TransactionsPublished under the care of the General Secretary and the Treasurer . ator varies too much. Hence follows that the greatest additional current «^„, m theshort-circuited coils proceeding from the voltage A/> is propor-tional to the hatched area which lies between the potential curveand the axis of abscissae. (Fig. 26.) In the experimenting room of a factory it is often desirable tobe able to investigate large direct-current machines in respect to 826 ARNOLD AND LA COUR: COMMUTATION. the commutation without being obliged to load them can be done in the following wa
TransactionsPublished under the care of the General Secretary and the Treasurer . ator varies too much. Hence follows that the greatest additional current «^„, m theshort-circuited coils proceeding from the voltage A/> is propor-tional to the hatched area which lies between the potential curveand the axis of abscissae. (Fig. 26.) In the experimenting room of a factory it is often desirable tobe able to investigate large direct-current machines in respect to 826 ARNOLD AND LA COUR: COMMUTATION. the commutation without being obliged to load them can be done in the following way very simply. One recordsthe potential curve under the brush at light load and normal volt-age, and on short-circuit with normal current. By superposingthese coirves one obtains a potential curve, which varies little fromthat with load. This is easily explicable.* In the short-circuitedgenerator a field arises which does not differ much from thecross-field of the loaded machine. The slot-field is on short-circuit, also the same as with load. Hence it follows that the field. Tig. 27. Potentiai,Curves Under theBrushes at No-LOAD, FOB Short- CiBCuiT AND WhenLoaded. curve with load results approximately from the field curves onno-load and on short-circuit. The same is true, of course, for the potential curves, if we dis-regard their deformation under the brushes. This deformation, asshown above, is not great, and would influence all curves corre-spondingly, if the specific resistance of transition B,, were constantfor all curves. In the potential curves (Figs. 27 and 28), which were recorded 4. See J. L. la Cour, Leerlauf und Kurzschhissversuch in Thoorie uiidPraxis. ARNOLD AND LA COUR- COMMUTATION. 827 b} Mr. K. Czeija at the Electrotechnic Institute in Karlsruhe,curves I represent potential curves at no load, curves //those with short-circuit, curves /// those with load under thebrushes, while curves 777 result from superposition of curves 7and 77. The curves in Fig. 27
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