3 phase motor?

I am not a big expert, but I think that square wave produces move vibration in windings due to its sudden rise, and hence can damage insulation in the long run.

I think that nothing beats a true sinewave for which the motors were designed...

A rotary phase converter is superior from all performance aspects: it can run many machines at once, with the electricity that they were designed for.

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

Getting 3 phase at home is, pretty much, out of the realm of possibility.

When the RPC spins up, the momentary power requirements are much larger, of course, unless it is started with a small pony motor.

Obviously different in the US, from the UK. Here, I asked, and it was only an installation charge for a different distribution unit. The wiring was already present, because the 'standard' here is to run all three phases into the building, and then have each house down the road, on the next phase, to try to keep the loads reasonably balanced.

Best Wishes

call the electricty supply company and say "I'd like to convert to 3 phase elecricity" have your cheque book handy.

It'd probably be easier to replace the motor with a single phase motor.

Bye. Jasen

This depends on the country you live in. I live in Finland where three phase to the building has been for a long time pretty much the norm. The power company feeds three phase power to the house main panel. Then different loads on the house are distributed more or less evenly to those three phases. And then there are some high power loads that use three phase power directly (oven etc..).

Practically everything but the smallest houses get three phase power by default.

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

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.

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

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

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.

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.

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.