Effects of 50Hz on a 60Hz motors.
Effects of 50Hz on a 60Hz motors.
(OP)
I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?
Thanks you much for your responses.
Thanks you much for your responses.





RE: Effects of 50Hz on a 60Hz motors.
You could use them with less load and/or put a larger fan on them if they are fan cooled!
RE: Effects of 50Hz on a 60Hz motors.
The flux that the stator winding creates is proportional to the line Voltage and inversely proportional to the number of turns and frequency ( flux/p= 4.44 Vn/Kp*Kd*N*F).
Leaving the actual winding, the voltage must be reduced in proportion to the frequency change.
For 480V- 60 HZ --? 440*50/60 = 400 Volts at 50 HZ ( hopefully it will work at 380 Volts with 5% flux reduction test it). You try to keep the flux to avoid saturation of the magnetic circuit. If saturation is reached, your no load current (magnetizing mainly) will be too high, the PF decreases and the motor will overheat or eventually burn ( even under no load).
The voltage reduction keeps the flux then the torque produced is close to constant, but the HP output will be reduced due to the speed reduction.
T=5252*HP/rpm or HP= T*rpm/5252
For instance: 10 HP, 480 V, 60 HZ, 1750 rpm. IT CAN WORK AT 400 Volts, 50 HZ.
T=5252*10/1750 =30 Lb*Ft
New HP at 400 V, 50 HZ (1458 rpm)
HP=30*1458/5252 = 8.33 HP
The reduction of speed will reduce the cooling air flow, but the reduction of HP will result in lower losses and the temperature rise is almost the same as the 60 HZ, 440 Volts temperature operation.
If the operating voltage at 50 HZ is different, the stator must be re-winded keeping the flux densities of the original 60HZ design and the power de-rated proportional.
RE: Effects of 50Hz on a 60Hz motors.
I remember some post (by jraef or skosgurra, sorry I do not recall the thread no) where he had actually tested some 60 Hz motor at 50 Hz with the same volatge and found no abnormal temp rise.
RE: Effects of 50Hz on a 60Hz motors.
When you lower the frequency to 50 Hz and the voltage stays the same, X Vac, you change the V/f ratio. If the motor operates at X Vac, 60 Hz, the V/f ratio will be X/60Hz. At 50Hz, the V/f ratio is X/50 in Vac/Hz. This increase in V/f ratio can cause more current to flow to maintain the same torque.
Output power reduces by 5/6 ths as shaft power is the product of torque (similar at both frequencies) and speed. If the speed reduces by 5/6 ths so does the shaft power.
RE: Effects of 50Hz on a 60Hz motors.
- V/f ratio should remain the same while changing frequency
- Rated HP should be decreased.
The thread edison123 is refering was posted by me and i gave practical values myself at the end. Unfortunately my memory is the same as edison123 (no offence edison123) and so i also cannot remember the thread. The thread concerned a motor rated for 400V, 50 Hz and running at 480V, 60 Hz.
RE: Effects of 50Hz on a 60Hz motors.
My reffered thread had posts about actual tests done by jraef or skosgurra (and No, I don't intend to go thru their profiles and start searching for their vast ocean of their much appreciated posts).
Anyway, I stick by my earlier post about winding burnout. While the flux density will go up at 50 HZ and at the original voltage, the eddy current loss (proportional to squares of both frequency and flux density) will not be drastically affected due to fall in frequency (60 to 50 Hz).
RE: Effects of 50Hz on a 60Hz motors.
Your statement “Even if it hits the saturation, the possibility of winding burn out is remote.” is too daring. Have you seen what happens to a motor connected for 230 Volts energized with 460 Volts (hitting saturation)? It will explode!
Some times when a 460V, 60 HZ motor is used in a country with 50 HZ the voltage has lower levels like 380V, 400V or 415V. If the motor moves the very same load the speed reduction will release some power demand from the motor. That particular condition could work.
I don’t think you are recommending to use those 60 HZ motors as equivalent in HP to operate on 50 HZ, 460 Volts, do you?.
RE: Effects of 50Hz on a 60Hz motors.
RE: Effects of 50Hz on a 60Hz motors.
