Author Topic: what happens when you run a 50Hz 3 phase motor at 60Hz  (Read 12738 times)

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Offline Simon

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what happens when you run a 50Hz 3 phase motor at 60Hz
« on: June 12, 2014, 02:06:19 pm »
If you have a motor with certain ratings for 50 HZ, what will happen when the same motor is run at 60Hz ? will it draw proportionately more power ? or will it have the same power but go faster (less torque) ?
 

Offline retrolefty

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #1 on: June 12, 2014, 02:22:10 pm »
Assuming a standard 3 phase induction motor, it will fun faster.

http://en.wikipedia.org/wiki/Induction_motor

 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #2 on: June 12, 2014, 02:31:30 pm »
yes i know but what about the power draw or power provided ?
 

Offline jlmoon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #3 on: June 12, 2014, 02:45:21 pm »
sounds like a EE motors & generators class test question.
Recharged Volt-Nut
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #4 on: June 12, 2014, 02:47:02 pm »
Well it's not, it's called I have a collegue who vhas a customer that is trying to use a motor at 60Hz that was originally speced for 50Hz
 

Offline vk6zgo

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #5 on: June 12, 2014, 02:58:08 pm »
Not sure,but I would be inclined to think it would be OK.
The other way round definitely causes problems.
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #6 on: June 12, 2014, 02:59:42 pm »
Well talking to my colleague it turns out it may actually be around the other way, it's a 60Hz motor run on 50Hz. What I'm wondering is what happens about the power etc because he is trying to drive a fan and it's not getting there.
 

Offline johansen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #7 on: June 12, 2014, 03:28:20 pm »
its not getting there?

then that means you need to cut the fan blades down.

running a 50hz pump or fan has a cubic power curve, so you're looking at 1.73 times more power required for 60hz.

50hz 200vac is electrically the same as 60hz 240vac, so the motor will deliver 20% more power at about the same temperature rise.
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #8 on: June 12, 2014, 03:30:57 pm »
so trying to run the 60Hz motor at 50Hz means it has less power, i need to have a chat with him, find out exactly what is going on.
 

Offline oldway

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #9 on: June 12, 2014, 04:33:58 pm »
Running a 60Hz motor on 50Hz need you to reduce the voltage at 5/6 x nominal voltage of the motor.
It will run at lower rpm (5/6 of nominal rpm at 60Hz).
 

Offline G7PSK

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #10 on: June 12, 2014, 05:30:44 pm »
If you run a 60HZ motor on 50HZ the windings will burn out, I know this from first hand experience. Some years ago I wanted to use the wast heat from a gen/set to heat my workshop and I came across a ships ventilator fan with motor rated at 440 volts 60HZ I thought that this would do so I connected it up to 415 volts 50hz and it ran for a time got very hot and then the smoke arose. The motor with fan was a brand new unused unit that I got at a military auction along with a whole lot of other motors.
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #11 on: June 12, 2014, 05:32:46 pm »
would the wattage of the motor make any difference ? we are talking about 4KW and many motors are made to work on both now.
 

Online IanB

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #12 on: June 12, 2014, 05:39:06 pm »
would the wattage of the motor make any difference ? we are talking about 4KW and many motors are made to work on both now.

It depends on the motor. Universal motors may not care so much, but induction motors are designed for a specific voltage and frequency. They will also run at a speed proportional to the frequency, so that 3600 rpm at 60 Hz will become 3000 rpm at 50 Hz.

In general, don't try to run an induction motor on a different supply than the rating plate says.
I'm not an EE--what am I doing here?
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #13 on: June 12, 2014, 05:48:32 pm »
Well i think this is specified for both 50 and 60HZ it's 750 rpm @ 50HZ and 875 rpm at 60 HZ, I think the problem is coming from the fact that when they do run it at 60HZ they will get 20% more power but the fan will put 50-70% more load on the motor leaving them 30-50% under power.
 

Offline jahonen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #14 on: June 12, 2014, 05:51:12 pm »
OP does not mention which kind of motor it is but I'll guess that is an induction motor.

In general, induction motor requires constant V/Hz to maintain the rated torque. If frequency is increased above the nominal, and voltage remains the same, we are in so called field weakening region. IIRC, torque drops ~1/f^2 in the field weakening region. That means that even if the motor runs faster at 60 Hz than 50 Hz, torque will drop by factor of (50/60)^2 =~ 0.69. So there is only 70% of nominal torque available, if voltage remains the same.

If you run a 60HZ motor on 50HZ the windings will burn out, I know this from first hand experience. Some years ago I wanted to use the wast heat from a gen/set to heat my workshop and I came across a ships ventilator fan with motor rated at 440 volts 60HZ I thought that this would do so I connected it up to 415 volts 50hz and it ran for a time got very hot and then the smoke arose. The motor with fan was a brand new unused unit that I got at a military auction along with a whole lot of other motors.

That makes sense since 440/60 < 415/50, so motor had too high voltage relative to the frequency. Increasing the frequency is safer in that respect.

