Electric traction

 

ELECTRIC TRACTION

Efforts to propel railroad cars the usage of batteries date from 1835, however the first profitable utility of electric powered traction was once in 1879, when an electric powered locomotive ran at an exhibition in Berlin. The first business functions of electric powered traction have been for suburban or metropolitan railroads. One of the earliest got here in 1895, when the Baltimore and Ohio electrified a stretch of music in Baltimore to keep away from smoke and noise issues in a tunnel. One of the first international locations to use electric powered traction for main-line operations was once Italy, the place a device used to be inaugurated as early as 1902.

 

By World War I a quantity of electrified traces have been working each in Europe and in the United States. Major electrification applications have been undertaken after that warfare in such international locations as Sweden, Switzerland, Norway, Germany, and Austria. By the give up of the Nineteen Twenties almost each European u . s . had at least a small share of electrified track. Electric traction additionally was once added in Australia (1919), New Zealand (1923), India (1925), Indonesia (1925), and South Africa (1926). A quantity of metropolitan terminals and suburban offerings had been electrified between 1900 and 1938 in the United States, and there have been a few main-line electrifications. The introduction of the diesel locomotive inhibited similarly trunk route electrification in the United States after 1938, however following World War II such electrification was once hastily prolonged elsewhere. Today a vast proportion of the standard-gauge music in countrywide railroads round the world is electrified—for example, in Japan (100 percent), Switzerland (92 percent), Belgium (91 percent),Spain (76 percent), Netherlands (76 percent), Norway (62 percent) Italy (68 percent), Sweden (65 percent), Austria (65 percent),, China (42 percent, South Korea (55 percent), France (52 percent), Germany (48 percent), and the United Kingdom (32 percent). By contrast, in the United States, which has some 225,000 km (140,000 miles) of standard-gauge track, electrified routes rarely exist outdoor the Northeast Corridor, the place Amtrak runs the 720-km (450-mile) Acela Express between Boston and Washington, D.C.The century’s 2d half of additionally was once marked by using the advent in cities global of many new electrified city rapid-transit rail systems, as nicely as extension of present systems.

Advantages and disadvantages

 Electric traction is usually viewed the most least expensive and environment friendly capacity of running a railroad, furnished that low cost electrical energy is handy and that the site visitors density justifies the heavy capital cost. Being clearly power-converting, as a substitute than power-generating, devices, electric powered locomotives have quite a few advantages. They can draw on the assets of the central strength plant to increase energy considerably in extra of their nominal scores to begin a heavy instruct or to surmount a steep grade at excessive speed. A ordinary cutting-edge electric powered locomotive rated at 6,000 horsepower has been discovered to strengthen as tons as 10,000 horsepower for a quick length beneath these conditions. Moreover, electric powered locomotives are quieter in operation than different kinds and produce no smoke or fumes. Electric locomotives require little time in the save for maintenance, their preservation prices are low, and they have a longer existence than diesels.

 The biggest drawbacks to electrified operation are the excessive capital funding and protection value of the constant plant—the traction present day wires and constructions and strength substations—and the high priced adjustments that are generally required in signaling structures to immunize their circuitry towards interference from the excessive traction-current voltages and to adapt their overall performance to the choicest acceleration and sustained speeds attainable from electric powered traction.

Types of traction systems

Electric-traction structures can be extensively divided into these the usage of alternating modern and these the use of direct current. With direct current, the most famous line voltages for overhead wire provide structures have been 1,500 and 3,000. Third-rail structures are predominantly in the 600–750-volt range. The negative aspects of direct contemporary are that luxurious substations are required at regularly occurring intervals and the overhead wire or 1/3 rail should be pretty massive and heavy. The low-voltage, series-wound, direct-current motor is properly appropriate to railroad traction, being easy to assemble and effortless to control. Until the late twentieth century it was once universally employed in electric powered and diesel-electric traction units.

The workable blessings of the use of alternating as a substitute of direct modern-day brought about early experiments and purposes of this system. With alternating current, specifically with particularly excessive overhead-wire voltages (10,000 volts or above), fewer substations are required, and the lighter overhead present day furnish wire that can be used correspondingly reduces the weight of buildings wanted to help it, to the in addition advantage of capital fees of electrification. In the early a long time of high-voltage alternating present day electrification, reachable alternating-current motors had been now not appropriate for operation with alternating modern of the popular business or industrial frequencies (50 hertz [cycles per second] in Europe; 60 hertz in the United States and components of Japan). It used to be imperative to use a decrease frequency (16 2/3 hertz is frequent in Europe; 25 hertz in the United States); this in flip required both distinct railroad electricity flora to generate alternating modern at the required frequency or frequency-conversion tools to alternate the on hand business frequency into the railroad frequency.

Nevertheless, alternating-current furnish structures at sixteen 2/3 hertz grew to be the popular on a number of European railroads, such as Austria, Germany, and Switzerland, the place electrification commenced earlier than World War II. Several main-line electrifications in the japanese United States had been constructed the usage of 25-hertz alternating current, which survives in the Northeast Corridor operated by using Amtrak.  

