360~400V power from 480V

[itsmoked]

Guy's got a 3 phase euro power supply for a bizarre machine that requires 360~400V and all he's got now is 480V. I was thinking that since this is only about a 17% difference some buck/boost magic might work. But alas, i'm not seeing it.

About 30A output is needed.

Any suggestions?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[iop95]

If machine use as main power a rectifier (controlled or not) need to check DC bus capacitors voltage rating and if at DC bus are connected all other loads by SMPS, such voltage input difference may be compensated by SMPS controllers.
If machine use some transformers inside, 17% higher voltage may be too much, so need to be replace them.
If machine modifications are not allowed or too complicated, auto-transformer may be a solution.
One input filter with high voltage drop (3-5%) or two cascaded may be explored if power losses level will be accepted. These with hope that a lower voltage difference will be tolerated by machine.

 

[xnuke]

There are three-phase 480-380 V transformers and autotransformers available according to a quick internet search. You could also roll your own: use three single phase 480-120 V transformers that you connect in a buck autotransformer configuration to get 360 V. My concern is 60 Hz ok instead of 50 Hz? If there are DOL motors or other frequency-sensitive devices in the machine it might not be.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[che12345]

Mr itsmoked (Electrical)(OP)16 May 23 06:47
"... a 3 phase euro power supply for a bizarre machine that requires 360~400V and all he's got now is 480V. I was thinking that since this is only about a 17% difference some buck/boost magic might work..."
I look at it this way, for your consideration
1. The European machines is rate 3-phase 360-400V 50Hz. Your power source is 3-phase 480V 60Hz.
2. The 50Hz machine would be suitable for 432-480V 60Hz.
Attention: the motor would run faster by a factor 60/50 Hz = 1.2 .
3. Install a 3-phase 480V 60Hz delta primary with 3-phase 480V with 432V, 456V taps in Y formation secondary.
Che Kuan Yau (Singapore)

 

[waross]

Hi Keith.
You know that I am going to say;
"Auto-transformers."
Two xfrmrs vs three xfrmrs?
Two transformer:
Often cheaper, but not always.
Full system available fault current on one phase, fault current is limited by the auto-transformers on two phases.
Neutral offset.
Will work on three wire circuits.

Three transformers:
Unbalanced loads may cause unbalanced voltages on three wire circuits.
Some cases may require the wye point to be connected to the system neutral.
In some cases, installing the fourth wire may be an issue.
This connection will supply equal and usable line to neutral voltages when the wye point is connected.
The available fault current is limited by the auto-transformers on all three phases.

For motor loads, the two transformer solution works well.
For loads using line to neutral voltages, the four wire, three transformer may be needed.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

Thanks all!

480/120!!! Don't know why I was stuck in 12/24/32/48V buck land? Well that's why I asked.

Thanks a bunch gents.

iop95; I don't want to get inside of their hardware if at all possible. If it was me doing it I'd consider some internal mods.
A 3 phase Variac might be a good choice as they're compact obvious and seem to be fairly available.

xnuke; Dang. That's probably the deluxe ticket! Thanks,

che12345; I believe there are no motors involved at all so 50/60Hz should not matter. I believe this is simply a rectified front-end.

waross; Greetings! Since this is rectifiers I'm thinking two xfrmrs might put a strain on the diodes or something else so I'm probably suck with three transformers.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

itsmoked: With the transformers on the AC feed to the rectifiers, I don't see a problem.
Given the non-linear characteristics of rectifier loads, I would definitely connect the wye point of a three transformer bank to the system neutral.
Another issue that I failed to mention with three transformers is voltage availability.
For example; for 600:480 Volts you may use 480:120 in auto-transformer connection or 600:120 in buck connection.
Google aside, finding the correct voltages on the shelf for immediate delivery may be difficult.
In our example of 600:480 Volts you would be looking for 277:70V or 347:70V.
The solution is to look for the correct ratio at higher voltages.
In my experience, the choice comes down to cost and two transformers almost always wins.
That said, If two transformers makes you nervous, by all means use three transformers.
Anecdote alert;
On a shut down, 480 Volt rental generators thru auto-transformers to 600 Volt switchgear. From the 600 Volt switchgear thru auto-transformers to 480 Volt rental equipment.
One set of auto-transformers was open delta and the other set was wye.
I don't remember which was which but there were no problems.
I Canada, 480:600 Volt auto-transformers are available from rental yards.
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

Thanks Bill.

This was almost the first thing I came to on epay:

3-Phase Multi Tap Auto Transformer (600,480,400,240,208V)

I suggested they use the 600 -> 480 taps and to make sure they weren't trying to change from delta to wye or wye to delta. Around here we have mostly delta 480 and I could see some euro supply expecting wye.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

That should work well.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!