3 The speed of a separately excited hp de motor is controlle

3) The speed of a separately excited hp de motor is controlled by a three phase full- 30 phase full converter drive. The field current is also controlled by a three converter and is set to its maximum possible value. The line to line rms voltage ofthe three phase source is vn 480 v The field resistance is Rf 294 Ohms, the armature circuit resistance is Ra -0.12 Ohms, the motor voltage constant is K 0.7032 V/A-rad/s For a load requiring a N.m at a speed of 1200 rpm, determine the required armature voltage va and the delay angle of the converter in armature circuit aa 1200 rpm z 2400 red P s 40 rod/see K 0.7032 x 40 K 1 Ja nja 13.76 US .37

Solution

the output voltage equation for three phase full converter vo=(3*1.732*vm*cosq)/3.14

here there are two full converters are used. one for armature side and another for field side.

the field side full converter firing angle is zero. because the condition is maximum output.

field converter output voltage vf=(3*1.732*1.414*480)/3.14=1122.76 volts

field resistance Rf=294 ohms

field current If=vf/Rf=1122.76/294=3.818 amps

we know T=K*If*Ia

85=0.7032*3.818*Ia

Ia=85/(0.7032*3.818)=31.659 amps

we know basic motor equation

Eb=k*w

Eb=0.7032*[(2*3.14*1200)/60]=88.366 volts

Va=Eb+Ia*Ra

Va=88.366+31.659*0.12

Va=92.165 volts

so the output voltage equation for three phase converter Va=(3*1.732*1.414*vrms*cosq)/3.14

92.165=(3*1.732*1.414*480*COSq)/3.14

cosq=0.08208

q=85.2914 degrees.