Distance Principles_basic Principle

7/29/2019 Distance Principles_basic Principle

1/76

GRID

Technical Institute

This document is the exclusive property of Alstom Grid and shall not be

transmitted by any means, copied, reproduced or modified without the priorwritten consent of Alstom Grid Technical Institute. All rights reserved.

Distance Protection


2/76

Distance Protection - P 2

Distance Protection

Popular, widely used on Sub-Transmission and Transmission

Systems

Virtually independent of Fault Current Level (ZS/ZL ratios)

Fast Discriminative Protection:- Zone 1 or Aided Distance Scheme

Time Delayed Remote Back-Up


3/76


Advantages of Distance Protection

Measures Z, X or R correctly irrespective of System

Conditions

Compare this with Instantaneous Overcurrent Protection:-


4/76



F1

115kV 50

IF1

ZS = 10 ZS = 10

ZL = 4

IF1 = 115kV/3(5+4) = 7380A Is > 7380A


5/76



Consider with one source out of service:-

IF2 = 115kV/3 x 10 = 6640A

Is 7380A - IMPRACTICAL

F2

50

IF2

ZS = 10


6/76


Simplified Line Diagram

XL = jL XC = -jC

at FN (50Hz) XC = large :-

LR R R RLLL

CCC

RL


7/76Distance Protection - P 7

Basic Principle of Distance Protection

ZLZS

Generation

Distance

Relay

IR

21 VR



Impedance Seen By Measuring Element

jX

ZL

R




LOADLR

RR ZZ

VZmeasuredImpedance

Relay

PT.

Normal

Load

IR ZLZS

VRVS ZLOAD




Ppp

Ppp

PppFault

IRZS

VRVS ZLOAD

ZL

ZF

Impedance Measured ZR = VR/IR = ZF

Relay Operates if ZF < Z where Z = setting

Increasing VR has a Restraining Effect VR calledRestraining Voltage

Increasing IR has an Operating Effect



Plain Impedance Characteristic

jX ZL

R

TRIP STABLE

Impedance Seen At

Measuring Location For

Line Faults



Impedance Characteristic Generation

Operate

IF

VF

Restrain

Spring

Trip

zF

Ampere Turns : VF IZ

Trip Conditions : VF < IFZ

jIX

IZV1V2

V3

IR

TRIP STABLE

Voltage to Relay = VCurrent to Relay = I

Replica Impedance = Z

Trip Condition : S2 < S1

where : S1 = IZ ZS2 = V ZF




Relays are calibrated in secondary ohms :-

RATIOV.T.

RATIOC.T.xZZ

/VV

/x

V

/x

/VVxV/VZ

PR

21

21

FP

FP

12FP

12FPRRR

IR

21 VR

I1/I2 ZP

V1

V2VFP



Example

ZP = 4; V1/V2 = 115kV/115V; I1/I2 = 600/5A

ZR(5) = 4 x (600/5) / (115x103/115) = 0.48 - 5A Relay

ZR(1) = 2.4 - 1A Relay

C.T. RATIOZR = ZP x

V.T. RATIO



Input Quantities for-Faults

FAULT VRESTRAINT IOPERATE

A - B VA - VB IA - IB

B - C VB - VC IB - IC

C - A VC - VA IC - IA

VRESTRAINT & IOPERATE are selected inside the relayNo setting adjustments are required apart from

Z1 = Phase Replica Impedance



Input Quantities for-Faults (1)

