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A railway electrification system supplies electrical energy to railway traction units for Propulsion purposes. In more simple terms, it supplies Electricity to Trains so they can move. There are many systems for doing this, each with distinctive advantages and disadvantages. , USA.]] CHARACTERISTICS The main advantage of electric trains is the superior Acceleration , due to the excess of Power-to-weight Ratio that can be obtained by modern electric trains. Other advantages include the lack of exhaust fumes at point of use, less noise and lower maintenance requirements of the traction units. In countries where electricity comes primarily from non-fossil sources, such as Austria and France, electric trains also produce fewer carbon emissions than diesel trains. The main disadvantage is the capital cost of the electrification equipment, which tends to militate against electrification of long distance lines that do not carry a heavy service. Suburban railways with closely-spaced stations and high traffic density are the most likely to be electrified, but main lines carrying heavy and frequent traffic are also electrified in many countries. CLASSIFICATION Electrification systems are classified by three main parameters: :The common voltages are simple multiples of each other: :: 1200 V DC = 2 x 600 V DC :: 1500 V DC = 2 x 750 V DC :: 3000 V DC = 2 x 1500 V DC
: This can be direct current ( DC ) or alternating current ( AC ). For AC systems, the frequency (Hertz) is also given. In general, it is assumed that AC systems are Single-phase , but if they are not (e.g. Three-phase ), then this should also be stated.
:This refers to the means by which traction current is collected by the traction unit. There are two main types: ( Conductor Rail and Overhead Line ). DIRECT CURRENT network uses 750 V DC overhead, in common with most modern Tram systems.]] Early electric systems used relatively low-voltage DC . Electric Motor s were fed directly from the traction supply, and were controlled using a combination of Resistor s and Relay s that connected the motors in Parallel or Series . The most common voltages are 600 V and 750 V for Tram s and Metro s, and 1500 V and 3000 V for railways. The lower voltages are often used with third or fourth rail systems, but voltages above 1000 V are generally limited to overhead wiring for safety reasons. Through the middle 20th century, Rotary Converter s or Mercury Arc Rectifiers were used to convert utility (mains) AC power to the required DC voltage at the feeder stations. Today, this is usually done by Semiconductor Rectifier s after transforming the voltage down from the utility supply. | ||
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