AC rotary UPS v DC rotary UPS

[Zealous]

I am installing a UPS system for power backup. I have decided that rotary UPS will be the better option rather than static. However I am faced with the decision to use a ‘conventional’ rotary UPS or a DC flywheel type. Other than the added electronics of the DC system I cannot see any major disadvantages to either. Any suggestions?

 

[ScottyUK]

The non-electronic types have better fault clearing ability than the ones that use DC-AC power conversion, because the power electronics usually have fast-acting overcurrent protection which operates faster than a typical distribution breaker or fuse.

Eurodiesel - just bought by GE Digital Energy, I've just discovered, but nothing on their website yet - make an interesting AC rotary product which is roughly double the cost of an equivalent kVA static type. The electrical machine is interesting just for how it works.

This type of unit is popular with the financial institutions, who have lots of cash and for whom downtime is almost inconceivable. Says a lot about the product - expensive but very effective.

 

[rbulsara]

AC rotary UPS (Like Piller and Russelectric makes) with adequate batteries are best IMHO. DC flywheel is, as I believe, are for ride thru capabilty for a few seconds, so that generators can come on line. They claim using little or no batteries, I am not fan of these type of systems. (See my profile).

As scottyUK mentioned AC rotary units provide good SCC capability to clear downstream faults, a major advantage over static type UPS or DC/AC type.

Also AC rotary units, provide a truely natural sine wave during its normal operation (as it is effectively a motor generator set). You can not get any cleaner power than that. All other mode involving inverter produce a synthesized wave.

AC Rotary units go on battery /rectifier and and inverters only in case of a power outage or motor/gen failure.

In USA the the price of rotaries have come down considerably, like 1.3 times a good static unit or so.

Getting opinion of more than one good consultants will also be helpful. Get more people (management) involved in making such decisions and document your decision making process, because no one cares when everything goes well but if something goes wrong you will be the one ending up holding the bag!

By the way, static UPS units also have come a long way in last few years. But there are only a few leaders.