What are the factors that control the speed of a dc motor? Describe Ward-Leonard system to control the speed of a dc motor

The speed of a motor is given by the relation.

Where, R_a = armature circuit resistance.

So, the factors that control the speed of a dc motor are

(i) flux/pole, Φ

(ii) Resistance R_a of armature circuit

(iii) Applied voltage V

Ward-Leonard system

The Ward-Leonard system uses the armature control method of lowering the speed without the use of series resistors. A generator is used solely to supply the motor armature with the required voltage. The output of a separately excited generator is connected to the armature of the variable-speed motor. The motor is also separately excited. Varying the setting of the generator field rheostat changes the output voltage of the generator. The output of the generator, being connected to the armature of the motor, thereby changes the motor speed.

This method is used in mills where it is necessary to increase or decrease the speed of an entire production line.

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