Armature control of DC motor
•For controlling speed through armature external resistance is used in armature.
• By adding variable resistance to armature the armature current is reduced hence the speed is reduced.
•More the resistance more the decrease in speed.
•From the equation it is seen that rotor speed is depend on voltage and field current.
•So by varying field current by variable armature resistance we can control the speed of the DC motor.
•We can also control speed by varying terminal voltage but it is rarely used because of high cost.