What is the function of differential protection relay?

What is the function of differential protection relay?

Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults that occur outside the protected zone.

What is differential relay protection scheme?

Introduction. Differential protection is a unit-type protection for a specified zone or piece of equipment. It is based on the fact that it is only in the case of faults internal to the zone that the differential current (difference between input and output currents) will be high.

Which relay is used in differential protection?

Voltage Balance Differential Relay For the protection of the feeders, the voltage balance differential relays are used. The voltage differential relay uses two similar current transformer places across the protective zone with the help of pilot wire.

Where is differential protection used?

Differential protection schemes are mainly used for protection against phase-to-phase fault and phase to earth faults. The differential protection used for power transformers is based on Merz-Prize circulating current principle. Such types of protection are generally used for transformers of rating exceeding 2 MVA.

What are disadvantages of differential protection?

When differential relaying is used for protection, the CTs at both sides of the generator winding must be of equal accuracy. Otherwise if the CT errors are excessive it will cause the mal-operation of the relay.

What are the types of differential protection?

Figure 1 – High impedance differential principle.

Figure 2 – High impedance “busbar” differential protection.

Figure 3 – Restricted earth fault protection of the secondary (a) or primary (b) windings of a transformer.

Figure 4 – Line or cable differential protection with pilot wires.

What is the two types of percentage differential relay?

Types of Percentage Differential Relay Three terminal system application of the percentage differential relay. Induction Type biased Differential Relay.

Can a difference in current operate a differential protection relay?

The difference in the current can operate the differential protection relay. The following are the essential condition requires for the working of the differential protection relay. The network in which the relay use should have two or more similar electrical quantities. The quantities have the phase displacement of approximately 180º.

How is a differential relay used in a transformer?

Should a fault occur inside the zone of relay protection (that is between the CT’s), the differential relay would receive current in the operating coil. The example differential protection relay shown in the below figure is a transformer differential relay. The following protection functions are used in this relay.

How does differential ( 87 ) current protection scheme work?

In order for this protection scheme to work, the two local 87 relays must somehow communicate with one another to continuously compare measured current values at both ends of the line. This is accomplished via a communication route between the two relays called a pilot channel.

What is the ANSI number for differential protection?

The ANSI/IEEE number code for differential protection is 87. Differential voltage relays also exist, with the same “87” ANSI/IEEE designation, making it necessary to specify whether the differential quantity in question is voltage or current whenever mentioning an “87” relay.