Railway_electrification_system

context: 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, maintenance, 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.
qas: answers: maintenance
question: What is of the factors the capital cost of electrification system depends on?

answers: can switch to different supply voltages
question: How do some locomotives function in order to be more flexible in operation?

answers: freight and passenger traffic
question: What are two types of revenue obtained through railway transportation?

answers: significant capital expenditure
question: What is the main disadvantage of railway electrification?

context: 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 and distributed to the trains. 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 distribution lines, switches and transformers.
qas: answers: electric locomotives
question: What is used to haul passengers cars?

answers: generating stations
question: How is electricity being generated for electric locomotives?

answers: railway
question: What entity provides distribution lines, switches and transformers?

context: In comparison to the principal alternative, the diesel engine, electric railways offer substantially better energy efficiency, lower emissions and lower operating costs. Electric locomotives are usually quieter, more powerful, and more responsive and reliable than diesels. They have no local emissions, an important advantage in tunnels and urban areas. Some electric traction systems provide regenerative braking that turns the train's kinetic energy back into electricity and returns it to the supply system to be used by other trains or the general utility grid. While diesel locomotives burn petroleum, electricity is generated from diverse sources including many that do not produce carbon dioxide such as nuclear power and renewable forms including hydroelectric, geothermal, wind and solar.
qas: answers: diesel engine
question: What is the principal alternative to electric railways?

answers: Electric locomotives
question: What locomotives are usually more reliable?

answers: regenerative braking
question: What do some electric traction systems provide?

answers: petroleum
question: What type of fuel do diesel locomotives use?

answers: geothermal
question: What is one of the sources electricity is being generated from?

context: Disadvantages of electric traction include high capital costs that may be uneconomic on lightly trafficked routes; a relative lack of flexibility since electric trains need electrified tracks or onboard supercapacitors and charging infrastructure at stations; and a vulnerability to power interruptions. 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. The lethal voltages on contact wires and third rails are a safety hazard to track workers, passengers and trespassers. Overhead wires are safer than third rails, but they are often considered unsightly.
qas: answers: voltages on contact wires
question: What is a safety hazard to track workers?

answers: different supply voltages and frequencies,
question: What issue can complicate electric railway service?

answers: Overhead wires
question: What is a safer alternative to third rails?

answers: considered unsightly.
question: Why overhead wires are not being widely used?

context: Railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, although such DC can be supplied from an AC catenary via on-board electric power conversion. 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 (subways) and trams. Speed was controlled by connecting the traction motors in various series-parallel combinations, by varying the traction motors' fields, and by inserting and removing starting resistances to limit motor current.
qas: answers: variable speeds
question: What is speed limit for railways?

answers: conversion was not well developed
question: Why is DC motor being used more than AC type?

answers: rapid transit (subways) and trams
question: What are two types of railway transportation still use DC motor?

context: Motors have very little room for electrical insulation so they generally have low voltage ratings. Because transformers (prior to the development of power electronics) cannot step down DC voltages, trains were supplied with a relatively low DC voltage that the motors can use directly. The most common DC voltages are listed in the previous section. Third (and fourth) rail systems almost always use voltages below 1 kV for safety reasons while overhead wires usually use higher voltages for efficiency. ("Low" voltage is relative; even 600 V can be instantly lethal when touched.)
qas: answers: low voltage ratings
question: Why do motors have little space for insulation?

answers: safety reasons
question: Why 1kV voltage is almost always used by rail systems?

answers: below 1 kV
question: What is most common volatage range used by railway system?

answers: overhead wires
question: Which system uses higher voltages?

answers: lethal
question: Is "low" voltage used by trains safe for people?

context: There has, however, been interest among railroad operators in returning to DC use at higher voltages than previously used. At the same voltage, DC often has less loss than AC, and for this reason high-voltage direct current is already used on some bulk power transmission lines. DC avoids the electromagnetic radiation inherent with AC, and on a railway this also reduces interference with signalling and communications and mitigates hypothetical EMF risks. DC also avoids the power factor problems of AC. Of particular interest to railroading is that DC can supply constant power with a single ungrounded wire. Constant power with AC requires three-phase transmission with at least two ungrounded wires. Another important consideration is that mains-frequency 3-phase AC must be carefully planned to avoid unbalanced phase loads. Parts of the system are supplied from different phases on the assumption that the total loads of the 3 phases will even out. At the phase break points between regions supplied from different phases, long insulated supply breaks are required to avoid them being shorted by rolling stock using more than one pantograph at a time. A few railroads have tried 3-phase but its substantial complexity has made single-phase standard practice despite the interruption in power flow that occurs twice every cycle. An experimental 6 kV DC railway was built in the Soviet Union.
qas: answers: DC
question: What type of electric power garantees lesser loss?

