GOVERNING OF M OTORti. —One of the earliest attempts to secure an automatic regulation of the speed was that of M. Marcel Deprez, who in Di78 applied an ingenious method of interrupting the current at a perfectly regular rate by introducing a vibrating brake into the circuit. It ran at a perfectly uniform speed, quite irrespective of the work it was doing. Deprez also showed that the torque of a motor depends only on the strength of the field and on the current, but does not depend on the speed. In dealing with this matter, in l.a Lumii?-re Pilectrigne of October 3. 18,S5. he says : "If a current traverses a motor having an armature of the Paeinot Li type, the turning effort of the latter is independent of its state of move ment or rest, and in motion it is independent of the speed, provided the strength of the cur rent is maintained constant. hi versely, if the static moment tending to resist the motion of the armature is maintained constant. the current will thereby automatically be kept constant, whatever means we may employ to vary it. Since with a. constant load the energy given out is proportional to the speed, and since the electrical energy supplied to the motor is the product of current and electro-motive force, it follows that if the current is constant tho speed must be proportional to the electro-motive force." Automatic GoverNing.—It was pointed out (see DyNAmo ELECTRIC MACHINERY) that a properly designed shunt-wound dynamo, if inn at constant speed, would generate a constant E. gtI. F. at all loads. Conversely. it can be shown that a shunt-wound machine, if supplied with current from mains at a constant potential, will maintain constant speed at all loads. For this reason the large majority of motors in use at present are of the shunbwound type, connected to constant potential circuit, as they regulate automatically.
In the same way. motors can be governed by compound winding of the field magnets ; but in such case the series coil must be wound differentially to the shunt winding to maintain constant speed. This method is claimed by Sprague and Ayrton and Perry. With this method of winding, the coil in series with the armature tends to weaken the field magnet ism, at any increase in load.
Centrifugal Governing.—Professors carton and Perry have also proposed several forms periodic " centrifugal governor, a device by which, in every revolution, power is sup plied during a portion of the revolution only, the proportion of the time in every revolu tion during which the power is supplied being made to vary according to the speed. The
main difficulty with such governors is to prevent sparking. But there is a still more radical defect in all centrifugal governors ; they all work too late. They do not perform their functions until the speed has changed.
Dynamometric Governing.—Prof. S. P. Thompson has devised another kind of gov ernor which is not open to this objection. He proposes to employ a dynamometer on the shaft of the motor to actuate a regulating apparatus, which may consist either of a periodic regulator to shunt or interrupt the current during a portion of each revolution. or of an adjustable resistance connected in part of the circuit. The regulator in this case is therefore worked, not according to the speed of the motor, but according to the load it is carrying. Any change in the load will instantly act on the dynamometrie governor before the speed has time to change.
Other _Methods of Governing.—Sprague and Andre have designed motors in which the field magnets are wound in two separate circuits, one with thick and the other with thin wire, the current dividing between them, and the armature connected as a bridge across these circuits, exactly as the galvanometer is connected across the circuits of a Wheatstone's bridge. Another method of governing, employed by Brush and Hochhausen, consists in building up the field-magnet coils in sections, and by varying the number of sections in circuit, or the mode of their connection, obtaining regulation of speed. This method is usually employed only on constant-current motors.
The method of constructing a motor with coils in sections, so that a movable internal core may be successively attracted as successive sections are switched in, has been made use of by Deprez in constructing an electric hammer. This principle of construction was employed by Page in his motors many years previously. For a complete discussion of the various methods of motor regulation, the reader is referred to a paper by Prof. F. B. Crocker, Trans. Am. Inst. Elect. Engrs., p. 237, vol. vi., 1880.