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A traction motor is an electric motor used for propulsion of a vehicle, such as an electric locomotive or electric roadway vehicle. Traction motors are used in electrically powered rail vehicles such as electric multiple units and other electric vehicles such as electric milk floats, elevators, conveyors, and trolleybuses, as well as vehicles with electrical transmission systems such as diesel-electric, electric hybrid vehicles, and battery electric vehicles. ==Motor types and control== Direct-current motors with series field windings were the oldest type of traction motors. These provided a speed-torque characteristic useful for propulsion, providing high torque at lower speeds for acceleration of the vehicle, and declining torque as speed increased. By arranging the field winding with multiple taps, the speed characteristic could be varied, allowing relatively smooth operator control of acceleration. A further measure of control was provided by using pairs of motors on a vehicle; for slow operation or heavy loads, two motors could be run in series off the direct current supply. Where higher speed was desired, the motors could be operated in parallel, making a higher voltage available at each and so allowing higher speeds. Parts of a rail system might use different voltages, with higher voltages in long runs between stations and lower voltage near stations where slower operation would be useful. A variant of the DC system was the AC operated series motor, which is essentially the same device but operated on alternating current. Since both the armature and field current reverse at the same time, the behavior of the motor is similar to that when energized with direct current. To achieve better operating conditions, AC railways were often supplied with current at a lower frequency than the commercial supply used for general lighting and power; special traction current power stations were used, or rotary converters used to convert 50 or 60 Hz commercial power to the 16 2/3 Hz frequency used for AC traction motors. The AC system allowed efficient distribution of power down the length of a rail line, and also permitted speed control with switchgear on the vehicle. AC induction motors and synchronous motors are simple and low maintenance, but are awkward to apply for traction motors because of their fixed speed characteristic. An AC induction motor only generates useful amounts of power over a narrow speed range determined by its construction and the frequency of the AC power supply. The advent of power semiconductors has made it possible to fit a variable frequency drive on a locomotive; this allows a wide range of speeds, AC power transmission, and rugged induction motors without wearing parts like brushes and commutators. 〔 Andreas Steimel ''Electric Traction - Motive Power and Energy Supply: Basics and Practical Experience '' Oldenbourg Industrieverlag, 2008 ISBN 3835631322 ; Chapter 6 "Induction Traction Motors and Their Control" 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Traction motor」の詳細全文を読む スポンサード リンク
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