421 series
Background and overview
Although the Kagoshima Line had been electrified with AC power, inter-running services with the DC-electrified Sanyo Line were anticipated. To accommodate such operations, Japanese National Railways (JNR) developed the 421 series suburban AC/DC dual-voltage electric multiple units (EMUs) for use on 60 Hz electrified lines in 1960. A total of two four-car trainsets were delivered to the Tsuruga No. 2 Depot that same year.
Car body
The vehicles feature wide steel carbodies measuring 19,500 mm in length and 2,900 mm in width, with a bogie centre distance of 13,800 mm. To reduce overall weight, lightweight shaped steel sections and press-formed beams are employed.
The cab end is gangway-equipped, incorporating a gangway door and curved front windscreens to improve forward visibility. A destination rollsign is installed above the gangway door.
Exterior lighting consists of two headlights positioned on either side of the gangway and two taillights mounted below.
Each car is equipped with three double-leaf automatic sliding doors, each 1,300 mm wide. Between the doors, the side panels feature two double-hung windows (1,075 mm wide) and two door pocket windows (515 mm wide) at both ends. At each end of the carbody, one standard double-hung window (1,075 mm wide), one narrower double-hung window (515 mm wide), and one door pocket window (419 mm wide) are provided. On the cab side only, immediately behind the driver’s compartment, a narrower double-hung window (515 mm wide) and a door pocket window (419 mm wide) are installed. Both the upper and lower sashes of the windows slide upward. Door operation is controlled by TK4F units mounted on the door headers.
Roof-mounted globe ventilators are provided as follows: four on Class Moha420 cars and six on the other cars. Class Moha420 vehicles also feature a low-roof section where the pantograph and high-voltage equipment are installed to maintain insulation clearance from the extra-high-voltage feeder. Two axial flow fans are also mounted in this section for ventilation.
The exterior livery is reddish-brown with a wide cream band below the windscreens.
Bogies
The powered bogies are designated DT21B, while the trailer bogies are designated TR64. Both types utilize coil springs as bolster springs and feature pedestal-type journal supports.
A parallel cardan drive system with a hollow shaft is employed for power transmission. The gear ratio is set at 4.82, enabling high acceleration performance while allowing for a reduced ratio of motored to trailer cars.
The braking system on powered bogies employs double-truck brake rigging with a single-action brake cylinder, whereas trailer bogies are equipped with double-truck brake rigging.
Power train and ancillary equipment
The 421 series EMUs employ a married-pair configuration and are equipped with eight MT46B series-wound brushed DC traction motors, each rated at 100 kW. These motors are controlled via the CS12B motor-driven camshaft control system and the MR16A forced-draught traction resistor, both installed on Class Moha421 vehicles. The system utilizes armature-resistance control to regulate acceleration and power output.
Class Moha420 vehicles are fitted with a TM3 shell-type traction transformer and an RS3 or RS4 traction rectifier, both mounted beneath the floor. Current collection is handled by a PS16B lozenge-type pantograph via a CB101 air-blast circuit breaker mounted on the roof of the Moha420 vehicles. A relay-actuated air-blast circuit breaker system, triggered by the electric discharge of a DC arrestor, is employed to prevent accidental entry into AC-electrified sections.
Class Kuha421 vehicles are equipped with a motor-generator unit (MH97-DM61) delivering 20 kVA, and a motor-driven air compressor (MH80-C1000), both mounted beneath the floor. These components supply electrical power for onboard systems and compressed air for braking and door operation.
The braking system consists of an electromagnetic straight air brake, supplemented by rheostatic braking on the motored axles, providing effective deceleration and thermal dissipation during extended braking cycles.
Accommodation
Passenger accommodation consists of a combination of two transverse four-person seating bays on each side between the doors, and one at each end of the saloon, arranged with a seating pitch of 1,420 mm. Longitudinal bench-type seating is provided in the areas adjacent to the doors. The backrests of the transverse seating bays are equipped with hand-grabs, and straps are installed above the longitudinal seating for standing passengers.
