PPT Slide
Section 13.11: Losses and Efficiency cont.
A 230 V., 10 hp shunt motor draws a full-load line current of 40 A. The armature and field resistances are 0.25 W and 230 W respectively. The total brush-contact drop is 2 V. and the core and friction losses are 380 W. (total). Calculate the efficiency of the motor assuming the stray-load losses are 1% of the motor’s rated output.
The input power is Pin = VtIline = 230V.´40A. = 9.2 KW
The (shunt) field circuit losses are Vt2/Rf = (230V.)2/230W = 230 W.
The armature losses are Parm.loss = (Iline - If)2Ra = (40A. - 230V./230W)2´0.25 W = 380.25 W.
The core + friction losses are 380 W. and the stray losses are 0.1 hp (1% of 10 hp) which is 74.6 W.
The brush-contact losses are Vb-c´Ia = 2V.´39A. = 78 W.
The total losses are 1142.85 W. So the output power is Pin - total losses = 8.05715 W. and the efficiency is (Pout/Pin)´100% » 87.58%