HEMU stands for high-speed electric multiple unit, but it is also a word in Korean which means sea fog, and is believed by Koreans to be a portent of something good.

Hemu430X is the country's third high-speed train. KTX, a 300km/h train based on TGV-R and designed by Alstom, was introduced in April 2004. This was followed by KTX-Sancheon, Korea's first domestically-designed high-speed train. KTX-Sancheon has an output of 8.8MW, double-skinned aluminium body shells and articulated bogies. It entered service in March 2010 with Korail which ordered 25 10-car trains, the last five of which were delivered in July. A further 22 trains are being built by Hyundai Rotem for the Honan line, which is under construction and will open in 2014.

KTX-Sancheon is based on Korea's first experimental high-speed train KHST360X, which was developed in 2007. It used IGBT large-capacity inverters controlled by1100kW ac asynchronous traction motors.

In 2007, a consortium of Korea Railroad Research Institute, Hyundai Rotem and 11 private companies and universities launched the project to build Korea's second experimental high-speed train - Hemu430X. The objective was to achieve a commercial operating speed of 350km/h by reaching up to 430km/h during test running. Korea's Ministry of Land, Transport and Maritime Affairs has invested Won 93.1bn ($US 79.7m) in the development of the train since 2007 with Korea Railroad Research Institute (KRRI) and consortium members engaged in the design and construction of the train.

Unlike previous Korean high-speed trains which had power cars, Hemu430X has distributed propulsion which is based on advanced power electronics and information technologies. The experiment train consists of six cars, five of which are powered (Tc-M1-M2-M3-M4-Mc). The train has an output of 8.2MW and a maximum tractive effort of 182kN, whereas the commercial version will have an output of 9.84MW as it will be an eight-car train with six motored cars.

Hemu430X is powered by combination of two different types of traction systems. The first consists of 16 units of 410kW asynchronous traction motors controlled by two IGBT PWM converters and a VVVF inverter system. The other system comprises four permanent magnet synchronous traction motors controlled by a new type of inverter. The combination test results of the system in the factory showed the entire train could reach 300km/h in 233 seconds, an improvement of about 120 seconds compared with KTX and KTX-Sancheon.

The primary objective of the Hemu430X project is to verify the performance of the distributed traction system for high-speed operation. Korean high-speed lines have relatively short distances between stations due to the high population of the cities served. This demands high rates of acceleration and deceleration from the propulsion system coupled with high adhesion to improve the average speed.

Optimised car body

Other objectives of the research project are to verify the environmental performance of the train. The car body has been optimised by using a lightweight cross-section. This was achieved by modifying the cross-section of the double-skinned panel structures, which reduces the axleload.

However, the motored cars fitted with the distributed traction system still have shortcomings which need to be improved. The noise from both the traction system and the bogie need to be isolated effectively. Research focused on the insulation and isolation of the passenger compartment from the noise generated by the main transformer, power semiconductor switching and main circuit breaker switching. The noise emitted by the bogies on trains with distributed traction is higher than that produced by an articulated bogie, which is located under both ends of the carbody and does not have any traction motors. To address these issues, effective noise insulation technologies are being examined for the interior design.

Nevertheless, the advances achieved with the design of Hemu430X have made it possible to add more seats in each coach to meet customer demand. Pantographs are fitted to the M1 and M2 cars, while the main transformers are installed under the floor of the M1 and M4 cars. The auxiliary power supply and static inverters are fitted beneath the floor of the driving trailer car and motored driving car.

The designer, Professor S R Kim, says the key words for developing Hemu430X are motion, pulse, flow and sensitivity to apply a genetic algorithm method with pragmatic, analogue and canonic design philosophies which are the basic design concept of the train. The interior improvements of the passenger compartments were examined based on these design concepts for future customer convenience.

The train is fitted with newly-developed advanced test facilities including monitoring cameras, while measurement data is recorded in the main test room in the M2 car during trial running. Test runs at up to 370km/h are currently being carried out between Ulsan and Shinkyungju on the Kyungbu high-speed line to examine the characteristics of an ultra high-speed train. The main fundamental interfaces - wheel-rail, pantograph-catenary, and others needed to achieve the ultra-high-speed record - will be carefully verified at every speed-up stage to fulfill the safety guidelines for the ultra-high-speed train. A newly-developed bogie, which was successfully proven through simulation of vehicle dynamics and by roller rig test, will be tested. Modification of the active suspension to achieve stable running and a high-quality ride index might be carried out if it is required during test running.

During the design stage, the aerodynamic and aero-acoustic characteristics of the train were estimated by using commercial simulation tools in a wind tunnel test facility. The estimated parameters will be verified during each increase in speed. Hemu430X will be rigorously tested and driven for at least 100,000km on main lines until 2015, while production trains are expected to enter commercial service in 2017.

The future commercial trains based on Hemu430X will have a maximum operating speed of between 350 and 370km/h depending on track conditions. This would enable passengers to reach any of Korea's major cities within 90 minutes. As a result, the next generation of high-speed trains could greatly increase the attractiveness of domestic travel and promote maximum use of the high-speed network.