OBJECTIVE OF SYSTEM PROTECTION

    PROTECTION DOES NOT MEAN PREVENTION. IT IS RATHER MINIMISING THE DURATION OF THE TROUBLE AND LIMITING THE DAMAGE.

    RELIABILITY, SELECTIVITY, SENSITIVITY, SPEED OF OPERATION, SIMPLICITY, AND ECONOMICS ARE SOME TERMS COMMONLY USED TO DESCRIBE THE OBJECTIVE OF SYSTEM PROTECTION.

RELIABILITY HAS TWO ASPECTS I.E., DEPENDABILITY & SECURITY

DEPENDABILITY

is the certainty of correct operation in response to system trouble.

SECURITY 

relates to the degree of ability that a relay system will avoid miss operation. Generally, enhancing security tends to decrease the dependability and vice versa.

SELECTIVITY

The ability of the protection system to “select” (search out) the point at which the fault appears and switch it out of the circuit by tripping the nearest circuit breaker.

SENSITIVITY

The capability of the protection system to respond to abnormalities in normal operating conditions

SPEED OF CONTROL 

Quick disconnection of a short-circuit, decreases the amount of damage incurred, maintains the machines running in synchronism (A high speed relay will operate in 3 cycles)

SIMPLICITY

The simpler the protection system the greater is its reliability.

ECONOMICS

Protection costs are considered high when considered alone, but they should be evaluated in the light of the much higher cost of the equipment they are protecting and the cost of an outage and/or the loss of the protected equipment.