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33kV/11kV delta delta transformer

KDY

When specifying 33kV/11kV and 11kV/400V transformers for new building project is it acceptable for 33kV/11kV transformer to be specified with delta-delta windings thus relying on cable screen and ground earth paths back to the remote DNO main substation? As opposed to delta-star with earthed neutral star point.

  • 0

    If it's delta delta, how do you provide an earth reference to the secondary side?

       - Andy.

  • 0

    My thinking is that the incoming cable screens are connected to the room earthing so as to provide earth fault path to upstream MSS transformer but admittedly I am not sure on validity of this approach. 

  • 0 in reply to KDY

    I may well be picturing your setup wrongly, but in the case of an earth fault, I'm not seeing that your earth fault loop would actually be a loop (circuit) - so no fault current and so no disconnection. A picture might help...

       - Andy.

  • 0

    I assume this is UK practice, and the 33kV and 11kV side will be distributed 3 wires, no neutral and have earth fault detection and protection of some kind ?  At the EHT side you sometimes find autotransformer but I assume this is double wound ?
    you will need some sort of earthing transformer on the secondary side  Delta star is the UK usual, with either solid earth or L or R...

    from page 25 of https://www.nationalgrid.co.uk/downloads-view-reciteme/361558

    Mike

  • 0 in reply to AJJewsbury

  • 0 in reply to KDY

    I think you have indeed drawn the problem.

    Mike.

  • 0 in reply to mapj1

    Mike/Andy

    1. Thanks for the advice and references that is understood. I can now see need for creation of own earth using star transformation on secondary probably with neutral earthing resistor.

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