Hysteresis loss and eddy current losses: Core losses types
Eddy current loss
Eddy current loss takes place when a coil is wrapped around a core and alternating ac supply is applied to it. As the supply to the coil is alternating, the flux produced in the coil is also alternating. By faradays law of electromagnetic induction, the change in flux through the core causes emf induction inside the core. Due to induction of emf eddy current starts to flow in the core. Due to this eddy current loss the energy is lost in the form of heat energy.
Eddy current losses can be reduced by laminations in the core. Thin sheet steels must be used which are insulated from each other. Due to insulated sheets the amount of current which flows get reduced and hence the eddy current losses.
Eddy Current Braking
One of the applications of eddy currents is that it produces braking effect in motors. Braking is required to control the speed of motor. The methods of speed control of a motor uses the principle of eddy currents. Speed control of motor is required for various speed applications required for motor operations.
The amount of energy absorbed by magnetic material is not returned back. It can be understand by the Hysteresis curve. When the magnetic field strength or the current is increased the flux density increase, after a point when we further increase current the flux density gets saturated. When we reduce the current from saturation to zero side the flux density starts to decrease. But when the current value reaches zero the flux density should also be zero but it is not zero. For zero current there is still some flux density present in the material, this is known as residual magnetic flux. Hence the amount of power is never recovered back. The power which gets trapped in the core of the material is lost in the form of heat. The area of the BH curve determines the amount of hysteresis loss. The larger the area greater is the loss, smaller the area of bh curve, lesser will be the hysteresis loss.
What is BH Curve?
The graph drawn between magnetic field strength and magnetic flux density. The magnetic field strength is taken on the x axis of graph while magnetic flux density is taken on y axis of the graph. The curve drawn for these two quantities for magnetic and non magnetic material is known as BH Curve.
Electrical engineering interview questions
Electrical engineering interview questions that are asked from the topics of machines and transformers often include these questions. Hysteresis and eddy current losses take place in transformer core as well as machines core. Here the major machine types in electrical engineering is DC generators and motors. AC generators and motors are also suffer from the losses discussed above.