60Hz motor at 50Hz

Guys,
I have a 460V 60Hz drive and would like to operate it in Australia at 415v and 50Hz. Is this OK? what problems should I consider?

Regards
Steve D

My understanding is that you are using the motor alone, NO VFD. You will have less efficiency, probably less hp, lower rpm, probably run hotter.

If you plan to use a VFD, one US brand will not work on 50.

Can you supply more info?

regards.....casey

Thanks

Thanks Casey, most helpfull. I may use a VSD yet but that will give me my 60Hz but still only 415v so I will still be under torqued. I will look deeper into it. Thanks again

In the early days of my apprenticeship I spent many hours, days, weeks re-winding 60 hZ motors in Sydney as they kept burning out. The company used to re-calculate the windings an re-wind the motors to work properly on 415V 50hZ.

Considering modern motors have far less "fat" and far smaller tolerances I would suggest you contact a reliable motor winding firm to re0wind the motor, or, probably cheaper, buy a new motor.

As I understand, if you use good VFD, then you can define exact motor parameters (Hz, V, A, etc).
Then I cannot see any problem.

A couple of items of clarification. First, while VFD's can do many things, the one thing they cannot do is make voltage. So, if the input is 415VAC, the output will not exceed that voltage either. There are a few inverters out there that will double 120VAC to 240VAC but that is for micro-drives and not what is being discussed here.

In a 415V 50Hz environment, a 460V 60Hz motor will be just fine as long as you don't expect it to produce nameplate horsepower. The limit on horsepower will be nameplate times 415 divided by 460. Or, another way of looking at it is to expect the same torque from the motor but at the lower speed.

If you hold to the constant torque rule, you should not have overheating problems with the motor since it is common practice to expect constant torque from 60Hz motors down to 1/3 and sometimes 1/4 base speed when operating on an inverter.

If you should decide to use an inverter, you will need to choose one that is rated for 415V 50Hz input. Then, set the motor nameplate parameters exactly as the nameplate reads including 460V for the voltage. This will give the proper volts per Hz ratio up to 415V where the voltage will then go flat. The motor will enter the field weakened range at that speed and continue on up to whatever maximum speed is programmed, reducing its available torque by the inverse of the overspeed.

Off topic (a little) for DickDV

Dumb questions:

1) Dick, do the 120 in 240 out VFDs really change the voltage, or are they really just reversing polarity relative to ground/neutral when they convert the DC? In other words, are they just creating 120 VAC twice relative to ground/neutral but 240 line to line?

2) Several VFD suppliers have cautioned me against trying to use a step-up transformer on the load side of a VFD to get to 4160 VAC on a low hp application. Others say they see no problem with doing this. What is the concern about transformers on the load side of a VFD?

Tom, where are the dumb questions?

Anyway, the 120V input drives I've seen use a simple voltage doubler circuit to build the DC bus--thus 340VDC instead of 170VDC.

That allows the inverter section to create 230VAC three phase.

Transformers in the motor leads always have severe problems due first to the high frequency pulses and associated harmonics causing excess heat. In addition, a transformer has trouble working properly as the frequency falls below its design frequency. As a result, the motor will have virtually no starting torque and poor speed regulation at low speeds. Even placing sine filters in front of a transformer results in low frequency problems even tho it does take care of the harmonics issues quite well.

Basically not a good idea although it has been done to get higher voltages for MV motors. Just barely ok for fans and centrifugal pumps. Not acceptable for most anything else.

I'll add one caveat to DickDV's post:

Voltage source inverters cannot make more voltage.

Current source inverters can (and some do) make more voltage.

The difference is that the current source's DC link active component is a reactor, causing current to continue to flow (increasing motor/output voltage) even when the input source voltage level has been exceeded.

Of course, no one really uses current source inverters any more, but the process and the physics do allow for a greater output voltage than the input voltage. This was more common 20 years ago, before computer-controlled voltage source drives.

