Tag Archives: Locomotive

Electric Locomotive – Technological Overview

Electric Locomotive is that locomotive which is powered in turn by electricity by means of third rail, on-board energy storages like fuel cell or battery or the overhead lines. Electric Locomotives along with on-board prime fueled movers like gas turbines or diesel engines are classified as gas turbine- or diesel- electric locomotives. Reason is that electric motor/ generator combination only serves as system of power transmission. Electricity has been used for eliminating smoke and taking benefits of high efficiency of electric motors. But electrification costs have meaning that only usually heavy used lines are electrified. Electric Locomotive is supplied with powers from ultracapacitor-mining powered locomotives or rechargeable energy storage systems or stationary sources. Designing features distinguishing of Electric Locomotive is: Electrical power types used DC or AC. Storing ways (ultracapacitors, batteries) or transmission (collecting) electrical powers. Means used for coupling traction motors to drivers (driving wheels).

Alternating current and direct current: Most important differences lie in choices of DC or AC. Early systems used DC as AC had not been understood nicely. Insulation materials for high lines of voltage are not available. The DC locomotives run typically at relative low voltages (600 volts to 3000 volts). Equipment is relatively massive therefore since involved currents are large for transmitting power sufficient. Power is supplied at intervals frequently as high current results in system losses of large transmission. AC motors have been developed. They had become predominant types. This is on long routes particularly. High voltages (10s of 1000s of volts) have been used since these allow uses of low currents. Transmission losses have been proportional to square of current, meaning 2 times current means 4 times loss. High powers are conducted over longer distances on light and cheap wires. The transformers in locomotives transform power to low voltages and high currents for motors. Same low current high voltage system is employed with locomotives of DC. There are no easy ways of doing current/voltage transformation for DC. This is efficient as got by AC transformers.

Transmission of power: Electrical circuits need 2 connections or 3 connections for 3 phase AC. From beginning, tracks are used for 1 circuit side. Unlike railroads model track supplies normally 1 side only. Other circuit side is separately provided. Original electrification of Baltimore and Ohio Railroad uses sliding shoe in overhead channels. This system found quickly being unsatisfactory. This was by third rail replaced. In this, “shoe” (pickup) rode on top or underneath of small rail paralleled to main tracks on top of ground level is there. Multiple pickups are there on 2 sides of locomotives for break accommodation in third rail. This is needed by trackwork. System is thereby preferred in the subway since it affords close clearances. Railways prefer overhead lines called often “catenaries” after support system is used for holding wires paralleled to ground. 3 collection ways are possible: Bow collector: It is frame which holds long collecting rods against wires. Pantograph: It is hinged frame which holds collecting shoe against wires in fixed geometries. Trolley Pole: It is flexible long pole that engages line with shoe or wheel. Driving wheels: During developments initially of electrical railroad propulsion, plenty of drive systems had been devised for coupling output of traction motors to wheels. Locomotive early often used jackshaft drives. In arrangement like this, traction motors are mounted inside locomotive body and drives jackshaft by means of gear’s set. System had been employed since 1st traction motors are too heavy and large for direct mountings on axles. Plenty of mechanical parts are involved. Frequent maintenance is necessary. Jackshaft drives are abandoned for all. But small units when light and small motors were developed.

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