Students in the second year of their lighting qualification at Massey University are learning about New Zealand’s electrical distribution network and how the network is affected by power factor.
Most people in the electrical industry are familiar with power factor, which is the difference between apparent power (VA) and active power (W), with the loss of energy or difference between the two being the power factor.
Applying this to a practical example, an office lit by twenty 35 W light fittings that had a power factor of 0.50 would have a 1400 VA demand rather than the 700 VA that might be expected. The electrical infrastructure would need to be specified to handle 1400 VA rather than 700 VA.
A low power factor can be caused by displacement, where an inductive load in a circuit causes the current to lag behind the voltage. This means more current must be supplied to make up for the lag.
It can also be caused by distortion, where a device like a computer or a microwave draws current in short bursts rather than in smooth wave forms and, as a result, harmonics might arise. Harmonics can shorten the lifespan of appliances and equipment through the failure of components or motors, or through overheating. Harmonics can also damage the distribution infrastructure, for example wiring and transformers, through power spikes or excessive heat generation.