Three phase UPS system 1

[tonycatterall]

We are installing a ups with an output of 208volts three phase and neutral ie 120 volts phase to neutral.
The system is rated at 80kVA. The system will be supplying critical instrumentation on a petro-chem complex. The supplies to the loads will be 3 x 120 Volt line-neutral.

My question (very basic I know!):
What will be the power available in each leg?
Is it 80kVA / 3 (ie 26.7kVA), OR 80kVA / 1.732 (ie 46.7kVA).

Regards,
TC

 

[mpparent]

80/3

Mike

 

[waross]

Mike said it all. End of thread.
yours

 

[arcflash99]

Are you installing a total machine bypass switch? i.e. You can turn the bypass switch and remove the machine.

 

[ruggedscot]

Bypass switches are a black art if you are not careful you can get a pretty large bang off of one of those.

If the UPS goes into operation you may ahve the output freewheel and then if you at that moment go into a manual bypass external with no reference to the UPS then you get some large currents flowing.

Usually on the larger UPS units there is some sort of internal electronic bypass - once that is in then you can put in the manual bypass and remove the UPS from service.

Got to watch as UPS's dont like the output linked to the input - if the power fails at this time you are in effect feeding the output to the input and you get some wierd results.....

Just my tuppenny's worth.

Rugged

 

[mpparent]

More than likely, since it's a 80kVA unit (pretty small) the only bypass is probably an internal one. That's not to say you can't get an external wrap-around bypass, but I'd be surprised if TC installs it. Also, I'm not sure but the 80kVA UPS in question may only have one input, ie both the rectifier input and the static bypass input. In ruggedscot's explanation, I think you would need a sync between the UPS and say, the backup generation source so that a wraparound bypass operation could take place. However, a UPS always sync's to its source, so you would be able to tell when you were out of sync by an alarm on the UPS, so a wraparound bypass should be ok? Missing anything?

Mike

 

[arcflash99]

It's fine not to have one. We are going through a lot of work to replace our original UPS machines that don't have an external bypasses (internal bypass only). The problem is through personnel changes and project philosphies people will keep putting more critical loads from multiple independant processes on these things and before you know it, you've got 2 million dollars a day process riding on an obsolete machine that will cost millions to replace a machine that costs a couple hundred thousand.