The Red Flag 6-class (Korean: 붉은기6 Pulg'ŭn'gi-6) is a 4,240 kW (5,690 hp)^[2] two-section, permanently coupled electric locomotive built by the Kim Chong-t'ae Electric Locomotive Works and used by the Korean State Railway for heavy freight trains on mountainous lines.^[3]

Quick Facts Type and origin, Power type ...

Red Flag 6
The first prototype of the Red Flag 6 class at its rollout in 1981.
Type and origin Power type Electric Builder Kim Chong-t'ae Works  North Korea Build date 1981-1987
Specifications Configuration: ​  • UIC Bo′Bo′+Bo′Bo′ Gauge 1,435 mm (4 ft 8+1⁄2 in) Wheel diameter 1,370 mm (4 ft 6 in) Wheelbase 3,300 mm (10 ft 10 in) Length 32,600 mm (106 ft 11 in) Width 3,100 mm (10 ft 2 in) Height 4,700 mm (15 ft 5 in) Loco weight 176 t (388,000 lb) Electric system/s 3,000 V DC Current pickup(s) Pantographs RPM: ​  • Maximum RPM 745 rpm Traction motors: ​  • Rating 1 hour 1520 A Gear ratio 1:3.86 Loco brake hand, air, regenerative brake Couplers AAR knuckle
Performance figures Maximum speed 120 km/h (75 mph) one hour: 49 km/h Power output: ​  • 1 hour 4,240 kW (5,690 hp) Tractive effort: ​  • 1 hour 306 kN (69,000 lbf)
Career Operators Korean State Railway Class 붉은기6 Pulg'ŭn'gi-6 Number in class ≥37 Numbers 6001-6037+
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As the electrification of the Korean State Railway's network continued into the 1980s, the Red Flag 1 and Red Flag 2 class locomotives were the dominant type in service under the wires. However, with the electrification of steep mountain lines, it was realised that a more powerful locomotive was needed. Therefore, the Kim Chong-tae Electric Locomotive Works began design work on an articulated locomotive to operate freight trains on the difficult mountainous sections.^[3]

Using the Red Flag 2 class as a starting point, the Red Flag 6 (붉은기6, Pulg'ŭn'gi-6) class was developed.^[3] The result was a permanently coupled Bo'Bo'+Bo'Bo' articulated locomotive with eight capacitors,^[4] made up of two sections; these sections are single-cab versions of the Red Flag 2. The Red Flag 6 class is thus an articulated descendant of the Škoda Type 30E, which had formed the basis for the design of the Red Flag 1 and Red Flag 2 after North Korea bought a licence to build the type, including technology transfer, from Czechoslovakia.^[3] The first prototype was shown in 1981.^[5]

Numbered in the 6000 series, production of the new design began in 1986, and was put into service in 1987 to haul freight trains on the P'yŏngra Line.^[6] These four-bogie, eight-axle articulated units are 33 metres (108 ft 3 in) long, weigh 176 tonnes (388,000 lb) and produce 4,240 kilowatts (5,690 hp). They have a maximum speed of 100 kilometres per hour (62 mph) and can pull 3,200 tonnes (7,100,000 lb).^[7] Trial runs with passenger trains were undertaken, but the type is now mainly used on east-west freight trains on the P'yŏngra Line.^[3] The first prototype received a cream over red paint scheme, but production units are painted in the standard light blue over dark green livery.

There are three known named Red Flag 6 locomotives:

• Light (광명호, Kwangmyong-ho) - one locomotive, painted in cream over blue with a white stripe, named personally by Kim Jong Il, symbolising the bright future of students and youth,^[8]
• Thousand-ri of liberation No.1 (광복의천리길1호, Kwangbokuicholligil1-ho) - one known locomotive,^[9]
• Thousand-ri of liberation No.2 (광복의천리길2호, Kwangbokuicholligil2-ho) - one known locomotive, painted in light green over dark green.^[10]