How to switch between DCS mains power and UPS power?
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Currently, DCS systems often have two power supply sources: mains power and UPS power. When the mains power fails, how does the UPS take over? I once looked at a drawing and had the feeling that the power supply for the control station wasn’t switched to the UPS?
All the DCS cabinets I’ve seen can be connected to two power supplies directly; I’m not sure whether the power is supplied simultaneously or through switching. Of course, you can also add an ATS yourself.
ATS seems to be commonly used in low-voltage cabinets. What is APC used for in the instrument power supply cabinets? I haven’t studied how this APC works
You can ask your colleagues in the electrical engineering field for advice; they are experts in this area.
Isn’t APC a brand? The ATS requirements for the control cabinet may be a bit higher, mainly due to the need for shorter switching times; the current requirements, on the other hand, are lower. Many DCS systems come equipped with modules for power switching, so no additional components are needed. But in reality, it’s not always a dual-power supply; there are also cases with triple power supplies and so on.
This power supply system is generally a challenge, as few DCS manufacturers specialize in power supply solutions. Typically, two switching power supplies are used inside the DCS cabinet, as the voltage within the cabinet is 24V. Apart from the lighting for maintenance purposes and the cooling fans, the outputs of these two switching power supplies are connected to a 24V dual-power switching device, which functions somewhat like a diode. The 220VAC inputs for these two switching power supplies come from either a UPS or the mains electricity; that’s how it works. In other words, both power sources supply power simultaneously
The DCS is powered by both mains electricity and a UPS; you can check this with a meter. Since there are two power sources, a power outage in one of them will not cause a disruption in power supply. If a power outage occurs and the UPS has to take over, it might not be fast enough, right?
There should be redundant 24V power supply modules to switch between the 24V power sources; the UPS and mains power are switched via electrical systems, and there is usually a power cabinet available
There is no simultaneous power supply; it just switches automatically internally.
They indeed are not powered simultaneously. At the same time, the power supply requirements are for the same frequency and phase; this method is generally used when there are loop-closing devices on the high-voltage side. Typically, a DCS’s power supply can accept two power sources simultaneously and switches internally between them; when one source is disconnected, the other takes over. There is also a switching time for this process – the switching time for high-voltage switches is around 200 milliseconds, though it can be shorter as well. Since 24V systems are generally not sensitive to voltage, a longer switching time is acceptable; the delay settings used in alarms can also help to overcome this switching time.
Providing power simultaneously does not mean that the DCS uses two power supplies at the same time; by power supply, I mean that the mains electricity and the UPS both output 220V, with the switching being handled by the DCS. Is that what I’m saying?