Although you may have decided to support your building with a standby generator, still you may be at risk. A generator even with an automatic start system will take typically between fifteen and thirty seconds to start and run up to speed, fifteen seconds is like a light year to an IT load, computers simply will not accept such a break and will crash, to bridge this gap most IT users install a UPS system (Uninterruptible Power Supply), the UPS sits between the generator and the critical load providing clean regulated unbroken power until the generator has synchronised.

Choosing the right UPS to work with your generator can be tricky for the inexperienced, the general rule for sizing is typically that the alternator should be two and a half times the size of the UPS, so a 100KVA UPS will require a 250KVA generator.

Like all calculations this can vary greatly depending on the technology of the UPS, transformer based UPS with conventional rectifiers tend to have higher harmonics which feed back to the generator which in turn affects the real power available, hence the formula of two point five, however AEC are able to offer transformerless power factor corrected UPS with IGBT rectifiers, the benefit of such technology means that the power calculation can normally be reduced from two point five to one point seven, this is a reduction of over thirty percent resulting in very substantial savings.

Using an Uninterruptible Power Supply with your Diesel Generator