Introduction to Distance Protection

J. Gosalia

Protection Types

Differential protection

Tfr., Bus, Gen. & line diff. protection

Pilot protection

Transfer trip schemes

Under/over reaching pilot protection

Unit Protection

Over Current protection

Time over current or inst. protection

3 Zones of distance protection

Non-Unit protection

Unit Protection

Protection

In Zone fault protection

No protection for fault outside the zones

Non-Unit Protection

A B DC

Distance

Tim

e

Zone 1 Protection : line AB

Zone 2 & 3 : Back up protection for line BC and CD

Zone 2

Zone 3

Zone 1

Presentation Topics

Distance Protection

Application

Basic Principle

Theory of operation

Design

5

Distance Protection

Impedance of the line

Impedance istance

Voltage & Current transformer inputs

Current an operating force & Volt. a restraining force

Distance Protection: Principle

Current Voltage

Fault condition

Normal condition 69 Volts and 1 A load current

Fault condition 20 Volts & 10 A fault current

A B DC

Fault condition

Quick isolation of the faulted section

Damage reduction

Stress reduction

Continuity of energy

Fast operation of the distance protection

A B DC

Distance Protection: Basics

Resistance : R

Reactance : X Z

RF

A B DC

R-X Diagram

11

Basics of R-X Diagram

Reach Representation

Fault Resistance

Voltage Diagram

R-X Diagram : Basics

12

R

XZ

R-X Diagram : Relay Reach

13

R

XZR

R-X Diagram : Fault Resistance

14

R

XZR

Rf

R-X Diagram : Voltage Diagram

15

I*R

I*XI*ZR

I*Rf

I Ref

Vf

ZR

Rf

R

X

Distance Protection

IR

IX IZ

V

V-IZ

Angle = 900

IX IZ

ZI

V

IZ

+ OutputAngleComparator

>= 900

Distance Protection

IR

IX IZ

V

V-IZ

ZI

V

IZ

+ OutputAngleComparator

>= 900

Principle

Angle between the two cords drawn from the diameter

Of a circle is always 90 degrees.

Internal Fault

IR

IX IZ

V

V-IZ

Internal fault

Angle >=900

ZI

V

IZ

+ OutputAngleComparator

>= 900

External Fault

IR

IX IZ

V

V-IZ

External fault

Angle < 900

ZI

V

IZ

+ OutputAngleComparator

>= 900

Distance Protection : Design

Set line impedance Replica : Relay Reach

Convert current I in to vector IZR

Derive voltage of the system : V = Vpol

Create Vpol IZR : Measure angle with Vpol

Output if the angle = 900 or > : MHO Char.

21

Distance Protection : Ph-G Fault

For A-G fault

IZR is IA*ZR Vpol is VA Vpol IZR is VA IAZR

Polarizing voltage = Fault voltage

Self polarized Relay

B-G fault

Polarized voltage = Fault voltage = VB

Earlier designs self polarized

Self Polarized Protection

Problem

Breaker terminal Fault Fault voltage = 0

Polarized voltage Vpol = 0

No Vpol to compare with V-IZ

No operation

Solution

Memory Voltage

Memory Polarized Protection

ZI

V

IZ

+Output

Angle

Comparator

>= 900

Memory

ZI

V

IZ

+Output

Angle

Comparator

>= 900

Memory

Memory Polarized Protection

Memory Voltage Effect on MHO characteristic?

Memory Polarization

A B

G LZs

E21

E

Load Current

Pre-Fault voltage = E

Memory Polarization

A B

G LZs

E21

VF

Fault Current : IF

Pre-Fault voltage = E

Fault Voltage E = IFZs + VF

Memory Polarization

IR

IX IZR

VF

V-IZ

Angle > 900

IFZs

Vpol = V pre fault= E

E = VF + IFZs

Mho Ch. : Memory Polarization

IR

IX IZR

VF

V-IZ

IZs

Vpol = V pre fault

Memory Polarization Effect

IR

IX

IZR

VF

V-IZ

IZsVpol = V pre fault More fault resistance

Coverage due to

memory Polarization

Memory Polarization Effect

Memory Polarization: Summary

Reference voltage (Vpol) under all faults

Char. expands : More Fault coverage

Memory, Self & Cross polarizations

Cross Polarization

Healthy phase voltage Polarizing volts for a zero voltage Fault

For A-G fault: Polarizing Voltage is -(VB+VC) Cross polarizing

Memory Polarization effect

VA

VC

VB

-(VB+VC)

Distance Protection: Architecture

ZRI

V

IZ

+Output

Timer = 0.25

Cycles

Memory

Distance Protection: Architecture

ZRI

V

IZ

+Output

Memory

Phase

Shift

- 900

Phase

Detector

V-IZ in phase

Or lag

Vpol

Distance Protection: Architecture

ZR

V-IZ

Zs

Vpol

ZRI

V

IZ

+Output

Memory

Phase

Shift

- 900

Phase

Detector

V-IZ in phase

Or lag

Vpol

Distance Protection: Architecture

ZR

V-IZ

Zs

Vpol

ZR

V-IZ

Zs

Vpol

ZRI

V

IZ

+Output

Memory

Phase

Shift

- 900

Phase

Detector

V-IZ in phase

Or lag

Vpol

Memory Polarization : Questions

How protection works for

3 phase zero voltage faults?

permanent 3 phase zero voltage faults during

reclosing?

