AC Mains Voltages

[threeseven]

Just checked the mains voltage here, 241v. I've seen it as low as 235 and as high as 248,
rural area, post mounted TX.

[McMurdo]

We have our own transformer off 11kV and no-one's changed it when the EU specs came in.
When I worked for a company who repaired instruments, we would often have the mains voltage dataloggers (Rustracks) in for repair and we'd leave them running all day. They plotted the mains voltage every 2 seconds or so. The printout resembled a sawtooth waveform. This was caused by the auto tap changing in the substations. As the morning crept on, the mains would increase to around 256 whenupon it would jumps back to 235 or 240 or so, or the other way round throughout the day. So an instantaneous voltage reading for most users is pretty meaningless...it wanders slowly but surely between limits.

[Gabe001]

I've been monitoring my mains voltage using a smart plug for a few months. I was really surprised by how much it fluctuates during the day.

Charts attached.

Is this normal?

Gabriel

[g8jzyian]

Uk voltage of a single phase supply can be between 253V and 216.2V

[broadgage]

Although the voltages observed are within the statutory tolerances, the variation is in my view greater than normal.
This suggests a large and intermittent load, either in your home or on the same DNO supply.

If incandescent lamps are used for lighting I would expect a very obtrusive flicker during the dips in the voltage.

[Gabe001]

The variation is quite high, I agree. There are no abnormally high loads in my house - I'm sure of this as I have an energy monitor. Looks like all the people in my area wake up as 6 and turn on the kettle!

[G6Tanuki]

More likely to be people with power showers, some of them are rated at 15KW. A couple of them on the same phase as your house can cause a significant voltage sag..

[G.Castle]

Originally Posted by G6Tanuki

More likely to be people with power showers, some of them are rated at 15KW. A couple of them on the same phase as your house can cause a significant voltage sag..

Electric heated throughput showers surely? Power showers just use a pump and household hot water normally.

[G6Tanuki]

I guess it is a matter of terms, most people don't really differentiate, calling anything that gives a healthy blast of nice hot water a 'power shower'.

[Jez1234]

Worst I ever saw was 208V. This was at a hi fi enthusiasts gathering (they go by the stupid name of a "Bake off"). A few items were behaving slightly oddly and then a valve amp with regulated HT started motorboating loudly! I explained that it looked like motorboating and probably a dodgy regulator section of the circuitry. Another enthusiast there (not even a tech guy) suggested I use the DMM I had with me to test the mains voltage... well I'll go to the bottom of our stairs it's only 208V!

It was largish function room of a pub. Quite a lot of hi fi gear plugged in but the whole lot would not have added up to more than 1-2KW.

[Sergeauckland]

Here in rural Suffolk, my mains is very stable at 240 +-3v. Highest I've seen it was 245, and the lowest 236, so nobody here has heard of 230!

Not noticed any large variations with my usage as my mains source impedance is nicely low, or a lot of variation during the day.

S.

[ms660]

There was a 270V event in the area where I worked back in the 1980's, lots of TV mains transformers, reservoir capacitors, X2 capacitors etc and fridge/freezer motors gave up amongst other things. The increased supply for peak time didn't return to normal for several hours after peak time, by which time the damage had been done.

Lawrence.

[broadgage]

When I was a child, an aged relative in a remote village had "summer bulbs" (250 volts) and "winter bulbs" (220 volts) at least for the most used lights.

That was back in the day when GLS lamps were sold retail in a selection of voltages.

The better informed users of lamps would often specify the "wrong" voltage lamps for some good reason.
Theaters often used 210 volt or 220 volt lamps on 240 volt circuits for the blue lights in footlights. The blue lamps tended to be rather dim otherwise.

Photographic studios often used 200 volt lamps on 240 volt circuits for a brighter light.

[kellymarie]

Here where I ami near weymouth I get around 233 to 241 volts measured on a fluke meter in my kitchen the voltage seems to vary more than it did partly because they built a new shopping unit with flats above that is supplied from the same 500Kva transformer as my road The shops have lots of of chilling and heating loads. In another part of town voltage rarely goes above 225 volts

[Beobloke]

Here in rural Hampshire we’re fairly consistent at 235-240V.

The only exception was after a power cut last winter when, after a hour or so, the power came on for 20 minutes or so at around 112V! Several neighbours had items damaged (including one central heating controller) but our only hiccup was our active loudspeakers that continually clicked on and off until I shut them off at the mains sockets.

