These locos are modified versions of the WDG-4 class locos, used for passenger operations. They have a reduced axle load of 20.2t (compared to the WDG-4’s 21t axle load), achieved mainly by trimming the weight of the underframe. The gear ratio is 17:77, horsepower rating of 4500hp (brake horsepower 4150hp), and the maximum tractive effort is 384.4kN. It has an operational design speed of 130km/h and a maximum speed of 150km/h. The cab is slightly wider to provide better visibility when running long hood forward. All other features are essentially the same as with the WDG-4. Please see the WDG-4 class information for more details on this loco. Other points to note are below.
Initially two prototypes of the WDP-4B class were built using components for the WDP-4 class loco (#20047, #20075 – in the number series for the WDP-4 class). Serial production of these locos began in March 2010.
Note that although the class designation makes it seem like a minor variant of the WDP-4 class, it has significant differences from it, being much closer to the WDG-4 class. In particular, the WDP-4 has 4 PAC traction motors (Bo-Bo) whereas the WDP-4B has 6 traction motors (Co-Co). In addition, the traction motors have individual inverters, so that in the case of one inverter failing, 5 traction motors are still available, allowing the loco to reach its destination under reduced power. Traction control uses IGBTs instead of GTOs. The control software has also been changed so as to squeeze out power at the top end of each traction motor under most conditions, unlike with the WDP-4 where the software was more constraining in terms of when it would allow maximum power to be drawn. The WDP-4B also has a provision for an inverter-driven head-end power unit, allowing running trains without a generating car (EOG) for hotel power.