VR1 = E - I1ZS1 = 2I1{ZS1 + ZL1} - I1ZS1

= I1ZS1 + 2I1ZL1

VR2 = - I2ZS2 = I1ZS1

VRB = a2VR1 + aVR2 = a2{2I1ZL1 + I1ZS1} + aI1Zs1

VRC = aVR1 + a2VR2 = a{2I1ZL1 + I1ZS1} + a

2I1ZS1

IRB = a2I1 aI1 = (a

2 a)I1

IRC = aI1 a2

I1 = (a a2

)I1

ZS1 I1

I2

F1

N1

F2

N2

ZL1

ZS2 ZL2

IR1

IR2

vR2

vR1

E


17/76


Consider a B-C Fault

VR1 = E - I1ZS1 = 2I1 {ZS1 + ZL1} - I1ZS1

= I1ZS1 + 2I1ZL1

VR2 = -I2ZS2 = I1ZS1

VRB = a2

VR1 + aVR2 = a2

{2I1ZL1 + I1ZS1}+ aI1ZS1

VRC = aVR1 + a2VR2 = a{2I1ZL1 + I1ZS1}

+ a2I1ZS1

IRB = a2I1 - aI1 = (a

2-a)I1

IRC = aI1 - a2I1 = (a-a

2)I1

ZL1ZS1

E

I1

F1

ZL1

ZS1 IR1

VR1

N1

I2

F2

ZL2ZS2 IR2

VR2

N2


18/76


Using VRB & IRB to Obtain ZRB

( ) ( )( ) ( ) ( )( )

S1L1S1L1

S12

2

L12

2

1

2

S112

L112

RB

RBRB

Z.903

1Z.30

3

2Z.

903

1801Z.

903

2401.2

Z.aa

aaZ.aa

2a

IaaZIaaZ2Ia

IVZ

---

-

-

-

Relay Will Not Measure The Same Impedance Under

All Conditions If V/N And I Are Used

ZS1 Is a Variable Factor


19/76


Correct Measurement for B-C Faultby Using VBVC & IB-IC

VB-VC = (a2-a) . (2I1ZL1 + I1ZS1) + (a-a

2)I1ZS1

IB - IC = 2(a2 - a)I1

ZRB = (VB-VC)/ (IB - IC) = ZL1 + ZS1/2 - ZS1/2

= ZL1

The relay can be calibrated in terms of the positive

sequence impedance of the protected line.

Distance relays are designed to use VBC & IBC and will

automatically take them from the connected 3voltages and currents.


20/76


Input Quantities for Phase to Earth Faults

FAULT VRESTRAINT IOPERATE

A - E VA ? IA ?

B - E

C - E


21/76


Neutral Impedance Replica Vectorial Compensation

Replica impedance circuit :-

Z1IRA

I

RN

IZN

Z1

N

Z1

ZN

Z1 = Phase replica impedance

ZN = Neutral replica impedance

IRA passes through Z1

IRN passes through ZN

ZT = Z1 + ZN


22/76


Neutral Impedance Compensation

For a single phase to ground fault the total earth loop

impedance is given by :- (Z1 + Z2 + Z0)/3 = ZT

ZT = (Z1 + Z2 + Z0)/3 = Z1 + ZN

ZN = (Z1 + Z2 + Z0)/3 - Z1

= (2Z1 + Z0)/3 - Z1

= - Z1 + Z0

= KN Z1

3 3

where KN = (Z0 - Z1)

3Z1


23/76


Neutral Impedance Vectorial Replica Compensation

Line CTs

A

ZPH

B

C

IAZPH

ZPH IBZPH

ZPH ICZPH

ZN INZN

Set ZPH = ZF1

Set ZN = (ZF0- Z F1)

3

Usually ZN = ZPH for OHLs


24/76


Neutral Impedance Replica Compensation

For cables Z0Z1VECTORIAL COMPENSATION MUST BE USEDKN = Z0 - Z1 = KNN

3Z1


25/76


Neutral Impedance Replica Vectorial Compensation

Vectorial compensation allows forZNZPH which isespecially important for cable distance protection where

ZN < ZPH and ZN is sometimes negative.

ZE = Earth-loop impedance

for - earth fault on acable

jX

R

ZE

ZPHZN


26/76

GRIDTechnical Institute



Characteristics


27/76


Distance Characteristics

MHOR

Zn

jXjX

R

Zs

Zn

CROSS-

POLARISED

MHO

QUADRILATERAL

Zn

R

OFFSET

MHO

jX

Zn

Zn

R

IMPEDANCE

jX

ZnR

LENTICULAR

jX

ZnR

POLYGON

Zn

R


28/76


Self Polarised Mho Relays

Very popular characteristic

Simple

Less sensitive to power swings

Inherently directional

Operates for F1, but not for F2

Mho = 1/OHM

Settings :-

Z = reach setting

= characteristic angle

jX

R

F2

F1

Z

OPERATE

RESTRAIN


29/76


Offset Mho Characteristic

Normally used as backup

protection

Operates for zero faults

(close up faults)

