Autotransformer for 575VAC to 400VAC?

One of the problems with autotransformers and YY is they are almost transparent to harmonics. A ∆Y acts as a harmonics filter but unfortunately it costs more.

If harmonics are not a problem to the supply system then an autotransformer is fine, otherwise go for ∆Y. But as you are selling these items to be used on unknown systems go for ∆Y.

I have seen a similar approach taken for high current primary injection testers for LV circuit breakers. For example, the units made by Megger® require 460V, but many customer sites have only 208V, 230V, or 575V. Megger sells a small, portable autotransformer with taps for the various voltages so that you can step the supply up or down to what the test set needs.

I'm sure there are manufacturers of dry-type autotransformers that could meet your requirements. I would recommend contacting people like ABB, Schneider, or Eaton as a starting point.

If the machine is entirely on 440/3/60, just transform the entire machine with a step down transformer from the 575/3/60 supply voltage. I have several pieces of European equipment in my shop which I have done this for(440, 480 and 240 three phase) and have had no problems. You will need to know what load(VA or KVA) the machine has to get the correctly sized transformer.

The step-down transformer solution is what we are trying to navigate away from, it was way too expensive and heavy.

The previous designs used a (cheap) 240V drive which was able to accept either single-phase or 3-phase supply, and a motor wound for 240V operation. A transformer handled the higher-voltage supplies, dropping them 240V.

We now have an offer from a major European drive manufacturer for a single drive that will accept anything from 240V single-phase to 460V 3-phase as the supply. When you are buying drives in reasonable production quantities, the manufacturers are a lot more helpful about supplying something that is just a little outside their normal offering, and that is what has been done here.

We are attracted to the autotransformer approach because it appears to be a technically valid solution which would cut some of the ugly fat out of the BOM for these machines. It appears from the responses so far that provided the drive harmonics are dealt with, a CSA-approved autotransformer may well be the answer.

"We now have an offer from a major European drive manufacturer for a single drive that will accept anything from 240V single-phase to 460V 3-phase as the supply. When you are buying drives in reasonable production quantities, the manufacturers are a lot more helpful about supplying something that is just a little outside their normal offering, and that is what has been done here."

I would still be willing to bet there is some sort of misunderstanding going on here, but honestly, I'd be really interested in knowing who this is if I'm wrong. I still think the supplier is referring to a model SERIES of drives that covers that voltage range, but not a SINGLE specific drive that you can connect to any voltage in that range without the over sizing I mentioned. I know one mfr who has a voltage input range that can be programmed to go down to 50% of the maximum, although they don't advertize it that way because it created problems of misinterpretation. So if you have a 2.2kW motor, 2.2kW at 240V single phase is 17A, whereas 2.2kW at 480V is only 4.8A, therefore you would have to buy a drive sized for 17A at 480V to make this work. That's going to be an expensive drive when you go for the 480V option. Still, maybe that's better than the transformers?

By the way, that drive will NOT accept 200V for Japan, nor 208V for here in the US. Maybe that's not important for your marketing people though; there is not a lot of mining in Japan, and not many mines use 208V here (although if it's a lab machine, labs sometimes are in offices, which might be 208V).

"One 'problem' voltage is the Canadian 575V supply. VFD manufacturers bork at this, they can do a VFD that will accept anything from 240V single-phase to 460V 3-phase but for 575V it needs a different drive."

Actually, there is a slight flaw in your statement here. I do not know of any single VFD that will accept any input voltage from 1phase 240V through 3phase 480V. Maximum voltage ratings have to do with the blocking voltage capability of the drive, so that means for this to be true, you would have to start out with a 480V rated drive to be capable of 480V. So let's then say you find one that can accept an input voltage down to 50% of the unit rating, which is extremely rare. That ostensibly gives you the 240V 3phase rating, but the CURRENT of the motor will double. So for a given power size, you would have to start with a drive that is rated for 2x the current capability it would need at the highest voltage possible. OK, let's say that is done, but now you throw in the possibility of 240V single phase input. That then means that the rating at 240V must be doubled to accommodate the diode current increase and the necessary added capacitance for the higher ripple, which now means your drive must be sized for 4x the current rating of the same motor at the highest voltage possible. Even if such a beast existed, and I don't think it does, this to me would be economically unfeasible.

So the more likely possibility is that your company uses one drive that handles 240V, and can take 1phase or 3phase input, very common at 2.2kW and below, then uses a DIFFERENT drive of the same make and model (for consistency in programming) for 380-480V input, which would only be sized for 3phase. Again, no problem.

The REAL problem then is just that your preferred drive supplier, likely Asian, has a poor product offering for North America, where 600V is possible (in more than just Canada by the way). Companies that REGULARLY do business in NA have 600V rated drives available in all of their product lines, often with little or no price premium. In addition, many of those can accept an input voltage as low as 380V, although one would need to size the CURRENT rating for the possibility of a 380V input, so the drive would be slightly over sized for a 600V motor. So in reality you could still have only two different physical drives offered on your machines, one for 240V (and by the way, size it for a possible 200V input to cover everything), and another for 380-600V.

I know this exists, my company makes them, but decorum prevents me from using this forum to advertise without solicitation. If you ask however, I will point you to them with a link.

I'll have to get back to this in the new year once I have seen some specifics, it is the last day of work for the year and everyone's gone home.

It is quite possible that I have been misinformed about the single-drive solution, but that was most definitely what we were looking for and what I was told had been offered. The thing is, our customers can, and frequently do shift this equipment from site to site around the world. And they expect it to work on whatever supply voltage from 240V single-phase up to 575V 3-phase happens to be available.

A couple of pertinent facts : The machines run off either 2 out of 3 phases or 1 phase and neutral (+E). The motors are 2.2kW 3-phase induction motors wound for 240V delta operation.

It wouldn't surprise me much if these drives on offer were being done by over-framing the rectifier of the drives. The economics will allow a bigger spend on the drive if it cuts the transformer cost and weight.

If only we could get a drive that would take from 240V single-phase to 575V, the transformer could be eliminated entirely.

So you are always using the same 240V motor, even if the line voltage is 480V?

If that's the case, and they are giving you a 480V drive rated for the 240V single phase service I can see how someone unfamiliar with the issues might think this is possible. But there may be a problem with this that your supplier is not telling you.

When you use a VFD it is rectifying the line to DC, then using the transistors to fire the DC in pulses that make the motor THINK it is getting AC. Those pulses are ALL going to be at the maximum peak value of the DC bus, the way it regulates the RMS voltage, PWM, is all about the WIDTH of the pulses, not the height. So although the RMS voltage that the motor THINKS it is getting can be made to look like 240VAC, in reality if the input voltage is 480V, the DC bus will be about 676VDC, so all of the PULSES that go to the motor will be at 676VDC as well. On a 480V motor, this is fine, they are made for that. On a 240V motor, not so much. You could damage the motor windings in a matter of weeks.