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Trends in Technological Development of EMUs in India

By on September 5, 2022


The electrification of Railway tracks and introduction of electric traction began on 3rd February 1925 in sections between Bombay VT(CSTM) and Coorla (Kurla) when the first EMU service with 4 cars was flagged off by Sir Leslie Wilson, the then Governor of Mumbai. The first service ran from the then Bombay VT (now Chhatrapati Shivaji Maharaj Terminus Mumbai) to Kurla on harbour line and later up to Pune and Igatpuri were electrified with 1500 Volt DC system. This was followed by electrification with 1500 Volt  DC in Chennai Beach – Tambaram Section and 1500 Volt DC between Howrah and Ranigunj.  Commuter trains were introduced in these sections as Electric Multiple Units (EMU) for travel within the cities. This DC electric traction system continued until Indian railways adopted a 25 kV AC electrification system in the 1960s.  Since then, these sub-urban sections of Chennai and Kolkata were converted to a 25 kV AC system, and the Mumbai sub-urban section was the last to be converted in the year 2015.  Indian Railways operate 5500 EMU trains in various sub-urban systems, i.e., Chennai, Mumbai, Kolkata, Delhi & Secunderabad, with ten million daily users.

2.0 Morden Technology for  EMUs in India

The Rolling Stock ( EMU) has undergone a transformation over the years, starting with rheostatic control in 1925, tap changers and rectifier system in the 1960s, which remained as mainstay till the 3 phase propulsion system were adopted in the year 2000 for EMUs. The first 1500V DC EMUs used around Bombay (the first EMUs in India, 1925) were from Cammell Laird (UK) (later Metro Cammell) and Uerdingenwagonfabrik (Germany). Later, units were supplied by Breda (Italy) as well. Birmingham Railway Carriage and Wagon Co. supplied 24 trailer cars for WR and 32 for CR in the early 1950s. In 1956-57, a few Hitachi and Nippon SSK WCU6 & WCU7, 1500V DC EMU rakes were serviced. These early EMUs were all vacuum-braked and in use until 1974. Later on, units were manufactured by Jessop, BEML, and ICF. In 1981, IR contracted with the Bhabha Atomic Research Centre (BARC) to develop energy-efficient control systems for the Mumbai EMUs. The BARC design included chopper (thyristor) control of the motor power supply instead of rheostatic control, thereby eliminating the energy wastage in the resistance grids. The EMUs were also provided with the capability for regenerative braking to convert the kinetic energy of the rake back to electrical energy fed to the catenary during braking. The first chopper rakes were introduced in 1993. By 1994, 5 such ‘chopper rakes’  were brought into service. BARC claimed a savings of 25% in energy consumption (18% from the elimination of rheostatic control and 7% from regenerative braking). This technology in EMUs in India faced with challenges of new generation AC-DC EMUs ( with GTO and three-phase drives) for Mumbai, which were to be introduced next.

Further, with the introduction of IGBT based 3 phase propulsion system in 2007, over 300 EMU trains (with this technology) have been manufactured and are in service in various sub-urban sections in India, namely Mumbai, Kolkata, New Delhi, Chennai, and Secunderabad.  The technology upgradation of EMUs since 2007 also has added the advantage of the reduction in weight of the propulsion equipment introduction of modern train control and management system (TCMS). This technology also provides lower net energy consumption due to the inherent feature of regenerative braking in these trains.  Further, long-distance train sets are also designed on this platform to enhance the energy efficiency, comfort, and high speed of inter-city trains.

2.1 Advantage of 3-phase propulsion system

Generally, the Electrical Multiple Units for suburban trains have distributed traction system, which has the following merits.

(1) Effective use of regenerative brakes and blending of pneumatic brakes

(2) Reduction in axle load

(3) Effective use of space for passengers

(4) Higher acceleration and de-acceleration performances are feasible due to the number of power axles.

As a result of the distributed traction system provided in EMUs, improved train performance with higher acceleration and de-acceleration reduced energy consumption, and lesser impact on track can be achieved.

