Railway electrification system
A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electrification has many advantages but requires significant capital expenditure, selection of an electrification system is based on economics of energy supply and capital cost compared to the revenue obtained for freight and passenger traffic. Different systems are used for urban and intercity areas, some electric locomotives can switch to different supply voltages to allow flexibility in operation, Electric railways use electric locomotives to haul passengers or freight in separate cars or electric multiple units, passenger cars with their own motors. Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network, some electric railways have their own dedicated generating stations and transmission lines but most purchase power from an electric utility. The railway usually provides its own lines and transformers.
Power is supplied to moving trains with a continuous conductor running along the track usually takes one of two forms. The first is a line or catenary wire suspended from poles or towers along the track or from structure or tunnel ceilings. Locomotives or multiple units pick up power from the wire with pantographs on their roofs that press a conductive strip against it with a spring or air pressure. Examples are described in this article, the second is a third rail mounted at track level and contacted by a sliding pickup shoe. Both overhead wire and third-rail systems usually use the rails as the return conductor. In comparison to the alternative, the diesel engine, electric railways offer substantially better energy efficiency, lower emissions. Electric locomotives are usually quieter, more powerful, and more responsive and they have no local emissions, an important advantage in tunnels and urban areas. Different regions may use different supply voltages and frequencies, complicating through service, the limited clearances available under catenaries may preclude efficient double-stack container service.
Possible lethal electric current due to risk of contact with high-voltage contact wires, overhead wires are safer than third rails, but they are often considered unsightly. These are independent of the system used, so that. The permissible range of voltages allowed for the voltages is as stated in standards BS EN50163. These take into account the number of trains drawing current and their distance from the substation, railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, since such conversion was not well developed in the late 19th century and early 20th century, most early electrified railways used DC and many still do, particularly rapid transit and trams
A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current of one frequency to alternating current of another frequency. The device may change the voltage, but if it does, these devices were electromechanical machines called a motor-generator set. Also devices with mercury arc rectifiers or vacuum tubes were in use, with the advent of solid state electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a stage which is inverted to produce AC of the desired frequency. The inverter may use thyristors, IGCTs or IGBTs, a battery may be added to the dc circuitry to improve the converters ride-through of brief outages in the input power. Frequency changers vary in power-handling capability from a few watts to megawatts, aside from the obvious application of converting bulk amounts of power from one distribution standard to another, frequency changers are used to control the speed and the torque of AC motors.
In this application, the most typical frequency converter topology is the three-phase two-level voltage source inverter, the phase voltages are controlled using power semiconductor switches and pulse width modulation. Semiconductor switching devices and anti-parallel connected freewheeling diodes form a bridge, the PWM changes the connections of the phases between the positive and the negative dc-link potentials so that the fundamental wave voltage has the desired frequency and amplitude. The motor reacts primarily to the frequency and filters out the effects of harmonic frequencies. Another application is in the aerospace and airline industries, often airplanes use 400 Hz power so a 50 Hz or 60 Hz to 400 Hz frequency converter is needed for use in the ground power unit used to power the airplane while it is on the ground. Airlines might utilize the converters to provide in-air wall current to passengers for use with laptops, in renewable energy systems, frequency converters are an essential component of doubly fed induction generators as used in modern multi-megawatt class wind turbines.
Frequency changers are used to control the speed of motors, primarily pumps. In many applications, significant energy savings are achieved, the most demanding application areas are found on industrial processing lines, where the control accuracy requirements can be very high. This is particularly true in the power and weapons industry. The STUXNET worm targets specific Siemens brand frequency converters, causing erratic operation of Irans centrifuge plant, an HVDC-system can serve as frequency converter for large loads. Frequency converter may refer to a circuit that converts radio frequency signals at one frequency to another frequency. Cascade converter Motor-generator Static inverter plant Variable-frequency drive HVDC
Three-phase electric power
Three-phase electric power is a common method of alternating-current electric power generation and distribution. It is a type of system and is the most common method used by electrical grids worldwide to transfer power. It is used to large motors and other heavy loads. The three-phase system was invented by Galileo Ferraris, Mikhail Dolivo-Dobrovolsky, Jonas Wenström. The common reference is usually connected to ground and often to a current-carrying conductor called the neutral. Due to the difference, the voltage on any conductor reaches its peak at one third of a cycle after one of the other conductors. This phase delay gives constant power transfer to a linear load. It makes it possible to produce a magnetic field in an electric motor. In a three-phase system feeding a balanced and linear load, the sum of the currents of the three conductors is zero. In other words, the current in each conductor is equal in magnitude to the sum of the currents in the two, but with the opposite sign. The return path for the current in any phase conductor is the two phase conductors.5 times as many wires.
