What is difference between earth fault and sensitive earth fault?

Sensitive Earth fault Protection scheme is used for the detection of earth fault. The sensitive earth fault protection is usually used in alternators and transformers with high resistance grounding. High resistance grounding restricts the earth fault current to a very less value and permits the operation of equipment.

What is the difference between standby earth fault and restricted fault?

Why it is called standby earth fault relay? It is backup protection for restricted earth fault (REF) relay. It operates the CB when REF is failed to trip the circuit, Heavy earth fault outside of the REF protective Zone, and all other earth faults. Simply we can say, it is standby protection for all other earth faults.

What is a restricted earth fault?

Restricted earth fault (REF) protection is a sensitive way to protect a zone between two measuring points against earth faults. The CT secondaries are wired to cancel each other’s currents during through faults and to drive all secondary current to the relay when the fault is inside the protected zone.

What is sensitive earth fault protection?

A system of earth fault protection in which the fault current is limited by design to a low value which generally requires amplification in order to operate an earth fault relay.

What causes sensitive earth fault?

If a conductor falls on to extremely dry ground, the fault impedance can be very high and only a small amount of zero sequence current will flow. Hence the need to a more sensitive earth fault protection.

What is derived earth fault?

– In Derived type Earth Fault protection, current to the relay is fed from the Phase CTs only. Hence, inside the relay, vector summation of Phase currents (Ia, Ib & Ic) is carried out and Earth Fault current (In) is derived. – Above vector sum is always zero in normal condition.

What is meant by earth fault?

A ground fault (earth fault) is any failure that allows unintended connection of power circuit conductors with the earth. Such faults can cause objectionable circulating currents, or may energize the housings of equipment at a dangerous voltage.

What are the causes of earth fault?

Causes of Earth Fault The main cause of earth fault in an overhead transmission or distribution line is the failure of the insulator. The insulator is used in an overhead transmission line to provide the insulation between the live conductor and the metallic tower which already connected to the earth.

What is meant by sensitivity of earth leakage?

Earth Leakage Tripping Current (Sensitivity) This is measured in milliamps (mA) and is referred to as the degree of protection in an accidental shock hazard situation.

What is the sensitivity of Restricted earth fault protection?

Therefore for protection of Transformer from such a fault we need more sensitive protection scheme which is implemented by using Restricted Earth Fault Protection. The sensitivity of REF protection is superior as compared to Differential Protection. Normally the setting of REF protection is kept as low as 5\%.

What is restricted earth fault protection of transformer?

Restricted Earth Fault Protection of Transformer. Restricted Earth Fault (REF) protection is basically a Differential Protection. The only difference in between the Differential Protection and REF Protection is that, latter protection is more sensitive as compared to the former protection scheme.

What is the difference between standby earth fault and ref?

The standby earth fault is just like a normal earth fault which acts on a CT connected at star (Y) point. it is used like a backup protection, usually provided to trip the HT breaker of the transformer. REF is a unit protection which can detect faults in transformer winding (upto 95\%) and is very sensitive protection just like differential.

What is the earth fault protection scheme?

The earth fault protection scheme consists the earth fault relay, which gives the tripping command to the circuit breaker and hence restricted the fault current.