Basic requirement of Protective Relaying

Basic requirement of Protective Relaying

The principal function of protective relaying is to remove the fault part of the system without affect the remain part of the system. The following are fundamental requirement of protective  relays  so as its can perform its function satisfactorily  

(i)                    Selectivity

(ii)                  Speed

(iii)                 sensitivity

(iv)                  reliability

(v)                   simplicity             

(vi)                  economy

1.  Selectivity. It is the ability of the protective system to select correctly that part of the system in trouble and disconnect the faulty part without disturbing the rest of the system.                                                                                             The following some of the example of power system protection zones 
   low-tension switch gear               
   transformers
   high-tension switchgear              
   transmission lines
2.   Speed. The protective  relay system should isolate  the faulty section as fast as possible for the safe of the rest part of system and without affect the health part
3. Sensitivity. It is the ability of the relay system to operate with low value of actuating quantity
4. Reliability. It is the ability of the relay system to operate under the pre-determined conditions. 
5. Simplicity. The relaying system should be simple