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Prof. S. N. Mahendra is a Professor at the Department of Electrical Engineering at Institute of Technology, Banaras Hindu University. He is better known for his untiring research about Linear Induction Motor Drive for railways. During his working with our institute, he has also taken additional responsibilities including that of IIT-JEE Coordinator (thrice).

Dr. Mahendra has an impressive academic career in the field of electrical engineering. He did his B. Tech. (1970) and M. Tech. (1972) in electrical engineering from our institute and PhD (1976) from City University, London in the field of Current & Flux Densities, Forces & Stiffness in Linear Induction Machines. He has been in the faculty of our institute for over 3 decades. He also served (2003-2005) as Director of NIT Kurukshetra, Haryana. Currently he is Professor and head of the Department of Electrical Engineering at our institute.

Recently, he has been in news media about his proposal to use Linear Induction Motor over conventional Rotary Motor for Metro Railways. Yogesh K. Upadhyaya finds our more about his proposal and research being done at our institute in the subject.

(Please read Campus View section of this chronicle issue for additional information about research being done at our institute, including photos.)

 

(Prof. S. N. Mahendra)

For bio-data of Prof. Mahendra, please click here.

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Q-1: Please explain how linear induction motor (LIM) works for railways

 

LIM BASICS

Figure conceptually explains principle of LIM.

A linear induction motor (LIM) is a developed form of its rotary counterpart. Primary member has a three-phase distributed winding. Secondary member usually consists of an aluminum-plate (known as reaction-rail) that is backed by a mild-steel plate for improving the magnetic circuit. When a three-phase current flows in the primary winding, a linear traveling field is produced in the air-gap that interacts with the secondary reaction-rail and develops a linear force much the same way as torque in a rotary induction motor. The linear synchronous speed in LIM is defined as Vs = 2tp.f where tp is the pole-pitch and f is the supply frequency.

 

Q-2: What is the advantage of LIM drive over rotary motor drive for metros?

The urban transportation problem in cities with population more than one million is becoming dangerously critical. If long-term corrective measures are not taken properly, the transport system of these cities will collapse. In this context Linear Induction Motor (LIM) based transport system has been proposed as a long-term economical and environment-friendly solution of the urban transport problem. The technology of LIM based traction system has been successfully indigenized in Institute of Technology, Banaras Hindu University and has been well appreciated at various levels. Specific advantages will be dealt later. (These will be based on experiences gathered from systems in operation for more than two decades.)

A typical blue-print for adoption of this technology for solving urban transport problem may include following objectives to develop and standardize methodology/technique:

1.      Survey of existing ground conditions.

2.      Excavation process and equipment selection.

3.      Design of terminal and platform.

4.      Track design.

5.      Design of Linear Induction Motor and Reaction Rail.

6.      Design of current collection, control system and controller.

7.      Conducting studies related to Socio-economic impact analysis of the proposed system

8.      Organize seminars for generating information listed above and bridging the perception gapes between technology, its implementation and the users.

 

Q-3: Where the LIM technology is in use for railways? Why it is not popular yet compared to rotary drive?

LIM technology is being primarily applied in metros with advantage. At international level activities related to development of LIM based transport system have been going on for quite some time. Bombardier Inc., Canada, & Japanese Subway Association, Japan, have achieved effective breakthrough by implementing the technology to urban transport system. Salient points related to experience of these organizations is given below.

 

JAPANESE SUBWAY ASSOCIATION

1.      Adopted in March 20, 1990

2.      Track length 15.0 km covering 17 stations.

3.      System with 1200 cars realises 3-minute headway for 4-car operation and carries about 2.7 million passengers daily.

4.      Line is essential means of transportation as it connects business districts & suburban residential areas approximately 30 minutes away.

5.      Lowered bogie floor reduced tunnel cross-section by 40%; length, width and height of subway cars by about 3 m, 0.3 m and 0.7 m respectively and total estimated construction cost by 20%.

6.      100 kW naturally cooled LIM mounted on each bogie.

7.      Reaction rail (360-mm wide, 5-mm thick aluminum-plate & 22-mm thick iron-plate) fixed to the sleepers along the rails.

8.      Accelerating/braking-force & LIM speed controlled by inverting overhead centenary 1500 V D.C. to 3-phase VVVF a. c.

Salient Features of Tokyo Metropolitan Subway Line 12

1.      Second Japanese Linear Metro. Established in December 1991. Extended in 1997 & 2000.

2.      Track length 12.9 km with 12 stations. Proposed track length 27.8 km with 26 stations.

3.      System has 124 cars for 8-car operation to realize a 5-minute minimum headway.

4.      Power supply is through 1500 V D.C. catenary.

5.      Subway Line 12 links busy areas in the heart of Tokyo via an underground loop and carries one million passengers a day.

