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VIII. Note on the Governing of Electromotors. 

 By W. E. Ayrtox and John Perry*. 



IN 1882 a method was brought forward by us for governing 

 electromotors, so that their speed should not be varied 

 by an alteration in the load. The method, which was worked 

 out theoretically and experimentally, was based on the com- 

 bination of a motor, which converted electric energy into me- 

 chanical energy, with a brake dynamo, which reconverted the 

 surplus mechanical energy into electric energy. After passing 

 through various stages the arrangement finally resolved itself 

 into an electromotor having the field-magnet wound with a 

 shunt- and a series-coil, the coils being so connected with the 

 rest of the circuit that the currents passed round them in 

 opposite directions. Hence the magnetic excitation of the 

 field-magnet was produced by the difference in the number of 

 ampere-turns of the two circuits passing round it. 



This method of governing motors, which has since 1882 

 been reinvented in France by M. Deprez, in America by Mr. 

 Sprague, and which has formed the subject of an exhaustive 

 series of experiments carried out in Germany by Dr. Frohlich, 

 answers well and produces a very fair constancy of speed 

 for very considerable variations of the load. But it has a 

 very decided defect, arising from the fact that since the 

 series- and shunt-coils on the field-magnet oppose one 

 another's action, the magnetization cannot be produced as 

 economically as if there w T ere no such differential action. 

 Mainly on this account w r e have not developed our method 

 of governing as energetically as we might otherwise have 

 been led to do. 



In our original investigation of the subject we considered 

 the conditions for governing motors either when a constant 

 PD. (potential-difference) or when a constant current was 

 supplied, and in both cases the practical solution we arrived 

 at was a differential winding of the field-magnet. But we 

 have since noticed that, in the case of the supply conditions 

 being constant current, our original equations could be 

 differently interpreted, and that the demagnetizing series 

 could be dispensed with. Consequently a motor for constant 

 current can be made to go at a constant speed with a varying 

 load, and in addition to have the high efficiency of a well- 

 made dynamo. 



We shall for the general consideration of the problem use 

 the simplest equations for a motor, disregarding saturation, 



* Communicated by the Physical Society : read May 26, 1888. 