Interest in the usage of commercial-frequency alternating present day in the overhead wire continued, however; and in 1933 experiments had been carried out in each Hungary and Germany. The German State Railways electrified its Höllenthal department at 20,000 volts, 50 hertz.In 1945 Louis Armand, former president of the French railroads, went in advance with in addition improvement of this device and transformed a line between Aix-Les-Bains and La Roche-sur-Foron for the first realistic experiments. This used to be so profitable that the 25,000-volt, 50- or 60-hertz device has turn out to be truely the general for new main-line electrification systems.With commercial-frequency, alternating-current systems, there are two sensible approaches of taking energy to the locomotive riding wheels: (1) by means of a rotary converter or static rectifier on the locomotive to convert the alternating-current furnish into direct modern-day at low voltage to force general direct-current traction motors and (2) through a converter device to produce variable-frequency cutting-edge to force alternating-current motors. The first method, the usage of nonmechanical rectifiers, was once trendy practice till the give up of the 1970s.

The power-to-weight ratios accessible with electric powered traction devices had been appreciably improved through the cease of World War II. Reduction in the bulk of on-board electric powered equipment and motors, coupled in the latter with a simultaneous upward jostle in doable energy output, enabled Swiss manufacturing for the Bern-Lötschberg-Simplon Railway in 1944 of a 4,000-horsepower locomotive weighing solely 80,000 kg (176,370 pounds). Its 4 axles had been all motored. There used to be no longer want of nonmotorized axles to maintain weight on every wheel-set inside limits suited by means of the track.

By 1960 the electric powered enterprise used to be producing transformer and rectifier applications slim ample to healthy beneath the frames of a motored city rapid-transit car, thereby making nearly its whole physique accessible for passenger seating. This helped to speed up and extend the industrialized world’s electrification of metropolitan railway networks for operation with the aid of self-powered train-sets (i.e., with some or all motors motored). A advantage of the self-powered train-set precept is its effortless adaptation to peaks of site visitors demand. When two or greater units are coupled, the extra units have the more wanted traction power. With each electric powered and diesel traction it is easy to interconnect electrically the strength and braking controls of all the train-sets so that the teach they structure can be pushed from a single cab. Because of this facility such train-sets are extensively regarded as multiple-units. Modern multiple-units are more and more equipped with computerized couplers that mix a draft characteristic with connection of all power, braking, and different manage circuits between two train-sets; this is accomplished by way of automated engagement, when couplers interlock, of a nest of electric powered contacts constructed into every coupler head.

From about 1960 most important advances in electric powered traction accumulated from the software of electronics. Particularly giant was once the perfection of the semiconductor thyristor, or “chopper,” manage of present day provide to motors. The thyristor—a rapid-action, high-power change with which the “on” and “off” durations of every cycle can be fractionally varied—achieved easily graduated software of voltage to traction motors. Besides casting off wear-prone components and appreciably enhancing an electric powered traction unit’s adhesion, thyristor manipulate additionally decreased contemporary consumption.

Three-phase alternating-current motor traction grew to become plausible in the 1980s. With electronics it was once viable to compress to manageable weight and measurement the complicated gear wished to transmute the overhead wire or third-rail cutting-edge to a grant of variable voltage and frequency appropriate for feeding to three-phase alternating-current motors. For railroad traction the alternating-current motor is preferable to a direct-current computing device on a number of counts. It is an induction motor with a squirrel-cage rotor (that is, stable conductors in the slots are shorted collectively by means of quit rings), and it has no commutators or brushes and no routinely contacting components barring bearings, so that it is lots easier to hold and extra reliable. It is greater compact than a direct motor, so extra energy is attainable for a certain motor measurement and weight; the 6,000-kg (14,000-pound) alternating-current motor in every truck of a contemporary French National Railways electric powered locomotive offers a non-stop 3,750 horsepower.

The torque of an alternating-current motor will increase with speed, whereas that of a direct-current motor is at the start excessive and falls with rising speed; consequently, the alternating-current motor presents greatest adhesion for acceleration of heavy trainloads. Finally, the alternating-current motor is extra without difficulty switched into a producing mode to act as a dynamic (rheostatic) or regenerative automobile brake. (In dynamic braking the present day generated to oppose the train’s momentum is dissipated via on-board resistances. In regenerative braking, adopted on mountain or intensively operated city traces the place the surplus cutting-edge can be with ease taken up with the aid of different trains, it is fed again into the overhead wire or 1/3 rail.) The drawbacks of three-phase alternating-current traction are the intricacy of the on-board electrical tools wished to convert the contemporary provide earlier than it reaches the motors and its greater capital value by way of assessment with direct-current motor systems.

A separate traction motor usually serves every axle by using a suitably geared drive. For simplicity of ultimate force it was once for many years trendy exercise to mount the traction motors on a locomotive’s axles. As instruct speeds rose, it grew to be increasingly more vital to restriction the have an impact on on the music of unsprung masses. Now motors are both suspended inside a locomotive’s trucks or, in the case of some high-speed units, suspended from the locomotive’s physique and linked to the axles’ remaining power gearboxes by way of bendy force shafts.

The direct-current motor’s torque:speed traits make a locomotive designed for quickly passenger trains, whether or not electric powered or diesel-electric, typically unsuitable for freight educate work. The heavier hundreds of the latter require distinctive gearing of the closing drives—which will minimize most speed—and perchance an enlarge in the quantity of motored axles, for extended adhesion. But tremendous mixed-traffic haulage functionality is available with three-phase alternating-current motors due to the fact of their top-quality adhesion characteristics.

