Help! Having trouble with OPEN DELTA 3 Phase Connection

Thread Starter

MH Ating

Joined Feb 9, 2016
A 3 phase load of two 50hp, 440v, 3phase motors is to be supplied by a transformer connected in Open Delta on a 2300V Line.
Assume a motor efficiency of 90% and a lagging pf of 85%.
a. Determine the KVA capacity of each transformer and their transformation ratio.
I started as 2 x 50 hp = 100hp = 74.57kw
if i consider 1 motor only, i have 37.285kw
Efficiency = Pout / Pin

I = 74.57kw / ((square root of 3) x 440v x 0.85)
= 115.1

How would i use the value of Efficiency?
Efficiency is going to tell us how much of the power going in is actually going to be converted into usable power out.

Therefore, Power(out) = Efficiency × Power(in).