Magnetic levitation (maglev) is a highly advanced technology which provides, through magnetic forces, contactless movement with no wear and friction and, hence, improved efficiency, followed by reduced operational costs. It can be used in many fields, from wind turbines to nuclear energy and elevators, among others. Maglev trains, which use magnetic levitation, guidance and propulsion systems, with no wheels, axles and transmission, are one of the most important application of the maglev concept, and represents the first fundamental innovation of rail technology since the launch of the railroad era. Due to its functional features, which replaces mechanical components by a wear free concept, maglev is able to overcome some of the technical restrictions of steel-wheel on rail (SWR) technology, running smoother and somewhat quieter than wheeled systems, with the potential for higher speeds, acceleration & braking rates and unaffected by weather, which ultimately makes it attractive for both high speed intercity and low speed urban transport applications. From a technical perspective, maglev transport might rely on basically 3 technological concepts: i) electromanetic suspension (EMS), based on the attraction effect of electromagnets on the vehicle body, that are attracted to the iron reactive rails (with small gaps and an unstable process that requires a refined control system); ii) Electrodynamic Levitation (EDL), which levitates the train with repulsive forces generated from the induced currents, resulted from the temporal variation of a magnetic field in the conductive guide ways and iii) Superconducting Levitation (SML), based on the so called Meissner Effect of superconductor materials. Each of these technologies present distinct maturity and specific technical features, in terms of complexity, performance and costs, and the one that best fits will depend on the required operational features of a maglev system (mainly speed). A short distance maglev shuttle first operated commercially for 11 years (1984 to 1995) connecting Birmingham (UK) airport to the the city train station. Then, high-speed full size prototype maglev systems have been demonstrated in Japan (EDL) (552 kph - 343 mph), and Germany (EMS) (450 kph - 280 mph). In 2004, China has launched a commercial high speed service (based on the German EMS technology), connecting the Pudong International Airport to the outskirts of the city of Shanghai. Japan has launched a low speed (up to 100 kph - 62.5 mph) commercial urban EMS maglev service (LIMINO, in 2005), followed by Korea (Incheon, in 2016) and China (Changsha, in 2016). Moreover, Japan is working on the high speed Maglev concept, with the so called Chuo Shinkansen Project, to connect Tokio to Nagoya, in 2027, with top speeds of 500 kph (310 mph). China is also working on a high speed maglev concept (600 kph - 375 mph), supported on EMS Maglev technology. Urban Maglev concept seeks to link large cities, with their satellite towns and suburbs, to downtown areas, as a substitute for subways, due to its low cost potential, compared to metros and light rail (basically due to their lower turning radius, grade ability and energy efficiency). High Speed Maglev is also seen as a promising technology, with the potential do provide high quality passenger transport service between cities in the 240–1,000 km (150–625 mi) distance range into a sustainable and reliable way. This work is supposed to present, based on a compilation of a multitude of accredited and acknowledged technical sources, a review of the maglev transport technology, emphasizing its potential and risks of the low and high speed (urban and intercity) market, followed by a brief summary of some case studies.

EMC/EMI is a source of concern from the beginning of planning a new railway line. High powered electrified railways such as HSR are usually AC electrified. This poses a hazard for nearby systems and users. Induced voltages can create electric shock risks or malfunction in signalling or other nearby systems. LRTs, metro lines or commuter systems are usually DC fed and can be located near electromagnetic sensitive equipment such as MRI equipment in hospitals or research equipment — such as electron microscopes — in campuses or laboratories. EMF calculation and impact assessment in early phases of the project rely on simulation and expertise in these complex multi system interrelations. Rail traction creates EM fields which tend to decrease rapidly as the distance from the track axis increases. However, considerations about passengers, workforce and public safety and system compatibility are always needed. As an example, transient currents in DC rail, especially due to short circuits or arcs can interfere with nearby equipment. Even semi steady state DC currents associated with normal operation of the line (traction and breaking currents) present EMC related hazards that need to be assessed in order to evaluate if mitigation measures for associated risks are needed. AECOM’s Madrid Transportation Design Center has developed a tool that provides 3D EMF calculations for railway lines, either AC or DC. This tool, called EMFRail, can deliver EMF estimations based on power load supply simulations considering alignment, separation between tracks, geometry of the electrification system (OCS, third rail), rolling stock mechanical and electric features as well as regenerative braking in order to provide decision support information to make educated project decisions from the beginning of the design. Regenerative braking is a common energy saving tool for railways these days, but has posed new EMF hazards since currents sent back to the OCS can be bigger than those related to traction and this process can occur in different locations of the line (usually when the train is decelerating from maximum speed). This tool can calculate both magnetic and electrical fields for traction frequencies. This tool has been used in several LRT and rail projects providing insightful information to adopt mitigation measures such as underground feeders or operational limitations. EMFRail can simulate mitigation measures for challenging situations such as EMF caused by semi steady state maximum currents (prior to the trip of protection systems). EMFRail can also provide EMF calculations for transmission or distribution power lines once the required current or voltage values (module and phase) are known as well as the position of the different conductors (OCS wires, feeders, rails) of the line under study. EMFRail is developed using MatLab programming suite taking advantage of matrix operation capabilities. Output results are isocurves that can be superimposed to a raised view drawing, 3D contours for specific magnetic field values or even time animated frames to understand worst case scenarios that sometimes are not easy to foresee based on common assumptions.