Generally time delayed (as

not discriminative)

jX

R

Z

-Z


30/76


Mho Relays

Directional circular characteristic obtained by introducing VPOLARISING

VF self polarised V

SOUND PHASE

fully cross-polarised

VF + xVS.F. partially cross-polarised VPRE-FAULT memory polarised

Purpose for this is to ensure operation for close up faults where

measured fault voltage collapses


31/76


Quadrilateral Characteristic

Z

jX

ZR

RR

Load

L

1

F

S


32/76


Lenticular Load Avoidance Characteristic

jIX

IR

ba

Lenticular characteristiccreated from two offset

Mho comparators

Aspect ratio = a/b


33/76


Lenticular Characteristic

X

R

a

b

Z3

Aspect ratios a/b

0.41

0.67

1.00

Load impedancearea

Z3 reverse


34/76


Forward Offset Characteristic

Z3

Z2

Z1

Rf

X

R

Load area

Forward blinder

Enhanced resistive coverage for remote faults


35/76




Zones of Protection


36/76


Z2A Z2C

Z3A Z3C

Time

T3

T2

Z1CZ1A

Z1B DCA

Z2B

T2

Z1A = 80% of ZAB (inst.)

Z2A = 120% of ZAB (~300ms)

Z3A(FORWARD) = 120% of {ZAB + ZCD} (~600ms)

Z3A(REVERSE) = 10-25% of ZAB

B

Zones of Protection


37/76


RA

D

C

B

Z1A

Z2A

Z3A

jX

Zones of Protection


38/76


FAST OPERATION

Trips circuit breaker without delay as soon as

fault within Zone 1 reach is detected.

REACH SETTING

Cannot be set to 100% of protected line or may

overreach into next section.

Overreach caused by possible errors in :-

CTs

VTs

ZLINE information

Relay Measurement

Zone 1


39/76


PossibleOverreach

ZONE 1 = ZL

ZL

F

ZONE 1 = 0.8ZL

ZL

Possible incorrect tripping for fault at F

Zone 1 set to 0.8ZL

Zone 1


40/76


Z1C = 0.8ZACA

C

Z1A = 0.8ZABZ1B = 0.8ZBA

B

Z1C

Z1AZ1B

Zone 1 Settings for Teed Feeders


41/76


Z1AReceiveSend

Trip B

Z1BReceive Send

Z1B

Z1A

ZLA

B

Zone 1 Settings for Direct Intertrip Schemes



42/76



Effective Zone 1 reaches at A and B must overlap.

Otherwise :- No trip for fault at F

Effective Z1A and Z1B must be > 0.5ZL

Settings for Zone 1 > 0.8ZL are o.k.

Z1B

Z1A

F

A

B

Minimum Zone 1 Reach Setting


43/76


Minimum Zone 1 Reach Setting

Dictated by :-

Minimum relay voltage for fault at Zone 1reach point to ensure accurate measurement.

Minimum voltage depends on relay design typically 1 3 volts.


44/76


SIR = ZS/Zn

where :- ZS = Source impedance behind relay

Zn = Reach setting

VRPA

= Minimum voltage for reach point accuracy

Can be expressed in terms of an equivalent value

of SIRMAX

SIRMAX = ZS MAX

Zn MIN

Zn MIN ZS MAXSIRMAX

System Impedance Ratio :- SIR


45/76


Covers last 20% of line not covered by Zone 1.

Provides back-up protection for remote busbars.

To allow for errors :-

Z2G > 1.2 ZGH

Zone 2 is time delayed to discriminate with Zone 1 on next

section for faults in first 20% of next section.

Z1H

Z2G

TIME

Z1G

G H

F

Zone 2


46/76


Overlap only occurs for faults in first 20% of following line.

Faults at F should result in operation of Z1H and tripping of circuit breaker H.If H fails to trip possible causes are :-

Z1H operates but trip relays fail.

Z2H may operate but will not trip if followed by the same trip relays.