The main thing on motors is not to exceed the nameplate volts to hertz ratio. Since the motor in question is 460V at 60 Hz, your V/Hz ratio is about 7.65. At 50 Hz, you should be running at about 385V to maintain the proper rotor currents. With the additional 10% rotor current (ballpark figures, again), you'll get about 20% more rotor heating, and can damage the rotor.

I'd say to knock down the voltage with some taps if possible to do what you want to do, or be prepared to buy another motor if the motor won't handle the additional load.

just a thought

I was always under the impression a motor would operate 10% over or under the rated voltage? Now if this is true 460 * .9 = 414 volts. Now this motor was designed to have 7.67 volts/hz on 460 volts at 60 hz. So if you have 415 volts at 50 hz and an AC drive. It looks like you could take
415 / 7.67 = 54 hz. In the drive 415 would be your max volts and Max hz would be 54.
So now your not going to over saturate anything because you won`t see 415 volts to the motor until you reach 54 hz. Would you not have full Hp and Torque out of this motor. I`m not saying this will work I`m just wondering why it wouldn`t. Any thoughts?

Motors typically are designed a little voltage starved. As is common in North America, 460V motors actually live better at 480 or 490V.

If we were to take 490Vac and divide by 60Hz we would get a ratio of 8.17. If you apply that to 50Hz you get 408V. I would say that 415V is close enough. Of course, as Thomas Cullens points out, you could take advantage of the extra voltage and set the drive parameters to a true 7.67 by entering 415V and base speed of 54 Hz.

The torque characteristic would be flat to 54Hz and then drop off from field weakening. You will never see full horsepower. The best that could be expected would be 90% if you set up for 415V at 54Hz (54/60).

If you set up the drive for 380V at 50Hz, then the maximum horsepower available would be 84% of nameplate (50/60).

Just to add a spanner to the works I have been under the impression that the the voltage supplies in OZ are actually 400V/230V and not 415V/240V that is commonly believed.
Can anyone confirm this?

Gunner

The nominal voltages in Oz are 240/415V. However, I have seen voltages, particularly in Western Australia, Queensland and all country areas as high as 258/260V single phase. Have also seen it a lot lower.

I normally set generators at 420V.

If you need any further info, please ask.

400/230V is, I believe, European and is supposed to happen in Ozz. Do not believe it. They would have to replace a lot of trannies and reset the tapping switch on a lot of others. Have not got the money to upgrade subs now let alone go into that nonsense.

Bob,

I must agree with your experience that running the motor as originally stated will cause it to burn out more often than not.

I suggest one NOT rely on anything beyond the nameplate ratings in the design of a system. If one tries to get "something for nothing" by reusing a motor at a different frequency/speed, then one should be careful that all other nameplate ratings be considered.

In this case, the V/Hz ratio is also being exceeded. I stand by my warning that running a motor designed for 460V/60Hz at 415V/50Hz will over-current the rotor and may cause a failure. You are likely to also get less air flow, assuming a shaft-mounted fan, as well as the increased rotor current/heat.

If you do this anyway, keep a fire extinguisher handy, and make sure your overloads are sized appropriately.

Don

Having re-read SteveD's original post, I have a question:

Do you want to operate a 60Hz nameplate MOTOR on 50Hz or do you have a 60Hz nameplate DRIVE that you want to operate at 50Hz/415V?

Your title says one thing (motor), but your post says another (drive).

If you have a motor you want to derate without the drive, I reiterate my previous posts.

If you have a drive you want to derate, then your only problem will be too little DC link voltage, as the 50/60 Hz should have little to no effect on your rectifier. You can run a standard 50Hz motor on the starved current with just parameter changes.

If you have a 60Hz motor as well, you can overcome the starved DC link with a decent transformer and some tap changing, and proper drive parameters. Without the ability to change the input voltage level, then DickDV's posts apply to changing the output to accommodate the motor requirements.

Please clarify.