speed control of dc motor | speed control of dc shunt motor | dc motor speed control | series motor

Summary

This lecture delves into the speed control of DC motors, converting electrical energy to mechanical energy. It discusses various methods such as armature resistance control, field flux control, and armature voltage control. The script explains the principles behind each method, how they affect motor speed, and their applications in different types of DC motors. It also covers the advantages of field flux control and its energy efficiency, as well as the use of DC series motors in applications like elevators and vacuum cleaners, and the role of permanent magnet DC motors in automotive starters and computer disk drives.

Takeaways

• 😀 The lecture provides a detailed understanding of speed control methods for DC motors, which convert electrical energy into mechanical energy.
• 🔧 The script discusses three main methods for controlling the speed of DC motors: armature resistance control, field flux control, and armature voltage control.
• 🔌 In the armature resistance control method, a variable resistor is connected in series with the armature to adjust the speed by changing the resistance.
• ⚙️ The equation provided, \( \omega = \frac{V - I \cdot R}{K_{5}} \), explains the relationship between speed (ω), voltage (V), armature current (I), armature resistance (R), and field flux (K5).
• 📉 Increasing the armature resistance decreases the speed of the motor, and vice versa, as per the equation.
• 🔋 The field flux control method involves controlling the current in the field winding to adjust the field flux, which in turn controls the motor speed.
• 🔄 The script explains that decreasing the field current (and thus the field flux) increases the motor speed, and increasing it decreases the speed.
• 🛠 Techniques such as shunt field diverters and tapped field control are used in the field flux control method to adjust the field current and, consequently, the motor speed.
• 🔌 The armature voltage control method is mentioned but not detailed in the script; it is a method where the voltage applied to the armature is varied to control the speed.
• 🏭 The applications of DC series motors are highlighted, including their use in current air compressors, lifts, elevators, winches, and electric traction.
• 🔧 The script also covers the applications of DC shunt motors, such as in vacuum cleaners and speed regulation applications, as well as in various industrial equipment like boring mills and centrifugal pumps.
• 🚗 The use of permanent magnet DC motors in applications like washer wind shields, car starters, and personal computer disk drives is briefly mentioned.

Q & A

What is the main function of a DC motor?

The main function of a DC motor is to convert electrical energy into mechanical energy, with its rotor speed being controlled by various methods.

What are the different methods used for controlling the speed of a DC motor mentioned in the script?

The script mentions three main methods for controlling the speed of a DC motor: Armature Resistance Control, Field Flux Control, and Armature Voltage Control.

How does the Armature Resistance Control method affect the speed of a DC motor?

In the Armature Resistance Control method, the speed of the DC motor is decreased by increasing the resistance, which causes a difference in the quantities, resulting in a decrease in the motor's speed (ω).

What is the equation used to understand the relationship between armature resistance and motor speed in the script?

The equation used in the script to understand the relationship between armature resistance and motor speed is ω = (V - I * R) / K, where ω is the speed, V is the voltage, I is the armature current, R is the armature resistance, and K is a constant.

How is the Field Flux Control method different from Armature Resistance Control?

The Field Flux Control method involves controlling the field current to regulate the field flux, which in turn affects the motor speed. Unlike Armature Resistance Control, it does not affect the field winding directly connected to the supply.

What is the purpose of a variable resistor (RCS) in the Field Flux Control method?

In the Field Flux Control method, a variable resistor (RCS), also known as a shunt field regulator, is used to control the field current, which affects the field flux and consequently the motor speed.

What is the inverse relationship between field flux and DC motor speed mentioned in the script?

The inverse relationship mentioned in the script states that if the field flux decreases, the motor speed increases, and vice versa, because the motor speed is inversely proportional to the field flux (n = E / (K * Φ), where n is the speed, E is the voltage, K is a constant, and Φ is the field flux).

What are the major disadvantages of using the Armature Resistance Control method for speed control?

The major disadvantages of using the Armature Resistance Control method include the waste of power due to the cross-lar resistance and its use being limited to controlling the speed of small motors.

What are the applications of DC series motors as mentioned in the script?

The applications of DC series motors mentioned in the script include current air compressors, lifts, elevators, winches, electric traction, and hair dryers.

What is the purpose of a diverter in the Field Flux Control method?

The purpose of a diverter in the Field Flux Control method is to reduce the field winding current, which in turn reduces the amount of flux, leading to an increase in motor speed.

What is the concept of Tapped Field Control in the context of DC motors?

Tapped Field Control is a technique used in DC motors to vary the field current by controlling the number of winding turns through which the current flows, thus controlling the field flux and the motor speed.