Table of Contents

Seminar On Eddy Current Brake Report PDF Download

ABSTRACT

This is an electric braking system which works on the principle that eddy current produced in it opposes the driving torque. This opposing torque is used to brake the automobiles. Mainly this system is purely based on Faraday’s laws of electromagnetic induction and Lenz’s law.
For operating this a control switch is provided on the steering column in a position for easy manual. The skidding and complexity of mechanical braking system can be minimized by this system. Also the wear and tear of the vehicles can be reduced.
Since researches are going on to eliminate some of the disadvantages of this system, we can accept it to be the norm one in a few years of time.

INTRODUCTION

Many of the ordinary brakes, which are being used now days stop the vehicle by means of mechanical blocking. This causes skidding and wear and tear of the vehicle. And if the speed of the vehicle is very high, the brake cannot provide that much high braking force and it will cause problems.

These drawbacks of ordinary brakes can be overcome by a simple and effective mechanism of braking system ‘The eddy current brake’. It is an abrasion-free method for braking of vehicles including trains. It makes use of the opposing tendency of eddy current
Eddy current is the swirling current produced in a conductor, which is subjected to a change in magnetic field. Because of the tendency of eddy currents to oppose, eddy currents cause energy to be lost. More accurately, eddy currents transform more useful forms of energy such as kinetic energy into heat, which is much less useful. In many applications, the loss of useful energy is not particularly desirable. But there are some practical applications. Such an application is the eddy current brake.

PRINCIPLE OF OPERATIONS

Eddy current brake works according to Faraday’s law of electromagnetic induction. According to this law, whenever a conductor cuts magnetic lines of forces, an emf is induced in the conductor, the magnitude of which is proportional to the strength of magnetic field and the speed of the conductor. If the conductor is a disc, there will be circulatory currents i.e. eddy currents in the disc. According to Lenz’s
law, the direction of the current is in such a way as to oppose the cause, i.e. movement of the disc.
Essentially the eddy current brake consists of two parts, a stationary magnetic field system and a solid rotating part, which include a metal disc. During braking, the metal disc is exposed to a magnetic field from an electromagnet, generating eddy currents in the disc. The magnetic interaction between the applied field and the eddy currents slow down the rotating disc. Thus the wheels of the vehicle also slow down since the wheels are directly coupled to the disc of the eddy current brake, thus producing smooth stopping motion.

WORKING

When the vehicle is moving, the rotor disc of eddy current brake which is coupled to the wheels of the vehicle rotates, in close proximity to stationary magnetic poles. When we want to brake the vehicle, a control switch is put on which is placed on the steering column in a position for easy operation. When the control switch is operated, current flows from a battery to the field winding, thus energizing the magnet. Then the rotating disc will cut the magnetic field. When the disc cuts the magnetic field, flux changes occur in the disc which is proportional to the strength of the magnetic field. The current will flow back to the zero field areas of the metal plate and thus create a closed current loop like a whirl or eddy. A flow of current always means there is a magnetic field as well. Due to Lenz’s law, the magnetic field produced by the eddy currents works against the movement direction. Thus instead of mechanical friction, a magnetic friction is created. In consequence, the disc will experience a “drag” or the braking effect, and thus the disc stops rotation. The wheels of the vehicle, which is directly coupled to the disc, also stop rotation.

Faster the wheels are spinning, stronger the effect, meaning that as the vehicle slows, the braking force is reduced producing a smooth stopping action. The control switch can be set at different positions for controlling the excitation current to several set values in order to regulate the magnetic flux and consequently the magnitude of braking force. i.e. if the speed of the vehicle is lpw, a low braking force is required to stop the vehicle. So the control switch is set at the lowest position so that a low current will be supplied to the field winding. Then the magnetic field produced will be of low strength, so that a required low braking force is produced.

ADVANTAGES

Less maintenance
Wide range of braking force available within the temperature limit
Prolonged braking is possible
Long life
Less strain to the operation
Smooth retardation, which cuts down, the tire wears

Eddy current brakes offer smooth retardation of vehicles without skidding. It is totally free of wear and tear. So it has long life compared to ordinary brakes. These need less maintenance.
In mountain areas continuous braking is needed for a long time. At this condition, eddy current braking is more suitable to function without overheating. By changing the excitation current to the field winding, i.e. by adjusting the position of the control switch, we can vary the braking force to required range. The operation of eddy current brake is very simple. i.e. the control switch is a soft switch which can be operated without any strain.

DISADVANTAGES

No breaking force at rest
Need of electric power

The main disadvantage of the eddy current brake is that it needs electric power to work. Researches are going on to overcome this disadvantage by making the brake regenerative i.e. by converting the kinetic energy of the vehicle into electric energy and storing it back into the battery.