1.
Trolleybus
–
A trolleybus is an electric bus that draws power from overhead wires using spring-loaded trolley poles. Two wires and poles are required to complete the electrical circuit and this differs from a tram or streetcar, which normally uses the track as the return path, needing only one wire and one pole. They are also distinct from other kinds of buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there have been, currently, around 300 trolleybus systems are in operation, in cities and towns in 43 countries. Altogether, more than 800 trolleybus systems have existed, but not more than about 400 concurrently, the trolleybus dates back to 29 April 1882, when Dr. Ernst Werner Siemens demonstrated his Elektromote in a Berlin suburb. This experiment continued until 13 June 1882, after there were few developments in Europe. In 1899, another vehicle which could run either on or off rails was demonstrated in Berlin, routes followed in Eberswalde and Fontainebleau. Max Schiemann on 10 July 1901 opened the worlds fourth passenger-carrying trolleybus system, although this system operated only until 1904, Schiemann had developed what is now the standard trolleybus current collection system. In the early days there were a few methods of current collection. The Cédès-Stoll system was operated near Dresden between 1902 and 1904, and in Vienna, the Lloyd-Köhler or Bremen system was tried out in Bremen, and the Cantono Frigerio system was demonstrated near Milan. Throughout the period, trackless freight systems and electric canal boats were also built, Leeds and Bradford became the first cities to put trolleybuses into service in Great Britain on 20 June 1911. Apparently, though it was opened on 20 June, the public was not admitted to the Bradford route until the 24th, Bradford was also the last to operate trolleybuses in the UK, the system closing on 26 March 1972. The last rear-entrance trolleybus in Britain was also in Bradford and is now owned by the Bradford Trolleybus Association, birmingham was the first to replace a tram route with trolleybuses, while Wolverhampton, under the direction of Charles Owen Silvers, became world-famous for its trolleybus designs. There were 50 trolleybus systems in the UK, Londons being the largest, by the time trolleybuses arrived in Britain in 1911, the Schiemann system was well established and was the most common, although the Cédès-Stoll system was tried in West Ham and in Keighley. Smaller trackless trolley systems were built in the US early as well, the trackless trolley was often seen as an interim step, leading to streetcars. Buses and trolleybuses in particular were seen as entry systems that could later be upgraded to rail as appropriate, some trolleybus lines in the United States came into existence when a trolley or tram route did not have sufficient ridership to warrant track maintenance or reconstruction. In a similar manner, a proposed tram scheme in Leeds, worldwide, around 300 cities or metropolitan areas are served by trolleybuses today. See also Trolleybus usage by country, for example, new systems opened in Lecce, Italy, in 2012 and in Malatya, Turkey, in 2015
2.
Tram
–
A tram is a rail vehicle which runs on tracks along public urban streets, and also sometimes on a segregated right of way. The lines or networks operated by tramcars are called tramways, Tramways powered by electricity, the most common type historically, were once called electric street railways. However, trams were used in urban areas before the universal adoption of electrification. Tram lines may run between cities and/or towns, and/or partially grade-separated even in the cities. Very occasionally, trams also carry freight, Tram vehicles are usually lighter and shorter than conventional trains and rapid transit trains, but the size of trams is rapidly increasing. Some trams may also run on railway tracks, a tramway may be upgraded to a light rail or a rapid transit line. For all these reasons, the differences between the modes of rail transportation are often indistinct. In the United States, the tram has sometimes been used for rubber-tired trackless trains. Today, most trams use electrical power, usually fed by a pantograph, in some cases by a sliding shoe on a third rail. If necessary, they may have dual power systems — electricity in city streets, trams are now included in the wider term light rail, which also includes segregated systems. The English terms tram and tramway are derived from the Scots word tram, referring respectively to a type of truck used in coal mines and the tracks on which they ran. The word tram probably derived from Middle Flemish trame, a Romanesque word meaning the beam or shaft of a barrow or sledge, the identical word la trame with the meaning crossbeam is also used in the French language. The word Tram-car is attested from 1873, although the terms tram and tramway have been adopted by many languages, they are not used universally in English, North Americans prefer streetcar, trolley, or trolleycar. The term streetcar is first recorded in 1840, and originally referred to horsecars, when electrification came, Americans began to speak of trolleycars or later, trolleys. The troller design frequently fell off the wires, and was replaced by other more reliable devices. The terms trolley pole and trolley wheel both derive from the troller, Modern trams often have an overhead pantograph mechanical linkage to connect to power, abandoning the trolley pole altogether. Conventional diesel tourist buses decorated to look like streetcars are sometimes called trolleys in the US, the term may also apply to an aerial ropeway, e. g. the Roosevelt Island Tramway. Over time, the trolley has fallen into informal use
3.
