UPS systems should be used in combination with a standby generator in situations where equipment and machinery must remain operational at all times, even during prolonged periods without mains electricity.

Where possible, it is beneficial to deal with a single supplier for both items as this eliminates any potential conflicts if the equipment doesn’t work well together.

It is important to correctly match a standby generator to the uninterruptible power supply it will be working with.

The generator must have the capacity to handle the load from the UPS, to recharge the batteries, and cover any conversion losses from the UPS. Factor in ancillary equipment such as air conditioning, emergency lighting, alarms, and communications and monitoring systems too. For most generators, the maximum step load is approximately 65% of the total rated capacity.

Another point to consider is frequency regulation. The worst-case scenario is that the UPS and generator aren’t able to synchronise. The two main causes of this are if the rate of change is too fast for the UPS to follow without endangering the load, or the frequency is too wide for the UPS to accept.

Other issues that can affect poorly matched UPS systems and generators include input harmonics, load acceptance, voltage intolerance, and poor response times.

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