RMweb Gold martin_wynne Posted November 4, 2015 RMweb Gold Share Posted November 4, 2015 I noticed lower than usual mains voltage today. And now, surprise, surprise: http://www.bbc.co.uk/news/business-34723259 Currently 216V here. Explains why my lunchtime toast took a lot longer than usual. If you are using a microwave, allow a lot longer for food to cook properly. Microwave ovens are very susceptible to low mains voltage. Martin. Link to post Share on other sites More sharing options...
APOLLO Posted November 4, 2015 Share Posted November 4, 2015 And it ain't winter yet. Stock up on batteries and wooly jumpers !!!!!!!!!!! Brit15 Link to post Share on other sites More sharing options...
RMweb Premium uax6 Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 I better dig my genny out and give it a service. I have 4 Kw capacity, do you think the grid would like to buy some off me? Andy G Link to post Share on other sites More sharing options...
RMweb Gold russ p Posted November 4, 2015 RMweb Gold Share Posted November 4, 2015 Everyone should switch everything on to teach the government a lesson! Link to post Share on other sites More sharing options...
Nearholmer Posted November 4, 2015 Share Posted November 4, 2015 But, mightn't 216V be just about within tolerance, depending upon exactly where/how you measured it? I may be wrong, but I thought the standard was 230V +10% -6% at the consumers terminals, which gives 216.2V. If you were measuring further downstream than the terminals, you could well get a result slightly lower. So, mightn't allowing "...... a lot longer ......." on the microwave be an overreaction? Thinking about it, the microwave timer is probably not that precise anyway. Ours only does 10s increments. K Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted November 4, 2015 Author RMweb Gold Share Posted November 4, 2015 But, mightn't 216V be just about within tolerance, depending upon exactly where/how you measured it? Sure it is within tolerance -- legally it is not allowed to go lower because it could be dangerous, for example to life-support equipment. If they can't maintain the minimum they are required to cut power entirely (load-shedding). But usually here it is around 239V. I noticed a significant reduction today. Power is proportional to the square of the voltage, so the effective reduction is 216^2 / 239^2 = 82% , i.e. one fifth of my usual power is missing today. Martin. Link to post Share on other sites More sharing options...
RMweb Gold Metr0Land Posted November 4, 2015 RMweb Gold Share Posted November 4, 2015 Permission to ask a dumb question? How are you guys actually measuring the voltage? How do I know what I'm getting? Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted November 4, 2015 Author RMweb Gold Share Posted November 4, 2015 No Martin, it isn't. A device with a specific power rating will consume more current when the voltage drops. P=U/I so a 1kW apparatus will consume 4.14Amps on 239V, while at 216V it saps 4.63 Amps from the National Grid. Don't be silly. Resistive devices such as ovens, heaters, kettles, toasters, irons, showers, don't change element resistance according to the applied voltage. If the voltage drops, so does the current and the power. You are correct for the switch-mode power supply in this computer and my TV, etc., but they are only a small proportion of my domestic power consumption, and I don't need them to cook a meal. Martin. Link to post Share on other sites More sharing options...
RMweb Gold Metr0Land Posted November 4, 2015 RMweb Gold Share Posted November 4, 2015 Look here: https://en.wikipedia.org/wiki/Voltmeter Unless I'm missing something that tells us what a voltmeter is, as if we didn't know already, but doesn't tell us how to go about measuring one's domestic supply? Are you sticking the device shown into your 13amp sockets? Methinks not. Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 It doesn't matter that much if the voltage drops by a significant amount on the grid - yes things like kettles might take longer to boil, etc but thats only a minor inconvenience. The BIG problems start when the FREQUENCY drops away from 50Hz - many vital bits of kits NEED to run at that frequency and lives can be put at risk if it drifts so the National Grid is setup to sacrifice voltage levels if necessary. Link to post Share on other sites More sharing options...
RMweb Premium jjb1970 Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 The principal parameter which grid are interested in is indeed frequency, whereas the allowable tolerance for voltage is quite wide the frequency band is extremely narrow. Link to post Share on other sites More sharing options...
tersono Posted November 4, 2015 Share Posted November 4, 2015 I don't care about my toast taking a bit longer, but if it stops me running trains there's going to be trouble! Link to post Share on other sites More sharing options...
