Motors and Phases

Why do you want to convert a three phase motor of this (kV voltage?, kW power?) to single phase? If you mean 15-40kW this is too large to run off a standard residential or business single phase supply due to the enormous starting and running current (check your local regulations for more guidance on maximum motor loads for single phase supplies).

What is the application?

Yes its surprisingly easy and if done properly there is no big reduction in starting torque or running efficiency. I have developed a balanced phantom phase conversion system that allows full running torque and efficiency with no major power loss or efficiency drop. I have built countless converter boxes for doing this in ranges from .25 Kw up to presently 20 Kw. The formulas and design is basically linear from small to large so a 40 KW system would be basically the same parts wise as two 20 KW units.

There is a considerable increase in the amps load though being the motor is puling off of one line source and not three. Figure about a 160% increase above the motors specs plate amps.

So if your motor had a plate rating of say 20 amps three phase at 230 VAC it would run at about 32 amps at full load on single phase. However due to the high starting current it may draw as much as 150 amps on start up for a several seconds depending upon what type of load it is driving. So you do have to resize any wiring in the machine up to the motor and factor that into your supply lines accordingly as well.

Its that high starting current that will limit how big of motor you can effectively run off of any single phase power. If you have a 120/240 volt 200 amp service like me supplied by a 15 KVA pad transformer you would be limited to about 20 HP or 15 KW.

I have my own 15 hp commercial air compressor that has been on single phase for about four years of daily use. It is in a unheated building and starts reliably down to about -20 F off of a standard 60 amp 240 volt single phase line. Its starting amps draw at that point is about 135 amps for 5 -6 seconds then drops to about 48 amps once up to full speed and pumping at 175 PSI.

I have a number of other commercial machines with three phase motors all running off of single phase and many friends with my systems who are also running surplus commercial equipment as well with years of in service run time on them.

It would be far far less expensive to buy a VFD to convert your 1 phase supply to 3 phase.

Assuming, of course, that you made the above mentioned error in saying kV instead of kW. If you really have 15kV and 40kV motors, you are out of your mind to want to run them on single phase, and besides, I don't think the technology exists. Not because it can't be done, but because anyone wanting to would be insane.

JRaef

he wants to do the reverse.

Quote "is there any way i can convert 3phase motor to 1phase motor. my motors are from 15KV to 40kv."

Right, but I was assuming he wanted to do this because he has 3 phase motors and a 1 phase supply. So rather than rebuild the motors as 1 phase, it would be less trouble to change the supply by using a VFD to give him 3 phase for his motors.

not at that voltage levels.starting will be a problem