Grounding of a Un-grounded System

[deepakbhai]

We have a 6600 V System, which is un-grounded. This system is fed by two 220/6.6 kV Transformers, which have delta connected secondary.

Now we want to ground this system through a zig zag transformer.

how do I size the zig zag transformer and what protections shall be provided to this transformer.

Thanks

 

[moreause]

i don't know the specific
but just make sure i wont diconeect it self on a fault
i had a customer how put the zigzag thoug a breaker
on the first falt the breaker opened to clear the FALT
no good lol

for protection you don't really protect the transformer you protect the device, so you should put some earth fault relay were neccessary

 

[aishu]

Refer IEEE Transactions on Industry Application Paper Vol. 28, No. 4, July/August 1992, Page 788- 796 "Grounding Transformer Applications and Associated Protection Schemes".

 

[cuky2000]

Check if the enclose links could help

http://www.eng-tips.com/viewthread.cfm?qid=187904&page=5

http://cuky2000.250free.com/Zigzag_Data.gif

 

[Rodmcm]

In simple terms a zig zag transformer will provide a ground reference. The design of the transformer, often in combination with a neutral resistor determines the level of allowable earth fault,so you need to decide how much earth fault (and for how long)you need to trip supply breakers or fuses. Zig Zag transformers are sized with a short term overload factor as well.
Usually the zig zag is protected by a breaker or fuse, and has a Ct on the earth leg to allow connection to an earth protection relay.

 

[sslobodan]

Well you should do it trough High resistance grounding system... You have applications of it all over the internet but best that I found is shown on

http://www.i-gard.com/

You should find everything you need there

 

[deepakbhai]

Thanks for the responses.