power system protection presented by: chandra bhushan singh electrical and electronics engineering...
TRANSCRIPT
POWER SYSTEM PROTECTION
Presented By:Chandra Bhushan Singh
Electrical and Electronics Engineering(7th sem)
Agenda Introduction Elements of protection system Electrical System fault and system
Protection with Protective Relays Conclusion
Why A System Needs Protection?
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 over current, over voltage, lighting, etc.
Element of protection system
(1)Current and Voltage Transformers
(2)Relays
(3)Circuit breakers
(4)Batteries
(5)Fuses
(6)Lighting Arresters
Current transformer
Current transformer consists at least of two secondary windings.
The first winding is usually designed for measuring, the second is used for protection.
The secondary of current transformers are almost connected in star
Voltage transformer
Voltage transformer is often consists of two windings.
The first winding is connected in star, and the stare point must be earthed.
The second winding is connected as open delta.
Relay Purpose
Isolate controlling circuit from controlled circuit.
Control high voltage system with low voltage.
Control high current system with low current.
Logic Functions
Advantages for Using Protective Relays
Detect system failures when they occur and isolate the faulted section from the remaining of the system.
Mitigating the effects of failures after they occur.
Minimize risk of fire, danger to personal and other high voltage systems.
CIRCUIT BREAKER
Low voltage circuit breaker Magnetic circuit breaker Medium voltage circuit breaker High voltage circuit breaker
Battery bankBattery bank are called as
backbone of protection systemEmergency use for power
system
Fuse
Fuses are selected to allow passage of normal current and of excessive current only for short periods.
It is used to protect the low voltage or current rating devices
Lighting arrester
A lightning arrester is a device used on electrical power system to protect the insulation damaging effect of lightning.
All lighting arrester are earthed
Protective Devices Comparison
Circuit Breaker v/s Relay Relays are like human brain; circuit
breakers are like human muscle. Relays ‘make decisions’ based on
settings. Relays send signals to circuit breakers.
Based the sending signals circuit breakers will open/close.
Generator Protection
Generator Differential Protection Loss of Field or Loss of Excitation Protection Negative Sequence or Current Unbalance
Protection Over Fluxing or Over Excitation Protection Over Current Protection Stator Earth Fault Protection
Rotor Earth Fault Protection Restricted Earth Fault Protection Backup Impedance Protection Low Forward Power Protection Reverse Power Protection Over Frequency Protection Under Frequency Protection Over Voltage Protection
Generator ProtectionDifferential and Ground Fault
Generator ProtectionPhase Unbalance
Negative SequenceVoltage example:
Negative Sequence:
The direction of rotation of a negative sequence is opposite to what is obtained when the positive sequence are applied.
Negative Sequence Relay will constantly measure and compare the magnitude and direction of the current.
TRANSFORMER PROTECTION
Gas and Temperature Monitoring
Thermal protection
Differential and Ground Fault Protection
Over current protection
Transformer ProtectionGround Fault and Differential Relay
Thermal Overload Relays
Use bimetallic strips to open/close relay contacts when temperature exceeds/drops to certain level.
Require certain reaction time Inverse time/current relationship
Transmission line protection
Distance protection
Earth fault protection
Over current protection
Carrier protection
Conclusion
Relays control output circuits of a much higher power.
Safety is increased Protective relays are essential for keeping
faults in the system isolated and keep equipment from being damaged.
Relay is like an insurance against damage due to fault.
THANK YOU