Regarding Earth Fault

1.Which Application you are refering to ?

2. Word Stand E/F protection is new to me. Do you mean ' Back up Protection ' ?

3. Restricted E/F normally used in Generator systems / Transmission grids, the relay senses the fault in particular equipment, & isolates the same, & major shut downs are restricted / neusance trippings in other feeders are prevented. Just use Directional E/F relay available, that are CT polarity sensitive.

Standby E/F is like a Backup protection .

the following answers were given by a cr-4 user before. so next time please use cr-4 search .

Restricted Earth Fault Protection Is a type of zone of protection, or a differential scheme. You get two types, low impedance and high impedance. Low impedance is normally current operated and high impedance voltage operated. High impedance REF is the most commonly used. Relay connected in parallel with three phase CTs and one neutral CT. It will look just for faults inside the transformer, and need not to coordinate with relays downstream (can operate very fast). With this kind of protection you can protect over 90% transformer windings. Need to use special class CTs, previously called class X CTs.

Standby earth fault protection Relay connected to the neutral CT. Normally a kind of back-up protection with a relative long delay or many times a long-time inverse curve. Need to coordinate with downstream E/F relays.

And how does the Directional Earth Fault protection scheme is implemented?

http://www05.abb.com/global/scot/scot229.nsf/veritydisplay/236e1594e56edb6ec2256c1d0044d195/$file/rej527_tob_751132enc.pdf

I would like to express my sincere thanks to you Mr. Shamtih Gambhir. The link you provided was extremely useful. Loooking forward to further discussions. Thanks again.