i have plenty of 3 phase 220 in my shop, but one of my machines requires 440 3 phase. i was going to use a 75 kva transformer with 440 primary 220 secondary in reverse to supply the machine. it is a 15 hp motor 40 amps. i figured my minimum kva requirment to be 37.5 but more cant hurt for the potential high cutting rates i may need to achieve. i simply wanted to buy the transformer, hook the 220 3 phase supply to the primary, and the output to my machine. I think this will provide me with 440 output. the motor plate says 7-1/2 hp/15- hp. 40/20 amps. Any help is welcome, i hate to buy the transformer and not have this unit work. i would change the motor wiring, but the diagram is gone, and the wires are not numbered, also i believe id have to change all the heaters, which are hard to come by, as well as various other parts in the panel. just seems the transformer is the easiest way to get this machine up and going in prouction.
Welll yes and no. The voltage ratio reversal is OK but one must remember that when going from 220 to 440 the amperage is cut in half in availability and when going from 440 to 220 the amperage is doubled in availability. Now here comes the NO partyou specified three phase.make sure that's what your input and output are and a 220 is generally wired star with a center tapped ground or delta with a corner ground. Look at the x-former before wiring it up it should have a schematic showing the connection details. Also in transformer reverse hookup with existing equipment make sure the secondary (440 side is large enough to do the work) . Like i said before you will get a loss in ampacity from 220 to 440 .here's is how to calculate it.P(watts) I(amps) x E(volts) x 1.732(sq rt of 3) just substitute in 220 and 440 in for the same wattage you stated (75,000) and solve for Ior you can look it up there are lots of transformer handbooks which explain ratios and transformer wiring out there.One of my favorites which you must purchase is called the Ugly's book of electrical facts. Sounds odd , has lots of good stuff in it for electriciansFrom the E.
The only real problem you have to worry about is the capacity of the primary winding to supply enough current for your needs without burning up. That information should be on the transformer. Otherwise, transformers work both ways!
transformers can either be step up or step down, it will surely work.
The main disadvantage of using a transformer with a motor is the high starting current in the neighborhood of 600% of rated full load current. The transformer impedance will cause a significant voltage dip on the secondary of the transformer when the motor is coming up to speed. Using an oversized transformer will probably take care of that. If this is some type of cutting tool, I assume that it is never started with the cutting head in contact with the load. That will also help. Edit 1 You should also consider provisions for grounding the load side. The secondary should be wye connected so that you can ground the neutral. That means that you should buy a wye-wye transformer so that you can use the low low vlotage side as the primary and still have a wye secondary.
