What is Eddy Current & Eddy's current loss?
Eddy current loss is a type of loss that occurs in a conductor (usually a metal) when it is exposed to an alternating magnetic field. This loss occurs because the alternating magnetic field causes currents to flow within the conductor, known as eddy currents. These eddy currents produce heat through a process called resistive heating, and this heat is dissipated as energy loss.
Eddy current loss is related to hysteresis loss, which is another type of loss that occurs in magnetic materials. Hysteresis loss is caused by the movement of the magnetic domains within the material as it is subjected to an alternating magnetic field. Both eddy current loss and hysteresis loss contribute to the overall loss of energy in a magnetic material, and are often referred to as "iron losses" or "core losses."
Eddy current loss can be reduced by using materials with a high electrical resistance (such as copper or aluminum) for the conductor, or by using a material with a high magnetic permeability (such as iron or steel) for the core of the conductor. These materials reduce the amount of eddy currents that are generated, which in turn reduces the amount of energy lost due to eddy current loss.
There are two main ways to reduce eddy current loss in a magnetic material. The first is to reduce the magnitude of the eddy currents. This can be done by splitting the solid core of the material into thin sheets, known as laminations, which are insulated from each other by a thin layer of coating. This reduces the area through which the currents can flow, and therefore reduces the magnitude of the currents.
The second way to reduce eddy current loss is to use a magnetic material with a higher value of resistivity, such as silicon steel. This increases the resistance of the eddy current path, which reduces the magnitude of the currents and therefore the amount of energy lost due to eddy current loss.
The magnitude of the eddy current depends on:
The magnitude of the eddy currents does depend on the
1. Resistance of the current path,
2. The frequency of the supply source,
3. The magnitude of the flux density, and
4. The thickness of the laminations (if the material is laminated).
1. Resistance of the current path:
The resistance of the current path refers to the resistance of the material through which the eddy currents are flowing. The higher the resistance of the material, the smaller the eddy currents will be because the material offers more resistance to the flow of current.
2. The frequency of the supply source:
The frequency of the supply source refers to the frequency of the alternating magnetic field that is inducing the eddy currents. At higher frequencies, the eddy currents will be smaller because the material has less time to respond to the changing field.
3. The magnitude of the flux density:
The magnitude of the flux density refers to the strength of the magnetic field that is inducing the eddy currents. The stronger the magnetic field, the larger the eddy currents will be.
4. The thickness of the laminations:
The thickness of the laminations (if the material is laminated) also affects the magnitude of the eddy currents. The thinner the laminations, the smaller the eddy currents will be because the area through which the currents can flow is reduced.
Mathematical Expression for Eddy Current Loss
The mathematical expression for eddy current loss in a magnetic material is given by:
Eddy current loss = Pe = Ke Bm2 t2
f2 V watts
where:
Ke – co-efficient of eddy current. Its value depends upon the nature of magnetic material
Bm – maximum value of flux density in wb/m2
T – thickness of lamination in meters
F – frequency of reversal of the magnetic field in Hz
V – volume of magnetic material in m3
This equation shows that the eddy current loss is directly proportional to the frequency and the maximum flux density of the magnetic field, and is also directly proportional to the square of the thickness of the material. This means that increasing any of these factors will increase the eddy current loss.
It is also worth noting that the eddy current loss is not the only source of energy loss in a magnetic material. There is also hysteresis loss, which is caused by the movement of the magnetic domains within the material as it is subjected to an alternating magnetic field. Both eddy current loss and hysteresis loss contribute to the overall energy loss in a magnetic material, and are often referred to as "iron losses" or "core losses."
Applications of Eddy Currents:
Eddy currents are circular currents that flow within a conductor when it is exposed to an alternating magnetic field. These currents can produce heat through a process called resistive heating, and this heat is often dissipated as energy loss. While eddy currents are a source of energy loss in many electrical devices, they also have some practical applications.
- One of the main applications of eddy currents is in induction heating. In this process, an iron shaft is placed as a core of an induction coil, and a high-frequency current is passed through the coil. This causes eddy currents to flow within the shaft, which produces a large amount of heat at the outermost part of the shaft. The heat produced by the eddy currents can be used to harden the surface of the shaft, a process that is commonly used in the automobile industry.
- Eddy currents are also used in electrical instruments, such as induction type energy meters and permanent magnet moving coil instruments. These instruments use the effect of eddy currents to provide braking or damping torque, which helps to control the movement of the instruments.
- Eddy current instruments are also used for detecting cracks in metal parts. In this application, an alternating magnetic field is applied to the metal, and the eddy currents that are induced in the material are used to detect any defects or anomalies.
- Finally, eddy currents are used in trains to provide braking torque, a process known as eddy current brakes. When the train slows down, the wheels create an alternating magnetic field, which causes eddy currents to flow within a conductive brake shoe. These eddy currents produce heat, which is used to slow the train down.