Transformer power usage

Does a 3 phase transformer use power if it is switched on but not running a machine?
Is it ok to leave it on for long periods if it is doing nothing?
I have 120/208 three phase coming in and I only use one small transformer to run the 575 volt motor on the lathe. I switch it on and off as needed but wondered about the power usage etc, the unit I have has a noticeable humm when powered on.

Thanks and sorry for the dumb question.

Michael

My 3 KVA is on when the Phase Perfect is going. Its quite the little warmer-upper, and if you can get any silence in that area, it hums.

johnoder said:

if you can get any silence in that area, it hums.

Click to expand...

Huh? ;-}


I've got a 10kva three phase transformer on one of my generators that's 240 Delta in, 208/125Y out, and it pulls about 3A just being connected. Obviously, it's a reactive circuit so the measurement of current may not be accurate with respect to actual power used, but as Bill and John noted- it's a heating element.

Aside from the slight power usage (probably 1% to 3% of rating) there is one other issue that may or may not be a problem.

The thing is a reactive load. For most shops with a lot of motors, that may not be an issue. But, a larger transformer, idling, will lower your power factor by an amount depending on the other loads.

Someone once asked here about a piece of vacant property (old factory, IIRC) where there was a 500 kW transformer on the property connected up to metered power, but not loaded. They had a significant electric bill, and wondered why. Odds are that their power factor was rotten, and the thing was pulling possibly 5 or 10 kW. With the adders, it could be significant.

In your case, "small" being an unknown rating, but maybe a few kW, and you having other motors and loads, it's unlikely to be a big issue, but then, there is no particular reason it needs to be on, either.

Thanks for all the replies, pretty much as I suspected so I wil continue as I have been.
My small unit is only 10 kva and I need to hook it up to my new Cinnci Mill that I posted about.

I am sure it is a rare machine, it has two incoming voltages and four motors. Two motors are 220 3ph and two are 600 3ph and I have no idea why they would make it like that. The built in control box on the side of the mill is a nightmare of wires and switches etc. I am really looking forward to getting it in place and up and running.

Michael

Questions galore

By the way Mr. Moore;

No one else remarked, but the only dumb question is the one you did not ask!

Without your questions we would not be here and this whole site would not exist.