What is ref transformer?
Restricted Earth Fault (REF) means an earth fault from a restricted/localized zone of a circuit. The term “REF protection method ” means not to sense any earth faults outside this restricted zone. This type of protection is prevalent in Dyn group of transformers (Delta Primary and Star Secondary).
What is ref and SEF protection?
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.
Why do we use NCT?
This test is used to check for glaucoma, an eye disease that can cause blindness by damaging the nerve in the back of the eye (optic nerve).
What is NCT in transformer?
Neutral Current Transformers (NCT) are common components in Electrical Distribution Systems. Resolution: A Neutral Current Transformer encircles the neutral conductor (or is placed in-line on a bus); required on circuit breakers with Ground Fault Protection when applied on a grounded system.
A number of transformer fault conditions can arise practically in any time following some special situations. These include the following five most common internal faults and few external: earth faults, core faults, interturn faults, tank faults, and external factors.
What is HV ref?
The HV REF function will compare the HV neutral current to the residual current from the HV phase currents, and the MV REF will compare the MV neutral current with the residual current from the MV phase currents.
What is difference between 51N and 51G?
Quote: As for 51N and 51G, the way modern relay manuals proposes, 51G actually measures the current in neutral using a CT (residual CTs), where as 51N is where current in neutral is calculated by vector sum of the 3 phase over currents by the relay.