Three phase 45 kva transformer

Sure. We have been using such a configuration for 5-6 years to power a large convection oven that melts the solder paste on circuit boards. The KVA rating is reduced about 10-15%.

We learned the hard way to never switch on an unloaded transformer. Blows a fuse in the metering panel almost every time. So, the transformer is never shut off using the circuit breakers.

Paul

Paul, can you clarify this, how else do you shut it off?

And how do you switch it on? I am confused.

We don't. The oven is turned on/off by an internal computer. So, if power is off, we can't turn it on before powering up the oven. I think the previous owner ran a 120 volt extension cord into the oven just to power the computer. We chose not to try that. So, power to the oven is on 24/7/365.

The transformer and oven are on their own 200 amp 208/3 meter. Each leg has a 200 amp fuse right after the meter. They blow at about 201 amp!

For your use, connect up the equipment and turn it on before powering up the transformer. Or permanently connect some other load, like a heater, to the 460/3 circuit. Then add your new equipment to the line.

Paul

you sure can, but may need to fiddle with the taps to get the voltages right.

OK, thanks.

I have another question. I bought a 50 HP rotary screw compressor for resale. I want to test it.

I realized today that it is 460v. Would this 45 kva transformer, be able to run this compressor UNLOADED, just as a power up test -- not pumping at full PSI.

Thanks

Hey Iggy,

Simple math says "Yes"....50Hp X 750 watts = 37500 Watts X 1.15 (15% derate) = 43125 Watts, so your 45000 Watt transformer should do. What size is the disconnect for the 45KVA fused at??? Needs close to 200 amps.

Brian Laws>>>> I have bought a 3 phase 45 kvs transformer 480 -> 240.

There is no disconnect, only the transformer in the back of my truck.

KVA is not watts and I am not sure if it is enough to start the compressor.

There is no RPC there.

That would be a hell of a load to start on temp wiring. Now, put a soft start on it and it would be a piece of cake.

Karl

I switch power into an unloaded 30kva transformer via a 20 amp triplex breaker every single day withouy any problems whatsoever.

Ours is a 75kva. A 100 amp circuit breaker is between it and the meter base with quick blow 200 amp fuses. Replaced one or more fuses in a two week period. That cost more than running continuously for several years.

Paul

What fuses do you need, I can sell you some cheaply. Let me know asap, I will visit my fuse contact tomorrow.

No, don't bother. I can't find out without shutting off the power to the oven and pulling the fuse. I believe they used silver elements rated for

It's been at least 4 years since we had the problem.

Paul

?????? What ???????? What does that mean, and what does any of this have to do with your truck?????

You are correct of course. A watt is not a volt-amp. But you only asked if the 45Kva transformer hooked step-up versus the step-down mode it was designed for would handle the load of the 50Hp compressor start-up. So send me the power-factor for the whole set-up I'll do it again, accurate to one watt.

Take care. Have fun.

Brian Lawson.

Brian, I will see, first, if I can rewire the compressor to 230v... It may be easier than messing around with power factors and unknowns.

Just sayin...

--people all around the world routinely switch unloades transformers on and off without any problem whatsoever--and so it's definitely something else that's wrong with whatever situation you have going on causing the problem there.

I may be your experience, but it is one of those "things that you know...That just ain't so"

The inrush to a transformer depends on several things, one of them is the load, but the load ALWAYS adds to the inrush.

THe other things are the magnetic state the transformer core was left at, and the where on the sine wave the voltage is at the moment you close in. jk

The typical fuse curves for a 200A fuse would probably never reach "minimum melt" at 201 A, at nominal temp, and would take several hundred to several thousands of seconds at 300A. For example an RK1 fuse

jk

He indicated that he has a very special fuse.