Obviating phase overload in a 10kVA UPS application.
Best practise guide for remote retail store or branch office standby power installations.
The overloading of a UPS (uninterruptible power supply) system via the dedicated red plug circuits due to rogue electrical connections and unsupervised electrical circuit expansions is a major cause of UPS malfunctions for many companies. Overloading can result in costly downtime and is often responsible for emergency support technician call-outs.
In large retail chain stores or distributed branch office environments, UPSs deployed to provide standby power are particularly susceptible to ‘phase overload’. It’s often an installation’s single biggest point of failure. In this light, phase balancing of UPS output is key.
The routinely adopted practice of using smaller 10kVA 3-phase in and 3-phase out (3/3) UPSs therefore needs to be reconsidered.
A 10kVA 3/3 UPS supplies a total of 43.4 Amps (non-reactive load) divided across the 3 phases. This means each phase on the output of the 3/3 UPS has a maximum current of 14.4 A.
This configuration is susceptible to phase overloads and resultant UPS bypass/reset. (A standard wall outlet is rated at 16A, so it does not take much to overload a particular phase.)
For this reason, over sizing a 3/3 UPS to least a 15kVA UPS or preferably the deployment of a 10kVA 3/1 (3-phase to single phase) UPS is strongly recommended.
A 10kVA 3/1 UPS has the full 43A on a single phase and therefore, if correctly sized, is much more robust in terms of phase overload and does not require output phase balancing.
A 3/1 UPS thus obviates the need to oversize the UPS and solves the problem of overloading the output of the UPS.
The benefits of a 3/1 UPS in distributed UPS installations include greater stability in the field as a result of reduced overloads from expansion or rogue connections and reduced need to balance phases on the output of the UPS.
It also offers simplified single phase electrical reticulation for rollouts of new branches as well as easy retro-fitting in existing 3-phase reticulated branches.
As a correctly sized 3/1 UPS runs at higher loading, it operates more efficiently and cost effectively than a 3/3 UPS.
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