. Electric traction and transmission engineering . TROLLEYSFig. 12. of a Scott transformer, each phase of which supplies single-phase current to the motors on one side of the 12 shows the scheme of connections. A single-phaseload drawn from one phase of a large polyphase systemunbalances the system for use otherwise. Phase convertersor modifiers are used to restore this balance. There are several types of alternating-current single-phase railway motors at present in operation, but of thesethe compensated series motor is the only one used in thiscountry. 30 TRACTION AND TRANSMISSIO
. Electric traction and transmission engineering . TROLLEYSFig. 12. of a Scott transformer, each phase of which supplies single-phase current to the motors on one side of the 12 shows the scheme of connections. A single-phaseload drawn from one phase of a large polyphase systemunbalances the system for use otherwise. Phase convertersor modifiers are used to restore this balance. There are several types of alternating-current single-phase railway motors at present in operation, but of thesethe compensated series motor is the only one used in thiscountry. 30 TRACTION AND TRANSMISSION. Series Motors. — Consider a direct-current armaturemounted within a single-phase alternating magnetic fieldsas in Fig. 13. When the armature is stationary an electro^motive force will be induced in the armature turns, dueto the alternating flux which passes between the fieldpoles. The greatest will be induced in the turnsperpendicular to the field axis, since these turns link with. Fig. 13. the greatest number of lines of force; and no willbe induced in the turns in line with the field axis. Thedirections of the induced in the armature turnsby the change in -field flux are indicated in the figure bythe full arrows, and it is seen that the maximum value ofthis is across BC. As in transformers, the effec-tive value of this electromotive force is „ 2 irf^„NKt = —=—-V 2 10* where $„ is the maximum value of the flux entering the (i) TYPES AND PERFORMANCE CURVES OF MOTORS. 31 armature and N is the equivalent number of armature turns. The maximum number of lines of force linked with a single turn depends upon the position of this turn in the magnetic field, and is proportional to the greatest value of $m times the cosine of the angle of displacement of the turn from the position AD. Assuming the turns to be evenly distributed over the periphery of the armature, the average value of the maximum flux linked with the arma- 2ture turns will
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