Thus, the ratio of capacity to conductor material is doubled, the same ratio of capacity to conductor material can be attained with a center-grounded single-phase system. However, two-phase power results in a smooth torque in a generator or motor. Three-phase systems may have a wire, particularly in low-voltage distribution. The neutral allows three separate single-phase supplies to be provided at a constant voltage and is used for supplying groups of domestic properties which are each single-phase loads. The connections are arranged so that, as far as possible in each group, further up the distribution system, the currents are usually well balanced. Transformers may be wired in a way that they have a secondary but a three-wire primary while allowing unbalanced loads. This makes it possible to reduce the size of the neutral conductor because it carries little or no current, with a balanced load, all the phase conductors carry the same current and so can be the same size
A paper mill is a factory devoted to making paper from vegetable fibres such as wood pulp, old rags and other ingredients. While the use of human and animal powered mills was known to Chinese and Muslim papermakers, the general absence of the use of water-power in Muslim papermaking is suggested by the habit of Muslim authors to call a production center not a mill, but a paper manufactory. Although scholars have identified paper mills in Abbasid-era Baghdad in 794–795, in the Moroccan city of Fez, Ibn Battuta speaks of 400 mill stones for paper. Since Ibn Battuta does not mention the use of water-power and such a number of water-mills would be grotesquely high, the passage is generally taken to refer to human or animal force. An exhaustive survey of milling in Al-Andalus did not uncover a single water-powered paper mill, Burns remains altogether sceptical given the isolated occurrence of the reference and the prevalence of manual labour in Islamic papermaking elsewhere. Likewise, the identification of early hydraulic stamping mills in medieval documents from Fabriano, the earliest certain evidence to a water-powered paper mill dates to 1282 in the Spanish Kingdom of Aragon.
A decree by the Christian king Peter III addresses the establishment of a royal molendinum, the first permanent paper mill north of the Alps was established in Nuremberg by Ulman Stromer in 1390, it is depicted in the lavishly illustrated Nuremberg Chronicle. From the mid-14th century onwards, European paper milling underwent an improvement of many work processes. The size of a paper mill prior to the use of machines was described by counting the number of vats it had. Thus, a one vat paper mill had only one vatman, one coucher, by the early 20th century, paper mills sprang up around New England and the rest of the world, due to the high demand for paper. At this time, there were many leaders of the production of paper, one of such was the Brown Company in Berlin. During the year 1907, the Brown Company cut between 30 and 40 million acres of woodlands on their property, which extended from La Tuque, Canada to West Palm, “Log drives” were conducted on local rivers to send the logs to the mills.
By the late 20th and early 21st-century, paper began to close. Due to the addition of new machinery, many millworkers were laid off, Paper mills can be fully integrated mills or nonintegrated mills. Integrated mills consist of a mill and a paper mill on the same site. Such mills receive logs or wood chips and produce paper, modern paper machines can be 500 feet in length, produce a sheet 400 inches wide, and operate at speeds of more than 60 miles per hour. The two main suppliers of paper machines are Metso and Voith, Paper pollution Cutting stock problem List of paper mills Burns, Robert I. Paper comes to the West, 800−1400, in Lindgren, mann Verlag, pp. biz - Paper world directory and search engine for the pulp and paper world List of paper mills on paper and print monthly
Electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. The term is used for electrical oxidation of anions onto a solid substrate. Electroplating is primarily used to change the properties of an object. The process used in electroplating is called electrodeposition and it is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit, in one technique, the anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises, at the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they plate out onto the cathode. The rate at which the anode is dissolved is equal to the rate at which the cathode is plated, in this manner, the ions in the electrolyte bath are continuously replenished by the anode.
Other electroplating processes may use a non-consumable anode such as lead or carbon, in these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution. The most common form of electroplating is used for creating coins such as pennies, the cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, for example, for copper plating, in an acid solution, copper is oxidized at the anode to Cu2+ by losing two electrons. The Cu2+ associates with the anion SO42− in the solution to form copper sulfate, at the cathode, the Cu2+ is reduced to metallic copper by gaining two electrons. The result is the transfer of copper from the anode source to a plate covering the cathode. The plating is most commonly a metallic element, not an alloy. However, some alloys can be electrodeposited, notably brass and solder, many plating baths include cyanides of other metals in addition to cyanides of the metal to be deposited.