Japanese Field trial Experiences

1.      For gap length 10mm to 13mm, gap-variation observed 3mm.

2.      Acceleration (7-10%) deceleration (6-9%) higher for 10mm gap as compared to 13mm gap.

3.      4% less electric consumption for 10mm gap than for 13mm.

4.      Insufficient rail greasing increased wave-like-pattern wearing of the rail surface & left-right swinging of trains. With sufficient rail greasing rail corrugation was prevented & wave-like-patterns of wearing disappeared.

5.      Tokyo Metropolitan Subway Line 12 was possible due to Linear Metro's advantages like ability to handle sharp curves & steep gradients (as existing subway and train lines did not permit new lines due to serious limitation of space availability).

BOMBARDIER INC. CANADA

·        Bombardier Inc. has been the world leader in applying LIM technology to urban transport system. First revenue service started in 1984.

·        Major user of LIM, the British Columbia Rapid Transit Company (also operator of Vancouver SkyTrain) reports great satisfaction.

·        Canadian consortium bid (headed by Bombardier Inc., SNC-Lavalin and BC Transit) for supply of LIM based advanced LRT system MK II for Kuala Lumpur, Malaysia, selected against rival bids of France, Germany & Japan offering rotary motor based systems.

·        Consortium’s bid was for supply of 70 ART MK II vehicles with LIM propulsion & steerable suspension to provide service for 24-stations spread over 29 km (4.4 km tunnel, 2.11 km at grade & 22.27 km elevated). Phase I made operational during the Commonwealth Games in 1998. Present 10,000 pphpd (Pallets per hour per direction) capacity can accommodate designed 30,000 pphpd.

Operational experiences

1.      Mechanical failures from debris or insulation failures are negligible.

2.      Maintenance of LIM limited to occasional blowing out of dirt from the end windings. No need for inspection or overhaul of gearboxes or couplings.

3.      Trucks made lighter than the conventional subway trucks.

4.      Axles of steerable-axle truck steer with the track curvature. Thus, almost eliminating flange-contact with the rails; reducing objectionable-noise found with fixed-axle trucks; improving ride quality; increasing wheel-life and reducing truck-maintenance

5.      Wheels machined after 1Lakh km. Removing 1mm to restore optimal conical profile, thus wheel-life is about 10 Lakh km.

6.      Wear rate of disc brakes very low as LIM provides almost all the braking.

7.      Braking overshoot does not occur and train performance is repeatable. Headway reliability thus is above 98% (at 3 minutes headway operation).

8.      SkyTrain per-unit energy-consumption cost same as Toronto subway.

9.      LIM ALRT success suggests its suitability for conventional transit operation. Hence issue is not technical but economical.

10.    After twenty years of service the selection of LIM traction to meet the performance and operational requirement remains the proper choice.

11.    Observation in favour of LIM propulsion negate criticisms like ‘Technology is not proven’, ‘Efficiency is lower than DC motors’, ‘air gap would be a serious maintenance problem’ and similar more.

12.    Bombardier Inc. appreciation of LIM based traction has special significance, as it is a supplier of both rotary steel-wheel-on-steel-rail (Ankara Metro & London Docklands Light Railways) and LIM automated system.

As regards answer to the question ‘why is it not popular yet compared to rotary drives?’ – Partly the Question has been answered in point 11 above. In addition, the other main reason perhaps is that there is a technology-appreciation-gap between the merits of the technology and the decision makers.

Q-4: Please describe the research work on LIM being done at our institute.

BHU has been working on LIM based propulsion working systems for more than 3-decades starting from:

•         shuttle-propulsion for weaving looms (1971-73)

•         surface-transport (1980 continuing)

•         overhead-transport (1983 continuing)

•         Conveyor-belt/material handling (1986 continuing)

•         testing-methodologies & test-rigs (1980-87)

•         design & analysis methodologies standardization (1973-97)

•         Malaviya Center LIM metro system (1997 continuing)

•         Independent control of forces of propulsion & attraction (2003 continuing)

Few working systems developed in IT-BHU

IT-BHU over the three-and-half-decades has pioneered and indigenously developed Linear Induction Motor (LIM) based traction technology for solving the urban transportation problem of Indian cities. A LIM based demonstrative system in the Malaviya Center for Development of Low Cost LIM Propelled Metro at IT-BHU is operating since 1999 along a 60-meter Meter-Gauge track and carries 15-20 adults.

The R&D has reached a stage when it has become necessary that related and supportive expertise already available at national level be integrated with the Linear Induction Motor (LIM) based traction technology developed at IT-BHU by adopting a consortium approach. If required, expertise available at International level may also be integrated suitably.

For additional information about research being undertaken at our institute, more discussion about LIM technology, photos, etc. please refer to Campus View section in this issue of Chronicle.