With the introduction of induction motor drives, the maintenance issues on drives, such as frequent replacement of parts, cleaning of commutators, etc., were completely avoided.  Further, the resistors used in 1500 V DC EMU for control were no longer required with the PWM converter and inverter system.  With the PWM converter inverter system, the system’s power factor can be controlled to 100% compared to 60 to 70% power factor achieved in 25 kV AC EMU with DC drive resulting in a reduction in the import of current from the catenary and also losses. The regenerative braking provided a full range of electrical braking up to a very low speed of 10 kmph blended with pneumatic brake has enhanced energy efficiency.  Thus, the introduction of 3-phase propulsion brought in an overall improvement in the EMUs, traction control, the weight of propulsion equipment, energy efficiency, and lesser maintenance time.

2.2 Arrival of GTO-based propulsion system:

In the year 1998, Mumbai sub-urban section needed more efficient and reliable rolling stock, deploying latest technology to meet the growing demand of travel.  Accordingly, 3 phase VVVF control propulsion system was planned for 24 trains, and two suppliers, namely M/s Alstom and M/s BHEL (with TOT from Traxis, Nederlands) developed this propulsion system for Mumbai suburban EMUs with dual-mode propulsion.  Between 2000 and 2006, the trains were built with GTO based 3-phase converter/inverter system and were introduced in Mumbai area.  With the introduction of 3 phase propulsion system, the Railways had the benefit of a reduction in maintenance downtime (due to the maintenance requirement of tap changers and DC traction motors requiring frequent attention in the earlier versions) and energy efficiency.  However, by the time this technology was introduced, the GTO technology was replaced the world over by IGBTs.  These new semiconductors had the promising advantage of an easier turn-off and turn-on control. The limited experience with the 3-phase propulsion system with GTO & associated advantages and issues came in handy for Indian Railways to adopt 3 phase propulsion system with an IGBT-based VVVF control system in the next generation of EMUs.

2.3 Adoption of IGBT-based propulsion

The first such development of VVVF control in EMUs was envisaged in 2002, and the contract was placed on M/s Siemens India for the design, supply, and commissioning of the propulsion system in the new trains to be built by Integral Coach Factory in 2004.  After detailed design, approval, and acceptance, the manufacturing of these trains commenced in the year 2007, and the first such train was rolled out as a prototype in July 2007.  This was followed by another prototype train, and subsequently, a series of 131 trains were built in-between 2007 and 2011 to augment the rolling stock in sub-urban sections of both Central and Western Railways. In addition to the state-of-art propulsion adopted for the first time in EMUs in India, many modern features and passenger-friendly interiors also had been provided.  There was a challenge to design EMU stock for sub-urban travel, and as Mumbai sub-urban section faced unprecedented traffic with a super dense crush load of up to 16 standing passengers per sq.m. of floor space.

About this time, metro systems in India at Delhi introduced the most modern rolling stocks in India in sections of the Delhi Metro and opened up avenues for developing indigenous sources.   With the introduction of modern rolling stock, passenger-friendly and upgraded interiors also had been the expectation of the commuters in the Mumbai area.  Thus, the trains were, for the first time, provided a pleasing interior with relatively newer materials such as  FRP, stainless steel fixtures & seats, and larger windows for better views, etc. These trains were also provided with state-of-art technology traction control systems. With these added features, the new rolling stock management system with intelligent computer-driven propulsion control for achieving precise traction control and braking to enhance the safety of trains and passengers and passenger information and public address was received very well by Mumbai commuters in 2007.

Mumbai Urban Transport Project had undertaken up gradation of Mumbai sub-urban areas with the assistance of  International Bank of Reconstruction and Development(World Bank) and joint funding of Govt. of Maharashtra and Ministry of Railways and added 90 km of the new section under MUTP-I and another 190 km under MUTP-II.  MUTP-II project also required 72 rakes of modern rolling stock, in addition to tracks and other signaling infrastructure between the years 2011 and 2016.  The next stage of modern rolling stock for Mumbai was developed. This time, the contract for the supply of propulsion was placed on M/s Bombardier Transportation,  India, and Germany as a consortium for 72 trains.  Thus, 200 new technology trains were introduced in Mumbai from 2007-2016.  The new design of modern EMU stock also added many features to overcome the limitations of the previous setup.  The system introduced IGBT-based propulsion control with Liquid Cooling Technology, efficient use of space, and further reduced size and weight of the equipment.  The train’s design also added several features to improve the rakes.  In the post-2016 period, Mumbai introduced all AC-EMUs after a complete switchover from  1500V DC traction to a 25 kV AC system, duly retiring all DC EMUs.  The process of the such changeover was very complex as a modification to the existing overhead system, power supply system, and also the rolling stock capable of running in both 1500 V AC and DC was challenging.  As most of the works such as OHE are required to be done during block time, meticulous planning of such a massive project without interruption of sub-urban service was a big challenge, and this itself was a great success story that any railway men to learn.

