A 200 V dc motor has a starting current of 100 A and fullloa

A 200 V dc motor has a starting current of 100 A and full-load torque 20 N-m. The armature current at full load is 5 A. (i) Determine the armature resistance, the equivalent field voltage, the starting voltage and the full load motor speed in RPM. (ii) Assuming the maximum current rating is 20 A, determine resistance that should be inserted in series with the armature of the motor to limit the starting current to the maximum rated value. (iii) If the armature voltage and load (torque) are the same as earlier, and it is desired to run the motor at 600 RPM, determine the required equivalent field voltage.

Solution

Given:

E = 200 V DC Starting current I = 100 Amp , Torque( Ful-load) = 20 N-m Armature current ( at full load) Ia = 5 bAmp

i. Armature resistance (Ra) => E = I ( armature current) x Ra => 200 = 100x Ra => Ra = 2 Ohm

Field voltage => V = E - I a Ra => 200 - ( 5 x 2) => 190 V