I am puzzled by your "explosion". Where did I mention that a 230 V motor can be run at 460 V ? I mentioned 50 Hz and original voltage. Also, I didn't say about anything same HP being retained at lower frequency.
I only contested last part of your statement "If saturation is reached, your no load current (magnetizing mainly) will be too high, the PF decreases and the motor will overheat or eventually burn ( even under no load).", with which I still disagree.
I have advised many of my clients to run 380 V/60 Hz motors at 415 V/50 Hz without any rewinding and they are all running well without any excessive temp rise. How could a no-load current equal to 100% load current could burn the stator beats me ?
RE: Effects of 50Hz on a 60Hz motors.
but then isn't eddy current loss also proportional to square of frequency ? hence, my opinion (and also my experience) is that winding would not see any abnormal heat. eventually, all motors do fail due to various reasons.
RE: Effects of 50Hz on a 60Hz motors.
I think this is the thread you are refering to:
Thread237-86353
Ralph
RE: Effects of 50Hz on a 60Hz motors.
RE: Effects of 50Hz on a 60Hz motors.
RE: Effects of 50Hz on a 60Hz motors.
What followsis nothing new, already known to aolalde and edison but I will post anyway an excerpt from NEMA MG-1 2003:
“14.34 OPERATION OF GENERAL-PURPOSE ALTERNATING-CURRENT POLYPHASE, 2-, 4-, 6-,
AND 8-POLE, 60-HERTZ MEDIUM INDUCTION MOTORS OPERATED ON 50 HERTZ
While general-purpose alternating-current polyphase, 2-, 4-, 6-, and 8-pole, 60-hertz medium induction motors are not designed to operate at their 60-hertz ratings on 50-hertz circuits, they are capable of being operated satisfactorily on 50-hertz circuits if their voltage and horsepower ratings are appropriately reduced. When such 60-hertz motors are operated on 50-hertz circuits, the applied voltage at 50 hertz should be reduced to 5/6 of the 60-hertz voltage rating of the motor, and the horsepower load at 50 hertz should be reduced to 5/6 of the 60-hertz horsepower rating of the motor. When a 60-hertz motor is operated on 50 hertz at 5/6 of the 60-hertz voltage and horsepower ratings, the other performance characteristics for 50-hertz operation are as follows:
14.34.1 Speed The synchronous speed will be 5/6 of the 60-hertz synchronous speed, and the slip will be 5/6 of the 60- hertz slip.
14.34.2 Torques The rated load torque in pound-feet will be approximately the same as the 60-hertz rated load torque in pound-feet. The locked-rotor and breakdown torques in pound-feet of 50-hertz motors will be approximately the same as the 60-hertz locked-rotor and breakdown torques in pound-feet.
14.34.3 Locked-Rotor Current The locked-rotor current (amperes) will be approximately 5 percent less than the 60-hertz locked-rotor current (amperes). The code letter appearing on the motor nameplate to indicate locked-rotor kVA per horsepower applies only to the 60-hertz rating of the motor.
14.34.4 Service Factor The service factor will be 1.0.
14.34.5 Temperature Rise The temperature rise will not exceed 90°C (see 14.30).”
What is stated by NEMA is the same approach as suggested by aolalde. It also stands to reason that many motors have some unknown amount of margin built in and we can often be successful in pushing motors beyond the limits identified in the standards. I was very interested to hear edison’s comments regarding actual experience of operating motors beyond rated volts per hertz. Knowing edison, I place a lot of weight on his experience and judgement regarding motors. Being perhaps an overly cautious person, I personally would be hesitant to specify operation of a motor outside of recommendations of the standards.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Effects of 50Hz on a 60Hz motors.
Bmax increase in proportion to frequency within the linear range.
I see a variety of formulations for eddy and hysteresis losses including the following
Pe = Vol * Pi^2* Tau^2 * f^ 2 * (Bmax)^2 / (6*rho)
Ph = k Vol* f* (Bmax)^1.1
Where:
Pe = eddty current losses
Ph = hysteresis losses
f: Frequency [Hz].
Vol: Volume of iron specimen [m ].
