Any problems running a UPS off a step-down transformer?

[Mark R]

Just curious. I recently heard a story about several hospitals that installed some modern X-ray equipment.

The equipment was supplied set up for the local 240V supply, although it had originally been designed for 110 V. The original design is supplied with a hardwired, basic off-line UPS. However, rather than modify the machines for 240V, they simply included a 240-110 V transformer which was hard-wired to the equipment, supplying 110 V to the UPS.

What surprised me was that this proved to be a problem. 2 hospitals in one town had installed these particular machines (as well as a whole lot of other expensive and sensitive equipment). One day there was a power outage affecting most of the town. However, when the power came back, all the equipment with this design failed with blown step-down transformers (both hospitals lost both their machines - a total of 4 blown transformers), no other equipment at either hospital was damaged.

I would have thought nothing of it, but I've now heard about another hospital with the same machines who suffered a power outage, and they lost all 3 of theirs when the power came back (again, blown step-down transformers).

So, is there a recognised problem with step-downs and UPSs/surge suppressors? Or was this just a cheap manufacturer?

 

[mpilchfamily]

Just sounds like there isn't a proper surge surpresor being used between the wall and the Transformer. I take it the setup goes from the wall to the transformer, into the UPS and then into the matchiens. This leaves that transformer unprotected from any surge that may happen durring a power outage.

 

[Navid]

If the UPS includes a surge protector, and it triggers on power-up, the output of the transformer would effectively be shorted (by the MOV). This could result in high current in the secondary and failure of the transformer.

But, it seems too fundamental of a concept for the designers to have overlooked.

 

[Rubycon]

There should be no problem as long as the transformer is properly rated. Many times in an industrial setting where only a 440V 3F circuit is nearby a transformer will be installed providing 208VAC 3F power with 120VAC 1F power available as well.

Loss of a single phase in the building will cause damage if missing phase protection is absent. (it should never be!)

Also a poorly designed UPS can actually output line voltage on its input terminals when running on battery power. This is extremely dangerous as well because - like an improper generator installation - can backfeed into the distro transformer secondaries producing lethal voltages on lines that lineman could contact. (thinking they are de-energized)