A dc, separately excited motor is driven by a full-wave, SCR, ac/dc converter. The voltage on the ac side is 120 V (rms). The field constant of the motor K? = 3 Vs. At a load torque of 300 Nm and triggering angle of 40o , the motor speed is 100 rpm, and the armature current is continuous.
a. The polarities of the terminal voltage of the motor (armature voltage) are
reversed, and the triggering angle is simultaneously changed. Assume that the
load torque is also reversed and is equal to 300 Nm. Calculate the triggering angle
that stops the motor and keeps it at the holding position. Assume that the current
is still continuous.
b. Sketch the speed-torque characteristics and indicate the steady state operating
points before and after polarity reversal.
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