Direct-current motor technological know-how was once employed in Japan’s first Shinkansen and France’s first Paris-Lyon TGV trains, however by way of the early Nineteen Nineties three-phase alternating-current traction had been adopted for each Japanese and European very-high-speed train-sets—and via extension the structures round the world that have been derived from them. In Europe, worldwide instruct operation barring a locomotive alternate at frontiers is tricky by means of the railways’ ancient adoption of special electrification systems, both 1,500 or 3,000 volts direct present day or 25,000 volts 50 hertz or 15,000 volts 16 2/3 hertz alternating current. For instance, TGV-type trains should now not operatie at full effectivity between London, Paris, and Brussels on the Eurostar line through the Channel Tunnel as lengthy ,The French had perfected traction gadgets succesful of running on extra than one voltage gadget quickly after they determined to undertake 25,000-volt alternating-current electrification in areas now not wired at their preceding 1,500-volt direct current. Nevertheless, the place very-high-speed traction was once concerned, it used to be not possible to comprise inside suited locomotive weight limits the gear wanted for equal high-power output underneath each system. Only after all the new high-speed strains have been electrified on high-voltage alternating contemporary used to be a actual high-speed carrier on hand on the Eurostar line.

Since about 1980 the overall performance and financial system of each electric powered and diesel traction devices have been drastically superior through the interposition between riding controls and imperative elements of microprocessors, which make certain that the elements reply with most effectivity and that they are no longer inadvertently overtaxed. Another product of the software of electronics to controls is that in the present day electric powered locomotive the engine operator can set the teach pace he needs to attain or maintain, and the traction tools will routinely observe or range the excellent strength to the motors, taking account of teach weight and tune gradient. The microprocessors additionally serve a diagnostic function, always monitoring the nation of the structures they manage for symptoms of incipient or genuine fault. The microprocessors are linked to a primary on-board pc that right away reviews the nature and place of an authentic or possible malfunction to a visible show in the using cab, normally with recommendation for the cab crew on how it may be rectified or its outcomes briefly mitigated. The cab show additionally shows the effectiveness of the countermeasures taken. The pc routinely shops such data, both for downloading to renovation body of workers at the journey’s quit or, on a railroad outfitted with train-to-ground-installation radio, for instantaneous transmission to a upkeep institution so that preparations for restore of a fault are in area as quickly as the traction unit ends its run. In more moderen very-high-speed, fixed-formation train-sets, a through-train fibre-optics transmission device concentrates records from the microprocessor controls—both those of passenger vehicle systems, such as air-conditioning and power-operated entrance doors, and these of the rear locomotive or, in the Japanese Shinkansen train-sets, the traction tools dispersed among a share of its cars. 

Diesel traction 

Diesel traction refers to the use of diesel-powered engines to provide locomotion or propulsion in various transportation applications, particularly in the railway industry. Diesel traction has been widely employed in locomotives, trains, and other heavy-duty vehicles for many years.

In the context of railways, diesel traction systems typically consist of diesel engines coupled with power transmission systems to convert the engine's rotational power into linear motion. These systems are commonly used in situations where electrification of the rail network is not feasible or cost-effective.

Diesel traction offers several advantages that make it a popular choice in certain scenarios:

1. Flexibility: Diesel-powered locomotives and trains are not dependent on external power sources, such as overhead electric lines or third rails. They can operate on non-electrified rail lines or in areas with limited or no electrical infrastructure, providing greater operational flexibility.

2. Mobility: Diesel traction systems offer greater mobility compared to electric traction systems. They can be deployed on various routes without the need for extensive electrification infrastructure, making them suitable for remote or temporary railway operations.

3. Cost-Effectiveness: Diesel traction can be more cost-effective than electric traction in certain situations. The infrastructure required for electrification, including power lines and substations, can be expensive to install and maintain. Diesel-powered trains eliminate the need for these infrastructure investments.

4. Versatility: Diesel traction can be used in both passenger and freight rail applications. It is commonly utilized in long-distance freight transportation, where the flexibility and range of diesel locomotives make them well-suited for hauling heavy loads over vast distances.

However, there are also some considerations and challenges associated with diesel traction:

1. Environmental Impact: Diesel engines produce emissions, including carbon dioxide (CO2), nitrogen oxides (NOx), and particulate matter (PM). These emissions contribute to air pollution and have implications for climate change. Increasingly, there is a push for cleaner and more sustainable alternatives to diesel traction, such as electrification or hybrid propulsion systems.

2. Noise and Vibrations: Diesel engines can generate noise and vibrations, which can be a concern, particularly in densely populated areas or when passing through residential neighborhoods. Efforts have been made to mitigate noise and vibration levels through improved engine design and the use of noise-reducing technologies.

3. Fuel Costs and Efficiency: Diesel fuel costs can vary and are subject to market fluctuations. Additionally, diesel engines may have lower energy efficiency compared to electric propulsion systems. However, advancements in engine technology have led to improved fuel efficiency and reduced environmental impact.

4. Maintenance and Operations: Diesel traction systems require regular maintenance and servicing to ensure optimal performance and longevity. This includes engine maintenance, fueling, and periodic inspections to comply with safety and regulatory standards.

Overall, diesel traction continues to play a significant role in railway transportation, particularly in regions or situations where electrification is not feasible or cost-effective. However, with increasing focus on sustainability and environmental concerns, there is a growing emphasis on developing cleaner and greener alternatives to diesel traction in the transportation sector.

Diesel development

Experiments with diesel-engine locomotives and railcars started nearly as quickly as the diesel engine used to be patented through the German engineer Rudolf Diesel in 1892. Attempts at constructing sensible locomotives and railcars (for branch-line passenger runs) persevered via the 1920s. The first profitable diesel change engine went into provider in 1925; “road” locomotives had been delivered to the Canadian National and New York Central railroads in 1928. The first absolutely putting consequences with diesel traction had been received in Germany in 1933. There, the Fliegende Hamburger, a two-car, streamlined, diesel-electric train, with two 400-horsepower engines, started strolling between Berlin and Hamburg on a agenda that averaged 124 km (77 miles) per hour. By 1939 most of Germany’s primary cities have been interconnected with the aid of trains of this kind, scheduled to run at common speeds up to 134.1 km (83.3 miles) per hour between stops .