Q-5 Does the Project have any commercial application

 The increasing explosion of population, industrialization, decrease of useable-land have compelled the scientist, technologist, planners, designers and government organization to search an alternative which is economical and eco-friendly both. The cities having population more than one million are eligible for underground metros, as most of these cities do not have any scope for:

• Widening of the existing roads (as this process is already saturated)
• Use of an over-head transport system (due to narrow roads)

For this reason there appears to be no other alternative except to go for effective and safe utilization of underground technology.

The Project has commercial application because underground metro, in the present situation, is the best solution for the urban transportation problem of Indian cities. The outcome of the project has good export market also because problem of urban cities in other countries is no different than that in India. The underground urban transport system is sustainable and safe mode for transportation. It will save:

• The city from pollution,
• The commuters from health-hazards & wastage of travel-time.

 

Q-6:

 The question now arises ‘Can LIM technology be developed indigenously?’

The answer has been best given by Late Shri J. Upadhyay, Former Member Railway Board, Visiting Professor & Advisor AICTE project entitled LIM Propelled Rail Metro System at I.T. - B.H.U. and the answer (Upadhyay 1999) has been reproduced below:

“Indigenous development of any technology reduces the overall initial and recurring costs drastically. It has been our experience in Indian Railway that an indigenously developed electric locomotive or its subsystem cost approximately 30-40% of the imported version. Hence it is relevant to dwell upon this aspect in some detail.

a) The test setup at IT-BHU, which perhaps is the first of its kind in this country in the context of a new technology, was developed locally including design of the LIM. The various track-related parameters have remained reasonably stable without much maintenance. Hence we may reasonably infer that design of the LIM and most of the subsystems can be done with the available expertise if pooled on all India basis. It may be necessary to borrow from the expertise developed abroad in same critical areas e.g. rolling stock, steerable bogies & VVVF control strategy, to shorten the over-all time frame.

b) Therefore, further development of this technology will call for formation of a consortium at the national level consisting of user ministries, public sector manufacturing companies including Railway workshops and technical institutions.

It must be clearly understood, that LIM rail-metro is a proven and cost-effective technology as borne out by the experience of LIM metros in Osaka and Tokyo. It is for us to recognize its virtues and do away with our reservations so as to achieve self sufficiency in this field of advanced technology by pooling resources available within the country through a consortium approach. This is in line with the strategy adopted even in advanced countries.”

Justification for indigenous development of LIM based traction technology in India

• At a later date if this technology is imported, we will not only pay for equipment and technology but also the developmental cost.
• In fact, the supplier of the equipment and technology will be gaining experience at our cost whereas we will remain ignorant even after paying for it.
• Furthermore, we will remain dependent on the supplier for any modification or up-gradation of the technology in future as it is happening in almost all the technology transfers.

 

Q-7: Please tell us more about yourself.

I was born in Khairabad (Dist. Sitapur) UP, India in 1949. My school and college education was done at Lucknow. I studied at Loreto Convent and Christ Church School. Then after, I joined Kanyakubi College and Colvin Taluqdars’ College. After passing Intermediate College exam by UP State Board in 1966, I joined IT-BHU for Electrical Engineering, where I obtained B. Tech. and M. Tech. degree in electrical engineering. Later on, I did my PhD in electrical engineering from City University in London. After returning to India, I have been teaching in the department of electrical engineering at our institute; except for few years, when I was appointed as Director of NIT, Kurukshetra.  

 

I am involved in activities of various technical societies and have been awarded as Fellow of Institution of Electrical Engineers (FIEE) U.K.

 

My family includes my wife Chhaya and children Ankur and Pallav. My hobbies include Reading, watching TV, etc. My life philosophy is to live a life by integrating one-self with nature in perfect harmony for happiness on Man & his environment

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Prof. Mahendra can be reached at: mahendra20@gmail.com

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Additional Links

1) LIM system better than the one used in Delhi Metro

http://www.hindu.com/2008/11/18/stories/2008111852510300.htm

2) LIM system better than used in Delhi metro: BHU Prof

http://www.zeenews.com/states/2008-11-16/484072news.html

3) News in Hindi-Development of cheaper metro rails

http://in.jagran.yahoo.com/news/national/general/5_1_4994170/

4) Funakawa Information & Environment Technology Co., LTD.

http://www.funaken.net/result01_en.php

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Philosophical difference between REM based & LIM based Traction - A Historical View

Primitive Transport: Carrying and Dragging

 

Green: Minimum Friction desired.         

Blue: Pull from pull-producer to pull-receiver

Red: Adhesion which is essentially desired in all types of transport systems between driving wheel and the facing stationary surface. However in LIM systems the LIM is used as pull producer and therefore all the wheels are only rolling wheels.  

 

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