Z1H and trip relays operate but circuit breaker fails to trip.

Fault must be cleared at G by Z2G.

Zone 2 on adjacent line sections are not normally time graded

with each other

Z1G Z1H

Z2G Z2H

HG

F

Zone 2


47/76


No advantage in time grading Z2G with Z2H

Unless Z2H + trip relays energise a 2nd circuit breaker trip

coil.

Zone 2


48/76


Z1H fails to operate.

Results in race between breakers G and H if Z2H and Z2Ghave the same time setting.

Can only be overcome by time grading Z2G with Z2H.

Problem with this :-Zone 2 time delays near source on systems with several line

sections will be large.

End zone faults on lines nearest the infeed source point will be

cleared very slowly.

Z1G Z1H

Z2G

Z2H

HG

Zone 2

Maximum Allowable Zone 2 Reach to Allow for


49/76


Z2A must not reach beyond Z1B

i.e. Z2A(EFF) MAX must not reach further than Z1B(EFF) MIN

Z1BSETTING = 0.8ZL2

Z1B(EFF) MIN = 0.8 x 0.8ZL2 = 0.64ZL2 Z2A(EFF) MAX < ZL1 + 0.64ZL2

1.2 Z2ASETTING < ZL1 + 0.64ZL2

Z2ASETTING < 0.83ZL1 + 0.53ZL2

Z2A(EFF) MAX

Z1B(EFF) MIN

ZL2ZL1BA

Maximum Allowable Zone 2 Reach to Allow forEqual Zone 2 Time Settings

Zone 2 Time Settings on Long Line Followed by


50/76


Z3H

Z2G

Z3J

Z2H

Z2J

Z1H Z1JZ1G

H JG

F

Z2G reaches into 3rd line section.

To limit remote back-up clearance for a fault at F, the time

setting of Z2G must discriminate with Z3H.

Zone 2 Time Settings on Long Line Followed bySeveral Short Lines


51/76


HG K

Z1G Z1H

Z2G

Z3G

REV Z3G FWD

Time

Typical settings : Z3FWD > 1.2 x (ZGH + ZHK)

Z3REV 0.1 to 0.25 of Z1G

Zone 3

Provides back-up for next adjacent line.

Provides back-up protection for busbars (reverse offset).

Actual Zone 3 settings will be scheme specified, i.e. permissive orblocking schemes.

Many modern relays have more than 3 Zones to allow the use of three

forward and an independent reverse zone.


52/76


Zone 1 :- tZ1 = instantaneous (typically 15 - 35mS)

Zone 2 :- tZ2 = tZ1(down) + CB(down) + Z2(reset) + Margin

e.g. tZ2 = 35 + 100 + 40 + 100 = 275mS

Zone 3 :- tZ3 = tZ2(down) + CB(down) + Z3(reset) + Margine.g. tZ3 = 275 + 100 + 40 + 100 = 515mS

Note: Where upper and lower zones overlap, e.g. Zone 2 up

sees beyond Zone 1 down, the upper and lower zone

time delays will need to be coordinated, e.g. tZ2(up) to

exceed tZ2(down).

Zone Time Coordination - Ideal Situation


54/76


Impedance presented > apparent impedance

%age Underreach = ZR - ZF x 100%

ZR

where ZR = Reach setting

ZF = Effective reach

Under-Reach

Underreaching Due to Busbar Infeed between


55/76


IA IA+IB

Relay LocationIB

ZA ZB

VR = IAZA + (IA + IB) ZB

IR =

IA

ZR = ZA + ZB + IB . ZB

IA

Underreaching Due to Busbar Infeed betweenRelay and Fault

Underreaching Due to Busbar Infeed between


56/76


Relay with setting ZA + ZB will underreach withinfeed.

Relay with setting ZA + ZB + IB . ZB will measure

IAcorrectly with infeed present but if infeed is removed the

relay will overreach.

Maximum allowable setting dictated by load impedance

Underreaching Due to Busbar Infeed betweenRelay and Fault

U d R h


57/76


IP

What relay reach setting is required to ensure fault at F is at

boundary of operation ?

