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Does an analogue kWh meter over charge for harmonic distortions?

  1. Aug 23, 2011 #1
    If a analogue kWh meter is made of coil windings and coil windings dissipate harmonics currents then is it possible that we are being charged more kWh if we create harmonics on our circuit? I did a test once with a low power factor motor and 200 meters of extension cable. The power was coming from the plug socket (240 volt 10 amp single phase) through a clipsal distal meter, then through a "Email Limited" brand kWh meter then through another digital meter then through a fuse box that had static power power factor correction device attached. The motor was the last on the circuit. When the motor was running without load so with a low power factor (about 0.46) the two digital meters we're giving two different readings. The one outside the circuit after the kWh meter was always showing a higher reading. When I turned on the power saver the kWh being charged and also displayed on the outside meter dropped by 16%.

    We are all told that power savers don't work and that residential customers are not billed for power factor or the kVAr leaving upstream.

    So what's causing the saving?

    After a lot of research I am coming to the understanding that it may have been the harmonic distortions on the line that are being recycled as it we're by the power saver.

    The problem with power savers like the one I used in this experiment and the "power saver 1200" and "KVAR" in the USA is that they don't seem to drop everyone's bill.

    Company's like the "Continental Power Corp" that have been selling there "Powerworx" product for 15 years claim a minimum of a 10% saving. Does there power saver work because it removes harmonics as well as help to correct the power factor and therefore amp draw as well as surge protection to remove voltage peaks and spikes.

    If anyone could shed some light as to why I got the different readings before and after the meter I would really appreciate it.

    Does an analogue kWh meter over charge for harmonic distortions?
  2. jcsd
  3. Aug 23, 2011 #2
    Power factor is a tricky business; you can't just toss a static device into the equation and expect it to fix everything. In my understanding, industry is billed by power companies for having a low power factor, in addition to being charged for the total power they consume, which is actual power divide by power factor (I think). When they say you aren't billed for power factor, I think they're just saying that they don't charge extra for having a high reactive load on the circuit; you're probably still being charged for the total power rather than actual power.

    I think those "static power factor correction devices" are just fancy names for a big capacitor. You can do some research into http://en.wikipedia.org/wiki/RLC_circuit" [Broken], but basically, power-factor nears one as capacitance and inductance come into balance. Electric motors have terrible power factors because they are designed to create magnetic fields, and thus have high inductance. A capacitor is needed to balance this. On the other hand it is possible to over correct. Too much capacitance and your power factor goes back up again. The minimum power factor, and thus minimum bill, occurs when the current and voltage are in phase; once this happens you're only being billed for the resistive load, and further improvement is not possible without decreasing the resistive load on the circuit.
    Last edited by a moderator: May 5, 2017
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