ABSTRACT
Electricity can be thought of as a means of delivering power from one place to another to do work. The laws and relationships for delivering power were originally developed for direct current (dc). Power delivered, expressed in watts, was calculated by multiplying the voltage and current. This chapter focuses on ac power relationships and the calculation of power factor; the physical meaning of these relationships; and measurement techniques and instrumentation for determining these relationships and calculating power factor. Electric loads in ac power systems with sinusoidal voltages are categorized by the way they draw current from the system. With the application of high-speed digital computing techniques to measurement of ac currents and voltages, together with digital filtering, the quantities necessary for accurate and correct calculation of power factor are susceptible to direct computation. In practice, the ac waveforms are sampled at a frequency greater than twice the highest frequency to be measured, in compliance with well-known sampling theories.
