VFd ~ 2 pole or 4 pole on a 2 speed motor?

I have a 2HP Jet mill with a two speed motor and a Hitachi SJ200-015NFU2 VFD.

Induction Motor Spec:

2HP
3Phase
2Pole~U2-V2-w2 4pole~U1-V1-W1
1700/3400 RPM

60 Hz 60 Hz
220 volt 220 volt
6.2 amp 5.6 amp


Input power:

Single Phase


First, which pole is the high speed of the motor?

Second, people have suggested to connect the VFD to the high speed on the motor, but wouldn't the motor loose torque at low speed operations compared to connecting the VFD to the low speed on the motor?

hunt3419,

The four pole connection is for 1800 (1750) operation while the two pole will get you 3600. I would think the lower speed connection would work better as the frequency drive has the ability to easily speed the motor up.

I ran my vertical mill on a static phase converter for years and never was shy of horsepower. I have a Woods drive on it now, run it at 1750 and use the smallest motor sheave with the largest spindle sheave and have all the speed range I need plus all the torque.

Stuart

It really doesn't matter much.

The motor will make the same amount of torque, and HP at the same RPMs wired either way. Common practice is to wire it for high speed, and use the VFD to adjust. You could wire it for 4 pole, and run it @ 120hz to get full speed, doesn't matter much. I'd wire it up for 2 poles, and just run it @ 60hz max.

4 pole

I wired it for 4 pole. It seems to need a few adjustments. The motor has a buzzin noise at all RPMs. I'll set it up using the two pole to see if it runs any better.

Thanks for the input guys,
Tracy

You state that the current draw is pretty much the same for both speeds - this indicates that it is a constant HP motor and it will have exactly half the torque when operating in 2-pole (3400) rpm mode.

Given this - the motor will perform better if you leave it in 4 pole (slow) mode and then overspeed to 120Hz to get the high speed operation.

Buzzing at all speeds of operation? Did you conduct an auto-tune for the current loop? It is normal for the motor to ring a little (it will emit a tone at the same frequency as whatever you set the switching frequency to). On a smallish motor like this - you should be able to run the switching frequency to 6kHz or 8kHz and knock the noise level down a little.

Correction - that's not *quite* accurate about torque, and a better recommendation...

JunkyardJ said:

The motor will make the same amount of torque, and HP at the same RPMs wired either way. Common practice is to wire it for high speed, and use the VFD to adjust. You could wire it for 4 pole, and run it @ 120hz to get full speed, doesn't matter much. I'd wire it up for 2 poles, and just run it @ 60hz max.

Click to expand...

[I know this is an 8-year old thread, but in case anyone finds it with a search, I wanted to correct and enhance the answer. It depends on where you want torque in the speed range:]

"Most AC Drives can have output frequencies of 120 Hz or greater. However, the output voltage is limited to the line voltage. A drive supplied by 220 volts cannot output more than 220 volts. Therefore, as frequency is increased above 60 Hz, the output voltage remains constant but the volts per hertz ratio decreases, resulting in a loss of torque, but only at the highest speeds.
So by using a 4 pole 1725/ 1800 rpm motor you keep full torque through the critical low speed range where the added power is needed most.
To compare this with a 2 pole 3600 rpm motor, you only have full torque close to the rated speed of 3600 rpm. As you decrease speed on a 2 pole motor, you also decrease the torque. So in the critical lower speeds you have the least amount of power and a greater chance of belt lag.
For this reason, we feel the full torque in the lower rpm range is the most important consideration and a 4 pole 1800 RPM motor is a win win given the options!" Source: Resources | Northridge Tool