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Earthing of MV Double Wound Transformers

Earthing of MV Double Wound Transformers

Earthing of MV Double Wound Transformers

(OP)
Hi Guys

I am busy with a project where the client has insisted on using an 11/3.3/0.4kV transformer. Meaning that the HV side of the Tx is 11kV and there are two LV winding's stepping the voltage down to 3.3kV and 400V. The vector grouping of the transformer is Ddyn11. The client has called for the 3.3kV delta connected winding to be solidly earthed via a NEC and the 400V star connected winding to be solidly earthed.

My question is.....
Do i need to have 2 separate earth mats? One for the 3.3kV winding and one for the 400V winding or can i use the same earth mat for both winding's?

To complicate things further, i have another configuration exactly the same as above connected in parallel. The actual distance between the 2 transformers will be about 10m so can i have one common earth mat and connect all earths to that?

Any comments / considerations on the above would be welcomed. Please see attached pdf for a more clear understanding.

RE: Earthing of MV Double Wound Transformers

The substation should have a single earth mat in both cases otherwise you risk having dangerous touch and step potentials developing between your two separately grounded systems. Bond everything to the single earth mat.
Regards
Marmite

RE: Earthing of MV Double Wound Transformers

NTK1987,
I'm interested in this representation of grounding.
The dashed rectangle around the three switchgear represents grounding grid OR frame of the switchgear?

RE: Earthing of MV Double Wound Transformers

(OP)
odlanor

This is simply how i have represented the steel frame of the complete switchgear panel and not the earthing grid. Do you agree with how i have drawn it?

Marmite...
Thanks for the response. So if i have a single earth mat that has less than 1ohm resistance, i can bond all of my MV equipment to the same mat? i.e. both RMU's, both transformers and the 3.6kV swicthgear?

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