After those 20 minutes, the power went off again, and we ended up on a generator for three weeks until the blown local mains transformer was replaced.

[Radio Wrangler]

Originally Posted by Jez1234

It was largish function room of a pub. Quite a lot of hi fi gear plugged in but the whole lot would not have added up to more than 1-2KW.

Given the liking for 'linear" power supplies with monster reservoir capacitors, long with transformers and rectifiers to scale, the current taken from the mains is focused into a large, short spike close to the peak. All the similar circuits will act with close synchronisation knocking a hell of a chunk out of the mains voltage.

On top of this, most DMMs read peak voltage on AC but are scaled to display the RMS that goes with it for an assumed perfect sinewave. And as the peak is the most nobbled part of the cycle...

Choke input filters (they have their own problems...) of power factor correction are fairly rare in the hifi world. My monster TIG welder has PFC, but my hifi amp flickers the lights.

I remember Bill telling me that Linn had gone over to SMPS some time ago for PFC and soft switch-on to meet mains harmonic regs with some of their larger amps.

David

[The Philpott]

I'm lucky that i'm very stable here (well my voltage is, anyway).
I did shut down all the 'old school' fairy lights a few christmases ago, as we had a lengthy peak at 256v, and a few of them popped off. I can only assume that it was an over compensation for many ovens cooking turkeys (along with everybody's festive lights)

Dave

[Jez1234]

Originally Posted by Radio Wrangler

Given the liking for 'linear" power supplies with monster reservoir capacitors, long with transformers and rectifiers to scale, the current taken from the mains is focused into a large, short spike close to the peak. All the similar circuits will act with close synchronisation knocking a hell of a chunk out of the mains voltage.

On top of this, most DMMs read peak voltage on AC but are scaled to display the RMS that goes with it for an assumed perfect sinewave. And as the peak is the most nobbled part of the cycle...

Choke input filters (they have their own problems...) of power factor correction are fairly rare in the hifi world. My monster TIG welder has PFC, but my hifi amp flickers the lights.

I remember Bill telling me that Linn had gone over to SMPS some time ago for PFC and soft switch-on to meet mains harmonic regs with some of their larger amps.

David

It was a true RMS DMM. It's a very good point but somehow I don't quite buy it in this case. Several of the amps in use were valved so no monster reservoir caps, there were no humongous class A Krells or anything like that, and systems were being demoed by their owners one at a time as it was just one large room (several of the systems would have been on but no music playing at the time and some simply not powered up).
My best guess is that either the wiring in the pub had a fault on the ring main for this room (maybe a high resistance fault somewhere or maybe the original electrical contractors had skimped on the wire) or maybe an unresolved issue with the local substation.
I've never experienced anything similar at any large pub gig where backline adds up to say 1500W and power amps for PA system kicking out 2-5KW plus sometimes many KW of lighting, some of it triac controlled.

[AndyWright]

I live in rural location here, but the pole mounted transformer is only about 150 yards from the house. There are 4 houses supplied from 2 of the phases according to the powergrid engineer.

Normal mains voltage is about 248V. Last month we had a neutral fault in the underground cable which runs to the pole transformer. The mains voltage was varying between 160 and 350V. Scary stuff, but all appliances survived.

[GrimJosef]

Originally Posted by Jez1234

... This was at a hi fi enthusiasts gathering (they go by the stupid name of a "Bake off") ...

The name's just a forum convention and no more stupid than calling a coupling capacitor feeding an output valve "that capacitor". It does confuse people who aren't part of the 'in crowd', but there you go ... To be honest I've been to quite a few bake-offs and they do seem to involve a wholly disproportionate amount of cake, and sometimes there's a hi-fi system playing in the background .

Back on topic, the poor quality of the mains, both in terms of RMS voltage and waveform purity, can be a trial when you're trying to carry out careful measurements. I believe I'm not the only one who's used a stand-alone synthetic mains supply (mine's based on a modified computer UPS) when I want repeatable results from my valve tester. The voltage here varies from about 234V to 249V (extreme values seen in checks carried out perhaps a few times a year over a decade). Slightly off-topic (again), given the thread title, but I also went through a phase of having a small DC offset (less than a volt if I remember rightly) which would appear around 19:00 and last through the evening. I was working at the time on some US-manufactured equipment with hard-working toroidal mains transformers and the DC caused them to buzz irritatingly. I never confirmed the source of the problem but I was aware that a nearby large supermarket started its overnight bakery operations at around that time.

Cheers,

GJ