The subsequent step used to be to construct a separate diesel-electric locomotive unit that may want to haul any train. In 1935 one such unit used to be delivered to the Baltimore and Ohio and two to the Santa Fe Railway Company. These had been passenger units; the first avenue freight locomotive, a four-unit, 5,400-horsepower Electro-Motive Division, General Motors Corporation demonstrator, used to be now not constructed till 1939.

By the give up of World War II, the diesel locomotive had end up a proven, standardized kind of cause power, and it swiftly commenced to supersede the steam locomotive in North America. In the United States a fleet of 27,000 diesel locomotives proved thoroughly succesful of performing greater transportation work than the 40,000 steam locomotives they replaced.

After World War II, the use of diesel traction extensively expanded in the course of the world, even though the tempo of conversion was once usually slower than in the United States.

Elements of the diesel locomotive

Although diesel engines have greatly improved in power and performance, the basic principles remain the same: drawing air into a cylinder, compressing it so that its temperature increases, and then injecting a small amount of oil into the cylinder. Due to high temperature the oil burns without spark. Diesel engines can operate on a two-stroke or four-stroke cycle. Rated operating speeds vary from 350 to 2,000 revolutions per minute, and rated output can range from 10 to 4,000 horsepower. Railroads in the United States use engines in the 1,000-revolutions-per-minute range; In Europe and elsewhere, some manufacturers have favored more compact engines of 1,500–2,000 revolutions per minute.

Most yard-switching and short-haul locomotives are outfitted with diesel engines ranging from 600 to 1,800 horsepower; avenue devices many times have engines ranging from 2,000 to 4,000 horsepower. Most builders use V-type engines, even though in-line kinds are used on smaller locomotives and for underfloor fitment on railcars and multiple-unit train-sets.

The most oftentimes employed technique of electricity transmission is electric, to convert the mechanical power produced by way of the diesel engine to present day for electric powered traction motors. Through most of the twentieth century the standard technique used to be to couple the diesel engine to a direct-current generator, from which, thru suitable controls, the contemporary was once fed to the motors. Beginning in the 1970s, the availability of compact semiconductor rectifiers enabled substitute of the direct-current generator through an alternator, which is capable to produce greater strength and is much less highly-priced to hold than an equal direct-current machine. For grant of series-wound direct-current traction motors, static rectifiers transformed the three-phase alternating-current output of the alternator to direct current. Then in the Nineteen Eighties European producers started out to undertake the three-phase alternating-current motor for diesel-electric traction devices in search of benefits comparable to these accessible from this science in electric powered traction. This requires the direct-current output from the rectifier to be transmuted via a thyristor-controlled inverter into a three-phase variable voltage and frequency provide for the alternating-current motors. 

"Advancements in Locomotive Technology: Axles,Power Systems, Transmissions"

In the realm of railway engineering, locomotives have evolved significantly to cater to specific needs and operational efficiency. One notable aspect of this evolution concerns the configuration of axles in locomotives. Particularly, on railways with lightly laid tracks, often those with narrow rail gauges, locomotives may require a combination of both motored and non-motored axles to ensure optimal weight distribution. However, the prevailing trend in modern diesel-electric locomotives leans toward having all axles powered, exemplifying technological advancements in rail transport.

Diesel locomotives employ various transmission systems to convert engine power into locomotion. One such system is the hydraulic transmission, which gained popularity in Germany. This transmission type is favored for diesel railcars and multiple-unit train-sets. It operates by utilizing a centrifugal pump or impeller to drive a turbine within an oil or similar fluid-filled chamber. The pump, powered by the diesel engine, transforms engine power into kinetic energy within the oil, impacting the turbine blades. The locomotive's speed is directly correlated with the blade's rotational speed, providing efficient propulsion.

In contrast, mechanical transmission, the simplest type, finds use in low-power switching locomotives and diesel railcars with minimal power requirements. Essentially, it functions like a clutch and gearbox system akin to those found in automobiles, occasionally substituting a hydraulic coupling for a friction clutch.

The adoption of alternating current (AC) over direct current (DC) power systems has also been a noteworthy development in railway electrification. AC systems, especially with high overhead-wire voltages exceeding 10,000 volts, have demonstrated distinct advantages. They necessitate fewer substations and enable the use of lighter overhead current supply wires, resulting in reduced infrastructure costs. However, the transition to AC was not without challenges, as early AC motors were incompatible with the standard commercial or industrial frequencies (e.g., 50 hertz in Europe, 60 hertz in the United States and parts of Japan). This required either dedicated railroad power plants generating AC at the necessary frequency or frequency-conversion equipment to align the available commercial frequency with the railway's requirements.

Despite these hurdles, several European railroads, including Austria, Germany, and Switzerland, adopted 16 2/3 hertz alternating current electrification, a system that predates World War II. Similarly, in the eastern United States, 25-hertz alternating current systems were employed in some main-line electrifications, with Amtrak's Northeast Corridor maintaining this legacy."

"Progress in overhead wire electrification: the rise of commercial-frequency alternating current"

 The interest in utilizing commercial-frequency alternating current (AC) in overhead wire electrification systems continued to grow. In 1933, pioneering experiments were conducted in both Hungary and Germany to explore this concept further. Notably, the German State Railways took a significant step by electrifying its Höllenthal branch at 20,000 volts and 50 hertz, marking a crucial milestone in AC electrification.

