INTRO: As the number of metros in South Korea increases, the range of vehicle types in use has proliferated. Following extensive research, specifications have been developed for a future standard metro trainset
BYLINE: Kwan-Sup Lee
Director General, Urban Transit Engineering Department, Korea Railroad Research Institute
NOW undergoing safety and reliability tests on Seoul’s Line 7 and test track is a prototype four-car EMU, developed by local industry under the leadership of the Korea Railroad Research Institute. It is proving the design and specifications for a standard trainset, which is intended to equip any future South Korean metros.
Offering enhanced reliability, maintainability and safety, the Korean Standard Urban Rail Vehicle has increased the value of locally-made components from around 60% to 95% or more. Total maintenance expenses are expected to fall by over 10%.
Metro construction in South Korea has taken off rapidly since Seoul’s first underground line opened in August 1974. The capital’s network has grown to eight lines totalling 278 km, and its share of the city’s transport market is expected to increase from 37% to more than 50%. Metros have also been built, or are under development, in other major cities across South Korea, including Pusan, Taegu, Inchon, Daejeon, and Kwangju. With several regional governments hoping to introduce light rail, the number of urban rail vehicles in the country is expected to increase from 6136 to over 10000 during the next 10 years.
Until now, South Korea has not had any standard specifications for metro trains. Each new line has used different equipment. In addition, the lack of home-grown technology has necessitated the import of many essential components, including inverters, traction motors and control equipment. These components are not interchangeable, leading to inefficiencies in maintenance and difficulties in identifying the causes of failures.
Realising a growing need for standardisation and local manufacture, the Ministry of Construction & Transportation has invested US$25m in a programme for ’standardisation and development of urban rail vehicles’. An Urban Transit Law passed in 1995 envisages co-operation between Korea Railroad Research Institute, public authorities and rolling stock manufacturers. The major objectives are the development of a set of standards for urban rail vehicles, and encouraging the local production of key components.
MOCT makes policy decisions and supplies research funding. KRRI is responsible for project management, establishing the standards and conducting research in partnership with universities and government bodies. Railway operators are charged with implementing standardisation. Rolling stock and component manufacturers are playing a central role in developing the local production of components, including vehicle bodies, inverters, traction motors and control systems.
Standardisation
The law is backed up by an enforcement policy setting out four areas of work: management, safety, operations and construction. The standardisation programme was set up to develop five documents: a standard specification; performance test criteria; safety criteria; fault diagnosis criteria; and quality assurance criteria. These standards documents do not stand alone, but interact and cross-reference to each other to produce a unified set of standards.
As the documents are produced, they are reviewed by the board of standardisation affairs before being published. The board also evaluates the results of research and development work. The specifications provide guidelines for the purchase of vehicles to be used in South Korea, including dimensions and minimum performance requirements. The exchangeability of parts, domestic technical capability, future technology trends and maintenance efficiency were taken into account when developing the standards.
There are two different metro car specifications, for high and medium capacity trains. In addition there are two light rail specifications, covering rubber-tyred and steel-wheeled vehicles.
The quality assurance criteria covers 45 major components, including wheels, door mechanisms and pantographs. Rolling stock manufacturers and operators are required to use only components that have been certified. The compulsory safety criteria specify minimum requirements that the vehicles must meet. They include general safety rules as well as details of body and major equipment design.
Performance testing standards specify the methods used to verify vehicle performance. There are three aspects: pre-assembly performance tests on major components; testing of complete vehicles; and commissioning. The criteria used are based on IEC and UIC international standards.
Diagnosis criteria prescribed by the urban transit law specify the inspection methods to be used on vehicles after 25 years. There is a list of items to be inspected, the evaluation methods to be used and reporting methods. If a vehicle is found to meet the criteria, its lifetime can be extended by a further five years.