2.4 Passenger-friendly features

The passenger amenities such as Passenger Information and display system, passenger and driver communication, CCTV cameras for monitoring the safety of passengers, and forced air ventilation have also been provided to have better travel experience. The introduction of CCTV in the trains later has been a significant step in the direction of safety of passengers, especially women commuters.  The passenger information and announcement system to alert the passengers for the next destination in very crowded trains were of great help to passengers.  To improve comfort and reduce carbon dioxide levels inside the coaches, forced ventilation were also provided for the first time in these non-AC trains in 2007. The studies indicated that in the Mumbai suburban trains, the peak hour carbon dioxide concentration used to be close to 1500 ppm before forced ventilation was introduced in the trains. However, these values were measured to be below the threshold of 700 ppm with 15000 cubic meters per hour of forced ventilation in new technology trains. The forced ventilation system was envisaged for such application in railways for the first time. Interiors were designed with non-corrosive materials and new materials such as FRP, polycarbonate, and stainless steel to improve maintainability.

2.5 Train Control and Management System

In the three-phase EMUs, complete train control is done through an onboard computer with a well-established ECN/ETB network and sensors for data acquisition and control. TCMS also integrates the task of fault diagnostics and displays the same in addition to its control task. It is capable of real-time monitoring of the status of all the vital equipment continuously, and the occurrence of faults and takes appropriate protective action, and shuts down the equipment whenever necessary. To improve safety, the new generation trains have vital and safety-related control & monitoring functions such as  Emergency brake, Standstill detection, Vigilance control,   Speed control,    Rollback detection, Speed indication,   Traction release,   Smoke and Fire detection SIL2 Compliant.

3.0 Advantage of new design

The new technology for propulsion systems deploying based PWM converter and 3 phase asynchronous traction motor have many added advantages. The efficiency of the system is higher than 87%. The system also offered regeneration during braking. There has been a further reduction in maintenance downtime due to the new technology. In addition, the new design of the propulsion system has offered lighter equipment used for power conversion, i.e.,  traction transformer, converter, traction motor, etc.; the details are tabulated in table 2. It can be seen that the weight of the major equipment has undergone a downward change due to changes in design. The new design of transformers with a higher capacity (25% higher) weighs less than 3 tons due to the integrated design. The power density of the transformer has also been 0.42 kVA/kg compared to 0.29 kVA/kg with DC propulsion system. The specific power density of the asynchronous traction motors has been 0.1 5kW/kg in new EMUs compared to 0.09 kW/kg (DC motor drives ). The tap changer, switch group, and rectifier had a weight of 3.9 tons, replaced by a PWM converter weighing around 1.5 tons with air cooling and 1300kg with liquid cooling. Wight of the train per passenger works out to 220 kg in the present design of SS coaches. The EMUs have a power intensity of 1.7 kW/passenger (normally designed loading) for suburban trains and 8kw/passenger for long-distance trains (Vandebharat Express). Thus, the new design of the propulsion system has brought down the weight of the propulsion system considerably because of the higher power-to-weight ratio of traction motors, transformers and reduced weight of control equipment. In addition to enhancing the efficiency of energy conversion (87%), lighter set of equipment provided more energy-efficient operation. The system also has regenerative braking having 30% regeneration resulting in lower specific energy consumption (by 30%  to 28.5 kWh/1000GTKM (from 40 kWh/1000 GTKM with DC propulsion system)

Table 2:  Technical features of EMUs deployed  in  India

 4.0 Indigenous Development :

Since 2004, the procurement of EMU propulsion system has been from sources that have developed the technology with a condition for localization of manufacturing in the country.  In 2009, the exercises for developing fully indigenous propulsion supplies were undertaken. As such, the first order was placed to indigenize the entire propulsion equipment within the country through TOT.  Though it took some time to develop a 3-phase IGBT-based propulsion system for EMUs successfully, 12 such Air-conditioned EMU trains were made for the first time and introduced in Mumbai in 2016. The successful development by indigenous suppliers since 2015 has also ensured the price stabilization of propulsion equipment and systems in addition to easier availability.   Benefits in terms of cost of propulsion equipment, the EMU trains, and ease of availability of 3-phase propulsion equipment have been possible due to indigenization.

