Transformer Configuration

[vennivivi]

Hi,

I am actually designing one 11 k V distribution switchboard for a factory. The national grid feeds at 22 k V. There is one 10 MVA 22/11 k V Yd11 transformer, rather new and in very good condition,and the management is pushing to use this transformer. The 11 k V distribution will feed four 11 kV/590 V transformers which are yet to be purchased.My concern is the earthing on the 11 k V side. I have the choice to purchase one new 10 MVA Yy or Dy 22/11 kV transformers or to use the existing 10 MVA Yd11 transformer and source one of the new distribution transformer and equip the latter with a neutral earthing compensator for the earthing on the 11 k V distribution. Is such type of transformer readily available and is such configuration commonly practiced ?
Any views ?

Grundig

 

[Marmite]

I would caution against combining your system earthing function in one of the distribution transformers, as if you ever switch it out you will lose your whole 11kV system earth. I suspect it's going to be cheaper to buy an earthing transformer than a new 10MVA 22/11kV transformer. You could ideally connect the earthing transformer direct to the 11kV terminals of the 22/11kV Tx or feed it from it's own breaker on your 11kV switchboard. The earthing transformer should be a zig zag or star delta. Schneider publish a Cahier Technique covering industrial MV system earthing.

http://www.schneider-electric.com/d...bility-safety/high-voltage-plus-1kv/ect62.pdf

Regards
Marmite