introdution to protection and switchgerars

8/6/2019 Introdution to protection and switchgerars

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S. Arunachalam

Department of Electrical Engineering

St. Josephs College of Engineering

Chennai

S.Arunachalam, St. Joseph's Chennai 2011


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Role of a Protection Engineer

Two Alternatives

Design a System so thatfault does not occur

Good System DesignGood Maintenance &

Insulation Coordination

NOT Possible toeliminate the Fault

How to prevent a fault

and reduce itsconsequence

Identify the fault andisolate the faulty

element from rest ofthe system



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Why Protection is an art?

Job a protection engineer is design protection schemeswhere closet match between fault characteristics andtripping characteristics is obtained.

When tripping takes place it has all the elements ofintrigue, drama and suspense.

It is ironic that a relay may itself malfunction andincrease the possibility of disturbance



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Need For Protection Under Abnormal operating conditions

protections is necessary for Safety of Equipment.

Safety of human personnel.



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Types of FaultsFault

Open circuitFault

Short CircuitFault

Ground Fault Phase Fault

Symmetrical

3 Phase

Unsymmetrical

1 and 2 Phase



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Arcing Fault It is a L-G fault due to break down of

insulation. When the path of the load current is cut

short due to break down of insulation

we say short circuit has occurred

If the short circuit is total and by pass the

entire current through it we say deadshort circuit has occurred. Also called

Metallic fault.



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Causes of shunt fault and over

voltages

Shunt Fault Insulation Break down Over Voltages

Ageing

Temperature

Chemical Pollution

Rain

Foreign Objects

Internal due to

Switching

External due to

Lighting



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SWITCH GEARS



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Isolator is an off-

load device, whereas

circuit breaker is an

on-load device.


Isolator


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MCB Miniature CBMCCB Molded

CASE CB


MCB Rated Current not more than 100AMCCB Rated Current up to 2500 A


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Relay


Over Current Relay


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Relays


Purpose of relay is to detect the fault withinits zone and issue trip signal to appropriate

number of circuit Breaker.


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Evolution of Relays


Electro Mechanical Relays

Static Relays

Numeric Relays


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Fuse



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CurrentTransformers



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Potential

Transformer



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Schematic Diagram of Relay and

Circuit Breaker


introdution to protection and switchgerars

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