Since the introduction of electrified transit systems in the United States there has been a number of advancements in the field of corrosion control related to light rail transit (LRT) systems. Modern day direct current (dc) powered LRT systems have been designed with a variety of corrosion control features built-in. Most of the research into corrosion control and the mitigation of stray currents known as electrolysis in the early days of electrified transit systems first appeared extensively in papers prepared and presented by personnel of the National Bureau of Standards. This research has led to better protection against corrosion of transit systems and nearby structures throughout the years. Due to the ever increasing number of transit systems being built or upgraded, it’s essential to incorporate the installation, testing and monitoring of corrosion control measures in these transit systems. By integrating these corrosion control features into the design of LRT systems and subsystems, it will help to prevent premature corrosion failures on LRT fixed facilities and other structures. This paper identifies the main causes of corrosion and how corrosion control can be implemented into the design of LRT systems to prevent damage to the transit system and other structures.

Several Authorities are procuring Hybrid Streetcars with OESS. The energy storage system needs to be protected from ground faults, external and internal to the vehicle. A Hybrid Streetcar has an OESS consisting of either Lithium Batteries or super capacitors, with an OESS converter connected to, or integrated with, the Traction Inverter. During a ground fault of the high voltage circuit, the freewheeling diode in an OESS charger creates a fault path between the energy storage elements and ground. Typical vehicle designs use a fuse for catastrophic protection, depending on the vehicle ground fault scheme for detection and protection. The vehicle’s primary ground fault detection device is an HSCB, usually connected between the shop switch and traction inverter; the auxiliary inverter is typically protected using a fuse. An HSCB is able to protect typical fault currents seen within the traction chain, but is not designed for OESS fault currents. If a fault occurs the fuse for the catastrophic protection of the OESS will blow before the HSCB will trip, potentially damaging equipment, making the vehicle inoperable. This paper compares alternative methods which can be deployed to detect and protect the OESS from a ground fault.

Stray current corrosion will occur at each point where the current transfers from a metallic conductor (such as structural reinforcement) to the electrolyte (i.e, the soil or concrete). Hence stray current leakage can cause corrosion damage to the rails, railway metallic structures, utility pipelines in the soil and any other low resistance metal buried in the vicinity. The hazard posed by stray current is not confined to structures that are within the vicinity of the railway. Stray currents can flow considerable distances (particularly in soils of low resistivity) and can therefore cause corrosion damage to what may be considered remote structures. This paper presents the importance of corrosion control on utility pipes and then presents and evaluates potential metal loss using arithmetic equations and basic modeling.

This paper describes the computer simulation methods for dc traction power systems and ac power traction power systems that have been used to develop the computer simulator TAROS ® at Gannett Fleming. The simulator has been designed and developed to support both load flow analysis and fault analysis. The paper also presents some examples of practical applications of the simulator in engineering and design under various operational conditions that may be encountered in transit and rail systems, such as normal, abnormal and fault conditions. Examples include: electric load cycles in various system components for their rating and size selection or verification; distribution of traction return currents in return conductors and ground for electromagnetic interference assessment; touch and step voltage analysis for the design of the traction return system grounding and bonding to meet safety requirements; and fault calculations for relay protection coordination.

