<P> The series motor responds to increased load by slowing down ; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings . If the motor is stalled , the current is limited only by the total resistance of the windings and the torque can be very high , but there is a danger of the windings becoming overheated . Series wound motors were widely used as traction motors in rail transport of every kind , but are being phased out in favour of power inverter - fed AC induction motors . The counter emf aids the armature resistance to limit the current through the armature . When power is first applied to a motor , the armature does not rotate , the counter emf is zero and the only factor limiting the armature current is the armature resistance . As the prospective current through the armature is very large , the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter emf . As the motor rotation builds up , the resistance is gradually cut out . </P>
<P> The series motor responds to increased load by slowing down ; the current increases and the torque rises in proportional to the square of the current since the same current flows in both the armature and the field windings . If the motor is stalled , the current is limited only by the total resistance of the windings and the torque can be very high , but there is a danger of the windings becoming overheated . Series wound motors were widely used as traction motors in rail transport of every kind , but are being phased out in favour of power inverter - fed AC induction motors . The counter emf aids the armature resistance to limit the current through the armature . When power is first applied to a motor , the armature does not rotate , the counter emf is zero and the only factor limiting the armature current is the armature resistance . As the prospective current through the armature is very large , the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter emf . As the motor rotation builds up , the resistance is gradually cut out . </P>
factors on which the speed of dc motor depends
factors on which the speed of dc motor depends
armature resistance
armature resistance