Looks like that protection can trip for a reverse faults

True?

IR

IX IZR

IZs

3 phase zero voltage Fault

ZR

V-IZ

Zs

Vpol

Protection memory of 16-20

Cycles of pre Fault Voltage

Permanent 3 ph. zero voltage

Faults during breaker reclosing

Breaker is closed with grounding chains on the breaker

Protection has no voltage in the memory

Fault voltage = 0

Protection sees only fault current.

Switch On To Fault - SOTF feature trips the breaker

Protection sees the current but no voltage following breaker close

A B

G Zs

21

Review Question - 3

Looks like that protection can trip for a reverse faults. True?

Characteristic is true only for forward faults for reverse fault protection will not operate

Zs

ZR

V-IZ

Vpol

Memory Polarization : FactsA B

G

21

ZsZL

Char. diameter : Zs - ZR Reverse Fault : ZS = Zs + ZR Substitute the value for Zs Char. diameter : Zs

ZR

V-IZ

Zs

Vpol

Memory Polarization : FactsA B

G

21

ZsZL

ZR

Zs

Char. diameter : Zs - ZR Reverse Fault : ZS = Zs + ZR Substitute the value for Zs Char. diameter : Zs

Memory Polarization : ConclusionA B

G

21

ZsZL

Memory polarized MHO :

Very secure & no operation

for reverse faults

ZR

Zs

Fault Res.: Memory Vs. Self Polarized

A B

G

21

ZsZLZs

RF

ZR

Zs

ZR

Zs

Fault Res.: Strong Vs. Weak Source

A B

G

21

ZsZLZs

RF

ZR

Zs

ZR

ZsStrong SourceWeak Source

Fault Res.: Short Vs. Long Line

G

21

ZsZLZs

RF

ZR

Zs

ZR

ZsStrong Source/Short line Weak Source/long line

Fault Resistance Coverage

Strong source & short line reduced fault resistance coverage

Quadrilateral char. Improves fault resistance coverage

Weak Source & long line increases fault resistance coverage

Memory polarization : more secure all fault conditions

Self polarization : limited fault resistance coverage

Memory polarization increases fault resistance coverage

Cross polarization : same effect as memory polarization

Quadrilateral Characteristics

Four comparators used for detection of fault conditions

If all four comparators produces output: protection trips

Quad characteristic :good fault resistance coverage

ZR

ZL

R

X

Dir

Reach

Load Blinder

KR

How Directional line works?

ZR

ZL

R

X

Dir

Reach

Load Blinder

KR

Directional line : Forward Fault

IR

IZ = Signal B

VF

VF

Directional line : Reverse Fault

IR

IZ = Signal B

VF

VF

Reach line : Ext. Fault

IR

IZ

VF

I*Kr = Signal B

IX

If A lags B

By 00 1800

VF - IZ = Signal A

Reach line : Int. Fault

IR

IZ

VF

I*Kr = Signal B

IX

If A lags B

By 00 1800

VF - IZ = Signal A

Reach line

IR

IZ

VF

I*Kr = Signal B

IX

If A lags B

By 00 1800

VF - IZ = Signal A

Quadrilateral Char. : Facts

Quad char. better : short line and/or strong source

Good for Ph-G fault : Fault Res. Coverage

Reactance & Resistance Reach set independently

Quad Char. : Reactance Line

Reactance line : not a straight line parallel to R axis.

Top line has a tilt of approx 30

The tilt for security against external fault

Without tilt : protection can operate for an external fault due to load on the line

How?

Effect of Load : Quad Ch.

G G

21

ZsZLZs

Vx

Impedance Seen at Protection X

(Ix+Iy)*R

(Ix)*ZL

Tilt of the reactance line

Prevents tripping for the

External faults

Ix

IyIx + Iy

G G

21

ZsZLZs

Vx

Effect of Load : Quad Ch.

G G

21

ZsZLZs

Vx

Impedance Seen at Protection X

G G

21

ZsZLZs

Vx

Quad Characteristics : Ext. Fault

Quad Characteristics : Int. Fault

Quad Characteristics : Int. Fault

By polarizing the top line with Ve or Zero sequence current, it will adapt to load Condition

MHO Characteristics : Zone 3

Zone 3 provides the back up protection

Zone 3 is typically time delayed zone

Used in blocking scheme to determine fault direction

Zone 3 is mostly offset characteristic

It can trip for a reverse fault

Lens shape used to avoid load encroachment

Zones of Protection

Load profile

Zone 3 : Offset MHO

OFFSET MHOIZ

-IZ

V-IZ

V-IZ

Z = Forward Reach

Z = Reverse Reach

OFFSET MHOIZ

-IZ

Load profile

Two Comparators are phase shifted by

same angle in opposite direction

OFFSET MHOIZ

-IZ

Load profile

Major axis to minor axis ratio is equal to tan (180 - )/2Each comparator is shifted by an angle

MHO or Quad : Pros and Cons

Simple and directional

Less sensitive to power swings Reach does not extend

as far along R-Axis

Limited fault resistance coverage for short lines

Good fault resistance coverage as char. can be set along R- Axis Good for short line and

strong source

Sensitive to power swing Characteristic extends on

R-Axis