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50/60 FAQ 4

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itsmoked

Electrical
Feb 18, 2005
19,114
Hello fellow members!

It was pointed out in the recent post [purple]"converting 60hz motor to 50hz"[/purple] that this question is the most frequent we see.

It is, as we all know, a fairly complex issue fraught with niggling lurking gotchas. Unfortunately we find ourselves having to work though the basics before we can even address those small often important details.

It was suggested someone produce a FAQ.

Tah Dah! I have done so. [orientalbow]

As soon as it is released I would appreciate you all taking a look at it so we can make sure everything you feel should be in it is covered and that what is covered is correct. I was told I once made a mistake.[cry]

Please keep in mind that it is written to cover the typical 'guy faced with a machine spec'ed for the "other" frequency', not all the finer details. If those questions come up, and they could more frequently now, then we can add to the FAQ (chapter 2) or create an additional one.

Stay tuned I'll put it up soon.

Keith Cress
Flamin Systems, Inc.-
 
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Hi Keith, My two cents worth.
Basically it's 50:60, or 60:50.
New voltage, = Old voltage x 6/5 or 6/5 as the case may be. +/- 10%
New speed, = Old speed x 6/5 or 6/5 as the case may be.
New horsepower, = Old horsepower x 6/5 or 6/5 as the case may be.
Usually the "Gotchas" don't "Getcha". 90% of the 'gotchas exist in the minds of those who have never actually done frequency conversions. This is not to deny the finer points usually raised but to point out that these points are usually of such a small magnitude as to have no noticeable effect.
Even the cooling issue is not an issue in 99+% of conversions.
The other common factor is wye to delta conversions and vice versa with NEC motors.

respectfully
 
Damn, you beat me to it, but you did a better job anyway. Well written.

I would have only added something about how the V/f ratio is the same for 460/60 as it is for 380/50 so that those using those voltages know that it's kind of a no brainer other than the other points you made. Sure anyone with a calculator can figure that out, but we are a lazy lot sometimes.

Eng-Tips: Help for your job, not for your homework Read faq731-376 [pirate]
 
Some of the folks that are asking this question are dealing with single phase motors. That adds another layer of complication (capacitors), but is it needed, for the scope of what is being attempted? Recently there have been a few good postings on this subject; they could be directed there, to resolve that issue.

BK
 
Here's the FAQ I mentioned.
faq237-1224


Thanks for the feedback waross and jraef!
I worked in your comments.


waross; I think you might revise your 90% number downward if you worked in refrigeration. [lol]

As others know, I often work with private rail cars. Refrigeration is the key technology that allows them to be habitable for use by people because they usually have acres of glass and huge insolation numbers(think Super Scenic-Cruiser dome cars with 180 degree glass roofs). The heat gains are so high that you cannot "air condition" them, you must actually "refrigerate" them. Most often they are supplied by under-slung generators. We have seen many, many, large very expensive compressors that have failed due to running them at lower frequencies. 59Hz is enough to toast them with almost a guaranteed result.

I agree some guy with a lathe where the motor essentially runs unloaded or with a 10% load duty cycle could probably get away with murder with respect to 50:60 stuff. Likewise fan people and to some extent centrifugal pump users and probably any other low duty cycle loaded motors; chippers, some conveyors, saws, drills, etc. etc. I think 100% loaded applications like refrigeration, plant air compressors, positive displacement pumps, vertical conveyors, etc, need careful consideration of the possible problems of frequency changes.

It mostly comes down to those pesky loads and what they be. Which is what I hope posters will now be able to focus more on.

As an engineer with a question about a frequency shift I want to know the general hazards to my equipment as apposed to a "it will probably work fine".

Thanks and respectfully:

Keith Cress
Flamin Systems, Inc.-
 
Hi bklauba;

The centrifugal switch part is in the FAQ.

I would welcome any specific suggestions about Cap start/run single phase 50:60 motor concerns. I don't understand the capacitor ramifications enough at this point to say anything about it.[reading]

Anybody care to jump in on this subject?