These free cyanides facilitate anode corrosion, help to maintain a constant metal ion level, non-metal chemicals such as carbonates and phosphates may be added to increase conductivity. When plating is not desired on certain areas of the substrate, typical stop-offs include tape, foil and waxes. The ability of a plating to cover uniformly is called throwing power, initially, a special plating deposit called a strike or flash may be used to form a very thin plating with high quality and good adherence to the substrate
A power inverter, or inverter, is an electronic device or circuitry that changes direct current to alternating current. The input voltage, output voltage and frequency, and overall power handling depend on the design of the device or circuitry. The inverter does not produce any power, the power is provided by the DC source, a power inverter can be entirely electronic or may be a combination of mechanical effects and electronic circuitry. Static inverters do not use moving parts in the conversion process, a typical power inverter device or circuit requires a relatively stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter, examples include,12 VDC, for smaller consumer and commercial inverters that typically run from a rechargeable 12 V lead acid battery or automotive electrical outlet. 24,36 and 48 VDC, which are standards for home energy systems. 200 to 400 VDC, when power is from solar panels. 300 to 450 VDC, when power is from electric vehicle battery packs in vehicle-to-grid systems, hundreds of thousands of volts, where the inverter is part of a high-voltage direct current power transmission system.
An inverter can produce a wave, modified sine wave, pulsed sine wave. The two dominant commercialized waveform types of inverters as of 2007 are modified sine wave and sine wave, the second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage. This is one of the simplest waveforms an inverter design can produce and is best suited to low-sensitivity applications such as lighting and heating, square wave output can produce humming when connected to audio equipment and is generally unsuitable for sensitive electronics. A power inverter device which produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter, to more clearly distinguish the inverters with outputs of much less distortion than the modified sine wave inverter designs, the manufacturers often use the phrase pure sine wave inverter. However, this is not critical for most electronics as they deal with the quite well. Where power inverter devices substitute for standard power, a sine wave output is desirable because many electrical products are engineered to work best with a sine wave AC power source.
The standard electric utility provides a sine wave, typically with minor imperfections, switch-mode power supply devices, such as personal computers or DVD players, function on quality modified sine wave power. AC motors directly operated on non-sinusoidal power may produce extra heat, may have different speed-torque characteristics, the modified sine wave output of such an inverter is the sum of two square waves one of which is phase shifted 90 degrees relative to the other. The result is three level waveform with equal intervals of zero volts, peak positive volts, zero volts, peak negative volts, the resultant wave very roughly resembles the shape of a sine wave. Most inexpensive consumer power inverters produce a sine wave rather than a pure sine wave
New York City Subway
Opened in 1904, the New York City Subway is one of the worlds oldest public transit systems, one of the worlds most used metro systems, and the metro system with the most stations. It offers service 24 hours per day, every day of the year, the New York City Subway is the largest rapid transit system in the world by number of stations, with 472 stations in operation. Stations are located throughout the boroughs of Manhattan, Queens, the Port Authority Trans-Hudson and the AirTrain JFK, in Manhattan and Queens respectively, accept the subways MetroCard but are not operated by the MTA and do not allow free transfers. Another mass transit service that is not operated by the MTA, the system is one of the worlds longest. Overall, the system contains 236 miles of routes, translating into 665 miles of track. In 2015, the subway delivered over 1.76 billion rides, averaging approximately 5.7 million daily rides on weekdays and a combined 5.9 million rides each weekend. Of the systems 25 services,22 of them pass through Manhattan, the exceptions being the G train, the Franklin Avenue Shuttle, and the Rockaway Park Shuttle.
Large portions of the subway outside Manhattan are elevated, on embankments, or in open cuts, in total, 40% of track is not underground despite the subway moniker. Many lines and stations have both express and local services and these lines have three or four tracks. Normally, the two are used for local trains, while the inner one or two are used for express trains. Stations served by express trains are typically major transfer points or destinations, alfred Ely Beach built the first demonstration for an underground transit system in New York City in 1869 and opened it in February 1870. The tunnel was never extended for political and financial reasons, although extensions had been planned to take the tunnel southward to The Battery, the Great Blizzard of 1888 helped demonstrate the benefits of an underground transportation system. A plan for the construction of the subway was approved in 1894, the first underground line of the subway opened on October 27,1904, almost 36 years after the opening of the first elevated line in New York City, which became the IRT Ninth Avenue Line.
