Earth Fault Types

tell us clearly with cases

what type of cases? Simply tell me about the types. by directional what it means? and by non-directional what it means?

Hello,

Earth fault current doesnt have directional or non directional types. It is upto us to decide whether the trippings should occur for fault in any direction or only for fault current flow in specific direction. So dont confuse it with the earth fault currents. directional or non directional is decided in relays.

Hope it makes clear..!

Dear Vijay,

I want to know that how relays will decide that some fault is directional or non-directional, sensitive or not-sensitive?

Best Regards,

In what context?

Dear PW Slack, In the context of current. Best Regards,

There's only one type of earth fault. It's one that operates the circuit protective device(s).

Hello,

If u have selected non-directional, then the relay will trip if the the Io or eartj fault current crosses the threshold which has been set in the relay. If it is directional, the relay will be getting the voltage as well as current feed from the instrument trafos and it will trip depending upon the torque angle which you have set in the relay. if the angle between the current and voltage are within the limits which you have set, it would trip. otherwise whatever the current value, it wont trip.

Coming to sensitive protection, Restricted earth fault is used to detect internal faults of the protected equipment. It will compare the three phase currents with the neutral current and will trip in case of any internal fault. The 3 phase CT secondaries will be connected in parallel and connected with the neutral CT secondaries. In case of any phase fault, the unbalance current will flow to the relay/ In case of non-sensitive, one earth fault relay will be connected directly to the neutral CT secondary and it will act as a stand by earth fault relay as a back up.

-Vijay

Dear AA, If power flow is in one direction,it is enough to have the earth fault relay as non - directional.[p} If power flow is bi-directional such as ring main, then it is neccessary to have directional feature to make relay operational for the selected direction.

This is achieved by applying polarising voltage signal also to the relay.

Non directional reley operates based on the CT current alone.

For the curious - how is a polarising voltage applied to an alternating current?

Dear PWSlack

For an Earth Fault Relay the current coil is supplied with zero Sequence current. To fix the directional feature Open Delta voltage will be fed to the voltage coil, which will fix the directional feature.

Term "directional" is ambiguous, you can have restricted earth fault REF (64) protection arrangement with the same relay which will act for a fault in the localized zone and will not act for out of that restricted zone (equipment) faults.