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News by Author – Cogent Power

Eddy Currents

Magnetic cores of electrical machines are constructed from laminations of magnetic steel core material alloyed with silicon to minimise the hysteresis and eddy current losses for high-efficiency operation. Since the magnetic cores are exposed to time-varying magnetic fields, eddy currents are induced in the laminations and consequently, energy is converted into heat in the resistance of the eddy current path.

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The laminations are coated with insulation material on either side to prevent electrical conduction between the sheets. However, punching and cutting of the electrical steel to the required dimension can cause edge burr which are one of the most serious obstacles to precision and process automation.

Burrs have to be removed by a de-burring process for functional and technical reasons after the blank has been sheared or stamped as the cut edge burrs could lead to short circuits between adjacent laminations. However, if edge burrs appear between two blanks of the magnetic core on one side only, it does not tend to create a closed current path, and therefore no change in the total iron loss of the core occurs.

However, if the same two blanks are short-circuited on both sides, a closed conductive path will be available which leads to a larger section for the flow of inter-laminar eddy current that will cause eddy current losses.