answers: AC
question: Which type of supply for electric motors creates electromagnetic radiation?

answers: AC
question: Which type of power does require three-phase transmission?

answers: signalling and communications
question: What can electromagnetic radiation interfere with?

answers: the Soviet Union
question: Where was an experimental 6kV DC railway built?

context: 1,500 V DC is used in the Netherlands, Japan, Republic Of Indonesia, Hong Kong (parts), Republic of Ireland, Australia (parts), India (around the Mumbai area alone, has been converted to 25 kV AC like the rest of India), France (also using 25 kV 50 Hz AC), New Zealand (Wellington) and the United States (Chicago area on the Metra Electric district and the South Shore Line interurban line). In Slovakia, there are two narrow-gauge lines in the High Tatras (one a cog railway). In Portugal, it is used in the Cascais Line and in Denmark on the suburban S-train system.
qas: answers: 1,500 V
question: What is most common voltage for DC supply?

answers: two
question: How many narrow-gauge lines in Slovakia?

answers: the Cascais Line
question: What railway line is DC being used in Portugal?

answers: Mumbai area
question: Where in India line has been converted to AC?

context: 3 kV DC is used in Belgium, Italy, Spain, Poland, the northern Czech Republic, Slovakia, Slovenia, South Africa, Chile, and former Soviet Union countries (also using 25 kV 50 Hz AC). It was formerly used by the Milwaukee Road from Harlowton, Montana to Seattle-Tacoma, across the Continental Divide and including extensive branch and loop lines in Montana, and by the Delaware, Lackawanna & Western Railroad (now New Jersey Transit, converted to 25 kV AC) in the United States, and the Kolkata suburban railway (Bardhaman Main Line) in India, before it was converted to 25 kV 50 Hz AC.
qas: answers: 3 kV DC
question: What voltage is being used in railway system of South Africa and Chile?

answers: 25 kV 50 Hz AC
question: Besides using 3kV DC what other power type is used in the former Soviet Union countries?

answers: Western Railroad
question: What was New Jersey Transit called before?

answers: AC
question: What does the railway system of US use DC or AC?

context: Most electrification systems use overhead wires, but third rail is an option up to about 1,200 V. Third rail systems exclusively use DC distribution. The use of AC is not feasible because the dimensions of a third rail are physically very large compared with the skin depth that the alternating current penetrates to (0.3 millimetres or 0.012 inches) in a steel rail). This effect makes the resistance per unit length unacceptably high compared with the use of DC. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.
qas: answers: overhead wires
question: What type is mostly used third rail or overhead wires?

answers: DC distribution
question: Is trird rail system being used exclusively with AC or DC ?

answers: skin depth
question: What depth does the alternating current penetrate in a steel rail?

answers: Third rail
question: What is more prefferable for subway lines?

answers: Third rail
question: What is physically more compact tird rail or overhead wires?

context: DC systems (especially third-rail systems) are limited to relatively low voltages and this can limit the size and speed of trains and cannot use low-level platform and also limit the amount of air-conditioning that the trains can provide. This may be a factor favouring overhead wires and high-voltage AC, even for urban usage. In practice, the top speed of trains on third-rail systems is limited to 100 mph (160 km/h) because above that speed reliable contact between the shoe and the rail cannot be maintained.
qas: answers: low voltages
question: Why DC system can effect the speed of trains?

answers: cannot
question: Can DC systems use low-level platform?

answers: air-conditioning
question: Besides speed and size what else the low voltage of DC system can effect?

answers: 160 km/h
question: What is the speed limit for third rail system trains?

answers: contact between the shoe and the rail
question: What can become unreliable if the speed exceeds the limit of 100 mph for DC system trains?

