. Electric traction and transmission engineering . nsatortaps, each of which supplies a definite fractional part of themotor current. The essential features of this method areillustrated in Fig. 43. In the particular scheme of connec-tions there depicted, three preventive coils are used todivide the motor current into four approximately equalparts. The first running position of the controller is at-tained by closing switches 1, 2, 3, and 4. The voltageapplied to the motor circuit when the controller is in thisposition is evidently equal to the potential relative toground of a point on the comp
. Electric traction and transmission engineering . nsatortaps, each of which supplies a definite fractional part of themotor current. The essential features of this method areillustrated in Fig. 43. In the particular scheme of connec-tions there depicted, three preventive coils are used todivide the motor current into four approximately equalparts. The first running position of the controller is at-tained by closing switches 1, 2, 3, and 4. The voltageapplied to the motor circuit when the controller is in thisposition is evidently equal to the potential relative toground of a point on the compensator winding midwaybetween taps 1 and 4. When the controller handle ismoved to the second running position switch 1 is opened, 94 TRACTION AND TRANSMISSION. followed by the closing of switch 5. Similarly, to pass tothe third running point, switch 2 is opened and then switch6 is closed; and so on until the motors are supplied withcurrent at rated voltage through switches 5, 6, 7, and is obvious that during transition from one running point. TO MOTORS GROUND Fig. 43. to another the full motor current is maintained withoutshort-circuiting any portion of the compensator each switch is required to handle only a fractionalpart of the total current supplied to the motor circuit, thismethod is well suited for use with railway equipments oflarge capacity. In cases where single-phase series motors are required to RAILWAY MOTOR CONTROL. 95 operate on direct current over a portion of the roadway,some form of rheostatic or series-parallel control must beinstalled for use during the periods of direct-current oper-ation. The losses that would result from the use of start-ing resistances during the intervals of alternating-currentoperation are, however, in general sufficient to justify theinstallation of compensator control for use on the sec-tions where alternating current is employed. This com-pensator may constitute a part of the autotransformerwhich is used to step do
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