Judge Dread Posted November 4, 2015 Share Posted November 4, 2015 The principal parameter which grid are interested in is indeed frequency, whereas the allowable tolerance for voltage is quite wide the frequency band is extremely narrow. Many years ago I went with a party on a visit to the Drax power station. One thing that really interested me was the sight of two clocks on the control panel. One was clockwork and the other electric. The clockwork one showed the "true" time and the other was used to warn of frequency drop off in the wee small hours as it became slower than the other. Frequency then could be adjusted so they both agreed with each other. Simple but effective thought I. Link to post Share on other sites More sharing options...
RMweb Premium Clive Mortimore Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 It doesn't matter that much if the voltage drops by a significant amount on the grid - yes things like kettles might take longer to boil, etc but thats only a minor inconvenience. The BIG problems start when the FREQUENCY drops away from 50Hz - many vital bits of kits NEED to run at that frequency and lives can be put at risk if it drifts so the National Grid is setup to sacrifice voltage levels if necessary. From my time as apprentice with the CEGB, Phil is right about the frequency being the most important part of the recipe. Radio 4 this evening had a short piece about the problem the National Grid is facing today. Owing to the lack of wind there is less power being generated, not made any better with the closure of our coal power stations with no replacement of any type of power so lack of back up and the very dull weather has meant lights going on earlier and using more than normal amount of electricity for this time of year. More used than being generated, something has to drop and the voltage is less important than the frequency. Power has been brought from Ireland today. Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted November 4, 2015 Author RMweb Gold Share Posted November 4, 2015 My voltage is now up to 228V from 216V earlier. The extra 12 volts from Ireland are to 5ft-3in gauge. Link to post Share on other sites More sharing options...
RMweb Gold 30801 Posted November 4, 2015 RMweb Gold Share Posted November 4, 2015 Meanwhile the government will chip in five grand to help you buy an electric car... Link to post Share on other sites More sharing options...
steve1 Posted November 4, 2015 Share Posted November 4, 2015 Whoosh! That was the sound of all that complex calculation about amps, volts, etc going over my head... steve Link to post Share on other sites More sharing options...
Judge Dread Posted November 4, 2015 Share Posted November 4, 2015 Whoosh! That was the sound of all that complex calculation about amps, volts, etc going over my head... steve Watts = Volts X Amps. As my lecturer used to say "A system is fed at 250* volts comma, don't touch the comma it's alive!" * Pre decimalisation Link to post Share on other sites More sharing options...
APOLLO Posted November 4, 2015 Share Posted November 4, 2015 The principal parameter which grid are interested in is indeed frequency, whereas the allowable tolerance for voltage is quite wide the frequency band is extremely narrow. Yes. Have a look at the National Grid real time frequency. A bit up and down at the moment. As far as I know the balance of ups (over 50Hz) and downs (under 50 Hz) needs to balance over a set time (whatever that is - anyone know ?). http://www2.nationalgrid.com/uk/Industry-information/electricity-transmission-operational-data/ Another interesting site http://www.gridwatch.templar.co.uk/ And a scary one http://www.dailymail.co.uk/news/article-2810651/Will-lights-winter-Biggest-danger-power-blackouts-eight-years-forces-energy-bosses-consider-paying-factories-shut-down.html Ex National Grid gas engineer myself. Stocking up on various things as said. I'm not joking, and hope we squeeze through the coming winter - but we WILL get caught out sooner or later. Edited to add - I see coal is generating only around 25% of the national demand at the moment. Last winter it was consistently around 35 to 40%. Is the shutdown of coal plant hitting already ?. If so, god help us over winter. Brit15 Link to post Share on other sites More sharing options...
RMweb Premium jjb1970 Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 :no:I take it we don't want to open up the subject of capacitive and inductive loads and power factor then....... Link to post Share on other sites More sharing options...
