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Synchronous And Parallel UPS System Operation

By Tony Bell

Most higher powered UPS systems can be connected in parallel in order to achieve redundancy. Redundancy is expressed as “n+x”. ‘n’ refers to the number of UPS Systems you have to meet your power loading and “x” is the number of UPS Systems you have over and above this – usually just the one.

Redundancy can also be achieved if your load has dual inputs and providing power by two separate UPS Systems. In such circumstances you could remove the need to parallel the UPS together.

If the output power waveforms are not in synchronisation, this could mean that a potential of 460V exists at you point of use. This is because the UPS outputs could become anti-phase. This situation should be avoided.

Usually a UPS output frequency is synchronised to the input power frequency. This allows the UPS to “bypass” without any loss of power in the event of a fault or overload. As a result, the AC power source feeding the UPS Systems must originate from the same supply.

During a power cut the UPS System no longer has anything to sychronise to and in this event relies on its own internal clock. The time taken to produce a power waveform is 20msec or 20 thousandths of a second. Antiphase waveforms are only 10msec apart. In a five minute power outage two systems need only have variances between their internal clocks of around 30 parts per million or 0.003% in order to become antiphase.

The UPS Systems clearly need to talk with one another to ensure that their outputs are synchronised. Not all UPS have this facility. Many UPS Systems will allow a parallel connection but not all have synchronisation. Thankfully the Dale Power Solutions 6KVA and 10KVA E200 Series UPS Systems have this feature. This allows the UPS to be independent, but have output waveforms that are in synchorisation. This is vital where the UPS are feeding the same environment but are not required to be connected in parallel.

Power Inspired offer the full range of Dale UPS Systems and other Battery Backup products.

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Article Citation
MLA Style Citation:
Bell, Tony "Synchronous And Parallel UPS System Operation." Synchronous And Parallel UPS System Operation. 16 Aug. 2010. 2 Aug 2014 <>.

APA Style Citation:
Bell, T (2010, August 16). Synchronous And Parallel UPS System Operation. Retrieved August 2, 2014, from

Chicago Style Citation:
Bell, Tony "Synchronous And Parallel UPS System Operation"

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