Tooth pulsation in rotating machines

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Abstract
1. An experimental method is presented of checking the magnitude of flux pulsations in the teeth of rotating machines where both members are slotted. The method consists in using metallic electrodes shaped like the teeth of a machine and an electrolyte or mercury to represent the air. Voltage is applied between the two members and the current through the tooth under consideration is measured. The magnitude of this current under different conditions is proportional to the magnitude of the flux which would flow under the analogous magnetic conditions. 2. The test results are compared with the pulsation amplitudes as calculated by two methods. The test results are in general slightly lower than the calculated but the agreement is fairly good. 3. It is believed that either of the above-mentioned methods can be used to calculate tooth pulsations without serious errors where saturation effects are not appreciable. These methods should be specially useful in determining which of two or more designs would be subject to the lesser pulsation losses. 4. The effect of saturation in the iron is determined experimentally by making the ratio of the mercury to the electrode resistance small. This ratio corresponds to the magnetic permeability. The effect of the tooth resistance on the amplitude of the pulsation is calculated by assuming three resistances in series, namely, the stator and rotor tooth resistances and the air gap resistance. The calculated and test values check reasonably well. 5. It is shown that the effect of saturation on pulsation amplitude for actual machines can not be calculated by adding directly the air gap and tooth reluctances due to the fact that the permeability of iron is not constant. In order to actually calculate the effect of saturation, it is necessary either to plot portions of the magnetization curve or to make use as we do of the incremental permeability values. 6. The method described of allowing for saturation is too complicated for ordinary design calculations but is useful in giving a clearer picture of just what these effects are and could be successfully used for special cases where the extra labor involved was warranted. 7. These methods do not apply when short-circuited windings are present in the slots. It is hoped at a later date to consider this aspect of the problem. 8. We believe it is possible by the use of the outlined methods below to calculate simple, reasonably reliable correction curves for saturation effects which may be used both for the case of uniform mean flux and for a sine distribution of the mean flux.

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