For illumination, the interior is fitted with two rows of ceiling-mounted fluorescent light fixtures, each rated at 40 watts. Class Moha420 vehicles are equipped with four ceiling-mounted fans, while the other cars are fitted with six.
Class Kuha421 vehicles are equipped with a Japanese-style toilet located at the rear end of the saloon.
Additional delivery
Vehicles manufactured from May 1963 onward incorporated an unpressurized air-blast circuit breaker system, replacing the earlier relay-actuated system triggered by the electric discharge of a DC arrestor. The traction resistor was upgraded to type MR16C.
Vehicles manufactured from November onward featured a raised cab floor, elevated by 300 mm to improve forward visibility and provide additional protection against obstacles at level crossings. End cars were provisioned for future installation of an overhead line voltage detector mounted on the cab roof. The low-roof section of Class Moha420 vehicles was lowered by 80 mm to improve insulation clearance. The air-blast circuit breaker was upgraded to the improved CB101E model for more secure operation.
An overhead line voltage detector was introduced on end cars manufactured from 1963 onward. The air-blast circuit breaker was further upgraded to type CB103A to accommodate increased current and shorten tripping time. The pantograph was upgraded to type PS16C, constructed from stainless steel for improved corrosion resistance.
Class Moha421 vehicles manufactured in 1966 employed the upgraded MR61 traction resistor, standardized with the high-power 423 series EMUs. Trailer bogies were changed to type TR62, featuring disc brake rigging to shorten braking distance.
Modifications
Overhead Line Voltage Detector Installation
Class Kuha421 vehicles that were not originally equipped with an overhead line voltage detector were retrofitted with the device between March and June 1962.
Cab End Reinforcement
Beginning in 1975, end cars received cab end reinforcement modifications, with additional steel plates welded to the cab structure to minimize damage in the event of a level crossing collision. Headlights were also upgraded to sealed-beam units.
Air Conditioning Retrofit
In 1987, four trainsets—and an additional three in 1988—were retrofitted
with two floor-mounted AU2X air conditioning units, offering significantly
lower cost compared to the AU1X model, which is rated at 18,000 kcal/h.
This retrofit completed the air conditioning installation programme by
the summer of 1988. The AU2X units were installed at the rear of the saloon.
The double-hung windows located at the rear of the vehicles were converted to intake louver windows, and two roof-mounted globe ventilators were replaced with larger air outlets. Air conditioning ductwork was installed on either side of the ceiling-mounted lighting fixtures.
Operations
In 1960, two trainsets of the 421 series were delivered to the Tsuruga No. 2 Depot for extensive test running, and subsequently allocated to the Minami-Fukuoka Depot for trial operation between Shimonoseki and Kurume. Revenue service commenced in June 1961 following the delivery of mass-production sets. In March 1962, the service was extended to Araki.
In 1965, the fleet was further deployed on the Sanyo and Kagoshima Line between Tokuyama and Kumamoto, operating alongside the newly introduced 423 series EMUs.
In 1966, the Nippo Line between Kokura and Shin-Tabaru was electrified, and the 421 series entered service. Six trainsets previously allocated to the Minami-Fukuoka Depot were reallocated to the Oita Depot in October 1967, coinciding with the opening of the newly electrified Nippo Line between Shin-Tabaru and Kozaki. An additional ten trainsets were transferred to the Oita Depot in 1968.
From 1978, the 421 series began to be replaced by the 415 series, and eight sets were scrapped by 1987.
Following the privatization and breakup of Japanese National Railways in 1987, 68 vehicles of the 421 series fleet were inherited by JR Kyushu. However, they were completely replaced by the 813 and 815 series EMUs in 1996.
423 series
Background and overview
Japanese National Railways (JNR) was concerned that extending electrified lines into areas with gradients of up to 25‰ would require a higher proportion of powered vehicles in EMU formations equipped with 100 kW traction motors. This, in turn, would necessitate substation reinforcement and lead to serious financial burdens.
