Use this guide when comparing generator specifications. Always check the manufacturer’s datasheet and the requirements of your installation.
kVA
Kilovolt-amperes: a measure of apparent electrical power. Generator sizing must consider both kVA and kW.
kW
Kilowatts: a measure of real electrical power delivered to the load.
Power factor
The ratio of real power (kW) to apparent power (kVA). For example, 100 kVA at a power factor of 0.8 corresponds to 80 kW.
Prime power (PRP)
A rating for supplying a varying load for extended operation under the manufacturer’s specified conditions. Check the permitted average load and any overload allowance for the particular set.
Standby power (ESP)
A rating for emergency supply during mains failures, subject to the manufacturer’s operating-hour and loading limits. It is not interchangeable with a prime rating.
Voltage and current
Voltage is the electrical potential difference, measured in volts (V). Current is the flow of electrical charge, measured in amperes (A).
Single-phase and three-phase
Different electrical supply arrangements. The generator must suit the voltage, phase and load requirements of the equipment it supplies.
Frequency (Hz)
The number of alternating-current cycles per second. UK mains equipment normally operates at 50 Hz.
Alternator
The part of a generating set that converts mechanical rotation from the engine into electrical energy.
AVR
Automatic voltage regulator: controls alternator excitation to regulate the output voltage.
ATS
Automatic transfer switch: switches a connected load between the normal mains supply and an alternative supply such as a generator.
AMF
Automatic mains failure control: monitors the mains supply and can initiate generator starting and a controlled transfer sequence when configured with suitable switching equipment.
Load bank
Equipment that applies a controlled electrical load to a generator for testing. A load-bank test helps assess operation under defined conditions.
Acoustic canopy
An enclosure designed to reduce generator noise and protect the equipment. Compare noise figures only when the measurement distance and operating conditions are stated.
Bunded fuel tank
A fuel tank with secondary containment intended to contain leakage from the primary tank.
Synchronisation
Matching electrical characteristics so compatible generators can operate together, or with another supply, using suitably designed controls and protection.
More generator guidance
kVA explained · Prime and standby ratings · Automatic transfer switches · Sizing and installation