7um62_rotor earth fault protection

The year of Profitable Growth

Global network of innovation

Rotor-Earth-Fault Protection

Power Automation 2

Power Transmission and Distribution

Power AutomationProgress. It‘s that

simple.

Presenter:Dr. Hans-Joachim Herrmann

PTD PA13

Phone +49 911 433 8266

E-Mail: [email protected]

Generator Protection

Rotor-Earth-Fault Protection

Power Automation 3



simple.

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

Power Automation 4



simple.

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

Power Automation 5



simple.

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

Power Automation 6



simple.

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)

Power Automation 7



simple.

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

Power Automation 8



simple.

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

Power Automation 9



simple.

Earth Current Criterion Logic

Power Automation 10



simple.

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.)

Power Automation 11



simple.

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

Power Automation 12



simple.

Earth Fault Resistance CalculationLogic

Power Automation 13



simple.

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)

Power Automation 14



simple.

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

Power Automation 15



simple.

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

Power Automation 16



simple.

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:

Power Automation 17



simple.

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

Power Automation 18



simple.

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

Power Automation 19



simple.

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

Power Automation 20



simple.

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

Power Automation 21



simple.

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

Power Automation 22



simple.

Generator with Rotating ExcitationFault Free Condition (Square Wave Principle)

Chance of charge ofrotor earth capacitance

Disturbances by the excitation generator

Power Automation 23



simple.

Generator with Rotating ExcitationTest Condition with a Fault Resistor

Fault resistor is inverse proportional to the difference voltage

Power Automation 24



simple.

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

Power Automation 25



simple.

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

Power Automation 26



simple.

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

7um62_rotor earth fault protection

Documents