To address this issue, JNR developed the high-power MT54 traction motor, enabling a 1:1 ratio of powered to trailer vehicles even on steep mountain routes. Based on this advancement, JNR developed the 423 series suburban AC/DC dual-voltage electric multiple units (EMUs) for use on 60 Hz electrified lines. A single four-car trainset, consisting of two powered and two trailer vehicles, was delivered to the Minami-Fukuoka Depot in 1965.
Car body
The vehicles feature wide steel carbodies measuring 19,500 mm in length and 2,900 mm in width, with a bogie centre distance of 13,800 mm. To reduce overall weight, lightweight shaped steel sections and press-formed beams are employed.
The cab end is gangway-equipped, incorporating a gangway door, curved front
windscreens, and a driver's cab elevated 300 mm above floor level. This
raised position, combined with the curved windscreens, improves forward
visibility and provides additional protection against obstacles at level
crossings.
Exterior lighting consists of two headlights positioned on either side of the gangway and two taillights mounted below.
Each car is equipped with three double-leaf automatic sliding doors, each 1,300 mm wide. Between the doors, the side panels feature two double-hung windows (1,075 mm wide) and two door pocket windows (515 mm wide) at both ends. At each end of the carbody, one standard double-hung window (1,075 mm wide), one narrower double-hung window (515 mm wide), and one door pocket window (419 mm wide) are provided. On the cab side only, immediately behind the driver’s compartment, a narrower double-hung window (515 mm wide) and a door pocket window (419 mm wide) are installed. Both the upper and lower sashes of the windows slide upward. Door operation is controlled by TK4F units mounted on the door headers.
Roof-mounted globe ventilators are provided as follows: four on Class Moha422 cars, six on Class Moha 423 cars, and five plus one box-shaped ventilator on Class Kuha411 cars. Class Moha422 vehicles also feature a low-roof section where the pantograph and high-voltage equipment are installed to maintain insulation clearance from the extra-high-voltage feeder. Two axial flow fans are also mounted in this section for ventilation.
The exterior livery is reddish-brown with a wide cream band below the windscreens.
Bogies
The powered bogies are designated DT21B, while the trailer bogies are designated TR64. Both types utilize coil springs as bolster springs and feature pedestal-type journal supports.
A parallel cardan drive system with a hollow shaft is employed for power transmission. The gear ratio is set at 4.82, enabling high acceleration performance while allowing for a reduced ratio of motored to trailer cars.
The braking system on powered bogies employs double-truck brake rigging with a single-action brake cylinder, whereas trailer bogies are equipped with double-truck brake rigging.
Power train and ancillary equipment
The 423 series EMUs employ a married-pair configuration and are equipped with eight MT54 series-wound brushed DC traction motors, each rated at 120 kW. These motors are controlled via the CS12D motor-driven camshaft control system and the MR61 forced-draught traction resistor, both installed on Class Moha423 vehicles. The system utilizes armature-resistance control to regulate acceleration and power output.
Class Moha422 vehicles are fitted with a TM10 shell-type traction transformer and an RS22 traction rectifier, both mounted beneath the floor. Current collection is handled by a PS16C lozenge-type pantograph via a CB101B air-blast circuit breaker mounted on the roof of the Moha422 vehicles.
Class Kuha421 vehicles are equipped with a motor-generator unit (MH97-DM61) delivering 20 kVA, and a motor-driven air compressor (MH80-C1000), both mounted beneath the floor. These components supply electrical power for onboard systems and compressed air for braking and door operation. End cars are also equipped with an overhead line voltage detector mounted on the cab roof. Unpressurized air-blast circuit breaker system is employed to prevent accidental entry into AC-electrified sections.
The braking system consists of an electromagnetic straight air brake, supplemented by rheostatic braking on the motored axles, providing effective deceleration and thermal dissipation during extended braking cycles.
