What are the possible options of controlling the speed of dc motor ?

The advantage of electronic speed control l for dc motor:

We can control the speed of a dc motor by two method:

· Field control

· Armature control

1) Field control: To increase the speed above the base speed it is only necessary to increase the resistance of the rheostat in the shunt field circuit. Increasing the resistance decreases the field current which in turns decreases the field flux. And from the basic equation we know that If we decrease the field flux then the speed is increased.

2) Armature control: To operate the speeds lower than the base speed it is necessary to reduce the voltage applied to the armature .The voltage applied is reduced by adding a resistor in series with the armature. From the basic equation we know that the speed is directly proportional to the voltage impressed across the armature. since voltage impressed across armature circuit also determines the magnitude of counter emf the motor speed therefore depends upon the counter emf.

Electronic speed controlling methods have higher accuracy , greater reliability ,quick response

and also higher efficiency as there is no power dissipations by resistor. It also has no moving parts and gives higher facility of controlling either the voltage across the armature, field current or both.

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Why it is impossible for the counter emf to equal the applied voltage in a motor?

What are the detrimental effects of armature reaction on the performance of a dc machine?

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