80kVA Standby generator - open set
80kVA Standby generator - canopy set
Standby generators consist very simply of an engine running at a fixed speed which drives an alternator to provide electricity at the correct frequency to suit the electrical equipment it supports. In the UK this is 50Hz, or 50 cycles per second.
Most generators come with a built in fuel tank, and are available as an open set, or are housed in a soundproof weatherproof canopy.
For standby power applications a separate wall mounted changeover panel is used. A changeover panel takes power from both the mains, and the generator, and supplies a distribution panel for the supported circuits.
For normal operation, the load is supplied from the mains, and in the event of a power failure, a signal is sent from the changeover panel to the generator, which then automatically starts up. When it is up to speed (normally takes between 15 to 30 seconds), the power supply is transferred to the generator. When mains power is restored, the generator keeps supplying power for a short period (normally about one minute) to ensure that there are no blips from the mains supply then the power supply is transferred back to the mains. The generator continues to run for another few minutes to cool down before shutting itself down.
Generator Sizing concepts
A standby generator is normally used to to provide power to both the critical and non-critical load. Critical load is also supported by a UPS which bridges the power gap between mains power fail, and generator startup. Non-critical load can be anything else, right up to the whole building.
Run time for generators is normally about 8 - 12 hours when using the built in base tank, however, longer run times can be achieved by refilling or using a separate fuel tank.
The main questions to ask before deciding on a standby generator are:
In the event of a long power outage do we need to:
1. - keep the server room operational (don't forget the air conditioning). This is a very effective cost efficient method for businesses who have international links and must keep operational 24/7.
2. - keep key areas operational. There is a danger with this option: any key area will need to be supplied from a separate distribution panel. In the longer term, the supported area may become too small in which case the generator may need to be replaced, or the key area may need to be moved, in which case there will need to be some re-wiring.
3. - keep the whole business/building operational. This option has the benefit of simplicity, flexibility, and total effectiveness.