UK Voltage Question

My plant has an inverter thats keeps tripping out
with an overvoltage error message.
I have taking readings from the meter in the main supply
panel with the following results.
ph1 - 435v
ph2 - 437v
ph2 - 433v
ph1-n - 249v
ph2-n - 253v
ph3-n - 249v
All phases were using around 500Amps at the
time, which is out average consumption.
So, my question is, are these voltages a bit high?
I was lead to believe that the UK voltage was now
around the 400/220 mark?
Thanks for any help.
Reply to
Curly Gouger
Loading thread data ...
It does seem on the high side - but when is the inverter tripping? If = it's tripping on decel, you may need a brake chopper and some braking = resistors - or perhaps extending the decel ramp time will help. Also = check the inverter setup - there may be a setting for supply voltage = that will alter the OV trip level.
cupra (remove nospam please to mail)
Reply to
On Thursday, in article "Curly Gouger" wrote:
The UK "legal" voltage is now 230V -6% to +10%, i.e. a range of 216.2 to 253V.
This means that your voltages are on the borderline of being too high, and if this is the on-load voltage at your equipment after drops due to the impedance (resistance) of the supply, then the voltage at the incoming terminals is probably a few percent higher, and definitely a case for a complaint to your electricty supplier, who can reduce the voltage by changing taps on the distribution transformer.
In talking to them you might find it helpful to have a look at
formatting link
and particularly the section "European Voltage Harmonisation" which will give you the correct regulation (Statutory Instrument) to quote when they start arguing with you.
The same technical note shows that a voltage reduction should be highly beneficial and while people like us supply transformers and voltage regulators, in this case it should be done by the electricity provider, not at your expense.
Reply to
Bill Lyons
Thanks for the advice,
The voltages quoted were when running fully loaded.
They swing quite a lot higher than that off load or at reduced load (have seen 265v ph-n)
We have our own HV transformer and we are on a long rural HV line.
I will give the suppliers a call and see what that say.... .... last time I spoke to them I was told it was quite normal to get high voltages off load.
regards, Curly/
Reply to
Curly Gouger
265 no load to 249 full load (the lowest you quoted) is a variation of approx 6%, due to the "regulation" of your transformer and cabling (and the incoming HV cable).
That does make things a little different. The -6% +10% limits apply if the electricity supply is at a nominal 230v.
For higher voltage supply to your own transformer, the supplier is required to keep the voltage at the input of your transformer within the limits of +/- 6% per paragraph 27(3)(c) of Statutory Instrument 2002 No 2665 - The Electricity Safety, Quality and Continuity Regulations, 2002.
[You can download your own copy at
formatting link
Does your transformer have taps - typically these might be at +5% +2.5% 0 -2.5% -5% ?
Reducing the supply by 5% would bring your no load voltage down to 252 and full load to approx 236 which would be much better for the inverter - I presume it is labelled for nominal 415/240 or 400/230 supply?
It is indeed normal to get high_er_ voltages off load. The IEE's practice is to allow 4% for on-load drops within the installation. Your 6% is a little high but not unusual. (Essentially this is why the MV limits are +/-6% but the LV limits are -6 +10%)
But the supplier has a statutory duty to declare the supply voltage (to your transformer) and maintain it within the regulations in the SI. Drops in the HV cable are part of his responsibility.
As you have your own HV transformer, what happens after it is up to you. If you can't drop the voltage by changing taps, there are other solutions.
I realise this is a slightly different answer than before, but things are different if the LV supply is from your own transformer.
Hope this helps but please feel free to contact directly by email
Reply to
Bill Lyons
is the load regenning back into the inverter? if so the DC link bus will trip out on overvoltage, you could rectify this by fitting a resistor module to the inverter or trying to up the overvoltage threshold on the unit above 150%
Reply to
Nigel Turton

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.