The descriptive plate (“la plaque signalétique”) of the induction motor of a milling machine shows the following indications:
3 ∼ 50Hz ; Δ 220V 11A; Υ 380V 6,4A ; 1455tr/min cosφ = 0,80
1- This motor is supplied by an electric grid 220 V / 380 V; 50 Hz. How do we have to couple the stator windings of this machine? Justify your answer.
2- Give the number of poles of machine stator.
3- Calculate the nominal slip gn (in %).
4- A no-load test (“essai à vide”) was performed for this motor powered by the grid mentioned above. We obtained the following results:
– No-load current : I0 = 3.2A
– No-load absorbed power : Pa0 = 260W
We neglect the joule losses of the rotor at no-load: Pjr0 . The mechanical losses Pmec are evaluated at 130 W.
The warm measurement of the resistance of a stator winding gives Rs = 0.65Ω. Deduce the iron losses in the stator at no-load : Pfs0.
In the following, we will consider that the iron losses in the stator is constant and equal to Pfs0.
5- We perform a test in the nominal conditions of the machine:
a) Calculate the stator joule losses Pjs b) Calculate the joule losses in the rotor Pjr
c) Calculate the useful torque Cu of the motor d) Calculate the efficiency of the motor η