session-1_fundamentals of power system protection

7/30/2019 Session-1_Fundamentals of Power System Protection

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Co-ordinator

P.Raja, M.Tech.,

Assistant Professor

Dept. of Electrical and Electronics Engineering

NIT, Trichy - 15

Short-term course on

Power System Protection Issues withDistributed Generators

3rd4th August 2012

Department of Electrical & Electronics Engineering

NIT Trichy

Welcomes You all


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Session 1

Fundamentals of Power System Protection

P.Raja, M.Tech.,

Assistant Professor

Dept. of Electrical and Electronics Engineering

NIT, Trichy - 15

Short-term course on

Power System Protection Issues with

Distributed Generators3rd4th August 2012


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BASIC PROTECTION RELAYING

Session I


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What is Protection? - General

The act of protecting something / somebody

Necessary when there is something wrong /

abnormal condition

Avoid the process of expansion should notallow the wrong / abnormal condition to spoil

something is good

In our discussion Protection of Power system


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Need for Protection Analogy Rain Umbrella

Sensing

Processing & Signaling

Action


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Discussion on

Need for Protection

Abnormal conditions of Electric Power

System

Components of Basic Protection system

Fault Statistics

Relaying schemes Different discrimination

Methodology of implementation


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Discussion on

Expected quality of a Relay

Basic operation of a Relay

Concepts of Over current relay

Directional over current relay

Differential protection

Distance relay


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Components of Power Systems

Generator

Bus Bar

Transformer

Transmission Line

Loads

Generator

Transformer

Transmission Line

Transformer

Bus Bar

RainCurrent

Voltage

Frequency

Voltage

Frequency


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Fault conditions

Insulation Failure in any component

Open conductor fault

Line faults


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Abnormal Conditions

Abnormal changes in

Current (Increment / Decrement)

Voltage (Increment / Decrement)

Frequency (Increment / Decrement)

Who causes the abnormality..?!

Fault

Basic Circuit concept Short circuit

Increase in current & Decrease in Voltage


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What is Protection?

The function of protective equipment is not

the preventive one its imply

Takes action only after a fault has

occurred

Its the ambulance at the foot of the cliff

rather than the fence at the top


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Fundamental Principles

The essential and discriminative removal

of an abnormality from a power system

To minimize loss of supply and damage

Two Basic requirements of the system

Must be provided with sufficient number of

CBs

Appropriate action of controlling and

disconnecting equipments and there by

remove the abnormal conditions


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Fault Statistic Probability of

Faults Overhead lines 50 %

CTs, PTs & control equipment 12%

Switch gear 12 %

Transformers 10%

Underground cables 9% Generators 7%

GeneratorTransmission LineBus Bar


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Overhead Line Protection

(Probability of Occurrence)

Line Ground (LG) 85% (least severe)

Line Line (LL) 8%

Line Line Ground (LLG) 5% Line Line Line (LLL) 2% (Most Severe)


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Methods of Discrimination

Generator

Transformer

Transmission Line

Transformer

Bus Bar

VoltageFrequency


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Methods of discrimination

By current magnitude

By time

By current with time

By time and direction

By distance measurement

By distance with time By current balance


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Methods of discrimination

By Opposed voltage protection

By Phase comparison

Distance protection with signaling channel


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The Mediator!?

Generator

Transformer

Transmission Line

Transformer

Bus Bar

Voltage

Frequency

Relay

SensingCB


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1900 1920 1940 1960 1980 2000 2005

OC

Differential

Directional

Electromechanical

Distance

Digital

DistanceTravelling

Wave

Adaptive

ANN

Wavelet

Wide area

Hybrid

Static

DigitalP based

Numerical

Network Based


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Components of Power System

Protection


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Instrumentation Transformers

CT

Characteristics

PT


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Expected qualities of Protective

Relay

Sensitivity

Selectivity

Speed

Simplicity

Reliability

Economics


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Relaying Over current

Sensing Current Current Transformer

Relaying Electromechanical Attraction

Induction

Comparison

Pick up value

Discrimination by level of current


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Over current relay

Disadvantage of only current

discrimination

Transmission system

Zonal protection

Primary and Back up protection

Importance of timing


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Over current Relay with Time

B1 B2B3

B4

R1 R2 R3 R4 R5 R6 R7 R8

R9

B1 B2B3

B4

R1 R2 R3 R4 R5 R6 R7 R8

R9

Primary Relay

Back up Relay


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Parameters

Pick up value Minimum operating value required to operate

the relay

How do you select? Plug setting multiplier (PSM)

PSM=Fault current at the relay coil/Pick up

current Pick up current = Rated secondary of the CT

x Current setting

Time multiplier setting


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Over current relay with timing

Inverse time over current relay A - IDMT

B - Very inverse

C - Extremely inverse

1

)(14.002.0

PSM

TMStop

1

)(5.13

PSM

TMS

top

1

)(802

PSM

TMStop

A

B

C


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Over current relay with Directional Element

Simple necessity of Directional element inOver current relay

G

A B

D C

Parallel Feeder

Ring Main system


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Implementation of Electro-Mechanical Relay

Fuse

Attraction Based

Induction based

Shaded pole

Watt-hour

structure

Induction cupstructure


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Shaded-Pole Structure

Derivation of Torque


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Watt-hour structure

E core

U core

Can be used fordirectional

operation


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Differential/ unit relay

Sensing two end currents

Find the difference

If the difference > set value Relay operates

Zonal ProtectionEnd 1 End 2

Pilot wire


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Applications of Differential Relay

Unit Protection

Apparatus of smaller distance

Transformer

Alternator

Motor

Transmission Line*

Di d t f O t l


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Disadvantage of Over current relayB1

R1B2

F1 F2 F3

Distance

From

Relay location

Fault Current

LG

LLG

LLLG

Ipu

Reach of LG

Reach of LLG

Reach of LLLG


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Distant Relays

Simple over current relay

Over reach or Under reach problemB1

R1

Fault Current at

Location

Voltage at

location

Compare Desired response

F3 IR3 VR3 |VR3|>|IR3||Zset| Restrain

F2 IR2 VR2 |VR2|>|IR2||Zset| Verge of Operation

F1 IR1 VR1 |VR1|>|IR1||Zset| Trip

B2

F1 F2 F3

ZL1

ZL2

ZL3


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Distance Relay

Simple Impedance Relay See saw

Reactance Relay

Mho Relay

General Torque Equation

43

2

2

2

1 )cos( kIVkVkIkT RRRR

Will be continued in Transmission Line protection


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Thank you

Questions if any?!

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