Accommodation
Passenger accommodation consists of a combination of two transverse four-person seating bays on each side between the doors, and one at each end of the saloon, arranged with a seating pitch of 1,420 mm. Longitudinal bench-type seating is provided in the areas adjacent to the doors. The backrests of the transverse seating bays are equipped with hand-grabs, and straps are installed above the longitudinal seating for standing passengers.
For illumination, the interior is fitted with two rows of ceiling-mounted fluorescent light fixtures, each rated at 40 watts. Class Moha422 vehicles are equipped with four ceiling-mounted fans, while the other cars are fitted with six.
Class Kuha421 vehicles are equipped with a Japanese-style toilet located at the rear end of the saloon.
Additional delivery
The traction rectifier on Class Moha422 vehicles manufactured from 1966 onward was upgraded to the improved RS22A model.
Vehicles manufactured from 1968 were fitted with forced-draught ventilators as follows: four on Class Moha422 cars, seven on Class Moha423 cars, and six plus one box-shaped ventilator on Class Kuha411 cars. The double-leaf sliding doors were upgraded to units constructed from stainless steel. The hand-grabs on the transverse seating bays were also changed to rectangular-shaped designs.
Modifications
Cab End Reinforcement
Beginning in 1975, end cars received cab end reinforcement modifications, with additional steel plates welded to the cab structure to minimize damage in the event of a level crossing collision. Headlights were also upgraded to sealed-beam units.
Traction Rectifier Changeover between Class Moha422 and Moha470
The capacity of the traction rectifier was insufficient to support air conditioning equipment on the 471 series EMUs. Therefore, between 1970 and 1973, the RS22 traction rectifiers from the 423 series and the RS7 traction rectifiers from the 471 series were exchanged between Class Moha422 and Moha470 vehicles.
AU75 Air Conditioning Retrofit
Between 1979 and 1985, air conditioning systems were retrofitted to 44 selected vehicles of the 423 series. These cars were equipped with AU75B roof-mounted air conditioning units, each rated at 42,000 kcal/h. To supply electrical power for these systems, even-numbered trailer-end cars were fitted with MH135-DM92 motor-generator units, rated at 160 kVA and mounted beneath the floor.
AU1X Air Conditioning Retrofit
In 1986, six trainsets were retrofitted with four roof-mounted AU1X air conditioning units per vehicle, offering lower cost compared to the AU75 model. Each unit was rated at 9,000 kcal/h and powered by 220 V AC converted from 1,500 V AC via a step-down auxiliary transformer installed on each vehicle. Four ceiling-mounted fans were also installed to assist with air circulation and enhance cooling performance.
AU2X Air Conditioning Retrofit
In 1987, thirteen trainsets were retrofitted with two floor-mounted AU2X air conditioning units, offering significantly lower cost compared to the AU1X model, which is rated at 18,000 kcal/h. This retrofit completed the air conditioning installation programme by the summer of 1988. The AU2X units were installed at the rear of the saloon.
The double-hung windows located at the rear of the vehicles were converted to intake louver windows, and two roof-mounted globe ventilators were replaced with larger air outlets. Air conditioning ductwork was installed on either side of the ceiling-mounted lighting fixtures.
Operations
In 1965, a single trainset of the 423 series was delivered to the Minami-Fukuoka Depot and deployed on services along the Sanyo and Kagoshima Lines between Tokuyama and Kumamoto, operating alongside the existing 421 series EMUs.
In 1966, the Nippo Line between Kokura and Shin-Tabaru was electrified, and the 423 series entered service. Six trainsets previously allocated to the Minami-Fukuoka Depot were reallocated to the Oita Depot in October 1967, coinciding with the opening of the newly electrified Nippo Line between Shin-Tabaru and Kozaki. An additional seventeen trainsets were transferred to the Oita Depot in 1968.
Following the privatization and breakup of Japanese National Railways in 1987, 120 vehicles of the 423 series fleet were inherited by JR Kyushu. However, they were completely replaced by the 813 and 815 series EMUs in 2001. |
|