context: Some street trams (streetcars) used conduit third-rail current collection. The third rail was below street level. The tram picked up the current through a plough (U.S. "plow") accessed through a narrow slot in the road. In the United States, much (though not all) of the former streetcar system in Washington, D.C. (discontinued in 1962) was operated in this manner to avoid the unsightly wires and poles associated with electric traction. The same was true with Manhattan's former streetcar system. The evidence of this mode of running can still be seen on the track down the slope on the northern access to the abandoned Kingsway Tramway Subway in central London, United Kingdom, where the slot between the running rails is clearly visible, and on P and Q Streets west of Wisconsin Avenue in the Georgetown neighborhood of Washington DC, where the abandoned tracks have not been paved over. The slot can easily be confused with the similar looking slot for cable trams/cars (in some cases, the conduit slot was originally a cable slot). The disadvantage of conduit collection included much higher initial installation costs, higher maintenance costs, and problems with leaves and snow getting in the slot. For this reason, in Washington, D.C. cars on some lines converted to overhead wire on leaving the city center, a worker in a "plough pit" disconnecting the plough while another raised the trolley pole (hitherto hooked down to the roof) to the overhead wire. In New York City for the same reasons of cost and operating efficiency outside of Manhattan overhead wire was used. A similar system of changeover from conduit to overhead wire was also used on the London tramways, notably on the southern side; a typical changeover point was at Norwood, where the conduit snaked sideways from between the running rails, to provide a park for detached shoes or ploughs.
qas: answers: streetcars
question: What is the other name for the street trams?

answers: below street level
question: Where is third rail situated in the street trams system?

answers: Washington, D.C.
question: What area in US discontinued using overhead wires for streetcars in 1962?

answers: leaves and snow
question: What external and weather factors can effect conduit slot?

answers: cost and operating efficiency
question: What are the main reasons the conduit lines were converted to overhead  wire system?

context: A new approach to avoiding overhead wires is taken by the "second generation" tram/streetcar system in Bordeaux, France (entry into service of the first line in December 2003; original system discontinued in 1958) with its APS (alimentation par sol – ground current feed). This involves a third rail which is flush with the surface like the tops of the running rails. The circuit is divided into segments with each segment energized in turn by sensors from the car as it passes over it, the remainder of the third rail remaining "dead". Since each energized segment is completely covered by the lengthy articulated cars, and goes dead before being "uncovered" by the passage of the vehicle, there is no danger to pedestrians. This system has also been adopted in some sections of the new tram systems in Reims, France (opened 2011) and Angers, France (also opened 2011). Proposals are in place for a number of other new services including Dubai, UAE; Barcelona, Spain; Florence, Italy; Marseille, France; Gold Coast, Australia; Washington, D.C., U.S.A.; Brasília, Brazil and Tours, France.
qas: answers: 2003
question: What year the "second generation" of tram system began to operate in France?

answers: 1958
question: When was the original system discontinued?

answers: energized segment
question: How is the circuit of the third rail divided?

answers: no danger
question: Does energized segment of third rail pose the threat to pedestrians if uncovered?

context: The London Underground in England is one of the few networks that uses a four-rail system. The additional rail carries the electrical return that, on third rail and overhead networks, is provided by the running rails. On the London Underground, a top-contact third rail is beside the track, energized at +420v DC, and a top-contact fourth rail is located centrally between the running rails at −210v DC, which combine to provide a traction voltage of 630v DC. London Underground is now upgrading its fourth rail system to 750v DC with a positive conductor rail energised to +500v DC and a negative conductor rail energised to -250v DC. However, many older sections in tunnels are still energised to 630v DC. The same system was used for Milan's earliest underground line, Milan Metro's line 1, whose more recent lines use an overhead catenary or a third rail.
qas: answers: four-rail system
question: What type of system does London Underground use?

answers: carries the electrical return
question: What is the purpose of the forth rail?

answers: +420v DC
question: What is the volatage surge of the third rail of London Underground system?

answers: −210v DC
question: What is the voltage of the return rail?

answers: Milan
question: Where was the system similar to London Underground used as well?

context: The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.
qas: answers: electrolytic damage
question: What danger can return currents cause?

answers: by using resistors
question: How are stray earth currents kept to a manageable levels? 

answers: ceramic chairs
question: What insures minimal current leak during power rails instalation?

answers: water and gas mains
question: How did return current effect water and gas in iron pipes?

