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HV & LV Metering Issue

Stuz
Hi All,

We have site which has been running for 6 months now. It's industrial process served via a 2MVA transformer fed from HV RMU at 11,000V. The transformer is cast resin with less than 1% loss. Our works were installing the transformer and LV panel with a significant post contract fitout by the developer including process supplies. It’s metered at HV but the site is reporting discrepancies between the HV and the LV meter on the incomer. The HV meter is indicating up to 50% more usage than the LV meter. Given that the 2 should generally even out, taking into account transformer and other losses I can only assume they have a significant harmonic issue caused by the process load which is greatly reducing the losses at the transformer. This was my initial thought when I saw the figures. Thoughts from the community?


Thanks in advance.
  • 0
    I had this problem, and the meter which was installed by the DNO's contractor had the CT ratio set incorrectly.
  • 0
    Johno12345:

    I had this problem, and the meter which was installed by the DNO's contractor had the CT ratio set incorrectly. 


    Not being party to their metering I don't know what it is, I assume it's 400/5. What was the outcome in the end?


  • 0
    we put our own meter on the LV side, which showed a consistent difference, told the DNO, who came and corrected the error and sent a credit note for about 150K!


    I cant remember what our ratio is but don't think its 400/5
  • Former Community Member
    0 Former Community Member
    The transformer is cast resin with less than 1% loss.


    Copper or iron, or both?


    What is the average usage from the LV meter?


    Regards


    BOD
  • 0
    Certainly sounds like a CT ratio setting error.


  • 0
    It has to be some metering cock-up like that - you my lose perhaps 5% to the angels and so much hot air and warm steel, but to lose 50% something would have to be on fire at that power level- you have not said that it is, so it has to be instrumentation. (harmonci curents are not lost, they end up as heat in the star delta trasformation) Check your meters first, and then get the DNO in (cheaper that way round, just in case it is not the HV side at fault.)
  • 0
    yes metering issue.  Check CT and VT ratios.  Also check the metering test blocks in case any short circuit links have been left in place.  Also possible that a VT fuse is missing or blown but that should have shown up on commissioning.
  • 0
    Thanks to everyone for their responses.

    The end user has approached the DNO and requested them to investigate their metering setup.
  • 0
    Seen this several times, either CT ratio on one of the meters, or HV setting on the DNO meter, I found a HV meter in Manchester set to 11kV on a 6.6kV network which resulted in a credit of £1.5m!

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