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Category: Power Capacitors Power Factor CorrectionPower Capacitors GeneralUnder normal operating conditions certain electrical loads draw not only active power from the supply (kilowatts kW) but also reactive power (reactive kVA, kVAr). This reactive power has no useful function, but is necessary for the equipment to operate correctly. Loads such as induction motors, welding equipment, arc furnaces and fluorescent lighting would fall into this category. CorrectionOpposing reactive power resulting from the connection of a correctly sized capacitor can compensate for the reactive power required by the load. This ensures that only a small amount of reactive power is drawn from the supply. PurposeAn apparent reduction in the total current drawn from the supply can be achieved as a result of connecting a capacitor to an inductive load. DefinitionThe Power Factor of a load is defined as being the ratio of active power to total demand, that is to say kW + kVA. The uncorrected power factor of a load is cosØ1 (where Ø1 is the phase angle between the uncorrected load and unity), and the corrected power factor is cosØ2 (where Ø2 is the phase angle between the corrected load and unity). The nearer the ratio kW+kVA=cos Ø is to unity, the less reactive power is drawn from the supply. BenefitThe connection of a capacitor capable of "correcting" half of the
reactive power of a load leads to a reduction in the demand on the
supply ofapproximately 15%. This results in the following: Methods of Power Factor Improvement1. Individual Power Factor Correction To individually correct the
power factor of a multiple load, a suitably sized capacitor is connected
to each element of the total load. Harmonic Distortion & FilteringIn recent years the development of modern thyristor technology has led to constant increases in the number of converter-fed loads. Unfortunately converters have undesirable effects on the incoming AC supply system since they often draw heavy inductive reactive power and/or a non-sine-wave current. The supply system should be kept free from distortion in order to prevent equipment malfunction. The converter current is composed of a mixture of sine-wave currents, a fundamental component at the supply frequency and a number of harmonics whose frequencies are integer multiples of the line frequency. When harmonic currents are superimposed on the AC supply, corresponding voltage distortion occurs which could lead to system disturbances and failures within the network. When the harmonic component is low, supply systems should be equipped with control units with reactor-connected capacitors in order to prevent resonance phenomena. Where the harmonic component is high, it may be necessary to systematically suppress the harmonics with a tuned filter circuit presenting a very low impedance to the individual harmonic currents. Reactive power compensation can be properly planned with the aid of the decision diagram shown opposite Capacitor SizingTo obtain capacitor sizes (in kVA) for a given power factor correction multiply the kW load by the number shown at the axis between existing power factor and required power factor. Power Capacitors Limited is able to recommend the most appropriate solution for each requirement. Reactive Power Compensation
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