How are Eddy Currents Produced

Eddy currents are produced due to changes in the magnetic field. They are created when a conductor moves through a magnetic field or when the magnetic field around a stationary conductor varies. In other words, anything that causes the conductor to experience a change in the direction or intensity of a magnetic field can produce eddy currents. It is produced in any metallic conductor when the magnetic flux changes around it. Electromagnetic induction creates these currents that are always present in closed loops. This is the nature of all metals. These currents produce significant power losses, known as eddy current loss, in the transformer as they increase the temperature inside the transformers. This is because these currents produce their magnetic field, which opposes the already present magnetic field of the transformer, hence forming these eddy currents. 

Eddy current testing

Eddy current testing is one of many methods used in nondestructive testing. It is mainly used in electromagnetic testing, where electromagnetic induction is used to check the presence of eddy current in a product or metal. It can also be used to detect the damage caused by the eddy currents. Its crucial applications are in surface and tubing inspections, used in many industries like automobile, aerospace, etc.

Working principle of eddy current

Eddy currents flow in closed loops in planes perpendicular to the magnetic field inside conductors. These currents are also known as Foucault’s currents. The working principle of eddy currents involves the presence of electromagnetic induction inside the coils, which is caused by passing alternating current in the coil. Eddy currents are produced when any conducting wire is brought near an alternating current. These currents are induced inside the conductor; hence, it is called self-inductance. Eddy current works on the principle of Faraday’s Law. The right-hand thumb rule can be used to determine the direction of the flowing magnetic field. 

The flow of eddy currents

These currents always work in a closed loop and act on the plane that is perpendicular to the magnetic field inside the conductor. The magnitude of the current produced in the conductor depends on the strength of the field, the area of a circle and the flux. The flow of eddy current can be formed by the change in the magnetic field, called magnetic flux. This shows that any change that occurs in the field can affect the direction or the intensity of the field. According to Lenz’s law, these currents form a magnetic field that opposes the present magnetic field. The current size is based on the amount of variation present in the magnetic field.

Eddy current loss

The amount of power lost due to eddy currents is large. The amount of power loss can be calculated using this formula. 

The current flowing in the coil (I) is passed through the resistance of the coil (r); hence, the amount of power dissipated is P = I2r. 

These losses are known as eddy current losses. Silicon steel with high resistivity or laminations on the coil, that create a smaller intersection area, can be used to reduce these losses. 

Minimising eddy currents

We can minimise the level of current flowing inside the coil by dividing these coils into some small, thin sheets so that these sheets become parallel to the flowing magnetic field.

Applications of eddy currents:

The primary applications of eddy currents are in:

• Gym equipment
• Checking whether a material or surface has any discontinuities, fractures or faults
• Electromagnetic damping
• Roller coasters
• High-speed trains 
• Mobile speedometers
• Induction furnaces 
• Galvanometers
• Trains that have brakes that use eddy currents
• PMMC devices

Braking system using eddy currents

Eddy current used in brakes is a system known as induction braking. This mainly focuses on eddy currents that stop objects from moving. This is a technique used to slow down the moving coil or the machine. In brake systems, the pressure present in the current for brake formation is an electromagnetic force produced between the magnet and the machine, using which the relative movement is caused. Eddy currents produce the brakes for the cars or other vehicles, helping them stop smoothly. Hence, these currents are now used in many vehicles for braking systems.

Conclusion

Eddy current is based on the principle of electromagnetic induction, that is, producing a current that flows opposite to the magnetic current flowing inside the coil. These currents can be affected by cracks or damage in the coil. Eddy currents help in many fields and are used in many devices nowadays. The working principle of these currents is based on Faraday’s Law. Eddy currents are primarily used in high-speed trains, induction furnaces, galvanometers, etc.