11-04-2014, 03:45 PM
[size=medium]Protection Requirements
Speed
Thermal damage
Electrodynamic forces
Sensitivity
High resistance faults
Reliability
Dependability
Security
Single failure criteria
Fault clearance must be executed even in case
of a single fault in the clearance chain
In the fault clearance system no part of the
clearance should have lower reliability
Back-up clearance function must be there
Remote back up
Local back up
Drawback of electromechanical relay:
Slow and sluggish operation
High error upto +/- 10% of measurement.
High burden on CTs and PTs which increases size of the switchgear.
Drift in characteristics due to aging of moving components.
No flexibility in use.
Bigger dimentation.
Frequent maintenance.