Electrical Design Specifications

How did u arrive at 75kva transformer? How did u get your power factor pf,how did u get your total load current? wt calculation using 480v or 220v?What criteria did u use to select your cable size of 50mm and 125mm for a 53kw total load?

If u are not very sure of your calculated values,consult a professional to do it for u or else provide a detailed information.

Patrick Whowha

- power factor pf= 0.8, P(W)=IV * PF, the light source HPMV = 400 W, V=220 V, I=2.3 A

- transformer size => 75 KVA* PF = 60 KW, 7KW higher than needed KW

- calculation using 220 V

-cable size according to transformer max. capacity = 75 KVA, I= KVA/V, V= 480 Pri. & 220 Sec. => I= 156 A (Pri), 340 A (Sec)

load = 53 KW, but we may add loads in the future so I chosed cable size for maximum use.

- Iam sure about my calculations, but these are all using formulas and theory, I just wnna make sure that i did not miss anything.

reagards

(75,000 VA ÷ 480) ÷ √3 ≈ 90.2 A.

For conductors, 90.2 x 1.25 ≈ 113 A.

For this size of transformer primary CB is also (if memory serves) 90.2 x 1.25; the next standard size is 125 A.

And calculate similarly for the secondary. It looks as though the 1/√3 factor was missing from the original 3-phase calculations.

thanks a lot, i missed that one

I wouldn't rely on the cable rating alone (max amps). The more thorough method would be to make in-depth voltage drop calculations. Your posting indicates that all loads will be on a single circuit. Multiple circuits (multiple contactors and CBs) would lower the load on each cable, reducing min. cable sizes, thus reducing costs.