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Indian locomotive class WAP-7
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The Indian locomotive class WAP-7 is a class of 25 kV AC electric locomotives that was developed in 1999 by Chittaranjan Locomotive Works (CLW) for Indian Railways. Its class designation denotes a broad gauge (W) alternating current (A) passenger (P) locomotive of the 7th generation (7). They entered service in 2000. A total of 2081 WAP-7 locomotives have been built, with more units being built at CLW, Banaras Locomotive Works (BLW) and Patiala Locomotive Works (PLW).
The WAP-7 has been serving passengers for Indian Railways since their introduction in 1999. 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 6,125 hp, it is the most powerful passenger locomotive in the Indian Railways fleet, and the most numerous passenger locomotive in India. The WAP-7 is capable of hauling 24 coach trains at speeds of 130 km/h.
History
[edit]The WAP-7 is largely used by most regional zones of Indian Railways. As of October 2021, all of these are fitted with H-type transition couplers which are compatible with both screw coupling and centre-buffer coupling.[original research?] In February 2017, Banaras Locomotive Works built their first WAP 7 class locomotive.[2]
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 September 2022, it has not been confirmed[according to whom?] if any others have been built, and the single completed WAP-7HS has remained[as of?] restricted to 130 km/h (81 mph) operation.[This paragraph needs citation(s)]
In 2025, a variant of the WAP-7, designated the WAP-7AD, was introduced with an aerodynamic design. The WAP-7AD has a maximum 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-7AD for Amrit Bharat Express & other Express trains. The first WAP-7AD 37873 entered service on September, 2025 hauling 12284 Ernakulam Duronto express. A pair of WAP 7AD, painted with Amrit Bharat livery are currently parked at ICF, Chennai waiting for rake & route allotment.
Head-on Generation (HOG)
[edit]
Many locomotives of this class are fitted with head-on generation (HOG), eliminating the need to have separate End on Generation (EOG) sets or DG (Diesel Generator) sets for supplying power to the train and thus resulting in significant savings on maintenance and running costs. The HOG 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.[3][4][5]
Locomotive sheds
[edit]See also
[edit]References
[edit]- ^ a b c "[IRFCA] Indian Railways FAQ - AC Electric Locomotives".
- ^ "Brief History of DLW". Ministry of Railways, Government of India. Archived from the original on 2 April 2019. Retrieved 30 December 2017.
- ^ "Train had WAP-7 engine, 'black box' may reveal cause". The Indian Express. 9 August 2010. Retrieved 25 August 2012.[dead link]
- ^ "Recent Developments". Chittaranjan Locomotive Works. Archived from the original on 10 May 2012. Retrieved 25 August 2012.
- ^ Development of Electric locomotive with Head On Generation (HOG) facility (PDF) (Technical report). Research Design and Standards Organisation. Archived from the original (PDF) on 19 February 2018. Retrieved 1 May 2025.
- ^ "e-Locos".