Light rail systems interact with utility AC power distribution systems in many areas where running rails run parallel to the utility AC power transmission and distribution lines. This interaction may produce a 60Hz voltage on the running rail relative to the earth, adjacent to that the running rail. Since the running rails on modern systems are reasonably well isolated, this can result in potentials that can cause significant AC voltage on the rail that can cause instrumentation problems and personnel safety issues working on right-of-way (ROW). This effect is generally seen in areas where electrical distribution lines (power lines) run parallel to the running rail. This paper will describe methodology used to mitigate the problems by selecting a suitable capacitor filter bank network that provides a highly conductive path for the induced AC voltages between the substation grounding grid and the running rail at the traction power substation location. The filter actually provides lower resistance to AC than the resistance to the ground, thus from an AC standpoint, the running rails are connected to the earth at that location. This drains much of the AC potential between running rail and the earth thus greatly lessening this potential even at significant distance from the substation. The filter network provides no path for DC current so it does not increase stray traction earth currents produced by rail drop voltage from an accelerating train. The adequate measurement and verification (M & V) techniques are adopted to achieve desired results. The paper describes a cost effective solution comprising of an RC network filter with NEMA 3R rating enclosure, along with monitoring devices for monitoring DC and AC voltages and currents at the negative rail. These devices are installed and tested to mitigate the stray current issues successfully at the Valley Transportation Authority’s (VTA) traction power substation #31.

The Los Angeles Metropolitan Transportation Authority (LACMTA), like many other transit agencies throughout the country, is currently addressing the stray current corrosion problems on its rail system. Numerous capital projects have been released by the authority for the rehabilitation of their corroded infrastructures along their right-of-way. In addition, new maintenance procedures have been implemented to minimize corrosion problems to the rail and utility infrastructures located adjacent to the electrified railroad. The corrosion effect on rail infrastructures is often overlooked by most electrified railroad authorities because an immediate corrective response is not necessary for train movement during rail operations. The corrosion process is a natural process that occurs slowly and continuously throughout the life span of all materials, and may be accelerated due to stray currents from the railroad electrification system. Several key locations along the right-of-way have greater impact from stray current corrosion issues: at street crossing due to poor rail insulated boots, switch machines and accumulation of brake dust near passenger platforms. Other significant locations that suffer from stray current effects are overhead and under grade bridges, tunnel structures, rail spikes, fire suppression pipes, sewage pipes and underground feeder cable connections. Moreover, stray current can also cause other vital systems such as signaling systems and communication systems to malfunction. The other aspect of stray current is intentional discharging of stray current into earth ground through Negative Grounding Device (NGD) to maintain negative rail over voltage level for safe operation and reliability of rail service to the public. Typical negative rail voltage with respect to earth ground in operation is over 100VDC which is over the recommended voltage of 50VDC. Corrosion problems can be controlled by the implementation of a cathodic protection system, proper inspection of the running rail, impedance bond connections and proper maintenance of the cathodic protection system and negative grounding devices. The purpose of this paper is to address corrosion issues associated with DC electrified railways, recommend maintenance practices to control stray current sources, recommended maintenance practices for cathodic protection systems and discuss the balancing act to control negative rail over voltage versus intentional discharge of stray current to earth ground.

All direct current traction power systems using rails for return of traction current have a level of current leakage. This leakage of current is dependent on both design and operating factors affecting the efficiency of the rail return path and is referred to as stray current. Stray currents have been detected since the first electric railways were placed into operation during the latter half of the nineteenth century and have serious effects on utility structures and the neighboring infrastructure at large. Stray currents can create safety hazards thereby rendering the design of stray current mitigation an important element of the overall design of a rail transit system. Like any other design/construction project, a baseline survey is an important and significant step in the data collection and fact finding process for a light rail system. Such a survey would aid in finding the soil resistivity data and the results of the stray current levels on existing buried metal utilities. Similarly defining the design criteria for stray current mitigation, monitoring, and testing for a new light rail design project is also important. Most of the design criteria for the older rail transit systems have been developed as an aftermath of the corrosion problem and/or after the design of new extension to the system. Some older transit systems still do not have a specified design or mitigation criteria for stray current, and corrosion issues are handled as they surface and are prioritized based on severity. In the absence of guidelines, it is hard to understand the reasoning behind the limiting criteria suggested in the transit agency manuals particularly when there is no record of testing or soil resistivity investigation. For these older transit systems the limiting criterion was developed based on the information from other transit services. Having applicable design criteria for stray current control and mitigation will help standardize the process for the transit and will lower the cost of mitigation. This paper has been written by a Civil Engineer with an effort to understand the source and the scientific reasoning behind the limiting values suggested by the transit agencies associated with stray current testing procedures and its control. In order to understand the limited stray current corrosion criteria and the respective testing, various transit agencies were interviewed. These interviews were supplemented by a thorough review of the respective transit agency criteria manual/guidelines (where such information was available and accessible). Critical evaluations of the testing procedures were conducted to analyze if these tests and mitigation methods were effective.