The fare was $0.05 and on the first day the trains carried over 150,000 passengers, the oldest structure still in use opened in 1885 as part of the BMT Lexington Avenue Line in Brooklyn and is now part of the BMT Jamaica Line. The oldest right-of-way, which is part of the BMT West End Line near Coney Island Creek, was in use in 1864 as a railroad called the Brooklyn, Bath. By the time the first subway opened, the lines had been consolidated into two privately owned systems, the Brooklyn Rapid Transit Company and the Interborough Rapid Transit Company, the city built most of the lines and leased them to the companies. This required it to be run at cost, necessitating fares up to double the five-cent fare popular at the time, in 1940, the city bought the two private systems. Some elevated lines ceased service immediately while others closed soon after, integration was slow, but several connections were built between the IND and BMT, these now operate as one division called the B Division
A steel mill or steelworks is an industrial plant for the manufacture of steel. Since the invention of the Bessemer process, steel mills have replaced ironwork, new ways to produce steel appeared later, from scraps melted in an electric arc furnace and, more recently, from direct reduced iron processes. In the late 19th and early 20th centuries the worlds largest steel mill was the Barrow Hematite Steel Company steelworks located in Barrow-in-Furness, the worlds largest steel mill is in Gwangyang, South Korea. An integrated steel mill has all the functions for primary production, iron making. The principal raw materials for a mill are iron ore, limestone. These materials are charged in batches into a blast furnace where the iron compounds in the ore give up excess oxygen and become liquid iron. At intervals of a few hours, the liquid iron is tapped from the blast furnace. Historically the Bessemer process was an advancement in the production of economical steel. Molten steel is cast into large blocks called blooms, during the casting process various methods are used, such as addition of aluminum, so that impurities in the steel float to the surface where they can be cut off the finished bloom.
Even during periods of low demand, it may not be feasible to let the blast furnace grow cold. Integrated mills are large facilities that are only economical to build in 2,000, 000-ton per year annual capacity. Final products made by a plant are usually large structural sections, heavy plate, wire rod, railway rails. Integrated mills may adopt some of the used in mini-mills, such as arc furnaces and direct casting. World integrated steel production capacity is at or close to world demand, a minimill is traditionally a secondary steel producer, Nucor, as well as one of its competitors, Commercial Metals Company use minimills exclusively. Usually it obtains most of its iron from steel, recycled from used automobiles. Direct reduced iron is used with scrap, to help maintain desired chemistry of the steel. Originally the mini mill was adapted to production of bar products only, such as reinforcing bar, angles, pipe. Since the late 1980s, successful introduction of the direct strip casting process has made mini mill production of strip feasible, often a mini mill will be constructed in an area with no other steel production, to take advantage of local markets, resources, or lower-cost labour
Rotary converter plant
A rotary converter plant is a facility at which one form of electricity is converted into another form of electricity by using a combination of an electric motor and an electric generator. The installed combinations of motors and generators at a plant determine the type of conversion. Such facilities allow the setting of voltages and frequencies, if appropriate equipment is installed, Rotary converter plants were commonplace in railway electrification before the invention of mercury arc rectifiers in the 1920s. At each facility, power from an AC power grid was converted to DC to feed into a line or a third rail of a railway. Rotary converter plants were used for coupling power grids of different frequencies. The former Neuhof Substation was an example of the latter, former machinery transmitters like the Alexanderson alternator were, strictly speaking, rotary converter plants. In spite of modern power semiconductor technology, rotary converters are common for feeding railway systems with AC of a different frequency from that of the main electricity grid.
In Europe, this would typically be for 15 kV AC railway electrification, traction current converter plant Rotary converter Motor–generator Static inverter plant Lyon-Moutiers DC transmission scheme
A printing press is a device for applying pressure to an inked surface resting upon a print medium, thereby transferring the ink. The printing press was invented in the Holy Roman Empire by the German Johannes Gutenberg around 1440, the printing press spread within several decades to over two hundred cities in a dozen European countries. By 1500, printing presses in operation throughout Western Europe had already produced more than twenty million volumes, in the 16th century, with presses spreading further afield, their output rose tenfold to an estimated 150 to 200 million copies. The operation of a press became so synonymous with the enterprise of printing that it lent its name to a new branch of media. The sharp rise of learning and literacy amongst the middle class led to an increased demand for books which the time-consuming hand-copying method fell far short of accommodating. Technologies preceding the press led to the presss invention included, manufacturing of paper, development of ink, woodblock printing.
At the same time, a number of products and technological processes had reached a level of maturity which allowed their potential use for printing purposes. The device was used from very early on in urban contexts as a cloth press for printing patterns. Gutenberg may have inspired by the paper presses which had spread through the German lands since the late 14th century. Gutenberg adopted the design, thereby mechanizing the printing process. Printing, put a demand on the quite different from pressing. Gutenberg adapted the construction so that the power exerted by the platen on the paper was now applied both evenly and with the required sudden elasticity. To speed up the process, he introduced a movable undertable with a plane surface on which the sheets could be swiftly changed. The known examples range from Germany to England to Italy, the various techniques employed did not have the refinement and efficiency needed to become widely accepted. Gutenberg greatly improved the process by treating typesetting and printing as two separate work steps, a goldsmith by profession, he created his type pieces from a lead-based alloy which suited printing purposes so well that it is still used today.
The mass production of metal letters was achieved by his key invention of a hand mould. Another factor conducive to printing arose from the existing in the format of the codex. Considered the most important advance in the history of the prior to printing itself