A 23 hp, dc shunt motor is running at 1000 rpm when the
armature voltage is 600 V. the armature resistance of the motor is
0.8 Ω, and the field resistance is 900 Ω. The efficiency of the
motor at full load is 92%.
a) Calculate the value of the resistance of the dynamic braking
at full load. The armature current should be limited to 150% of the
rated value.
b) If the motor operates in regenerative braking at a speed of
1100 rpm, calculate the line current.
c) Design a circuit for countercurrent braking (by reversing the
supply voltage) so that the line current will not exceed 120% of
the rated value.