Earth Fault Relay 64

Ah, unbalance current again, it is pricking me.

For this protection, the relay will monitor the currents in phase and in neutral or will only monitor the current in the neutral?

If there is unbalance current, so the relay considers it as a earth fault?

How many percent or amp are required for unbalance current, let's say 3-phase system?

Unbalance had been pricking me too for so long! Thanks to some good reading! I have overcome the pricks now!

1) Now, there are three methods of connecting 51N

i) Connect 51N only in the residual path of the phase CTs only, with no neutral CT. Here, you set the 51N relay to, say, 10%. This means that even when the 51N relay sees upto 10% of its setting, it shall remain mute, an indirect way of telling the relay that upto 10% is no earth fault, but only system unbalance due to unequal distribution and/or utilistaion of phase loads.

ii) Connect 51N relay in the residual path of 3 Phase & 1 Neutral CTs. Here, the 51 N relay would sense only genuine earth faults as any phase unbalance would be offset by the neutral current fed into the relay equal in magnitude but opposite in direction. Here, the 51N relay settings can be made more sensitive.

iii) Install a CT is the Primary Neutral Bar and the secondary of this CT is connected to the 51 N relay. The scenario is similar to (i) above.

2) As explained above. If the current thro the 51N relay is less than or equal to the setting made in the relay, it is perceived by the relay as "normal" system unbalance current. Anything above is perceived to be earth fault and the relay reacts.

3) Depends upon the single phase loads distribution/utilistaion in your system.

electricalexpert65:

ii) For this section, how much percent would be appropriate? In the case we have earth fault (phase touch ground), the grounding wire will carry the current not the neutral. Could you put more detials on how the relay will react in this case please?

What is the connection methodology for 64 Relay? Core Balnce CT (Zero sequence CT) is the mandatory one for 64 protection. Please, provide your advice.