Transformer

Is it a 480 vac step down transformer to 220 vac?

You will have taps on the secodary side where you will have 110 and 110 vac. these will give you 110 (120) on each phase to neutral( L1,L2,L3) and 220 (240) phase to phase ( L1, L2 ) Mostly used are higher voltages, now ( 277/480) less amps are used more efficiently. A delta transformer is needed for higher voltages But a Wye connction will give you more choices more amps used/required

If you have 415VAC 3ph delta, then the unconnected phase will have 415V to either of the other two phases. For voltage on a wye connection, divide by square root of 3.

If this is a high power transformer, leaving one phase unconnected could present a problem due to an unbalanced load. You might need to shift some other loads around so that each phase is supplying the same power. If it's smaller than, say, 3KVA then I wouldn't worry too much about load balancing. It's not the most efficient use of power but it's not going to blow anything up.

Dear Guest!

Whenever the transformer is fully loaded, the primary winding willbe burnt out.

Please do not do such a mistake!

Peter

Providing 2 phases out of 3 on the primary simply reduces the entire transformer to a 2 phase in/ 2 phase out. This will not present any problem electrically.

The voltage measured at the un-connected primary terminal represents the half-way point across 2 equal coils that parallel the actively energized coil and thus will voltage divide to about 1/2 of the 415v.

I am assuming that if the transformer was supplied with all 3 primary phases, there would be 3 secondary phases = 24 vac, though that was not the statement. Either way, only one 2phase output will be available at 24 volts. Due to internal connections, the other 2 secondary 2phase connections would measure in at around 12vac.

Regards, CJM

There is no such thing as "A transformer with 3-ph 415 V primary & 2-ph 24 V ac secondary."

Anyway, this is obviously homework & anybody who provides detailed answers is not not helping this person.

Dear, There is such kind of thing since, i am using at my factory. Yet, i haven't faced any problem with the arrangement.

Well dear, I'll bet that it is not a "transformer"!! It may have a transformer in it...along with some electronics.

Again, there is no such thing as a transformer that can convert 3 phases to 2 phases. For example, the input of the transformer is 3 wire & the output of the transformer is 2 wire AND it does not contain any electronics.

Best example is 3 phase arc welding. If 1 ph is removed you get normal voltage but as you apply load then only voltage will drop. If current is low you can still use with just 2ph.