DC Motor Starting
When voltage is applied to the armature of a dcmotorwith the rotor stationary, no emf is generated and the armature current is limited only by the internal armature resistance of the machine. So, to limit the starting current to the value that the motor can commutate successfully, all except very small dc motors are started with variable external resistance in series with their armatures. This starting resistance is cut out manually or automatically as the motor comes up to speed.