Background and overview
In 2003, JR Hokkaido modified surplus trailer-end vehicles—made available
through the conversion of 721-5100 series sets—by inserting newly built
powered intermediate vehicles (class Moha721-5100 and Moha721-5200) and
trailer intermediate vehicles (class Saha721-5100 and Saha721-5200). This
reconfiguration formed 6-car sets and enabled the release of surplus 721-0
series vehicles, which were subsequently used to replace aging 711 series
EMUs. The modified sets were reclassified as the 721-5100 series. A total
of four 6-car sets, each comprising two powered vehicles and four trailer
vehicles, were delivered between October and December 2003.
Car body
The carbody of the 721-5100 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. Cab ends are constructed from weather-resistant steel and incorporate gangway doors and curved windscreens. Headlight and taillight clusters are mounted above the windscreens and enclosed in glass to maintain visibility in snowy conditions, with additional headlights installed below.
Anti-fall plates are fitted between vehicles, excluding the cab ends. Cab ends are painted silver, with olive-green waistline bands and black framing around the windscreens. Class Saha721-5200 vehicles feature a distinctive exterior with blue waistline bands, red accent stripes below the windows, and vertical blue bands adjacent to the doorways.
Class Saha721-5200, Kuha721-5100, and Kuha721-5200 vehicles are equipped with three 1,000 mm-wide single-leaf automatic stepped sliding doors, along with two fixed windows, one drop window, and one door case window fitted with polycarbonate glazing. Other vehicles feature manually operable sliding doors with push-button controls, two fixed windows, and one drop window with polycarbonate glazing. Door operation is controlled by TK103A equipment mounted above the door headers.
A roller-type destination indicator is installed on each side of the carbody. Powered vehicles are fitted with snow separator louvers employing a cyclone system to remove airborne snow from the intake used for traction motor cooling. Kuha721-5100 and Kuha721-5200 vehicles are fitted with roof-mounted N-AU721A air conditioning units rated at 23,000 kcal/h. Other vehicles are equipped with N-AU722 units rated at 30,000 kcal/h using R407C refrigerant, and feature 1 mm-thick stainless-steel cover plates between underfloor equipment to prevent snow and ice accumulation.
Bogies
Motored bogies are designated N-DT721B. Trailer bogies used on Kuha721-5100 and Kuha721-5200 are N-TR721A, while those on Saha721-5100 and Saha721-5200 are N-TR721B. The N-DT721B and N-TR721B bogies feature reinforced frames and a lowered bolster suspension position to accommodate the step structure. All bogies incorporate bolster-less secondary air suspension, trailing arm link journal box supports, single-link traction gear, and anti-yaw dampers to ensure stable ride quality at speeds up to 130 km/h.
Power transmission utilizes Twin Disc (TD) flexible joints with carbon-fiber reinforced plastic (CFRP) deflecting plates. The gear ratio is 5.19, optimized for high acceleration performance at medium to high speeds. All bogies employ double-tread brake rigging.
Traction unit and ancillary equipments
Class Moha721-5100 and Moha721-5200 vehicles are equipped with traction system N-CI721-2, controlling four AC induction motors (N-MT731), each rated at 230 kW per truck. The system comprises a three-level PWM converter and a two-level variable-frequency drive (VFD), both employing insulated gate bipolar transistors (IGBTs). A travelling wind self-cooled traction transformer (N-TM721A-AN) is mounted beneath the floor.
Trailer-end vehicles (Kuha721-5200) and intermediate trailers (Saha721-5100) are fitted with motor-driven air compressors (N-MH1785-C2000ML). Kuha721-5200 vehicles also feature an auxiliary power supply unit (N-APS721B) rated at 8 kVA, while Saha721-5100 vehicles are fitted with N-APS721A units rated at 4.25 kVA. The braking system is an electric-command pneumatic type featuring regenerative and holding brake functions, with control logic prioritizing trailer vehicles.
Accommodation
Class Saha721-5200 vehicles feature reserved "U-seat" accommodation
with partition walls and automatic doors separating the passenger compartment
from the doorways. Seating consists of 2+2 reclining seats with a pitch
of 1,030 mm. A conductor's room is located at the front end, and an LED
passenger information display is installed above the doorway.
Kuha721-5100 and Kuha721-5200 vehicles include partition walls and double-leaf
sliding doors separating the passenger compartment. Seating consists of
2+2 switchable transverse seats with a pitch of 910 mm at the centre and
1+1 seating at the car ends. Other standard vehicles do not include partition
walls or automatic doors, and feature a mix of longitudinal bench seating
adjacent to the sliding doors and 2+2 switchable transverse seating with
a pitch of 910 mm. Seat fabric is brown in Kuha721-5100 and Kuha721-5200
vehicles, and dark gray in other standard vehicles. Strap hangers are installed
above the longitudinal seating.
Accessibility features include:
- Kuha721-5200: wheelchair space at the front of the passenger compartment,
Japanese-style toilet with chemical holding tank, and water tank at the
rear
- Saha721-5100: wheelchair space and universal access toilet with chemical
holding tank at the rear
Modification
Kuha721-5100 and Kuha721-5200 vehicles, converted from the 721-1000 series, were additionally fitted with 1 mm-thick stainless-steel cover plates between underfloor equipment to prevent snow and ice accumulation.
Operations
The 721-5100 series entered service in 2003, primarily assigned to "Airport"
rapid services operating between Otaru and Shin-Chitose Airport. In addition
to express duties, these units are also deployed on regional services along
the Sapporo, Chitose, and Sassho Lines, operating alongside other 721 series
variants and newer EMUs. |
|
| 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 |
|
|
