Three phase UPS system information for the design of secure power protection plans for server rooms, datacentre and industrial applications.
Most UPS manufacturers supply a three phase UPS from 10kVA or 10kW upwards. This unit will either be only available as a 3/3 (3phase-input/3-phase output) or a 3/3 and 3/1 (3-phase input/1-phase output) system. When installing a UPS capable of 3/3 or 3/1 configuration, the final set-up is usually made during installation either through hardware or hardware and firmware settings.
Phase imbalance occurs in a 3-phase UPS system when one or more of the three phases has a higher load than the other phases. The unbalanced voltages lead to unbalanced currents and increased temperature on the ‘overloaded’ phases. Long term phase imbalance can lead to component or catastrophic failure of the uninterruptible power supply.
A 3-phase UPS system will have a built-in automatic bypass for overload and fault conditions. The bypass will generally be a static bypass rather than a relay-based bypass. The UPS will also have a built-in maintenance bypass to allow the UPS to be isolated for maintenance by a manufacturer certified engineer. The UPS installation may also have an external wrap-around UPS bypass switch. This allows the uninterruptible power supply to be fully powered down and if necessary swapped-out, without disruption to the connected loads. The external bypass switch may use a rotary switch or breaker arrangement.