moroney@jon.DEC (Mike Moroney) (03/29/85)
I want to provide some input on power factor and power meters. First, the "gumball" machine on the side of your house does take into account the power factor, so you do actually only pay for the power you use. I will post a reference if anyone is interested (if I can find the book - this is from memory) Second, power companies charge a surcharge to large industrial users with a low power factor. The reason for this is the size of the transformers and distribution lines is proportional to the product of voltage * current, so if a plant had a power factor of 0.5, it would need a power transformer/ distribution lines twice as large as the same plant with a power factor of 1.0 (which is usually difficult to obtain in practice, at least all the time) The power companies don't harass homeowners with this since the power factor of the average house is pretty high (most people run few motors for any length of time, except refrigerators and furnace motors) and what power factor there is is all inductive so the power companies just add capacitors to the line as needed. Third, those "black boxes" which reduce power consumption based on power factor do not actually work by reducing the power factor but measure the power factor and reduce the voltage to the motor if it has a low power factor, making it work harder. The reasoning behind this is a motor which is just loafing will draw about the same amount of current as one working hard, but uses less power because the phase angle changes, lowering the power factor. But all that current still produces a lot of heat in the windings of the motor, which is just waste. Lowering the voltage (when possible as determined by the device) lowers the current. An easier to understand analogy is imagine two cars, identical except one has a huge V8 engine, the other a small 4 cylinder. If both drive from point A to B at the same speed, the V8 is loafing along while the small engine is working hard. Who is going to get the better milage? The "black boxes" work almost as if they reduce the size of the motor that is connected to them. "There's a madness to my method" Mike Moroney ..decwrl!rhea!jon!moroney