answers: running rail carries any current
question: What is the crucial advantage of four-rail system?

context: On tracks that London Underground share with National Rail third-rail stock (the Bakerloo and District lines both have such sections), the centre rail is connected to the running rails, allowing both types of train to operate, at a compromise voltage of 660 V. Underground trains pass from one section to the other at speed; lineside electrical connections and resistances separate the two types of supply. These routes were originally solely electrified on the four-rail system by the LNWR before National Rail trains were rewired to their standard three-rail system to simplify rolling stock use.
qas: answers: to simplify rolling stock use
question: Why some sections of Bakerloo and District lines were rewired to three-rail system?

answers: 660 V
question: What is the voltage shared two types of trains UK railroad system?

answers: the centre rail is connected to the running rails
question: How did it become possible to share the voltage for different types of train?

context: A few lines of the Paris Métro in France operate on a four-rail power scheme because they run on rubber tyres which run on a pair of narrow roadways made of steel and, in some places, concrete. Since the tyres do not conduct the return current, the two guide rails provided outside the running 'roadways' double up as conductor rails, so at least electrically it is a four-rail scheme. One of the guide rails is bonded to the return conventional running rails situated inside the roadway so a single polarity supply is required. The trains are designed to operate from either polarity of supply, because some lines use reversing loops at one end, causing the train to be reversed during every complete journey. The loop was originally provided to save the original steam locomotives having to 'run around' the rest of the train saving much time. Today, the driver does not have to change ends at termini provided with such a loop, but the time saving is not so significant as it takes almost as long to drive round the loop as it does to change ends. Many of the original loops have been lost as lines were extended.
qas: answers: rubber tyres
question: Why some lines of Paris Metro have to operate on a four-rail system?

answers: two guide rails
question: What was the solution for the return current problem in Paris Metro?

answers: a single polarity supply
question: What is required in order for the guide rails to operate properly?

answers: reversing loops
question: How train is able to turn around after each completed journey?

answers: having to 'run around' the rest of the train
question: Why was the reversing loop created?

context: An early advantage of AC is that the power-wasting resistors used in DC locomotives for speed control were not needed in an AC locomotive: multiple taps on the transformer can supply a range of voltages. Separate low-voltage transformer windings supply lighting and the motors driving auxiliary machinery. More recently, the development of very high power semiconductors has caused the classic "universal" AC/DC motor to be largely replaced with the three-phase induction motor fed by a variable frequency drive, a special inverter that varies both frequency and voltage to control motor speed. These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation.
qas: answers: multiple taps on the transformer
question: How can different range of voltages be supplied for AC locomotives?

answers: power-wasting resistors
question: What was a disadvantage of DC system?

answers: low-voltage transformer windings
question: What taps can provide lighting supply?

answers: three-phase induction motor
question: What will AC/DC motor be replaced with?

answers: can run equally well on DC or AC of any frequency
question: What is the main advantage of an induction motor?

context: DC commutating electric motors, if fitted with laminated pole pieces, become universal motors because they can also operate on AC; reversing the current in both stator and rotor does not reverse the motor. But the now-standard AC distribution frequencies of 50 and 60 Hz caused difficulties with inductive reactance and eddy current losses. Many railways chose low AC frequencies to overcome these problems. They must be converted from utility power by motor-generators or static inverters at the feeding substations or generated at dedicated traction powerstations.
qas: answers: if fitted with laminated pole pieces
question: How can DC motor turn universal?

answers: inductive reactance and eddy current losses
question: What problems did AC distribution cause?

answers: low AC frequencies
question: How do railways try to solve the problem of inductive reactance of AC system?

answers: converted from utility power
question: How can low frequencies be obtained?

context: High-voltage AC overhead systems are not only for standard gauge national networks. The meter gauge Rhaetian Railway (RhB) and the neighbouring Matterhorn Gotthard Bahn (MGB) operate on 11 kV at 16.7 Hz frequency. Practice has proven that both Swiss and German 15 kV trains can operate under these lower voltages. The RhB started trials of the 11 kV system in 1913 on the Engadin line (St. Moritz-Scuol/Tarasp). The MGB constituents Furka-Oberalp-Bahn (FO) and Brig-Visp-Zermatt Bahn (BVZ) introduced their electric services in 1941 and 1929 respectively, adopting the already proven RhB system.
qas: answers: adopting the already proven RhB system.
question: How did non-standard gauge trains start to operate with high-voltage AC?

