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FAULT ANALYSIS

Submitted by:-Malay niraj

Roll no.:-1307438

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CONTENT

INTRODUCTION PROTECTION SYSTEM SYMMETRICAL COMPONENT FAULT OVERCURRENT RELAY ALGORITHM SIMULATION DISTRIBUTION SYSTEM RESULTS CONCLUSION

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INTRODUCTION

The concept of symmetrical components for enhancing protection scheme by providing a practical technology for understanding and analyzing power system operation during unbalanced condition.

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PROTECTION SYSTEMWhat is need of protective system ? In order to maintain steady state of power system by

taking correct and quick remedial action during any faulty condition.

Properties of a good protective systemAutomaticQuickMinimum amount of disruption

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SYMMETRICAL COMPONENT

Unbalanced systems are difficult to handle. It provide balanced analysis of an unbalanced

system The unbalanced three phase system can be

transformed into three balanced phasorsPositive SequenceNegative SequenceZero Sequence

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POSITIVE PHASE SEQUENCE

Each have the same magnitude.

Each positive sequence voltage or current quantity is displaced 120° from one another.

The positive sequence quantities have a-b-c, counter clock-wise, phase rotation.

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NEGATIVE PHASE SEQUENCE

Each have the same magnitude.

Each negative sequence voltage or current quantity is displaced 120° from one another.

The negative sequence quantities have a-c-b, counter clock-wise, phase rotation.

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ZERO PHASE SEQUENCE

Each zero sequence quantity has the same magnitude.

All three phasor with no angular displacement between them, all in phase.

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FAULT

o General Causes of faultFault due to lightningTree limbs falling on the lineWind damage

Effects of faultFlow of excessive currentAbnormal voltagesInduces over voltages on neighbouring equipments. Hazards to human, equipment and animals

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TYPES OF FAULTS• Balanced Faults :

– Three-phase fault

• Unbalanced Faults :– Single line to ground fault– Line to line fault– Double line to ground fault

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UNBALANCED FAULTS

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SINGLE LINE TO GROUND FAULT The most common type of fault is the single

line to ground fault:

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The SLG fault can be described by the following voltage and current relationship: Ib=0 & Ic=0

Va=IaZf

The Sequence current can be given as:

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LINE TO LINE FAULT

It occurs when two conductors are short circuited.

There is no zero sequence component due to absence of ground return path.

The positive and negative sequence components are connected in parallel.

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DOUBLE LINE TO GROUND FAULT In double line to ground fault two line

conductors come in contact with each other and ground .

The networks are connected in parallel.

For the zero sequence component it requires to add an external impedance of Zf+3Zg

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OVER CURRENT RELAY Short-circuit currents are generally several times (5 to 20) full

load current. Hence fast fault clearance is always desirable on short circuits.

A relay that operates or picks up when it’s current exceeds a predetermined value (setting value) is called Over current Relay.

Over current includes short-circuit protection, and short circuits can be: Phase faults Earth faults Winding faults

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TYPES OF OVER CURRENT RELAY

I. Instantaneous Over current (Definite Current) Relay

II. Definite Time Over current RelayIII. Inverse Time Over current Relay (IDMT Relay

)i. Moderately Inverseii. Very Inverse Timeiii. Extremely Inverse

IV. Directional over current Relay

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ALGORITHM The criterion function for discriminating fault

from non fault switching is defined as follows :

R= |I1|-|I2| / |I1|+|I2|

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SIMULATED DISTRIBUTION SYSTEM

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RESULTSSeveral non faults events are applied to

this system along with some short circuit events a different time.

The discrimination of fault from a non fault event could be done by representing two cases Transformer energizingFault

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TRANSFORMER ENERGIZING Various inrush current condition were simulated. Various parameters which have considerable effect

on the characteristic of the current signal were changed and was analysed.

FAULT In this case a single line to ground fault occurs.

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NON FAULT CONDITIONWHEN VALUE OF R>=.35s

FAULTY CONDITION WHEN VALUE OF R<.35s

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THREE PHASE CURRENT BEFORE FAULT

THREE PHASE CURRENT AFTER FAULT

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CONCLUSION Simple method of improving over current relays

operation by algorithm, based on different behaviour of the current amplitudes. Based on the differences, a criterion function R is defined such that undesirable operation of the over current relays to the switching is prevented.