All electrical devices require active power to operate. Active power is used for actual work, such as driving an electric motor. Many electrical devices also require reactive power to operate. In an electric motor, reactive power is needed to maintain the motor’s magnetic field.
Reactive power can be produced by power plant generators and transmitted through the grid and transformers to the metering point. During transmission, reactive power consumes the grid’s capacity and causes losses. In the figure below, an electric motor represents a metering point.
Rather than a single motor, the metering point could be, for example, a building. In this case, many devices that require reactive power are connected to the facility’s switchgear.
The network operator aims to eliminate the transmission of reactive power in the network. The network operator uses reactive power fees to incentivise customers to manage reactive power compensation locally, as close as possible to the metering point. Compensation equipment installed in the immediate vicinity of the metering point produces reactive power locally, freeing up the network’s capacity to transmit active power. A single motor can be compensated using a capacitor unit installed on its poles.
The most common solution is to install a detuned compensation bank in the switchboard to compensate for the reactive power required by all the devices connected to the switchboard.
The power factor (Cosϕ) of an electric motor is in the range 0.7–0.85. A reactive power compensation system raises the power factor to close to 1.0. It never exceeds 1.0, but remains slightly under it, just to be safe. As noted earlier, rather than referring to a single electric motor, we can speak of the power factor of a facility (building, industrial plant, etc.) and the compensation of its reactive power.
