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Japan and Germany are developing different types of normal-conductive magnetically levitated linear motor trains. Japan is developing the High Speed Surface Transport (HSST) system, while Germany is developing the Transrapid system.
The two systems are similar in the sense that they both use linear motors for propulsion, and electromagnets for levitation. However, the type of linear motor used is different.
The HSST is propelled by linear induction motors. The HSST primary coils are attached to the carriage body and the track configuration is simple, using steel rails and aluminium reaction plates. On the other hand, Transrapid trains are propelled by a linear synchronous motor. The motor primary coils are mounted on the guideway, and the levitation magnets are attached to the car and act as field magnets.
These differences can be explained by the fact that in the early development, the Japanese and German systems were not meant to operate at the same speed. Early plans called for the HSST to run at a maximum speed of 300 km/h, although development efforts are now focusing on intra-urban trains running at about 100 km/h. For their part, Transrapid developers are aiming for cruising speeds of 450 to 500 km/h.
Since the recent decision to use the HSST system on the Tobu Kyuryo Line in Aichi Prefecture, central Japan, this new technology is now closer to practical application. Once constructed, the track will become the world’s first commercial line. This article briefly explains Japan’s HSST system.
The HSST System
HSST research began in earnest in 1974 when Japan Airlines (JAL) began promoting a new linear motor car system. At the time, high-speed access between Tokyo and New Tokyo International Airport (Narita) was considered a matter of priority, because the airport was being constructed about 60 km from Tokyo’s core. To reduce access time, JAL proposed a maglev train propelled by linear motors at a target speed of 300 km/h
Magnetic levitation
The HSST levitation system uses ordinary electromagnets that exert an attractive force and levitate the vehicle. The electromagnets are attached to the car, but are positioned facing the underside of the guideway’s steel rails. They provide an attractive force from below, levitating the car (Fig. 1).
This attractive force is controlled by a gap sensor that measures the distance between the rails and electromagnets. A control circuit continually regulates the current to the electromagnets, ensuring that the gap remains at a fixed distance of about 8 mm. If the gap widens beyond 8 mm, the current to the electromagnets is increased to create more attraction. Conversely, if the gap becomes less than 8 mm, the current is decreased. This action is computer controlled at 4000 times per second to ensure stable levitation.
As shown in Fig. 1, the levitation magnets and rail are both U-shaped (with the rail being an inverted U). The mouths of each U face one another. This configuration ensures that whenever a levitational force is exerted, a lateral guidance force occurs as well. If the electromagnet starts to shift laterally from the centre of the rail, the lateral guidance force is exerted in proportion to the extent of the shift, bringing the electromagnet back into alignment.
The use of an electromagnetic attractive force to both levitate and guide the car is a significant feature of the HSST system
Propulsion
We can visualize an HSST linear motor as an ordinary electric induction motor that has been split open and flattened. This type of linear motor has recently been used in various fields.
As Fig. 2 shows, in the HSST, the primary side coils of the motor are attached to the car body, and the secondary side reaction plates are installed along the guideway. These components act as an induction motor, and ensure both propulsion and braking force without any contact between the car and the guideway.
The system is called a car-mounted primary linear induction motor system. The ground side requires only a steel plate backed by an aluminium or copper plate, meaning that the rail structure is simple.
Module structure
One of the HSST’s unique technical features is its modules that correspond to the bogies on conventional rolling stock. As Fig. 3 shows, each module consists primarily of a number of electromagnets for levitation and guidance, a linear motor for propulsion and braking, and a hydraulic brake system.
The two modules on the left and right sides of the car are connected by beams, and this unit is called a levitation bogie. Because the levitation bogies run the entire length of the car, the load of the car and the load on the guideway are spread out and the advantages of magnetic levitation can be fully exploited.
Advantages offered by HSST system
HSST cars do not need wheels and this offers a number of advantages that are summarized below.
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Safe
The vehicle is designed so that it ‘interlocks’ with the guideway, so there is no risk of derailment. The electromagnetic field level inside the vehicle is no more than that in conventional electric trains.
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Reduced noise and vibration
When the vehicle is running there is no physical contact between the carriages and the guideway which minimizes rolling noise and vibration.
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Accelerates and decelerates quickly
Acceleration and deceleration can be rapid and fairly steep grades can be climbed easily.
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Low maintenance
There are fewer moving and rolling parts so wear and tear is less, ensuring easy maintenance of vehicles and guideways.
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Economical
The HSST can operate on fairly steep gradients and tight curves, and there is no axle load on small spans of track, so guideway construction costs are quite low.
