Q.3: A 250 V DC shunt motor has armature resistance of 0.25. It takes an armature current of 50 A and runs at 750 r.p.m. If the flux of the motor is reduced by 10% without changing the load torque, find: (i) The new speed of the motor (ii)The developed torque.

A 4-pole series motor has 800 lap connected armature conductors. At a certain load, the flux per pole is | 60mWb and the total mechanical torque developed is 400 N-m. Calculate the line current taken by the motor and the speed at which it will run with a back emf of 400 V. Total motor resistance is 4 ohm.

Q3. Write if the shown statements are TRUE or FALSE. 1- In DC machine the induced e.m.f is proportional with flux only. 2- The Ta/l a graph of a d.c. series motor is a straight line throughout. 3- In a DC motor the direction of the shaft rotation can be change by changing the polarity of the power supply. 4-The critical resistance is less than armature resistance in shunt generator. 5-As the load is increased, the speed of a d.c. shunt motor increases slightly.

A shunt generator delivers 195 A at a terminal voltage of 250V. The armature resistance and the shunt field resistance are 0.02 and 50 ohms, respectively. The iron and the friction losses are equal to 950 W. Find the commercial efficiency of the generator.