50/51N Stands for what ?

[Elecme]

Could someone advise about the protection relays symbols of the 11kV networks.I mean for example what 50/51N stands for. Elecme

 

[jnims]

It is a relay with time overcurrent (ANSI/IEEE Device 51) and instantaneous overcurrent (ANSI/IEEE Device 50)functions connected to the neutral (or residual) of wye-connected CTs.

A 50/51N relay can be set more sensitively than the same relay connected directly to phase current because it only senses zero sequence currents (i.e., unbalanced phase to neutral loads or ground faults).

 

[redtrumpet]

See thread279-10208

Scroll down the thread, the device numbering Q and A appeared near the bottom of the thread.