LV Transformer Voltage rating

Nothing is going to happen. You need to determine what is the proper voltage level that you need at the LV Board. If that level gets too low then you know you have problems at the transformer. If the transformer is close to the LV Board then there is little VD and the levels will be the same.

Thanks so much for your reply. My trafo is connected next to my LV board and there will not be any voltage drop from trafo to LV board. However is there any chance that at full load, due to IZ drop voltage available at the LV winding is less than 400V(rated voltage of the LV system)?. What is the normal practice?

Depends on the distance, load, wire size and transformer size. Why don't you calculate it?

What do u need at yr voltage boad,is it 400v or 415v etc,if yr step down xformer output gives 400v or 415v,okay!.But if yr loads drops yr voltage lower(say 370v),then u can increase yr voltage at the xformer using d xformer tappings to about 430v according to yr expected operating voltage.

Yr xformer output should normally be thesame with yr boad voltage expected b4 purchase,but if higher it is meant to take care of drop in voltage along d line or drop in voltage due to poor power factor of yr loads.Based on what voltage value u require,u can adjust from yr xformer tappings.

Patrick Whowha

Please note that 433V is the Voltage mentioned in the transformer name plate and it is the OPEN CIRCUIT VOLTAGE of the transformer. It would be there only as long as the transformer is not loaded. But, when you load the transformer, there would be voltage drop (IZ Drop) inside the transformer's secondary winding. After this internal voltage drop, the terminal voltage available on a fully loaded transformer is about 415V. That is why your motors are rated in 415V.

If you take the LV winding voltage same as that of the board voltage (415V), then during loading there will be voltage drop in the LV winding and the board will not get its rated voltage.

420V is for equipments manufactured in UK (like a STAMFORD UK Alternator)

400V is for IEC or European Equipments

In answer to yr second question,according to wareagle,why dont u calculate it.However,u dont know yr IZ value on full load for now,do u?

The length and sizes of cables in yr cct and current drawn or full load current will actually determine d IZ drop.But u simply nd to maintain acceptable voltage of yr load at d LV board.If yr loads are rated 380v,400v or 415v,makesure u maintain same at d low voltage bursbar.though d drop may be negligible,but for safety maintain d rated voltage of yr equipment(loads) at d bursbar.If d voltage is low,increase from d xformer tappings by steps until u are satisfied wt d voltage at d bursbar(LV board).

Makesure u maintain at a good level d voltage ratings of yr loads at d bursbar to serve yr loads well.Makesure yr xformer is able to carry yr total load confortably.But if yr loads drop d voltage so low due to poor power factor,and yr xformer tappings couldnt step it up to required voltage,then use power factor correction (PFC) cct to compensate or boost d voltage.

Patrick Whowha