59N For Medium Voltage

[rayas91]

Hi friends,

I would like to ask you a question.

If the residual overvoltage fault occurs on F1 , What will A and B see ? Same residual overvoltage magnitude ? Or Will they see the fault ?

Thanks.

 

[pwrengrds]

The voltage would be the same at all three points, assuming that this is an ungrounded system with either high resistance grounding or no grounding. 59N usually implies a broken delta configuration to detect it, typically there would only be one of them.

The problem with a high resistance grounding system is that it's hard to detect where it is and the entire system is shut down to find it. That's why with any complex system low resistance grounding is used.

 

[rayas91]

pwrengrds Thank you for your help. I would like to know more details from you or from other guys if it s possible.

 

[Fuse4]

For earth fault both neutrals of the transformers YNyn should be conected to ground

 

[Kiribanda]

rayas91,
From the SLD given, it looks to me that the main transformer is WYE/wye solidly grounded.
That means during a ground fault, the voltages of the healthy phases depends on the COG
or the Earth Fault Factor of the network and hence you should have a coordinated ground fault protection scheme.
In my opinion 59N does not work.A more detailed SLD showing voltages & grounding method,
is appreciated for a detailed reply.