The WAP-7 is one of the most successful locomotives of Indian Railways serving passenger trains for over 21 years. It is a passenger variant of the WAG-9 freight locomotive with a modified gear ratio to pull lighter loads at higher speeds. With an output of 6,350 hp (4,740 kW), it is the most powerful passenger locomotive in the Indian Railways fleet, and the most numerous passenger locomotive in India, with a total 1422 locomotives built as of January 2022. The WAP-7 is capable of hauling 24 coach trains at speeds 110–140 km/h (68–87 mph).
In 2019, a variant of the WAP-7, designated the WAP-7HS, was introduced for higher speeds. The WAP-7HS has a max speed of 180 km/h (110 mph), and is capable of hauling a 24-car train at 160 km/h (99 mph) as opposed to the 140 km/h (87 mph) of the original. Indian Railways plans to use the WAP-7HS for Shatabdi, Rajdhani, and Duronto express trains. However, as of November 2021, it has not been confirmed if any others have been built, and the single completed WAP-7HS has stayed restricted to 130 km/h (81 mph).
A main feature of some locomotives of this class is that they eliminate the need to have separate End on Generation (EOG) sets or DG (Diesel Generator) sets for supplying power to the train resulting in significant savings on maintenance and running costs. This technology, called HOG or "Head On Generation", transfers electric power from the loco's pantograph to the coaches instead of EOG where a power car equipped with diesel generator capable of generating adequate power of 3-phase 50 Hz 415 V / 750 V AC (called 'head-end power') is provided at either end of the train rake to supply power.[2][3][4]