 In 1945, Louis Armand, a former president of the French railroads, spearheaded the ongoing development of this AC system. He initiated practical experiments by converting a rail line between Aix-Les-Bains and La Roche-sur-Foron, which yielded remarkable success. This achievement led to the establishment of the 25,000-volt system operating at either 50 or 60 hertz as the de facto standard for new main-line electrification projects.

Commercial-frequency AC systems offer two practical approaches for delivering power to locomotive driving wheels:

1. Rotary Converter or Static Rectifier: This method involves installing a rotary converter or static rectifier on the locomotive. These devices transform the incoming AC supply into direct current (DC) at low voltage, which is then used to drive conventional direct-current traction motors.

2. Converter System for Variable-Frequency Current: An alternative approach is to employ a converter system capable of producing variable-frequency AC current. This variable-frequency current is utilized to power alternating-current motors.

For much of the 20th century, the first method, employing nonmechanical rectifiers, was the prevailing practice in rail electrification, remaining in use until the late 1970s."

"Advancements in Electric Traction: Efficiency and Compact Design"  The power-to-weight ratios achievable with electric traction units saw significant improvements by the conclusion of World War II. This transformation was driven by a reduction in the size of on-board electric components and motors, coinciding with a substantial increase in their power output. A notable example of this progress occurred in 1944 when Swiss engineers designed a locomotive for the Bern-Lötschberg-Simplon Railway. This locomotive boasted a remarkable 4,000-horsepower capacity while weighing just 80,000 kg (176,370 pounds) and featured all four axles as motored, eliminating the necessity for non-motorized axles to ensure acceptable weight distribution on the track.

 Fast-forward to 1960, and the electric industry had developed transformer and rectifier packages that were slender enough to fit beneath the frames of urban rapid-transit cars equipped with electric motors. This innovation effectively opened up almost the entire body of the train for passenger seating. Such developments played a pivotal role in accelerating the electrification of metropolitan railway networks worldwide, enabling the operation of self-powered train-sets, with some or all of their vehicles equipped with motors. An advantage of this self-powered train-set concept is its adaptability to fluctuations in passenger demand. When multiple sets are coupled together, they collectively provide the additional traction power needed. In both electric and diesel traction systems, it is straightforward to establish electrical connections between the power and braking controls of all train-sets, enabling centralized operation from a single cab. Due to this feature, these train-sets are commonly referred to as multiple-units.

Modern multiple-units are increasingly equipped with automatic couplers that not only facilitate coupling but also establish connections for power, braking, and other control systems between two train-sets. This functionality is achieved through the automatic engagement of a set of electric contacts integrated into each coupler head when the couplers interlock.

Revolutionizing Electric Traction with Electronics

Around 1960, significant strides in electric traction technology were achieved through the integration of electronics. A pivotal breakthrough during this period was the refinement of the semiconductor thyristor, often referred to as the 'chopper,' for controlling current supply to motors. The thyristor, a high-power switch capable of rapid action, allowed for precise modulation of voltage application to traction motors. Its ability to finely adjust the 'on' and 'off' periods of each cycle resulted in smooth and gradual voltage application. This advancement not only eliminated components prone to wear but also greatly enhanced the adhesion of electric traction units while simultaneously reducing current consumption.

In the 1980s, three-phase alternating-current motor traction became a practical reality, thanks to advancements in electronics. With electronic technology, it became feasible to miniaturize and reduce the weight of the intricate equipment required to convert overhead wire or third-rail current into a variable voltage and frequency suitable for three-phase alternating-current motors. Three-phase alternating-current motors offered several advantages over their direct-current counterparts in railway traction. These motors were induction-based, featuring a squirrel-cage rotor (where solid conductors in the slots are interconnected by end rings), eliminating the need for commutators, brushes, or any mechanically contacting parts except for bearings. This design made them simpler to maintain and highly reliable. Furthermore, three-phase alternating-current motors were more compact, allowing for increased power output within a specified motor size and weight. As an example, modern French National Railways electric locomotives are equipped with 6,000-kg (14,000-pound) alternating-current motors in each truck, delivering a continuous 3,750 horsepower."

The Advantages and Challenges of Alternating-Current Traction

The performance characteristics of alternating-current (AC) motors bring distinct advantages to the realm of railway traction. Unlike direct-current (DC) motors, AC motors exhibit a torque that increases with speed, making them particularly adept at providing superior adhesion for accelerating heavy trainloads. Furthermore, AC motors can be seamlessly transitioned into a generating mode to function as dynamic (rheostatic) or regenerative vehicle brakes. In dynamic braking, the generated current that opposes the train's momentum is dissipated through on-board resistances, while in regenerative braking, typically employed on mountainous or highly trafficked urban lines where surplus current can be absorbed by other trains, the energy is fed back into the overhead wire or third rail.

However, it's important to acknowledge some drawbacks associated with three-phase AC traction. One notable challenge lies in the complexity of the on-board electrical equipment required to convert the current supply before it reaches the motors. Additionally, the initial capital cost of AC systems tends to be higher when compared to their DC motor counterparts.

In the design of railway traction systems, a separate traction motor is typically allocated to each axle, with a suitable geared drive mechanism. For many years, a common practice was to mount traction motors directly on a locomotive's axles to simplify the final drive. However, as train speeds increased, the impact of unsprung masses on the track became a critical concern. Consequently, modern motor designs now often suspend the motors within a locomotive's trucks or, in the case of high-speed units, hang them from the locomotive's body, connecting them to the axles' final drive gearboxes via flexible drive shafts."

