Armature Resistance Control (Rheostatic Control) - DC Motor - Electrical Machine 1 | Summary and Q&A

TL;DR

This video discusses the armature resistance control method to control the speed of a DC motor, using external resistances in series with the armature or field winding resistances.

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.

Transcript

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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).