Mass transit systems are gaining increased attention and popularity in the country. With this increased activity, more and more lines are getting added under public transit systems in more and more cities. One of the essential elements in the transit system is the traction transformer which powers the trains. With the emphasis on reliability, there is also increased awareness of the energy efficiency required of the traction substation equipments and the transformer in particular. Traction transformers are not ordinary power or distribution transformers. They have to meet several special requirements, including parameters like voltage regulation, impedance, commutation, short circuit withstand, operation with rectifiers, harmonic losses, wide fluctuation of load currents depending on the cyclic nature, etc. The reliability criteria are stringent and the traction transformers have to be properly designed, manufactured and tested, including short circuit testing for validation. Use of modern design tools like electric and magnetic field mapping and estimation of forces and stresses are helpful in computing them accurately. With the extensive use of vacuum circuit breakers, the subject of interaction of transformers and breakers have come to the foreground. New standards (like IEEE C57.142) have come into existence, which recommend methods to mitigate such effects. The author of this paper and his team has successfully applied these techniques in real life situations to solve problems. Work is in the final stages for preparation of a standard specifically for Traction Power Rectifier Transformers for transit applications (IEEE draft standard 1653.1) under the IEEE Vehicle Standards Committee.

The negative return portion of a modern direct current (dc) traction power system, which includes the tracks (the running rails), is normally isolated from earth to the maximum extent practical. The purpose of this isolation is to prevent stray dc currents from flowing through the earth and potentially causing corrosion of nearby metallic infrastructure. The isolation of the tracks from the earth is not perfect. Each track tie and insulated rail fastener assembly can be electrically represented as a resistor of high ohmic value connected between the rails and the earth. With many of these resistors in parallel over miles of track, a distributed “leakage resistance” is established between the rails and earth. For modern dc traction power systems in particular, however, this resistance is high enough for the rails to be considered essentially ungrounded with respect to local electrical ground (earth). The lack of an intentional connection between the tracks and earth allows voltage differences to occur along the rails, and between the rails and nearby structures. These voltage differences are caused by the flow of current through the running rails back to the substations. Since the shells of rail vehicles are typically at the same voltage as the wheels and rails, this voltage difference could be impressed on a passenger entering or exiting a train from a grounded platform. Or they could be impressed on a person walking along the tracks. In the USA, these voltage differences have generally been limited through system design; North American standards for substation grounding are referenced for design purposes, in particular IEEE Standard 80, Guide for Safety in Substation Grounding . In Europe, a standard has been developed specifically to address control of voltages between rails and structures, BS EN 50122-1 (IEC 62128-1), Railway Applications – Fixed Installations – Part 1: Protective Provisions Relating to Electrical Safety and Earthing . Voltage-limiting equipment that can be installed in passenger stations and other accessible locations has been developed in response to the requirements of EN 50122-1. These devices quickly connect the running rails to the station structure to eliminate unsafe voltage differences. If an earth fault occurs (broken catenary conductor falling on the ground, for example), there may not be a low-resistance circuit back to the substation due to the electrical isolation between running rails and earth ground. Without a low-resistance path back to the substation, there may be a resulting low-level short circuit current flow insufficient to operate the substation protective systems. As a result, the area in the vicinity of the fault may potentially be elevated to unsafe voltage levels. Equipment intended to detect this condition and connect the substation negative dc bus to the substation grounding grid is gradually being incorporated into modern North American dc traction power substation design. These devices are known by several names such as “substation grounding contactors”, “automatic grounding switches”, and “negative grounding devices”. Devices built to comply with EN 50122-1 are termed “Voltage Limiting Devices”. EN 50122-1 includes voltage-time curves that dictate the maximum permissible magnitudes and durations for ac and dc voltages; equipment built to EN 50122-1 must clamp the highest voltages in no more than 20 milliseconds. This paper will review current American and European standards and codes for maximum permissible rail voltage on direct current traction power systems. The maximum permissible voltage levels will be explained and compared. The principles of negative grounding device operation and corresponding voltage settings will also be discussed.