5.0 Proliferation of technology to other Metro Cities;

With these developments of the EMUs for the Mumbai sub-urban system, the other sub-urban sections of India also started looking for modern EMUs to replace their existing EMU stock, which is about to retire.  While the previous two projects, the design, development, and supplies were made from Germany initially, followed by the localization of supply of major equipment from subsidiaries of these companies in India, no major effort was undertaken to indigenize the technology within the country till 2009. With the Indigenisation efforts and the Make in India initiative, many new designs have evolved in the country, and this equipment is now sourced from within the country since 2015. By now,  the Railways have introduced  300, 12 car wide body EMU rakes and  100, 8 car MEMU rakes with 3 phase IGBT based propulsion in various sub-urban sections such as Mumbai, Chennai, Kolkata, New Delhi, and Secunderabad and in various railways, respectively. With the added advantage of energy efficiency and maintainability, these new technology stocks have provided cost-effective and efficient rail travel.  Since 2017-18, over 100 EMU trains have been manufactured, and another 100 are under manufacture to meet the need of other metro cities.

6.0 Conclusion

The advancement of technology for propulsion has brought in higher efficiency, lower weight of equipment, 30 % regeneration, better maintainability, reduced downtime, and higher availability of the EMUs. The swift changeover to stainless steel car body, secondary air suspension of bogies, and the corrosion-free interior has also resulted in enhanced life of the cars and passenger comfort.

The indigenization of technology has enhanced the availability of propulsion equipment at an affordable and competitive cost and helped the faster proliferation of technology. Due to this energy efficiency, lighter equipment, and advanced design features, the carbon footprint of suburban travel has also become lower. These AC EMU trains, on average, reduce Carbon dioxide production by 1136 tons per annum per train(Mumbai operations) compared to the earlier EMUs with DC propulsion.

With further advancements in semiconductor devices, the system will be more efficient, and the trains will be more environmentally friendly. As time progresses, further reduction in size and weight of the traction system can be achieved with the introduction of SiC devices for converter/ inverter and PM motors for traction, which will have positive environmental impacts.  Once fully operationalized, it is hoped that the development of new generation power devices will also pave the way for the introduction of future EMUs and train sets in India.

7.0 Future challenges of Air-conditioned Suburban travel:

Till 2015, Sub-urban systems of Indian Railways, including Mumbai Sub-Urban, have been provided with non-air-conditioned EMUs without an automatic door closing system. The provision of automatic door closer in the EMUs was envisaged many years back but considered difficult because of regular passenger footboard travel due to overcrowding. The overcrowding and footboard travel is despite the train length changing from 9 to 12 cars and now to 15 cars.

The first such attempt was made in 2015-16 to introduce Air-Conditioned EMUs in Mumbai Suburban with an automatic door closing system. This system faced many challenges in maintaining punctuality on account of additional time of stoppages for the automatic door closing system and also an obstruction to the door closing due to overcrowding.

In trains with an automatic door closing system, doors are interlocked with both the traction system and speed so that unless doors are closed, traction cannot start, and similar to the train coming to zero speed, the doors cannot be opened. Since the desire to deboard and entrain the passenger immediately is very high, the habit change was another challenge.

Developing higher capacity air conditioning to take care of super dense crush loading of passengers.

Thus, the new train design will have to overcome the issues of additional time during stoppages by

  1. enhancing acceleration from the present level of 0.54 m/s2 to 0.8 m/s2 with 50% powering instead 33% as of now
  2. underslung mounting of traction converter, auxiliary converter, etc., with a redesign to have floodproofing of higher levels up to 600 mm.
  3. developing higher capacity air conditioning with the loading going to 16 passengers/sq.m during peak hours.


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