RMweb Gold Joseph_Pestell Posted June 11, 2015 Author RMweb Gold Share Posted June 11, 2015 PowerInc.png Kev. That's the bit that I had not understood. An over-delivery of voltage will also lead to an over-delivery of watts. PowerInc.png Kev. Brain not in gear. Lot of different things to worry about at the moment apart from this electrical problem. And O level Maths was 43 years ago! I am struggling to apply that formula to our situation. But taking your figure of 240v as the "correct" supply rather than 230v, we have been over-supplied by 32.5% on that Phase. That suggests to me that we have been overcharged 32.5 x 8.8/4.3 = 66%. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted June 11, 2015 Share Posted June 11, 2015 PowerInc.png The problem in that table is simple. It treats the resistance calculated at the 240V condition as a constant under the two supply voltage conditions, and then uses that value for the power calculation at 250V. This simply isn't true for 'dumb' devices which are almost purely resistive like filament light bulbs, electric fire elements and immersion heaters: the resistance varies proportional to temperature in the resistive element. It is however a worst case estimate for the power draw running a complex device which is able to maintain near constant resistance against varying voltage input. There should be a rubric to the table explaining this. Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 11, 2015 Author RMweb Gold Share Posted June 11, 2015 The problem in that table is simple. It treats the resistance calculated at the 240V condition as a constant under the two supply voltage conditions, and then uses that value for the power calculation at 250V. This simply isn't true for 'dumb' devices which are almost purely resistive like filament light bulbs, electric fire elements and immersion heaters: the resistance varies proportional to temperature in the resistive element. It is however a worst case estimate for the power draw running a complex device which is able to maintain near constant resistance against varying voltage input. There should be a rubric to the table explaining this. You have lost me there! We are fairly sure (pending confirmation from contractor as to which phase runs what) that the big problem item on single-phase is the water-heater (immersion). If I have understood properly what you have written, the oversupply/overcharge will only be 32.5% (318/240) rather than the 66% implied by the table as resistance in the element would not go up. What about the effect on our single-phase air-source heatpump? How would a wrong voltage, low or high, impact on its performance? The other aspect, very important to the business, is what damage may have occurred to the 3-phase equipment that we run. During last year's harvest, our press performed very poorly until, after much chivvying, the manufacturer agreed to replace the compressor. Apart from lost production, I don't want to run into the same problem again with a compressor, no longer under guarantee, breaking down because it has been damaged by this current problem. Link to post Share on other sites More sharing options...
RMweb Gold SHMD Posted June 11, 2015 RMweb Gold Share Posted June 11, 2015 The problem in that table is simple. It treats the resistance calculated at the 240V condition as a constant under the two supply voltage conditions, and then uses that value for the power calculation at 250V. This simply isn't true for 'dumb' devices which are almost purely resistive like filament light bulbs, electric fire elements and immersion heaters: the resistance varies proportional to temperature in the resistive element. It is however a worst case estimate for the power draw running a complex device which is able to maintain near constant resistance against varying voltage input. There should be a rubric to the table explaining this. True, but lets take a 1 kW kettle as an example. At 230v the kettle gets hot, boils the water and 'clicks off' in x minutes. Now increase the voltage by %32.5. (V now at 304.75volts) The kettle is switched on, gets hot, boils the water and 'clicks off' in y minutes. Where y=(x-extra power), ie it boiled quicker. The thing is, yes the heating element gets hot quicker BUT it reached EXACTLY the same temperature as the 230v boil. That temerature is ~100'C. Also, the power consumed will be similar. Whilst ON it consumed more power BUT for less time. You are charged by the average power (kW*Hr) not by the peak power consumed. Kev. Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 11, 2015 Author RMweb Gold Share Posted June 11, 2015 True, but lets take a 1 kW kettle as an example. At 230v the kettle gets hot, boils the water and 'clicks off' in x minutes. Now increase the voltage by %32.5. (V now at 304.75volts) The kettle is switched on, gets hot, boils the water and 'clicks off' in y minutes. Where y=(x-extra power), ie it boiled quicker. The thing is, yes the heating element gets hot quicker BUT it reached EXACTLY the same temperature as the 230v boil. That temerature is ~100'C. Also, the power consumed will be similar. Whilst ON it consumed more power BUT for less time. You are charged by the average power (kW*Hr) not by the peak power consumed. Kev. Well that's what I would have thought, based on my grade 6 O level. But the document says that a 4.3% oversupply leads to 9% more power consumption (not 9% more per minute, 9% total). And the water-heater does seem to be on more than one might expect, as evidenced by our remote monitor. Link to post Share on other sites More sharing options...
