WAG-7 class locomotive retrofitted with regenerative braking, trials successful

Indian Railways (IR) has successfully trialled a WAG-7 class locomotive fitted with regenerative braking. The experimental upgrade was carried out on locomotive number 24517 homed at Jhansi shed. Trials were held on 17th January 2019, according to sources.

Regeneration has been identified as an important measure for reduction in electricity consumption costs of IR. This project is expected to save the transporter Rs. 25 lakh per unit per year, according to the Ministry.

The Railway Board had in September 2017 approved development of regenerative braking feature for WAG-7 by RDSO in partnership with BHEL. The original timeline for delivery of the prototype was March—April 2018. However, technical issues delayed the project. BHEL’s system was able to recover regenerated energy at speeds above 30 kph. However, IR wanted regeneration abilities at speeds above 10 kph.

Medha Servo Drives, a private vendor supplying key components to IR, was also asked to design and build a prototype regenerative system on another locomotive. Subsequently, WAG-7 27512 was nominated for Medha’s version of the project.

WAG-7

The WAG-7 locomotive class is designed for heavy freight haulage. Based on a design that traces its origins to the 1960s, the class is rated for approx. 5,000 hp. 1,959 units operate on IR’s network as of February 2019.

Legacy Design

Like other locomotives from the same design family, the WAG-7 uses Direct Current (DC) powered traction motors to turn its wheels. These motors are also capable of generating power when used in the ‘dynamic braking’ mode. This mode utilises the electricity generation ability of traction motors to convert kinetic energy of the train into electric energy. Dynamic Braking helps slow the train down without having to use air brakes.

However, in the legacy power equipment design of the loco, electricity regenerated by traction motors cannot be converted to a form suitable for feeding overhead wires. Therefore, it has to be fed into a grid of resistors that convert the electricity to heat. The heat is then dissipated into the atmosphere.

Regenerative braking.

The idea behind regenerative braking is to recover this large amount of otherwise wasted electricity. The electricity can be converted and fed back into the same overhead wire that the loco normally draws power from. Other units elsewhere on the line, and hauling other trains, can theoretically utilise this flow of power rather than from the main electricity grid. Such reuse can result in substantial savings in electricity bills for the railways.

Locomotive classes with modern designs, such as the WAG-9, WAP-5 and the WAP-7, as well as the currently under-trial WAG-12, all have the feature built in. The modern EMUs in use for local trains in Mumbai also feature regenerative braking.

Image source : Ministry of Railways

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