Electric locomotive
–
An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or fuel cell. Electricity is used to smoke and take advantage of the high efficiency of electric motors. One advantage of electrification is the lack of pollution from the locomotives, electrification results in higher performance, lower maintenance costs and lower energy costs. Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines, the power can come from clean or renewable sources, including geothermal power, hydroelectric power, nuclear power, solar power and wind turbines. Electric locomotives are quiet compared to locomotives since there is no engine and exhaust noise. The lack of reciprocating parts means electric locomotives are easier on the track, Electric locomotives are ideal for commuter rail service with frequent stops. They are used on high-speed lines, such as ICE in Germany, Acela in the U. S. Shinkansen in Japan, China Railway High-speed in China, Electric locomotives are used on freight routes with consistently high traffic volumes, or in areas with advanced rail networks. Electric locomotives benefit from the efficiency of electric motors, often above 90%. Additional efficiency can be gained from regenerative braking, which allows energy to be recovered during braking to put power back on the line. Newer electric locomotives use AC motor-inverter drive systems provide for regenerative braking. The chief disadvantage of electrification is the cost for infrastructure, overhead lines or third rail, substations, public policy in the U. S. interferes with electrification, higher property taxes are imposed on privately owned rail facilities if they are electrified. In Europe and elsewhere, railway networks are considered part of the transport infrastructure, just like roads, highways and waterways. Operators of the rolling stock pay fees according to rail use and this makes possible the large investments required for the technically and, in the long-term, also economically advantageous electrification. Because railroad infrastructure is owned in the U. S. railroads are unwilling to make the necessary investments for electrification. The first known electric locomotive was built in 1837 by chemist Robert Davidson of Aberdeen and it was powered by galvanic cells. Davidson later built a locomotive named Galvani, exhibited at the Royal Scottish Society of Arts Exhibition in 1841. The seven-ton vehicle had two direct-drive reluctance motors, with fixed electromagnets acting on iron bars attached to a cylinder on each axle. It hauled a load of six tons at four miles per hour for a distance of one and it was tested on the Edinburgh and Glasgow Railway in September of the following year, but the limited power from batteries prevented its general use
4.
Electric multiple unit
–
An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as traction motors are incorporated within one or a number of the carriages. An EMU is usually formed of two or more semi-permanently coupled carriages, but electrically powered single-unit railcars are also classed as EMUs. EMUs are popular on commuter and suburban rail networks around the world due to their fast acceleration, being quieter than DMUs and locomotive-drawn trains, EMUs can operate later at night and more frequently without disturbing residents living near the railway lines. The first EMUs were used on the elevated Liverpool Overhead Railway in 1893, the southern terminal of the railway was underground, giving the LOR the distinction of also being the first to use EMUs underground. Each carriage had a traction motor and was specifically designed and constructed to be light in weight while running on elevated steel sections. The first EMUs were two-carriage trains later graduating to three carriages, with the front and rear carriages powered, Liverpool Museum retains an example of the Liverpool Overhead Railway EMU carriage. An early proponent of EMUs was the American engineer Frank J. Sprague, 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 car or power-driving car. A power car carries the equipment to draw power from the electrified infrastructure, such as pickup shoes for third rail systems and pantographs for overhead systems. Motor cars carry the traction motors to move the train, and are combined with the power car to avoid high-voltage inter-car connections. Driving cars are similar to a cab car, containing a drivers cab for controlling the train, an EMU will usually have two driving cars at its outer ends. Trailer cars are any cars that carry little or no traction or power related equipment, 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 2-car EMU sets are set up as married pair units, while both units in a married pair are typically driving motors, the ancillary equipment are shared between the two cars in the set. Since neither car can operate without its partner, such sets are permanently coupled, advantages of married pair units include weight and cost savings over single-unit cars while allowing all cars to be powered, unlike a motor-trailer combination. Disadvantages include a loss of 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. The retired New York–Washington Metroliner service, first operated by the Pennsylvania Railroad and later by Amtrak, also featured high-speed electric multiple-unit cars, diesel multiple unit Battery electric multiple unit British electric multiple units Media related to Electric multiple unit at Wikimedia Commons
5.
