Hello, I have a question about bus 1

[Eng.Edward.M]

Hello, I have a question about bus protection. Can I leave the 50N function of my relay 1 disabled? What are the recommended settings for 51N protection?
Can someone please help me about 50 / 51N protection?

 

[thermionic1]

Is that a 100:5 zero sequence CT connected to the relay? If that is the case, don't you want to provide ground protection for the cables?

 

[RRaghunath]

Incomer protection needs to coordinate with the outgoings. Hence, instantaneous over current protection 50 and 50N are not set in the incomer. If arc flash protection of the switchboard is using this relay, that is an exception.
The setting of 51N will depend on the system earthing and the settings in the outgoing feeders downstream (as the incomer protection has to coordinate with that in outgoing feeders).
Generally speaking, Definite Time based coordination can e adopted if it is resistance earthed system with pickup same as that in the outgoing feeders (I can see the CBCT ratio is same) and time delay about 0.25s more than that in the outgoing feeders.

 

[Eng.Edward.M]

Example: In the image, there is a relay above (red curve) to protect the bus, this relay has the 50N function disabled. And a relay below (green curve) that is protecting a transformer.
Is it correct to leave the 50N function disabled?Example: In the image, there is a relay above (red curve) to protect the bus, this relay has the 50N function disabled. And a relay below (green curve) that is protecting a transformer.
Is it correct to leave the 50N function disabled?