Background and overview
In March 2002, Eniwa Station was added to the stop pattern of the “Airport”
rapid services linking Otaru and Shin-Chitose Airport. To maintain the
existing journey time between Sapporo and Shin-Chitose despite the additional
stop, JR Hokkaido introduced 130 km/h operation on these services. As part
of this initiative, seven 3-car sets (F-15 to F-21) and one 6-car set (F-22+F-23)
of the 721-0 series were modified between November 2001 and March 2002
to support higher-speed operation and were reclassified as the 721-3000
series.
Car body
To improve durability and winter resistance, the side windowpanes were
replaced with polycarbonate panels. Headlights located below the windscreens
were upgraded to high-intensity discharge (HID) lamps.
Bogies
Yaw dampers were replaced from type YA40 to OD65A-1. Brake lever ratios
were adjusted to improve braking performance: powered vehicles from 10.08
to 8.31, trailer vehicles from 8.05 to 6.15. Brake cylinder diameters were
increased from 140 mm to 160 mm.
Traction unit and ancillary equipments
The brake cylinder pressure control pattern of the electric-command brake
system was revised. The vehicle information and control display were upgraded
from a plasma display to an LCD-based human–machine interface (HMI). Automatic
announcement equipment was newly installed.
Modifications
U seat removal
Between December 2003 and March 2004, Kuha721-3015, -3017, and -3019 underwent
interior modifications to remove the reserved “U-seat” accommodation and
convert the space to standard seating.
U-Seat Expansion
In October 2003, Saha721-3022 was modified to expand “U-seat” accommodation across the entire passenger compartment. The high-level floor was removed, and the exterior was updated with a blue waistline band, a red accent stripe below the windows, and vertical blue bands adjacent to the doorways.
Wheelchair space installation
Between December 2003 and March 2004, the front single-abreast seat of
Kumoha721-3015 to -3019 was removed to create a designated wheelchair space
for improved accessibility on “Airport” rapid services.
Refurbishment Programme
Background and overview
In January 2011, JR Hokkaido refurbished one 6-car set of the 721-3000 series to improve reliability following frequent traction system failures. The refurbishment included replacement of the traction system with a variable-frequency drive and structural upgrades to the carbody. The modified set was reclassified as the 721-3100 series.
As part of the conversion:
- Kumoha721-3022 was reconfigured into trailer-end car Kuha721-3222.
- Moha720-3023 was converted into trailer intermediate car Saha721-3123.
- Moha721-3022 and -3023 were renumbered as Moha721-3222 and -3123.
- Saha721-3022 became Saha721-3222.
- Kuha721-3022 became Kuha721-3122.
The resulting formation consists of two powered vehicles and four trailer vehicles.
Car body
Corroded floor panels, aged floor sheets, and thermal insulation were replaced.
Moha721-3200 and Kuha721-3100 class vehicles were fitted with 1 mm-thick
stainless-steel cover plates between underfloor equipment to reduce surface
undulation and prevent snow and ice accumulation. Anti-fall plates were
installed between vehicles, excluding the cab ends.
Bogies
Motored bogies are N-DT721. Kuha721-3122 and Saha721-3222 are fitted with N-TR721 trailer bogies, while Kuha721-3222 and Saha721-3123 employ N-DT721T bogies converted from motored bogies previously carried by Kumoha721-3022 and Moha720-3023. All bogies feature bolster-less secondary air suspension, conical multilayer rubber spring journal supports, and a Watts linkage draw gear. Power transmission utilizes Twin Disc (TD) flexible joints with carbon-fiber reinforced plastic (CFRP) deflecting plates. The gear ratio was changed to 5.19 to enhance acceleration performance at medium to high speeds, with a maximum service speed of 130 km/h. All bogies employ double-tread brake rigging with enhanced-adhesion alloy cast iron brake shoes.
Traction unit and ancillary equipments
Moha721-3123 and Moha721-3222 are equipped with traction system N-CI721-2, controlling four AC induction motors (N-MT731), each rated at 230 kW per truck. The system comprises a three-level PWM converter and a two-level variable-frequency drive (VFD), both employing insulated gate bipolar transistors (IGBTs). The original traction resistor units for rheostatic braking were removed.
A travelling wind self-cooled traction transformer (N-TM721A-AN) is mounted beneath the floor. Air compressors on Kuha721-3122 and Saha721-3222 were replaced with N-MH1045-C2000ML units, and auxiliary power supplies were upgraded to N-APS721C, rated at 8 kVA. The braking system is an electric-command type featuring regenerative and holding brake functions, with control logic prioritizing trailer vehicles.
Operations
The 721-3000 series entered service on “Airport” rapid services in 2002. Over time, the 3-car sets were replaced by the 733-3000 series, and surplus units were reassigned to replace 711 series EMUs on the Hakodate Line. A 6-car set was converted into the 721-3100 series and continues to operate on regional services along the Sapporo, Chitose, and Sassho Lines, in addition to “Airport” rapid services. The remaining 3-car sets of the 721-3000 series are currently assigned to regional services on the same lines, operating alongside the 731 and 733 series. |
|
| 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 |
20,800mm |
| Width |
2,954mm |
| Height |
3,670mm |
| Bogie |
N-DT721 (powered) N-TR721, N-DT721T (trailer) |
| Collector |
N-PS785 |
| Traction
motor |
N-MT721A (250 kW) |
| Gear ratio |
5.6 |
| Transformer |
N-TM721A-AN |
| Traction system |
Converter and variable frequency drive on truck basis: N-CI721-1 |
| Air conditioner |
N-AU721 (20,000 kcal/h×1) |
| Designed
by |
JR Hokkaido |
|
|