answers: 1913
question: When was the first trail of RhB system tested?

context: In the United States, 25 Hz, a once-common industrial power frequency is used on Amtrak's 25 Hz traction power system at 12 kV on the Northeast Corridor between Washington, D.C. and New York City and on the Keystone Corridor between Harrisburg, Pennsylvania and Philadelphia. SEPTA's 25 Hz traction power system uses the same 12 kV voltage on the catenary in Northeast Philadelphia. This allows for the trains to operate on both the Amtrak and SEPTA power systems. Apart from having an identical catenary voltage, the power distribution systems of Amtrak and SEPTA are very different. The Amtrak power distribution system has a 138 kV transmission network that provides power to substations which then transform the voltage to 12 kV to feed the catenary system. The SEPTA power distribution system uses a 2:1 ratio autotransformer system, with the catenary fed at 12 kV and a return feeder wire fed at 24 kV. The New York, New Haven and Hartford Railroad used an 11 kV system between New York City and New Haven, Connecticut which was converted to 12.5 kV 60 Hz in 1987.
qas: answers: 25 Hz
question: What frequency was typically used on US Amtrak?

answers: 12 kV voltage
question: What voltage does SEPTA system use?

answers: catenary voltage
question: What specification is similar for both Amtrak and Septa systems?

answers: 1987
question: When was a 11kV system of NY, New Haven and Hartford was converted to 12.5 kV?

context: In the UK, the London, Brighton and South Coast Railway pioneered overhead electrification of its suburban lines in London, London Bridge to Victoria being opened to traffic on 1 December 1909. Victoria to Crystal Palace via Balham and West Norwood opened in May 1911. Peckham Rye to West Norwood opened in June 1912. Further extensions were not made owing to the First World War. Two lines opened in 1925 under the Southern Railway serving Coulsdon North and Sutton railway station. The lines were electrified at 6.7 kV 25 Hz. It was announced in 1926 that all lines were to be converted to DC third rail and the last overhead electric service ran in September 1929.
qas: answers: 1 December 1909
question: When was overhead wires system being used for the first time in UK?

answers: Victoria to Crystal Palace
question: What line used the overhead wire system first Victoria to Crystal Palace or Peckham Rye to West Noorwood?

answers: the First World War
question: What was the cause of lines not being extended?

answers: 6.7 kV 25 Hz
question: What voltage was used in the two lines opened in 1925 of Southern Railway?

context: Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, for lines in the mountainous regions of northern Italy from 1901 until 1976. The first lines were the Burgdorf-Thun line in Switzerland (1899), and the lines of the Ferrovia Alta Valtellina from Colico to Chiavenna and Tirano in Italy, which were electrified in 1901 and 1902. Other lines where the three-phase system were used were the Simplon Tunnel in Switzerland from 1906 to 1930, and the Cascade Tunnel of the Great Northern Railway in the United States from 1909 to 1927.
qas: answers: Italy, Switzerland and the United States
question: What countries  used three-phase AC system in the the beginning of 20th century?

answers: Italy
question: What country was a bigger user compare to the three of them?

answers: in the mountainous regions of northern Italy
question: Where did Italy start using the AC system?

answers: 1901 until 1976
question: How long did the AC system last in northern Italy?

answers: 1909 to 1927
question: How long did three-phase system operate in Cascade Tunnel?

context: The first attempts to use standard-frequency single-phase AC were made in Hungary as far back as 1923, by the Hungarian Kálmán Kandó on the line between Budapest-Nyugati and Alag, using 16 kV at 50 Hz. The locomotives carried a four-pole rotating phase converter feeding a single traction motor of the polyphase induction type at 600 to 1,100 V. The number of poles on the 2,500 hp motor could be changed using slip rings to run at one of four synchronous speeds. The tests were a success so, from 1932 until the 1960s, trains on the Budapest-Hegyeshalom line (towards Vienna) regularly used the same system. A few decades after the Second World War, the 16 kV was changed to the Russian and later French 25 kV system.
qas: answers: Hungary
question: What country has first tried to use single-phase AC?

