[lazy_mosquito]

Hi,
I have bought 2 cnc routers which were originally used on a 3p 380V net and want to install them on a new location. The net on the new location is 3phase 220V. Now I have 2 options:
Solution 1: installing an expensive step up transformator to create 3phase 380 out of our network and just connect everything as it was. 2 problems: expensive and a lot of loss in the conversion.
solution 2: convert the cnc to 3phase 220V. for the drives and internal electronics no problems, there is already an internal transfo (Juche BK 800) installed that can be reconnected from 380 to 220. So internals are ok, but the spindle and vfd are a problem. the spindle is an HSD at/mt 1073-120 a 3p/380V spindle (which as far as I know can't be converted to a 3p/220V spindle. So my idea was to install a new vfd that converts 3p/220V to 3p/380V. I can't find any decent vfd which converts 3p/220 to 3p/380 only single phase 220 to 3p/380. Any suggestions?

the spindle
Attachment 514084
the vfd
Attachment 514086
the internal transfo for internal electronics, steppers and drives
Attachment 514088

[joeavaerage]

Hi,

So my idea was to install a new vfd that converts 3p/220V to 3p/380V. I can't find any decent vfd which converts 3p/220 to 3p/380 only single phase 220 to 3p/380. Any suggestions?

Unlikely at best. VFDs all rectify and smooth the incoming AC supply voltage and create DC, called the DC link voltage. From that DC voltage it switches very rapidly (many kilohertz) to generate three phase output,
but the rub is that the peak AC voltage can be no greater the the DC link voltage from which it is derived.

A 220VAC input creates a 308VDC link voltage.
A 380VAC input creates a 532VDC link voltage.

There are a number of devices that include a boost circuit in the input rectification, most common for power factor control, and I suppose its not impossible that you might find a VFD that has such a circuit built-in
but would be costly. With very large VFDs, tens of kilowatts, often the power factor control device, in recent times a booster type circuit are available as a standalone and separate unit. Perhaps you might investigate
such a unit, I think however it would be cost prohibitive.

2 problems: expensive and a lot of loss in the conversion.

You are right about cost, but wrong about loss in conversion. A decent transformer will be over 95% efficient. Large distribution transformers in our power supply network are better again, 99% and more. Can you imagine any power
company tolerating buying 100 million dollars worth of electricity only to have 95 million dollars of it to sell because of transformer inefficiency? No bloody way!

To be honest I suspect that any credible boost type VFD, or boost type power factor unit will cost more than a step-up transformer, and with the best will in the world its hard to beat the reliability of a transformer.

Craig

[joeavaerage]

Hi,
another thought that might allow you extra choices is that in effect you don't need 380V three phase, but rather you need 532VDC.

There are a number of servo systems where there was a servo drive for each servo, but it had no power supply. The power supply was a separate module, and that my power two three or more servos.
It meant that the expensive high voltage power supply was shared across multiple servos.

Have a look on your existing VFD, is there terminals for VDC?. For instance all my Delta servo have terminals for the DC link, and thus even if I did not have the correct AC voltage to allow the VFD to rectify
and provide the required DC, but I had a separate DC supply, I could hook that direct to the DC link and the VFD would work normally.

This is commonly how large VFD's are arranged, the VFD in one enclosure and the DC supply in another. This allows you to choose that power supply module to match the available AC supply to the VFD.

Electronics is my thing and so I would probably build a three phase input to boosted DC output, if I could not find a three phase boost transformer cost effectively.

Craig

[lazy_mosquito]

Thanks for the both replies. If i understand you right, i would add an internal transfo only for the spindle with the right dc?

[joeavaerage]

Hi,

If i understand you right, i would add an internal transfo only for the spindle with the right dc?

No, not quite. I would suggest that if you do not have 380VAC three phase to feed your VFD, that you leave it disconnected, but instead feed it with 532VDC at the DCLink terminals on the VFD (if present).
In reality it is the DCLink voltage that the VFD requires to run, and the VFD does not really care whether that is derived form regular 380VDC or your own DC supply. It may be that you can supply the required
532VDC in a simpler or cheaper manner than having a three phase step-up transformer.

Quite some years ago an electronically switching type boost supply would have been considered expensive and complicated, certainly more expensive and more complicated than a three phase step-up transformer,
but in more recent years with the great advances made in high power electronic devices that boundary is increasingly blurred, and may now in fact be cheaper than a step-up transformer.


Craig

[lazy_mosquito]

thanks for the clarification, i understand now, but we will indeed go for the stepup transformator. there is still a cost involved for the dc-suply and with the step up transformator we will at least have 3phase 380 which we can also use in the future to connect other stuff. which is rather easy available here instead of the 3x220V variant.

[joeavaerage]

Hi,
yep, sometimes the easiest and age-old solution is still the best.

I worked repairing welders for some years. Miller decide they wanted to produce a TIG welder of about 250A but able to run on anything from 208V single phase through to 560V three phase,
with 208 single phase being common in the US while 560V three phase being used in Canada. This required a pretty sophisticated input rectifier and supply.

The input, be it three phase or single phase, was rectified but immediately boosted to 800VDC. This meant that any reasonable input voltage (208 thru 560V) would result in an 800VDC link
voltage which was then used by the inverter welder. These were very impressive piece of work, and remarkably reliable. They did of course break down and so I became reasonably adept at
fixing them, but you had to be extremely careful. The DC link capacitors were charged to 800VDC, and one hit from those and that was the end, the probability of survival is virtually zero.
These Dynasty model welders have done amazing work over the years, and plenty of them in service still.

Craig