Background and overview
The transportation demand in Sapporo was increasing in the mid-1980s. However, 711 series EMU having partition walls between the passenger room and the doorways for the protection against sever coldness caused the chronic delay due to the increased boarding and alighting time during peak hours. Therefore, JR Hokkaido developed 721 series suburban AC electric multiple unit trains in 1988 which incorporated the accommodations for services linking Sapporo downtown and New Chitose airport which would open in 1992, as well as provided the higher service speed and acceleration/deceleration capability. 8 three-car sets comprising 2 powered vehicles, and a trailer vehicle were delivered over the period from September 1988 until October.
Car body
The vehicle design has 21200mm long and 2900mm wide body incorporating the lightweight stainless-steel construction. Bodies are unpainted and have an olive-green waistline and headline bands running the length of each car below and above the windows. The cab end section constructed by whether proof steel is fitted with the gangway door and curved surface windscreens on the front. A classification rollsign is fitted above the gangway door. A pair of clusters of the head light and the taillight covered the glass to keep the visibility even if covered with snow are fitted above the windscreens. The additional headlights are also fitted under the windscreens. The cab end section is painted in silver, having an olive-green waistline band and around the windscreens are painted in black. They are equipped with three 1000mm wide single-leaf automatic stepped sliding doors and two fixed windows and a drop window is fitted between the sliding doors. The door operating equipment is TK103A fitted above the door header of the sliding doors. A roller-binding destination screen is fitted on each side of the body and the louver of the snow separator employing the cyclone to remove airborne snow from intake for cooling the traction motor is also fitted on each side of the powered vehicles. An air conditioner, N-AU721, rated at 20,000kcal/h is fitted on the centre of the roof.
Bogies
Motored bogies are N-DT721 and trailer bogies are N-TR721, featuring bolster-less secondary air suspension, corn-shaped multilayered rubber spring journal supporting system, and the Z link traction device. Conical roller bearings are adopted, and yaw dampers are prepared to ensure smooth ride characteristics even at 130km/h. The parallel cardan drive device with hollow shaft is applied for power transmission device. The gear ratio is 4.82. Both motored and trailer bogies employ the double tread brake rigging employing the enhanced adhesion alloy cast iron brake shoe.
Traction unit and ancillary equipments
Eight shunt-wound brushed DC traction motors, N-MT721, which class kumoha721 and moha721 vehicles are equipped with, with a power output of 150kW employing forced ventilation are controlled by the traction system, N-CS721, employing thyristor phase control and field weakening control to improve high speed performance. Class moha721 vehicles are equipped with a traction transformer, N-TM721, the second wiring of which is split into 4 sections, with built-in smoothing reactor, N-IC721, and a traction rectifier, N-RS721, employing thyristor/diode hybrid bridge connected in series beneath the floor. Class kumoha721 vehicles are equipped with a traction resistor unit, N-MR721, for rheostatic brake on the roof and a motor-driven air compressor, MH-1045A-C2000, and an auxiliary power supply, N-APS721, with a power output of 8kVA. Class kumoha721 vehicles are equipped with a cross-arm type current pickup, N-PS721, and a vacuum circuit breaker, N-CB721, on the roof. The brake system is the electric command pneumatic brake with not regenerative brake but rheostatic brake.
Accommodation
Passenger rooms and the doorways are separated by partition walls with double leaf sliding doors. Seating accommodation consists of 2-2 abreast switchable transverse seating with 910mm seating pitch at the centre and 1-1 abreast seating at the ends. The seating fabric is coloured red. Straps are fitted above 1-1 abreast seating. Class kuha721 vehicles are equipped with a Japanese style toilet employing a chemical holding tank, and a water tank. As for the device for driving cab, one handle master controller operated by the left hand is featured for the first time among JR companies.
Additional delivery
Vehicles built in 1989 onward employe brown seating fabric. The casing of the traction resistor of class kumoha721 vehicles built in September 1991 onward was changed. 6-car strain sets were introduced in 1992. For this reason, the powered intermediate vehicle with the traction system, class moha720, and the trailer intermediate vehicle, class saha721, were introduced. 3-car unit comprising class kumoha721, moha721, and saha721 is classified into -100 subclass and the other 3-car unit comprising class moha720, moha721, and kuha721 is classified into -200 subclass. The car body of class saha721 vehicles employs that the cab section of class kuha721 is replaced with the conductor room and a Japanese style toilet employing a chemical holding tank and a water tank are fitted at the rear of the vehicle. Trailer intermediate vehicle, saha721-22, and powered intermediate vehicles, moha720-23 and moha721-23 were additionally delivered to make 3-car train set, F-22, built in 1991 a 6-car train set.
Modifications
Seating accommodation improvement for paid reserved seating service branded "U seat"
JR Hokkaido commenced paid reserved seating service improvement programme that improved paid reserved seating branded "U seat" of 721 series used on "Airport" rapid services. Class saha721 vehicles and kuha721-15, -17, -19 received the improved accommodation of the front passenger room featured 2-2 abreast reclining seating with 1030mm seating pitch fitted on the high-level floor over the period from November 2000 until January of the following year. Their exterior has the red waistline and blue headline bands running the length of the front passenger room section below and above the windows for easy identification.
Current pickup replacement
The current pickup of class moha721-0 vehicles was displaced with single-arm type current pickup, N-PS785, to prevent contact loss from overhead current feeder due to snow accretion from 2004.
Side windows replacement by polycarbonate
The windowpanes of the side windows were displaced with polycarbonate plates over the period from 2002 until the following year for protection against the breakdown of the windowpane.
Operations
721-0 series entered "Airport liner" rapid services linking Sapporo and Tomakomai, "Marine liner" rapid services linking Sapporo and Otaru, and regional services on the Hakodate and Chitose lines in 1988. "Airport liner" and "Marine liner" rapid services were unified to "Airport" rapid services linking Otaru and New Chitose airport in 1992. However, "Airport" rapid services started to be operated by 721 series which could travel at 130km/h. Therefore, 721-0 series were used on regional services on the Hakodate, Chitose, and Sassho lines along with 731 and 733 series. Meanwhile, 721 series used on rural services linking Iwamizawa and Asahikawa were displaced with 737 series and began to be withdrawn in 2024. |
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