Background and overview
In 2003, JR Hokkaido modified existing 3-car sets of the 721-1000 series
used on “Airport” rapid services by inserting additional trailer intermediate
vehicles—class Saha721-4100 and Saha721-4200—to form 6-car formations.
This reconfiguration 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 721-4100 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 721-4100 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 Saha721-4200 vehicles feature a distinctive exterior with blue waistline bands, red accent stripes below the windows, and vertical blue bands adjacent to the doorways.
Vehicles converted from the 721-1000 series and class Saha721-4200 are equipped with three 1,000 mm-wide single-leaf automatic stepped sliding doors, along with two fixed windows, one drop window, and a door case window fitted with polycarbonate glazing. Newly built class Saha721-4100 vehicles also feature three 1,000 mm-wide sliding doors with manual push-button operation, 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. Newly built class Saha721-4100 and Saha721-4200 vehicles are equipped with roof-mounted N-AU722 air conditioning units rated at 30,000 kcal/h using R407C refrigerant. These vehicles also feature 1 mm-thick stainless-steel cover plates between underfloor equipment to prevent snow and ice accumulation. Other vehicles are fitted with N-AU721A air conditioning units rated at 23,000 kcal/h.
Bogies
Motored bogies are designated N-DT721A. Trailer bogies used on Kuha721-4100 and Kuha721-4200 are N-TR721A, while those on Saha721-4100 and Saha721-4200 are N-TR721B. The 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 Moha721-4100 and Moha721-4200 vehicles are equipped with traction system N-CI721A, which includes a thyristor phase control converter with a hybrid bridge rectifier and a three-step variable-frequency drive (VFD) employing gate turn-off (GTO) thyristors. This system controls four AC induction motors (N-MT785A), each rated at 215 kW per truck.
In addition, the following components were carried over from donor vehicles and reinstalled:
- •Traction resistor unit (N-MR721) for rheostatic braking
- •Cross-arm type pantograph (N-PS721B)
- •Traction transformer (N-TM721B), mounted beneath the floor
Trailer-end vehicles (Kuha721-4200) and intermediate trailers (Saha721-4100)
are fitted with motor-driven air compressors (N-MH1785-C2000ML). Kuha721-4200
vehicles also incorporate an auxiliary power supply unit (N-APS721B) rated
at 8 kVA, while Saha721-4100 vehicles are fitted with N-APS721A units rated
at 4.25 kVA. The braking system is an electric-command pneumatic type utilizing
rheostatic braking only.
Accommodation
Class Saha721-4200 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.
Class Saha721-4100 vehicles feature standard seating without partition walls or automatic doors. The layout includes longitudinal bench seating adjacent to the sliding doors and 2+2 switchable transverse seating with a pitch of 910 mm. Other standard vehicles include partition walls and double-leaf sliding doors separating the passenger compartment. Seating consists of 2+2 switchable transverse seats at the centre and 1+1 seating at the car ends. Seat fabric is dark gray in Saha721-4100 vehicles and brown in other standard vehicles. Strap hangers are installed above the longitudinal seating.
Accessibility features include:
- Kuha721-4200: wheelchair space at the front of the passenger compartment,
Japanese-style toilet with chemical holding tank, and water tank at the
rear
- Saha721-4100: wheelchair space and universal access toilet with chemical holding tank at the rear
Modification
Vehicles converted from 721-1000 series are additionally feature 1 mm-thick
stainless-steel cover plates between underfloor equipment to prevent snow
and ice accumulation.
Operations
721-4100 series entered “Airport” rapid services in 2003. They are also
used on the regional services on the Sapporo, Chitose, and Sassho lines. |
|
| 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-DT721A (powered) N-TR721A, N-TR721B (trailer) |
| Collector |
N-PS721B |
| Traction
motor |
N-MT785A (215 kW) |
| Gear ratio |
5.19 |
| Transformer |
N-TM721B |
| Traction system |
hybrid bridge rectifier and 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 |
|
|
