Question

Mr. Alex is preparing laboratory report for BEE2123 course. He is reading his friend’s report as reference and trying to understand it. The report mention that based on calculation of the data from the no load test, short circuit test and dc resistance test on 25 hp, 450 V, 50 Hz, 4 poles, Y- connected 3-phase induction motor, the following are the parameters of the motor: Rs = 0.55 Ω RR’ = 0.75 Ω Xs = 4.5 Ω XR’ = 8.5 Ω Xm’ = 27.2 Ω fr = 11.5 Hz The total rotational losses constant at 500 W and core loss is neglected. Based on the analysis, the following data are presented in Table 1. No mention on the slip in the report thus Mr. Alex comes and seeks your help.

Table 1

Parameters	Calculated Data
Rotor speed, nr	1470 rpm
Power factor, p.f	0.65
Mechanical power, Pm	4835 W

Based on the above-mentioned description,

i) With the details of calculations, justify whether all the calculated data obtained by Mr. Alex’s friend were right or wrong. Briefly comment on the results. If you found that Mr. Alex’s friend calculated data were wrong, provide the corrected data.

Otherwise, determine

ii) The efficiency of the machine

iii) The mechanical torque

iv) The output torque

Answer 1