answers: 16 kV at 50 Hz
question: What frequency did the line of Hungarian rail system used in 1923?

answers: four-pole rotating phase converter
question: What type of the converter was used in hungarian locomotives of that time?

answers: motor could be changed using slip rings
question: How could the locomotives run on four speed levels?

answers: Russian
question: What system was adopted in Hungary after WWII?

context: To prevent the risk of out-of-phase supplies mixing, sections of line fed from different feeder stations must be kept strictly isolated. This is achieved by Neutral Sections (also known as Phase Breaks), usually provided at feeder stations and midway between them although, typically, only half are in use at any time, the others being provided to allow a feeder station to be shut down and power provided from adjacent feeder stations. Neutral Sections usually consist of an earthed section of wire which is separated from the live wires on either side by insulating material, typically ceramic beads, designed so that the pantograph will smoothly run from one section to the other. The earthed section prevents an arc being drawn from one live section to the other, as the voltage difference may be higher than the normal system voltage if the live sections are on different phases and the protective circuit breakers may not be able to safely interrupt the considerable current that would flow. To prevent the risk of an arc being drawn across from one section of wire to earth, when passing through the neutral section, the train must be coasting and the circuit breakers must be open. In many cases, this is done manually by the drivers. To help them, a warning board is provided just before both the neutral section and an advance warning some distance before. A further board is then provided after the neutral section to tell drivers to re-close the circuit breaker, although drivers must not do this until the rear pantograph has passed this board. In the UK, a system known as Automatic Power Control (APC) automatically opens and closes the circuit breaker, this being achieved by using sets of permanent magnets alongside the track communicating with a detector on the train. The only action needed by the driver is to shut off power and coast and therefore warning boards are still provided at and on the approach to neutral sections.
qas: answers: line fed from different feeder stations must be kept strictly isolated
question: What was the main requirement for electric feeder stations?

answers: Phase Breaks
question: What invention prevented lines from getting mixed?

answers: The earthed section
question: What was the part of wire in Phase Break sections an arc being drawn from one wire to another?

answers: warning board
question: How were the drivers warned to start coasting the train?

answers: to shut off power and coast
question: What should the driver do in order to open and close the circuit breaker?

context: Modern electrification systems take AC energy from a power grid which is delivered to a locomotive and converted to a DC voltage to be used by traction motors. These motors may either be DC motors which directly use the DC or they may be 3-phase AC motors which require further conversion of the DC to 3-phase AC (using power electronics). Thus both systems are faced with the same task: converting and transporting high-voltage AC from the power grid to low-voltage DC in the locomotive. Where should this conversion take place and at what voltage and current (AC or DC) should the power flow to the locomotive? And how does all this relate to energy-efficiency? Both the transmission and conversion of electric energy involve losses: ohmic losses in wires and power electronics, magnetic field losses in transformers and smoothing reactors (inductors). Power conversion for a DC system takes place mainly in a railway substation where large, heavy, and more efficient hardware can be used as compared to an AC system where conversion takes place aboard the locomotive where space is limited and losses are significantly higher. Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for.
qas: answers: DC motors which directly use the DC or they may be 3-phase AC motors
question: What nowdays electrification systems can use?

answers: converting and transporting
question: What is the main action AC and DC systems have to deal with?

answers: ohmic losses
question: What type of losses happen during conversion and transmission in wires and electronics?

answers: magnetic field losses
question: What kind of losses take place in transformers and inductors during conversion/transmission process?

context: In the Soviet Union, in the 1970s, a comparison was made between systems electrified at 3 kV DC and 25 kV AC (50 Hz). The results showed that percentage losses in the overhead wires (catenary and contact wires) was over 3 times greater for 3 kV DC than for 25 kV AC. But when the conversion losses were all taken into account and added to overhead wire losses (including cooling blower energy) the 25 kV AC lost a somewhat higher percent of energy than for 3 kV DC. Thus in spite of the much higher losses in the catenary, the 3 kV DC was a little more energy efficient than AC in providing energy from the USSR power grid to the terminals of the traction motors (all DC at that time). While both systems use energy in converting higher voltage AC from the USSR's power grid to lower voltage DC, the conversions for the DC system all took place (at higher efficiency) in the railway substation, while most of the conversion for the AC system took place inside the locomotive (at lower efficiency). Consider also that it takes energy to constantly move this mobile conversion hardware over the rails while the stationary hardware in the railway substation doesn't incur this energy cost. For more details see: Wiki: Soviet Union DC vs. AC.
qas: answers: 3 kV DC and 25 kV AC (50 Hz
question: What two systems were compare in the Soviet Union in 1970?

