Background and overview
Eniwa station was added to stops of "Airport" rapid services linking Otaru and Shin-Chitose airport from March 2002. Nevertheless, the journey time between Sapporo and Shin-Chitose airport remained not changed. Therefore, "Airport" rapid services started 130km/h operation to keep the journey time and JR Hokkaido modified F-15 to F-21 3-car sets and a F-22+F-23 6-car set of 721-0 series to raise the maximum service speed at 130km/h over the period from November 2001 until March of the following year and classified them into -3000 subseries.
Car body
The windowpanes of the side windows were displaced with polycarbonate plate for the protection against the breakdown of the windowpane. In addition, headlights located below the windscreens were displaced with high intensity discharge (HID) lamps.
Bogies
The yaw dampers were replaced from YA40 to OD65A-1. The brake lever ratio of powered vehicles was changed from 10.08 to 8.31, that of trailer vehicles was changed from 8.05 to 6.15, and the brake cylinder diameter was changed from 140mm to 160mm.
Traction unit and ancillary equipments
The brake cylinder pressure control pattern of the electric commanding brake was changed. The vehicle information and control display were changed from the plasma display to LCD HMI. The automatic announcement equipment is additionally fitted.
Modifications
U seat removal modification
U seat accommodation of kuha721-3015, -3017, and -3019 was removed to convert regular accommodation over the period from December 2003 until March of the following year.
Modification of U seat accommodation expansion to whole passenger room
Saha721-3022 vehicle was modified in removing the high-level floor and applying U-seat accommodation to all passenger rooms over the period from October 2003. The exterior has a blue waistline band and red narrow band running the length of each car below the windows and vertical blue bands running outward of both ends of doors.
Wheelchair space installation
The front 1 abreast seat of kumoha721-3015 to -3019 used on "Airport" rapid services was removed to introduce the wheelchair space over the period from December 2003 until March of the following year.
Refurbishment Programme
Background and overview
JR Hokkaido modified one 6-car set of 721-3000 series to improve the reliability with the traction system replacement with Variable Frequency drive and the refurbishment of the car body in January 2011 due to frequent failures occurred on the traction system. A powered end vehicle, kumoha721-3022, was converted to trailer end vehicles, kuha721-3222 and a powered intermediate vehicle, moha720-3023, was converted to trailer intermediate vehicles, saha721-3123. As for the other vehicles, moha721-3022 and -3023 were renumbered into moha721-3222 and -3123, saha721-3022 was saha721-3222, and kuha721-3022 was kuha721-3122. Therefore, modified 721-3000 series 6-car set consists of two powered vehicle and four tailer vehicles.
Car body
Corroded floor panel and superannuated floor sheet and thermal insulation were renovated. Class koha721-3100 and moha721-3200 have 1mm thick stainless cover plates which are fitted between equipments fitted under their floor to reduce the waving for preventing snow and ice from sticking thereon. Anti-fall plates between vehicles are additionally introduced excepting the cab end.
Bogies
Motored bogies are N-DT721, trailer bogies of kuha721-3122 and saha721-3222 are N-TR721, and trailer bogies of class kuha721-3222 and saha721-3123 are N-DT721T which are converted from motored bogies carried from class kumoha721-3022 and moha720-3023 with the modification to the trailer bogie. These bogies feature bolster-less secondary air suspension, corn-shaped multilayered rubber spring journal supporting system, and the Z link traction device. Twin Disc (TD) flexible joint employing deflecting plates made of carbon-fiber reinforced plastic (CFRP) is applied for power transmission device. The gear ratio is changed into 5.19 to get high acceleration performance at the range of middle and high speed and the maximum service speed at 130km/h. Their bogies employ double tread brake riggings employing the enhanced adhesion alloy cast iron brake shoe.
Traction unit and ancillary equipments
Moha721-3123 and moha721-3222 vehicles are equipped with a traction system, N-CI721-2, which controls 4 AC induction motors, N-MT731, with a power output of 230kW on truck basis. This traction system consists of a 3-level PWM converter employing Insulated Bipolar Transistor (IGBT) and a 2-level Variable-frequency drive (VFD) employing IGBT. The traction resistor kumoha721-3022 and moha720-3023 were equipped with for rheostatic brake was removed. Class moha721-3123 and moha721-3222 vehicles are also equipped with a travelling wind self-cooling traction transformer, N-TM721A-AN, beneath the floor. An air compressor kuha721-3122 and saha721-3222 vehicles were equipped with is replaced with N-MH1045-C2000ML and an auxiliary power supply they are equipped with is replaced with N-APS721C with a power output of 8kVA. The brake system is the electric commanding brake with regenerative brake and holding brake, featuring brake control of trailer priority.
Operations
721-3000 series entered "Airport" rapid services in 2002. However, the 3-car sets of them were displaced with 733-3000 series and surplus 3-car sets displaced with 711 series EMU used on the Hakodate line. On the other hand, a 6-car set of 721-3000 series were converted to 721-3100 series and are subsequently used on the regional services on the Sapporo, Chitose, and Sassho lines besides "Airport" rapid services. 3-car sets of 721-3000 series are now used on the regional services on the Sapporo, Chitose, and Sassho lines. |
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