I'm a little confused about AC power.If a circuit has only resisters in it, then it's easy to calculate the total resistance of the circuit and from that the current and power. But does putting capacitors or inductors in a circuit change the resistance of the circuit, and thus change the average power being dissipated? I think the answer is yes, but it's a little confusing because I read that capacitors and inductors are reactive elements and draw no power?
It does not change the average power being dissipated, i.e. the energy that is being converted from electrical to say thermal. It's not the fact that they draw no power, but that there is no net power associated with L and C. The energy is just being exchanged back and forth between the Electric field(for capac.), the magnetic field(for induct.) and the source driving the circuit. I look at inductors and capacitors when it comes to energy as a car that goes from point A to point B, and returns to point B. There is no net displacement, but you still had to use energy(gas). That's why the notion of apparent power is so important; it takes into account both average(real) power and reactive power.
Theoretically inductors and capacitors draw no real power, but in the real world there is a tiny sometimes a significant power loss that is resistive. Most motors have an inductive component. CFL lights are somewhat capacitive, I think. Some times we add capacitors to improve the power factor. This makes transformers and power lines, and maybe the giant alternators at the power plant more efficient. Neil
We have the concept of IMPEDANCE for exactly that reason. We also have a distinction between the kilowatt and the kilovolt-ampere for exactly that reason (related by the concept of power factor). Impediance is a complex number combination that is to be analogous to resistance. Only resistors contribute to the real component of impedance. The capacitors and inductors are modeled as the imaginary component of resistors. If you aren't ready to understand complex and imaginary numbers yetyou aren't ready to learn about the impedance method of analyzing multicomponent circuits. The reactive elements don't draw power, but rather they STORE energy. They delay when the energy gets released from when it enters.
Reactive power does not register on your wathour meter. You don't pay for it. But it adds to the total KVA of the power company;s system. As such, power is wasted in the transmission lines. It doesn't ride free. The power company is penalized by low power factors because they have to furnish the equipment and fuel to supply the KVAR component of their power lines. You, as a customer of the power company, pay for this wasted energy as the power company passes the cost on to you. The resistance is not changed when capacitors are added to the circuit. Resistance applies to the KW portion of the power triangle. The reactance of inductors and capacitors are 180 degrees out of phase. When capacitors are installed, the total impedance of the circuit is reduced, as well as the KVA of the circuit. The capacitor stores energy in one half of the cycle and releases it during the next half cycle. This energy circulates around the circuit supplying the inductance for motor and other inductive equipment.
