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Technical Presentation On

Protection

Distance Protection Basics

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Agenda

1 2 3 4 5 6

Basics Characteristics

Load

Encroachment

Zones of

Protection

Resistive Faults

Remote Infeed

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Principle of Distance Protection

ZK=Uk/ Ik

Uk=0Uk

IkZ<

A B

metallic faultZk

The impedance is proportional to the distance!

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Relay Performance Parameters

Reach Accuracy

• Reach accuracy is a

comparison of the actual

ohmic reach of the relay

under practical conditions

with the relay setting value

in ohms.

• Reach accuracy particularly

depends on the level of

voltage presented to the

relay under fault conditions.

Operating Time

• Operating times vary with

Depending on the

measuring techniques

employed, transient errors

etc.

• Operating Time

Specification is more often

used in electromechanical/

static relays.

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Zones of Protection

Zone-4

•Time Delayed

•Reverse Direction

•10-25% of Zab

Zone-1

•Instantaneous Trip

•Under reaching

•80-85% of Zab

Zone-3

•Time Delayed

•Remote Backup

•120% of ( Zab+Zbc)

Zone-2

•Time Delayed

•Cover adjacent line

•120% of Zab

RA

~~RB

BUS A BUS B BUS CZab Zbc

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Simulation of Zone Trips

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R3

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R1

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R2

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R4R1-Z1

R1-Z2

R1-Z3R2-Z1

R2-Z2

R2-Z3

R3-Z1

R3-Z2

R3-Z3

R4-Z1

R4-Z2

R4-Z3

NORMAL OPERATING CONDITION

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Simulation of Zone Trips

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R3

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R1

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R2

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R4R1-Z1

R1-Z2

R1-Z3R2-Z1

R2-Z2

R2-Z3

R3-Z1

R3-Z2

R3-Z3

R4-Z1

R4-Z2

R4-Z3

FAULT NEAR TO RELAY R1

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Simulation of Tele Transfer Trips

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R3

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R1

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R2

21

-

Z1

21

-

Z2

21

-

Z3

0.2 s

0.6 s

R4R1-Z1

R1-Z2

R1-Z3R2-Z1

R2-Z2

R2-Z3

R3-Z1

R3-Z2

R3-Z3

R4-Z1

R4-Z2

R4-Z3

FAULT NEAR TO RELAY R1

POTT POTT

Rx

Tx

Rx

Tx

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Distance Characteristics

Characteristic Reactance Impedance Mho Quadrilateral

R-X Diagram

Directionality Non directional Non directional Directional Directional

Applications Short Lines where

arc resistance is

the same order of

the line length

Fault Location

purposes.

Operate for Bus

Faults also

Commonly

Used in Long

Lines. Do not

operate for bus

side faults

Commonly used

due to

independent

setting for R

and X Reach

R

X

Operate

Restrain

R

X

Operate

Z

Restrain

R

XOperate

Max sen. Line

Restrain

δ, RCA

R

X

Operate

Restrain

Restrain

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Mapping of Faults in R-X Plane

METALLIC FAULT RF=0

120%

40% 60%

80% 100%

20%

140%

XL

RL R

jX

ZL=RL + jXL

ZL

WITH FAULT RESISTANCE

Distance Proportional to ZL.

ZL

RF

120%

40% 60%

80% 100%

20%

140%

XL

RL R

jX

ZL=RL+RF + jXL

1Ω 2Ω 3Ω 4Ω

•Distance Proportional to RF+ZL.

•RF=RARC + RTOWER FOOTING

The relay measures the sum between line impedance (if fault at 100% of the line) and

the fault resistance

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Quadrilateral Characteristics

R1

R2

R3

R4

R5

Z1

ZN

The Grey region is the impedance

locus we want to cover with the

distance protection characteristic.

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MHO Vs. Quad Characteristics

ZL

X

LOAD

RF

Quad

Rf Mho

Short line

ZL

X

LOAD

Long line

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During Double Infeed

F

A

BFA

A

Am R

I

IRZ

I

VZ FBAAAA RIIIZV

• The fault has more or less fault resistance.

• If the fault is an arcing fault the fault resistance is normally very small.

• The influence of the fault resistance depends on the fault current infeed from the

remote line end.

• The fault resistance seen by the distance protection is increased compared to its

real value. This applies if EA &EB are approximately in phase i.e no load transfer

across the feeder.

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Resistive Fault During Double Infeed

FR

F

A

B RI

I

AZ

UNDERREACH!

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Remote Backup

• Due to fault current contribution substation B (not ”seen” by relay in ”A), the distance

protection in station A will measure a higher impedance than the "true" impedance to

the fault.

• The relay will under reach and this means in practice it can be difficult to get a

remote back-up.

1 2A L A A B B FV Z I I I I Z

Z<

IA IB2

IB1 If=IA+IB1+IB2

ZL

ZFUA

1 2A A B Bm L F

A A

V I I IZ Z Z

I I

In feed Factor

A B

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Load Encroachment

X

Zone 01

Zone 02

Zone 03 Remote back-up

R

Zone 05

Remote fault

that has to be

detected

Zone 04 Remote back-up

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Reduced Resistive Reach

X

Zone 01

Zone 02

Zone 03 Remote back-up

R

Zone 05

Remote fault that has to be

detected. But Can’t Detect due

to reduced Resistive Reach

Setting

Zone 04 Remote back-up

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Customized Reach SettingX

Zone 01

Zone 02

Zone 03 Remote back-up

Zone 04 Remote back-up

R

Zone 05

Remote fault to be detected

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Remote Backup with Load Encroachment

schemeZone 03

Zone 02

Zone 01

Zone 04

The green area represents the load encroachment area and “cuts” any impedance

protection that might enter in it

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Any Questions???