Introduction

This chapter covers single phase and polyphase power distribution and loads, power factor correction, transmission line calculations at power frequencies, and wattmeter measurements. Unless otherwise stated, the material in this chapter assumes all waveforms are 60 cycle sine waves. The vector, or phasor, diagram is used to aid in solution of problems.

Single-Phase Power

The phase angle is a very important parameter for properly locating different alternating quantities with respect to one another. If the applied voltage is v = V _max sin ?t and it is known, from the nature and magnitude of the circuit parameters, that the current comes to a corresponding point on its wave before the voltage wave by ? degrees, the current can be expressed as i = I _max sin ( ? t + ?). This is an example of a positive phase angle due to an RC circuit which produces leading current and a leading power factor, where the power factor is:

The phasor diagram for this example is as shown below:

For an RL circuit, the phasor diagram is as shown below:

In this case, the current lags the voltage by ? degrees.

Power in ac circuits is either resistive ( real) or reactive.