what happens when you run a 50Hz 3 phase motor at 60Hz - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 02:06:19 pm
content: 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) ?

author: retrolefty
author_rank: Super Contributor
timestamp: June 12, 2014, 02:22:10 pm
content: Assuming a standard 3 phase induction motor, it will fun faster.http://en.wikipedia.org/wiki/Induction_motor

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 02:31:30 pm
content: yes i know but what about the power draw or power provided ?

author: jlmoon
author_rank: Unknown
timestamp: June 12, 2014, 02:45:21 pm
content: sounds like a EE motors & generators class test question.

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 02:47:02 pm
content: 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

author: vk6zgo
author_rank: Super Contributor
timestamp: June 12, 2014, 02:58:08 pm
content: Not sure,but I would be inclined to think it would be OK.The other way round definitely causes problems.

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 02:59:42 pm
content: 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.

author: johansen
author_rank: Super Contributor
timestamp: June 12, 2014, 03:28:20 pm
content: 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.

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 03:30:57 pm
content: 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.

author: oldway
author_rank: Super Contributor
timestamp: June 12, 2014, 04:33:58 pm
content: 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).

author: G7PSK
author_rank: Super Contributor
timestamp: June 12, 2014, 05:30:44 pm
content: 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.

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 05:32:46 pm
content: would the wattage of the motor make any difference ? we are talking about 4KW and many motors are made to work on both now.

author: IanB
author_rank: Super Contributor
timestamp: June 12, 2014, 05:39:06 pm
content: Quote from: Simon on June 12, 2014, 05:32:46 pmIt 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.

author: Simon
author_rank: Unknown
timestamp: June 12, 2014, 05:48:32 pm
content: 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.

author: jahonen
author_rank: Super Contributor
timestamp: June 12, 2014, 05:51:12 pm
content: 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.Quote from: G7PSK on June 12, 2014, 05:30:44 pmThat 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

author: johansen
author_rank: Super Contributor
timestamp: June 12, 2014, 09:35:40 pm
content: 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.

author: fallwithstyle
author_rank: Newbie
timestamp: June 12, 2014, 11:38:47 pm
content: 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.pdfYour blower manufacturer should be able to provide similar information.

author: oldway
author_rank: Super Contributor
timestamp: June 13, 2014, 05:12:38 am
content: Quote from: G7PSK on June 12, 2014, 05:30:44 pmYou 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.

author: johansen
author_rank: Super Contributor
timestamp: June 13, 2014, 06:21:31 am
content: Quote from: oldway on June 13, 2014, 05:12:38 am48v 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 happenhere's a photo:http://johansense.com/induction_heater/7/P1050002cs.JPGthe 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

author: Simon
author_rank: Unknown
timestamp: June 13, 2014, 06:23:58 am
content: 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.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 13, 2014, 06:28:40 am
content: 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.

author: Simon
author_rank: Unknown
timestamp: June 13, 2014, 06:38:28 am
content: 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

author: johansen
author_rank: Super Contributor
timestamp: June 13, 2014, 06:48:00 am
content: 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)

author: johansen
author_rank: Super Contributor
timestamp: June 13, 2014, 06:50:01 am
content: Quote from: vk6zgo on June 13, 2014, 06:28:40 ami 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.

author: SeanB
author_rank: Super Contributor
timestamp: June 13, 2014, 04:50:23 pm
content: 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.pdfShort google search.If you have motor issues go to a higher power motor in the same frame size if possible.

author: ignator
author_rank: Regular Contributor
timestamp: June 13, 2014, 06:16:41 pm
content: G7PSK:I don't see that anyone said this directly.Think of the motor as an inductor. What does impedance do in an inductor when you change frequency. The 2 pi f L impedance equation. So the input current given the same voltage will decrease.As Johansen very well describe, the torque capability is reduced, which makes sense if the input power is less.

author: Simon
author_rank: Unknown
timestamp: June 13, 2014, 08:41:30 pm
content: that is why I assumed, faster speed less power, supper fail

author: IanB
author_rank: Super Contributor
timestamp: June 13, 2014, 11:14:26 pm
content: Quote from: Simon on June 13, 2014, 08:41:30 pmBut the faster speed part is not directly important.The power requirement of a fan is determined by the characteristics of the fan and the operating conditions (and not the motor). So if a fan requires a certain power to run at 750 rpm, then it requires the same power to run at that speed whether the motor is supplied at 50 Hz or 60 Hz. The motor power demand at 750 rpm is exactly the same whatever the line frequency.Now the power is also given as the product of shaft torque and rotation speed. Therefore to deliver the required power at 750 rpm the motor must be able to provide sufficient torque on the output shaft when turning at that speed.What happens at the higher line frequency is that the motor has no trouble turning at 750 rpm with no load, but when the fan is attached the motor can no longer generate sufficient torque to develop the required output power at this speed. Therefore the motor runs at a slower speed until the power developed by the motor and the power consumed by the fan become equal.One way to compensate for this is to replace the fan impeller with a smaller diameter one that has a lower input loading (but then it will move less air). Another possibility is to boost the input voltage to compensate for the higher frequency, but this may not be cheap or easy.

author: Simon
author_rank: Unknown
timestamp: June 14, 2014, 08:35:34 am
content: well the motor is speced at 875rpm @ 60 Hz so we need the extra power to run the same fan. although it sounds like it will just slow the motor down if the motor can't provide the power. Will the motor inherently take more or less power at 60 Hz ?

