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60-Hz Motor in 50-Hz System

07/20/2009 5:04 AM

My system frequency is 50Hz. Is there any problem if I connect and operate a 60Hz motor with a VFD?

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#1

Re: 60Hz Motor Running in 50Hz System

07/20/2009 7:22 AM

No.

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#2

Re: 60Hz Motor Running in 50Hz System

07/20/2009 7:42 AM

no because VFD control speed by frequency

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#3

Re: 60-Hz Motor in 50-Hz System

07/20/2009 9:22 PM

These VDF can operate more than 75Hz for 50Hz motor, so 60 Hz motor no problem

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#4
In reply to #3

Re: 60-Hz Motor in 50-Hz System

07/20/2009 11:18 PM

what if i operate the 50Hz motor to run on 75Hz (long term) setting on VFD? is there a damaging effect on the motor?

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#7
In reply to #4

Re: 60-Hz Motor in 50-Hz System

07/21/2009 1:22 AM

Don't Worry. I have been running my motor rated at 50Hz with VFD to 75Hz since my plant start in 1995 till now. My plant operate 24hr a day and 360 days a year excepts 6 days for 3 schedule maintenance/year

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#24
In reply to #7

Re: 60-Hz Motor in 50-Hz System

01/24/2025 7:31 AM

Well, that's fine, although it suggests that the <...motor...> is oversized for the mechanical load being presented.

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#8
In reply to #4

Re: 60-Hz Motor in 50-Hz System

07/21/2009 1:25 AM

Yes, it will be detrimental. In fact, most likely running it at 60Hz will be detrimental.

An AC motor produces rated torque based on maintaining ratio of voltage and frequency it was designed for. As long as you maintain the V/Hz ratio, everything is fine. So if, for example, you have a 460V 60Hz motor, it has a V/Hz ratio of 7.67:1 (460/60). If you set the VFD to run at 1/2 speed (30Hz), it will reduce the voltage to 1/2 of the voltage (230V) which maintains that 7.67:1 ratio.

Now, take your 60Hz motor and connect it to a VFD fed from a typical 50Hz supply voltage of 400V. The problem is, the VFD cannot boost the voltage higher than what is fed into it. So now at 60Hz, your maximum voltage will be 400V, so the V/Hz ratio is 400/60 = 6.67:1. Your motor is now under-fluxed and will not produce rated torque, which means the slip will increase and if the motor doesn't stall, it will at the very least over load. Increase the speed to 75Hz and the V/Hz ratio drops to 5.33:1 and it gets even worse. So the only way you can get away with this is if your motor is grossly over sized to begin with for the required work load.

The only way to make t work at 60Hz is to use a transformer to boost the line voltage to 480V, or in the case of 75Hz, to 575V.

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#11
In reply to #4

Re: 60-Hz Motor in 50-Hz System

07/21/2009 2:32 AM

Your motor should run fine, even long term, unless you push it well beyond its design limits.

The VFD's I've used can usually output 1 Hz-120 Hz. The V/Hz ratio and current(torque) limit control can also be adjusted for most applications.

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#16
In reply to #11

Re: 60-Hz Motor in 50-Hz System

07/22/2009 1:09 PM

But you CANNOT increase the voltage beyond the incoming!

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#18
In reply to #16

Re: 60-Hz Motor in 50-Hz System

07/22/2009 1:53 PM

Use 480volt drive on 240v motor (at double motor NP hp).

Then keep the v/hz constant to 100hz at double the voltage.

Many motors have 600V insulation system and will take the over Volts over freq condition (V/Hz constant).

Yes, there is a calculated risk here. Insulation, max rpm, etc all have to be considered.

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#23
In reply to #4

Re: 60-Hz Motor in 50-Hz System

01/24/2025 7:30 AM

It depends upon the mechanical load presented to the motor at <...75Hz...>. If the product of the torque and angular velocity at that speed exceeds the maximum rated power for the motor at that speed, then one can expect one of the following to happen:

  • The motor will cook itself
  • The motor will cease to turn, and operate as a convector heater instead
  • The motor overload protection device(s) will disconnect it from the circuit
  • The circuit protection device(s) will operate, disconnecting the motor from the supply

depending on the arrangements in place on its being called to run at the faster speed. The first two would be described as <...damaging effect...>; the others not.

