Monitoring and logging domestic mains voltage? Crutches for sagging voltages?

[Chris Wilson]

I have noticed our house mains voltage is wandering significantly. I
noticed this a while ago but it seemed to settle. The other day I was
"gettering" a tube and saw the filament voltage had dropped from 7.5V
down to 6.5V. I checked the mains voltage and it was around 200V. We
normally see about 230V. I am going to approach our supplying company,
but anyone with experience of UK utility companies will sympathize
with my predicament. Is there any simple means of logging the voltage
over a few days?


Long term, assuming the worst and the utility company doesn't fix the
issue, is there a means of controlling the mains voltage buck / boost
wise, for supplying a big 5kV @ 1.2 Amps HV supply for a 3CX3000A7
and its 52amps center tapped filament
supply? It's a big 3kW plasma generator. I certainly don't want to
have to consider a generator. We are
out in the sticks, and I can't see me getting much support from
neighbors as none are particularly interested in electronics so long
as the heating and TV work Thanks.

[ElectroIrradiator]

Not sure about the UK, but here in Denmark you would normally need a very solid industrial grade electric installation to run something of that power level, like something you'd find on a large farm. Even then you need a triple phase 400V mains supply to even out the load. The issue is that a transmitter varies enormously in the power input due to the modulation, so on a 'feeble' mains supply everything will just fall apart as you key up. Think wildly flashing light bulbs etc. This starts to become a problem at much lower power levels than what you are contemplating.

Most generators will not like the load either, for the same reason. The load is too uneven for them to properly regulate, unless the generator is *very* oversize for your actual load.

[Whuffo]

A generator would probably be your least expensive option. Otherwise, you'll need a huge ferroresonant transformer - or a huge UPS with lots of batteries.

If it was me, I'd get (or rent) a generator and use that while I worked through the power company bureaucracy.

[dr.diesel]

Is there any simple means of logging the voltage
over a few days?

Simplest method, a bench meter with serial out, or something like a Fluke 289 that has logging capabilities.

[Chris Wilson]

Not sure about the UK, but here in Denmark you would normally need a very solid industrial grade electric installation to run something of that power level, like something you'd find on a large farm. Even then you need a triple phase 400V mains supply to even out the load. The issue is that a transmitter varies enormously in the power input due to the modulation, so on a 'feeble' mains supply everything will just fall apart as you key up. Think wildly flashing light bulbs etc. This starts to become a problem at much lower power levels than what you are contemplating.

Most generators will not like the load either, for the same reason. The load is too uneven for them to properly regulate, unless the generator is *very* oversize for your actual load.

Ah, I see where you are coming from, but the mains is down at circa 200 V with no load on it, not with anything heavy loading it. At least not here. It may be another local property (like a big chicken farm with huge shed cooling blowers etcetera, fairly nearby) is loading the supply.  It's not dropping due to MY demands, its low from time to time even if we just have a few house lights on. Today it's up at 240V. When all is well I can run a BIG TIG welder that draws at least 55 Amps and there isn't a lot of sag.  It would be nice to log voltage over time to a file so I can present them with some evidence gathered over a week or two. Cheers.

[ElectroIrradiator]

OK, that makes a lot more sense. I seem to recall we talked about this before, in relation to your PS project, but there the emphasis was to ensure your own mains supply was up for the task.

15% down from 230V is a bit much, to say the least, especially if you intend to try and maximize tube life by optimizing the heater voltage.

One silly - but potentially viable - option if you get desperate, would be to have an extra transformer or two, through which you can raise the primary mains voltage by a suitable amount, like 20 or 30V as and when needed. You'd need to keep an eye on the input voltage, but that is less of a problem.

Eg. an extra 24V/40A transformer would provide an additional 20V when fed with 200Vac (for a sinusoidal current load). This needs to be double checked though, as the load from the HT transformer won't be sinusoidal, but rather very peaky due to the rectifiers. If the total reflected resistance in the extra transformer is too high, then you may end up with a net voltage loss under load.

You could even run the main rig PSU-, the filament- and the HT transformer on each their own series transformer, in order to isolate the varying load on the high power HT rail.

[richard.cs]

In the UK if you complain about supply voltage then the distribution network operator will come and fit a voltage logger for a few weeks. I don't think they charge for it but I've never had to do it.

[Chris Wilson]

In the UK if you complain about supply voltage then the distribution network operator will come and fit a voltage logger for a few weeks. I don't think they charge for it but I've never had to do it.

I'll check that out Richard, thanks, I wasn't aware that they might do that. Useful info, cheers.

[SeanB]

If they do not the look at renting a voltage recorder for a week yourself, or use any DMM with logging function and DIY.

