04 Rotor Earth Fault Protection

Rotor-Earth-Fault Rotor-Earth-F ault Protection

Requirement for Rotor Earth Fault Protection Rotor

+

Excitation system

Earth fault in the rotor Stator R E

⇒

C E

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

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Protection Principle

+ 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 Copyright © Siemens Australia & NZ 2007. All rights reserved.

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Earth Current Criterion Principle (50 Hz/60Hz - Voltage Injection) Connection on the earthing brush

L1 L2 L3

>40V

I E,Distr.

I E,Fault

105Ω 4µF IE

If disturbance influence from the excitation is to large

Pick-up limit: IE,Fault > IE,Dist...

0,75H Coordinated resonant circuit to fN

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Protection

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Earth Current Measurement Connection Connection on the phase to phase voltage

AC Voltage Source appr. 42V or 65V

100 V - 125 V AC

105Ω

+

7UM6

7XR61

1A3 1A1

4A1

2B1

Also IEE2 at 7UM62 is possible J7 J8

Err.

3PP1336 4B1

-

IEE1

1B3 1B1

105Ω

External resistors at excitation voltages > 150 V (circulating current >0,2A)

Documentation for Coupling Device in the Internet www.siprotec.com Copyright © Siemens Australia & NZ 2007. All rights reserved.

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Calculation of the Fault Resistance R E (50Hz/60Hz- Voltage Injection) L1 L2 L3

100V

R V

RE

C E

Copyright © Siemens Australia & NZ 2007. All rights reserved.

u

Digital protection (7UM62) calculation of RE

C K

L1) R V

42V

i

C K

1) Recommended at static excitation with inject harmonics (3rd harm.; 6th harm.)

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Calculation Formula of the Fault Resistance R E Model:

X*K

R*V

Zers

(1)

(3)

Z ers = R * V +

R E ⋅ X E

, R  =

2

R E R E

, X  =

X E

2

+ X E

2

  R  + j  - X  * K - E   

R E

2

2

  2  + X E  X E

Z

(2) Z Mess = R e {Z } + j I m {Z }

2

R E + X E

(4)

2

ZMess

RE

X E

2

= R E {Z } - R * V

2

R E ⋅ X E 2

R E + X E

2

= I m {Z } - X  * K

combining (3) and (4):

R E

,2 (- I m {Z } - X  * K )2 , = , + R  = + R e {Z } R  R  {Z } - R *  X 

e

R * V

V

Note: R V* and X K* are measured during commissioning Copyright © Siemens Australia & NZ 2007. All rights reserved.

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Injection of Square Wave Voltage with Low Frequency Basic Diagram

Typical frequency: 1 - 3 Hz

7XR6004

R V

Controlling device (7XT71)

I E R V

+

U H

Excitation

-

U control

R E

C E

R M

R E R V U H

R M C E

Copyright © Siemens Australia & NZ 2007. All rights reserved.

Fault resistance Coupling resistor Auxiliary supply ( ± 50V) Measuring shunt resistor Rotor capacitance

U meas.

Digital Protection (7UM62)

Measuring transducer

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Injection of Square Wave Voltage Connection Diagram (7UM62) Connection on the phase to phase voltage

7UM62

120 V 100 V 110 V 7 7XT71 9

+

40 k Ω

11 27

25

Exc. 7XR6004

K13 +

27

Control voltage

17 -

Copyright © Siemens Australia & NZ 2007. All rights reserved.

40 k Ω

15

K14 K15 +

Measuring voltage

TD1

TD2

K16

25

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Injection of Square Wave Voltage with Low Frequency Basic Principle Equivalent circuit:

50V

U H

RV

t 

2

- 50V

UH

R E

C E

U M

RM

UM

1,88V

iE

τ   ≈

R V

2

R E = ∞

⋅ C E

∆U M ≈ 0

t 

U M = R M ⋅ i E R V

2

- 1,88V

= 20k Ω

R M = 375 Ω U H = ± 50V

R E  ≈ 5k Ω

U M

0,75V

∆U M ~

1 R E t 

- 0,75V

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Sources of Error and Error Compensation 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 U M

U M

U dc U M1

U M2

U dc1 U M2

U M1

U M3

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)

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U M4

U dc2

∆ U3 = |UM3 - UM4|

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Calculation Formulas C E

R E

R V

U H

2 R M

U M

Voltage divider: U H U M

R V

= 2

+ R E + R M

 U H  R   1 R M - V  U   2   M 

R E = 

R M

Algorithm Filtering:

UM

U 1

U 1 = U 2

U M : = ∆U  : =

U 1 - U 2

2

Continuity supervision: Validity requirement ∆U IK ≈ ∆U IK +1

otherwise

1 8 ∆U = ∑ ∆Uk 8 k =1

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1

N 

∑ u 1,i ;

N  i = 1

U 2 =

1

N 

∑ u 2,i

N  i = 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 270300

f in Hz

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Logic Diagram Rotor Earth Fault Protection (1-3Hz)

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Rotor Earth Fault Protection (1-3Hz) Setting Values

Measuring circuit supervision Advanced parameter only visible in DIGSI

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If the integrated test function is used, pick-up value of test resistor

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Connection of the Rotor Earth Fault Protection EM

G

RW

RE

4µF

C E

(50/60 Hz)

(1 - 3 Hz) 40kΩ

a) rotating diodes L+

EX-T

4µF UG

RW L-

b) separate Exciter (static excitation)

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(50/60 Hz)

RE

40kΩ

(1 - 3 Hz)

C E

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Generator with Rotating Excitation Fault Free Condition (Square Wave Principle)

Chance of charge of rotor earth capacitance Copyright © Siemens Australia & NZ 2007. All rights reserved.

Disturbances by the excitation generator Siemens. Innovation for generations.

Generator with Rotating Excitation Test Condition with a Fault Resistor Fault resistance is inverse proportional to the difference voltage

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