In my last blog, I wrote about choosing the right UPS topology for IIoT and critical power applications. Getting the topology correct is vital to ensuring that manufacturing, processing, production, and building equipment operates reliably and continuously according to the business requirement. However, it’s also important that you size the UPS according to the application need, and the purpose of this blog is to give you some pointers to making a wise selection. I’ll address runtime requirements in a later blog post.
Losing power to critical applications can be disastrous financially, causing lost productivity and materials; dangerous, creating conditions for a loss of life or limb; or damaging reputationally causing a long term loss of trust and goodwill throughout the supply chain. In driving cost out of manufacturing through, for example, just-in-time techniques, a significant safety net in time and materials has also been taken out. Today equipment must work when it needs to.
Sizing a UPS is pretty straightforward and really consists of four steps:
- Calculate the theoretical maximum load drawn by the load by listing all the equipment that is going to be protected by the UPS, and then determining how many amps are drawn by each. Multiply distribution voltage by Amps to get the VA requirement.
- With an existing load you can make a measurement directly from the electrical distribution, however, be aware that some loads are dynamic and evolve throughout the day and night. In this case set up a recorder for the full cycle of the process to measure the highest level of energy required.
- For future installations or upgrades, include the details of new equipment or distribution requirements.
- Make a careful note of exceptional inrush current characteristics of specific equipment or devices being protected. Some loads such as AC electrical motors, scanners, transformers etc., may draw several times their normal full-load current when they are first turned on, and this needs to be allowed in order to prevent, for example, the selected UPS transferring the load to the bypass.
- Apply a simultaneity (or diversity) factor to get the estimated load level. It is common practice that the simultaneous operation of all equipment at full power never happens; simultaneity factor is an estimated value that takes the probability of concurrent operation into consideration.
- Add on possible load growth requirements to the estimated load level and the result is the Final Load Level.
From there you need to ensure the VA rating of the UPS you specify is at least equal to, if not greater than the Final Load Level. In the past, estimating future load growth was a bit of a hit or miss affair which generally led to the system being oversized (better to have protection and not need it, than need protection and not have it).
The advent of modular, scalable UPS such as Schneider Electric’s Symmetra and Galaxy V series UPS families enable rightsizing according to the actual load within the facility to increase protection (power and runtime) when required. In addition to enabling a more efficient system with lower operating costs, such equipment also allows capital budgets to be conserved.
If you’d like to learn more about how the UPS enables system availability and uptime, access this free Schneider Electric white paper 24 “Effect of UPS on System Availability”, which also provides quantitative data regarding uptime in real-world environments.
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