presented by:
Rajesh Sharma

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Power System Protection
definition
 Overcurrent Coordination
A systematic study of current responsive devices in an electrical power system
Objective
 To determine the ratings and settings of fuses, breakers, relay, etc.
 To isolate the fault or overloads.
Criteria
 Economics
 Available Measures of Fault
 Operating Practices
 Previous Experience
Design
 Open only PD upstream of the fault or overload
 Provide satisfactory protection for overloads
 Interrupt SC as rapidly (instantaneously) as possible
 Comply with all applicable standards and codes
 Plot the Time Current Characteristics of different PDs
Analysis
When:
 New electrical systems
 Plant electrical system expansion/retrofits
 Coordination failure in an existing plant
Protection vs. Coordination
 Coordination is not an exact science
 Compromise between protection and coordination
 Reliability
 Speed
 Performance
 Economics
 Simplicity
Protection
 Prevent injury to personnel
 Minimize damage to components
 Quickly isolate the affected portion of the system
 Minimize the magnitude of available short-circuit
Spectrum Of Currents
 Load Current
 Up to 100% of full-load
 115-125% (mild overload)
 Overcurrent
 Abnormal loading condition (Locked-Rotor)
 Fault Current
 Fault condition
 Ten times the full-load current and higher
Coordination
 Limit the extend and duration of service interruption
 Selective fault isolation
 Provide alternate circuits