3 phase ups

[dbuckley]

Yes and no. The staic switch is a common device between the two UPS's and thus a single point of failure.

It is, which is why dual distribution is better. Dual distribution (assuming the loads can handle it) gives a great increase in uptime whilst removing the perceived need to work hot. Wins all round.

 

[Besoeker]

1. UPS's are not designed for motor inrush characteristics.
2. Disagree. Application people have no detailed information on the UPS's internal design nor on the software parameters that controls the UPS.
3. 15kVA was suggested, but that it is correct is anyone's guess. No inrush parameters were taken into consideration nor the UPS's overload capacity duration was established. Anyone who would go ahead on that basis is a fool.
4. Gen'sets are required to sustain full load within 10 sec.
5. As a rule of tumb a reliable battery system beyond 30 minutes becomes more expensive that the generator/battery system.
6. Reliable battery system consist of dual banks an Cellwatch type battery monitoring. Lifecycle cost needs to be considered since VRLA can be eitehr 4 or 10 years, but it has been found that seldom will you get that life out of them, so the cost of a new bank neds to be considered every 3/5 years. If you choose the wet cell option then you would have to add the building cost and change the replacement to 20 years.
7. UPS systems only recently started paying attention to the battery monitoring issue and even though they are sophisticated when it comes to the internal health of the UPS electronics itself, the battery 'monitoring' is nothing else but a show. Battery remains teh weakest part of the U.
8. A properly designed system for optimum reliabilty is a UPS with dual battery banks equipped with individual cell monitoring for about 5 minutes duration and a life-safety grade gen'set that feeds the UPS via a transfer switch. Overall it has higher reliability as a redundant UPS with gen'set backup.

1. But, as I said, if you remain within the UPS kVA and kW rating it can handle the starting current. The OP gave the starting current and that's how the 15kVA was arrived at.
2. Fair point. I deal with both the internal power electronics and the application but I accept that might not be typical.
3. See point 1. I gave a figure for overload capacity but not duration. Typically 30 seconds is stated but that was my omission. Mea Culpa.
4. I'll take your point about the 10 seconds. It isn't a mandatory requirement that I'm familiar with but then I'm from planet UK. Is the 10 seconds from standstill on a dead board?

The remainder of your post is mainly about the reliability and life of VRLA cells and, based on my experience, I generally agree with your comments.
For systems requiring high integrity, we have mostly used Plant?.
Expensive though......

 

[weressl]

It is, which is why dual distribution is better. Dual distribution (assuming the loads can handle it) gives a great increase in uptime whilst removing the perceived need to work hot. Wins all round.

If cost is no object.

Single UPS with bypass and generator backup with two sets of monitored batteries is my choice. If dual power supplies available then the second source is direct utility.