Regards,
Janne
« Last Edit: June 12, 2014, 05:53:09 pm by jahonen »
 

Offline johansen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #15 on: June 12, 2014, 09:35:40 pm »
most large motors should run at the lower frequency without burning out given a cubic power curve.
that said, most motors are very cheaply built.

an 8 pole motor is not the norm and usually those motors are properly designed.. for the simple fact that the shaft spins at a much lower velocity, and they can't throw a cheap fan on the back of the motor and pull 300 cfm through the case.

so if its 50/60 hz rated, that's fine. the problem is the higher frequency needs more voltage to push the same flux, and given the cubic power curve, you need 1.44 times as much torque to push 1.728 times as much power into the pump at 1.2 times the rpm.

so, that's why its not coming up to speed.
a short term work around is boost the voltage 20% and try again.
as long as the name plate amps are in range. (note that power dissapation is amps squared) the motor shouldn't burn out.
 

Offline fallwithstyle

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #16 on: June 12, 2014, 11:38:47 pm »
I work for a company that manufactures material handling equipment. 60 HZ motors must be de-rated for 50 HZ applications. We give our supplier the specs and they de-rate and re-nameplate standard 60 HZ motors.

Centrifugal fans are variable torque loads. The power required for you application will vary based upon blower speed and static pressure. Refer to page 8 of the following link. http://www.nyb.com/Catalog/Bulletins/231.pdf

Your blower manufacturer should be able to provide similar information.
 

Offline oldway

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #17 on: June 13, 2014, 05:12:38 am »
If you run a 60HZ motor on 50HZ the windings will burn out, I know this from first hand experience. Some years ago I wanted to use the wast heat from a gen/set to heat my workshop and I came across a ships ventilator fan with motor rated at 440 volts 60HZ I thought that this would do so I connected it up to 415 volts 50hz and it ran for a time got very hot and then the smoke arose. The motor with fan was a brand new unused unit that I got at a military auction along with a whole lot of other motors.
You make it wrong: supply voltage of the motor would be 5/6 x 440V = 366,7V in 50Hz.
With 415V (48V too much), it had to burn out.
 

Offline johansen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #18 on: June 13, 2014, 06:21:31 am »
If you run a 60HZ motor on 50HZ the windings will burn out, I know this from first hand experience. Some years ago I wanted to use the wast heat from a gen/set to heat my workshop and I came across a ships ventilator fan with motor rated at 440 volts 60HZ I thought that this would do so I connected it up to 415 volts 50hz and it ran for a time got very hot and then the smoke arose. The motor with fan was a brand new unused unit that I got at a military auction along with a whole lot of other motors.
You make it wrong: supply voltage of the motor would be 5/6 x 440V = 366,7V in 50Hz.
With 415V (48V too much), it had to burn out.

48v too much isn't enough to justify a burn out though.

generally, motors are specified at 40C temperature rise, so, if you have twice as much electrical current flowing you would get 160C temperature rise, which SHOULD take 1000 hours minimum to burn out.

so if it burns out within 10 hours folks.. you're looking at 300+C winding temperatures. and yes, i've seen this happen
here's a photo: http://johansense.com/induction_heater/7/P1050002cs.JPG

the copper in that fried section was as soft as lead. seriously, i've never seen copper that soft. i don't know the temps it got, but it was in the range of 400C i would imagine, the photo doesn't do it justice. the insulation was black, like carbon. but it didn't short out.

the replacement was 20 or so strands of 24 awg, wound as two coils, but that's just details.
http://johansense.com/induction_heater/7/P1050019cs.JPG
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #19 on: June 13, 2014, 06:23:58 am »
In a brushed axial fan I've seen molten copper due to insulation failure and shorts, it was only because it was asealed motor that it did not make a fire but just melted the wire until it fused.
 

Offline vk6zgo

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #20 on: June 13, 2014, 06:28:40 am »
We had some blower motors in Harris transmitters---they were reasonably small,so I'm pretty certain they were single phase.(30 years ago!!!)

Anyway,these things would cook up regularly on a 50Hz supply.
After we had them rewound locally,no more problems--not sure if the rewinder had a few magic tricks,or what?
Maybe Harris' suppliers scrimped somewhere.
 

Offline Simon

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #21 on: June 13, 2014, 06:38:28 am »
well our motors simply used bad insulation that melted in the high temperature you get in a sealed motor and caused massive shorts so just melted away until a wire broke
 

Offline johansen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #22 on: June 13, 2014, 06:48:00 am »
i understand, insulation life is cut in half every 10C temp rise.

most motor burn outs are due to overloads.

most transformers i run across and detail, they should be running at 2/3rds the voltage, so when a motor burns out at 1.2 times the voltage, no crap, it had a 120C temperature rise in the first place (or higher)
 

Offline johansen

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #23 on: June 13, 2014, 06:50:01 am »
blower motors in Harris transmitters

i spent some time in the usmc and we replaced 400 hz blowers which spun at 23500 rpm all the time.
as far as individual failure rates, they were on average.
« Last Edit: June 13, 2014, 06:52:05 am by johansen »
 

Offline SeanB

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Re: what happens when you run a 50Hz 3 phase motor at 60Hz
« Reply #24 on: June 13, 2014, 04:50:23 pm »
The original probably had a class A,B or F rated insulation on the windings, and the rewinder used a class H wire in the rewind, giving an improved heat resistance. Very likely as well he simply wound on as many turns as would fit on the cores as well, more than the original most likely.

http://toshont.com/ag/mtrldesign/AG05%20%28Temperature%20Rise%29.pdf

 Short google search.

If you have motor issues go to a higher power motor in the same frame size if possible.
 


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