50hz motor run in 60hz environment

[alliedcp]

I have a problem that I hope someone can help me with quickly.

We are using a 100 hp 380v/3ph/50hz motor in a pedestal boom that we produce. We need to test this boom/motor combination in house. How can we test this assembly in house where we have 460/3/60hz supply. We need to simulate end user conditions (380/3/50hz). How can we do this? This is a direct drive situation which is powering the hydraulic circuit of the boom.

Ken

 

[acmotorengineer]

From a motor standpoint, 60HZ, 460Volts is magnetically equivalent to 50HZ, 380. In fact has the same amps at the same torque - i.e 125HP at 60HZ.

The problem you may have is: can the driven equipment can be safely run at 60HZ speed. You can estimate this load by multiplying measured load current at 460 Volts by 1.25.

You may run at high overload, up to breakdown, for short periods. If you need determine the time period, place a thermocouple on the windings and measure the temperature. To be safe, shut down at 105 degreeC total. If you can't access the winding, place the tc on the iron core and drop the same temp to 95 degreeC.

 

[ischgl99]

Use a VFD. This can easily be done, just program the VFD with the motor nameplate parameters and set the output speed to 50 hz. Your local vendor would be able to help you select whick one is best for your application. Will you be doing this often or is it a one time deal? If it's a one time deal, it may be cheaper to rent a generator set up for your voltage/frequency. The last company I worked for did it both ways on their test stand. Mike Bensema

http://www.dutchmenservices.com

 

[d23]

alliedcp

You may consider renting a generator set if you just need a short term test.
I don’t know the area you’re in, but I did a MSN search for:

“caterpillar generator rentals”

and had a list all over the USA.

David

 

[alliedcp]

mbensema, d23, acmotorengineer,

Thanks for your responses.

I will be looking into the potential of purchasing a VFD but with the economy the way it is we will probably rent a generator to help us for now. This situation appears about once every year or two so I don't know if I can justify the purchase of a VFD but I will try.

Thanks again for the responses.

Ken

 

[alliedcp]

I have a question concerning VFD's. When I set the output frequency (50hz) will the output voltage be reduced to 380V as well or is that a programmable function?

I really don't know much if anything about VFD's but I am trying to learn as much as I can, as fast as I can.

Thanks

Ken

 

[DanDel]

A VFD provides a Volts/Hertz ratio, insofar as a reduction in Hz for speed will also provide a corresponding reduction in voltage. Sometimes the parameters are programmable, and you should always check with the manufacturer before perchase, but for 460V 60Hz, a decrease to 50Hz will decrease the voltage by the same ratio, i.e. 383V.
The other option is a motor/generator set; 460V 60Hz motor, and a 380V 50Hz generator.

 

[ischgl99]

Ken, the generator sounds like it would be the better choice if only needed once a year.

For programming of the VFD, you would enter the motor parameters of 380v 50 hz, motor speed, FLC, etc. and then the VFD will adjust the voltage and frequency in the proper ratio. So when running at 50 hz, it will output 380 v. If you had a different motor that runs on a different voltage at that frequency, or another frequency, you can program it to run that way too. The VFD is very flexible that way.

If you ran into problems with your machine and wanted to run the motor slower to test something, you could easily do that with the VFD. Once it's programmed, you could adjust the running speed anywhere from the minimum to maximum speeds the motor or pump could safely run at. The VFD will then adjust the voltage and frequency to maintain the ratio that was programmed in from the nameplate settings.

Feel free to let me know if you have any more questions.

Mike Bensema

http://www.dutchmenservices.com

 

[busbar]

"I really don't know much if anything about {...} but I am trying to learn as much as I can, as fast as I can."

Aren't we all? Please be very careful about using the web as a sole resource for one’s understanding.

 

[Lewish]

Excuse me, but let me drop a note of caution in here. If the motor windings are not Inverter Duty rated, you may kill the motor using a VFD. The instantaneous voltage across the motor will be a minimum of 1.414 times higher than the motor nameplate voltage. This may arc-over the winding insulation.

Just $0.02 worth on the side of caution.

 

[jbartos]

Suggestion: Initial rentals and experimentations would be better than to purchase a VFD or generator and experience problems or find out late that one or the other solution was better and associated hardware should have been purchased.

 

[acmotorengineer]

Lewish has an excellent point. even if you do not plan to use a VFD, you should use or specify inverter grade wire in your motor. application trend is to increased usage of electronically controlled motors.

 

[UKpete]

Note that the VFD (and to a certain extent the generator option, depending on its rating) will give a relatively soft start compared to a somewhat harsher direct-on-line start that your end user will be applying. I don't know if this matters, just covering bases.

 

[d23]

All:

One more question about a VSD.

Assume the VSD is running at 50 hertz and 0 load then you hit it with a D-O-L starter and 100 HP motor connected. Would you expect the inverter to survive this type abuse for very many starts?

I would think the drive would not be very happy in this type operation. Would there be any expected problems doing this?

David

 

[ischgl99]

The VFD will not last long, maybe only once, if you use a starter on the output of the VFD. All the VFD manuals I have state to never switch the load when the VFD is running, it can't handle the sudden load. It should be connected directly to the motor and use the VFD to ramp up the motor. Mike Bensema

http://www.dutchmenservices.com

 

[d23]

Mike:

I may have read more into the original question than was there. What I see implies that they want to test the electrical and/or possible hydraulic operation of the boom and controls. I would think that this would include a test for a motor starter of some type to operate the 100 HP motor.

Maybe I don’t understand the test, but that is why I was confused about all the VFD answers. It would seem that a gen set is the only real choice.

David

 

[jbartos]

Suggestion: A lot depends on the VFD engineering and design. E.g. if a Navy ship needs a sudden speed reversal of a propulsion motor driven via VFD, then the VFD has to be engineered and designed for such motor direction of speed reversals.

 

[d23]

jbartos

I'm not trying to ask stupid quistions. I just don't know.

Most drives have a reverse on the fly option. Reverse on the fly ramps down then back up.

Does reverse on the fly mean that you can close a D-O-L starter on the output of a not loaded VSD?

David

 

[electricpete]

I don't think so. The reverse on the fly would be controlled so slip remains low and current remains low. DOL start on output of drive would give unacceptable high currents.

 

[d23]

electricpete

Once again I apoligize, but I don't understand. Does this mean that some drives can take a D-O-L start on the secondary?

David