answers: 3 kV DC
question: Which system had higher losses in overhead wires?

answers: 3 kV DC
question: Which system was used in Soviet Union after all calculations?

answers: stationary hardware
question: What came with lesser lesser cost mobile conversion hardware or stationary hardware?

context: Newly electrified lines often show a "sparks effect", whereby electrification in passenger rail systems leads to significant jumps in patronage / revenue. The reasons may include electric trains being seen as more modern and attractive to ride, faster and smoother service, and the fact that electrification often goes hand in hand with a general infrastructure and rolling stock overhaul / replacement, which leads to better service quality (in a way that theoretically could also be achieved by doing similar upgrades yet without electrification). Whatever the causes of the sparks effect, it is well established for numerous routes that have electrified over decades.
qas: answers: "sparks effect"
question: What can be seen in the newly electrified lines?

answers: patronage / revenue
question: What can electrification of modern trains effect? 

answers: rolling stock overhaul / replacement
question: How can better service quality be achieved?

context: Network effects are a large factor with electrification. When converting lines to electric, the connections with other lines must be considered. Some electrifications have subsequently been removed because of the through traffic to non-electrified lines. If through traffic is to have any benefit, time consuming engine switches must occur to make such connections or expensive dual mode engines must be used. This is mostly an issue for long distance trips, but many lines come to be dominated by through traffic from long-haul freight trains (usually running coal, ore, or containers to or from ports). In theory, these trains could enjoy dramatic savings through electrification, but it can be too costly to extend electrification to isolated areas, and unless an entire network is electrified, companies often find that they need to continue use of diesel trains even if sections are electrified. The increasing demand for container traffic which is more efficient when utilizing the double-stack car also has network effect issues with existing electrifications due to insufficient clearance of overhead electrical lines for these trains, but electrification can be built or modified to have sufficient clearance, at additional cost.
qas: answers: Network effects
question: What is a major factor whn it comes to electrification?

answers: through traffic to non-electrified lines
question: What was the reason some electrifications were removed after a while?

answers: electrification to isolated areas
question: What can be a drawback of electrification of long distance freight trains?

answers: long distance trips
question: Where can the issue of through traffic benefits occur?

answers: diesel trains
question: What does the increasing demand for container traffic make companies use more often?

context: Additionally, there are issues of connections between different electrical services, particularly connecting intercity lines with sections electrified for commuter traffic, but also between commuter lines built to different standards. This can cause electrification of certain connections to be very expensive simply because of the implications on the sections it is connecting. Many lines have come to be overlaid with multiple electrification standards for different trains to avoid having to replace the existing rolling stock on those lines. Obviously, this requires that the economics of a particular connection must be more compelling and this has prevented complete electrification of many lines. In a few cases, there are diesel trains running along completely electrified routes and this can be due to incompatibility of electrification standards along the route.
qas: answers: connections between different electrical services
question: What is the other issue that comes to sight when using electrification system?

answers: the implications on the sections it is connecting
question: Why the commuter lines built to different standards can cause be complicated?

answers: to be overlaid with multiple electrification standards
question: What is the solution many lines came up with in order to avoid replacing present rolling stock?

answers: due to incompatibility of electrification standards
question: Why are disel trains  still used on electrified routes?

context: Central station electricity can often be generated with higher efficiency than a mobile engine/generator. While the efficiency of power plant generation and diesel locomotive generation are roughly the same in the nominal regime, diesel motors decrease in efficiency in non-nominal regimes at low power  while if an electric power plant needs to generate less power it will shut down its least efficient generators, thereby increasing efficiency. The electric train can save energy (as compared to diesel) by regenerative braking and by not needing to consume energy by idling as diesel locomotives do when stopped or coasting. However, electric rolling stock may run cooling blowers when stopped or coasting, thus consuming energy.
qas: answers: Central station
question: Which of two can be more efficiently electricified?

answers: it will shut down its least efficient generators
question: How can electric power plant become more power efficient?