RMweb Gold SHMD Posted June 11, 2015 RMweb Gold Share Posted June 11, 2015 It will consume ~%9 more power IF the power is not interrupted. (By a thermal cut-out or temperature feedback circuit.) The kettle, emersion heater, lots of cookers (depending upon control strategy) will 'switch' the power off sooner and for longer. Things like light bulbs and AC motors will get 'hotter' as 34theletterbetweenB&D suggests. (~Only DC motors will go faster though!) Bulb (that's globes to you ozzies) life is directly proportional to temperature. The motor windings life will be greatly reduced by increasing their temperature - the insulation breaks down. Amongst other effects... (Like PSUs popping when their maximum ratings are exceeded!) Kev Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted June 11, 2015 RMweb Premium Share Posted June 11, 2015 You are charged by the average power (kW*Hr) not by the peak power consumed. Kev. Throwing a spanner into the works (Phut!!) Aren't three phase supplies metered by KvA rather that Kwh? This is to encourage premises to have unity power factor e.g. on domestic premises something like a normal ballasted fluorescent batten (not electronic!) will have a power factor way off unity (due to the mainly inductive load) but a commercial one will be fitted with a power factor correction capacitor to return it to unity. Keith Link to post Share on other sites More sharing options...
Robert Posted June 11, 2015 Share Posted June 11, 2015 Aren't three phase supplies metered by KvA rather that Kwh? For commercial properties at least, in some cases, I believe so - I haven't done anything much with three phase for quite a few years now. However, a place I used to work had a large number of mercury vapour grow lamps - and they had a large capacitor bank associated with them for power factor compensation. At home, I have three phase (it's pretty much standard in German homes) but that is metered in kWh. Of course, three phase in UK homes is very unusual. Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted June 11, 2015 RMweb Premium Share Posted June 11, 2015 At home, I have three phase (it's pretty much standard in German homes) but that is metered in kWh. Of course, three phase in UK homes is very unusual. It depends on the house and the sort of load. I used to have a 9 bedroom guest house which had three Electric showers (the rest were hot water driven) If I had increased to 4 or more the electric company would have required three phase to even the load. A fellow guest house owner with a smaller house but with more electric showers was on three phase. Keith Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted June 11, 2015 Share Posted June 11, 2015 ...The thing is, yes the heating element gets hot quicker BUT it reached EXACTLY the same temperature as the 230v boil. That temperature is ~100'C... Have you done the experiment? The assumption of constant temperature in the conductor is incorrect I promise you. The conductor runs way hotter than that, and simple physics tells you this must be so: notice that there is still energy transfer to the water when it is at 100C; which cannot occur if the element is at 100C. Expose such a water cooled element to greater voltage and it runs hotter, this is very basic physics. It used to be easy to prove with exposed element kettles, you can see the element glow with a fully dark-adapted eye in a blacked out darkroom, and alter in colour with changes in voltage (the olde A level physics course of actually being shown what's happening). And that's the outer insulating sheath you are looking at, inside the conductor is yet hotter. Link to post Share on other sites More sharing options...
Ozexpatriate Posted June 13, 2015 Share Posted June 13, 2015 You are charged by the average power (kW*Hr) not by the peak power consumed. kW*Hr is of course energy (not power) but I think you know that. It is cumulative energy that a kW*Hr meter measures. Link to post Share on other sites More sharing options...
Ozexpatriate Posted June 13, 2015 Share Posted June 13, 2015 with U=230V and an R of 50 Ohms, your current is 4.6A and P=1058W with U=240V and an R of 50 Ohms, the current is 4.8A and P=1152W Divide one with the other and you have about 9.5% increase (1152/1058x100%=109.5%) Still an 8.9% increase in power. (1152 - 1058) / 1058 = 8.9% It's the same as Kev's maths at the top of the page. P = V2 / R P1 = V12 / R If V2 = 1.0435 * V1 then: P2 = (1.0435 * V1)2 / R (P2 - P1) / P1 = 1.04352 - 1 = 8.9% Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 13, 2015 Author RMweb Gold Share Posted June 13, 2015 Well the mystery deepens. As one might expect (given the danger of stray 318v currents), our supplier got on to the distribution company who sent out an emergency team late yesterday afternoon. They took readings and everything was.........................perfect! A little above 240v on each phase and apparently a good impedance reading (whatever that is). Link to post Share on other sites More sharing options...
