Delta Autotransformer

[roskel]

I am currently involve installing power for a European machine that requires three Phase 380V. The original owner had a three phase 480V primary 208V secondary Delta ? Y transformer connected to an Autotransformer that stepped up the voltage from 208V to 380V.
I want to supply the autotransformer with 240/120 Delta to get the required 380V. The Autotransformer appears to be configure as an ungrounded Y. Is this going to be a problem with the supply being 240V Delta.

 

[templdl]

If I am interpreting you post correctly these are voltages that can be applied through use with an autotransformer? The voltage to be transformed is to great to make an autotransformer application practical. The voltages as you have stated are most likely that of a common transformer application.
The advantage of an autotransformer when properly applied is a great deal of cost savings because you only need enough va to make up the voltage difference. The down side is that there is no isolation.
With the voltages that you have stated there would basically be no advantage to try applying an autotransformer.
I'm not saying that you don't have an autotransformer setup but that it is uncommon at those voltages.

 

[frenchelectrican]

the other issuse you probly overlooked on this one with european stuff that majorty of european stuff do run at 50 HZ and try to run on 60 HZ.

somehow it will going affect the electric motor if have in there useally speed up but watch the hp rating and nameplate for derating or current limit to prevent overcurrent along the way.

If electric heating stuff like heating element [ restanice type ] genrally dont affect the HZ but voltage it will do some effect there.

if my memory serve me right [ please do correct me if i am wrong here ] the 380 [400 volt] 50 HZ system is very simuair to 480 volt at 60 HZ.

as i mention here again i will stress this again please do check the nameplate on motors and transformer etc to make sure it is ok


Merci. Marc

 

[jim dungar]

What voltage does your machine really need 380V 3-wire or 380Y/220V 4-wire?

In this area it would be common practice to use a single transformer from 480-380Y/220 instead of two transformers.

But to answer your question. Yes, you can use a wye auto transformer on a 4-wire delta system as long as you do not ground or use the "neutral" on the secondary side.

 

[roskel]

The machine requires three phase 380V 3-wire. My intentions are to remove the 480delta/208Y transformer that is connected to the 210V taps of the Autotransformer. I will then connect the building 240/120delta supply to the 240V taps on the Autotransformer and remove the ground wire that is connected to the "Neutral". (Previous installer tapped a wire to the "Neutral" center of the autotransformer and ground)

 

[cduranph2006]

if my memory serve me right [ please do correct me if i am wrong here ] the 380 [400 volt] 50 HZ system is very simuair to 480 volt at 60 HZ.

You're right for this 400V, 50Hz and 480V, 60Hz for 380V, 50Hz that is not similar to 480V, 60Hz. As long as you'll be able to maintain the V/f ratio, there will be no changes in the performance of motors, because flux and torque are very dependent on that ratio. For transformer, eddy current might be changed as the frequency is dependent to change in frequency. Remember that transformer is operating by induction.

Charlie D.
________________________
Project Sales Engineer
Schneider Electric Phils.

 

[cduranph2006]

if my memory serve me right [ please do correct me if i am wrong here ] the 380 [400 volt] 50 HZ system is very simuair to 480 volt at 60 HZ.

You're right for this 400V, 50Hz and 480V, 60Hz for 380V, 50Hz that is not similar to 480V, 60Hz. As long as you'll be able to maintain the V/f ratio, there will be no changes in the performance of motors, because flux and torque are very dependent on that ratio. For transformer, eddy current might be changed as the frequency is dependent to change in frequency. Remember that transformer is operating by induction.

Charlie D.
________________________
Project Sales Engineer
Schneider Electric Phils.