This method is applicable speed control above the base speed. This method reliable only to gain high speed only. Its not work properly in low speed because its gain huge errors in low speed.
By Changing Armature Voltage:-
In this method we see to understand the speed of motor is low or high to base speed. When a voltage source is connected across the armature as the voltage across the terminal of armature increase according to this armature current increase. In this case the speed of d.c shunt motor increase. Same this the voltage across the terminal of armature decrease according to this armature current decrease and in this case the speed of motor also decrease. This method is more reliable for speed control below to base speed.
By Changing Armature Resistance:-
By using this method when armature resistance increase the armature current decrease and induced torque will be decrease and so the speed of d.c shunt motor decrease. This method is useful both and below the base speed control but due to waste of energy this method is not reliable for using below speed according to base speed d.c shunt motor. I am sure to all of you, who read this blog is understand this topic.
Thanks For Regard...................YASIR ALI