Operating 50 Hz motor on 60 Hz using VFD

[Junaid16]

Can We operate a 50 Hz motor on 60 Hz using variable frequency drive (VFD)?

 

[moltenmetal]

Is the motor "inverter duty"? If so, and the motor and VFD are both sized properly, I don't see why not.

 

[ScottyUK]

The motor torque will drop away above base speed unless you maintain the V/Hz ratio at 60Hz, i.e. a 400V 50Hz motor will require 480V at 60Hz to maintain output torque at nominal value.

 

[jraef]

There is no connection between the line input frequency and the drive output frequency. The output frequency is whatever you tell it to be.

The voltage does matter though. The drive cannot create voltage that is not there, meaning that it is limited to the maximum line voltage. It can however provide any LOWER voltage than the line voltage.

Without further details we cannot help you more than that.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[powerjunx]

Junaid16, i had recent problem with this stuff.

400V/50HZ motor, 440V/60HZ VFD output control by pot full scale. Burn out motor winding, i suspected the motor over-voltage/over-frequency due to mis-configuration of VFD setting. Prior replacement of the motor, i set VFD output 400V/50HZ with pot full scale. Hope the setting will suffice motor lifetime..

Any thoughts?



"..the more, the merrier" Genghis Khan

 

[ScottyUK]

Did you factor in the load increase when you go to 20% above normal running speed for the motor (and presumably whatever it is attached to)? If the drive doesn't know enough about the motor to protect it then it won't be able to protect it.

 

[LionelHutz]

Do you want to run the 50Hz motor at 50Hz while powered from a 60Hz supply or do you want to run the 50Hz motor at 120% speed?

 

[Junaid16]

I want to run 50 Hz motor at 120% speed.

 

[Junaid16]

I want to operate 50 Hz motor at 60 Hz using Inverter ( means at 120% of motor speed)
is there any disadvantages ? If yes then Please Explain ??

 

[itsmoked]

Depending on the load that could require more power than the motor will develop at that speed.

Just as ScottyUK said above, unless your power supply voltage is raised above your 50Hz voltage the torque will drop with the increased speed over nameplate.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[moltenmetal]

Typically, assuming you've checked the power and torque requirements, you can spin most small 3 phase motors at up to twice its nominal speed, i.e. 100 Hz for a 50 Hz nominal inverter duty motor. But if the motor is not inverter duty, don't do it.

 

[advidana]

Check with the motor manufacture if this is okay.

 

[jraef]

I would never generalize that one can spin "any" motor at twice the rated speed. That is a potentially fatal assumption.

As itsmoked and ScottyUK have mentioned, there are specifics involved that need attention not only to the equipment, but also to the nature and dynamics of the load attached to the equipment.

For example, as ScottyUK mentioned you need to increase the voltage at the same ratio as the speed in order to maintain the motor torque. But even if you DID increase the voltage, if your load is a centrifugal pump or fan, at 120% speed the PUMP will require 172% power (shaft kW) from the motor. But at 120% speed the motor power only increases to 120%, so unless your motor started off being more that 50% over sized to begin with, you will come up short and overload the motor. If you can't increase the voltage, it's even worse.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[iop95]

120% speed the PUMP will require 172% power, but if suppose motor torque is equal with PUMP required torque at rated, motor can't supply a higer torque than rated (suppose can increase voltage at 60Hz accordingly), so PUMP speed can't increase and don't require 172% power. At 60Hz, motor torque curve may intersect PUMP curve in unstable zone. It's very important to know PUMP torque value at rated speed and corelate with motor curve.

 

[waross]

so PUMP speed can't increase and don't require 172% power

This is where the magic smoke comes out.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[iop95]

waross, it's true if motor have enough torque to accelerate pump at that speed, so will be in overload, but if don't have torque will go in unstable region or stop, depending of motor curve.
To reach 120% speed, max motor torque must be at least 144% of rated torque (considering rated torque = pump torque at 50Hz speed).

 

[waross]

At full load the slip frequency is about 2.2% at 60 Hz.
If the load holds the speed to 1500 RPM with 60 Hz applied, that is a slip frequency of about 17% That's over a 700% overload.
In practice, with that much slip, the motor will develop more than rated torque and run faster than 1500 RPM, but you will still be in a serious overload condition.
If your protection settings allow this condition, then either the motor, the drive or both are liable to emit the magic smoke.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[moltenmetal]

jraef: I suggest you re-read my post. The first complete phrase of my post mentions that you need to check the (load's) power and torque requirements before you do anything. Nobody said anything about just cranking the knob and seeing what happens!

A fan or centrifugal pump's power requirement depends on flow, not just on speed. Not every centrifugal pump or fan application has an unregulated discharge, nor is every pump or fan motor sized for full (flow) "run out". Many, particularly small ones, are operated quite far to the left hand side of the pump curve. The ones that require full run-out performance etc. obviously cannot have their speed increased meaningfully beyond their nominal operating speed.

Many other types of pumps (i.e. positive displacement types) are far less steep in their torque versus speed curve, and in fact the dominant sizing case for the motors for such applications is often the torque required at minimum speed.

As to "the magic smoke coming out"- that's where a VFD's 2nd function- as an overload and soft starter- comes usefully into play.

 

[ScottyUK]

moltenmental,

I know you said 'small' but remember in some industries anything which doesn't require an MV supply is considered 'small'.

There's a big difference in stresses on the rotor if you run a 4-pole machine at 100Hz compared to running a 2-pole machine at 100Hz. Many 2-pole machines won't be good for 100Hz operation, especially as the size increases, due to factors like mechanical strength, bearing limitations, balance accuracy, and so on. Some motors certainly are capable of operation at these higher speeds but it's not wise to assume without checking, especially with modern motors which are designed to meet their stated spec but often don't have much margin on it as manufacturers strive to cut costs to a minimum.

 

[moltenmetal]

Understood ScottyUK- context is everything in this. To qualify, to me a "small" 3 phase induction motor is 5 hp or less. Even then it's worth checking with the manufacturer before operating anything outside the nameplate range- and of course you should expect them to say "no", because what's in it for them to say "yes"? You need to ask more specific questions to understand whether the "no" given is just a "buzz off- operate it per the nameplate and don't bother us", or if it actually has some substance behind it. And even for a "small" motor as defined above, spinning it at twice its nameplate rated speed is going to have a negative effect on its service life- it can't be otherwise. But we've done it, often, particularly with motors driving small positive displacement pumps, and have never had a customer complaint arising from doing so. I felt that this experience was worth sharing, as many are just scared to even try doing things like this and the vendors are not going to allay that fear.