. Electric railway journal . serbeing operated by an air motor similarly to the series-parallel switch. The shunts and similar apparatus as-sociated with the motor fields are also designed forlow voltage. This current at reduced voltage is ob-tained from a motor-generator set directly connected tothe 3000-volt trolley supply. The set consists of a 3000-volt driving motor, a direct-connected fan for ventilat-ing the traction motors, an exciter and a small 125-voltgenerator. The exciter is used during electric brakingto super-excite the traction motor fields, and while notthus employed to rechar
. Electric railway journal . serbeing operated by an air motor similarly to the series-parallel switch. The shunts and similar apparatus as-sociated with the motor fields are also designed forlow voltage. This current at reduced voltage is ob-tained from a motor-generator set directly connected tothe 3000-volt trolley supply. The set consists of a 3000-volt driving motor, a direct-connected fan for ventilat-ing the traction motors, an exciter and a small 125-voltgenerator. The exciter is used during electric brakingto super-excite the traction motor fields, and while notthus employed to recharge storage batteries for lightingin passenger service. The 125-volt generator supplies October 21, 1916] ELECTRIC RAILWAY JOURNAL 893 power for the master control circuits, cab lights, head-light and other low-voltage auxiliary circuits. Regenerative Electric Braking Regenerative electric braking is, doubtless, the mostinteresting feature of the control equipment. With thesimple direct-current motor adopted for the Milwaukee. C, M. & ST. P. LOCOMOTIVES—MOTOR-GENERATOR SET WITH FANHOUSING REMOVED locomotives, operation as a motor or a generator de-pends upon whether the trolley voltage at the locomo-tive is above or below the voltage at the motor ter-minals. Hence, when the locomotive descends a gradeand is to brake regeneratively, it is necessary only toeffect an increase in the voltage across the motor ter-minals so that power is pumped from the locomotiveinto the transmission system. The means for thusraising the voltage level of the motor rests in the useof the before-mentioned exciter, which is so connectedas to super-excite the traction motor fields. By prop-erly proportioning the design of the exciter for itsservice, the stable characteristic of the series motor isinherent in the braking connection as in the motor con-nection. Since the generative function is a reversalof the motor function, the traction motors provide inregeneration that, with an increase in speed, the
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