[subcooledheatpump]

6 phase almost sounds like it would do more harm than good. The same stator would be sharing twice as many currents and twice as many magnetic field lines/flux. Plus the inverters semiconductor count would double. As was said before, pricey and difficult

Bigger motor=more constant torque. Makes sense. More magnetizeable material. But really, anyone could figure that out. a Factory rated 100 HP motor for example is quite a size. whereas a 1 HP factory rated motor is quite small. I haven't actually measured anything apart from the current and voltage readings, but if they are true to what the motor is actually doing, I am able to get about 4X torque out of a 15 HP 6 pole motor. Of course as I said though, thats not dyno proven and could well be a false assumption. Works well in my van though.

[JimDanielson]

an update:

today the motor spun, nothing too exciting though. the curtis controller is still programmed for the ac50 and I am trying to mess with all the motor settings to get it to work better. wouldnt go over 15rpm

[leong]

as someone mentioned before, beyond 4 poles you will experience a lot worse on the power factor (reactive power) thus your controller rating needs to go may be doubled or tripled to deliver the same power. Usually induction machine for traction purpose is 4 pole or 6 pole at most.

[major]

Originally Posted by leong

as someone mentioned before, beyond 4 poles you will experience a lot worse on the power factor (reactive power) thus your controller rating needs to go may be doubled or tripled to deliver the same power. Usually induction machine for traction purpose is 4 pole or 6 pole at most.

Hi leo,

I think you exaggerate. I could see maybe 10 -20% higher rated, not 2 to 3 times. I recalled this study to support this http://www.reliance.com/pdf/motors/w...pers/B7100.pdf See figure #1. Have you a support citation?

Regards,

major

[leong]

Hi, major

I was referring to the 12 - 24 pole case. yes i have seen this whitepaper a while back. You might have noticed that the peak torque power factor is reducing at a faster pace when the pole pair number increases. The figure stops at 8 pole, for 24 pole, you may get well under 40%, comparing to 90% power factor, you need an inverter with over 2x KVA rating. From the machine efficiency point of view, higher pole count actually gets better machine efficiency, but from the system point of view, the efficiency saved on the machine would be shifted to the drive electronics due to higher KVA. I don't have a citation for the pole count vs. power factor. I did some numerical study a while back and reached the conclusion not to design an IM with more than 6 poles, then read the paper you mentioned as a verification.

Originally Posted by major

Hi leo,

I think you exaggerate. I could see maybe 10 -20% higher rated, not 2 to 3 times. I recalled this study to support this http://www.reliance.com/pdf/motors/w...pers/B7100.pdf See figure #1. Have you a support citation?

Regards,

major

[JimDanielson]

My power factor is about 72% at no load right now and improves at higher load. At 200 amps draw it goes up to 75%. These tests were done on my 24 pole motor prototype at 1500rpm on Curtis controller at 300hz.



I am still working on getting a test dyno set up for measuring torque at that speed.

I did get a 0 speed torque output of 40ftlbs. It is not too high but this motor is much smaller than any production version would be. And the amount of power I can put into the machine is low because the current on the controller is limited. If anyone knows of an affordable 1500amp controller, I would be interested to test with it.

[leong]

Jim, how did you measure the power factor? If you are running the machine with an inverter, the motor terminals would be driven by switching PWM voltages. You would need some sophisticated instrument to filter, compensate in order to measure the power directly going into the motor. If you are measuring the power factor going into the drive, that is totally different than the power factor on the motor. The drive itself may have a PFC stage and the power factor would approach unity.

Originally Posted by JimDanielson

My power factor is about 72% at no load right now and improves at higher load. At 200 amps draw it goes up to 75%. These tests were done on my 24 pole motor prototype at 1500rpm on Curtis controller at 300hz.



I am still working on getting a test dyno set up for measuring torque at that speed.

I did get a 0 speed torque output of 40ftlbs. It is not too high but this motor is much smaller than any production version would be. And the amount of power I can put into the machine is low because the current on the controller is limited. If anyone knows of an affordable 1500amp controller, I would be interested to test with it.

[JimDanielson]

Yes, I understand how to measure power factor... I measured on the motor. My oscilloscope can filter/average pwm signals.

The inverter is powered by a DC battery.

[leong]

did you filter both the voltage and current with the same settings? did you measure the line to line voltage and line to neutral current? is your motor Y connected? did you use VIsin(theta) formula to calculate power/reactive power?

Originally Posted by JimDanielson

Yes, I understand how to measure power factor... I measured on the motor. My oscilloscope can filter/average pwm signals.

The inverter is powered by a DC battery.

[PStechPaul]

It's really important to use a proper wattmeter (or simultaneous samplng A/D converters) if the voltage and current waveforms are at all distorted. I can believe the 72% PF at no load or light load but at full load I would think it would be much higher than 75%. I'm not sure how much this will affect efficiency. A low PF essentially means that the current will lag the applied voltage because of inductancebut the losses are mostly determined by the current. It may mean that a higher voltage is required for the same amount of power because of the phase angle, but I think the motor will still draw the same current for the same torque. Of course a motor with more poles will have more torque at slower speed for the same applied voltage and frequency. It would be good to see details of the meaurement and actual data and graphs,