Question

Determine the minimal value of pull-up torque (in percent) for a 50 hz, NEMA B, 3 phase, 4 pole induction motor, with a rated shaft output of 45 kw, and a speed of 1490 rpm.

Answer 1

Pull-up Torque: The minimum torque developed by the motor at which breakdown torque occurs as it accelerates from zero to full-load speed. i.e., pull-up torque is simply defined as the reduction of maximum torque applied as the rotor slip decreases.

Hence,the pull-up torque is expressed as,T=9550 P_kw / n_r

Where       T = Rated Torque(Nm)

P_kw = Rated Power

n_r   = Rated Rational speed (rpm)

Therefore, T=9550 X 45/1490 =288.42

In percentage, Pul;l-up torque , T= 288.42/100= 2.88%