Keith Cress
Flamin Systems, Inc.-
 
Hi itsmoked
Re the capacitors, at lower frequency, the inductive current will be more (20%?) and the capacitive current will be less (20%?). You may have to add some capacity going to 50 Hz. For most applications probably not. And I am thinking about the -20/+80% tolerances you mentioned for capacitors. If in doubt, add 40% more capacitance.
Going to 60 Hz. Don't worry unless you have a machine that may be damaged by extra starting torque. If you have high starting current try reducing the capacitor.
I'd be inclined to get the voltage right and try it. If it is a demanding application that is having problems starting then I would add some capacity. (50 Hz.)
60 Hz. I wouldn't worry.
I had a couple of very large sliding doors 8 or 9 years ago.
The owner bought heavy duty industrial operators with the smaller motors. The motors couldn't start the doors moving. I doubled the capacitance on each one and they have been working for years. We had a capacitor failure a few years ago The capacitor was replaced with the same size and it's been running ever since.
Any other comments?
 
One minor point, maybe too esoteric for all but the real motor geeks, but the need for a constant V/Hz actually applies at the air gap, not at the terminals. Voltage drop across the stator resistance can become significant as frequency and voltage drop, maybe not enough to worry about at 50Hz on a 60Hz motor, but the terminal voltage can be somewhat above 5/6 the 60Hz terminal voltage.
 
Hi waross;
I am trying to sum up your capacitor comments into something.. short and sweet for our FAQ.

To wit:
############### Proposed addition to FAQ #############
Some single phase motors have start or run capacitors and some both. If the motor is being shifted from 50 to 60Hz then their effect will increase. This will usually pose no problem.

Alternatively taking a motor from 60 to 50Hz will reduce the capacitor effects. This will result in possibly lower running and starting torques. This may mean the motor cannot successfully start its load or maintain running a load.

A failure to start may result in a rapid burnout(seconds) so this should be carefully monitored initially. Larger capacitors or additional ones may be needed.
########################################################

davidbeach; Interesting. Would this be a second or third order effect as apposed to a first order one?

Thanks.

Keith Cress
Flamin Systems, Inc.-
 
Probably at least a second order; it really begins to show below about 40Hz on a 60Hz machine.
 
In my understanding, the effect David is describing is the reason for the voltage boost function present on most simple drives. The boost of stator terminal voltage as frequency drops is intended to maintain constant airgap flux.

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I don't suffer from insanity. I enjoy it...
 
Thank you davidbeach
I like your addition to the faq, itsmoked.
respectfully
 
Dear Fellows,

Take care with the new European 50 Hz Six Leads motors designed at 400 (Wye) /230 (Delta) because they work proper in America only at 480 Volts not at 230 Volts.

The only way this motors work proper at Both voltages in America is 480 Volts(Delta) and 230 volts (Two Wyes).So you Need 12 leads.

Regards

Petronila
 
Hello Keith

Thank you for a very well written FAQ I did attempt sending you a message using the Send a comment to itsmoked About This FAQ feature which may not have gone through.

I have a question about the paragraph on single phase complications in the last sentence you state "Likewise a 50Hz motor placed into 60Hz service may switch off the start winding at too low a speed for the motor to make the transition to running."

It is my understanding this motor will run 20% faster and a centrifugal switch is designed to open and deenergize the start winding at rated speed, How is it the start winding can be switched off at too low a speed? [ponder]

Thanks, Chuck
 
A 50 Hz. (1450 RPM) motor may have the switch operating at 1000 RPM. On 60 Hz. the motor may not have enough torque to pull up to running speed.
Please note, I picked a figure to illustrate Keiths point. I have no idea what the operating speed may actually be or if it will make a difference. I have done several conversions, both ways, but only on three phase motors.
respectfully
 
Hello waross

Under this condition the motor would for sure turn into toast quickly, Most motors I use are designed for 50/60 Hz operation.

Thanks, Chuck
 
Hi machmech.

Yes failure to start can burn them up shockingly fast.

To essentially repeat waross's fine response:

The C. switch is going to operate at its design speed. For an example on a 50Hz 1425RPM motor the switch might open at say, 1200RPM (84% of full speed) because the motor has reached a point where it can sustain accelerating the load up to its rated RPM.

Moving the motor to 60Hz service means the motor will now be trying to achieve 1725RPM but remember the switch is still going to open at 1200RPM or only 69% of rated speed. This may be too slow for the motor to transition.

Yes a 50/60 motor will be designed correctly so that this is not problem but a strictly 50Hz designed motor 'could' have a problem.

Keith Cress
Flamin Systems, Inc.- <
 
Hello Keith
[medal]

Thanks, I am now crystal clear and understand completely.
Soon we are getting a machine made in Germany from Poland,
this knowledge will help.

Sincerely, Chuck
 
Hi machmech.

That's great! I love it when someone can say that about something we've been working to illuminate.

Good luck with your machines.

Keith Cress
Flamin Systems, Inc.- <
 
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