Background and overview
When the 721-1000 series was reorganized into the -4100 and -5100 subseries to form seven 6-car train sets, two trailer end cars remained surplus. To make use of these, JR Hokkaido manufactured a new powered intermediate car, Moha721-5001, and converted the surplus trailer end cars in 2003. These cars were subsequently reclassified as the 721-5000 series.
Car body
The carbody of the 721-5000 series measures 21,200 mm in length and 2,900 mm in width, with a bogie centre distance of 14,400 mm. The structure is primarily composed of lightweight stainless steel to reduce overall weight, except for the bolster beams, the end sections of the centre beam, and selected cross beams, which are fabricated from water-resistant atmospheric corrosion-resistant steel plate. Underfloor sealing is applied 3 mm thicker than on the earlier 721-0 series, enhancing durability against snow and moisture.
The exterior features unpainted bead-processed stainless panels, with olive-green waistline and headline bands running the full length of the car below and above the windows.
The cab-end structure is made of weather-resistant steel and incorporates a gangway door and curved windscreen panels. A classification rollsign is mounted above the gangway door. Above the windscreens, clusters of headlights and taillights are enclosed in glass covers to maintain visibility even when snow accumulates. Additional headlights are installed below the windscreens.
Anti-fall plates are fitted between cars, excluding the cab ends. The cab-end exterior is finished in silver, with the olive-green waistline band and black paint surrounding the windscreens.
Kuha721-5000 cars are equipped with three 1,000 mm wide single-leaf automatic stepped sliding doors. Between these doors are two fixed windows, one drop window, and one door pocket window fitted with polycarbonate panels.
Moha721-5000 car also features three 1,000 mm wide single-leaf automatic stepped sliding doors, designed with provisions for future installation of manual door operation buttons adjacent to the side doors. Between the doors are two fixed windows and one drop window, also incorporating polycarbonate panels.
Door operation is controlled by TK103A units mounted above the door headers. Each side of the car body is fitted with a roller-type destination indicator. On a powered car, snow separator louvers employing a cyclone mechanism are installed to remove airborne snow from the intake used for traction motor cooling.
Kuha721-5000 cars are equipped with N-AU721A air conditioning units rated at 23,000 kcal/h, mounted at the centre of the roof. Moha721-5000 car is fitted with N-AU722 units using R407C refrigerant, rated at 30,000 kcal/h, also roof-mounted. Additionally, 1 mm thick stainless-steel cover plates are installed between underfloor equipment to reduce turbulence and prevent snow and ice accumulation.
Bogies
The powered bogies are designated N-DT721B, while the trailer bogies are N-TR721A. The N-DT721B bogies feature a reinforced frame and a low-mounted bolster suspension, necessitated by interference from the doorstep structure. These bogies incorporate bolster-less secondary air suspension, a trailing arm link journal box support system, single-link traction gearing, and anti-yaw dampers to ensure stable ride quality even at speeds up to 130 km/h.
Power transmission utilizes Twin Disc (TD) flexible joints with deflecting plates made of carbon-fiber-reinforced plastic (CFRP). The gear ratio is set at 5.19, providing strong acceleration performance across mid- to high-speed ranges, while supporting a maximum service speed of 130 km/h.
Both powered and trailer bogies are equipped with double-tread brake rigging systems.
Traction unit and ancillary equipments
The Moha721-5000 car is equipped with traction system N-CI721-2, which controls four N-MT731 AC induction motors. Each motor delivers a power output of 230 kW per bogie. The traction system comprises a three-level PWM converter utilizing Insulated Gate Bipolar Transistors (IGBTs), paired with a two-level variable-frequency drive (VFD), also employing IGBTs. A self-cooling traction transformer, model N-TM721A-AN, is installed beneath the floor and uses traveling wind for thermal regulation.
The trailer-end car Kuha721-5002 is fitted with a motor-driven air compressor (N-MH1785-C2000ML) and an auxiliary power supply unit (N-APS721B) rated at 8 kVA, both mounted underfloor.
Braking is managed by an electrically commanded system incorporating regenerative braking and a holding brake function.
Accommodation
The Kuha721-5000 cars feature partition walls and double-leaf sliding doors to separate passenger compartments. Seating consists of 2+2 flip-over transverse seats with a pitch of 910 mm in the central area, and 1+1 transverse seating at both ends of the car.
In contrast, the Moha721-5000 car is equipped with partition walls and single-leaf sliding doors that separate both the passenger compartments and the doorways. Seating arrangements include longitudinal bench seats adjacent to the doorways, and 2+2 flip-over transverse seats with a 910 mm pitch located between the longitudinal benches.
Seat upholstery in Kuha721-5000 cars is finished in brown fabric, while other standard-class vehicles use dark grey upholstery. Hand straps are installed above the longitudinal bench seats.
The Kuha721-5002 car includes a wheelchair space located at the front of the forward passenger compartment. The Kuha721-5001 car is equipped with a Japanese-style toilet utilizing a chemical holding tank, along with a water tank installed at the rear of the vehicle.
Modification
Kuha721-5000 cars are additionally fitted with 1 mm thick stainless-steel cover plates installed between underfloor equipment. These plates are designed to reduce airflow turbulence and prevent the accumulation of snow and ice on exposed components.
Operations
The 721-5000 series train is deployed on regional services operating along
the Hakodate, Chitose, and Sassho lines. This unit is operated in conjunction
with the 731 and 733 series, providing flexible formations to meet service
demands across the network. |
|
| Technical Data |
| Items |
Data |
| Supply Voltage |
20,000 V AC, 50 Hz |
| Service speed,
etc. |
Acceleration: 2.4 km/h/s Deceleration: 4.1 km/h/s Service speed: 130 km/h |
| Length |
20,800 mm |
| Width |
2,954 mm |
| Height |
3,670 mm |
| Bogie |
N-DT721B (powered) N-TR721A, N-TR721B(trailer) |
| Collector |
N-PS721B |
| Traction
motor |
N-MT785 (215 kW) |
| Gear ratio |
5.19 |
| Transformer |
N-TM721B |
| Traction system |
Converter and variable frequency drive on truck basis: N-CI721A |
| Air conditioner |
N-AU721 (20,000 kcal/h×1), N-AU731 (30,000 kcal/h×1) |
| Designed
by |
JR Hokkaido |
|
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