repulsion motor | repulsion motor in hindi | repulsion motor construction and working | animation

Summary

This lecture provides an in-depth explanation of the repulsion motor, a special-purpose machine that converts electrical input into mechanical output, commonly used in electric trains. The lecture covers the construction, working principles, torque-speed characteristics, and applications of repulsion motors. It discusses key components like the stator, rotor, and brush assembly, along with the interaction of magnetic fields and torque generation. The lecture also explains how to control torque and speed by adjusting the brush positions. Additionally, it highlights the advantages of repulsion motors, including high starting torque and speed flexibility, along with some drawbacks.

Takeaways

• ⚙️ Repulsion motors are a special type of machine that convert electrical input into mechanical output, typically used in applications requiring high starting torque, such as electric trains.
• ⚡ Repulsion motors are single-phase induction motors that operate on AC supply and transition from repulsion motor mode to induction motor mode as they start and run.
• 🔧 The construction of a repulsion motor is similar to a single-phase induction motor with two main parts: the stator (stationary part) and the rotor (rotating part).
• 🌀 The rotor of a repulsion motor has commutator and brush assemblies like a DC machine, with brushes short-circuited to create a repulsion effect.
• 🧲 When AC supply is provided to the stator winding, a changing magnetic flux is produced, inducing EMF (electromotive force) in the rotor and creating torque based on the brush position.
• 🔄 Torque on the rotor depends on the position of the brushes. At certain brush angles (0° and 90°), no torque is produced, but at intermediate angles, torque develops, causing the rotor to rotate.
• ⏩ Adjusting the position of the brushes can control the direction of rotation and speed of the motor, which is typically high at no load.
• 📈 Repulsion motors provide high starting torque and relatively low starting current, making them useful for applications requiring quick acceleration and high-speed performance.
• 💡 The torque equation for a repulsion motor is influenced by factors like the stator field current and the number of effective turns in the stator winding.
• ⚖️ While repulsion motors offer flexible control over speed and torque, they have disadvantages such as variable speed with load and lower power factor, except at high speeds.

Q & A

What is a repulsion motor, and how does it work?

A repulsion motor is a type of special-purpose machine that converts electrical input into mechanical output, which can be in the form of force or torque. It is a single-phase AC motor, primarily used in electric trains. It starts as a repulsion motor and operates as an induction motor, providing high starting torque.

What are the main components of a repulsion motor?

The main components of a repulsion motor are the stator and the rotor. The stator is the stationary part, and the rotor is the rotating part. The stator has poles with windings made of high-conductivity material, while the rotor is similar to that of a DC machine with a commutator and brush assembly.

How does the repulsion motor start, and what influences the direction of its rotation?

The repulsion motor starts when AC supply is given to the stator windings, creating a variable magnetic flux. The direction of torque on the rotor depends on the position of the brushes. By adjusting the brush position, the torque and direction of rotation can be controlled.

What happens when the brush axis is aligned with the field axis in a repulsion motor?

When the brush axis is aligned with the field axis (0-degree angle), the changing magnetic flux cuts the rotor conductors, inducing EMF. However, due to the alignment, the net torque on the rotor becomes zero, and the rotor does not rotate.

What occurs when the brush axis is perpendicular to the field axis in the repulsion motor?

When the brush axis is perpendicular to the field axis (90-degree angle), the induced EMF in the upper and lower halves of the rotor conductors results in opposing torques, neutralizing each other. Consequently, no net torque is produced, and the rotor remains stationary.

How does the rotor rotate when the brush axis is shifted between 0 to 90 degrees?

When the brush axis is shifted between 0 and 90 degrees (typically around 45 degrees), a repulsion force is generated. The stator's magnetic poles repel the rotor's magnetic poles, causing the rotor to develop torque and rotate in the clockwise direction.

What are the key characteristics of a repulsion motor?

Key characteristics of a repulsion motor include high starting torque, high speed at no load, low starting current, and speed control based on the position of the brushes. The torque equation is given by t = k/2 * ns1 sin2(α), where α is the angle between the brush axis and field axis.

What are some advantages of a repulsion motor?

The advantages of a repulsion motor include high starting torque, the ability to adjust torque by changing the brush position, and flexibility in controlling speed and direction. The motor's speed is not limited, and it can be easily controlled by adjusting the brush position.

What are the disadvantages of a repulsion motor?

Disadvantages of a repulsion motor include speed variation with load changes and a low power factor, except at high speeds. Despite its controllability, it may not be as efficient at lower speeds or under heavy loads.

What are the main applications of repulsion motors?

Repulsion motors are used in industries, toys, and lifts due to their high starting torque and adjustable speed. They are also commonly employed in electric trains and other applications requiring variable speed and torque control.