WAP-4 is one of the most important electric locomotives used in India. It is a highly powerful class capable of hauling 26 coaches at the speed of 160 km/h. It is also among the most widely used locomotive.
The locomotive was developed, after a previous class WAP-1 was found inadequate to haul the longer, heavier express trains that were becoming the mainstay of the Indian Railways network. It was introduced in 1994, with a similar bodyshell to the WAP-1 class, but with Hitachi traction motors developing 5000hp (5350 hp starting).
Electricals are traditional DC loco type tap changers, driving 6 traction motors arranged in Bo-Bo fashion. This locomotive has proved to be highly successful, with over 450 units in service and more being produced. Newer examples have been fitted with Microprocessor Controlled diagnostics, Static Convertor units (instead of arnos) and roof mounted Dynamic (Rheostatic) Brakes.
The locomotive can be seen in service across the electrified network of Indian Railways and is homed at 11 sheds (depots).
Design
The loco has a streamlined twin cab carbody design, with top-mounted headlamps. The first 150 or so units had the headlamp mounted at waist level, with the lights being mounted in a protruding nacelle. Later on the headlamps were placed in a recessed nacelle, and from road # 22579 onward, the headlamps were moved to the top. Newer locos also feature larger windshields, more spacious driver cabin with bucket type seats and ergonomic controls. The control panel also features a mix of digital and analog displays in newer units (all analog display in older versions).
The loco features higher power rated silicon rectifiers and indigenously-designed 5400kVA transformer coupled with Hitachi HS15250 traction motors. Starting power is 5,350 hp (3,990 kW), with 5,000 hp (3,700 kW) being supplied continuously.
Original units were weighed 120 tonnes, which was brought down to 112 tonnes through the usage of lighter material.
Some WAP-1 and WAP-6 units were rebuilt to WAP-4 specifications after replacing the bogies & electricals.
Performance
The WAP-4 class hauls 24 coach (1430 tonne) trains at 110 km/h. It is also used to haul the premier Rajdhani & Shatabdi Expresses at 130 km/h. In trials, the loco has achieved a top speed of 169.5 km/h, though Indian Railways limits its top speed to 140 km/h.
With a 24 coach passenger train, the acceleration time / distances are:
110 km/h - 338 seconds (6.8km)
120 km/h - 455 seconds (10.5km)
130 km/h - 741 seconds (20.5 km)
Starting Tractive Effort (Te) - 30800 kg/force
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