The path lengths of eddy currents in a rectangular cross-section magnetic conductor are longer than those in circular cross-section magnetic conductor. Thus, for equal electrical conductivities, the effective eddy current inductance in a rectangular conductor is lower. To mitigate eddy current effects in magnetic materials, we see from Equations 4. The cost of such construction is only justified for devices which must operate at very high speeds i.
Download the Circuit Breaker Selection Guide. Covering ratings of 0. For further details, the individual Series Data Sheets may be downloaded. Need help? Find a Distributor. Search Mechanical Products Website. So, by reducing surface or by using thin laminated sheets in core will reduce the eddy currents. The advantages of eddy current testing are: Sensitivity to surface defects.
Able to detect defects of 0. Can detect through several layers. Thus the eddy current loss per unit volume is ; Proportional to the square of the frequency. Proportional to the square of the flux density.
Proportional to the square of the thickness of the laminated sheet. Inversely proportional to the resistivity of the material. Thus we find eddy current loss per unit volume of the material directly depends upon the square of the frequency, flux density and thickness of the plate.
Also it is inversely proportional to the resistivity of the material. The core of the material is constructed using thin plates called laminations. The most significant difference between the Eddy current and Hysteresis loss is that the eddy current loss occurs because of the relative motion between the conductor and the magnetic field.
Whereas the hysteresis loss occurs because of the reversal of the magnetism. To have maximum sensitivity and accuracy, the balance must be as friction-free as possible. But if it is friction-free, then it will oscillate for a very long time. Magnetic damping is a simple and ideal solution. With magnetic damping, drag is proportional to speed and becomes zero at zero velocity. Thus the oscillations are quickly damped, after which the damping force disappears, allowing the balance to be very sensitive.
See Figure 4. In most balances, magnetic damping is accomplished with a conducting disc that rotates in a fixed field. Figure 4. Magnetic damping of this sensitive balance slows its oscillations. Since eddy currents and magnetic damping occur only in conductors, recycling centers can use magnets to separate metals from other materials.
Trash is dumped in batches down a ramp, beneath which lies a powerful magnet. Conductors in the trash are slowed by magnetic damping while nonmetals in the trash move on, separating from the metals. See Figure 5. This works for all metals, not just ferromagnetic ones. A magnet can separate out the ferromagnetic materials alone by acting on stationary trash. Figure 5. Metals can be separated from other trash by magnetic drag. Eddy currents and magnetic drag are created in the metals sent down this ramp by the powerful magnet beneath it.
Nonmetals move on. Other major applications of eddy currents are in metal detectors and braking systems in trains and roller coasters. Eddy current losses and hysteresis losses are categorized as core losses also referred to as iron losses or magnetic losses because they depend on the magnetic paths through the iron core of the motor.
Although eddy currents are an undesirable occurrence in electric motors, they are useful in other applications, such as eddy current brakes , non-destructive testing devices, and inductive proximity sensors.
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