230Volts vs 460 Volts

I have a system that has 4 takeaway conveyors.Each one feeds the next. The first three motors are 460 running at 60 hertz. The last one is 230 running at 110 hertz. I am trying to understand why the last one would run at 230. The answers i have gotten to this point do not make a lot of sense. I am asking for enlightenment.

thecannonhouse,

Assumptions:

It is a dual-voltage motor wired as 230v, correct?

It is wired to a drive served by 480v, correct?


In that case, what you may have is a system where the drive has been programmed with a custom v/Hz curve, set to put out 230v at 60Hz, and 480v at 120Hz. This effectively gives you (up to) twice the motor speed with no fall-of in torque. Since you said that the motor is set to run at 110Hz, this setup is logical, since you can overspeed the motor without torque reduction. Understand though, that the motor must be mechanically capable of this higher speed (bearings, balance, fan, etc...), and that the motor's insulation must be rated for inverter use at 480v.

Hopefully, DickDV can chime in here if I've missed anything.

Those connections can be very confusing for those not used to them, and has caused issues when motors are replaced without carefully noting the wiring.


-rpoet

The last conveyor was probably fitted later than the first three.
It was possibly ordered with a 230 volt motor or perhaps a dual voltage 460/230 motor.
The main problem was that the conveyor speed was incorrectly specified as being
Approximately half what it should be. When the conveyor was fitted the problem was realised and the easy solution was to fit a variable speed drive to up the conveyor speed.
A 230volt drive is considerably less expensive than a 460 volt unit, so this option was chosen, for pure economic reasons.

You've got it right, rpoet. The basic principle to remember with three phase induction motors is that the motor develops torque based upon the volts/hz ratio while its speed is determined by hz only.

Theoretically, you could keep running the voltage up without limit as long as you keep increasing the hz to keep the ratio constant. If that were possible, the motor would continue to increase its output hp without limit as the voltage and hz go up without limit.

Of course, there is a limit. It is the design voltage limit of the insulation system.

So, you can take a dual voltage motor, say 230/460V and size the 460V drive for the 230V current. Then you set the motor data in the drive as if the motor were a 460V 120hz motor and you wire the motor as a 230V 60hz motor. You will get constant torque up to 120hz which is twice the nameplate hp.

The statement in one of above posts about a 230V drive being cheaper is only true at the same hp. Since you need 460V at the 230V current, the drive hp is doubled too.

Sorry, no free ride. Not even with modern technology!

Thank you, Dick,
I learned that trick from other posts of yours over that past few years. It's nice to be able to pass on a little of that knowledge to someone else.


-rpoet

DickDV

If you do this setup does the torque increase as you go up on voltage and hz or does it just not fall off as it normally would when you overspeed?

Is this a new technique? I am just laernig some about drives and I found this very interesting.

Thank You.

Tim, as I pointed out earlier, if you hold the volts/hz ratio constant, you will have constant torque available from the motor. And, that is true at any allowable voltage and any allowable hz.

As to being new, it was new to me several years ago but I learned it from the Europeans who have been doing this for many years. Of course, they do it by changing a motor from delta (low voltage) to wye or star (high voltage rather than by being dual coil windings as with NEMA motors. As a result, our ratio between the two voltages is 2/1 where the Europeans ratio is the square root of three or 1.73. (As in 230/400 and 400/690)

rpoet, I'm 66 years old and have a lot of experience collected over the 24 years I've been doing motor control work. It pleases me greatly to be able to help someone else, especially young people, to understand the principles involved in my work. For this same reason, I became a certified instructor for NTT (National Technology Transfer) in Denver. They put on three day technical seminars around the US and it is a delight to teach these classes. I am certified to teach their VFD/DC drive class, their motors class, and their non-plc discreet component ladder logic troubleshooting class.

Thank you for your responses. It is has been helpful. The drive is a powerflex 40 drive.It is fed by 460. The nameplate voltage is set to 230 on the drive.Will the power out of the drive to the motor to be 460V? Im asking becasue if the voltage out is 230 three phase wouldnt i want the wires to be black,red blue vs brown,orange,yellow. Thanks again for your information.

It is has been helpful. The drive is a powerflex 40 drive. The nameplate voltage is set to 230 on the drive. Will the power out of the drive to the motor to be 460V?

Click to expand...

If the setup is as expected, then the power out at 110 Hz would be approximately 422 volts. At 60 Hz it would be 230 volts.

I have seen this method used on a lot of European equipment with small motors and a worm gear box. It looks to me like they are using a VFD to run the motor at higher speed but keeping the torque constant, and thus getting more power out of the motor than is listed on the nameplate. The gearbox then is a higher ratio to compensate. Below is a link from Siemens describing this method.

https://support.automation.siemens....lib.csinfo&lang=en&objid=21139232&caller=view

DickDV said:

For this same reason, I became a certified instructor for NTT (National Technology Transfer) in Denver. They put on three day technical seminars around the US and it is a delight to teach these classes. I am certified to teach their VFD/DC drive class, their motors class, and their non-plc discreet component ladder logic troubleshooting class.

Click to expand...

Not to hijack this thread, but:
Dick, where and when do you teach your class on VFD/DC drives? I think I could learn a lot from your class.

-rpoet

Check the NTT website for the public seminar schedule. It's usually published about 6 monthes in advance. We also do onsite seminars where we bring all the training materials into a facility and conduct a private class for a single customer. There is no schedule for these private classes.