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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.
S.Arunachalam, St. Joseph's Chennai 2011
Isolator
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MCB Miniature CBMCCB Molded
CASE CB
S.Arunachalam, St. Joseph's Chennai 2011
MCB Rated Current not more than 100AMCCB Rated Current up to 2500 A
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Relay
S.Arunachalam, St. Joseph's Chennai 2011
Over Current Relay
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Relays
S.Arunachalam, St. Joseph's Chennai 2011
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
S.Arunachalam, St. Joseph's Chennai 2011
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
S.Arunachalam, St. Joseph's Chennai 2011
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