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#25
In reply to #4

Re: 60-Hz Motor in 50-Hz System

01/24/2025 7:33 AM

Not if the <...VFD...> has been set correctly. Operating a motor outside its design envelope is subject to increased risk and the settings on the <...VFD...> need to be chosen to minimise the risk.

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#5

Re: 60-Hz Motor in 50-Hz System

07/20/2009 11:43 PM

Motor will run at lesser speed. If motor rpm at 60 Hz is 1200 then at 50 Hz it will run at 1000 RPM maximum.

Harish Kumawat

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#6

Re: 60-Hz Motor in 50-Hz System

07/21/2009 12:38 AM

Most but not all motor can run with VFD,

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#9

Re: 60-Hz Motor in 50-Hz System

07/21/2009 1:25 AM

No problem, VFD will give the proper frequency.

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#10

Re: 60-Hz Motor in 50-Hz System

07/21/2009 1:29 AM

Just ensure VFD is rated for 50Hz input. Most are.

Re: running at 75 HZ, if v/Hz tracks (and you don't damage the insulation) you will have 1.5 x the 50Hz HP rating. If you keep the rated volts and continue to 75 HZ you have a torque drop associated with the over frequency. Pull out torque will drop with approximately 1/(per normal overspeed)^2 or 1/(1.5)^2. If your application stays within the boundary condition the motor will run.

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#12

Re: 60-Hz Motor in 50-Hz System

07/21/2009 3:36 AM

Just check with the manufacturer. Some motors designed for VFD "abuse" and some will die on you........

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#13

Re: 60-Hz Motor in 50-Hz System

07/21/2009 8:57 AM

Make sure your VFD is rated to accept 50HZ power.

You may have to play around with the parameters to make it do what you want.

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#14

Re: 60-Hz Motor in 50-Hz System

07/21/2009 9:44 AM

Although I haven't experienced any of the problems noted above, you should initially monitor the VFD and the motor for any signs of distress (like excessive heat).

A typical VFD input stage uses a 3-phase bridge rectifier and capacitor filter to form an internal DC bus. Under heavy loads, the DC bus ripple will be larger at 50Hz than at 60Hz. The VFD may run hotter and the reduced peak output voltage could cause some loss in expected performance.

A VFD output can contain a broad spectrum of high frequency components. These harmonics usually get converted to heat in copper and iron losses and may increase the running temperature of a motor. They can also degrade the insulation and cause premature winding failure.

If long term reliability is CRITICAL, you may want to research "inverter rated" motors which are specifically designed to work with VFD's.

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#15
In reply to #14

Re: 60-Hz Motor in 50-Hz System

07/22/2009 9:48 AM

no problem at all, because frequncy controll is one of the best method of speed control in AC motors.

all AC motor speed control is achived by VFDrive only.
so u can use 50Hz frequncy motor at 75Hz frequncy.

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#17

Re: 60-Hz Motor in 50-Hz System

07/22/2009 1:50 PM

WOW!

I cannot believe the number of posters here who have no clue as to how VFDs work and how they control the speed of AC asynchronous motors!

You are ALL wrong.

VFDs convert the incoming line power from AC to DC. They know not if the incoming line is 50Hz, 60Hz, 25Hz, 1 phase, 3 phase, it makes almost no difference. The AC line supply is just the "raw material" by which the DC power is created. The only issue is the amount of ripple in the DC circuit as a result of the incoming power rectification. 1 phase creates more ripple, as would extremely low frequency (i.e. 25Hz), but even those issues can be corrected with enough capacitance on the DC bus. So the incoming line being 50Hz or 60Hz is completely irrelevant.

