3 phase motor?

Sure, but the motor might be on the other end of 20' of wire. The waveform right at the MOSFET or IGBT in the drive will not have the spikes.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Lots of ideas here, but I think ken o's comment, "I also omitted tha I need 550 volts to tun this baby," slipped under everybody's radar

That's a pretty big hooker unless he has 440 VAC service or a step-u transformer capable of transforming the full power demanded by th motor plus reserve. In fact, while I strongly disagree with th comment by another poster that 3-phase conversion at home is no practical, doing it for a 550 volt motor may well be. ken o wil either have to provide a single-phase transformer to transform hi input power to the converter up so the DC bus in his VFD is hig enough to provide 550 volts AC out, or he will have to provide

3-phase transformer between the converter and the motor

The former is reasonably practical, depending upon power requirements

In fact, the manufacturer of the VFD I installed in my garage abou

25 years ago mandated that the input be supplied via a 5 KW isolatio transformer. Such a transformer can as easily be a step-u transformer as the unity-ratio transformer that I installed

The latter is very risky and/or expensive for a several reasons. (1

You need a 3-phase transformer. (2) You are subjecting th transformer to the high rise-time switching transients that can lea to insulation breakdown unless its insulation is specificall designed to withstand them. (3) You CAN NOT use a transformer on th output of a VFD that could possibly be set to lower frequency than th transformer is designed for. The transformer would saturate, leadin to very large currents damaging either (or both) the VFD or th transformer

I have been using a solid-state VFD to drive my 3-phase geared-hea

drilling machine, bench grinder, and Bridgeport milling machine wit complete satisfaction for more than two decades. Before I installe the VFD, I changed the motor on my first milling machine (a Rockwell to single-phase. It worked fine, but changing the motor on th Bridgeport was not an option, and the variable speed of the VFD i extremely valuable, especially for drilling large holes with th drilling machine. No more burned drills

Ignoring the high voltage ken o requires, I strongly recommen

investing in a VFD instead of buying or building a rotary converter primarily to get the variable speed capability. I think that carefu shopping and not going for bells and whistles like an LCD readout o programmability will get you a VFD good for up to about a 1 HP moto for well below US$ 100

The threat of a VFD to motors not designed for "Inverter Duty," i

from the fast transients from the IGBTs or MOSFETs. A couple o things can happen. One is insulation punch-through. An equall damaging, but less obvious phenomenon is capacitively-coupled curren spikes through the ball bearings leading to erosion of the balls an races and ultimate failure. This is not an academic issue to me, a the electronically controlled motor in my new, high-efficienc clothes washing machine failed in less than a year. A post-morte clearly revealed severe bearing erosion. In replacing the motor, lifted the motor ground to interrupt the path fo capacitively-coupled transients to ground via the motor bearings. N subsequent failures for 5 years. (I know that this is a seriou violation of safety codes, but the motor is fully enclosed and I hun BIG warning sign on it explaining exactly what had been done.

awrigh

Rarely, in the US. If you just HAPPEN to live above a grocery store, for instance, then it may only require changing the power entry box and your breaker box, and if they agree to do it, it can be affordable, but still quite expensive.

If not, like me, there is NO three-phase on my pole. I happen to live close to where there IS 3-phase, but it is 14,400 V, and the 3-phase just runs past to another substation. They'd have to run 7000 volts a couple of blocks, and then put a 3-phase breaker on my pole. it would cost thousands of $, if they would even agree.

I know of only one "house" in the St. Louis, MO area that has 3-phase service. I know it has it, because there are 3 transformers on the pole. It is 14,000 sq. ft., and when I first moved into that general region, I thought the thing was the COMMUNITY CENTER it was so big!

A VFD is the best solution now, as a used one may be cheaper than the start and run caps needed for a rotary converter! In this case, the OP needs 550 V, so that is a bigger problem. But, 240 can be stepped up to the required mains voltage for a high-voltage VFD.

Jon Jon

Yes, but the ends of the motor winding are exposed to 400 V square waves with rise times of around 100 ns! Because of leakage inductance in the windings, the end few turns get most of this voltage during the transition.

It seems that running dual-voltage (ie 240/480 V) motors with a 240 V VFD gives adequate protection so problems with the motor windings are very rare.

(The unusual case where the drive faults out under overcurrent can cause some big surges as the transistors just all shut off. The "clamp diodes" may not be very fast or effective compared to the transistor's on state.

One other advantage, especially when running huge motors in the residential environment, is slow starting. A VFD will ramp up the speed of a motor, eliminating the blinking of lights when big motors start across the line. I can see all the lights in my house blink when the garage door opener, disposal, washing machine, etc. start on 120 V single phase. There is NO blink when my milling machine (1 Hp) or lathe (7.5 Hp) start up due to the VFD's smooth start action.

Both machines also have active braking, which stops the lathe in under one second. With any other source of 3-phase, it takes almost

15 seconds to coast down. So, that is a safety bonus with the VFD.

Jon

No. Almost all static converters are electronic 3 phase inverters. Output quality (harmonics, frequency accuracy, etc.,) and reactive load (motor start) capabilities vary with price.

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JosephKK

Correct mostly. All the good and better VFD's and phase converters produce sine waves, including fractional horsepower to 250 horsepower.

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JosephKK

I expect your VFD is producing sine wave (clean) outputs. please check it and report back to us.

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JosephKK

?? Those are usually called VFDs.

Here is a familiar example of a static phase converter:

Note that it only yields 0.5 to 0.67 of rated horsepower.

Here, from another company, is an explanation of what a static phase converter is:

And another one:

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Inductor input on the filter does wonders for harmonics and helps PF, but PFC switchers for 1 kW to 10 kW are better still. 10 HP at 240 single phase is still less than 50 A, no worse than starting every element of an electric stove and oven at the same time. Of course motor start surges are an issue, but successful VFD vendors have taken this in to account.

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JosephKK

In that case you had a crappy VFD + motor implementation. And the VFD in the washer is a piece of crap. do not buy that brand for years and scream at the manufacturer, the press , and all your friends, associates, neighbors, and acquaintances. Selling short lived pieces of crap must be punished.

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JosephKK

Not only that, but they are pretty quick to remove the transformers if the demand drops. I moved a TV transmitter a few years ago, after the station built a new site with a new transmitter. The power company called and wanted their three pad mounted transformers and didn't want to replace them with smaller ones to power the other equipment at the site, or the engineer's house at the site. We finally had to rewire the buildings for standard 120/240 volt service and replace some motors with single phase.

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Michael A. Terrell
Central Florida

In the US they run three phase into a subdivision, then run a single phase down each street, alternating phases from street to street to balance the load. Less wire to run, and keeps it simple to balance the phases.

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Michael A. Terrell
Central Florida