Power Factor

The real electrical power used to perform a certain task is called active power. However, certain loads, especially motors, expend energy to establish the magnetic field, which is another form of power called reactive power. Although this is a virtual power, added to active power, it determines the actual demand or total power load of an electrical system. Power factor is the ratio between active power and total power and a higher reactive power implies that less active power is distributed. Theoretically, if all power loads only require active power, the power factor equals one, and the maximum power that can be transferred equals the distribution system capacity. However, if a significant number of motors in the plant are oversized by design and underloaded on operation, below 75% nominal power, higher reactive power is demanded, reducing effective energy distribution capacity. Low power factors can cause power losses in the distribution system. Voltage drops may increase, and if they happen too frequently, may provoke overheating and early failure of motors and inductive equipment. Secondary losses may occur like heat in wiring by higher current values to compensate power losses.

Energy efficiency opportunity here is to guarantee a power factor closer to 1, preferably higher than 0.85, by appropriate selection of motors capacity, matching process demand. Since this low power factor can affect third party supplier systems, penalty charges are imposed by contract, if a minimum factor is reached, increasing electricity cost. The power factor can be improved by installation of correction capacitors. This option can reduce distribution losses within the plant network while maintaining available capacity. Voltage level at consumption is increased, improving motors performance. Simultaneously total current in the system is reduced, hence reducing Joule effect losses.

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