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HV & LV Metering Issue
Stuz 11001202379
3 Posts
Question
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.
8 Replies
Johno12345 11001196760
64 Posts
I had this problem, and the meter which was installed by the DNO's contractor had the CT ratio set incorrectly. 
Stuz 11001202379
3 Posts
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?

Johno12345 11001196760
64 Posts
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
perspicacious 20955492
327 Posts
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
Certainly sounds like a CT ratio setting error.

 
mapj1 80733779
2070 Posts
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.)
statter 16416862
53 Posts
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.
Stuz 11001202379
3 Posts
Thanks to everyone for their responses.
The end user has approached the DNO and requested them to investigate their metering setup. 

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