An eddy current is a current set up in a conductor in response to a changing magnetic field. Eddy Current tends to oppose the very cause that is generating it. This post will discuss about what is Eddy Current, how is it generated, Lenz’s Law, Effects of this current, How to reduce Eddy Current Loss, Applications and advantages.
What is Eddy Current
Eddy Current is the electrical current that is induced within conductors in the form of loops. This is caused due to the changing magnetic field in the conductor and results in heat dissipation. This current flows in loops in planes perpendicular to the Magnetic Field.
Fig. 1 – Introduction to Eddy Current
Eddy Currents flowing in a loop induces magnetic field which opposes the field that created them. This is illustrated in the Fig. 2. In each loop, the magnitude of the current is directly proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux and is inversely related to the resistivity of the material i.e. as the current increases, resistivity decreases and vice versa. This type of currents are commonly found in Car speedometer, energy meters, electric brakes etc.
Fig. 2 – Representation of Eddy Current in Conductor
Lenz’s Law interprets the interaction between magnetic fields and Electric current within a coil of wire. The law states that:
“EMF or Electro Motive Force causes the current to flow through the loop and the magnetic field which is induced opposes the field causing it”. In other words, it states that, electric current, induced by a source such as a changing magnetic field, always creates a counterforce opposing the force inducing it. Fig. 3 shows illustration of Lenz’s Law from which we can observe that the motion of the magnet causes change in flux.
Fig. 3 – Illustration of Lenz’s Law
From Fig. 3 (1), (2) we can see that the induced magnetic field is upwards to oppose the increasing downward flux. The induced current is anti-clockwise with respect to the loop. Similarly, Fig. 3 (3), (4) shows that the induced magnetic field is downwards due to the change in flux and the induced current is clockwise.
How Eddy Currents are Generated
To understand how the current is generated, let us take the example of Induction cooktop. Induction cooktops work on the principle of Electromagnetic Induction where electricity is produced due to magnetism. The vessels used to cook on Induction cooktop should be of ferromagnetic metal such as stainless steel.
Fig. 4 – Representation of Eddy Current Generation
The Induction hob basically contains a coil of copper wire under the ceramic plate. When the cooktop is switched on, AC (Alternating Current) flows through it and magnetic field is induced. Oscillating magnetic field induces magnetic flux. This generates Eddy Current in the stainless-steel pot/ pan which is placed on the hob. This acts as a secondary winding of the transformer and the resistance to the induced AC current causes heating of the utensil. The utensil heats from the bottom and food cooks faster.
Eddy Current Effects
Eddy Current effects are:
- They induce Magnetic Field.
- They cause electrical power loss.
- As the Magnetic field exerts force on the charged particle, Lorentz force is also induced.
How to Reduce Eddy Current Loss
Few key points mentioned below helps in reducing Eddy Current Loss.
- Resistance of the core of induction coils and Transformer is increased to minimize the current loss.
- Laminations of the core reduces current loss.
- If the core is built with magnetic material such as silicon steel, Eddy Current loss can be minimized.
Applications of Eddy Current
The applications include:
- The concept of induced current is used in Induction heating.
- It is used in magnetic shielding.
- It is widely used for levitated trains and rollercoasters.
- It is also used in Electromagnetic Braking.
- They are extensively used in Gym equipment.
- Eddy Current Effects are used in medical equipment for cancer treatment.
Advantages of EddyCurrent
The advantages are:
- It brakes requires less maintenance.
- It can bring a machine running at high speed to rapid halt safely and smoothly.
Disadvantages of EddyCurrent
The disadvantages of Eddy Current are:
- Magnetic Flux leakage occurs.
- Heat dissipation in the core of Transformer is more.
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Give three uses of Eddy current