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| Figure 16-3 Effect of capacitor in circuit. |

| Principle of Operation.. |

| A capacitor consists of two parallel plates that are conductors, separated from one another by an insulating or dielectric material. The interacting magnetic fields that are found in motors, transformers, and overhead circuit wires that parallel each other are all causes of inductance. In an ac system, the current flowing in the circuit supplying the equipment will therefore lag the voltage. The alternating movement of electrons to and from each of the plates of the capacitor when an ac voltage is applied across them constitutes a flow of current, but one that will appear to lead the voltage. If a capacitor is connected as a load on the circuit, the current it will cause to flow will lead the voltage. If the current in the circuit lags the voltage because of the inductance previously mentioned, the effect of the leading current will be to neutralize the lagging current, thereby improving the power factor of the circuit and reducing the current flow necessary to supply the load (Fig. 16-3). |

| Another way of looking at this phenomenon is to envision the capacitor as a source of supply for volt-amperes, or reactive power, that will tend to neutralize the effects of inductive reactance. Capacitors are therefore normally rated in the kVA of reactive power they supply. Their capability, or capacity, depends on the size of the plates, the distance between them, and the kind of insulating or dielectric material used. |

| Construction |

| Capacitor plates may be made of copper, brass, or aluminum, and the insulating material may be air, vacuum or gas, mica, porcelain, or other ceramic, glass, oil-treated paper, or a special plastic. The most practical plates in general use however, appear to be made of aluminum foil separated by oil-impregnated paper or plastic. These are first wrapped into bundles, and a number of such bundles are then connected in series-parallel to attain the required capacitance and voltage rating. The whole unit is usually enclosed in a metal case or tank and the leads brought out through bushings of porcelain (Fig. 16-4). |

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