Electric power
–
Electric power is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second, Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries. It is usually supplied to businesses and homes by the power industry through an electric power grid. Electric power is sold by the kilowatt hour which is the product of power in kilowatts multiplied by running time in hours. Electric utilities measure power using an electricity meter, which keeps a total of the electric energy delivered to a customer. Electrical power provides a low form of energy and can be carried long distances and converted into other forms of energy such as motion. Electric power, like power, is the rate of doing work, measured in watts. The term wattage is used colloquially to mean electric power in watts, the potential energy of the charges due to the voltage between the terminals is converted to kinetic energy in the device. These devices are called passive components or loads, they consume electric power from the circuit, converting it to other forms of such as mechanical work, heat, light. Examples are electrical appliances, such as bulbs, electric motors. In alternating current circuits the direction of the voltage periodically reverses, devices in which this occurs are called active devices or power sources, such as electric generators and batteries. Some devices can be either a source or a load, depending on the voltage, for example, a rechargeable battery acts as a source when it provides power to a circuit, but as a load when it is connected to a battery charger and is being recharged. Since electric power can flow either into or out of a component, Electric power flowing out of a circuit into a component is arbitrarily defined to have a positive sign, while power flowing into a circuit from a component is defined to have a negative sign. Thus passive components have positive power consumption, while power sources have negative power consumption and this is called the passive sign convention. In alternating current circuits, energy storage such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a cycle of the AC waveform. That portion of power due to stored energy, that returns to the source in each cycle, is known as reactive power. Real power is represented as a vector and reactive power is represented as a vertical vector
6.
Overhead line
–
An overhead line or overhead wire is used to transmit electrical energy to trams, trolleybuses, or trains. Overhead line is designed on the principle of one or more overhead wires situated over rail tracks, the feeder stations are usually fed from a high-voltage electrical grid. Electric trains that collect their current from overhead lines use a device such as a pantograph and it presses against the underside of the lowest overhead wire, the contact wire. Current collectors are electrically conductive and allow current to flow through to the train or tram, non-electric locomotives may pass along these tracks without affecting the overhead line, although there may be difficulties with overhead clearance. Alternative electrical power transmission schemes for trains include third rail, ground-level power supply, batteries and this article does not cover regenerative braking, where the traction motors act as generators to retard movement and return power to the overhead. To achieve good high-speed current collection, it is necessary to keep the wire geometry within defined limits. This is usually achieved by supporting the wire from a second wire known as the messenger wire or catenary. This wire approximates the path of a wire strung between two points, a catenary curve, thus the use of catenary to describe this wire or sometimes the whole system. This wire is attached to the wire at regular intervals by vertical wires known as droppers or drop wires. It is supported regularly at structures, by a pulley, link, the whole system is then subjected to a mechanical tension. As the contact wire makes contact with the pantograph, the insert on top of the pantograph is worn down. The straight wire between supports will cause the wire to cross over the whole surface of the pantograph as the train travels around the curve, causing uniform wear. On straight track, the wire is zigzagged slightly to the left. The movement of the wire across the head of the pantograph is called the sweep. The zigzagging of the line is not required for trolley poles. Depot areas tend to have only a wire and are known as simple equipment or trolley wire. When overhead line systems were first conceived, good current collection was only at low speeds. Compound equipment - uses a second wire, known as the auxiliary
7.
Third rail
–
A third rail is a method of providing electric power to a railway locomotive or train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a transit or rapid transit system. Third rail systems are supplied from direct current electricity. The third-rail system of electrification is unrelated to the third used in dual gauge railways. Third-rail systems are a means of providing electric power to trains. On most systems, the rail is placed on the sleeper ends outside the running rails. The conductor rail is supported on ceramic insulators or insulated brackets, the trains have metal contact blocks called shoes which make contact with the conductor rail. The traction current is returned to the station through the running rails. The conductor rail is made of high conductivity steel. The conductor rails have to be interrupted at level crossings, crossovers, tapered rails are provided at the ends of each section, to allow a smooth engagement of the trains contact shoes. Because third rail systems present electric shock hazards close to the ground, a very high current must therefore be used to transfer adequate power, resulting in high resistive losses, and requiring relatively closely spaced feed points. The electrified rail threatens electrocution of anyone wandering or falling onto the tracks. This can be avoided by using platform screen doors, or the risk can be reduced by placing the rail on the side of the track away from the platform. There is also a risk of pedestrians walking onto the tracks at level crossings, the Paris Metro has graphic warning signs pointing out the danger of electrocution from urinating on third rails, precautions which Chicago did not have. The end ramps of conductor rails present a practical limitation on speed due to the impact of the shoe. The world speed record for a rail train is 174 km/h attained on 11 April 1988 by a British Class 442 EMU. In the event of a collision with an object, the beveled end ramps of bottom running systems can facilitate the hazard of having third rail penetrate the interior of a passenger car. This is believed to have contributed to the death of five passengers in the Valhalla train crash of 2015, third rail systems using top contact are prone to accumulations of snow, or ice formed from refrozen snow, and this can interrupt operations
8.
