DuPont™ Nomex® for rolling stock locomotive transformers and traction motors

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Issue

Indian Railways (IR) is one of the world's largest railway networks comprising 115,000 km of track over a route of 65,436 km. In 2013-14, IR carried more than 23 million passengers daily and 1050 million tons of freight. Indian Railways is also the world's ninth largest commercial or utility employer, by number of employees, with over 1.307 million employees.

With the ever-increasing population and the need for mobility with emergence of rapidly expanding cities and metros, Indian Railways recognizes the need to enhance capacity and deploy right equipment to run smooth operations. The new government’s plans and budgets for introducing high speed trains, a dedicated freight corridor and increasing A/C coaches in trains, are expected to further increase the need for on-board equipment.

The Indian Railways has committed to embrace technology - from choosing the right technology for driving engines to implementing sound material and technology combination for building a robust rail network in the country.

Challenge

One of the major equipment required by the network is rolling stock traction transformers to ensure reliable power supply to run its 9,000 locomotives. On an average, four locomotive transformers fail every month due to high temperatures and harsh environments bringing the railway network to a halt, causing wide scale disruption in operations and safety risk to travelers. According to Railway Design and Standards organization (RDSO), a failed transformer means an idle locomotive, which is equivalent to a revenue loss of 30,000 USD per day for Indian Railways. RDSO is the principle organization that controls the specifications and designs of equipment used by the IR.

The loads on the traction locomotives have increased thus increasing the expectation of reliability from this equipment. Traction transformers are subjected to higher mechanical stress due to constant vibration when mounted on the rolling stock and frequent overcurrent, which creates dynamic stress on the windings. The transformer failure occurs mainly due to high temperature at the windings which causes deterioration of the insulating paper, which then contaminates the oil in the transformer. Currently, transformers are repaired by the Railways by changing the complete insulation of the transformer once it has failed. The repairs are done with the normal cellulose paper and the press boards, which require two to three months to repair and refurbish the transformers. IR identified an immediate need to address the insulation related challenges of transformers to increase the life of transformers and bring operational failures to Shunya.

Tasked with the objective of reducing failure of transformers, RDSO began its search for a reliable industry face that supplies quality equipment. The challenge was bigger because of lack of local manufacturers who have the capacities to fulfill the increasing demand from IR. Moreover, RDSO required equipment that could withstand and perform under harsh and highly arduous environment.

Solution

DuPont conducted an initial analysis of data of failures of transformer and presented a proposal of using traction transformers with DuPont™ Nomex® insulation. DuPont™ Nomex® for locomotive transformers are equipped with a unique high temperature insulation material that can withstand more heat than the incumbent solutions used by RDSO.

Nomex® insulation technologies in fluid-filled transformers can:

Improve reliability: Insulation systems based on Nomex® technologies maintain excellent electrical and mechanical characteristics over a transformer's service life. Nomex® is chemically inert and does not release CO, CO2 and water in oil, reducing the risk of failure. Negligible aging, resistance to shrinkage and compression, and the superior resilience of Nomex® help coil structures remain tight and withstand short-circuit forces, even after years of service.

Increase reserve capacity: Transformers insulated with Nomex® can be designed for extra power capacity in emergency peak load situations.

Reduce equipment size and weight: While maintaining top oil temperatures at constant levels with only modest increases in average oil temperatures, the weight of a transformer can be reduced up to 25 percent for a given kVA output. Conversely, the kVA rating can be increased up to 50 percent for a given size and weight. This weight reduction allows mobile substations and railway traction transformers to be designed with operating capabilities larger than before.

To prove the benefit of DuPont™ Nomex®, DuPont conducted a trial with two transformers of similar designs of 5400 KVA one made with Nomex® and other with cellulose paper. The team conducted actual heat run on the transformers by extending the overload period to simulate the effect of overload over a longer time. The results showed that the cellulose transformer developed carbon dioxide and water in the oil, indicating deterioration of transformers. Thus, Nomex® proved itself to be an optimum and sustainable solution for the environment in which the locomotive transformers operate in India.

Benefits

The electrical Nomex® insulation paper used in the transformers of electric locomotives helps absorb load variations without any breakdowns, thus ensuring smooth operations. Further, Indian Railways is reducing environmental impact by choosing an environment friendly technology that reduces the amount of combustible material present in the transformer and the locomotive.

Passengers of IR can rest a bit more knowing that brilliant science is at work to achieve “zero operational breakdowns” and “zero safety concerns” – commitments Indian Railways is upholding.