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PRESENTED BY
ANUTOSH KR. ROY (09101016008)AMIT KR. GHOSH (09101016004)ANJAN
KR. DAN (09101016006)CHOWDHURY MD. ASIF (09101016017)
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Introduction of Protective Relays
Comparison with CB & FUSES
Discussion about protection with ProtectiveRelays
Conclusion
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There is no fault free system. It is neither practical nor
economical to build a
fault free system.
Electrical system shall tolerate certain degree of
faults. Usually faults are caused by breakdown of
insulation due to various reasons: system aging,lighting,
etc.
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Relays are electricalswitches that open or closeanother circuit
under certain
conditions.
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Isolate controlling circuit from controlled circuit.
Control high voltage system with low voltage.
Control high current system with low current.
Logic Functions
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Electromagnetic Relays (EMRs)
Solid-state Relays (SSRs) There is no mechanical contacts to
switch the circuit.
Microprocessor Based Relays
Commonly used in power system monitoring and protection.
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Electromagnetic Relays (EMRs)
Simplicity
Not expensive
Solid-state Relays (SSRs) No Mechanical movements
Faster than EMR
Microprocessor-based Relay Much higher precision and more
reliable and durable. Capable of both digital and analog I/O.
Higher cost
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Detect system failures when they occur andisolate the faulted
section from the remaining ofthe system.
Mitigating the effects of failures after they occur.Minimize
risk of fire, danger to personal andother high voltage systems.
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majority are phase-to-ground faults phase-to-phase
phase-phase-phase
double-phase-to-ground
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Circuit Breakers V.S. Relays Relays are like human brain;
circuit breakers are
like human muscle.
Relays make decisions based on settings.
Relays send signals to circuit breakers. Based thesending
signals circuit breakers will open/close.
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PROTECTION WITH RELAY:
1.MOTOR PROTECTION
2.TRANSFORMER PROTECTION
3.GENERATOR PROTECTION
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Timed Overload Locked Rotor
Single Phase and Phase Unbalance
Other
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Solution: Thermal overload relays
Plunger-type relays
Induction-type relays
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Most frequently used when AC powerpresents
Change taps to adjust time delay
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Instantaneous Overcurrent Differential Relays
Undervoltage Electromagnetic Relays
Ground Fault Differential Relays
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Gas and Temperature Monitoring Differential and Ground Fault
Protection
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For a wye connection, ground fault can bedetected from the
grounded neutral wire.
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Differential and Ground Fault Protection Phase Unbalance
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Negative Sequence Relay will constantlymeasure and compare the
magnitude anddirection of the current.
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Relays control output circuits of a muchhigher power.
Safety is increased
Protective relays are essential forkeeping faults in the system
isolatedand keep equipment from beingdamaged.
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Sources:1. Books on Power System2. Internet source
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