RMweb Premium Clive Mortimore Posted November 4, 2015 RMweb Premium Share Posted November 4, 2015 Yes. Have a look at the National Grid real time frequency. A bit up and down at the moment. As far as I know the balance of ups (over 50Hz) and downs (under 50 Hz) needs to balance over a set time (whatever that is - anyone know ?). http://www2.nationalgrid.com/uk/Industry-information/electricity-transmission-operational-data/ Another interesting site http://www.gridwatch.templar.co.uk/ And a scary one http://www.dailymail.co.uk/news/article-2810651/Will-lights-winter-Biggest-danger-power-blackouts-eight-years-forces-energy-bosses-consider-paying-factories-shut-down.html Ex National Grid gas engineer myself. Stocking up on various things as said. I'm not joking, and hope we squeeze through the coming winter - but we WILL get caught out sooner or later. Edited to add - I see coal is generating only around 25% of the national demand at the moment. Last winter it was consistently around 35 to 40%. Is the shutdown of coal plant hitting already ?. If so, god help us over winter. Brit15 Hi Apollo It is very scary we will not have the power to provide what is required if we have a bad winter. It is a very shortsighted nation that has not invested in new plant to replace the old with both private and public money. Apart form the lack of coal trains the closure of our polluting worn out coal fired power stations should of happened. It is the non replacement that is a scandal. Every government since the 1980s has not worried about our future, if they had the new nuclear plants would be generating power not headlines, there would have been modern less polluting gas/oil/coal fired stations built as well as much more investment in renewables. Back to John's comment about the clocks in a power station control room, I can remember there being two clocks at Goldington next to the civil defence speaker ready to give us the four minute warning. I cannot remember what the senior engineer in the control room said we had to do in the 4 minutes. That wasn't the most scary thing, they got me at 16 to connect a 30MW set to the grid. I was stood next to the big panel with all the dials on it. I had two pistol grip switches, one in each hand. I had to wait for the frequency being generated and that of the national grid to match then turn the switches. If the set was brought on line at the wrong frequency then something to do with the back EMF (if I remember correctly) would make the exciter and/or generator act as a brake for the turbine and would twist the turbine rota and that would be the end of it. Or were they just making me feel more nervous? Link to post Share on other sites More sharing options...
APOLLO Posted November 4, 2015 Share Posted November 4, 2015 Capacitance lead, inductive lag, phasor rotating vector diagrams, star & delta connections - forgotten it all long ago !!! Not bad for a lifelong gasman, then it was my ONC mechanical engineering back in 1969. 12 volt DC man since then - simple and safe !!!! Brit15 Link to post Share on other sites More sharing options...
Nearholmer Posted November 4, 2015 Share Posted November 4, 2015 All good stuff, but I'm still unconvinced of the need to worry about microwave cooking durations while supply voltage remains (barely) within tolerance, there being so many other variables involved in food preparation. Will be interesting to see what the political fall-out is if we do experience "aggressive load shedding" - in the public mind it's a sort of basic test of government competence to be able to "keep the lights on". Anyone else remember the 1970s? (I do find it comforting that the Daily Mail is running a scare-story though; that strongly implies that it isn't anything worth getting worked-up about.) K Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted November 4, 2015 Author RMweb Gold Share Posted November 4, 2015 If the voltage is low that equilibrium may well result in a higher than rated current, which can be dangerous. ??? For a simple resistive heating element the curve is not a straight line, but the gradient doesn't go negative. More volts = more amps, regardless of the element temperature. Here is the curve for a lamp filament: Martin. Link to post Share on other sites More sharing options...
APOLLO Posted November 4, 2015 Share Posted November 4, 2015 Agree Clive, the non replacement of closed and soon to be closed coal fired plant is most scary. I also think clean burn coal should have been looked at more here in the UK. Too late now probably. Germany is building new lignite (dirty coal) powered plants as I type. The generators from the recently demolished Didcot coal plant were exported to - Germany - for use in a new coal plant there. As to burning gas (a premium fuel) to make electricity - economics of the mad house long term in my opinion, seeing we are more and more dependant on imported LNG from "unstable regime" countries. Don't forget that on a freezing cold winters evening, it's peak load for both electricity and gas. Gas loads are also shed at times of peak demand - known as interuptibles. Large industrial users usually with in house alternative energy supplies that can be instantly turned on (dual fuelled oil / gas burners etc). This has saved our (gas industry's) bacon more than once in cold winters. So, I hope the current gas fired power stations have agreed fixed and secure supplies in peak times over winter, or it will really be lights out. Domestic gas supplies are secure (or as secure as can be - nothing is 100%) for if you loose pressure to a district you can't just turn it off / on like water or electricity. I've 40 years experience of this. We never lost supplies very often, but when we did (Pipeline failure at Runcorn back in the late 90's) - it was a week's job to get everybody safely back on, A nightmare. Trouble is none of "our leaders" are engineers. Good at folding towels etc and sod all else. Brit15 Link to post Share on other sites More sharing options...
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