Is it necessary to combine the outputs of UPS power supplies?
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Modern DCS and SIS systems require two UPS inputs as well as one mains power input. Do the outputs of these two UPS units need to be connected using a parallel connection card, or can they each supply power independently?
Looking at the power supply of UPS systems separately, such systems inherently have dual power supplies internally, and the UPS can also provide battery power to sustain operation for half an hour; therefore, there is no need to use the UPS in parallel mode for power output； For instruments powered by a single power source, it has indeed been proposed to use UPS for parallel power supply; however, what is being discussed at present is switching. Since the device itself has only one power connection circuit, what is the meaning of implementing such switching? Moreover, switching takes time – at least 200ms. As for the parallel approach, if the voltage is 380V, parallel connection isn’t possible; at least the output should be single-phase after balancing. I’ve never used parallel connection cards, so we can discuss this further.
If there’s a problem with the parallel connection card, then the entire UPS will be ruined. I have encountered problems with the parallel connection cards of GE UPSs on-site in the past, which caused the units to stop operating. Most DCS systems are equipped with dual power supplies, each corresponding to one UPS. For systems without dual power supplies, an STS static transfer switch can be considered. For example, if there are 6 operation stations, three of them are powered by UPS1, while the other three are powered by UPS2.
Generally, the UPS output and mains power are supplied to the DCS and SIS system cabinets. Both types of cabinets are equipped with dual power switching devices. All that is needed is to connect the two power supplies to the cabinet’s power terminals in accordance with the specifications and requirements.