system neutral grounding

[smur]

I used to work in a plant where they disallowed anyone grounding more than 1 system neutral at any time. So in a specific system such as 13.8kv or 3.3 kv etc, you can only have 1 system neutral grounded. Any reasons for this?
thanks

 

[ScottyUK]

If it was an impedance earthed system, multiple earths increase the available earth fault current. If it was a four-wire system then multiple earth connections lead to current flow in the bulk of earth, a condition which is normally prohibited and even if permitted can cause strange behaviour of protection and control equipment.


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Sometimes I only open my mouth to swap feet...

 

[smur]

Thanks. It is impedance earthed system Resistance. But I have also worked at places where people have muliple system grounds. Ofcourse you must set the ground relays accordingly. Is ther any benefit beteen the 2 systems in any manner?

 

[rbulsara]

Refer to this abrreviated version of IEEE sample green book. Buy the books if you need entire reference.

http://standards.ieee.org/colorbooks/sampler/Greenbook.pdf