Currently, I have a software which able to read voltage, current, active power, apparent power and reactive power from appliances which I assume the readings should be approximately same even though I have changed the venue for setup the same appliances. But after I have moved the same setup to a different floor or a different power source, I encounter the issue of readings have apparently run out of the range from my previous reading.

Is there any cause that can make such changes?


The previous reading I get is :

Voltage:240.2 Current: 9.9 Real Power: 1.818 Apparent Power: 1.7003081 Reactive Power: 1.589 Power Factor: 0.7721

After setup changed to the different place with the same appliance setup:

Voltage:240.1 Current: 11.1Real Power: 1.817Apparent Power: 1.965097Reactive Power: 2.0375Power Factor: 0.66605

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    \$\begingroup\$ How do you manage to get higher real power than apparent power? \$\endgroup\$ – winny Jan 25 '18 at 11:37
  • \$\begingroup\$ @winny that's a good call dude. \$\endgroup\$ – Andy aka Jan 25 '18 at 11:50
  • \$\begingroup\$ @Andyaka Thanks! I'm thinking some strange STATCOM or other mean to inject harmonics, but I'm still not sure it would be possible. Also, can't see how you manage to get a PF of 0.66 with that low apparent power. \$\endgroup\$ – winny Jan 25 '18 at 15:19
  • \$\begingroup\$ @winny for the software compensate adjustment, my apparent power should be 2.1803081 and 2.445097 \$\endgroup\$ – Oli Jan 26 '18 at 1:21

The power consumed (what you are billed on basically) is 1.818 kW in venue A and 1.817 kW in venue B so there is no difference in power consumed to speak of.

If you look at the numbers V x I x PF = 1836 watts in venue A and, in venue B it comes to 1775 watts. So there is some small discrepency but this can be down to interpretation of numbers. For instance, the larger current of 11.1 amps in venue B may be an approximate representation of RMS current and won't necessarily have the mathematical resources applied when calculating power.

Power is the important figure because that is what you are billed on.

Is there any cause that can make such changes?

I would say that it is reasonable to expect the same power readings but for the currents there could be some mathematical approximations taking place that produce this error. In reality power is calculated not with the formula I used but by multiplying instantaneous values of V and I together (then averaging mathematically) and this is where the numerical processing resources will be placed.

  • \$\begingroup\$ +1 Though you did not mention different locations means different wiring with attendant differences in inductances and resistances and possible variations in the purity of the sine wave caused by other equipment on the same line. The kind of effects he is seeing is well within the bounds of those differences. Which was his actual question.. I guess. \$\endgroup\$ – Trevor_G Jan 25 '18 at 11:41
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    \$\begingroup\$ @Trevor_G My thinking was that the RMS voltage is virtually the same in both venues but why should the current be vastly different so, I'm waiting for the OP to come back to follow that line of enquiry. It could be that some power factor correction equipment might be still connected but, with very little to go on other than the numbers..... \$\endgroup\$ – Andy aka Jan 25 '18 at 11:49
  • \$\begingroup\$ Yup, it's just that folks don't tend to understand the AC is not such a rock solid sine wave as they think, which of course affects the RMS. \$\endgroup\$ – Trevor_G Jan 25 '18 at 11:54
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    \$\begingroup\$ I recall a question a week or two ago showing a really bad AC wave... Of course I cant seem to find it now... \$\endgroup\$ – Trevor_G Jan 25 '18 at 11:57
  • \$\begingroup\$ electronics.stackexchange.com/questions/346361/… \$\endgroup\$ – Trevor_G Jan 25 '18 at 12:00

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