External links
[edit]Indian locomotive class WAP-7
View on GrokipediaOverview
Design and Purpose
The WAP-7 class represents a high-horsepower electric locomotive engineered for Indian Railways' electrified broad gauge (1,676 mm) networks, optimized to meet the escalating demands of passenger traffic following the significant expansion of electrification in the late 1990s and early 2000s.[10][11] As a dedicated passenger variant derived from the WAG-9 freight locomotive platform, the WAP-7 features upgraded three-phase IGBT-based traction technology with a one-hour rating of 6,350 hp (4,740 kW), which facilitates superior acceleration and a maximum operational speed of 140 km/h for express services.[4][12] This design intent emphasizes efficient hauling of long-distance passenger formations, capable of managing 24-coach trains exceeding 1,500 tonnes in weight, thereby enhancing throughput on busy corridors without compromising safety or reliability.[12][11] Evolutionary advancements in the WAP-7 build upon the robust WAG-9 chassis by incorporating a revised gear ratio tailored for high-speed passenger duties.[4][11] These modifications, including subtle aerodynamic enhancements to minimize drag, address the need for versatile locomotives in the WAP (Wide-gauge AC Passenger) series. The first prototype, designated "Navkiran," was rolled out and commissioned for trials in May 2000 by Chittaranjan Locomotive Works.[13]Classification and Nomenclature
The nomenclature of the Indian locomotive class WAP-7 adheres to the standardized coding system used by Indian Railways for classifying locomotives based on gauge, power type, service role, and sequential variant. The prefix "WAP" breaks down as follows: "W" denotes broad gauge (1,676 mm track width), "A" indicates alternating current (AC) electric traction, and "P" specifies primary suitability for passenger train operations. The trailing numeral "7" signifies that this is the seventh distinct variant within the WAP series, reflecting evolutionary improvements in design and performance over predecessors.[14] In technical classification, the WAP-7 is designated as a high-speed passenger electric locomotive featuring a Co-Co wheel arrangement, which consists of two three-axle bogies with all six axles powered for optimal traction and stability. It is engineered for compatibility with Indian Railways' 25 kV 50 Hz AC overhead electrification system, enabling efficient operation on electrified broad-gauge networks. Within the broader WAP family—encompassing variants from WAP-1 to advanced models such as WAP-7HS—the WAP-7 occupies a pivotal position, offering enhanced power output compared to the mid-range WAP-4 (5,350 hp starting rating) while paving the way for experimental higher-capacity iterations like the WAP-7HS and the WAP-7AD introduced in 2025. As of 2025, the fleet comprises approximately 2,000 units in active service across Indian Railways, with individual locomotives serially numbered starting from WAP-7 30201, the prototype introduced in 2000.[12][15]Development and Production
Historical Background
In the late 1990s, amid rising demand for efficient long-distance travel and shaped by international advancements in electric traction, notably ABB's three-phase AC systems that promised higher efficiency and speed for broad-gauge networks.[16] A pivotal step occurred on July 23, 1993, when Indian Railways signed a transfer-of-technology agreement with ABB Transportation of Switzerland for 3-phase locomotives using IGBT converters, enabling the shift from older thyristor-based designs to more powerful, regenerative braking-capable units suitable for passenger duties.[16] The Research Designs & Standards Organisation (RDSO) launched the WAP-7 project in 1998, building on this collaboration to create a high-speed passenger variant adapted from the WAG-9 freight locomotive by adjusting the gear ratio, aimed at hauling 20-24 coaches at elevated speeds without intermediate locomotives.[17] The first prototype, numbered 30201 and named Navkiran, was assembled at Chittaranjan Locomotive Works (CLW) in 1999, incorporating ABB's propulsion technology for a 6,000 hp output.[15] Initial trials commenced in 2000 on the Howrah-Delhi route, validating its 140 km/h operational capability with loads simulating premium express trains like the Rajdhani.[18] Early deployment faced challenges, including pantograph-catenary interactions causing arcing and overhead line wear during high-speed runs, which prompted modifications to the pantograph design and catenary supports by 2001 to ensure reliable performance.[4] These refinements, informed by RDSO's field testing, solidified the WAP-7's role in modernizing Indian Railways' passenger fleet.Manufacturers and Production Details