[M. András]

borrow a fluke 289 from a friend. set up the logging for 10min intervals or the one what you want and set the event treshhold. it will log at the set intervals then it will log anything immediatly when falls outside the current scale by the treshold value

[G7PSK]

The power company's by law have to maintain the voltage within certain limits and if you complain they come along and fit monitoring equipment. It could well be that your line has a bad joint some where, one thing you can do yourself if you have overhead feed line is turn on every thing in the house on a dark night and walk along the line you can often see arcing at bad joints, I have done this myself, make a note of the nearest pole number and phone the power company. If the problem is due to a large load like a grain dryer the only solution is an upgrade on the line.
The other thing is to get yourself an automatic boost transformer.

http://www.charlesindustries.com/main/ma_iso_boost.html

http://www.wmjmarine.com/w93100a.html

But for what they cost you could get a couple of diesel gen sets.

[minime72706]

http://www.minute-man.com/acatalog/Online_Catalog_Step_Up_and_Down_with_Voltage_Regulatoion_187.html

[Psi]

You can get servo controlled variacs that maintain a steady AC output within a wide input range. Ya can even build them pretty easy using a variac and a windscreen wiper motor from a car and some simple logic.

They dont respond instantly to changes of course, it takes a fraction of a second to wind the variac to the correct position if the line changes suddenly.

[jc101]

Interesting thread, I had the opposite, my incoming mains voltage was 255v for long periods - my UPS* was trimming this down and reported this.  I contacted UK Power Networks (via twitter @UKPowerNetworks) and they called me back a couple of hours later.  Explaining the problem they first visited the local substation and measured the supply in the house.  They caught it up at 252v so arranged for a logger at the meter for a week, some oddities noted, things have been very stable since.  I believe they work on 208-253 is "normal" and my supply does move around a bit but now tracks closely to 240v most of the time.

Depending on where you are in the UK, it may not be the people above, but they were amazingly helpful and always kept me informed what was happening.  What the people who visited did say is they reply on end users reporting things like this, they do not proactively monitor voltages at the end user level.  They are, however, busy at the moment following the recent storm...

* I have an APC UPS on my computer gear, which also acts as a logger for the incoming supply.  I records an average over a minute with min/max/ave and dumps that log to an FTP server each day.

[grumpydoc]

I believe they work on 208-253 is "normal"

EU regs state 230V +10% -6% which gives a range of 216V to  253V, so 200V is definitely out of spec - if that's what Chris is getting.

[richard.cs]

I believe they work on 208-253 is "normal"

EU regs state 230V +10% -6% which gives a range of 216V to  253V, so 200V is definitely out of spec - if that's what Chris is getting.

That's not quite true. It's +10% -6% in former 240V countries (such as the UK) and +6% -10% in former 220V countries, with the eventual aim of standardising on +/- 10% and no-one in reality ever changing the supply voltage on existing installations. There are quite a few substations in the UK still on the 250V tap anyway, but due to load they stay under 253V (230+10%) most of the time.

[grumpydoc]

That's not quite true. It's +10% -6% in former 240V countries (such as the UK) and +6% -10% in former 220V countries, with the eventual aim of standardising on +/- 10% and no-one in reality ever changing the supply voltage on existing installations.

Trust the EU to come up with something like that - surely it would have made more sense to start at 230V +/- 10% (which would cover the legacy 220V and 240V supplies) and then move to +/- 6% after a transition period.

[Chris Wilson]

Some great advice and suggestions. I have a little Ebay digi display hooked up on my desk showing mains voltage and it has been 238 to 243 every time I have looked at it during the last couple of days. The display is surprisingly accurate for the price, although it won't log or do anything fancy. I will contact Scottish Power and see what they think. In hindsight I believe the low voltage may occur for a longish period of time after a power outage, of which we in this hamlet suffer at least once every couple of months. Usually they are of less than 5 minutes duration. Next time we have one I'll look at the post event supply voltage. If I get any useful feedback from the utility company I'll post here. Thanks again!

[richard.cs]

That's not quite true. It's +10% -6% in former 240V countries (such as the UK) and +6% -10% in former 220V countries, with the eventual aim of standardising on +/- 10% and no-one in reality ever changing the supply voltage on existing installations.

Trust the EU to come up with something like that - surely it would have made more sense to start at 230V +/- 10% (which would cover the legacy 220V and 240V supplies) and then move to +/- 6% after a transition period.

I think the actual intention was a direct move to +/-10% but individual countries pushed back claiming legacy equipment leading to various places adopting asymmetric limits. Of course the incandescent lamp manufacturers (the few that are left) hate it because it has a huge effect on lamp-life and they have to produce 220V 230V and 240V models yet none of their customers really know what they need since everything is nominal 230V.