Power System Protection




Definition


Overcurrent Coordination
A systematic study of current responsive devices in an electrical power system.

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


Protection vs. Coordination


Coordination is not an exact science
Compromise between protection and coordination
Reliability
Speed
Performance
Economics
Simplicity


Coordination


Limit the extend and duration of service interruption
Selective fault isolation
Provide alternate circuits


Current Limiting Fuse(CLF)


Limits the peak current of short-circuit
Reduces magnetic stresses (mechanical damage)
Reduces thermal energy