concept of symmetrical component as a technique for analysis of fault and improvement of overcurrent...
DESCRIPTION
CONCEPT OF SYMMETRICAL COMPONENT AS A TECHNIQUE FOR ANALYSIS OF FAULT AND IMPROVEMENT OF OVERCURRENT PROTECTION SCHEMETRANSCRIPT
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A SEMINAR PRESENTATION ON
“CONCEPT OF SYMMETRICAL COMPONENT AS A TECHNIQUE FOR ANALYSIS OF FAULT AND IMPROVEMENT OF OVERCURRENT PROTECTION SCHEME”
Submitted to: Submitted by:
Mr. Ankush Tandon Saurabh Varshney
Mrs. Deepti Arela (10ESKEE106)
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CONTENT
INTRODUCTION PROTECTION SYSTEM SYMMETRICAL COMPONENT FAULT OVERCURRENT RELAY ALGORITHM SIMULATION DISTRIBUTION SYSTEM RESULTS CONCLUSION
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INTRODUCTION
Aim of my seminar topic is better understanding 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 Relay
III. Inverse Time Over current Relay (IDMT Relay)
i. Moderately Inverse
ii. Very Inverse Time
iii. 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 CONDITION
WHEN 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.
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THANK YOU
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