240Volt 3Phase Step up to 480Volt 3Phase?

[Troubleshootinmofo]

I have a client who wants to go from 240V 3Phase to 480Volt 3Phase for some equipment that must be powered at 480V. Cant I just reverse wire a 480/240V 3Phase xfmr to get the desired voltage? The xfmr is 75KVA so I believe that the overcurrent protection on the 240V primary actually needs to be 225A to get 100A of 480V? Anyone know if this is correct? Thanks

 

[Dennis Alwon]

Yes, it can be done but the transformer should be rated for it. I really don't know much about this but check out this PDF

 

[augie47]

The actual output of a 75kva would be 90 amps I believe. They are designed for some overloading. I don't know if your 100 amp load is actual or continuous, but keep in mind a transformers enemy is heat.
Your 225 amp breaker would be correct for 240 volt at 125% rating.

 

[kwired]

If reverse wiring do not connect anything to the X0 terminal, just input 3 phase conductors. You also are likely to not have a H0 terminal, which means you will probably will need to corner ground the output. Make sure if input voltage is 240 that the low side of the transformer is rated 240 and not 208.

 

[templdl]

If reverse wiring do not connect anything to the X0 terminal, just input 3 phase conductors. You also are likely to not have a H0 terminal, which means you will probably will need to corner ground the output. Make sure if input voltage is 240 that the low side of the transformer is rated 240 and not 208.

240v 3ph is usually a delta and as such does not have a neutral except if it has been build as a 240 wye for the secondary of a drive transformer. As such the transformer most likely is a 480v delta to 240 delta which can be easily feed in either direction. The only issue is that the taps on a common transformer built as a step down transformer will be built with the taps on the HV windings because they are on the outside with the LV winding on the inside next to the . When used as a step up the taps are now on the load side which may be somewhat confusing to configure.
A 240d-build is built with the LV windings on the outside which allows for the taps for the taps to be placed on the LV windings.

 

[kwired]

240v 3ph is usually a delta and as such does not have a neutral except if it has been build as a 240 wye for the secondary of a drive transformer. As such the transformer most likely is a 480v delta to 240 delta which can be easily feed in either direction. The only issue is that the taps on a common transformer built as a step down transformer will be built with the taps on the HV windings because they are on the outside with the LV winding on the inside next to the . When used as a step up the taps are now on the load side which may be somewhat confusing to configure.
A 240d-build is built with the LV windings on the outside which allows for the taps for the taps to be placed on the LV windings.

If the transformer has one phase tapped for 120 volt loads (a high leg delta) you would want to leave the X0 terminal float, and disconnect any existing bonding jumpers from X0 if there are any connected when backfeeding a step up transformer.

 

[templdl]

If the transformer has one phase tapped for 120 volt loads (a high leg delta) you would want to leave the X0 terminal float, and disconnect any existing bonding jumpers from X0 if there are any connected when backfeeding a step up transformer.

Yes,I agree. I may have missed something but the response has deviated from the Op stating 480 and 240 which infers a basic 480d-240d step down being used as a step. As such there would be no X0 as there would be with a delta with a 'lighting tap' that's why I didn't want to add any confusion to the issue.