Low power factor in your facility can lead to costly penalties. Power factor correction equipment increases power factor levels to help avoid these charges. But what is the correct power factor level? If your power factor is 90%, then 100% is better, right? Not necessarily. Overcorrecting power factor can result in motor failure and costly equipment damage. Finding the right power factor solution can save you money while protecting your valuable equipment.
Explaining power factor in four easy steps
Power factor is a difficult concept to understand. Let's break it down:
- All electrical equipment requires power to work, which is called "real" power and is measured in kilowatts (kW).
- Some equipment, such as induction motors, requires an extra current to create a magnetic field to operate. This current is called "reactive" power and is measured in kilovar (kVAR). It causes current and voltage to be out of phase.
- "Apparent" power, expressed in kilovolt-amperes (kVA), is the vector sum (legs of a triangle) of real and reactive power in a circuit.
- To calculate power factor, divide real power (kW) by apparent power (kVA).
If your power factor is too low or too high, you may be charged a penalty. Facilities with low power factor draw more apparent power, causing additional strain on the electric grid.
The complexities of power factor correction
Facilities often use capacitors to correct power factor up to unity, in which current and voltage are in phase. Although unity sounds good, it can cause excessive current draw and over-voltage conditions that can damage equipment.
Inductance causes the current to lag voltage, while capacitance causes the current to lead voltage. Although inductance decreases power factor, it enables the magnetic fields necessary to run a motor. Adding too much capacitance results in a leading power factor that cancels inductance. Motors draw excess current to sustain magnetic fields. That excess current can overheat the motor and degrade insulation.
If the power factor leads by too much, then a subsequent rapid voltage rise may cause equipment damage. The voltage rise can exceed the capacity of the electrical equipment or the capacitors themselves. In the case of a leading power factor, the load current leads the load voltage.
Correcting power factor correctly
To avoid problems resulting from leading power factor, correct power factor to a maximum of 90% to 92%. This correction level allows greater flexibility to avoid leading power factor when conditions result in higher power factor than normal.
Proper design and operation depend on the type of capacitor. With an automatic switching capacitor bank, the kVAR can be more precisely tuned to the actual amount needed as it varies. Over-voltage can more easily build up in a static capacitor bank. Be careful when applying a switched capacitor bank because a capacitor takes about one minute to discharge. When the electrical equipment is unloaded, power factor increases, as does voltage.
Bring capacitors online only when needed. It's also a good practice to disconnect capacitors when you disconnect a motor or other electrical equipment.
By following a few simple practices, you can avoid costly power factor charges while keeping valuable motors and other electrical equipment safe from damage.