Using of 67N and 51N

[freetown]

Hi all,

When we have to use residual earth protection 51N and 67N and what's the difference?
Is it true that 67N is only used on the incomers and 51N on the outgoing feeders?

 

[System Protection]

51 is Inverse Time Overcurrent, so the more current there is the faster it will trip. There are curves associated with the inverse time overcurrent element that will give you the relay operate time with different current levels and time dials. With a modern relay you get to pick the pickup, time dial and curve shape.

67 is a directional overcurrent element/relay. Generally, with either an instantaneous operation or definite time delay.