04 rotor earth fault protection

8/7/2019 04 Rotor Earth Fault Protection

http://slidepdf.com/reader/full/04-rotor-earth-fault-protection 1/17

Rotor-Earth-Fault Protection



Copyright © Siemens Australia & NZ 2007. All rights reserved. Siemens. Innovation for generations.

Requirement for Rotor Earth Fault Protection

⇒ 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

Task: Detection an earth fault already when it starts to build up

⇒ Destruction of the Rotor (Generator)

Earth fault in the rotor

R EC E

Rotor

Excitation

system

+

-Stator




Protection Principle

Excitationsystem

+

-

Voltage

Source

„Earthing brush “

CouplingUnit 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:HigherSensitivity




Earth Current Criterion

Principle (50 Hz/60Hz - Voltage Injection)

Coordinatedresonant 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

I E,Distr.

I E,Fault

4µF105Ω

0,75H

Connectionon the earthingbrush




Earth Current Measurement

Connection

Also IEE2

at 7UM62

is

possible

IEE1

J7

J8

1B1

1B3

1A1

1A3

+

-

4A1

4B1

3PP1336Err.

2B1

7UM6

Connection on the

phase to phasevoltage

7XR61

100 V - 125 V AC

105Ω

105Ω

AC VoltageSource

appr. 42V or65V

Documentation for Coupling Device in the Internet

www.siprotec.com

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




Calculation of the Fault ResistanceR E

(50Hz/60Hz- Voltage Injection)

100V 42V u

Digitalprotection(7UM62)

calculationof RE

RE

C E

R V C K

R V C K

L1 L2 L3

iL1)

1) Recommendedat static excitationwith inject harmonics

(3rd harm.; 6th harm.)




Calculation Formula of the Fault ResistanceR E

(1) (2)

(3)

(4)

combining (3) and (4):

Note: R V* and X K* are measured during commissioning

Model:

Zers ZMess Z

X*K R*V

X E

RE

VE2

E

2

E

2

EE *R - , Z R X R

X R R =

+⋅=

Z Z R Z j meMess I +=

++

++=

2E

2

E

E

2

EK

2

EE

2

EEV

- - j

2

ers

X R

X R * X

X R

X R * R Z

Km2

E

2

E

E

2

E - ,* X Z

X R

X R X I =

+

⋅=

( )

V

Ve

2

Km2

E - e -

- - , ,

, * R Z R

* R Z R

* X Z R

R

X R +=+=

I




Injection of Square Wave Voltage with Low Frequency Basic

Diagram

Excitation

+

-C E

R E

DigitalProtection

(7UM62)

U H

R V

R V

U control

U meas.R M

7XR6004

Controlling device(7XT71)

I E

Measuringtransducer

R E Fault resistanceR V Coupling resistorU H Auxiliary supply ( ± 50V)R M Measuring shunt resistorC E Rotor capacitance

Typical frequency:1 - 3 Hz




Injection of Square Wave Voltage

Connection Diagram (7UM62)

Connection on thephase to phasevoltage

Exc.17

15

11

25

+

-

27

7XR600425

27

7UM62

7XT71

TD1K14

K13 +

TD2K16

K15 +

40 k Ω

40 k Ω

Control voltage

Measuring voltage

100 V

110 V

120 V

9

7




Injection of Square Wave Voltage with Low Frequency

Basic Principle

RV

2

R EC EUH

UMRM

U H

U M

U M

50V

- 50V

1,88V

- 1,88V

0,75V

- 0,75V

t

t

t

iE

50V 375

20k 2

H

M

V

±=Ω=

Ω=

U

R

R

EMM i R U ⋅=

∞= ER

Ω≈5k E

R

0 M ≈∆U

EV

2 C R

⋅≈τ

E

M 1 ~ R

U ∆

Equivalent circuit:




Sources of Error and Error Compensation

Influence of field voltage and earth fault location

a) Earth fault location

Shifting of measuring voltage witha positive or negative dc voltage

b) Jumps in the field voltage

a change in the field voltage takesto 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. ∆∆∆∆U1≠∆∆∆∆U2)

U M

U dc

U dc1

U M1

U M2

U M3U M4

U M1 U M2 U dc2

U M




Calculation Formulas

R EC EU H

U MR M

R V

2

UMU 1

U 2

Algorithm

Voltage divider:

Filtering:

Amplitude-log frequency curve: fA = 800 Hz; N = 64

2- 1 - 2 V

M

M

HE

M

MEV

M

H R R U U R

R

R R R

U U

=

++

=

∑=∑===

N N

u N

U u N

U 1 i

i2,21 i

i1,1 1 ; 1

2

- : :

21

M

U U U U =∆=

1KK I I +∆≈∆ U U

∑∆=∆=

8

1 k

kU

8

1 U

0 30 60 90 120150180210240 270300

0.001

0.01

0.1

1

f in Hz

G(f)

Continuity supervision:

Validity requirement

otherwise




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




Rotor Earth Fault Protection (1-3Hz)

Setting Values

Measuring circuit supervision

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

Advanced parameteronly visible in DIGSI




Connection of the Rotor Earth Fault Protection

GRW

REC E

EM

EX-TL+

RWUG

REC E

L-

(50/60 Hz)

(1 - 3 Hz)

(50/60 Hz)

(1 - 3 Hz)

40kΩΩΩΩ

4µF

4µF

a) rotating diodes

b) separate Exciter(static excitation)

40kΩΩΩΩ




Generator with Rotating Excitation

Fault Free Condition (Square Wave Principle)

Chance of charge of

rotor earth capacitance

Disturbances by the

excitation generator




Generator with Rotating Excitation

Test Condition with a Fault Resistor

Fault resistance is inverse proportional to the difference voltage

04 rotor earth fault protection

Documents