ASSIGNMENT-1

Q 1. A 220 V, 1500 rpm, 11.6 A separately excited motor is controlled by a l-phase fully

controlled rectifier with an ac source voltage of 230 V, 50 Hz. Enough filter inductance is

added to ensure continuous conduction for any torque greater than 25 percent of rated

torque, Ra = 2 ohm

a) What should be the value of the firing angle to get the rated torque at 1000 rpm?

b) Calculate the firing angle for the rated braking torque and -1500 rpm.

c) Ca1culate the motor speed at the rated torque and α = 160° for the regenerative

braking in the second quadrant.

Q 2. Let the motor is having La = 28.36 mH for above example. calculate type of conduction

for the following cases:

a) α= 60° and speed = 400 rpm

b) α= 60° and speed = 995 rpm

Q 3. A 220 V, 1500 rpm de motor has the armature resistance and inductance of 2 ohm

and 28.36 rnH, respectively. It is controlled by a 3-phase fully-controlled rectifier from an

ac source operating at 50 Hz.

i. CaIculate the ac source voltage required to get the rated voltage across the motor

terminals when operating in continuous conduction.

ii. For the ac source voltage obtained in (i), caIculate the motor speed for the following

points:

a) α = 60°, T = 1 N-m

b) α = 60°, T = 20.0 N-m

c) α = 120°, T = 20.0 N-m

Q 4. A 30 kW, 230 V, 860 rpm, 144 A de motor has an armature resistance of 0.07 ohm. It

is fed by a 3-phase fully-controlled rectifier from an ac source of 170.3 V (line), 60 Hz.

Assuming continuous conduction, calculate motor speeds for the following cases:

a) α = 60°, T = 300 N-m

b) α = 150°, T = 400 N-m

c) α = 120°, T = -400 N-m