What is Reactive Power? and how is it measured?

Reactive Power (kVArh) is the difference between working power (active power, measured in kW) and total power consumed (apparent power, measured in kVA). Some electrical equipment used in industrial and commercial buildings requires an amount of ‘reactive power’ in addition to ‘active power’ in order to work effectively.

Reactive power therefore generates the magnetic fields which are essential for inductive electrical equipment to operate, especially transformers and motors.

This load is measured via the reactive register on your half-hourly meter.

What is Power Factor and how is it caused?

Power Factor is a term used to describe the relationship between ‘active’ and ‘reactive’ power; it denotes how effectively electrical power is being used:

• Bad power factor - is low (less than 0.95), indicating that more reactive power is required.
• Good power factor - is high (greater than 0.95) indicating that power is used more effectively.
• ‘Perfect’ power factor - (1.0) is known as unity and does not use any reactive power.

Most electrical equipment, such as motors, compressors, welding sets and even fluorescent lighting, create an inductive load on the supply. An inductive load requires a magnetic field to operate which then causes the electrical current to “lag” the voltage i.e. the current is not in phase with the voltage.

How is Reactive Power charged?

Reactive power is charged according to the accumulated volume on your reactive register. These charges will also vary depending on two elements:

1) Contract type: If you have a fully inclusive contract, you will pay the rate to which you agreed on your contract. If you have an energy only (supply only) contract, you will pay the rate which has been passed through from your Local Network Operator, which may vary if they change their charging methodology.

2) Local Network Operator charging methodology: Charging steps differ depending on your site location in Great Britain and the operator serving your network.

Where the first step excludes a percentage figure, the LNO does not currently charge for reactive power.

Where the first step is 33%, the Local Network Operator does not charge for reactive power for the first 33% of units (kWh).

Charges therefore apply when the difference between the total units recorded on the reactive register (kVArh) is less than 33% of the total units consumed (kWh).

Where the first step is 50%, the Local Network Operator does not charge for reactive power for the first 50% of units (kWh).

Charges therefore apply when the difference between the total units recorded on the reactive register (kVArh) is less than 50% of the total units consumed (kWh).