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When HSST development began in 1974, research focused on the basic technology required for levitation, propulsion and braking. In the early days, the target speed was 300 km/h. A 1.6-km test track was constructed on Higashiogishima in Kawasaki where the HSST-01 unmanned experimental vehicle reached a speed of 308 km/h. In demonstration runs, the 8-seat HSST-02 achieved a maximum speed of 100 km/h. Some 7 years after these development efforts, the basic technology was recognized as sound.
The HSST-03 (1984) was the first to model to use modules and could carry 50 passengers. It showed great promise and carried more than 1 million passengers when demonstrated at The International Exposition, Tsukuba in Japan in 1985, and at EXPO ’86 Vancouver in Canada.
The HSST-04 was completed in 1988 and ran at the Saitama Expo in Kumagaya, Saitama Prefecture. The vehicle ran on an elevated guideway and the Variable Voltage Variable frequency (VVVF) inverter was mounted on the car, instead of on the ground as in previous models. By this time, it appeared that the HSST system was ready for commercial use.
The HSST-05 composed of two HSST-04 cars ran at low speeds at the Yokohama Expo in 1989, although its basic design concept envisioned a speed of 200 km/h.
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The basic design of the system up to and including the HSST-05 aimed for speeds of about 200 km/h. But the focus changed in 1989 when a project was launched to develop the HSST for urban transport.
Until then, researchers had only determined what basic technical specifications were required for an HSST-100 vehicle. Under the new project, a test track and vehicles were constructed and test runs were conducted. The objective was to determine the practicality of such a system for mass transit. The evaluation examined various factors, including safety, reliability and cost.
The private Nagoya Railroad Co. Group in Aichi Prefecture spearheaded the project. After the Chubu HSST Development Corporation was established in 1989, it was given the task of testing and developing the HSST-100 series. At the same time, the Aichi prefectural government established a committee that later issued a report entitled A Feasibility Study of Urban Mass Transit by Linear Motor-Driven Maglev. The committee, chaired by Professor Eisuke Masada, was composed of technical experts, as well as representatives from the Ministry of Transport, the Ministry of Construction, manufacturers and other organizations. It set out guidelines recommending how the test track should be constructed and how trial runs should be conducted, and carefully scrutinized test results. A wide variety of trials were successfully completed, and in 1993 the committee reported that the HSST was sufficiently developed to be used for public mass transit.
The test track constructed by Chubu HSST Development Corporation is 1.5-km long and extends from Oe Station on the Chikko Line of Meitetsu in the southern part of Nagoya City (Fig. 4). The track is elevated, except for about 400-m at ground level. To test operations under such extreme conditions, it includes a steep grade (70 per mill) and sharp curves.
The test vehicles are the two-car 100S and 100L built in 1991 and 1995, respectively. Each 100S car has three levitation bogies (6 modules). Car size is about the same as the new Automated Guideway Transit (AGT) cars such as Yurikamome (JRTR 16, pp. 15–19) that run on rubber tyres. Each 100L car has five levitation bogies. Although the 100L is larger than the 100S, the basic configuration is exactly the same. One reason for developing the 100L was to achieve more efficiency with greater carrying capacity. Table 1 shows the basic specifications of the 100L and its test track.
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The Tobu Kyuryo Line will extend about 9.2 km from Fujigaoka subway station in Meito Ward, Nagoya (Aichi Prefecture) through Nagakute Town to Yakusa Station on the Aichi Kanjo (Loop) Line in Yakusa-cho of Toyota City.
In 1992, the government Council for Transport Policy recommended that the Tobu Kyuryo Line be constructed as a medium-weight track, and that the transit system for this line be completed by 2008. A committee was asked to recommend what type of train should be used and it recommended a maglev system; this proposal was accepted in 1999. In February 2000, Aichi High Speed Transport Inc. was established, and given primary responsibility for operating the line. The stage has been set for construction and plans call for the line to open in time for the EXPO 2005 Aichi.
The line will extend from Fujigaoka Station to Yakusa Station (both station names are still provisional) and trains will take about 15 minutes to travel the 9.2 km at a maximum speed of 100 km/h (Fig. 6). Daily passenger density is forecast to be about 30,000.
According to the plans, a double guideway will serve nine stations (including the two termini) with an underground section of 1.4 km and a surface section of 7.8 km. The line will be regulated by normal railway regulations and twenty 100L trains will run during each peak hour.
More information on the Tobu Kyuryo Line project can be obtained by visiting the Aichi Prefecture website at:
http://www.pref.aichi.jp/index-e.html
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