Strange Ac Drive Wiring

[mordred]

OK I understand how this works thus far however I'm curious as to what
other side effects this trick has say on carrier frequency, Harmonics? motor life expectancy? etc not that I ever plan on using this procedure but its an excellent discussion on drive vs motor principals

 

[DickDV]

This is a fairly common trick in Europe and is only for use on dual voltage (for example, 230/460v) motors.

Essentially, you buy a higher voltage (460) drive with the ampacity to cover the motor's lower (230) volt FLA.

Since motor current and torque at a given load is a function of the volts per hertz ratio, you set up the drive for a constant ratio from 0 to 120Hz. That gives the motor the same potential torque output over the whole speed range to 120Hz.

Yes, that does result in twice the motor nameplate hp at 120Hz but remember that the cooling fan is turning twice as fast also. And, motor heating is much more related to current than to hp output.

The end result is a motor with a constant torque speed range up to double nameplate speed and, possibly, (heat and balance permitting) up to twice the nameplate hp.

Crafty, I must say, but you must be a bit carefully that you don't ruin the motor. There is very little in this world that comes for free and that includes the world of drives too!

 

[milldrone]

Dick,

Wouldn't there be iron losses also? Because the laminations are too thick for 120 hz. Which would lead to heating of the laminations

 

[DickDV]

If there are iron losses, they must not be significant. Running these motors and many inverter duty motors to 120hz is getting to be common practice.

Evidence for this is in the fact that these motors are labeled constant hp up to 120hz. You can see this in the specs for Marathon Black Max motors, for example.

 

[rsdoran]

The issue is running a motor wired 230 when at 120hz it will supply 460.

 

[DickDV]

Ron, you cannot do this to a motor labelled 230V only. It has to be a dual voltage motor, typically 190/380 or 230/460. That way the insulation is ok at the higher voltage.

 

[mordred]

Would the optimal duty of the motor for this application be the inverter duty motors? As the higher frequencies tends to breakdown the stator windings at a faster rate on most motors.

 

[plc noob]

Dick

i do not quite understand what to do about setting up the volts per hertz ratio . how do you set it up for this application max hertz at 120 and do a custom profile for voltage per hertz . how many volts per hertz should be applied in this setup

 

[kamenges]

The drives I have used simply take the motor nameplate voltage divided by the motor base frequency to determine the volts/hertz ratio. 460/120 is the same number as 230/60. However, many drives will automatically switch to constant horsepower operation (constant output voltage with increasing output frequency) once the base frequency is reached even if the drive has additional bus voltage headroom. So I think you want to make sure you enter 120 as the base frequency. You shouldn't need to mess with any kind of custom volts/hertz ratio to make thins happen.

Keith

 

[plc noob]

what is this type of setup called . what is the correct terminology for it

 

[milldrone]

what is this type of setup called . what is the correct terminology for it

If you ask the electrician that stumbles upon this and doesn't pay attention to the prints or any warning labels placed there for his benifit. He might say Oooopps! As he fans the smoke away from his face.

 

[plc noob]

im curious . do you mean if some one replaces the motor and wires it 480 vac ? what will happen ? will the drive not overload trip correctly on these settings ?

 

[allscott]

No, it won't. If it was running at 230V then the current setting on the drive would have been for the 230V setting on the drive which is twice what the 480V setting would be.

Also the motor would only be getting 230V @60HZ which would cause the current to go up and probably wreck your day.