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50hz motor run in 60hz environment

50hz motor run in 60hz environment

50hz motor run in 60hz environment

(OP)
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

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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
www.dutchmenservices.com

RE: 50hz motor run in 60hz environment

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

RE: 50hz motor run in 60hz environment

(OP)
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

RE: 50hz motor run in 60hz environment

(OP)
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

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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
www.dutchmenservices.com

RE: 50hz motor run in 60hz environment


"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.
  

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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

RE: 50hz motor run in 60hz environment

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
www.dutchmenservices.com

RE: 50hz motor run in 60hz environment

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

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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

RE: 50hz motor run in 60hz environment

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.

RE: 50hz motor run in 60hz environment

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

RE: 50hz motor run in 60hz environment

I recommended the VFD since I thought from the original post that he would be testing the motor only, if he wants to run it through the control panel with the starter then he should look at a generator.
I have not come across any drives that can reliably run a motor starter on the output, but there certainly could be some if one was willing to pay the premium.  I had a paper on the problems associated with that and can't find it now, but the reason for not using a starter on the output is the sudden current inrush to the motor overloads the IGBTs and they fry.  If you specified components that could handle the inrush, then it should be possible to do as jbartos mentioned, but for people with budgets lower then the Navy, it's probably not practical and why you don't see them.  

Mike Bensema
www.dutchmenservices.com

RE: 50hz motor run in 60hz environment

Suggestion: The Navy also rotates the propeller blades to achieve the reverse speed.
What about all those motors that are of a plugging type? These would not be suitable for VFDs or a special VFD would have to be developed.

RE: 50hz motor run in 60hz environment

Suggestion: Visit
http://www.control.com/1026161072/index_html
for more info.
The VFD can have current regulators on its output that prevent the switching devices from being damaged.

RE: 50hz motor run in 60hz environment

I hate to be the one with the simple answer but, run the hydraulic pump @ 460/60. I work for an OEM and we regularly test our europe bound equipment at 460/60. We are running vacuum pumps, hydraulic pumps, molecular pumps.
Maybe I am missing something, but it works for us.

RE: 50hz motor run in 60hz environment

I I were a customer I would certainly prefer my equipment to be tested at it's intended speed. Just because it works at some higher speed, we still don't know:
#1 - Will the mechanical load work properly at higher speed.
#2 - Is there a speed-dependent resonance at the lower speed which doesn't show up testing at higher speed? How do we know that equipment will meet vib limits at the lower speed if we haven't tested it?

RE: 50hz motor run in 60hz environment

My $0.02:

The VFD & generator ideas both sound good to me.  Another idea:  motor-generator set or other power converter.

My understanding is VFD's generally work as current sources, so they should generally never have their output open-circuited.  I could be wrong, but I'd definitely check with the manufacturer before you tried to put a downstream starter.  I've seen various installations where downstream safety switches are interlocked with the VFD to prevent open circuiting.

Whatever solution you come up with, be aware that you need to account not only for full-load current, but also starting current of your motor.  This can imply substandtial derating of your generator/VFD/converter/etc; that is, you might need a 200hp/kW/kVA-rated source (or bigger) to properly start your motor.


RE: 50hz motor run in 60hz environment

As stated by acmotorengineer the motor is magnetically identical at 460/60HZ.  The cheapest and easiest soultion is to hook directly to your 460 3-phase and test the motor. Is the piece of equipment you are manufacturing being used in the US or Europe? or was a cheaper solution to the manufactuering procees found in procuring a european motor?

Bottom line is that it will function flawlessly at 460 in your application.

RE: 50hz motor run in 60hz environment

bmodrow, that doesn't sound right to me.

If he drives his hydraulics at 60Hz, the bhp will increase, possibly to the point of overloading the motor.  Yes, if the motor works at 60Hz, it should work at 50Hz.  But this could be overconservative:  the motor could fail at 60Hz but still work at 50Hz.

Am I missing something here?

RE: 50hz motor run in 60hz environment

I agree with electricpete and peebee, a system should always be tested at it's rated speed, that is the point of checking the system.  Running the system at 60 hz instead of 50 will not duplicate the operation of the system and could create problems or hide them.  As a customer, I would require my system be checked as it will be used.

Running hydraulics or an oil pump at a higher speed will pump more through the system.  Take an oil pumping unit supplying oil to the machines bearings.  At 60 hz you are pumping 20% more and can easily hide an overheating bearing or a design problem that does not supply enough oil at the rated speed.  It's cheaper to find a problem on the test stand then it is at the customers site.

Mike Bensema
www.dutchmenservices.com

RE: 50hz motor run in 60hz environment

Suggestion: One can see more and more of equipment that has a dual rating, namely for 50Hz and 60Hz. In that case, all testing tasks for 50Hz or 60Hz go away. However, the bearings would have to be taken into consideration for the flow range caused by the frequency range from 50Hz to 60Hz.

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