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Volt drop % - Private Supply Def

Peter Hartley

Good day everyone 

Public supply Volt drop 3% Lighting 5% Power.

Private supply Volt drop 5% Lighting 8% Power.

Define private supply?

Option 1 - HV public grid supply to privately owned transformer. Is LV supply private?

Option 2 - Main source of supply is from Privately owned source of generation such as PV, diesel/gas/nuclear generator?

Why is this not defined in BS7671?

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  • 0

    Quite simpy, if you receive a supply at HV, and under certain other conditions according to ESQCR if you take a supply at LV, you will have a connection agreement that tells you what you should expect at the supply terminals, which will not necessarily be U0 + 10 % / - 6 % for a "standard" LV public supply.

    There's no way that BS 7671 could know what terms you have agreed with the supplier ... and therefore the standard can't be specific about this.

  • 0 in reply to gkenyon

    Just a thought here. Is there any provision which specifies voltage drop at HV. Surely, if HV is low, Lv must also be low?

  • 0 in reply to gkenyon

    I trust what you are saying is correct, but not following how this is applicable to the question. 

    What I'm trying to understand is how the designer of the installation specify the volt drop in terms of BS7671, when faced with the above scenarios? Assuming he has no knowledge of ESQCR.

  • 0 in reply to Peter Hartley

    Assuming he has no knowledge of ESQCR.

    The ESQCR should be freely available public knowledge -

    https://www.legislation.gov.uk/uksi/2002/2665/contents/made

    (including subsequent amendments:

    https://www.legislation.gov.uk/uksi/2006/1521/contents/made

    https://www.legislation.gov.uk/uksi/2009/639/contents/made

    )

       - Andy.

  • 0 in reply to Chris Pearson

    HV and EHV voltage variations are defined in the ESQCR and will normally be repeated in the connection agreements.  For HV supplies below 132kV the requirement is +/- 6% and for supplies of 132kV and over its +/-10%.   

    After that its up to the designer.  Normally once you go above 11kV the transformers would have on line tap changers controlled by suitable relays to keep the secondary voltage within pre-set limits.

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  • 0 in reply to Chris Pearson

    HV and EHV voltage variations are defined in the ESQCR and will normally be repeated in the connection agreements.  For HV supplies below 132kV the requirement is +/- 6% and for supplies of 132kV and over its +/-10%.   

    After that its up to the designer.  Normally once you go above 11kV the transformers would have on line tap changers controlled by suitable relays to keep the secondary voltage within pre-set limits.

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