Is a poor power factor dragging your profits down?
Many businesses overlook the fact they pay more for electricity depending on how it is used. The how depends on the type of electrical load as some loads have a poor power factor. Most electrical equipment, such as motors, compressors, welding sets, fluorescent and LED lighting create an inductive load on the supply. In most cases, ‘improving’ the power factor will reduce running costs.
An inductive load requires a magnetic field to operate and this is called reactive power. Reactive power is the difference between working power (active power measured in kW) and total power consumed. Power Factor is the relationship between ‘active’ and ‘reactive’ power and indicates how well electrical power is being used. According to utility EDFenergy, unity power factor – (1.0) does not use any reactive power and should be the target.
Charges for reactive power change according to the accumulated volume on your reactive register. These charges also vary depending on the user’s contract and operator and the worse the power factor the higher the charge. If reactive power charges are applicable for a site, they appear as a consumption charge.
Getting back to unity
In industry and commerce, electric motors account for more than 50% of power consumption, making them a good place. By installing variable speed drives (VSDs) there are two benefits. Firstly, they improve the power factor and reduce losses in the supply systems. Secondly, when used for controlling fan and pump motors, they also offer significant energy savings.
The total efficiency of the drive system depends on the losses in the motor and its control. Both drive and motor losses are thermal, so they appear as heat. Input power to the drive system is electrical in form, while output power is mechanical.
Electrical input power depends on voltage, current and the power factor (cosϕ). The power factor shows what proportion of the total electric power is active power and how much is so called reactive power. To produce the required mechanical power requires active power. Reactive power produces magnetisation in the motor.
Mechanical output power depends on the required torque and rotating speed. The greater the speed or torque required, the greater the power required. This has a direct effect on how much power the drive system draws from the electrical supply. The VSD’s frequency converter regulates the voltage fed to the motor. In this way it controls the power used in the motor as well as control of the process.
Electrical switching with transistors is very efficient, so the efficiency of the frequency converter is very high, from 0.97 to 0.99. Motor efficiency is typically between 0.82 and 0.97 depending on the motor size and its rated speed. In this way, the efficiency of the drive system is always improve when controlled by a VSD.
Drives partners can also help to improve the power factor with variable speed drives advice and support services. Leading brands of VSDs from ABB, IMO, Mitsubishi, Omron and Schneider electric help solve the power factor problem while improving the process control, saving electrical energy and reducing machine wear.
Recent blog posts