Electrical Engineering ⇒ Topic : Iron losses

Peter
 
Iron losses. Iron losses s are a function of both flux and speed. Hysteresis loss. The "hysteresis loss P_{h} is a measure of the electric energy required to overcome the retentivity of the iron in the magnetic flux path, using watts as unit, P_{h} = K_{h}B^{x}fV where V = volume of iron in dynamo subject to change of flux, Kh = constant for the grade of iron employed, V = flux density raised to the Steinmetz exponent. With modern values of dynamo x is no longer 1.6 but closer to 2.0. This is not to imply that for a given volume, V, of iron the loss has increased, because K_{h} has been reduced considerbly, and f = frequency (hz) of reversal of flux. Eddy current losses. These losses occur not only in the dynamo iron but in all conductive materials with the flux path of the rotating or varying magentic field of the dynamo. The eddy current loss P_{s}, in watts is P = K_{e}t^{2}B^{2}f^{2}V where K_{e} = an eddy current constant for the grade of iron employed, t = thickness of the laminations of the pole core and armature, B = flux density, f = frequency (hz) of reversal of flux, and V = Volume of iron subject to change of flux For a D.C. dynamo the frequency, f, reversal of flux varies with speed. Thus the hysteresis loss varies directly with speed, whereas the eddy current loss varies as the square of speed. Both hysteresis loss and eddy current loss vary approximately as the square of the flux density. For this reason core losses are considered a function of both flux and speed  
 
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