Do domestic Kwh meters (ordinary electric meters) record reactive power. - diyAudio
 Do domestic Kwh meters (ordinary electric meters) record reactive power.
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 29th October 2011, 07:36 AM #1 diyAudio Moderator     Join Date: Sep 2007 Do domestic Kwh meters (ordinary electric meters) record reactive power. Haven't been able to find a definite answer to this. When a capacitor is placed across an AC supply although it draws current it doesn't dissipate power. So a specific example. If a 0.22uf capacitor has a reactance of approx 15k at 50hz then over a year (8760 hours) how many Kwh would a domestic meter clock up ? If it were a resistor it would average out at around 34Kw over the year at 240 Vac. What would the cap clock up ? Does the meter type make a difference as the old mechanical ones with a rotating disc have been replaced with small electronic types ?
 29th October 2011, 07:50 AM #2 diyAudio Member     Join Date: Sep 2006 No, the domestic meters implement a true vectorial calculation, P=U*I*cosφ Of course, they are relatively crude electromagnetic devices, and the quadrature may deviate slightly, causing a "leak" of the reactive power into the active one. But the leak can work in either direction. If you connect a very large polypropylène capacitor to your mains, you will see some consumption though, because the wiring of your home will introduce a very slight resistive component, but for "normal" values ,like suppression capacitors, this is negligible. Except if they are paper type, as they have ~2% losses. __________________ . .Circlophone your life !!!! . . ♫♪ My little cheap Circlophone© ♫♪
 29th October 2011, 08:14 AM #3 diyAudio Moderator     Join Date: Sep 2007 Thanks Elvee... So you are saying that apart from wiring resistive losses the meter would not record the current (power) that has flowed (because no "real" power has been generated). What about the newer all electronic meters which have the capability (but is it used ?) to record reactive power/power factor etc. So the 15k resistor would consume a real 34Kw over a year and cost say £5 a year. So would the cap "cost" essentially £0.00 over a year ? (apart from miniscule power due to resistive losses).
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Join Date: Sep 2006
Quote:
 Originally Posted by Mooly Thanks Elvee... So you are saying that apart from wiring resistive losses the meter would not record the current (power) that has flowed (because no "real" power has been generated).
No, only active power is recorded
Quote:
 What about the newer all electronic meters which have the capability (but is it used ?) to record reactive power/power factor etc.
In the industry, reactive power is billed under the form of penalties when it exceeds a certain level.
For domestic installation, there is at present no similar scheme.

Quote:
 So the 15k resistor would consume a real 34Kw over a year and cost say £5 a year. So would the cap "cost" essentially £0.00 over a year ? (apart from miniscule power due to resistive losses
Yes, and also the dielectric losses: negligible for PP, medium for mylar, and high for paper.
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 29th October 2011, 11:01 AM #5 diyAudio Moderator     Join Date: Sep 2007 Thanks Elvee
 29th October 2011, 11:19 AM #6 diyAudio Member     Join Date: Sep 2010 Here is an interesting read on it all http://www.nlcpr.com/Deceptions1.php
 29th October 2011, 11:57 AM #7 diyAudio Moderator     Join Date: Sep 2007 Thanks... Reason for the question was actually to do with "watless droppers" vs small transformer for a particular circuit. A small transformer that gets hot obviously consumes real power and you are charged for it, the cap supplying the same circuit doesn't and from what I gather you don't get charged for it (although obviously the circuit it's powering consumes real power that is chargeable). Not trying to make the meter run backwards... honest
 29th October 2011, 12:04 PM #8 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Look inside a mains voltage LED lamp bulb. You can see the series cap that "drops" the voltage down to a LED suitable voltage. They tell us on the label it is a 240Vac, 1W or 3W or whatever bulb. It registers/consumes ~1W of Power. __________________ regards Andrew T. Sent from my desktop computer using a keyboard
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Join Date: Sep 2007
Quote:
 Originally Posted by AndrewT Look inside a mains voltage LED lamp bulb.
Never looked in one of those... but yes I see your point.

 29th October 2011, 12:11 PM #10 diyAudio Member     Join Date: Sep 2006 Small transformers are a disaster from an energetic point of view: a typical 1 VA transformer can use 3 watt or more open circuit. (of course, you don't use them without a load, and you have to add copper losses). From that perspective, capacitive droppers are much more effective, even when most of the quiescent power is dissipated in a zener. __________________ . .Circlophone your life !!!! . . ♫♪ My little cheap Circlophone© ♫♪

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