rotor earth fault

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 1
Training: Numerical Unit and
Station Supply Protection
Rotor Earth Fault Protection
Presenter: Dr. Hans-Joachim Herrmann
PTD EA13
Phone 0911-433-8266

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 2
 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
• high currents at the fault location
Task: Detection an earth fault already when it starts to build up
 Destruction of the Rotor
Earth fault in the rotor
RE
CE
Rotor
Excitation
system
+
-
Stator
Requirement for Rotor Earth Fault Protection

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 3
Excitation
system
+
-
Voltage
Source
„Earthing brush “
Coupling
Unit
Measuring
- Incoupling of an AC voltage (50 Hz or 60 Hz)
- Measuring of the earth fault current
- Measuring of the earth fault resistance
- Incoupling of low frequency square wave voltage
Principles: Higher
Sensitivity
Protection Principle

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 4
Also IEE2
at 7UM62
possible
IEE1
J7
J8
1B1
1B3
1A1
1A3
+
-
4A1
4B1
3PP1336
Err.
2B1
7UM6
Connection on the
phase to phase
voltage
7XR61
100 V - 125 V AC
105
105
AC Voltage
Source
appr. 42V or
65V
Documentation for Coupling Device in the Internet
External resistors
at excitation voltages
> 150 V (circulating current >0,2A)
Earth Current Measurement
Connection

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 5
coordinated
resonant circuit to fN
>40V
If disturbance influence from the excitation is to large
IE
Protection
Pick-up limit:
IE,Fault > IE,Dist...
L1 L2 L3
IE,Distr.
IE,Fault
4F
105
0,75H
Connection
on the earthing
brush
Earth Current Criterion
Connection Principle (50 Hz/60Hz - Injection)

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 6
Z 50
( ) 169.65
 Z 60
( ) 69.531

0 50 100 150 200 250 300
0
500
1000
1500
2000
Filterverhalten Bandpaß
Frequenz in Hz
Impedanz
in
Ohm
Z f
( )
f
mA
27
k
1,5
170
V
45
I
R
Z
U
I
f
Coupling







Imax approx. 300 mA
Gain Characteristic of the R, C, L-Circuit

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 7
Protection with two stages: Measuring circuit supervision
mA
23
k
1,5
400
V
45
I
R
Z
U
I
f
Coupling







ZCouplingl(50Hz) = 400
ZCouplingl(60Hz) = 335
Imax ca. 100 mA
(voltage source decreases a little bit )
Protection Settings
Earth Current Criterion

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2008.
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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 8
Earth Current Criterion
Logic

9. Energy Sector
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2008.
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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 9
100V 42V u
Digital
protection
(7UM62)
calculation
of RE
RE CE
RV CK
RV CK
L1 L2 L3
i
L1)
1) Recommended
at static excitation
with inject harmonics
(3rd harm.; 6th harm.)
Calculation of the Fault Resistance RE
(at 50Hz/60Hz-Injection)

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2008.
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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 10
(1) (2)
(3)
(4)
combining (3) and (4):
Note: RV* and XK* are measured during commissioning
Model:
Zers ZMess Z
X*K R*V
XE
RE
  V
E
2
E
2
E
2
E
E
*
R
-
, Z
R
X
R
X
R
R 



   
Z
Z
R
Z j m
e
Mess I















2
E
2
E
E
2
E
K
2
E
E
2
E
E
V -
-
j
2
ers
X
R
X
R
*
X
X
R
X
R
*
R
Z
  K
m
2
E
2
E
E
2
E
-
, *
X
Z
X
R
X
R
X I




 
 
 
  V
V
e
2
K
m
2
E -
e
-
-
-
,
,
,
*
R
Z
R
*
R
Z
R
*
X
Z
R
R
X
R 



I
Calculation Formula of the Fault Resistance RE

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 11
Earth Fault Resistance Calculation
Logic

12. Energy Sector
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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 12
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)
Earth Fault Resistance Calculation
Settings

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2008.
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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 13
Excitation
+
-
CE
RE
Digital
Protection
(7UM62)
UH
RV
RV
Ucontrol
Umeas.
RM
7XR6004
Controlling device
(7XT71)
IE
Measuring transducer
RE Fault resistance
RV Coupling resistor
UH Auxiliary supply (  50V)
RM Measuring shunt resistor
CE Rotor capacitance
Basic Diagram: Injection of Square Wave
Voltage with Low Frequency (1- 3 Hz)

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 14
Connection on the
phase to phase
voltage
Exc.
17
15
11
25
+
-
27
7XR6004
25
27
7UM62
7XT71
TD1
K14
K13 +
TD2
K16
K15 +
40 k
40 k
Control voltage
Measuring voltage
100 V
110 V
120 V
9
7
Injection of Square Wave Voltage
Connection Diagram 7UM62

