nc33/MultiSpan_SQUAD huggingface dataset:
Railway_electrification_system

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.)

Question: Why do motors have little space for insulation?
Answer: low voltage ratings

Question: Why 1kV voltage is almost always used by rail systems?
Answer: safety reasons

Question: What is most common volatage range used by railway system?
Answer: below 1 kV

Question: Which system uses higher voltages?
Answer: overhead wires

Question: Is "low" voltage used by trains safe for people?
Answer: lethal
Railway_electrification_system

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.

Question: What type of electric power garantees lesser loss?
Answer: DC

Question: Which type of supply for electric motors creates electromagnetic radiation?
Answer: AC

Question: Which type of power does require three-phase transmission?
Answer: AC

Question: What can electromagnetic radiation interfere with?
Answer: signalling and communications

Question: Where was an experimental 6kV DC railway built?
Answer: the Soviet Union
Railway_electrification_system

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.

Question: What is most common voltage for DC supply?
Answer: 1,500 V

Question: How many narrow-gauge lines in Slovakia?
Answer: two

Question: What railway line is DC being used in Portugal?
Answer: the Cascais Line

Question: Where in India line has been converted to AC?
Answer: Mumbai area
Railway_electrification_system

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.

Question: What voltage is being used in railway system of South Africa and Chile?
Answer: 3 kV DC

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

Question: What was New Jersey Transit called before?
Answer: Western Railroad

Question: What does the railway system of US use DC or AC?
Answer: AC
Railway_electrification_system

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.

Question: Why DC system can effect the speed of trains?
Answer: low voltages

Question: Can DC systems use low-level platform?
Answer: cannot

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

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

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

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.

Question: What is the other name for the street trams?
Answer: streetcars

Question: Where is third rail situated in the street trams system?
Answer: below street level

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

Question: What external and weather factors can effect conduit slot?
Answer: leaves and snow

Question: What are the main reasons the conduit lines were converted to overhead  wire system?
Answer: cost and operating efficiency
Railway_electrification_system

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.

Question: What year the "second generation" of tram system began to operate in France?
Answer: 2003

Question: When was the original system discontinued?
Answer: 1958

Question: How is the circuit of the third rail divided?
Answer: energized segment

Question: Does energized segment of third rail pose the threat to pedestrians if uncovered?
Answer: no danger
Railway_electrification_system

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.

Question: What type of system does London Underground use?
Answer: four-rail system

Question: What is the purpose of the forth rail?
Answer: carries the electrical return

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

Question: What is the voltage of the return rail?
Answer: −210v DC

Question: Where was the system similar to London Underground used as well?
Answer: Milan
Railway_electrification_system

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.

Question: What danger can return currents cause?
Answer: electrolytic damage

Question: How are stray earth currents kept to a manageable levels? 
Answer: by using resistors

Question: What insures minimal current leak during power rails instalation?
Answer: ceramic chairs

Question: How did return current effect water and gas in iron pipes?
Answer: water and gas mains

Question: What is the crucial advantage of four-rail system?
Answer: running rail carries any current
Railway_electrification_system

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.

Question: Why some lines of Paris Metro have to operate on a four-rail system?
Answer: rubber tyres

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

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

Question: How train is able to turn around after each completed journey?
Answer: reversing loops

Question: Why was the reversing loop created?
Answer: having to 'run around' the rest of the train
Railway_electrification_system

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.

Question: How can different range of voltages be supplied for AC locomotives?
Answer: multiple taps on the transformer

Question: What was a disadvantage of DC system?
Answer: power-wasting resistors

Question: What taps can provide lighting supply?
Answer: low-voltage transformer windings

Question: What will AC/DC motor be replaced with?
Answer: three-phase induction motor

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

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.

Question: How can DC motor turn universal?
Answer: if fitted with laminated pole pieces

Question: What problems did AC distribution cause?
Answer: inductive reactance and eddy current losses

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

Question: How can low frequencies be obtained?
Answer: converted from utility power
Railway_electrification_system

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.

Question: What frequency was typically used on US Amtrak?
Answer: 25 Hz

Question: What voltage does SEPTA system use?
Answer: 12 kV voltage

Question: What specification is similar for both Amtrak and Septa systems?
Answer: catenary voltage

Question: When was a 11kV system of NY, New Haven and Hartford was converted to 12.5 kV?
Answer: 1987
Railway_electrification_system

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.

Question: When was overhead wires system being used for the first time in UK?
Answer: 1 December 1909

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

Question: What was the cause of lines not being extended?
Answer: the First World War

Question: What voltage was used in the two lines opened in 1925 of Southern Railway?
Answer: 6.7 kV 25 Hz
Railway_electrification_system

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.

Question: What countries  used three-phase AC system in the the beginning of 20th century?
Answer: Italy, Switzerland and the United States

Question: What country was a bigger user compare to the three of them?
Answer: Italy

Question: Where did Italy start using the AC system?
Answer: in the mountainous regions of northern Italy

Question: How long did the AC system last in northern Italy?
Answer: 1901 until 1976

Question: How long did three-phase system operate in Cascade Tunnel?
Answer: 1909 to 1927
Railway_electrification_system

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.

Question: What country has first tried to use single-phase AC?
Answer: Hungary

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

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

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

Question: What system was adopted in Hungary after WWII?
Answer: Russian
Railway_electrification_system

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.

Question: What was the main requirement for electric feeder stations?
Answer: line fed from different feeder stations must be kept strictly isolated

Question: What invention prevented lines from getting mixed?
Answer: Phase Breaks

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

Question: How were the drivers warned to start coasting the train?
Answer: warning board

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