These are GM EMD GT46PAC locos. Starting in June 2001, 10 of them (#20000 to #20009) were provided by GM, operating out of Hubli (but frequently seen at Guntakal, Gooty, Bangalore and Secunderabad). In April 2002 DLW started producing these locomotives with 20011, 20013 and 20014 being assembled from completely knocked down kits. 20012 was the first indigenously manufactured WDP-4 and features a modified fibre glass shell over the standard cab. DLW had plans only for these 5 in its first production batch, but started to produce them in large numbers starting in late 2003.

These are 4000hp locos with the 16-cylinder EMD 16-710 (16-V-710G3B-EC) turbocharged engines (AC-AC transmission) with unit fuel injection. The fabricated underframe has a rigid design. The bogies are GM's light-weight cast HTSC bogies similar to those of WDG-4 locos but meant for passenger use. (See the WDG-4 notes for some more information.) The bogies are said to have a 'million mile' overhaul interval because of a reduction in the number of wearing surfaces. The suspension is a two-stage suspension. They have an interesting Bo1-1Bo wheel arrangement. At 119t they are 7t lighter than the WDG-4 because they have 2 fewer traction motors. Max. speed 160km/h, although in trials it is said to have been run at speeds up to 180km/h.

However, in most cases today [2/05] the loco is restricted to 110km/h or so since it used for hauling heavier 24-coach passenger trains. Factor of adhesion is claimed to be around 32% (all-weather). The EM2000 onboard microprocessor system provides a flexible and expandable control system with complete self-diagnostic and unit history features. The cab body is made of fibreglass. It is expected that these will need to return to their home sheds only once in about 90 days for regular maintenance. However, the links at Hubli [1/05] are such that these end up being 'home' every 15 days in any case. Indigenization has proceeded well with many components being made in India now: motors by Crompton, alternators by Kirloskar, etc.

Unusually for IR locos, the DLW-built WDP-4's have cab air-conditioning factory-installed. However, the Hubli shed apparently discourages the use of the air-conditioning equipment for fear it affects fuel consumption adversely [10/04].

Starting in April 2005, these locos were allocated in large numbers to Krishnarajpuram shed of the SWR with Siliguri in the NFR receiving a few locos in late 2006. [12/08] More sheds are expected to home these locos, but currently, along with Hubli, these are the only sheds that handle this class. The current holding of all sheds combined is 75+.0040 homed at KJM shed is the first IGBT based WDP-4. The traction conversion system was supplied by Siemens.

Builders : GM EMD, DLW
Engine : GM-EMD 16-710, 4000hp
Transmission : Electric (AC - AC), GM components?
Weight : 118t
Tractive Effort : 27.0t (264.8kN). Some sources say 27.5t (269.8kN)
Brake horsepower : 3939hp
Engine rpm: 950
Fuel tank capacity: 6000 Liter

A 24-coach (1430t) passenger rake can be accelerated to 110km/h in 1020 seconds (over 25.7km) by a WDP-4.

This class designation does not follow the directive to use the suffixed letter to indicate an increase in power over the base model. Instead, the "4D" designation here refers to a dual-cab version of the WDP-4 / WDP-4B design, intended to eliminate the problem of running long hood forward. The cabs have a slightly wider profile (as in the WDP-4B), to improve visibility.

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