Terminology

Understanding electrical power factor and its effects in both electrical equipment and system performance, as well as in plant economics is a significant consideration for the electrical power system.

Some of the positive effects of an improved power factor include:

• Reduced power costs
• Release of electrical capacity within the existing distribution system equipment
• Raise and provide stability to the voltage levels within the facility
• Reduced overall system losses

Typical means for power factor improvements include:

• Utilisation of high power factor equipment, particularly for lighting
• Installation of capacitors, particularly for large low power factor motors
• Installation of synchronous motors and generators

Power factor is the ratio between the kW and the kVA drawn by an electrical load where the kW is the actual load power and the kVA is the apparent load power.

It is a measure of how efficiently the load current is being converted into useful work output.

• The power that is used in equipment (heating, lighting, driving motors), is known as real power.
• Reactive power is power that is drawn down which is not directly used (or in other words power where the current is out of phase with the voltage and doesn't do any real work. Current that charges a capacitor or that creates the magnetic field around a coil for example.)
• The combination of then two is known as apparent power.
• Power Factor is the relationship between real and apparent power.

Another way to describe this is that there are two types of current in AC circuits

• Power producing current – converted by equipment into useful work.
• Magnetising current – wattless, reactive, or non-working current.

The terms “Leading” and “Lagging” power factor are used to describe the flow direction of VARs. When describing the load, the power factor is lagging when the load requires VARs and leading when the load furnishes VARs. For a generation source, the convention is reversed.

• Loads that receive VARs like induction motors and other induction loads (transformers) have a “Lagging” power factor.
• Loads that furnish VARs, like synchronous motors have a “Leading” power factor.

• For Generators the convention is reversed. A synchronous generator producing VARs (over excited) has a “Lagging” power factor. And an under excited synchronous generator or induction generator receiving VARs has a “Leading” power factor.

• The relationship of the voltage and current waveforms indicate the type of load. Resistive (in phase), inductive (voltage leads current) and capacitive (current leads voltage).

Resistive loads
(Power factor = 1.0):

• Incandescent lighting
• Resistance heating

Inductive loads
(Lagging power factor – receiving VARs):

• Transformers
• Induction motors and generators
• HID lighting

Capacitive loads
(Leading power factor – producing VARs)

• Synchronous motors and generators
• Capacitor banks