Background and overview
During peak hours in the Sapporo area, some locomotive-hauled trains continued
to operate, even after the introduction of the 721-0 series EMUs, which
had gradually replaced many such services following their delivery beginning
in 1988. In 1993, JR Hokkaido developed the 721-1000 series EMUs, incorporating
the variable-frequency drive system previously adopted on the 785 series,
to replace 721-0 series units assigned to "Airport" rapid services.
This allowed the 721-0 series vehicles to be reassigned to services that
had formerly relied on locomotive-hauled trains. A total of five three-car
sets—each consisting of one motored car and two trailer cars—were manufactured
between December 1993 and April 1994.
Car body
The carbody of the 721-1000 series measures 20,800 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 fabricated from 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 under snow accumulation. Additional headlights are installed below the windscreens. The cab-end is finished in silver, with the olive-green waistline band retained and the area surrounding the windscreens painted black.
Each car is equipped with three 1,000 mm-wide single-leaf automatic stepped sliding doors. Between the doors, two fixed windows and one drop window with heat-absorbing glass are installed. Door operation is controlled by TK103A equipment mounted above the door headers.
A roller-type destination indicator is fitted on each side of the carbody. On powered vehicles, snow separator louvers employing a cyclone mechanism are installed to remove airborne snow from the intake air used for traction motor cooling. An N-AU721A air-conditioning unit, rated at 23,000 kcal/h, is mounted centrally on the roof.
Bogies
The motored bogies are designated N-DT721A, while the trailer bogies are N-TR721A. Both types feature bolster-less secondary air suspension, a trailing arm link journal box support system, single-link traction gear, and anti-yaw dampers, ensuring stable and smooth ride quality even at speeds up to 130 km/h.
Power transmission utilizes a Twin Disc (TD) flexible coupling incorporating deflecting plates made of carbon-fiber reinforced plastic (CFRP), providing both strength and vibration damping. The gear ratio is set at 5.19, optimized for high acceleration performance across medium to high-speed ranges, with a maximum service speed of 130 km/h.
All bogies are equipped with double-tread brake rigging systems to ensure reliable braking performance under snowy and high-speed conditions.
Traction unit and ancillary equipments
Class Moha721-1000 vehicles are equipped with the N-CI721A traction system, which comprises a thyristor phase-control converter incorporating a hybrid bridge rectifier, and a three-step variable frequency drive (VFD) utilizing Gate Turn-Off (GTO) thyristors. This system controls four AC induction motors (type N-MT785A), each rated at 215 kW per bogie.
Additional equipments installed on class Moha721-1000 vehicles include the N-MR721 traction resistor unit for rheostatic braking, a cross-arm type pantograph (N-PS721B), a vacuum circuit breaker (N-CB721) mounted on the roof, and a traction transformer (N-TM721B) located beneath the floor.
Trailer-end vehicles, designated class Kuha721-2000, are fitted with a motor-driven air compressor (N-MH1785-C2000ML) and an auxiliary power supply unit (N-APS721B) rated at 8 kVA.
The braking system is an electrically commanded pneumatic brake. Regenerative braking is not employed; instead, rheostatic braking is used to dissipate kinetic energy during deceleration.
Accommodation
Passenger compartments and doorways are separated by partition walls fitted with double-leaf sliding doors. Seating consists of flip-over transverse seats arranged 2+2 abreast in the centre section, with a seat pitch of 910 mm, and 1+1 abreast seating at both ends of the car. Seat upholstery is finished in brown fabric. Hand straps are installed above the 1+1 seating areas for standing passengers.
Class Kuha721-2000 vehicles are equipped with a wheelchair-accessible space located at the front of the forward passenger compartment. At the rear of the vehicle, a Japanese-style toilet is provided, utilizing a chemical holding tank system along with an onboard water tank.
Additional delivery
Additional four 3-car sets delivered in 1994 to displace existing locomotive hauling passenger trains running between Otaru and Iwamizawa featured taillights employing LED.
Modifications
Seating Accommodation Upgrade for Reserved "U Seat" Service
JR Hokkaido launched a seating upgrade program for its paid reserved seating service branded as "U Seat," implemented on 721 series EMUs operating "Airport" rapid services. Between November 2000 and January 2001, class Saha721 vehicles and Kuha721-15, -17, and -19 were retrofitted with enhanced seating arrangements in the forward passenger compartment. These upgrades included 2+2 abreast reclining seats installed on a raised floor, with a generous seat pitch of 1,030 mm to improve passenger comfort.
To facilitate easy identification, the exterior of the upgraded section features red waistline and blue headline bands running the length of the forward passenger compartment, positioned below and above the windows respectively.
Expansion of "U Seat" Accommodation to Entire Passenger Compartment
In September 2003, vehicle Kuha721-1009 underwent modification to remove the raised floor section and extend "U Seat" reserved seating throughout the entire passenger compartment. The exterior was updated with a blue waistline band and a narrow red band running the full length of the car below the windows, along with vertical blue bands positioned outward of both door ends for easy visual identification.
Removal of "U Seat" Accommodation
Between October 2003 and March 2004, vehicles Kuha721-1001, -1003, -1005,
and -1007 were modified to remove "U Seat" reserved seating.
These cars were converted to standard seating configurations to meet changing
operational requirements.
Pantograph Replacement
Beginning in 2004, the pantographs on class Moha721-1000 vehicles were replaced with single-arm type current collectors (model N-PS785). This modification was implemented to reduce the risk of contact loss with overhead feeders caused by snow accretion, thereby improving operational reliability in winter conditions.
Operations
The 721-1000 series entered service on "Airport" rapid trains
in 1993. However, all sets except for set F-1009 were later converted to
either the 721-4000 or 721-5000 series to meet evolving service requirements.
Set F-1009 continued to operate on "Airport" rapid services alongside
the 721-5000 series for some time. It has since been reassigned to regional
services within the Sapporo area. |
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