Electric multiple unit
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An electric multiple unit or EMU is a
EMUs are popular on commuter, and suburban rail networks around the world due to their fast acceleration and pollution-free operation,[1] and are used on most rapid-transit systems. Being quieter than diesel multiple units (DMUs) and locomotive-hauled trains, EMUs can operate later at night and more frequently without disturbing nearby residents. In addition, tunnel design for EMU trains is simpler as no provision is needed for exhausting fumes, although retrofitting existing limited-clearance tunnels to accommodate the extra equipment needed to transmit electric power to the train can be difficult.
History
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Multiple unit train control was first used in the 1890s.
The Liverpool Overhead Railway opened in 1893 with two-car electric multiple units,[2] controllers in cabs at both ends directly controlling the traction current to motors on both cars.[3]
The multiple unit traction control system was developed by
Types
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The cars that form a complete EMU set can usually be separated by function into four types: power car, motor car, driving car, and trailer car. Each car can have more than one function, such as a motor-driving car or power-driving car.
- A power car carries the necessary equipment to draw power from the overhead systems, and transformers.
- Motor cars carry the traction motors to move the train, and are often combined with the power car to avoid high-voltage inter-car connections.
- Driving cars are similar to a cab car, containing a driver's cab for controlling the train. An EMU will usually have two driving cars at its outer ends.
- Trailer cars are any cars (sometimes semi-permanently coupled) that carry little or no traction or power related equipment, and are similar to passenger carsin a locomotive-hauled train.
On third rail systems, the outer vehicles usually carry the pick up shoes with the motor vehicles receiving the current via intra-unit connections.
Many modern two-car EMU sets are set up as twin or "married pair" units. While both units in a married pair are typically driving motors, the ancillary equipment (air compressor and tanks, batteries and charging equipment, traction power and control equipment, etc.) are shared between the two cars in the set. Since neither car can operate without its "partner", such sets are permanently coupled and can only be split at maintenance facilities. Advantages of married pair units include weight and cost savings over single-unit cars (due to halving the ancillary equipment required per set) while allowing all cars to be powered, unlike a motor-trailer combination. Each car has only one control cab, located at the outer end of the pair, saving space and expense over a cab at both ends of each car. Disadvantages include a loss of operational flexibility, as trains must be multiples of two cars, and a failure on a single car could force removing both it and its partner from service.
As high-speed trains
Some of the more famous electric multiple units in the world are high-speed trains: the Italian
Fuel cell development
EMUs powered by
Battery electric multiple unit
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Many battery electric multiple units are in operation around the world, with the take up being strong. Many are bi-modal taking energy from onboard battery banks and line pickups such as overhead wires or third rail. In most cases the batteries are charged via the electric pickup when operating on electric mode.
Comparison with locomotives
EMUs, when compared with electric locomotives, offer:[5]
- Higher acceleration, since there are more motors sharing the same load, more motors allows for a higher total motor power output
- Braking, including regenerative braking, on multiple axles at once, greatly reducing wear on brake parts (as the wear can be distributed among more brakes) and allowing for faster braking (lower/reduced braking distances)
- Reduced axle loads, since the need for a heavy locomotive is eliminated; this in turn allows for simpler and cheaper structures that use less material (like bridges and viaducts) and lower structure maintenance costs
- Reduced ground vibrations, due to the above
- Lower adhesion coefficients for driving (powered) axles, due to lower weight on these axles; weight is not concentrated on a locomotive
- A higher degree of redundancy – performance is only minimally affected following the failure of a single motor or brake
- Higher seating capacity, since there is no locomotive; all cars can contain seats.
Electric locomotives, when compared to EMUs, offer:
- Less electrical equipment per train resulting in lower train manufacturing and maintenance costs
- Easily allows for lower noise and vibration in passenger cars, since there are no motors or gearboxes on the bogies below the cars
See also
- Electro-diesel multiple unit
- Diesel multiple unit
- Battery electric multiple unit
- British electric multiple units
- MEMU
References
- ISBN 9788120314924.
- ^ "Liverpool Overhead Railway motor coach number 3, 1892". National Museums Liverpool. Retrieved 2011-01-21.
This is one of the original motor coaches which has electric motors mounted beneath the floor, a driving cab at one end and third class accommodation with wooden seats.
- Frank Sprague (18 January 1902). "Mr Sprague answers Mr Westinghouse". The New York Times. Retrieved 16 June 2012.
- ^ "What you need to know about Alstom's hydrogen-powered Coradia iLint – Global Rail News". globalrailnews.com. 24 October 2017.
- ^ Hata, Hiroshi. "What Drives Electric Multiple Units?" (PDF). Railway Technology Today. Archived from the original (PDF) on 1 November 2021. Retrieved 13 March 2022.
External links
Media related to Electric multiple units, motor coaches and railcars at Wikimedia Commons