The WAP-7 locomotive class was developed under a 1998 project by the Research Designs and Standards Organisation (RDSO), with initial production commencing at Chittaranjan Locomotive Works (CLW) in 1999, where the prototype unit was assembled. CLW served as the primary initial producer from 1999 to 2005, manufacturing approximately 50 units during this period to establish the class for high-speed passenger service.[19] Bulk production expanded to include Banaras Locomotive Works (BLW) and Patiala Locomotive Works (PLW), with PLW—formerly the Diesel Loco Modernisation Works—beginning assembly of 3-phase IGBT-based WAP-7 units in February 2018.[20] By the end of fiscal year 2022-23, PLW had produced 250 units, while BLW targeted 159 units for fiscal year 2025-26, including variants with enhanced features.[21] Limited contributions came from the BHEL-Titagarh consortium, which supplied locomotive shells for select batches integrated into the main assembly lines.[22] Production occurred in distinct phases: a prototype phase yielding 1 unit in 1999; a ramp-up from 2001 to 2010 producing around 200 units as electrification networks grew; and an accelerated phase from 2011 to 2025 exceeding 1,700 units, driven by nationwide electrification initiatives and the Dedicated Freight Corridors project.[19] In fiscal year 2024-25 alone, 272 WAP-7 locomotives were manufactured across these facilities.[23] The manufacturing process entails assembling imported core components, such as early traction motors from suppliers like ABB, alongside locally fabricated bogies and underframes at the production units.[24] The unit cost stood at approximately ₹11.10 crore as of 2021-22 figures, reflecting material, labor, and proforma charges. By November 2025, cumulative production exceeded 2,000 units, with recent models incorporating upgrades like energy-efficient regenerative braking for improved sustainability.[12][25]Technical Specifications
Power and Traction System
The WAP-7 locomotive obtains electrical power from the 25 kV 50 Hz AC overhead catenary via a single pantograph mounted on the roof. This high-voltage supply is routed through a circuit breaker to the main step-down transformer, rated at 7775 kVA with oil-forced air-forced cooling, which reduces the voltage on its traction winding to 1269 V AC at no load. The transformer also features dedicated secondary windings for auxiliary (1000 V), harmonic filter (1154 V), and hotel load (960 V) purposes to support onboard systems.[1][26] The AC traction power from the transformer secondary is rectified by a line converter into a DC link with a nominal voltage of approximately 2800 V, providing an intermediate stage for efficient power distribution. This DC output feeds two parallel IGBT-based variable voltage variable frequency (VVVF) inverters from ABB, which convert it back to three-phase AC for propulsion. These inverters enable precise control of motor speed and torque through pulse-width modulation, operating at frequencies up to 132 Hz. The propulsion system drives six three-phase asynchronous squirrel-cage induction motors of type 6FRA6068, each with a continuous rating of 850 kW at 2180 V phase-to-phase, 270 A, and 1283 rpm, yielding a total locomotive power output of 6000 hp (4474 kW) continuous at wheels.[27][28][29][1] The tractive effort generated by the motors is determined by the formula where is the total tractive effort, is the combined motor torque, is the gear ratio (72:20 for the WAP-7), is the transmission efficiency, and is the wheel radius. This configuration delivers a peak starting tractive effort of 32.88 tonnes (approximately 323 kN) at 25 km/h, emphasizing the system's capability for high initial acceleration in passenger service.[30][31][1] Auxiliary systems are powered by a dedicated 3 x 130 kVA converter drawing from the transformer's auxiliary winding, producing 415 V three-phase AC for motors such as the compressor, blowers, and pumps, alongside a battery charger that maintains a 110 V DC supply for control circuits and monitoring equipment. The compressor ensures pneumatic supply for braking and other functions, while the battery charger supports standalone operations during pantograph lowering.[32][27]Performance and Dimensions
The WAP-7 locomotive features robust physical dimensions optimized for high-speed passenger service on Indian Railways' broad gauge network. Its overall structure includes a length over buffers of 20.56 m, a body width of 3.15 m, and a height of 4.04 m, allowing compatibility with standard platform clearances and overhead electrification. The axle load stands at 20.5 tonnes, contributing to a total locomotive weight of 123 tonnes, which balances stability and track-friendly operation.[33][1]| Dimension | Value |
|---|---|
| Length over buffers | 20.56 m |
| Width | 3.15 m |
| Height | 4.04 m |
| Axle load | 20.5 tonnes |
| Total weight | 123 tonnes |