Tau_: Thickness of lamination [m].
resistivity [_ m].
k: A constant for a given iron type and given range of flux density.
Bmax : Maximum flux density [Tesla].
The above formulas would suggest Pe is constant and Ph increases when we decrease frequency with votlage constant. I’m sure there are other formulations. It will get more complex if Bmax is limited by saturation effects. As mentioned above there are also increase in no-load current. May be difficult to measure due to high harmonic currents.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Effects of 50Hz on a 60Hz motors.
Your formulae for eddy current and hysteresis looses are universally accepted. Besides having practically seen the worst possible scenario (higher voltage/lower frequency) of 380 V, 60 Hz motors running at 415 V, 50 Hz satisfactorily over the years, I also have a theoretical explanation.
For the same voltages at 50 and 60 Hz (though in practice they seldom are) eddy current loss, as deduced from your formula remains the same due to the same amount of increase/decrease in Bm and F respectively.
As for the hysteresis loss, which is proportional to frequency and Bm^x, (the exponent x, as a rule, is 1.5 to 1.6 at 1 Tesla, 2.2 at 1.5 T and falls to 0.8 at 2T as per design books) may increase or even decrease (!). Depending on the original Bm at 60 Hz, the exponent x can be at worst 2.2 and at best 0.8. Taken in conjunction with the fall in frequency, the hysteresis loss may be 4% less (best case with x = 0.8) or 25% more (worst case with x = 2.2).
Out of typical 10% total loss, I figure hysteresis loss may be around 1%. So, an increase of 25% in this 1% loss is not going to start any fireworks. Also, with lower I^2R loss at 50 Hz (due to capacity reduction and due to original winding copper area being retained), one may actually end up even in cooler motor - at least theoretically - even with reduced cooling at 50 Hz.
Apart from all the theory, my opinion is still based on actual experience of seeing these motors operating well at higher V/Hz.
Of course, others may disagree (especially will all the above rambling)
RE: Effects of 50Hz on a 60Hz motors.
JBartos The original posting does not specify motors designed for 50/60 Hz but 60 HZ.
///I am aware of it. So what?
Have you visited
http://kingsolar.com/catalog/mfg/dayton/4fn68.html
for:
These highly efficient 3-phase TEFC motors make pumps, fans, blowers and other industrial equipment operate at peak performance levels. Uses: Pumps, blowers, machine tools, air compressors, and other industrial applications where 3-phase power is available.
Mounting: Rigid welded base
Ambient: 40°C
Thermal protection: None
Bearings: Double-shielded ball
rotation: CW/CCW
NEMA Design: B
NEMA Frame: 184T
Volts 60Hz: 230/460
====================
Service Factor: 1.15
NEMA Nominal Efficiency: 89.5
Frame Material: Cast Iron
Insulation Class: F
50Hz operation on 190/380Volts at 5/6 of 60Hz horsepower
========================================================
and RPM at 1.0SF
2 year warranty
Inverter-Duty, meets NEMA MG 1 Part 31: 10:1 variable and 4:1 constant torque
NEMA Premium™ efficient product.
Now in this context the original posting states:
"""mikepz (Electrical) Apr 27, 2004
I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz.
What can I do to run these motors at 50Hz ? """
===========================================
Simply: Refer to the above for:
50Hz operation on 190/380Volts at 5/6 of 60Hz horsepower
========================================================
and perform similar adjustments for different voltages.
Now, what seems to be at a question?\\\
=======================================
RE: Effects of 50Hz on a 60Hz motors.
As a member of the 50Hz world, I can confirm that I have seen amny 60Hz motors run on 50Hz at the same rated voltage and fail due to overheating.
If the motor is specifically designed for maximum efficiency at rated voltage on 60Hz, then you can expect a dramatic increase in iron loss at 50Hz and this will cause an early failure.
Motors tend to be wound to minimise losses. As you increase the turns for a geven voltage, the flux will reduce and the copper loss will increase. Similarly, as you reduce the turns, the copperloss will reduce and the flux increase, increasing the iron loss. The optimum point is usually just below saturation flux, so if you increase the flux beyond this point (60Hz -> 50Hz), you will drive the fux into saturation and this will result in a major increase in iron loss and premature failure. If the motor has been well overwound, then this is not a problem.
