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

 

[ischgl99]

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

http://www.dutchmenservices.com

 

[jbartos]

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.

 

[jbartos]

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.

 

[pekan]

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.

 

[electricpete]

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?

 

[peebee]

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.

 

[bmodrow]

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.

 

[peebee]

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?

 

[ischgl99]

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

http://www.dutchmenservices.com

 

[jbartos]

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.