RMweb Premium melmerby Posted June 13, 2015 RMweb Premium Share Posted June 13, 2015 Well the mystery deepens. As one might expect (given the danger of stray 318v currents), our supplier got on to the distribution company who sent out an emergency team late yesterday afternoon. They took readings and everything was.........................perfect! A little above 240v on each phase and apparently a good impedance reading (whatever that is). So who came up with the rather odd readings in the first place? Keith Link to post Share on other sites More sharing options...
raymw Posted June 13, 2015 Share Posted June 13, 2015 I would hope the electricity supply company measured the voltage at your supply point, with your load disconnected. If you have the wide variation in voltages that you think you have, then that is due to things on your side of the supply point - unbalanced loads, corroded terminals/whatever. I would suggest you get a competent electrician to check it all through, one who does not use a clamp meter to guess at voltage. From what you have said, it appears that maybe the wiring has been extended over the years, possibly leading to an unbalanced system, which will cause the voltages to vary as large single phase loads come on line, particularly if earth/neutral connections are flaky. Most likely the 'impedance' value is the earth resistance value - if that was high, then the neutral point could move around as load is applied to different phases, and it would effect the rest of their network. The supplier has said it is OK at their last point of responsibility, everything beyond that point is your problem. Best wishes, Ray Link to post Share on other sites More sharing options...
RMweb Gold SHMD Posted June 13, 2015 RMweb Gold Share Posted June 13, 2015 Had it been dry for quite a while before and during the first measurements? Was it wet when the second lot turned up to make their measurements? Can you see the three phases coming onto your property? (Overhead lines.) If yes – are there 3 wires or 4? If you only have 3 wires coming along to you and the answer to the first two questions is yes then check your main Earth connection to ground. (Do you know how substantial your Ground connection is? Details?) May as well get your Earth/Ground checked out anyway. (Did SSB take any interest in it?) What is your heaviest load? (Immersion heater, Storage heaters, cooker, central heating, trace heating, green houses, frost stats, etc... Do you have any wind turbines/solar cells?) One of these loads may have a fault to Earth causing, (whilst not tripping any protection), a 'Rising Earth' fault but this would only be seen when the device is in operation. (Of course, one of your neighbours may be pulling down their phase causing your lines to be unbalanced – but maybe only intermittently!) Do you have any cattle/milking parlour? If so, are your beasts 'super sensitive' (read twitchy and, er, “messy”) in the parlour? Do you have a multi-meter and are you confident enough to use it safely? If so, are you willing/confident to measure what's coming out of your wall sockets? (Live to Neutral, Live to Earth, and Neutral to Earth.) (Both when all seems fine and when you "sense" a problem in progress!) Again, more questions than answers - sorry. Maybe a 'line' Data Logger is required. Kev. Link to post Share on other sites More sharing options...
APOLLO Posted June 13, 2015 Share Posted June 13, 2015 Blimey, I thought it was just live to live, neutral to neutral and earth to earth. !!! Glad I chose gas engineering !!!!!!!!!!!! Brit15 Link to post Share on other sites More sharing options...
raymw Posted June 13, 2015 Share Posted June 13, 2015 Hi Joseph, Ignore most of the postings on here - the answer is simple - I would suggest you get a competent electrician to check it all through... I will not advise anyone on a forum to rely on their confidence in poking the usual crappy multimeter probes into sockets, or otherwise mess with mains wiring in particular when there is no idea as to what the voltages may be. By your own admission, you do get confused by 3phase, so I fail to understand how you could be expected to discover anything useful in diagnosing your problems. Link to post Share on other sites More sharing options...
Junctionmad Posted June 13, 2015 Share Posted June 13, 2015 I suspect nothing was wrong and the original readings were taken incorrectly. 3 phase would typically be measured phase to phase , neutral being largely irrelevant Link to post Share on other sites More sharing options...
Satan's Goldfish Posted June 13, 2015 Share Posted June 13, 2015 Possible causes are pretty endless to list here, especially if it's potentially an intermittent fault. As mentioned above, a good professional is what you need. Sometimes it can be the simplest thing you over look that can cause the problem. I worked at a 3 phase site at 'the end of the line' once and we went through a period where the supply would twitch enough to cause our standby generators to kick in (and all our kit needing running back up) but each time the supply was checked no issues were found. None of our neighbours reported any problems either so the supply company blamed our equipment..... ......until I pointed out the tree that had just reached the point of growing through the wires before they dropped into the distribution building, and all the issues had been when it was windy...... Link to post Share on other sites More sharing options...
