Even if very untypical, in case of synchronized UPS (see description below) it is possible to have different power ratings between UPS (A) and UPS (B), as long as the smaller UPS rating is still right sized for the load.
Synchronized UPS are usually used when a plant (load) is supplied by two power supply sources, one is the main and the other is the emergency one (redundant sources). Only one source is supplying the load; in normal conditions the main source is supplying the load; in case of a power outage on the main source the load is transferred to the emergency source. Since the two sources, which are typically called (A) feed and (B) feed, can have a possible phase shift among them - (A) and (B) are in this case unsynchronized - there is the need to synchronize them upstream the load.
There are basically two ways to do that:
The second solution is by far the best solution because there is no interruption during the transfer. Moreover, applications which require a redundant source typically require also UPS systems plus batteries (sometimes also diesel generators) which guarantee electrical power to the load also in case of longer power outage of both sources.
Carlo Kufahl is the Product Manager for 3-phase modular UPS at the center of excellence for UPS, Power Protection Product Group of ABB, Quartino, Switzerland. He joined in 2010 and as a Sales Engineer for two years and then he took over as Product Manager. Today he coordinates and manages the complete life cycle of the 3-phase modular UPS which includes pre-development, development, launch, sales and phase out of products. Carlo holds a Bachelor’s degree in Electrical Engineering from the University of Applied Sciences and Arts of Southern Switzerland. Carlo also holds a Master in Business Administration obtained at Zürich University of Applied Sciences.
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