Several modern streetcar systems have been designed and implemented in the USA. Recently, the Portland streetcar extensions to River Place and Gibbs Street have been opened for revenue operation and construction for the Seattle South Lake Union streetcar project just got started. Installation of these new streetcar systems in dense urban areas like Portland and Seattle downtown areas posed several design challenges such as installation of the overhead contact wire system, coordination with street lighting, interface with traffic signal, streetcar-trolley bus crossings, and substation location sites. Other issues include connection to the 480 VAC utility system, stray currents, and utility relocations. These challenges and issues will be discussed in this paper. Construction packaging and cost impacts will also be covered.

The paper describes the findings of an experiment that is a result of close collaboration among four companies. The paper discusses the experiment on one locomotive by using a microprocessor-based relay, Multiple Function Relay (MFR) SEL-701, for on-line measurement, control and optimization of a HEP (Head End Power) group. The HEP has a Diesel engine, 810 HP/908 HP, 1800 rpm, and a double wound three-phase self excited synchronous alternator, 625 kVA, 575 V. The HEP group is installed on the locomotive and supplies the electrical hotel power to the train’s coaches. The relay SEL-701 ( S chweitzer E ngineering L aboratories) measures the Diesel engine temperatures on 7 different points and the winding temperatures at 3 internal points, one per each phase. The SEL-701 monitors alternator output currents and voltages and controls one (or both) train lines when the Diesel engine’s hottest temperature equals the maximum admissible temperature. Amongst others the paper highlights the benefits derived by use of on-line measurements of the Diesel engine before and after relocation of a pre-existent engine shutdown temperature probe. In addition, the paper discusses the decrease in the numbers of Diesel engine shut downs due to the modified mode of protection and the increase in available electrical power supplied to the train lines together with the comparison of the HEP group efficiency before and after modification.

Major factors affecting the reliability of railroad or transit systems are assigned at the design stage of a project. After the design of the system has been finalized changes that can be implemented to improve the reliability are generally of the second order level and subsequently have a lesser effect. An area that has traditionally been a source of unreliable operation for railroad and transit systems has been the interfaces between the various systems. The system-to-system interfaces cover the whole of the range of areas in a railroad or transit system and are often visible to the passengers using the railroad or transit system. The interfaces to be controlled have a wide variety of characteristics and features. These interfaces can consist of mechanical issues like for the platform and vehicle interface. The interfaces can also be mainly electrical in nature as with the control of conducted interference currents at the vehicle power supply interface to achieve compatibility. Interfaces may also be a mixture of mechanical and electrical characteristics. Railroad and transit systems are becoming more sophisticated, it is now common for a rail vehicle to have multiple microprocessors on board to control the various systems needed for a modern rail vehicle. Similar technologies are also being applied to different systems of a railroad or transit system. For example the technology required to control a vehicle propulsion system is very similar to that required by the modern regenerative substation. Modern integrated systems are also spreading across the traditional system boundaries. For example an integrated passenger information system for an LRT or Metro system would span vehicles, stations, train control and communication systems. A key factor to improving the reliability of a railroad or transit system is early and effective control of the system interfaces and having the appropriate organization(s) responsible for the interface. This paper will explore the factors that would need to be considered for appropriate management of the interfaces. It will relate the management of the interfaces to the types of contract mechanisms that can be used for procurement of equipment and consider the associated advantages and risks.

Due to the dynamic characteristics of traction load and unevenly train dispatch schedule, the unbalances currents are generally presented at Point of Common Coupling (PCC). To suppress the degree of unbalance, a specially connected transformer or/and reactive power compensation device can be applied. Traditionally, a Phase-Shifted Scott transformer type SVC was installed in front of Scott connection transformer to improve the voltage fluctuation which is caused by High Speed Railway (HSR) Systems. However, this solution is the most effective only in case that the power factor angle of each phase load equals π/6 lagging; otherwise, a quite severe negative sequence current still presented at PCC. In this investigation, a new hybrid SVC scheme is proposed to improve this disadvantage. The results show that the proposed scheme can effectively restrict the negative sequence current to zero no matter what power factor of traction load.