Author Topic: Three Phase Motors, Single Phase Power  (Read 4892 times)

Cary Austin

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Three Phase Motors, Single Phase Power
« on: July 30, 2008, 07:40:14 AM »
The evolution of VFDs has certainly been interesting, I remember being blown away the first time I saw one over 40 years ago, before that it was either DC or very expensive Schrage motors. Is it just me or are the modern VFDs much harder on motors than the early SCR based designs, I don't recall special motors or cable length as an issue even 20 years ago.

BTW, how many 3 phase VFD motors do you have in your house? I have a F&P washing machine with no gearbox. The 3 phase 28 pole permanent magnet motor directly coupled to the agitator swishes back and forth just like a regular washer only without all the mechanical clanking.

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Cary Austin

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Three Phase Motors, Single Phase Power
« Reply #1 on: July 30, 2008, 07:40:58 AM »
Yes, OEMs are volume users of VFDs. Washing machines and HVAC - especially air conditioners are huge applications. And, a whole new generation of jacuzzis is emerging.

If VFDs are tough on motors? You bet. The earlier thyristor designs and GTO designs had slow switches. The new IGBT ones are much faster and kill windings and bearings. It is so bad that that is my main occupation nowadays. I will even be running a seminar on bearing problems (EMD) caused by VFDs this fall (sorry, in Sweden - and in Swedish, so it won't of any use to you fellers).

You don't seem to have anything against my mentioning about the two-phase thing? Actually, that is how induction motors started. Tesla's first system was a two-phase, 90 degree system. So the thought isn't really new. But newish.

Cary Austin

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Three Phase Motors, Single Phase Power
« Reply #2 on: July 30, 2008, 07:41:40 AM »
I expect IGBTs must have some advantage over thyristors otherwise why are we putting up with them "killing windings & bearings".
Yes I read several books on Tesla, what a facinating character. I wonder how he would utilize the advances we have today.

Cary Austin

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Three Phase Motors, Single Phase Power
« Reply #3 on: July 30, 2008, 07:42:16 AM »
VFDs are being incorporated into a lot of home appliances now. They are just using small 3 phase motors. Most appliance motors are custom made anyway, so they just make them 3 phase. Not a big deal really.

Cary Austin

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Three Phase Motors, Single Phase Power
« Reply #4 on: July 30, 2008, 07:42:52 AM »
In Europe there are huge restrictions on the high volume domestic use of the traditional concept of VFD's due to EMI and harmonic controls. Single phase into a 3-phase diode bridge rectifier introduces very high triplen harmonic distortion and this is a key area for the power supply companies and general "energy Efficient building' trend to focus on. It requires large inductors or other mitigation techniques to reduce the harmonics and then there are the filter techniques for the High Frequency interference levels. All the restrictions add huge amounts of cost into the traditional methods of frequency control.