As a rule, keep the V/F ratio constant and there will not be a problem. Raise the V/F ratio and you could cause overheating, even at no load.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Effects of 50Hz on a 60Hz motors.
In my opinion, Engineering recommendations should not be based on special cases but be consistent for every application.
As a conclusion: May I expect satisfactory operation of a 60 HZ motor operating at 50 HZ?
Yes; if the V/HZ ratio is kept and the power output is reduced to 5/6 of original.
RE: Effects of 50Hz on a 60Hz motors.
I do not for a moment dispute the theory to maintain V/Hz in electrical machines (trafos included).
I recommend to my clients to always try the 60 Hz motors at 50 Hz and watch for the abnormal temperature rises, before deciding on rewinds, which is a costly proposition. The fact that the clients imported these motors second-hand (as part of whole system) speaks for their economic priority.
Except for some 2 pole motors, the recommended motors are working with temperatures well within limits of B class. I based my recommendation on the fact that these were very old (30 odd years) sturdy motors with good factor of safety (unlike the modern motors which are always on death wish) and that a reasonable risk can be taken with them without any major problems.
Believe me, as a rewinder, I would have been happy to rewind them and make some money. My curiosity (whether they will really fail) got the better of me but it has earned the goodwill of my clients.
RE: Effects of 50Hz on a 60Hz motors.
Those countries with 50Hz power systems provide that power at "standard" or "nominal" voltages just like the U.S. The most common voltage in 60HZ 3-phase countries is 480VAC (nominal).
The most common voltage in 50Hz 3-phase countries is 400VAC (nominal). Get a good quality VFD that will run on the Canadian systems, which are 60Hz 600VAC nominal. Just like Mikey, they will eat anything.
Configure the VFD to run your 60Hz motors at 60 Hz. I have thousands of times shipped machines in this configuration, from the Philippines to India. Even attaching the input of these drives to 600VDC systems then running 3-phase motors at 60 Hz, or any frequency needed.
RE: Effects of 50Hz on a 60Hz motors.
This thread seems to have moved in a number of different directions. Perhaps it is time to go back to your original question "I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?"
1. Yes, if you operate these motors at the same voltage, but at 50Hz, there is no coubt that the iron loss will be increased significantly and in many cases this will lead to damage to the motor. While some have experienced no short temr failure from this practice, others have so I would suggest that you take care if you choose this option.
2. The motor will spin at 5/6 speed and this may affect the operation of your machine.
3. You can safely run the motor at 50Hz (lower speed) provided that you reduce the voltage to 5/6 of the 60Hz voltage, and you reduce the load to 5/6 of the 60Hz load.
4. You could rewind the motor for 50Hz 220 volt operation, but you may still need to derate the power output of the motor. 50Hz needs more iron for the same power rating.
5. You could use a variable speed drive to convert the 50Hz to 60Hz and run your motor as normal. (Must be three phase motors)
Mark Empson
http://www.lmphotonics.com
RE: Effects of 50Hz on a 60Hz motors.
I recommend to my clients to always try the 60 Hz motors at 50 Hz and watch for the abnormal temperature rises, before deciding on rewinds, which is a costly proposition.
///The "watch" for the abnormal temperature rises may prove to be detrimental to the motor; especially, when it is totally enclosed. Which method do you recommend to "watch" for temperature rises?\\\
RE: Effects of 50Hz on a 60Hz motors.
The same way as you would "monitor" as per your april 8 post in Thread237-91817.
RE: Effects of 50Hz on a 60Hz motors.
RE: Effects of 50Hz on a 60Hz motors.
http://www.leeson.com/cgi-bin/fetchpdf.cgi?/literature/bulletins/pdf/1050/AC50Hertz.pdf
See page 68.
RE: Effects of 50Hz on a 60Hz motors.
I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?
///Beside a lot of good advice in the above postings, the motor manufacturer tech supports might be contacted for recommendations. The manufacturers should know whether the motor has any design constraints preventing one running the motor at 50Hz. What if the linear scaling from 60Hz to 50Hz is not linear; therefore, it may or may not be "very accurate."\\\