"Distinguishing Characteristics of Direct-Current and Alternating-Current Motors in Rail Traction"

The performance attributes of direct-current (DC) motors dictate their suitability for specific railway applications. Locomotives designed for high-speed passenger trains, whether electric or diesel-electric, are typically ill-suited for freight train operations due to the torque-to-speed characteristics of DC motors. Freight trains, with their heavier loads, require different gearing in the final drive, which reduces maximum speed. Additionally, they may necessitate an increased number of motored axles to enhance adhesion. In contrast, three-phase alternating-current (AC) motors, known for their superior adhesion characteristics, exhibit considerable versatility in handling mixed-traffic scenarios.

Japan's initial Shinkansen and France's early Paris-Lyon TGV trains relied on DC motor technology. However, by the early 1990s, both Japanese and European very-high-speed train-sets had transitioned to three-phase AC traction systems, influencing railway systems worldwide.

In Europe, seamless international train operations without locomotive changes at borders posed challenges due to historical variations in electrification systems, including 1,500 or 3,000 volts DC, 25,000 volts 50 hertz AC, or 15,000 volts 16 2/3 hertz AC. For instance, efficient travel between London, Paris, and Brussels on the Eurostar line through the Channel Tunnel was hindered as long as trains needed to accommodate different voltage systems, such as French 25,000-volt AC overhead wires, Belgian 3,000-volt DC overhead wires, and British 750-volt third-rail supply. The French developed traction units capable of operating on multiple voltage systems, especially when transitioning from 1,500-volt DC to 25,000-volt AC electrification. Nevertheless, for very-high-speed traction, it was challenging to keep locomotive weight within acceptable limits while maintaining high-power output under each system. A true high-speed service on the Eurostar line became viable only when all new high-speed lines were electrified using high-voltage AC."

"Revolutionizing Traction Units with Electronics Since the 1980s"

Significant strides in enhancing the performance and efficiency of both electric and diesel traction units have been achieved through the integration of microprocessors. These microprocessors act as intermediaries between the driving controls and critical components, ensuring that these components operate at maximum efficiency while avoiding inadvertent strain.

One notable outcome of applying electronics to control systems is the ability of modern electric locomotives to allow the engine operator to set the desired train speed for acceleration or maintenance. The traction equipment then automatically applies or adjusts the necessary power to the motors, factoring in variables like train weight and track gradient. Microprocessors also serve a diagnostic function, continuously monitoring the state of the systems they control to detect signs of potential faults or existing issues. These microprocessors are linked to a central on-board computer that promptly reports the nature and location of any actual or potential malfunction to a visual display in the driving cab. Additionally, the display offers guidance to the cab crew on potential remedies or temporary mitigation measures. It also provides feedback on the effectiveness of these measures.

The computer records this data, making it available for download by maintenance staff at the end of the journey. In railroads equipped with train-to-ground installation radio systems, the data can be instantly transmitted to a maintenance facility. This ensures that preparations for addressing any faults are underway as soon as the traction unit completes its run.

In more recent high-speed, fixed-formation train-sets, a comprehensive train-to-ground fiber-optic transmission system centralizes data from microprocessor controls. This encompasses not only passenger car systems like air conditioning and power-operated entrance doors but also systems in the rear locomotive or, in the case of Japanese Shinkansen train-sets, the traction equipment distributed among some of its cars."

Diesel traction

"The Diesel Revolution in Railroad Transportation"

By the late 1960s, diesel power had largely displaced steam locomotives as the standard motive power for nonelectrified railroad lines worldwide. This transition occurred most swiftly and decisively in North America. Over a span of 25 years, from 1935 to 1960, and particularly during the period from 1951 to 1960, U.S. railroads fully replaced their steam locomotives.

Several key factors contributed to the rapid replacement of steam with diesel locomotives. First and foremost, the pressure of competition from other modes of transportation and the ongoing increase in labor costs compelled railroads to enhance their services and implement measures to boost operational efficiency. Compared to steam locomotives, diesel traction units offered a range of significant advantages:

1. Extended Operating Durations: Diesel locomotives could operate continuously for extended periods with minimal maintenance interruptions. In North America, diesel locomotives could cover distances exceeding 3,200 kilometers (2,000 miles) before requiring servicing, enabling them to complete a round trip after maintenance. In contrast, steam locomotives demanded extensive servicing after just a few hours of operation.

2. Fuel Efficiency: Diesel locomotives consumed less fuel energy compared to steam locomotives, with a thermal efficiency roughly four times greater.

3. Enhanced Performance: Diesel locomotives could accelerate trains more rapidly and maintain higher sustained speeds with reduced track wear.

Additionally, the diesel locomotive offered advantages such as smoother acceleration, greater cleanliness, availability of standardized repair parts, and operational flexibility. Multiple diesel units could be combined and operated by a single operator under multiple-unit control.

The diesel-electric locomotive essentially functions as an electric locomotive that carries its own power source. This configuration brought some of the benefits of electrification to railroads without the substantial capital investments required for power distribution and overhead wire systems. However, compared to electric locomotives, diesel-electric locomotives had a significant drawback: their output was essentially limited by the capacity of their diesel engine. Consequently, they could generate less horsepower per locomotive unit. Given that high horsepower is essential for high-speed passenger services and extremely fast freight operations, diesel locomotives were less preferable than electric counterparts for such applications.