Impedance seen for fault at F

= ZG + IG + IP . ZKIG

Limit of operation is when Impedance Seen = Reach Setting

Reach setting required= ZG + IG + IP . ZK

IG

ZK FIG+IP

ZG IG

RELAY

Under-Reach

O R h


58/76


Impedance seen < apparent impedance

%age Overreach = ZF - ZR x 100%

ZR

where ZR = Reach setting

ZF = Effective reach

Over-Reach


59/76





Mutual Coupling

M t l C li


60/76


Mutual Coupling

Mutual coupling causes distance relays to eitherunderreach or overreach.

Positive and negative sequence has no impact.

Zero sequence mutual coupling can have a significantinfluence on the relay.

Only affects ground fault distance.

M t l C li E l U d R h


61/76


Z2 Boost G/F

Z2 PH

Zmo

Mutual Coupling Example Under Reach

M t al Co pling E ample O er Reach


62/76


Z2 reduced G/F

Z2 PH

Mutual Coupling Example Over Reach



63/76


Z1 G/F (optional)

Z1 G/F (normal)

Zmo



64/76





Ancilliary Functions

Switch on to Fault (SOTF)


65/76


X

X

X

Switch on to Fault (SOTF)

Fast tripping for faults on line energisation, even where

line VTs provide no prefault voltage memory

Voltage Transformer Supervision


66/76


Voltage Transformer Supervision

A VT fault and subsequent operation of VT fuses or MCBs results inmisrepresentation of primary voltages

Relay will remain stable as the current phase selector will not pick up

Subsequent system fault may cause unwanted / incorrect tripping

VTS operating from presence of V0 with no I0 or V2 with no I2 is usedto block relay if required

VT Supervision


67/76


VT Supervision

Under load conditions

Loss of 1 or 2 phase voltages Loss of all 3 phase voltages

Upon line energisation Loss of 1 or 2 phase voltages Loss of all 3 phase voltages

Digital input to monitor MCB

Set to block voltage dependent functions

Zone 1 Mho Relay


68/76


Will not operate for load or

stable power swing

1, 2, 3, = Anglesbetween system voltagesat K and L

increases as power

swingapproaches relay at G

J is point where power swingenters relay characteristic

At J the angle between

voltages at G & H is 90

Normal limit of angle betweenvoltages at G & H for

load is ofthe order of 30

L

K

ZS

HH

Z13 J

G

ZS

G

1

Power Swing Locus

2 LOA

D

Zone 1 Mho Relay

Comparison between Stability of Mho and Quadrilateral


69/76


p yImpedance Elements during a Power Swing

jX

PowerSwingLocus

R

Illustration of Basic Power Swing


70/76


jX

Power SwingLocus

R

Z3

ZP

Blocking System

Power Swing Blocking


71/76


A power swing will result in continuous change of current

Continuous output from the relay superimposed current element canbe used to block for a power swing

Using this method the relay is able to operate for faults occurringduring a power swing

Power Swing Blocking

Directional Earth Fault Protection (DEF)


72/76


High resistance ground faults

Instantaneous or time delayed

IEC and IEEE curves

Single or shared signalling channel

Directional Earth Fault Protection (DEF)


73/76





Transformer Feeders

Transformer Feeders


74/76


Zone 1 = ZL + 0.5ZT

T1 = Instantaneous

Zone 2 = 1.2 (ZL +ZT)

T2 = Co-ordinate with downstream protection

Zone 3

T3- Back-up use as appropriate

ZL

ZT

21

Transformer Feeders

Low Voltage VT High Voltage CT


75/76


Low Voltage VT, High Voltage CT

* 1 VT may be required to account for phase shift.

Example 1

ZT = 10 , ZL = 1

Set relay Z1 = 0.8 x (ZT + ZL) = 8.8

Z1 does not reach through transformer.

Example 2

ZT = 10 , ZL = 1

Z1 = ZT + 0.8ZL = 10.8

with 20% error = 12.96 - overreach problem

ZT

21

ZL


76/76


Date post:	03-Apr-2018
Category:	Documents
Upload:	manu2020
View:	216 times
Download:	0 times

Distance Principles_basic Principle

Documents