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Mains in UK can go up to 292VAC for periods of several minutes

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treez

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Hello,
Sorry to discuss UK, but i think the mains is more badly deviant in UK than some other countries.

Some time ago, a very kind edaboarder, KlausST sent me some data of the second-by-second mains voltage level in Bavaria , Germany. This was extremely interesting since the mains voltage was never seen to go above 235VAC, and that over 3 days.
We are suffering failures in our UK based products which appear to correspond to persistently high mains voltage….ie not short switching induced transients or lightning induced transients. We suspect that the mains is simply going up to around 413Vpk (292VAC) , or more, for sustained periods.
We believe that this is entirely possible since the UK mains voltage is not strictly regulated. The UK mains is in fact regulated mostly by probability which says that at any given time of day the amount of loading will be roughly equal to the previous days. As such, the power stations adjust their output throughout the day to kind of give feed-forward regualtion. There are also tap changers in the transformer sub-stations which roughly adjust the turns ratio of the mains transformers to kind-of regulate the mains to a degree.
However, these don’t operate quickly, so therefore the mains in certain areas of UK can easily go up to 292VAC for sustained periods of minutes…do you agree?
 

I've never witnessed anything like that and power stations basically can't adjust their output voltage, only the frequency. They have to produce the correct number of cycles per day in order that synchronous timers are accurate over a 24 hour period.

I've never heard of sub-station transformers having tap changers either. I think if stepped output from 100+ KVA transformers took place it would be noticed as regular dimming or speed change of appliances.

The most likely cause of higher than normal voltages is TP+N distribution with poorly balanced loads on the phases. Pulling one phase down makes the other phase voltages increase because Neutral adopts an offset. Why this would happen over a period of minutes is a mystery though.

Brian.
 

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Anyway, when in doubt, you can always employ a power datalogger to determine what is going on.

Dataloggers come in many flavors, capabilities and prices.
You may lease one.

If all you want is to timestamp overvoltages, those should not be that expensive.
 

Expectable voltage variations are specified in the test standards IEC 61000-4-14 (voltage fluctuations) and IEC 61000-4-27 (voltage unbalance). The applicable test levels don't exceed +12% variation (257 Vac).
 

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Deviations of that magnitude would be very noticeable to everyone. Incandescent and CFL lights would get substantially brighter, and many other devices would fail. Unless you've observed this directly, I highly doubt it's the case.
 
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Shifting the goalposts won't solve your problem. You need to pinpoint the failure mode in your device, then work back to the original cause. That's how investigations generally work.

Can you tell us more about the failure mode? Are you seeing multiple devices failing simultaneously? Milliseconds apart, or seconds?

If you haven't been able to observe the problem directly, then your don't have many leads...
 

Mtwieg has a good point: what is failing?

If the failure signature appears to be a sustained overvoltage, then the next step is to prove it:
Take a few units, and with a Variac and perhaps autotransformer elevate the voltage to the point of failure.

Then analyze the unit and compare the failure signature to the field failures.

Do they match?
 

As far as I see, treez didn't report any actual device failure. He's just considering possible failure mechanisms.
 
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As far as I see, treez didn't report any actual device failure. He's just considering possible failure mechanisms.
_____________
We are suffering failures in our UK based products which appear to correspond to persistently high mains voltage….
 
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Thanks. In this case, installing voltage monitoring devices is the only way to a reliable answer.
 

I've never witnessed anything like that and power stations basically can't adjust their output voltage, only the frequency. They have to produce the correct number of cycles per day in order that synchronous timers are accurate over a 24 hour period.

I've never heard of sub-station transformers having tap changers either. I think if stepped output from 100+ KVA transformers took place it would be noticed as regular dimming or speed change of appliances.

The most likely cause of higher than normal voltages is TP+N distribution with poorly balanced loads on the phases. Pulling one phase down makes the other phase voltages increase because Neutral adopts an offset. Why this would happen over a period of minutes is a mystery though.

Brian.

Small comment but sub-station make-before-break tap changers are quite common. They operate in a matter of seconds so a well designed system can in-fact regulate quite responsively. Though tap changers have limits naturally and for large shifts generation needs to be added or removed.


One other scenario I've heard of high lines is in residential areas with lots of installed solar.


I'm also wondering what the failure is. I'm accustomed to primary path components with 450V minimum voltage ratings. So I wouldn't expect 413V to cause a straightforward failure of, say, a cap.
 

Hi

I've never witnessed anything like that and power stations basically can't adjust their output voltage, only the frequency.

Speaking for Germany:

Voltage:
We definitely have transformers with variable output voltage in substations with 50...300kW. But it is not used for automatic output voltage adjust.
There are several tpas to adjust for some +/-xx percent.

Frequency_
I´m very sure whole Germany (and most of Europe) is fixed to the same frequency. The whole grid is tied togehther - impossible for different frequencies. Frequency control is made by huge central power plants (they are under the control of so called "TSO" like "TenneT"
See: https://www.mainsfrequency.com/
other interesting mains frequency informations (German language) https://www.netzfrequenz.info/

Klaus
 
Our designs for laptop chargers for Samsung specify no damage at 300Vac for 1 minute ....
 

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