answers: by regenerative braking
question: How can electric train be more energy efficient?

answers: diesel
question: Which type of train continues to use energy while coasting or being stopped?

answers: cooling blowers
question: What causes electric trains to waste energy?

context: Energy sources unsuitable for mobile power plants, such as nuclear power, renewable hydroelectricity, or wind power can be used. According to widely accepted global energy reserve statistics, the reserves of liquid fuel are much less than gas and coal (at 42, 167 and 416 years respectively). Most countries with large rail networks do not have significant oil reserves and those that did, like the United States and Britain, have exhausted much of their reserves and have suffered declining oil output for decades. Therefore, there is also a strong economic incentive to substitute other fuels for oil. Rail electrification is often considered an important route towards consumption pattern reform. However, there are no reliable, peer-reviewed studies available to assist in rational public debate on this critical issue, although there are untranslated Soviet studies from the 1980s.
qas: answers: unsuitable
question: Can renewable source of electricity be used in mobile power plants?

answers: to substitute other fuels
question: What is the recent incentive in  order to overcome oil scarcity?

answers: liquid fuel
question: What type of natural resources is more scarce?

answers: Soviet studies from the 1980s
question: What research can be used in the future if translated?

context: In the former Soviet Union, electric traction eventually became somewhat more energy-efficient than diesel. Partly due to inefficient generation of electricity in the USSR (only 20.8% thermal efficiency in 1950 vs. 36.2% in 1975), in 1950 diesel traction was about twice as energy efficient as electric traction (in terms of net tonne-km of freight per kg of fuel). But as efficiency of electricity generation (and thus of electric traction) improved, by about 1965 electric railways became more efficient than diesel. After the mid 1970s electrics used about 25% less fuel per ton-km. However diesels were mainly used on single track lines with a fair amount of traffic  so that the lower fuel consumption of electrics may be in part due to better operating conditions on electrified lines (such as double tracking) rather than inherent energy efficiency. Nevertheless, the cost of diesel fuel was about 1.5 times more (per unit of heat energy content) than that of the fuel used in electric power plants (that generated electricity), thus making electric railways even more energy-cost effective.
qas: answers: electric
question: What type of trains became more energy-efficient in the former Soviet Union?

answers: 1965
question: What year could be marked as year when electric railways more efficient than diesel ones?

answers: 25% less fuel per ton-km
question: How much fuel did electric train used less than diesel in the middle of 1970 in USSR?

answers: better operating conditions on electrified lines
question: What could be a factor of lower energy consumption for electric trains?

answers: 1.5 times more (per unit of heat energy content
question: How much more expensive was diesel compare to electricity per unit?

context: Besides increased efficiency of power plants, there was an increase in efficiency (between 1950 and 1973) of the railway utilization of this electricity with energy-intensity dropping from 218 to 124 kwh/10,000 gross tonne-km (of both passenger and freight trains) or a 43% drop. Since energy-intensity is the inverse of energy-efficiency it drops as efficiency goes up. But most of this 43% decrease in energy-intensity also benefited diesel traction. The conversion of wheel bearings from plain to roller, increase of train weight, converting single track lines to double track (or partially double track), and the elimination of obsolete 2-axle freight cars increased the energy-efficiency of all types of traction: electric, diesel, and steam. However, there remained a 12–15% reduction of energy-intensity that only benefited electric traction (and not diesel). This was due to improvements in locomotives, more widespread use of regenerative braking (which in 1989 recycled 2.65% of the electric energy used for traction,) remote control of substations, better handling of the locomotive by the locomotive crew, and improvements in automation. Thus the overall efficiency of electric traction as compared to diesel more than doubled between 1950 and the mid-1970s in the Soviet Union. But after 1974 (thru 1980) there was no improvement in energy-intensity (wh/tonne-km) in part due to increasing speeds of passenger and freight trains.
qas: answers: energy-intensity dropping
question: What caused the energy efficiency to go up?

answers: electric
question: What type of locomotives got improved during 1950-1973 in Soviet Union?

answers: 2.65%
question: How much of energy was saved and re-used due to regenerative braking in 1989?

answers: no improvement
question: Was there an energy efficiency improvement in the period 1974 through 1980?

answers: 2-axle freight cars
question: Elimination of what helped the efficiency of diesel traction to go up?