Select the correct type of relays for which the following statement is true  "They are frequently used on large equipment or switchgear. These units check whether all of the current entering a system comes back out of the system. If it does not, the relay closes a contact that shuts down the equipment."

Select the correct type of relays for which the following statement is true  "They are frequently used on large equipment or switchgear. These units check whether all of the current entering a system comes back out of the system. If it does not, the relay closes a contact that shuts down the equipment." Correct Answer Differential relays

Differential relay:

• A differential relay is one that operates when the phasor difference of two or more similar electrical quantities exceeds a pre-determined value.
• Thus a current differential relay is one that compares the current entering a section of the system with the current leaving the section.
• Under normal operating conditions, the two currents are equal but as soon as a fault occurs, this condition no longer applies.
• The difference between the incoming and outgoing currents is arranged to flow through the operating coil of the relay.
• If this differential current is equal to or greater than the pickup value, the relay will operate and open the circuit breaker to isolate the faulty section.

Applications of differential relay:

• Generally, differential relays are used to protect the equipment against internal faults in large pieces of equipment.
• Merz price protection scheme is one form of the differential relay which is used to protect the stator winding of Alternator from the internal faults and transformer.
• Differential relay is also used for the protection of transformer winding.
• We can make use of differential relay in the protection of the Transmission line and Bus bar protection also.