What are eddy current and the definition?
Definition: Eddy current is defined as the circulating current induced on a conductor, whenever we place a metallic material on a magnetic field.
The meaning of the word “EDDY” means circulation, so EDDY+ CURRENT known as circulating of current, the name already suggests the whole theory of eddy current.
For example: when we throw a stone into a pool of water, it forms a traverse wave on the water called the EDDY or circulation of the water, but on electrical EDDY means circulating current on a conductor due to faraday’s law.
From the above example, the transverse wave formation on the water due to the force of a stone, like the same a circulating current is induced on the conductor when we place it on a magnetic field.
What are the eddy current loss and definition?
Definition: Eddy current losses are the heat losses acquired on a conductor due to the circulating current also called the eddy current.
Eddy current losses are the type of static losses which may acquire on the core-based electrical devices, but here we use a transformer to explain the eddy current losses.
The figure shows the eddy current formation on a transformer, we already mentioned how eddy current formed at a conductor placed on a magnetic field.
At the same time, static devices like transformers have no movable parts, transformers have primary and secondary coils winded on the core, so whenever a magnetic field is induced on the coil, an EMF is produced on the core due to faraday’s law of electromagnetic induction.
The formation of eddy current at metallic core due to magnetic field will generate heat at the core of the transformer, this may cause heat losses and result in lesser efficiency on the transformer.
How to reduce eddy current loss?
Eddy current losses are been mainly happen on the core of the electrical machine, so different methods are used to reduce eddy current losses such as making core with thin sheets of metallic plates, making core with silicon steel material, laminating the core, and also placing paper between the thin metallic plate and tightly pack it for to increase the overall resistance of the core.
What is the mathematical expression for eddy current loss?
Pe = ke Bm2m t2f2V watt
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
The mathematical expression for eddy current shows the quantities depending on the eddy current at a material.
The Ke eddy current co-efficient depends on the nature of the material, which means the conductivity of the material.
The flux production on the main coil will result in the flux density Bm, the strength of the magnetic energy will support effective eddy current generation of secondary material.
The thickness and volume of magnetic material had an important role in eddy current production.
the applications of eddy current and its explanation?
The theory behind eddy current may base on electromagnetic induction, most of the time eddy currents are been consider as losses for the device.
But utilizing the eddy current principle on different applications will be a common thing, most modern devices utilize electromagnetic principle at sensing and transfer systems.
List of applications of eddy current
- Induction cooker
- Metal detector
- Electric power meter
- Proximity sensor
- Regenerative braking
- Magnetic levitation trains
- Speed controlling systems
- Vibration and position sensing systems
- Crack detection device
- Wire testing device
- Material sorting device
- Electromagnetic damping
- Induction furnace
- Material structural testing devices
- Safety hazard and defect detection systems
- Sheet resistance detection device
Eddy current principle on induction cooker
Important applications based on eddy current is at induction cookers, main parts of induction cooker are electromagnet and power coils.
When the power supply is given to the electromagnet it gets excited and electromagnetic induction energizes the power coil.
After we place a metallic vessel on the top of the ceramic top plate on the induction cooker, the electromagnetic flux on the bottom portion of the vessel will increase and generate heat.
The heat generated on the vessel will transfer to the food item and they get cooked.
Eddy current on Regenerative braking
Regenerative braking is a widely spread application of eddy current on locomotives, the figure shows the simple arrangement of regenerative braking.
The disk or wheels of the locomotive is placed between two electromagnets, and the working of braking is quite simple.
When the braking is happen, the electromagnets get excited and due to electromagnetic induction.
Then wheel disk in the middle of the electromagnet will absorb and eject electromagnetic energy and the wheel stops eventually.
The wheels disks are made with the plane surface, this will support the regenerative braking.
Metal detector eddy current
The metal detectors are used to detect metallic material in unknown places, the bomb squids use metal detectors to detect bombs in hidden places.
The main theory behind the operation of metal detectors is eddy current or electromagnetic induction.
The main parts of the metal detector are the power coil and data processing unit, the working of the detector is simple,
When we give power to the metal detector, the coil gets excited and it starts transmitting electromagnetic waves outside.
When the electromagnetic waves strike the metallic object it waves bonus back to the metal detector and it senses the metal.
The coils used for transmitting and receiving for sensing are the same on metal detectors.
So, the eddy current generation happens on detected material and the metal detector coil generates and transmits the electromagnetic waves.
Electric power meter eddy current
The watt-hour meter is one of the main applications of the eddy current principle, the arrangement of the electric power meter will be with a rotating aluminum disc, voltage and current coils, magnetic brake, and copper shading ring.
The eddy current principle will be utilized here at the rotation of the disc, several rotations will be counted and measure the energy usage.
The detection of the count of disc rotation will be sensed by a hole on the surface of the disc, each time the hole reaches a particular point on the meter, and it will count the rotating frequency value.
Magnetic levitation trains
Magnetic levitation trains are high-level applications based on eddy current, magnetic levitation of a metallic object is happened by the interaction between magnetic forces.
In magnetic levitation trains, the train will elevate above the track on air, the eddy current or electromagnetic induction principle will help the train for the levitation.
The magnetic force is powerful than the gravitational force, so a high amount of magnetic alternative flux helps the levitation train.
The elevation locomotive had a less frictional effect, less fuel consumption and lesser maintains.
Crack detection device
The crack detection based on eddy current is an important application because at transformers the thin metal packing of the core will be used to minimize the eddy current effect, but here at crack detection device, a single crack at the surface may be detected with the eddy current principle.
Eddy current on Material sorting devices
Eddy current principle will be used on material sorting device applications, there are different material sorting devices are available, sorting based on the conductivity of the material and also the shape and size of material.
The eddy current principle will be work differently on each material and that information is used to sort different material.