Bert Cheese Posted June 13, 2015 Share Posted June 13, 2015 Blimey, I thought it was just live to live, neutral to neutral and earth to earth. !!! Glad I chose gas engineering !!!!!!!!!!!! Brit15 Same here but on fridge (not that I chose it though!) 415V between phases 230V between any one phase and neutral Thats what they told me at college in 1987 anyway, and I've playing with the stuff ever since with any complaint or incident personally. I've done hundreds of coldroom installs since in my time, but always remained slightly terrified/cautious of the sparks side when wiring up the control panels etc...being a full time sparky has never really appealed, though the SEC house bashers I see are usually earning good money for relatively simple work. Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 14, 2015 Author RMweb Gold Share Posted June 14, 2015 So who came up with the rather odd readings in the first place? Keith An SSE engineer (one who works for the supply side of the company rather than the distribution side - but he used to work on the distribution side). I see no reason to think that he does not know how to use his meter. Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 14, 2015 Author RMweb Gold Share Posted June 14, 2015 I would hope the electricity supply company measured the voltage at your supply point, with your load disconnected. If you have the wide variation in voltages that you think you have, then that is due to things on your side of the supply point - unbalanced loads, corroded terminals/whatever. I would suggest you get a competent electrician to check it all through, one who does not use a clamp meter to guess at voltage. From what you have said, it appears that maybe the wiring has been extended over the years, possibly leading to an unbalanced system, which will cause the voltages to vary as large single phase loads come on line, particularly if earth/neutral connections are flaky. Most likely the 'impedance' value is the earth resistance value - if that was high, then the neutral point could move around as load is applied to different phases, and it would effect the rest of their network. The supplier has said it is OK at their last point of responsibility, everything beyond that point is your problem. Best wishes, Ray Correct. Load was disconnected when they tested on Friday. It wasn't for the first test. The building is only about 20 months old. So not really any question of corrosion and so far as anyone can see the loading spread round the various single-phase circuits is OK. I don't mind testing any of them with a multimeter but I will not go anywhere near the 3-phase circuits. The impedance value (as tested by the distribution guys on Friday evening was, they told me, very good. Given that the original voltage reading was taken on the company side of the meter, I don't see how that can be due to a fault anywhere in the building. Link to post Share on other sites More sharing options...
RMweb Gold Joseph_Pestell Posted June 14, 2015 Author RMweb Gold Share Posted June 14, 2015 Had it been dry for quite a while before and during the first measurements? Was it wet when the second lot turned up to make their measurements? Can you see the three phases coming onto your property? (Overhead lines.) If yes – are there 3 wires or 4? If you only have 3 wires coming along to you and the answer to the first two questions is yes then check your main Earth connection to ground. (Do you know how substantial your Ground connection is? Details?) May as well get your Earth/Ground checked out anyway. (Did SSB take any interest in it?) What is your heaviest load? (Immersion heater, Storage heaters, cooker, central heating, trace heating, green houses, frost stats, etc... Do you have any wind turbines/solar cells?) One of these loads may have a fault to Earth causing, (whilst not tripping any protection), a 'Rising Earth' fault but this would only be seen when the device is in operation. (Of course, one of your neighbours may be pulling down their phase causing your lines to be unbalanced – but maybe only intermittently!) Do you have any cattle/milking parlour? If so, are your beasts 'super sensitive' (read twitchy and, er, “messy”) in the parlour? Do you have a multi-meter and are you confident enough to use it safely? If so, are you willing/confident to measure what's coming out of your wall sockets? (Live to Neutral, Live to Earth, and Neutral to Earth.) (Both when all seems fine and when you "sense" a problem in progress!) Again, more questions than answers - sorry. Maybe a 'line' Data Logger is required. Kev. Weather here has not been particularly dry. The earth from SSE transformer is in soil close to a stream so pretty damp all the time. The supply (being recent) is sheathed so no way of telling if three or four wires (EDIT: Four wires. One can see at the point the cable has been connected). But from what the engineer said on Friday we earth back via their line. Our heaviest load on single-phase most of the time would be the hot-water cylinder. But there is also an air-source heat pump, oven, hob and the usual kettles. No solar yet although we are thinking about it. As a new installation, we have sensitive RCDs etc and I would expect any Earth fault to lead to cut-outs. We don't know who else is on our local network but nobody around here who would obviously suddenly draw down a lot of power on one phase. Anyway, that might (at a stretch) explain the 147V but not the 318V. (Hmm! Take that back, there is someone who could if he was using a single-phase supply to run 3-phase equipment via a converter. Must go and have a word with him). We don't do that sort of farming. The only heavy use 3-phase equipment is a pneumatic press which is only used for a few weeks each harvest. I wanted a 3-phase ASHP but somehow ended up with a single-phase one. The engineers did give me a few signs to look for as indicators of a problem. If I see any of those, I will whip out the multimeter and take some readings. Link to post Share on other sites More sharing options...
stewartingram Posted June 14, 2015 Share Posted June 14, 2015 No local houses with cannabis farms in the loft then? But again I guess that would be a constant heavy current... Stewart Link to post Share on other sites More sharing options...
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