Background and overview
JR Hokkaido modified F-21 set of 721-0 series to improve the reliability with the traction system replacement with Variable Frequency drive and the refurbishment of the car body in July 2010 due to frequent failures occurred on the traction system and classified them into -2100 subseries. Powered end vehicles, class kumoha721-0, were converted to trailer end vehicles, class kuha721-2200. Therefore, 721-2100 series converted from F-7 set of 721-0 series are 3-car set consisting of 1 powered vehicle and two tailer vehicles.
Car body
Corroded floor panel and superannuated floor sheet and thermal insulation were renovated. Moha721-2107 has 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
The motored bogies are N-DT721, trailer bogies of kuha721-2107 are N-TR721, and the trailer bogies of kuha721-2207 are N-DT721T which are converted from motored bogies carried from kumoha721 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
Moha721-2107 is equipped with a traction system, N-CI721-1, which controls
4 AC induction motors, N-MT721A, 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 kumoha721-7 was equipped with
for rheostatic brake was removed. Moha721-2107 is also equipped with a
travelling wind self-cooling traction transformer, N-TM721A-AN, beneath
the floor. An air compressor kuha721-2107 was equipped with is replaced
with N-MH1045-C2000ML and an auxiliary power supply 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
721-2100 series are used on regional services on the Hakodate, Chitose, and Sassho lines along with 731 series and 733 series. |
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