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 15
RV
2
RE
CE
UH
UM
RM
UH
UM
UM
50V
- 50V
1,88V
- 1,88V
0,75V
- 0,75V
t
t
t
iE
50V
375
20k
2
H
M
V






U
R
R
E
M
M i
R
U 



E
R

5k
E
R
0
M 
U
E
V
2
C
R



E
M
1
~
R
U

Equivalent circuit:
Basic Principle: Injection of Square Wave Voltage with
Low Frequency

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 16
Influence of field voltage and earth fault location
a) Earth fault location
 Shifting of measuring voltage with
a positive or negative dc voltage
b) Jumps in the field voltage
 a change in the field voltage takes
to jumps in the dc-voltage shifting
Udc = dc voltage shifting
Solution:
Calculation of the difference voltage
 U = |UM1 - UM2|
U1 = |UM1 - UM2|  U3 = |UM3 - UM4|
 U2 = |UM2 - UM3|
Solution:
Block of measuring
at jumps (e.g. DU1 = DU2)
UM
Udc
Udc1
UM1
UM
2
UM3
UM4
UM1 UM
2
Udc2
UM
Sources of Errors - Error Compensation

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 17
RE
CE
UH
UM
RM
RV
2
UM
U1
U2
Algorithm
Voltage divider:
Filtering:
Amplitude-log frequency curve: fA = 800 Hz; N = 64
2
-
1
-
2 V
M
M
H
E
M
M
E
V
M
H R
R
U
U
R
R
R
R
R
U
U


















N
N
u
N
U
u
N
U
1
i
i
2,
2
1
i
i
1,
1
1
;
1
2
-
:
:
2
1
M
U
U
U
U 


1
K
K I
I 


 U
U




8
1
k
k
U
8
1
U
0 30 60 90 120 150 180 210 240 270 300
0.001
0.01
0.1
1
f in Hz
G(f)
Continuity supervision:
Validity requirement
otherwise
Calculation Formulas

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 18
Logic Diagram Rotor Earth Fault Protection (1-3Hz)

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 19
Measuring circuit supervision
If the integrated test function is used,
pick-up value of test resistor
Advanced parameter
only visible in DIGSI
Earth Fault Resistance Calculation
Settings (1-3 Hz Principle)

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 20
G
RW
RE
CE
EM
ERT
L+
RW
UG
RE CE
L-
(50/60 Hz)
(1 - 3 Hz)
(50/60 Hz)
(1 - 3 Hz)
40k
4µF
4µF
a) rotating diodes
b) separate Exciter
(static excitation)
40k
Connection of the Rotor Earth Fault Protection

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 21
Chance of charge from
rotor earth capacitance
Disturbances by the
excitation generator
Generator with Rotating Excitation
Fault Free Condition

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 22
Fault resistor is inverse proportional to the difference voltage
Generator with Rotating Excitation
Test Condition with a Fault Resistor

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 23
100V 45V
CK;4µF
CK;4µF
RK;100
RK;100
RV;40k
RV;40k
RE
7UM62 7UM62
uControl
uMeas.
iREF
uREF
7UM61
nur
iREF
oder
1- 3 Hz principle 50 Hz principle
Parallel Operation of Rotor Earth Fault Protections

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 24
( )

20k
2
RV
*
K
R *
K
C
E
R
2
ll
:
* V
E
E
R
R
R 





20k
2
* V
E
E
R
R
R




4k
*
5k
E
E
R
R
 Measurement 7UM61 or 7UM62
(RV is earthed for an AC voltage)
Equivalent circuit:
seen from the 7UM6, RV already
is interpreted as a rotor-to-earth
resistance
Measurement:
measured as a fault resistance
Case 1:
Case 2:
alarm stage becomes less sensitive
 open brushes are not find out
Parallel Operation of Rotor Earth Fault Protections

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Siemens Power Academy TD
06 Rotor Earth Fault Protection
Using numerical machine and motor protection
Version: C 3_Page 25
RV
2
RE
RM
2CK
(8µF)
Umeas
U
2
 Measurement 7UM62 (1- 3 Hz)
(CK is earthed for a DC voltage)
Equivalent circuit:
 seen from the 7UM6:
high rotor capacitance
 capacitors will not be
completely loaded
  U ~ RE
-1
under no-earth-fault conditions
a fault resistance is already measured
 alarm stage becomes less sensitive
(approx. 50k)
 longer measuring time
Parallel Operation of Rotor Earth Fault Protections