380/60hz motor on 380/50hz circuit

[toastedhead]

So knowing what I know about electric motors, which is nothing, why wouldnt this work with a VFD? Can I just "turn the knob" on the VFD to give the motor the 60hz its looking for to negate the 17% loss I would normally occur without a VFD?

My bet is its not that easy since nothing is that easy.

 

[LionelHutz]

Yes, you can use a VFD as a frequency converter.

 

[ScottyUK]

If the VFD is configured for a 60Hz motor and produces 380V at 60Hz then no problems, provided that the load is suited to VFD operation.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Scotty what does that mean?

Is there a single load that couldn't be VFD run? Note: I'm asking 'couldn't' not 'shouldn't'.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

That's a key difference! It probably leads into how long before it fails...

Some bearings don't behave well at low speeds - white metal types can't form the oil wedge or example - and anything which drives its own lube pump from the main shaft may not be too happy with prolonged running at low speed.


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If we learn from our mistakes I'm getting a great education!

 

[rmw]

To the OP, are you sure it is a 380V 60 Hz motor? That seems unusual. 460 or 480V 60 Hz is more common, and if one of those, then the answer is different for running that motor on 380 V and was given in a recent thread in this forum.

In other words, if you are running a 380V 50Hz motor at 60 Hz, search for the recent thread on this topic.

rmw

 

[waross]

Where in the world are you?
Are you sure that the motor is rated for 380 Volts at 60 Hertz? Much of the 60 Hz world is also NEMA world and NEMA standard motor voltages are multiples of 115 Volts.
115 Volts
230 Volts
460 Volts
575 Volts
380 Volts at 60 Hz is not a standard voltage.

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

 

[toastedhead]

Yeah Im sure. Here's the deal. The motor is going to CHina. They are 380/50Hz std.

The issue is I already this motor in 60hz. Buying another explosion proof motor in 50hz clothes means going up a frame size and adding 2000 bucks to the cost. If I can save about $11k - I would like to.

 

[LionelHutz]

Make sure the motor maintains it's explosion proof rating when operating on a VFD then.

 

[toastedhead]

The motor is inverter duty rated.

Im hung up on this. Since HP is calculated by (Eff X V X Amps)/746 I wouldnt be losing any HP when hooking this motor up to 50hz. I would still lose torque though because I would lose speed BUT if I make the VFD provide the motor with 60hz then I should be running the motor as it was designed right?

 

[waross]

As ScottyUK posted

provided that the load is suited to VFD operation.

What will the motor be driving. I know that some loads need encoders for VFD operation. I will have to do some research to find the details. But if you tell us what you are driving our VFD gurus will probably post some good information.

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

 

[toastedhead]

Its driving a 1.95 speed down gearbox which in turn will be driving a set of 2 extruder screws.

 

[LionelHutz]

No, the calculation doesn't work that simply. You can't "specify" the motor current and efficiency. The motor characteristics all change when the frequency changes.

You either have to de-rate the motor or use a VFD to get back to 60Hz.

 

[jraef]

Maybe you are not fully grasping what is being said, I'll give it a shot.

A motor is DESIGNED around a voltage and frequency and thereby the RaTIO of the voltage and frequency becomes critical. If you mess with that ratio, you mess with the motor's performance and capabilities.

You said this is going to China, they are 380V 50Hz. No problem.

But you ALSO said that you have a 380V 60Hz motor. That is what we are saying is unlikely. There are only a small number of countries that actually have 380 or 400V 60Hz power; Brazil, parts of South Korea, parts of Tahiti, parts of Suadi Arabia, the Philipines and several of the Leeward Island Nations of the Carribean. With the exception of Brazil and South Korea, most of those countries do not manufacture motors for export, and the two that do make the 380V 60Hz versions pretty much just for domestic use. So if you do indeed have one, it's an oddball.

But if you investigate it, a 460V 60Hz designed motor has a V/Hz ratio of 7.67:1, and a 380V 50Hz motor has a V/Hz ratio of 7.6:1, so close we consider it the same. Those motors will each put out the same torque. So if you have a 380V 50Hz supply, you can use a 460V 60Hz designed motor just fine. But it will spin 17% slower (50/60) and therefore put out 17% less power (same torque, lower speed). BUT THE TORQUE REMAINS THE SAME in both cases.

So if your motor is doing work that is related to torque, you don't need to do anything. If the work is directly related to POWER, as in kW or HP, then you have to do something; it all depends on the type of load you have. Screw Extruders tend to be torque related loads, meaning you are not necessarily sizing the motor to maintain a particular speed, you are more concerned with having the right amount of shaft torque at the opearting end of your gearbox. You may end up extruding a little slower, but you will not stall the motor.

Now a SEPARATE issue brought into the fray by ScottyUK is that, REGARDLESS of the fact that it is an "Inverter Duty" motor, the regulations for "Explosion Proof" applications in some countries require that SPECIAL motors be used for inverter use in explosive areas. We don't have those rules here in the US, so you may not have been aware of that. But ScottyUK, being NOT in the US, is giving you fair warning that this may in fact rear up to bite your backside when it arrives in China, where the solution will cost you FAR more than whatever you have to spend here to deal with it ahead mof time.


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[controlsdude]

I thought there was another post on here about what regulations does China follow as it relates to explosion proof.

jref
I noticed this on a lot of motor nameplates. Most motors I see have a 50/60hz stamped on them. So I assuming the motor is made to work at the lower freq since it has to be bigger in size for ths 50hz frequency.

So basically the poster could of bought a explosion proof 460vac motor, and just raised the frequency on the VFD to get the necessary speed out for this torque application?

 

[waross]

You must be working on a lot of small motors, less than one horse power. Once you get into industrial sizes, (most motors above one horse power and probably everything above 10 horse power and just about anything three phase) you will not see a dual frequency rating. It is common to see dual frequency and voltage ratings on the coils of motor starting contactors.

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

 

[rmw]

Unless you pay extra for it.

rmw