105
or
7UM61
7UM62
uControl
uMeas.
RV;40k
RE
7UM62
CK;4µF RK;105
iREF
100V
42V
nur
iREF
uREF
Power Automation
24
Power Transmission and Distribution
Parallel Operation of Rotor Earth Fault Protections
Measurement with the 50/60 Hz Principle
Power Automation
Progress. It‘s that simple.
Measurement 7UM61 or 7UM62
(RV is earthed for an AC voltage)
Measurement:
measured as a fault resistance
Equivalent circuit:
RK * CK *
RE * :  RE ll
Case 1:
RV
2
RE  
RE * 
RE
RV
(20k)
2
seen from the 7UM6, RV already
is interpreted as a rotor-to-earth
resistance
Case 2:
RV
 20k
2
RE  5k
RE *  4k
alarm stage becomes less sensitive
 open brushes can not be find out
Power Automation
25
Power Transmission and Distribution
Parallel Operation of Rotor Earth Fault Protections
Measurement with the Square Wave Principle
Power Automation
Progress. It‘s that simple.
Measurement 7UM62 (1- 3 Hz)
(CK is earthed for a DC voltage)
Equivalent circuit:
Umeas
RV
2
U
2
RM
RE
2CK
(8µF)
 seen from the 7UM6:
high rotor capacitance

 capacitors will not be
completely loaded
 alarm stage becomes less sensitive
(approx. 50k)
 U ~ RE-1
under no-earth-fault conditions
a fault resistance is already measured
 longer measuring time
Power Automation
26