author: johansen
author_rank: Super Contributor
timestamp: June 14, 2014, 07:58:37 pm
content: Quote from: Simon on June 14, 2014, 08:35:34 amno load idle draw will be slightly more, but this is voltage dependent.what you fail to understand is the cubic power curve. this is why, as you said earlier "the motor isn't getting there"its probably running at 300 rpm or something.google:torque-rpm curve induction motorpull out torquepull in torque.depending on that motor's specific torque curve, you could be running the motor anywhere from 300 to 700 rpm on the 60hz line.unless you change the pulley diameter(if it has one?), or cut the blades down you need to find a 7KW motor, which is about 10 hp.

author: G7PSK
author_rank: Super Contributor
timestamp: June 14, 2014, 09:31:01 pm
content: Increase the load or decrease the power into an induction motor and you will increase the percentage of slip, that means that the bars of the squirrel cage cut fewer lines of force so the back emf is reduced therefore the current rises and you get increased heating.Percentage of slip = Difference between actual speed and synchronous speed / synchronous speed X 100.Synchronous speed = HZ X 60/ number of pairs of poles.Normally the slip % is around 2 to 5 much more than this and the motor is in trouble.

author: IanB
author_rank: Super Contributor
timestamp: June 14, 2014, 09:40:36 pm
content: Quote from: Simon on June 14, 2014, 08:35:34 amThe motor and fan are designed together as a combination. The characteristics of the motor are matched to the characteristics of the fan. It's a bit like impedance matching in electrical systems.Just because the motor has 60 Hz on its nameplate, it doesn't mean thatthe motor and fan in combinationare specced to run at 60 Hz.In electrical systems impedance matching can be achieved by a transformer. In mechanical systems impedance matching can be achieved by gearing. So in this case, if there is a pulley system connecting the motor to the fan, then it may be possible to change the gear ratio with different pulleys so the faster speed of the motor can be matched to the slower speed of the fan.You haven't told us where this motor/fan combination came from, and why it is being used on the wrong specification of electrical supply? Is it a surplus component that is being re-used, or did incorrect information get given to the original supplier? Someone would have designed it to do a certain job, and now it seems it is being used outside its design. If the opportunity exists, you could go back to the designer to have the problem remedied.

author: ConKbot
author_rank: Super Contributor
timestamp: June 14, 2014, 10:01:26 pm
content: If you cant pass the problem onto someone else, then it sounds like a VFD may be an easy way out. Since your load is a fan, a simple V/Hz one should suffice. Plus that adds 'features' like a logic-level on/off, variable speed, and a ramped start. Obviously the motor is rated at 60 Hz, so you probably shouldnt run it past 60 Hz on the VFD, especially if its not rated for a VFD. I'm no expert in VFDs, but if its non rated to run on a VFD, then reactor on the motor may be required to keep harmonics and parasitic capacitance in the motor from causing issues, but I'd get a second opinion on that.

author: johansen
author_rank: Super Contributor
timestamp: June 15, 2014, 02:06:11 am
content: Quote from: ConKbot on June 14, 2014, 10:01:26 pmyou can run most small induction motors at 400hz if you think the bearings can handle it. the problem is, he needs a 7 KW motor to run a 4KW fan at 20% faster than design rpm.as it is, the fan "isn't getting there" which most likely means the motor is not coming up to synchronous speed.

author: IanB
author_rank: Super Contributor
timestamp: June 15, 2014, 02:51:51 am
content: Let me ask this question, for which I am not clear about the answer:Suppose we take a 750 rpm motor that can generate its designed maximum power output when supplied with 50 Hz, and we change the supply frequency to 60 Hz so that it wants to run at 900 rpm. If we keep the supply voltage the same, will its maximum power output at the new faster speed be the same, be less, or be greater than it was at 50 Hz?My impression is that the total power will be less, because the decrease in torque will outweigh the increase in speed. Is this correct?

author: johansen
author_rank: Super Contributor
timestamp: June 15, 2014, 04:25:41 am
content: Quote from: IanB on June 15, 2014, 02:51:51 amhttp://www.usmotors.com/TechDocs/ProFacts/Voltage-Frequency-Variation.aspx

author: IanB
author_rank: Super Contributor
timestamp: June 15, 2014, 06:25:40 am
content: Quote from: johansen on June 15, 2014, 04:25:41 amUnfortunately neither that document nor others I have found give a direct and unambiguous answer to my question.However, from considering the information provided it would appear that the power output would remain approximately the same. Speed is proportional to frequency and torque is proportional to voltage/frequency, so if the frequency is changed without changing the voltage the two effects of frequency will cancel out.

author: pickle9000
author_rank: Super Contributor
timestamp: June 15, 2014, 07:00:41 am
content: Does this help?http://myelectrical.com/tools/induction-motor-calculator

author: johansen
author_rank: Super Contributor
timestamp: June 15, 2014, 02:38:47 pm
content: Quote from: IanB on June 15, 2014, 06:25:40 ami don't understand your question. maximum power output does not equal maximum efficiency.A 1 hp motor's maximum power output is approximately 2 hp, but could be as much as 3 hp or as little as 1.5, depending on what it was designed for.Its reasonable temperature rise will limit the hp to 1, its "rated" load.running the motor at 20% more hz but keeping volts the same will reduce the "maximum power output" by a lot. however, it will still operate at its "rated" load, provided its "rated load" is measured in watts, not torque, at similar conditions. the slip will be higher however, due to the reduction in voltage.if the voltage is increased as well, you get 20% more power for a slight increase in windage and iron losses.