How Does Armature Resistance Control DC Motor Speed?

TL;DR

Armature resistance control varies the speed of a DC motor by increasing the armature resistance, which decreases voltage and, consequently, speed. This method utilizes external resistances connected in series with the armature or field winding, and it's limited to controlling speed below the rated value while causing power loss in the resistances.

Transcript

hello friends in previous video we have studied what is equation for speed and what is speed regulation now in this video we are going to study what are the methods to control the speed of dc motor the first method to control the speed of dc motor is armature resistance control let us study this method in detail we know that the equation for speed ... Read More

Key Insights

• 🧑‍🦼 The speed of a DC motor can be controlled by varying the armature resistance.
• 🧑‍🦼 For DC shunt motors, an external resistance is connected in series with the armature resistance.
• 💨 For DC series motors, an external resistance is connected in series with the field winding resistance.
• 🐎 Armature resistance control method can only control the speed below the rated speed.
• 🐎 Drawbacks of the method include power loss and limitation in controlling the speed above the rated speed.

Questions & Answers

Q: How is the speed of a DC motor controlled using armature resistance control?

By increasing the armature resistance (ra), the voltage drop (ia * ra) increases, leading to a decrease in the supply voltage (v) and eventually decreasing the speed (n) of the DC motor.

Q: What is the block diagram for armature resistance control in a DC shunt motor?

In a DC shunt motor, the armature resistance (ra) is connected in series with an external resistance (re), and the supply voltage (v) is connected in parallel with the shunt resistance (rsh).

Q: How does the use of series resistor affect the speed of a DC shunt motor?

The presence of the series resistor (re) decreases the total voltage, resulting in a decrease in the speed of the DC shunt motor, allowing speed control below its rated speed.

Q: How is the speed of a DC series motor controlled using armature resistance control?

In a DC series motor, an external resistance (re) is connected in series with the field winding resistance (rac). The presence of the series resistor decreases the voltage drop and thus controls the speed below the rated speed.

Summary & Key Takeaways

• The equation for speed (n) of a DC motor is n = (v - ia * ra)/(k * phi).

• By increasing the armature resistance (ra), the voltage (v) decreases, leading to a decrease in speed.

• For DC shunt motors, the armature resistance (ra) is connected in series with an external resistance (re).

• For DC series motors, an external resistance (re) is connected in series with the field winding resistance (rac).