Speed Control Of Separately Excited DC Motor By Armature Voltage Control And Field Control

July 18, 2020June 9, 2022 CS Electrical And Electronics

Hello Guys, welcome back to our blog. In this article, we will discuss what is separately excited dc motor is, its applications, speed control, a circuit diagram of speed control of separately excited dc motor by armature voltage control method, and field flux control method.

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Speed Control Of Separately Excited DC Motor By Armature Voltage Control And Field Control

What Is Separately Excited DC Motor

In the separately excited dc motor, the field coil is connected to a separate field excitation power supply and which does not supply power to the armature. The advantage of a separately excited dc motor is that the field flux is always available irrespective of the applied armature voltage which the high torque can be developed at low armature voltages and speeds.

Applications Of Separately Excited DC Motor

In a Separately excited motor, the supply is provided separately to the field and armature windings. The fact of this motor is that the armature current does not flow through the field windings, the supply to the field winding is given separately from other dc sources. Thus, one can obtain very accurate speed by using separately excited dc motors.

The separately excited dc motor is most suitable for the applications requiring speed variation from very low value to high value. This type of motor is used in steel rolling mills, diesel-electric propulsion of ships, paper machines, etc.

Speed Control Methods Of Separately Excited DC Motor

The speed control of the dc motor is obtained by two methods:

01. Armature Voltage Control

02. Field Flux Control

Circuit Diagram Of Speed Control Of Separately Excited DC Motor By Armature Voltage Control

What Is Armature Voltage Control Method

The speed of the dc motor depends on the back emf which is directly proportional to armature voltage and the flux which is inversely proportional. Therefore, to change the speed of the dc motor, the flux is kept constant and we change the back emf of the motor. The back emf of the motor is changed by changing the armature voltage. This is why it is called Armature Voltage Control of dc motor. As the armature voltage increases the speed of the motor also increases.

Nature Of Graph

Circuit Diagram Of Speed Control Of Separately Excited DC Motor By Field Flux Control

What Is Field Flux Control Method

The field flux is one of the methods of speed control of the dc motor. The speed of the dc motor is directly proportional to the field flux. The static field flux at the field coil increases then the torque over the shaft automatically increases. The emf induced across the rotor terminal is kept constant as the field flux increases as well as rotor speed decreases.

We can vary the field flux by varying the field voltage, by connecting a variable resistance in series with the field coil creates a voltage drop across the coil. The voltage drop can be varied by using a variac. So by varying flux, we can control the speed of the motor. As the field current decreases, the speed of the motor will also reduce. While varying field current the armature voltage is kept constant.

Nature Of Graph

Procedure To Perform

01. Connections as made as per the circuit diagram.
02. At the beginning keep the variac at zero position
03. Give DC supply.
04. For Armature Control Method – While conducting, the field current is kept constant and the armature voltage is varied.
05. For Field Control Method – While conducting, armature voltage is kept constant and the field current is varied.
06. Bring variac to zero position and turn off the supply.

I hope this article may help you all a lot. Thank you for reading.

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