Diesel development

"The Diesel Revolution in Rail Transportation"

Almost immediately following the patenting of the diesel engine by German engineer Rudolf Diesel in 1892, experimentation with diesel-engine locomotives and railcars commenced. Early attempts to develop practical locomotives and railcars for branch-line passenger service persisted through the 1920s. The first successful diesel switch engine entered service in 1925, with "road" locomotives being delivered to the Canadian National and New York Central railroads in 1928. However, the true breakthrough in diesel traction was achieved in Germany in 1933 with the introduction of the "Fliegende Hamburger." This streamlined, two-car, diesel-electric train, featuring two 400-horsepower engines, operated between Berlin and Hamburg at an average speed of 124 kilometers (77 miles) per hour. By 1939, most of Germany's major cities were interconnected by trains of this kind, scheduled to run at average speeds of up to 134.1 kilometers (83.3 miles) per hour between stops.

The next milestone was the development of a standalone diesel-electric locomotive unit capable of hauling any type of train. In 1935, one such unit was delivered to the Baltimore and Ohio Railroad, while the Santa Fe Railway Company received two passenger units. The first road freight locomotive, a four-unit, 5,400-horsepower model by Electro-Motive Division of General Motors Corporation, wasn't constructed until 1939.

By the conclusion of World War II, diesel locomotives had established themselves as a proven and standardized motive power type, quickly overshadowing steam locomotives in North America. In the United States alone, a fleet of 27,000 diesel locomotives proved more than capable of handling the transportation workload that previously required 40,000 steam locomotives.

After World War II, the adoption of diesel traction gained momentum worldwide, although the pace of transition was generally slower than in the United States."

Elements of the diesel locomotive

"Diesel Engine Development and Power Transmission in Railroads"

While the diesel engine has seen significant advancements in terms of power and performance, its fundamental principles remain unchanged: drawing air into the cylinder, compressing it to elevate its temperature. The high temperature causes the oil to ignite without the need for a spark. Diesel engines can operate on either the two-stroke or four-stroke cycle, with rated operating speeds ranging from 350 to 2,000 revolutions per minute and rated output varying from 10 to 4,000 horsepower. In the United States, railroads typically employ engines in the 1,000 revolutions-per-minute range, whereas in Europe and other regions, some manufacturers favor more compact engines operating at 1,500 to 2,000 revolutions per minute.

Yard-switching and short-haul locomotives typically feature diesel engines ranging from 600 to 1,800 horsepower, while road units are commonly equipped with engines ranging from 2,000 to 4,000 horsepower. Most locomotive builders use V-type engines, although in-line engine types are utilized for smaller locomotives and for underfloor installations in railcars and multiple-unit train-sets.

The primary method of power transmission in diesel locomotives involves converting the mechanical energy generated by the diesel engine into electric current for electric traction motors. Throughout much of the 20th century, the prevailing approach was to connect the diesel engine to a direct-current generator, from which the current was directed to the motors through suitable controls. Starting in the 1970s, the availability of compact semiconductor rectifiers allowed for the replacement of direct-current generators with alternators. Alternators were more cost-effective to maintain and capable of generating greater power. To supply series-wound direct-current traction motors, static rectifiers converted the three-phase alternating-current output of the alternator into direct current. In the 1980s, European manufacturers began adopting three-phase alternating-current motors for diesel-electric traction units, seeking similar advantages to those seen in electric traction. This necessitated the transformation of direct current output from the rectifier into a three-phase variable voltage and frequency supply for the alternating-current motors using a thyristor-controlled inverter.

In some cases, particularly on railroads with lightly laid tracks or narrow rail gauges, locomotives may still require nonmotored axles in addition to motored ones to ensure proper weight distribution and bulk. However, the majority of diesel-electric locomotives now have all axles powered.

Different types of transmissions are also utilized in diesel locomotives. The hydraulic transmission, initially popularized in Germany, is commonly preferred for diesel railcars and multiple-unit train-sets. It operates using a centrifugal pump or impeller driving a turbine in an oil-filled chamber. The pump, powered by the diesel engine, converts engine power into kinetic energy in the oil, which impacts the turbine blades. Faster blade movement results in reduced relative impingement speed of the oil, thus propelling the locomotive more quickly.

Mechanical transmission represents the simplest type and is primarily used in low-power switching locomotives and low-power diesel railcars. It essentially consists of a clutch and gearbox similar to those found in automobiles. In some cases, a hydraulic coupling is used as a substitute for a friction clutch."

Types of  Diesel motive

There are three primary categories of railroad equipment that utilize diesel engines as prime movers:

1. Light Passenger Railcar or Rail Bus (up to 200 horsepower): Typically four-wheeled with mechanical transmission, these vehicles may be designed to pull a light trailer car, but their usage is quite limited.

2. Four-Axle Passenger Railcar (up to 750 horsepower): These railcars can operate independently, haul nonpowered trailers, or form part of a semi-permanent train-set, such as a multiple-unit with all or some of the cars powered. In powered cars, the diesel engine and all related traction components, including fuel tanks, can fit beneath the floor, creating space above the frames for passenger seating. Transmission systems can be either electric or hydraulic. Modern railcars and train-sets are often equipped for multiple-unit train operation, with centralized driving control from a single cab.

3. Locomotives (10 to 4,000 horsepower): Locomotives may feature mechanical transmission for very low power outputs or hydraulic transmission for outputs of up to approximately 2,000 horsepower. In most cases, they employ electric transmission, with the choice influenced by power output and intended use.

