Fundamentals of Protection

A relay is used to

• Break the fault current

• Sense the fault

• Sense the fault and direct to trip the circuit breaker

• All of these

The ability to protect system to determine the point at which the fault occurs and disconnect the faulty part is known as

• Speed

• Sensitivity

• Selectivity

• Reliability

As a rule, the protection cost should not be more than _______ of the total cost.

• 5%

• 10%

• 15%

• 30%

1.     The possibility of occurrence of line to ground fault in power system is _____.

• Less than 2%

• 10%

• 15%

• 85%

During first one to three cycles, the fault current is very high but later on decreases very rapidly. This zone is called as ____________.

• Sub transient state

• Transient state

• Steady state

• All the Above

The fault on the power system which gives rise to symmetrical current is known as _______.

• Open circuit fault

• Short circuit fault

• Line to line to line fault

• Line to ground fault

The arc extinguishes and restrikes in a repeated manner is known as

• Short circuit fault

• Arcing ground

• Current chopping

• Arc interruption

_______ is the minimum value of operating quantity at which the relay operates and closes its contacts.

• Pickup value

• Reset value

• Plug setting multiplier

• Time setting multiplier

_________ is a low current interrupting device made up of copper or aluminum wire.

• Fuse

• Relay

• Isolator

• Circuit breaker

Earthing transformer is used to

• Improve neutral wire’s current capacity

• Avoid overheating of transformer

• Avoid harmonics

• Provide artificial earthing