04 Rotor Ground Fault Protection

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Rotor-Ground-Fault Protection

Power Automation 2

Power Transmission and Distribution

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Presenter: Dr. Hans-Joachim Herrmann PTD PA13Phone +49 911 433 8266E-Mail: [email protected]

Generator ProtectionRotor-Ground-Fault Protection

Power Automation 3



Requirement for Rotor Ground Fault Protection

? in case of a ground fault, only small currents flow due to the galvanic isolation

Problem:Double ground faults and interturn faults as a consequence of an ground fault cause:• magnetically unbalance (unbalanced forces; violent vibration)• high currents at the fault location

Task: Detection a ground fault already when it starts to build up

? Destruction of the Rotor (Generator)

Ground fault in the rotor

RECE

Rotor

Excitationsystem

+

-Stator

Power Automation 4



Protection Principle

Excitationsystem

+

-

Voltage Source

„Grounding brush “

CouplingUnit

Measuring

- Incoupling of an AC voltage (50 Hz or 60 Hz)- Measuring of the ground fault current- Measuring of the ground fault resistance

- Incoupling of low frequency square wave voltage

Principles:

HigherSensitivity

Power Automation 5



Ground Current CriterionPrinciple (50 Hz/60Hz - Voltage Injection)

Coordinatedresonant circuit to fN

>40V

If disturbance influence from the excitation is too large

IE

Protection

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

L1 L2 L3

IG,Distr.

IG,Fault

4?F105?

0,75H

Connectionon the groundingbrush

Power Automation 6



Ground Current MeasurementConnection

Also IEE2

at 7UM62is possible

IEE1J7J8

1B11B3

1A11A3

+

-

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)

Power Automation 7



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 O

hm

Z f( )

f

mA27k 1,5 170

V 45 I

R ZV

I

fCoupling

????

?

??

Imax approx. 300 mA

Frequency in Hz

Impe

danc

e in

Ohm

Power Automation 8



Ground Current CriterionProtection Settings

Protection with two stages:Measuring circuit supervision

mA23k 1,5 400

V 45 I

R ZV

I

fCoupling

????

?

??

ZCouplingl(50Hz) = 400?

ZCouplingl(60Hz) = 335?

Imax approx. 100 mA

(voltage source decreases a little bit )

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

Power Automation 9



Ground Current Criterion Logic

Power Automation 10



Calculation of the Ground 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.)

Power Automation 11



Calculation Formula of the Ground 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

EK2

EE

2EE

V

- - j

2

ersXR

XR*X

XR

XR*RZ

? ? Km2E

2E

E2

E -

, *XZXRXR

X I???

?

? ?? ?? ? ? ? V

Ve

2Km

2

E - e - - -

, ,,

*RZR*RZR*XZ

RRX

R ????I

Power Automation 12



Ground Fault Resistance CalculationLogic

Power Automation 13



Ground 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)

Power Automation 14



Injection of Square Wave Voltage with Low FrequencyBasic Diagram

Excitation

+

-CE

RE

Digital Protection (7UM62)

VH

RV

RV

Vcontrol

Vmeas.RM

7XR6004

Controlling device(7XT71)IE

Measuring transducer

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

Typical frequency:1 - 3 Hz

Power Automation 15



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

TD1K14K13 +

TD2K16

K15 +

40 k?

40 k?

Control voltage

Measuring voltage

100 V110 V

120 V

9

7

Power Automation 16



Injection of Square Wave Voltage with Low FrequencyBasic Principle

RV2

RECEVH

VMRM

VH

VM

VM

50V

- 50V

1,88V

- 1,88V

0,75V

- 0,75V

t

t

t

iE

50V

375

20k 2

H

M

V

????

??

U

R

REMM iRU ??

?? ER

?? 5k ER

0 M ?? UE

V 2

CR

???

EM

1 ~ R

U?

Equivalent circuit:

Power Automation 17



Sources of Error and Error Compensation

Influence of field voltage and ground fault location

a) Ground 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

Vdc = dc voltage shifting

Solution:Calculation of the difference voltage

? V = |VM1 - VM2|

? V1 = |VM1 - VM2| ? V3 = |VM3 - VM4|? V2 = |VM2 - VM3|

Solution:Block of measuring at jumps (e.g. ? V1 = ? V2)

VM

VdcVdc1

VM1

VM2

VM3VM4

VM1 VM2 Vdc2

VM

Power Automation 18



Calculation Formulas

RECEVH

VMRM

RV

2

VM V1

V2

Algorithm

Voltage divider:

Filtering:

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

2- 1 -

2 V

MM

HE

M

MEV

M

H RR

VV

RR

RRR

VV

???

????

??

???

????

??NN

vN

VvN

V1 i

i2,2

1 ii1,1

1 ;

1

2 -

: : 21M

VVV ??? V

1KK I I ???? VV

??

???8

1 k k

81

VV0 30 60 90 120150180210240 270 300

0.001

0.01

0.1

1

f in Hz

G(f)

Continuity supervision:

Validity requirement

otherwise

Power Automation 19



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

Power Automation 20



Rotor Ground 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

Power Automation 21



Connection of the Rotor Ground Fault Protection

GRW RE

CE

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?

Power Automation 22



Generator with Rotating ExcitationFault Free Condition (Square Wave Principle)

Chance of charge ofrotor ground capacitance

Disturbances by the excitation generator

Power Automation 23



Generator with Rotating ExcitationTest Condition with a Fault Resistor

Fault resistor is inverse proportional to the difference voltage

Power Automation 24



Parallel Operation of Rotor Ground Fault Protections

100V 42V

CK;4µF

CK;4µF

RK;105?

RK;105?RV;40k?

RV;40k?

RE

7UM62 7UM62VControl

VMeas.

iREF

uREF

7UM61

nuriREF

or

1- 3 Hz principle 50 Hz principle

Power Automation 25



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

( )?20k 2

RV

*KR *KC

ER

2 ll : * V

EER

RR ?

???

??

20k 2

*

VE

E

RR

R

????

4k *

5k

E

E

R

R

Measurement 7UM61 or 7UM62(RV is grounded for an AC voltage)

Equivalent circuit:

seen from the 7UM6, RV alreadyis interpreted as a rotor-to-groundresistance

Measurement:

measured as a fault resistance

Case 1:

Case 2:

alarm stage becomes less sensitive

? open brushes can not be find out

Power Automation 26



RV

2

RERM2CK(8µF)

Vmeas

? V2

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

Equivalent circuit:

? seen from the 7UM6:high rotor capacitance

? capacitors will not becompletely loaded

? ? V ~ RE-1

under no-ground-fault conditions a fault resistance is already measured

? alarm stage becomes less sensitive (approx. 50k? )

? longer measuring time

Parallel Operation of Rotor Ground Fault ProtectionsMeasurement with the Square Wave Principle

Documents

04 Rotor Ground Fault Protection