what is the purpose of a starting resisitance in series with the armarture of adc motor?

Answer 1

There really shouldn't be a resistor in series with the DC armature (at least, not one that's external to the machine itself). The DC machine - unlike an induction machine or synchronous machine - does NOT draw 'extra' current during start.

When the main DC stationary field is energized, voltage is applied to the armature circuit to bring the machine up to its base operating speed. If it then needs to go faster, the stationary field is weakened while holding the armature voltage constant.

A DC machine is a variable speed/constant torque device. The torque is constant while the armature voltage is changing and the stationary field is held constant; in the field weakened (higher than base speed) range, power is constant.

If you are looking at a schematic for a DC machine, it may show what looks like a resistor or inductor in the circuit (depends on who draws it). This is a winding that is internal to the machine, and includes both the commutating pole (also called the interpole) winding and the compensating (poleface) winding. These two windings carry armature current and are used to tune the commutation performance of the machine under varying load conditions.

For AC machines like synchronous and induction, the 'starting resistor' is used to limit the inrush current that results from spinning the rotor in a powered stationary field (the induced current).

Answer 2

The only starting resistance in a dc motor is the windings its wound with.You must be talking about the start windings of an ac motor and they are put there to add torque so the motoe windings dont burn up at start up and they are taken out of the curcuit when the motor reaches a certain speed.

Answer 3

Until the armature is spinning, there is no back e.m.f. generated to oppose the applied input voltage. Without a starting resistance, this results in an excessive current flow which would overheat and possibly damage the windings.

Answer 4

in the starting time of any motor it takes a big amount of current more than what is needed , this current can spoil the motor .. so the starting resistance was provided to decrease the amount of current in the start of any motor

Answer 5

since at the time of starting there will be heavy amount current flow through the armature and this heavy current may spoil the winding of the armature so we are providing the resistance along with the armature.

Answer 6

controls the current, thus magnet power. So it controls the speed.

Answer 7

http://en.wikipedia.org/wiki/Dc_motor