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Build a rotary converter with a transfo to run a 10 HP 575 volts 3 phases motor.

jfroux_1

Plastic
Joined
Apr 8, 2018
I want to build a rotary converter with a transfo to run a 10 HP 575 volts 3 phases motor. I have a 10 hp 240/480 and a 5 hp 240/480 that I’m planning to run in parallel to be able to run that 10 HP 575 volts and I’m planning to get a 15 KVA transfo. But before I start, I’d like to know if someone already did it and if it worked.
 
It definitely works, best to find a 347/600y to 240v transformer so you can ground the neutral the 600v side.

If you can only find a 600v delta transformer, it would be best to permanently wire the motor, switch the 240v side of the transformer, and use the Y neutral point of the motor as a ground.

Because otherwise your option is to corner ground the 600v transformer, or use 3, 347v lightbulbs connected in Y to ground. If the lights burn out, it has a ground fault.

Or just leave it ungrounded.
 
But before I start, I’d like to know if someone already did it and if it worked.

Yes, reported on here several times when the question repeats, as yours just did. :)

My Diehl lumber jointer is 575 and has 3 ea 5HP motors of which at least 2, and sometimes all 3 run at the same time.
However, dinner is calling. Good luck!

smt
 
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There are more like the above if you search transformer, with my name. Or transformer 575

Here are missing pix



Notice that i am using a 208 to 480+ transformer with higher taps at 492v and 504V; and feeding it 240V plus as received from the 1 ph service entrance, to get to the 575v range out of the transformer.
Have not looked inside the transformer for over a decade, it works transparently. However IIRC, i ended up using the 492v taps. Simplistically on paper that should come out to 568V but it is often higher because i discovered that line to my house is often (usually) somewhat over 240V nominal. [(492v/208v) 32V + 492V = 567.7V ] I don't recall if i posted my checks over several iterations, so don't want to second guess anything i wrote, but IIRC after balancing, the voltage was well within limits for 575. I just did not want it much, if any, higher since most of the wiring insulation is only nominal rated for 600v.

Balancing the legs, cut 'n try, with run caps. They go in the device box below the panel.
The 240V converter feeds directly into a 3ph distribution panel (3ph breaker box from the converter) seen on the wall. Also as seen, the transformer is on its own circuit with breakers; physically it sits on the floor beside the lumber jointer.


smt_diehl6604.jpg
smt_diehl6604.jpg
have fun, play safe, good luck!
smt
 
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Yes, reported on here several times when the question repeats, as yours just did. :)

My Diehl lumber jointer is 575 and has 3 ea 5HP motors of which at least 2, and sometimes all 3 run at the same time.
However, dinner is calling. Good luck!

smt
I'm not very good to find what I'm looking for when I navigate in those forums. I'll try to find a post that show step by step how to proceed to install a transfo 600 volts. It shouldn't be so hard... I build a rotary converter with a 10 hp 240/480 few years ago. Now I just have to add a 5 hp 240/480 in parallel and connect a transfo on it. But at the same time, I've never done it and I'd like to do it right the first time and I like to learn from the mistake that the other did. I all have to bring more amp capacity in the garage. Right now I have 30 amp 220 volts capacity that I installed few years ago. My plan is to install a sub panel of 100 amp in the garage that is about 70 feet from the main panel.
 
This is the transfo I'm planing to buy. His is asking 360$ for it. I guess it is a good price. Even if I wait, I don't think I'll find a better price. Is 15 KVA good to run a 575 volts 10 hp motor?
1699107995572.png
 
Figure one kVA in per 1 HP out for a motor. So, 10 kVA right there. And you need some margin for starting current, so 15 kVA or 20 kVA.

You certainly would not want a smaller transformer than that. I would probably prefer 20kVA to avoid voltage drops on start. You probably will want to consider a soft starter..
 
It will work fine if there is no load on the largest motor you are starting.
If it is for a motor that starts under load such as a compressor (even with an unloader) it should be OK on paper but could be a bit under-sized.
While my system potentially runs 15HP on 15 KVA, none of the motors have load at start-up and it would be almost impossible in my shop to ever get close to maxing out the 2 ea 5HP cutterhead motors even if both were running at the same time, though the feed motor might have some load at times.

That said, my lines are protected at the panel, the motors have correctly sized heaters and magnetic starters.

smt
 
It may be less effort to just change the 600v motor for a 240v with a vfd. Or just a 240v with your existing rpc.

With regard to startup:

The impedance on the transformer at 3.8% means that's how much voltage drop there is at 15kva. Your 10hp motor will pull a lot more than that, but only at startup, so lets say 20% voltage drop.

If it wont start quick enough, then add a bunch more starting capacitance at the load motor, or at the RPC. You can also leave some of the capacitors permanently connected, to offset the transformer's inductive parasitic load.

A voltage relay that automatically connects additional capacitors as the third leg drops is a good method.

Another method which i use to start my RPC, is a 24vac 40amp contactor as is found in billions of 2 to 5 ton hvac systems, but the 24vac coil is removed, and replaced with 4 turns of 12 gauge wire.

The initial current at startup pulls the contactor in, and the start capacitor engages the load, but only to start up. As soon as the current drops the contactor opens and is disconnected


You can change the number of turns to suit the load and trigger point, as well as use more than one contactor to keep the 3rd leg balanced with varying loads
 
Many problems would be potentially solved by simply using a transformer to power a VFD made for the higher voltage. You would get soft start, etc. And, of course, variable speed.

That transformer is 3 phase, you would use a single phase transformer to power the (oversized/derated) VFD.

How much is it worth to you to not change out the motor in whatever is being powered? That could end up being the least trouble, and perhaps the cheapest method as well.
 








 
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