That's intriguing: I had never heard of a domestic customer managing to annoy the supply people in that way. Would this be likely to happen with a truly domestic load, say with a lot of air conditioning, or more likely a small business using machines being run out of somebody's home?It is supposed to be true power (Watts). If the power factor of your house gets too low (and you are pulling to many VARs), they can install a VAR meter and charge for those too. Most houses have PFs around .85 so it's not a problem.
Small business, especially if it has a lot of motors running. It would be unusual, but the reason the power company cares is because it causes too much phase shift along the line. They have to put giant correction caps next to a house that looks too inductive. They care about the phase because it affects the generator's efficiency.That's intriguing: I had never heard of a domestic customer managing to annoy the supply people in that way. Would this be likely to happen with a truly domestic load, say with a lot of air conditioning, or more likely a small business using machines being run out of somebody's home?
I recall from 40 years back, there is a way to get the true power by putting the inductors of the meter motors at right angles (?) The old mechanical meters were supposedly true watt power. The new electronic ones are totally different.Thanks for the reply. I also believe it is true power as the unit is kWh in the electricity bill. I am wondering how the traditional meter works and how the power is measured.
The meter may be able to measure the r.m.s values of the voltage and current. But how can it get the power factor?
The most common type of electricity meter is the electromechanical induction watt-hour meter.
The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts.
The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil. This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power being used. The disc drives a register mechanism which integrates the speed of the disc over time by counting revolutions, much like the odometer in a car, in order to render a measurement of the total energy used over a period of time.
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by Robert Keim
by Robert Keim
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