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Autotransformers & Buck/Boost - use in the UK

willy

I need to reduce a 400V 3P+N supply voltage as it can drift over the +10% limit, I don't particularly need to regulate it, just get it a bit lower.


Initially I though a double wound transformer close to 1:1 with a few tap links to let me select a lower output.


From a bit of searching I can see a lot of information on the use of autotransformers and buck-boost transformers in the US, but not much for the UK.
Is using auto/buck-boost acceptable for the UK or are there some fundamental reason not to do this? These transformers will be significantly cheaper and much smaller, which makes them appealing.

The rating would be around 100-120kVA

Thanks

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  • 0

    I see nothing to prohibit or otherwise prevent use of an autotransformer in the UK. I believe that you will need three transformers, star connected so as to reduce the voltage on each phase by say 5% or 10%. Ensure that the neutral is continuous throughout, and remains nominally at earth potential.

    Why is this needed though ? a voltage at the upper end of nominal is often preferred. Older equipment was probably intended for 240/415 volts in any case, rather than for todays 230/400 volts.

    If only one or two items are suffering, a local to the load transformer might be cheaper and simpler.

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  • 0

    I see nothing to prohibit or otherwise prevent use of an autotransformer in the UK. I believe that you will need three transformers, star connected so as to reduce the voltage on each phase by say 5% or 10%. Ensure that the neutral is continuous throughout, and remains nominally at earth potential.

    Why is this needed though ? a voltage at the upper end of nominal is often preferred. Older equipment was probably intended for 240/415 volts in any case, rather than for todays 230/400 volts.

    If only one or two items are suffering, a local to the load transformer might be cheaper and simpler.

Children
  • 0 in reply to broadgage

    it is as a result of equipment failures and if I can get upstream tapped I will, but having a quicker alternative fix is needed as well.  I've seen 3ph auto transformers are available, so I'm assuming with it being a 3P+N supply it can only be YY wound auto transformer.  (Had it been a double wound transformer I guess DY or YY would suit)

  • 0 in reply to willy

    it is in effect Y but more like just the one Y with variable length legs ;-)
    There are normally either 3 single phase toroids, or a 3 legged core with a phase on each limb, with a thinner winding doing the the neutral up to the lowest tap, and the fatter wire doing the buck windings. There is a very small one that shows the construction on Ebay at  the moment. Its  not anything like large enough for your application but shows the 3 legged core construction nicely.
    3 toroids however just look like 3 toroids;-)
     

    The voltage optimiser companies sell you something like one or other of these shapes with some contactors for tap selection and extra ADS wrapped around it in a large box. 
    The smaller domestic ones sold in countries with really bad voltage control are often motorised  variac designs.

    As noted, beware the effect on Zs and ADDS operating times

    Mike.

  • 0 in reply to mapj1

    Ha yes, it's just a 'Y'  good point!

    Thanks

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