Question
A 22 kW, 3-phase, 415 V, 40 A, 50 Hz, 960 rpm, 0.88 PF squirrel cage induction motor drives a pump. The total inertia of the drives system is 1.2 kg-m2.
Determine the number of starts per minute this drive can be subjected to without exceeding the total power dissipated in the motor under rated conditions. Assume a ratio of stator to rotor resistance of unity and neglect magnetizing current and rational losses.
Hint: Energy lost by the motor during starting under no load = ½ * J * wS2
(1 +Stator resistance / Rotor resistance).
Question
Considering the same 22 kW of the above problem and the same assumptions, what will be the effect of the no. of starts restriction if the motor is of 2 pole construction?
Question
Consider a motor of 1000 kW, 996 rpm rating with an inertia of 80 kg-m2; driving a fan of Load Inertia: 1875 kg-m2. Load torque required at 650rpm can be assumed to be 45%. Frictional Torque can be assumed to be 10%. Calculate the acceleration time of the motor up to 650 rpm assuming that the motor has to accelerate without driving the load (solo).
Hint: Angular acceleration = (Final speed, rps - Initial speed, rps) / Acceleration Time.
Question
The above referred drive system is engineered such that the motor gets coupled to the load at 650 rpm. What is the torque available for the motor to accelerate in this loaded condition? Calculate the acceleration time to reach a speed of 700 rpm.