Electrical resistivity and conductivity
–
Electrical resistivity is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ, the SI unit of electrical resistivity is the ohm-metre. Electrical conductivity or specific conductance is the reciprocal of electrical resistivity and it is commonly represented by the Greek letter σ, but κ or γ are also occasionally used. Its SI unit is siemens per metre and CGSE unit is reciprocal second, many resistors and conductors have a uniform cross section with a uniform flow of electric current, and are made of one material. All copper wires, irrespective of their shape and size, have approximately the same resistivity, every material has its own characteristic resistivity – for example, resistivity of rubber is far larger than coppers. If the pipes are the size and shape, the pipe full of sand has higher resistance to flow. Resistance, however, is not solely determined by the presence or absence of sand and it also depends on the length and width of the pipe, short or wide pipes have lower resistance than narrow or long pipes. The above equation can be transposed to get Pouillets law, R = ρ ℓ A, the resistance of a given material increases with length, but decreases with increasing cross-sectional area. From the above equations, resistivity has the SI unit ohm metre, the formula R = ρ ℓ / A can be used to intuitively understand the meaning of a resistivity value. For example, if A = 7000100000000000000♠1 m2 ℓ = 7000100000000000000♠1 m, Conductivity, σ, is defined as the inverse of resistivity, σ =1 ρ. Conductivity has SI units of siemens per metre, the above definition was specific to resistors or conductors with a uniform cross-section, where current flows uniformly through them. A more basic and general definition starts from the fact that a field inside a material makes electric current flow. Conductivity is the inverse, σ =1 ρ = J E, for example, rubber is a material with large ρ and small σ—because even a very large electric field in rubber makes almost no current flow through it. On the other hand, copper is a material with small ρ, according to elementary quantum mechanics, electrons in an atom do not take on arbitrary energy values. Rather, electrons only occupy discrete energy levels in an atom or crystal. When a large number of such allowed energy levels are spaced close together —i. e. have similar energies— we can talk about these energy levels together as an energy band. There can be many such bands in a material, depending on the atomic number
9.
Insulator (electricity)
–
An electrical insulator is a material whose internal electric charges do not flow freely, very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily, the property that distinguishes an insulator is its resistivity, insulators have higher resistivity than semiconductors or conductors. A perfect insulator does not exist, because even insulators contain small numbers of mobile charges which can carry current, in addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as the voltage of an insulator. Some materials such as glass, paper and Teflon, which have high resistivity, are good electrical insulators. Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature, insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation, the term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground, electrical insulation is the absence of electrical conduction. Electronic band theory says that a charge flows if states are available into which electrons can be excited and this allows electrons to gain energy and thereby move through a conductor such as a metal. If no such states are available, the material is an insulator, most insulators have a large band gap. This occurs because the valence band containing the highest energy electrons is full, there is always some voltage that gives electrons enough energy to be excited into this band. Once this voltage is exceeded the material ceases being an insulator, however, it is usually accompanied by physical or chemical changes that permanently degrade the materials insulating properties. Materials that lack electron conduction are insulators if they lack other mobile charges as well, for example, if a liquid or gas contains ions, then the ions can be made to flow as an electric current, and the material is a conductor. Electrolytes and plasmas contain ions and act as conductors whether or not electron flow is involved, when subjected to a high enough voltage, insulators suffer from the phenomenon of electrical breakdown. These freed electrons and ions are in turn accelerated and strike other atoms, creating more charge carriers, rapidly the insulator becomes filled with mobile charge carriers, and its resistance drops to a low level. In a solid, the voltage is proportional to the band gap energy. The air in a region around a conductor can break down and ionise without a catastrophic increase in current. Even a vacuum can suffer a sort of breakdown, but in case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself
10.
Switch
–
In electrical engineering, a switch is an electrical component that can make or break an electrical circuit, interrupting the current or diverting it from one conductor to another. The mechanism of a switch removes or restores the conducting path in a circuit when it is operated, the most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. The mechanism actuating the transition between two states can be either a toggle or momentary type. A switch may be manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit. Switches may be operated by process variables such as pressure, temperature, flow, current, voltage, for example, a thermostat is a temperature-operated switch used to control a heating process. A switch that is operated by electrical circuit is called a relay. Large switches may be operated by a motor drive mechanism. An ideal switch would have no voltage drop when closed, and it would have zero rise time and fall time during state changes, and would change state without bouncing between on and off positions. Practical switches fall short of ideal, they have resistance, limits on the current and voltage they can handle, finite switching time. The ideal switch is used in circuit analysis as it greatly simplifies the system of equations to be solved. Theoretical treatment of the effects of non-ideal properties is required in the design of networks of switches. In the simplest case, a switch has two pieces, often metal, called contacts, connected to an external circuit, that touch to complete the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working, contact materials are also chosen on the basis of electrical conductivity, hardness, mechanical strength, low cost and low toxicity. Sometimes the contacts are plated with noble metals and they may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design, in electronics, switches are classified according to the arrangement of their contacts. A pair of contacts is said to be closed when current can flow from one to the other, when the contacts are separated by an insulating air gap, they are said to be open, and no current can flow between them at normal voltages. The terms make for closure of contacts and break for opening of contacts are also widely used, the terms pole and throw are also used to describe switch contact variations
.jpg)