In that Conversion (rectification) section of the VFD, the DC bus voltage ends up being roughly equal to the PEAK voltage of the AC sine wave, not the RMS, because in a full bridge rectifier, you are conducting at the peaks. A standard VFD cannot increase the voltage beyond that level. Given that, the maximum RMS pseudo-sine wave output voltage from the Inverter section then CANNOT be higher than what the RMS voltage was on the input side. So if he has a 380V incoming line, the peak RMS output voltage will be 380V (actually, slightly lower but that's insignificant). Even if he increases the output frequency to 50Hz, 60Hz, 120Hz or 400Hz, the maximum voltage will remain 380V! Read my earlier post about how a motor responds to voltage and frequency because unless the user has addressed the voltage issue, it will not work without compromising the motor.

Please refrain from posting assumtions, guesses and feelings. Be accurate or read to learn.

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#19
In reply to #17

Re: 60-Hz Motor in 50-Hz System

07/22/2009 4:39 PM

Those of us who have actually used VFD's understand that the V/Hz ratio is only maintained for low speed up to rated speed (60Hz). ABOVE rated speed V/Hz is no longer constant. The output voltage is fixed at some max value while the frequency and motor speed continue to increase. Available torque and horsepower are reduced, but most motors will run just fine if the load is properly derated as well.

Not every induction motor application is based solely on max horsepower or max torque loading. For example, many conveyor systems and some pump applications can run more efficiently when a VFD is used to control motors both below and above the nominal speed rating.

Basic, but a good start for "read to learn".

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

http://en.wikipedia.org/wiki/Variable-frequency_drive

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#21
In reply to #17

Re: 60-Hz Motor in 50-Hz System

07/23/2009 2:38 AM

Your comment is not well taken.

The reason I cautioned about the 50/60Hz input was not for the front end power conversion, but for the auxiliary AC controls. Operating a VFD on single phase when it is rated for 3 phase will often cause a derating of the input bridge. If auxiliary power is taken from the phase you did not connect those controls will not work. Things like auxiliary blower motors, AC contactors, any relaying etc has to be rated for 50/60 hz operation also. One example is the Reliance SA3100 drive, the controller runs from 115vac, the front end power conversion can be from a dc supply, rectifier with resistor precharge, or a synchronous rectifier with harmonic compensation (and yes, that unit can achieve a DC bus voltage well above the normal peak AC line volts). There are also controlled rectifier front ends that can regenerate power back to the AC line. Some front ends use a three phase SCR control (possibly regenerative) for controlling the DC bus voltage and soft charging the capacitor banks. I stand by my comment to verify with the manufacturer before taking a VFD outside its rated input parameters.

I have run AC motors (small 1 HP ones) in the field range up to 90Hz, when the rated speed was 60HZ. The torque requirement was low at the high rpm. (This will generally not work for fan pump loads).

I have also deliberately used larger HP and higher voltage VFD's on lower rated motors not only for the duty cycle head room, but to run the motor above NP. This can be handy especially if there is a service factor for the motor you wish to utilize.

Similarly I have used 480V converters on 600V motors when the required speed was well below the NP.

The bottom line is you have to intimately know the limits of the VFD and the motor you are using. There are many tricks you can play with a VFD. Also, motors for VFD's need not be rated 50 or 60HZ, but can have odd ratings like 38HZ, 6 pole, 480vac.

I have been there and played with many of the combinations for every thing from fan pumps (1500HP), slitter drives, press feeders, plywood veneer lathe spindles (500Hp), paper machine winders (300 - 500 HP), and many other applications.

"Please refrain from posting assumptions, guesses and feelings. Be accurate or read to learn" (and use spell checker)

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#20

Re: 60-Hz Motor in 50-Hz System

07/23/2009 1:49 AM

No problem as long as you are getting the speed and torque for that chanegd frequecny through VFD

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#22

Re: 60-Hz Motor in 50-Hz System

07/24/2009 9:36 AM

Variable frequncy drive nothing relation with DC to AC / AC to DC,


For VFD input as well output is AC only.

for controling DC motors speed servo drives are used.
and for AC motor speed control VFD are used.

in AC motor speed control is possible by 2 ways either controlling supply frequncy or changing the noumber of polls.

as u change the supply frequncy speed of rotating magnetic flux will change and according to speed of magnetic field motor speed will change.


As per my knowladge...........

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