Significant advancements in diesel engine power-to-weight ratios and the integration of electronics into component control and diagnostic systems resulted in remarkable improvements in the efficiency of diesel locomotives during the latter part of the 20th century. By 1990, a diesel engine with a continuous rating of 3,500 horsepower weighed almost half as much as a comparable model from 1970, while simultaneously achieving improved fuel efficiency.

Electronics played a crucial role in enhancing the load-hauling capabilities of diesel-electric locomotives in road freight operations, particularly during acceleration from a standstill or uphill climbs. These locomotives can generate 33 to 50 percent more tractive force when their powered wheels are allowed to engage in a controlled slip known as "creep." A "creep control" system, equipped with Doppler radar mounted beneath the locomotive, precisely measures true ground speed. Microprocessors then calculate the optimal creep speed limit based on prevailing track conditions and automatically adjust the current supply to the traction motors. This process is continuous, ensuring immediate adaptation to changes in track parameters. In the 1960s, it was commonly believed in North America that a diesel-electric locomotive with a rating of 3,000 to 3,600 horsepower or more required six motored axles for effective traction. However, since the mid-1980s, four-axle locomotives with up to 4,000 horsepower have become viable and are widely used in high-speed freight service (though six-axle locomotives remained preferred for heavy-duty freight). Today, a 4,000-horsepower rating can be achieved with a 16-cylinder diesel engine, a significant advancement compared to the 1960s when a 3,600-horsepower output necessitated a 20-cylinder engine. This reduction in locomotive requirements, coupled with improved adhesion, has played a key role in lowering locomotive maintenance costs.

 

Outside North America, extensive electrification projects virtually eliminated the production of diesel locomotives specifically designed for passenger train operations by the 1960s. The last notable development for high-speed diesel service occurred on British Railways, which mass-produced the InterCity 125, a semi-permanent train-set featuring a 2,250-horsepower locomotive at each end of seven or eight intermediate cars. In 1987, one of these sets set a world speed record for diesel traction at 238 kilometers (148 miles) per hour. Some InterCity 125 sets are expected to remain in service under different designations well into the 21st century. In North America, Amtrak in the United States and VIA Rail in Canada, along with certain urban mass-transit authorities, still exclusively operate diesel locomotives for passenger trains. In other regions, road haul diesel locomotives are designed for either exclusive freight hauling or mixed passenger and freight services."

Traction operating methods

"Utilization of Multiple Units and Slave Locomotives in Rail Operations"

The practice of connecting and operating multiple locomotives to adapt power output to load and track gradient demands is standard in North America and widespread elsewhere. In situations with significant gradients or unusually lengthy and heavy freight trains, concentrating locomotives at the front of a train can stress couplings and lead to delays in transmitting full braking power to the rear of the train. In such scenarios, several railroads, particularly in North America, employ crewless "slave" locomotives inserted partway along the train. Radio signals transmitted from the leading locomotive prompt the slave locomotive's controls to automatically and synchronously respond to all control inputs. In August 1989, a world record for freight train weight and length was established on South Africa's electrified, 830-kilometer (516-mile), 1,065-millimeter (3-foot 6-inch) gauge Sishen-Saldanha ore line. During research into the feasibility of increasing regular trainloads on the line, a 660-car train weighing 71,600 tons and stretching 7.2 kilometers (4.47 miles) in length traversed the entire route. Power was provided by five 5,025-horsepower electric locomotives at the front, an additional four inserted after the 470th freight car, and seven 2,900-horsepower diesel locomotives at the rear. This arrangement helped prevent overtaxing the traction current supply system.

Post-World War II, the ability to easily reverse the direction of passenger train-sets became increasingly important for short- and medium-haul services with intensive operations. This was aimed at reducing turnaround times at terminals and minimizing the number of train-sets needed to maintain service levels. The favored medium for achieving this was the self-powered railcar or multiple-unit train-set, equipped with a driving cab at each end. Reversing direction only required the crew to change cabs. Another approach, known as "push-pull," featured a conventional locomotive at one end and a nonpowered passenger or baggage car, referred to as the driving or control trailer, at the other. The control trailer had a driving cab at its far end. In one direction, the locomotive pulled the train, while in the other, it pushed the train, controlled via through-train wiring from the control trailer's cab. An operational advantage of push-pull, compared to self-powered train-sets on a railway serving both passenger and freight trains, was that during nighttime when passenger services ceased, the locomotives could be detached and used for freight transport."

Turbine propulsion

In the 1950s, there were trials of gas-turbine propulsion instead of diesel for a few locomotives in both the United States and Britain. However, the results did not justify further development of this technology. A longer but limited career in rail transport was seen for compact and lightweight gas turbines that were originally developed for helicopters and became available in the 1960s. These turbines had a superior power-to-weight ratio compared to contemporary diesel engines, making them favorable for lightweight, high-speed train-sets. They were initially applied to train-sets built in Canada, which entered service in 1968 between Montreal and Toronto and in 1969 between New York City and Boston. However, these ventures were short-lived due to equipment issues, operational noise, and the high cost of fuel. Nevertheless, the technology has not been entirely abandoned. At the turn of the 21st century, Bombardier, a Canadian company, introduced its gas-turbine JetTrain locomotive as an alternative to electric traction for new high-speed rail systems in North America.

There have been several attempts to adapt steam turbines for railroad propulsion. One of the early experiments was a Swedish locomotive built in 1921. Europe and the United States saw the development of other steam turbine prototypes. While they demonstrated functionality, these steam turbine locomotives appeared too late to compete with diesel and electrification technologies.

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