Three phase motors and equipment design. WHY?

[Eltigrechino]

Hello all,

At our shop we have a benchtop size piece of mixing equipment that uses a 3 phase motor (Machine 1). The equipment's power entry is 220V single phase, but inside the machine (from what I've been told) there is a Variable frequency drive that converts this single phase power into 3-phase power for the motor. We have another very similar machine (Machine 2) that performs the same function and also has a 3-phase motor. The difference is that Machine 2 requires a 3-phase supply directly from the outlet. Machine 2 is a much higher quality, German engineered, and overall better machine compared to the Chinese built Machine 1.

It seems to me like the much nicer option is to have a VFD inside of the of the machine to convert from single phase into 3-phase power, than to need an outlet for 3-phase power which requires an electrician to install and is costly to the consumer. So my question is:

Why does Machine 2 require a 3 phase outlet connection instead of converting the power internally like Machine 1 does? Can anyone tell me the benefits to this design? It seems like there is a big disadvantage for the consumer to have to hire an electrician to use this type of equipment, and therefore can be limiting to sales.


Thanks

 

[davidbeach]

Machine 1 is cheaper to install if all you have is single phase. Machine 2 will be less expensive to run because it won't have all of the losses associated with the VFD. If 3-phase power is available, as it is in many commercial and industrial establishments, and the equipment runs at a constant speed, machine 2 will be the better option.

 

[jraef]

We are going to assume here that the aspect of being able to vary the speed does not play into the functioning of the machine.
If so, it costs less for the Chinese mfr. to just design it around a 3 phase motor and let the consumer deal with the consequences. Single phase motors cost more and are larger / heavier for the same mechanical power capability, plus have more reliability issues (although usually not an issue with regard to surviving a warranty period) compared to 3 phase. In addition, the Chinese machine would need to possibly have two different versions, one for countries that have 50Hz, a different one for countries that have 60Hz. But in my experience they actually do NOT do that and the motors are 230V 50Hz, so they leave that issue up to the buyer to sort out after the fact, much to the chagrin of installing electricians who usually end up having to swap out the motor. Bottom line, the "bargain" is not always as much of a bargain as it appears.

The German mfr. is providing a more flexible installation option to their user; their machine can be installed where there is single phase, or where there IS 3 phase available. It also allows for it to be installed anywhere in the world, because regardless of the frequency being 50Hz or 60Hz, the machine runs exactly the same.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

I understand that the Chinese machine has the VFD.
The importer may have added the VFD to make the machine more saleable in the US. The importer may have, in the past, had issues with customers having difficulty powering a 50 Hz motor with a non standard (In the US) voltage and had the manufacturer add the VFD. It's a nice solution.


Bill
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"Why not the best?"
Jimmy Carter

 

[jraef]

Huh. Yeah, I got that backward for sure. End of a long day...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Skogsgurra]

Thee phase is extremely common in Europe. Even small one family houses, like ours, have three-phase installed.
So, European machinery very seldom use VFD:s - unless it adds to functionality.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[LionelHutz]

It's cheaper not to install a VFD.

I'd also tend towards the most likely explanation for the Chinese machine to have a VFD is to match the motor frequency to the local power supply frequency.