Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . r anyparticular voltagewith the main cir-cuit open, say 112volts, and theswitch is now closedso that more cur-rent flows from thearmature, the volt-meter at once indi-cates a lower volt-age, say 108 the speed is thesame as before, thisloss is due to twocauses: first, there is an increased drop in the armature dueto the additional current flowing through it, which lowers thepotential difference at the brushes ; second, the potentialdifference at the brushes being lowered, les
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . r anyparticular voltagewith the main cir-cuit open, say 112volts, and theswitch is now closedso that more cur-rent flows from thearmature, the volt-meter at once indi-cates a lower volt-age, say 108 the speed is thesame as before, thisloss is due to twocauses: first, there is an increased drop in the armature dueto the additional current flowing through it, which lowers thepotential difference at the brushes ; second, the potentialdifference at the brushes being lowered, less current flowsaround the field, so that there are not quite so many lines offorce cut as before. When the load is switched on to a shuntdynamo, the resistance in the field rheostat must therefore bediminished so that the voltage will be raised to its former value. Again, in the above case, if after the voltage is raised from108 to 112 volts the load be disconnected, the voltmeter will,indicate a higher voltage than 112 volts, say 116, and resist-ance must now be inserted in the field rheostat to lower the. Fig. 363.—Regulating the E. M. F. at the Brushesof a Shunt dynamo by the Shunt Field Rheostat. 382 PRACTICAL ELECTRICITY. voltage. The potential difference at the brushes thus varies,in a shunt dynamo, with each change in load, increasing asthe load decreases and decreasing as the load increases. If thecurrent fluctuations are wide and quite frequent, as on trolleylines where the cars are started and stopped so often, an at-tendant would be constantly required to manipulate therheostat, or some automatic device employed for this purpose,so that this machine is not suitable for such work. Shuntdynamos are adapted to cases where the load is constantwhen they will require very little attention after the properregulation has been made ; they are classified as constantpotential dynamos and may be connected in parallel when
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