Developing a standard EMU
Once the standards documents were complete, design work began on the standard Korean electric multiple-unit, known as K-EMU. A four-car prototype was built by Korea Rolling Stock Corp in 1999. This serves two purposes. The first is to test Korean-produced components in a real environment, and the second is to prove the technical validity of the standards. During 2000 the K-EMU was tested on Seoul Line 7, where it was evaluated against the performance and safety test criteria. This year it has been undergoing reliability tests (Table I).
The prototype unit is formed of two motor cars and two trailers. Korean-manufactured equipment includes traction motors, VVVF inverter, and TCMS (Train Control & Monitoring System).
The car body is designed for low weight, minimum air resistance in tunnels, a stylish appearance and low internal noise. In order to reduce weight the bodyshell is made from hollow extrusions of A6005A aluminium alloy. This satisfies the strength requirements while producing a car 30% lighter than an equivalent steel vehicle. The streamlined driving car ends are made from FRP. Finite-element structural analysis was performed using Nastran software, and static load test was carried out on the prototype.
The 2100mm wheelbase bolsterless bogies were designed for low running noise and a UIC ride comfort index of less than 2·5. Software developed by KRRI was used during the design process to optimise bogie parameters including the spring constant, damping coefficient and unsprung mass (Fig 1). Table II shows the specifications and test results.
Traction and control
The inverter was designed for high-speed switching and low-power voltage control, using VVVF (Variable Voltage Variable Frequency) technology. Integrated Gate Bipolar Transistor control elements are used, with natural cooling. Woojin Industrial Systems manufactured the prototype inverter, and an inertial load simulator was used for testing. The resulting production inverter satisfies the standard specification (Table III).
The cars use the 1C4M configuration, with one inverter controlling four motors. Pulse-width modulation is used for control, based on a Digital Signal Processor to improve reliability and maintenance efficiency.
Hyosung Corp played the main role in developing the three-phase traction motor. It is a naturally-cooled 4-pole squirrel-cage induction motor designed for ease of maintenance. Analysis of key components at the design stage focused in particular on the slot assembly, cooling, switching and insulation, with the aim of improving performance.
The control and monitoring equipment forms the interface between the traction equipment, braking, and passenger information systems. K-EMU uses a hierarchy of car and train computers. This is also linked to the signalling communication equipment, as the train is equipped for Automatic Train Operation. Software and hardware was developed by Woojin Industrial Systems using available domestic protocols.
TABLE: Table I. Specification and test results for Korean standard EMU
Item Specification Prototype
Power Supply 1500VDC 1500VDC
Length mm 19500 19500
Width mm 3120 3120
Height mm < 3600 < 3600
Speed km/h 100 110
Acceleration m/s2 > 0·8 0·9
Braking m/s2 > 1·0 1·1
Ride comfort (UIC) < 2·5 2·4
Noise level dB(A) < 80 79
Speed control VVVF inverter blended with regenerative braking
Passengers Driving trailer 48 seated 100 standing
Centre car 54 seated 106 standing
TABLE: Table II. Car body and bogie test results
Car body Requirements Test Result
Vertical load test (stress) kg/mm2 12·4 8·97
Vertical load deflection between bolsters mm 13·8 10·6
Compression test (stress) kg/mm2 12·4 5·49
Torsional load test (stress) kg/mm2 8·7 0·45
Natural vibration test (bending mode) Hz > 10 16·75
Bogies
Critical speed (using new wheels) km/h > 120 157
Static wheel unloading at 80 km/h < 60% 50%
Derailment < 0·8 0·7
Wheel lateral force tonnes > 5·3 4·5
TABLE: Table III. Inverter and motor specifications
Inverter Specification Test result
Input voltage (DC) V 1500 (1000 to 1800)
Continuous output kVA > 1100
Control capacity kW > 800
Output voltage (AC) V 1170
Control voltage (DC) V 100 (70 to 110)
Traction motors
Current A < 125 121
Efficiency > 92% 92·5%
Power factor > 88% 89·1%
Temperature increase < 160°C 118°C
Noise dB at 4800 rev/min < 115 105·8
Vibration mm/s < 5·25 2·54
Maximum speed rev/min 5800 for 2 min OK
Insulation M
