Try this: Draw two circles about six inches apart, and connect them with a straight line. Label the point at which the line hits the left circle as point “A.” Label the point at which the line hits the right circle as point “B.” Label a third point, about one inch to the left of B, as point “C.” Finally, label a point in the middle of the line as point “D.”
Let’s say the left circuit is a generator, the right circle is a motor, and the line represents the branch circuit wires that connect them. The generator windings store and release energy by using the magnetic fields that vary up and down with the alternating current. So too do the motor windings. There is a continuous exchange of energy, back and forth, between the two sets of windings. This exchange is sort of a “necessary evil,” in that it produces no work on its own right, but without it the generator could not make the motor spin.
Thus, there are two types of energy being exchanged between the two machines, between points A and B, as shown on your drawing. One type, which we describe as “real power,” is the energy exchange that causes the motor to produce work. The other type, which we describe as “reactive power,” is the (sort of, almost, perhaps “useless”) exchange between the magnetic fields of the two machines. The utility must produce energy at a rate that is sufficient to supply both types of power. The two types are added up in the way I describe with the triangle, in the other thread, with the result being called “apparent power.” So if the utility were to install an “apparent power meter,” and place it at point D, it would give you a measurement that is greater than the “real power” needed to perform the motor’s work.
Now let us install a “power factor capacitor” at point C, and size it to achieve a 1.0 power factor. This device will store and release energy by using an electric field (between the capacitor’s parallel plates) that varies up and down with the alternating current. What happens now is that you get an exchange of energy between the electric field of the capacitor and the magnetic field of the motor. It is the same sort of energy exchange we saw before, but now it is taking place between points C and B. Because of this, the energy exchange that had been taking place between the generator windings and the motor windings no longer happens. That is, the utility meter at point D will no longer see this energy exchange. Thus, the utility sees a value of apparent power that is exactly the same as the real power drawn by the motor. That is a smaller value then the meter had measured before, so to do the same work the utility need not supply as much power.
If you were to stand between points C and B, with blinders on, so that you could see neither left nor right of your position, and if you were to measure power factor before and after the capacitor were installed, you would not know that anything different had happened. Before the capacitor is connected, you witnessed an energy exchange between something to your left and something to your right. After the capacitor is connected, you still see that energy exchange. What you could not know was that beforehand, the energy exchange involved a generator and its magnetic field, and afterwards the energy exchange involved a capacitor and its electric field. Only if you were allowed to move to point D could you discern a difference in the two situations.
