I believe someone was recently talking about voltage spikes, though I can't find the thread in Google Groups to hang this on. I happened to be watching my consumption thingy this morning and noticed that it was constant at 249 volts. Then it went up to 250 for 30 seconds, back down to 249, then back up to 250 again. For a good five minutes it hovered around 249-250. Then it came down to 248, then 247.
Aren't these spikes damaging to sensitive equipment? (TVs, DVD Players etc) I don't worry about the PC because I have a UPS on it. The voltage is ~supposed~ to be 240 in the UK.
Voltage in the UK was harmonised with Europe on 1st January 1995 and is supposed to be 230V +10%-6% (216.2?253 V).
So, your fluctuations are within tolerance. Most equipment is designed to work at 110v - 220v (at 50 or 60Hz) look at the rating plate. That voltage is nominal and will not include the tolerance.
So only 3v change, depending on the quality of you supply you may well get a bigger fluctuantion when you drop a decent load on, say
5kW or more.
They aren't spikes just norm fluctuation caused by local load variations, either in your imdeiate vicinty or in your home. The nominal UK voltage hasn't been 240v for years. See other post. Note that the "harmonised" range covers the old 240v spec so nothing had to change. The only comment I'd make about the voltage sitting at 250 odd is that incandescent light bulbs will have a much shorter life.
We used to get through 40W candles in the living room (6 in use
18hrs/day) at about one per month and other odd 60W bulbs at several a year. Bought a UPS plugged it in and it went straight into "voltage trim" mode I thought it was faulty! Measured the volts up at 250 or so, reported it, men arrived in a couple of hours confirmed the reading and came back a day or two later to adjust the tapping on our transformer. Voltage now sits between 235 and 245 (was 245 to 255) and incandescent light bulbs last "forever".
The post about voltage variation was probably mine from the 3rd March wondering if the grid had had a problem as our volts had risen to 253 for quite long periods overnight 2nd/3rd. Since then things have been with the normal 235 to 245 range.
Some time before Christmas, I inherited from a deceased works colleague a purpose-built home-made meter for measuring the mains voltage (a 4" moving-coil meter + rectifier). After testing it and tweaking it slightly so that it read correctly at 230V, I left it plugged in, sitting on the desk, so that I could instantly see how the mains was doing. I have seen some considerable variations.
Before Christmas, the typical 'normal' voltage was 230V, occasionally going up to 235. However, when the really cold weather started, after around 5pm, the voltage would start to drop and, on several days, regularly fell to 215V. The lowest (checked on a couple of digital meters) was 214.4V.
After the New Year, have noticed that the typical 'normal' seems to be
235V (even when it was still very cold), and I occasionally see as high as 245V. [Presumably someone decided to change the output tap at the substation.] However, a couple of nights ago, I noticed that, every 30 seconds or so, the lights were very obviously suddenly going alternately dim and bright. The mains was abruptly jumping between 230 and 220V, and I was rather concerned that this might indicate that a power cut was about to happen. However, an hour later, things settled down, and the mains was a steady 235V again.
I don't measure the mains voltage but I do notice fluctuations. All the lights dim noticably in the house for a short time. It happens fairly frequently in the early evening. It does not appear to cause any problems to computers etc.
Nor should it - SMPS should be very tolerant of such things - after all, they're usually considerably over rated in PC applications and only have to up the duty-cycle briefly.
I'll second that and just add that unless all the supply cables are superconductors then the voltage will vary according to the load in both MMs house and neighbouring houses.
MM - It is not unusual for the voltage to drop by as much as 8 volts in a house when an electric shower is switched on depending upon the external resistance of the supply to the house.
but did the frequency go down with the volts? I have a far eastern LED Lloytron clock that seems to sync to the mains. If the frequency goes down the clock runs slow.
No. I haven't been monitoring the mains frequency. I've only been keeping an eye on the volts (simply because I acquired the meter, which sits permanently plugged in, on a corner of the desk).
I was surprised to see how low the voltage sometimes went (right down to the minimum limit). When it was really cold over Christmas and New Year, I expect the guys at the power stations were shovelling coal for all they were worth, and that the frequency (which is of less interest than the voltage) was well down on normal.
Obviously, any type of clock which uses the mains frequency will run fast or slow if the frequency varies. My understanding is that the generating people are supposed make sure that, come hell or high water, during a 24 hour period the correct number of cycles are delivered, so that the clocks are correct at 8am. I'm not sure that they always achieve this!
The frequency is very important, it's maintained at 50Hz +/- 1% ie
49.5 to 50.5 Hz nut National Grid work to an operational limit of +/-
0.4% (+/- 0.2Hz).
Oh they do! Questions get asked in the house if they don't. IIRC the last time they had to announce that mains driven clocks had the wrong time and would need to be corrected was during the winter of 1947...
Almost all LED clocks are mains synched. Since they have to be mains powered anyway (yeah, mostly) then they're already connected to a well regulated (by statute) frequency source.
As it happens, I have an exception, an LED clock that uses the RDS data to set the time, though in the absence of decent reception it seems to cope tolerably - presumably off the mains frequency or a crystal.
Maybe 20-30 years ago it dropped to minus 4 secs or so on one occasion when there was a split system. It *might* have been October 1987. Not sure if they got the clocks back to zero error at +24hours.
During winter on another occasion the frequency dropped to somewhere in the mid to high 47's before a system split and load shedding gave a high frequency in the north and midlands and a low one in the south.
It took a hell of a lot of work to get the two systems back in sync, and as a consequence over the next couple of years they changed the synchronising relays associated with a very large number of circuit breakers across the 400kV and 275kV grid such that a second method of automatic closure was possible dependent on slip angle and rate of change of slip angle rather than just the slip angle. These could be primed and left for 15mins so that if the system either side of the breaker met the targets it would automatically close, previously the only method was a 2 minute timer for 'perfect sync' or a manual closure that ran the risk of exploding the breaker into copper and porcelain shrapnel.
The long period of split running during this incident gave a clock error such that various bits of the country were out of sync by a second or more. None of this made the papers at the time :)
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