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. Therefore, "Airport" rapid services started 130km/h operation to keep the journey time and JR Hokkaido modified three 6-car sets of 721-100 series to raise the maximum service speed at 130km/h over the period from June 2001 until February of the following year and classified them into -3100 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 were changed. The vehicle information and control display was changed
from the plasma display to LCD HMI. The automatic announcement equipment
is additionally fitted.
Modifications
Modification of U seat accommodation expansion to whole passenger room
Saha721-3201 to -3203 vehicles were modified in removing the high-level floor and applying U-seat accommodation to all passenger rooms over the period from November 2023 until February of the following year. 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.
Refurbishment Programme
Background and overview
JR Hokkaido modified three 6-car sets of 721-3100 series to improve the
reliability with the traction system replacement with Variable Frequency
drive and the refurbishment of the car body in January 2012 due to frequent
failures occurred on the traction system. Powered end vehicles, class kumoha721-3200,
were converted to trailer end vehicles, class kuha721-3200 and powered
intermediate vehicles, class moha720-3100, were converted to trailer intermediate
vehicles, class saha721-3100. Therefore, modified 721-3100 series are 6-car
set consisting 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 class kuha721-3100 and class saha721-3200 are N-TR721, and trailer bogies of class kuha721-3200 and saha721-3100 are N-DT721T which are converted from motored bogies carried from class kumoha721-3200 and moha720-3100 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
Class moha721-3100 and moha721-3200 vehicles are equipped with a traction
system, N-CI721-1, which controls 4 AC induction motors, N-MT721A, with
a power output of 250kW 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
kumoha721-3200 and moha720-3100 were equipped for rheostatic brake was
removed. Class moha721-3100 and moha721-3200 vehicles are also equipped
with a travelling wind self-cooling traction transformer, N-TM721A-AN,
beneath the floor. The air compressor class kuha721-3200 and saha721-3100
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
721-3100 series entered "Airport" rapid services in 2002. They also used regional services on the Sapporo, Chitose, and Sassho lines. |
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