7um62_rotor earth fault protection

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Rotor-Earth-Fault Protection

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Presenter:Dr. Hans-Joachim Herrmann

PTD PA13

Phone +49 911 433 8266

E-Mail: Hans-Joachim.Herrmann@siemens.com

Generator Protection

Rotor-Earth-Fault Protection

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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

RECE

Rotor

Excitationsystem

+

-Stator

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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

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Earth Current CriterionPrinciple (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

IE,Distr.

IE,Fault

4F105

0,75H

Connectionon the earthingbrush

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Earth Current MeasurementConnection

Also IEE2 at 7UM62is possible

IEE1

J7

J8

1B1

1B3

1A1

1A3

+

-

4A1

4B1

3PP1336Err.

2B1

7UM6

Connection on the phase to phase voltage

7XR61

100 V - 125 V AC

105

105

AC VoltageSourceappr. 42V or65V

Documentation for Coupling Device in the Internetwww.siprotec.com

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

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Gain Characteristic of the R, C, L-Circuit

Z 50( ) 169.65 Z 60( ) 69.531

0 50 100 150 200 250 3000

500

1000

1500

2000Filterverhalten Bandpaß

Frequenz in Hz

Impe

danz

in

Ohm

Z f( )

f

mA27k 1,5 170

V 45 I

R Z

U I

fCoupling

Imax approx. 300 mA

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Earth Current CriterionProtection Settings

Protection with two stages:Measuring circuit supervision

mA23k 1,5 400

V 45 I

R Z

U I

fCoupling

ZCouplingl(50Hz) = 400

ZCouplingl(60Hz) = 335

Imax ca. 100 mA

(voltage source decreases a little bit )

Note: Coupling impedance only with R and CFinally setting during commissioning

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Earth Current Criterion Logic

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Calculation of the Fault Resistance RE

(50Hz/60Hz- Voltage Injection)

100V 42V u

Digitalprotection(7UM62)calculationof RE

RE CE

RV CK

RV CK

L1 L2 L3

iL1)

1) Recommendedat static excitationwith inject harmonics(3rd harm.; 6th harm.)

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Calculation Formula of the Fault Resistance RE

(1) (2)

(3)

(4)

combining (3) and (4):

Note: RV* and XK* are measured during commissioning

Model:

Zers ZMess Z

X*K R*V

XERE

VE2

E2

E

2EE *R -

, ZR

XR

XRR

ZZRZ j meMess I

2E

2E

E2

EK

2EE

2EE

V

- - j

2

ersXR

XR*X

XR

XR*RZ

Km2E

2E

E2

E -

, *XZ

XR

XRX I

V

Ve

2Km

2

E - e -

- - , ,

, *RZR

*RZR

*XZR

R

XR

I

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Earth Fault Resistance CalculationLogic

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Earth Fault Resistance CalculationSettings

Measured during commissioning

Measuring circuit supervision

Measured current can be influenced by disturbancesCorrection during primary test,(in most case the alarm stage is concerned)

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Injection of Square Wave Voltage with Low Frequency Basic Diagram

Excitation

+

-CE

RE

Digital Protection (7UM62)

UH

RV

RV

Ucontrol

Umeas.RM

7XR6004

Controlling device(7XT71)IE

Measuring transducer

RE Fault resistanceRV Coupling resistorUH Auxiliary supply ( 50V)RM Measuring shunt resistorCE Rotor capacitance

Typical frequency:1 - 3 Hz

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Injection of Square Wave Voltage Connection Diagram (7UM62)

Connection on the phase to phase voltage

Exc.17

15

11

25

+

-

27

7XR600425

27

7UM62

7XT71

TD1K14

K13 +

TD2K16

K15 +

40 k

40 k

Control voltage

Measuring voltage

100 V110 V

120 V

9

7

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Injection of Square Wave Voltage with Low FrequencyBasic Principle

RV

2

RECEUH

UMRM

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

EMM iRU

ER

5k ER

0 M UE

V 2

CR

EM

1 ~ R

U

Equivalent circuit:

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Sources of Error and Error Compensation

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. U1 = U2)

UM

Udc

Udc1

UM1

UM2

UM3UM4

UM1 UM2 Udc2

UM

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Calculation Formulas

RECEUH

UMRM

RV

2

UM U1

U2

Algorithm

Voltage divider:

Filtering:

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

2- 1 -

2 V

MM

HE

M

MEV

M

H RR

U

UR

R

RRR

U

U

NNu

NUu

NU

1 ii2,2

1 ii1,1

1 ;

1

2

- : :

21

M

UUUU

1KK I I UU

8

1 kkU

8

1 U

0 30 60 90 120150180210240270300

0.001

0.01

0.1

1

f in Hz

G(f)

Continuity supervision:

Validity requirement

otherwise

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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

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

Advanced parameteronly visible in DIGSI

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Connection of the Rotor Earth Fault Protection

GRW

RECE

EM

EX-TL+

RWUG

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

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Generator with Rotating ExcitationFault Free Condition (Square Wave Principle)

Chance of charge ofrotor earth capacitance

Disturbances by the excitation generator

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Generator with Rotating ExcitationTest Condition with a Fault Resistor

Fault resistor is inverse proportional to the difference voltage

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Parallel Operation of Rotor Earth Fault Protections

100V 42V

CK;4µF

CK;4µF

RK;105

RK;105RV;40k

RV;40k

RE

7UM62 7UM62uControl

uMeas.

iREF

uREF

7UM61

nuriREF

or

1- 3 Hz principle 50 Hz principle

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Parallel Operation of Rotor Earth Fault ProtectionsMeasurement with the 50/60 Hz Principle

( )20k 2

RV

*KR *KC

ER

2 ll : * V

EE

RRR

20k 2

*

VE

E

RR

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 alreadyis interpreted as a rotor-to-earthresistance

Measurement:

measured as a fault resistance

Case 1:

Case 2:

alarm stage becomes less sensitive

open brushes can not be find out

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RV

2

RERM

2CK

(8µF)

Umeas

U2

Measurement 7UM62 (1- 3 Hz)(CK is earthed for a DC voltage)

Equivalent circuit:

seen from the 7UM6:high rotor capacitance

capacitors will not becompletely 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 ProtectionsMeasurement with the Square Wave Principle