Control of Electric Drive

A 230V, 25kW d.c. shunt motor running at its rated speed of 1500 rpm is to be braked by reverse current braking. The armature resistance is 0.1 ohm and the rated efficiency of the motor is 88 percent. Calculate (i) the resistance to be connected in series with the armature to limit the initial braking current to twice the rated current, (ii) the initial braking torque and (iii) the torque when the speed of the motor falls to 600 rpm.

A 220 V separately excited motor running at 1000 rpm draws 100 A from the source. The motor is braked by plugging. Calculate (i) Resistance to be inserted in the armature circuit to limit the braking current to twice the full load current, (ii) Initial braking torque, (iii) The braking torque when speed has reduced to 500 rpm.

A 220 V, 20 kW dc shut motor running at its rated speed of 1200 rpm is to be braked by reverse current braking. The armature resistance is 0.1 Ω and the rated efficiency of the motor is 88%. Calculate: (i) The resistance to be connected in series with the armature to limit the initial braking current to twice the rated current. (ii) The initial braking torque. (iii) The torque when motor falls to 400 rpm.