ABSTRACT

Most industrial loads such as induction motors operate at moderately low power factors. Around 60% of the utility load consists of motors and hence the overall power factor of the power system is low. Depending on the level of the load, these motors are inherently low power factor devices. The power factor of these motors varies from 0.30 to 0.95, depending on the size of the motor and other operating conditions. Therefore, the power factor level is always a concern for industrial power systems, utilities, and the user. The system performance can be improved by correcting the power factor. The system power factor is given by (see Figure 8.1):

Power factor ¼ P=kVA ð8:1Þ

where P and kVA are the real and apparent power, respectively. The relation between the power factor and the Q/P ratio is shown in Table 8.1. From Table 8.1, it can be seen that even at 90% power factor, the reactive power requirement is 48% of the real power. At low power factors, the reactive power demand is much higher. Therefore, some form of

power factor correction is required in all the industrial facilities. The power factor of any operating system can be lagging or leading. The direction of active and reactive power can be used to determine the nature of the power factor. If both the real and reactive power flow are in the same direction, then the power factor is lagging. If the reactive power flows in the direction opposite to that of the real power, then the power factor is leading. A typical lagging power factor load is an induction motor [1-3]. A typical leading power factor load is a capacitor. Some typical power factors of industrial plants are presented in Table 8.2.