Check my calcs please

[kwired]

Not sure what you mean by "inverter".
I've got a single phase source and a 3 phase piece of equipment.
I thought a vfd or a phase converter were the only way to manufacture 3 phase from single phase.
On another note, why would a plasma cutter care about the incoming wave? Does it not condition the input and put out a modified wave?
Maybe a call to hypertherm is in order.

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The VFD rectifies incoming AC to DC then converts the output to a pulsed DC over three lines that approximates a three phase source. It is by no means perfect sinusoidal wave like would be from a generator, nor is is as perfect as an inverter from a UPS, PV, or other similar systems would produce.

That said, the plasma cutter may not have a problem with what a VFD will produce for output, but I can almost assure you the VFD will not like the plasma cutter connected to it's output. You turn drive on and get it up to 60 Hz and 460-480 volts and then suddenly switch some load on - it will see that like a short circuit and will trip if you are lucky. If not luck will burn out components. It is designed for ramping a motor up from low voltage and low frequency, not suddenly throwing a load onto it's output.

Some of the drive experts can explain the technicalities much better then I can.

 

[Shaneyj]

The VFD rectifies incoming AC to DC then converts the output to a pulsed DC over three lines that approximates a three phase source. It is by no means perfect sinusoidal wave like would be from a generator, nor is is as perfect as an inverter from a UPS, PV, or other similar systems would produce.

That said, the plasma cutter may not have a problem with what a VFD will produce for output, but I can almost assure you the VFD will not like the plasma cutter connected to it's output. You turn drive on and get it up to 60 Hz and 460-480 volts and then suddenly switch some load on - it will see that like a short circuit and will trip if you are lucky. If not luck will burn out components. It is designed for ramping a motor up from low voltage and low frequency, not suddenly throwing a load onto it's output.

Some of the drive experts can explain the technicalities much better then I can.

Thank you for the explanation.

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[Besoeker]

The VFD rectifies incoming AC to DC then converts the output to a pulsed DC over three lines that approximates a three phase source. It is by no means perfect sinusoidal wave like would be from a generator, nor is is as perfect as an inverter from a UPS, PV, or other similar systems would produce.

That said, the plasma cutter may not have a problem with what a VFD will produce for output, but I can almost assure you the VFD will not like the plasma cutter connected to it's output. You turn drive on and get it up to 60 Hz and 460-480 volts and then suddenly switch some load on - it will see that like a short circuit and will trip if you are lucky. If not luck will burn out components. It is designed for ramping a motor up from low voltage and low frequency, not suddenly throwing a load onto it's output.

Some of the drive experts can explain the technicalities much better then I can.

I think you explained it very well indeed. The pulsed output voltage in fairly sinusoidal current as a result of the motor inductance. I have no idea what a plasma cutter would do with it. But I'm pretty sure it is not a VFD application.

 

[winnie]

I agree that a vfd is not the way to go; I was trying to focus on the calculation that the OP was asking about.

As an aside, does anyone make a 240V input 480V output rotary phase converter? I know that the typical approach is RPC plus step up transformer, but if you have a dual voltage motor and feed 240V to one half of a phase, you should be able to combine the voltage boost and synthesizing the third leg...

-Jon

 

[kwired]

Is plasma cutter capable of being connected to single phase supply? From electrical perspective it is mostly just a rectifier, might have reduced capacity with only single phase input though. Seems pointless to do all this conversion when it ultimately will get converted to DC at the end of the entire process - probably would cost less to just purchase a plasma cutter designed to run on 240 volts single phase with the kVA rating you need.

 

[Besoeker]

Is plasma cutter capable of being connected to single phase supply? From electrical perspective it is mostly just a rectifier, might have reduced capacity with only single phase input though.

For three phase each diode conducts for a third of a period. With single phase it is half the time.

Seems pointless to do all this conversion when it ultimately will get converted to DC at the end of the entire process - probably would cost less to just purchase a plasma cutter designed to run on 240 volts single phase with the kVA rating you need.

I'm inclined to agree.