My Journey with Linear Induction Motor

My Journey with Linear Induction Motor Dr. S. N. MAHENDRA* More than 4-decades agoR&D related to Linear Induction Motor based propulsion was started in the Department of Electrical Engineering. Initially it started as a working model for Engineering Models Exhibition.Later the activities covered a range of applications like shuttle-propulsion in power-looms to material-handling to surface/ overhead/underground/ people-mover transportation systems. The applications developed and the R&D activities in chronological order have been as follows: • • • • • • • • • • • • •

[1]

Shuttle-propulsion for weaving looms (1971-73) Design & analysis methodologies standardization (1973-97)[11] Surface-transportsystem (1980 continuing)[3, 12] Testing-methodologies & test-rigs (1980-87) Overhead-transportsystems (1983 continuing)[9] Conveyor-belt/material handling (1986 continuing)[9] LIM Powered People Mover system for closed-loop circular track for Connaught Place people transport system (1986-2013[4, 5] Malaviya Center for low cost LIM metro system (1997 continuing)[3, 9, 11] Independent control of forces of propulsion & attraction (2003 continuing)[12] LIM powered sieving system for sorting ore near mines (2003 continuing) LIM based traction elevator for vehicle parking (2012 continuing)[7] Linear Switched reluctance motor (2014 continuing) Segmented linear motor based propulsion for circular looms (2014 continuing)[4]

The present article is based on the experiences, problems-faced and developments made during the journey of the author with Linear Induction Motor (LIM). The Journey Begins The journey started in an interesting manner during MODEX-70. Professor S. K. Kak, formerVice Chancellor GoutamBudh Technical University, Noida, was the student Convener of the famous Engineering Models Exhibition and I was a member of his core organization team. He asked me tomake and present a model in the exhibition. He was himself heading a huge team of dedicated students in making a working model of Musical Fountain (similar to the first of its type made and exhibited during EXPO-70 in Japan). When I asked him what shouldI make? He

suggested me to make a set of U-cores with DC coils which are excited in a sequence such that a horizontal component of the attraction force is produced in the iron plates fixed to the moving member facing the cores resulting innecessary force for linear motion (similar to that inalinear stepper motor). With detailed diagrams and design I met Professor M. Bhattacharrya in the Electrical Machines Lab for his suggestions and advice. He patiently listened to the whole idea and encouraging me (as if I was in the process of inventing something new and great) said „why not give A.C. supply instead of D.C. supply‟. To this I said „Sir, why not provide a 3-phase distributed winding in the core like in an induction motor and energies the three-phases with 3-phase A.C.‟. He just said „Good. Go ahead.‟ Thus unknowingly my journey with Linear Induction Motor (LIM) started. The working model was made and exhibited in room no. F-5 (Rampur Hall) near the first pillar on the left side. Objects of different shapes made of aluminum were shown moving from one end of the core to the other in a linear direction along the length of the core when the winding was energized. I was feeling great as if I have done something really great, till a visitor after seeing the exhibit said that a similar machine was made by Professor E. R. Laithwaite long back. I met Professor Bhattacharryathe next day and asked him „Sir,do you know this fact‟. He coolly said „Yes‟. I was pained (I do not know why) and complained „Sir why did you not tell me this during the first meeting itself so that I would not have exhibited my ignorance and felt embarrassed‟. The words he spoke after this have inspired me and encouraged me during all the development work that I have done and narrated in this article. He said, “If I had told you earlier you would not have experienced in you the ability to create/invent something new. Now you have confidence that you can also think original and may be in future you may make new things”. I can say that this is a true quality of a teacher wherein a teacher not only teaches but creates opportunity in his student to realize the inherent strengths/weaknesses in him/her. His words did come true at many occasions whenever

*Professor, Department of Electrical Engineering, IIT (BHU), Varanasi-221005

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a new machine was made and for all this I give credit to him. Now I will take you along with this journey from 1971 till date highlighting milestones and pitfalls and also the positive effect of a good teacher. Period 1971 to 1972 During this period I continued with development of LIM for shuttle propulsion in power looms as one of the industrialist of Varanasi showed interest and offered to support for development of handloom propelled by LIM. During implementation shortcomings were observed and three modified versions of the system were made as shown in Figs.1-3. Fig. 3 shows a novel geometry conceived and made by the author. It consists of a Single Primary Double Secondary LIM (1972). This was modified later by fitting bearings for movement and lateral guidance of an Overhead transport system. The running-rails apart from mechanical strength to the overhead system also provided return-path for magnetic flux, thusthere was additional requirement of Aluminum Reaction Rail only (1983) and a net saving of backing iron along the length of track which would have been provide otherwise for strengthening the magnetic circuit.

Fig.3Single Primary Double Secondary LIM (fitted with bearings for movement and lateral guidance of OH transport system) [1972, 1983] The small motor has carried the load of 1-adult/2children and has application in over-head transport system.

Fig.1 Back to back 3-phase LIM for automatic shuttle propulsion (1971)

Fig.2 single phase LIM with starting windings at the ends for producing starting force (1972)

The 1972 M. Tech. project report based on the work concluded as follows: “The study of various types of linear oscillating induction motors made has clearly shown the possibility of developing self-oscillating/switchoscillating linear motors operating on threephase/single-phase supply systems. The conclusions drawn out by consideration of force/speed characteristics and mathematical analysis of respective machines clearly indicate a definite possibility of developing a method of designing of such machines. It must be realized that the perpetual oscillation of these machines and their constructional features make them one of the most complex of the electromagnetic devices and these are, therefore, not amenable to any simple analytical treatment. Moreover, the basic shortcoming of such machines is the existence of an inherent mechanical friction and the problem of perfect alignment. The ideal arrangement will be one in which the runner moves in air under the influence of electromagnetic field developed in such machines, without touching the stationary member. The above motion must always maintain a constant „air-gap length‟ through its

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length of traverse. Another requirement to make an ideal machine is a long bed of traverse – preferably lying between -∞ and +∞. Although none of the above requirements are practical, they do point towards definite possibility of further development.” Period 1973 to 1978 The concluding remarks of the report were challenging hence I got registered with Professor M. Bhattacharrya in 1973 to work further on this problem. We had long sittings in the Department and in his RajputanaHostel warden quarter. Then one day he said, “Som now the time has come that you go out and get far better environment, facilities and exposure”. This again exhibited the greatnesses of Professor M. Bhattacharrya because normally not many Ph.D. supervisors will tell this to their research scholars. I was bit disturbed but then the „Government of India‟s National Scholarship for Study Abroad‟ award letter indicating that with this scholarship I could go to any part of the world to work in the field of LIM. I was excited and contacted the giants in this subject at that time - Professor E. R. Laithwaite at Imperial College of Science & Technology, London, and through him Professor A. J. Ellision, Head of Electrical Engineering Department, The City University, London, Professor SakaeYammamura of Tokyo University, Japan, and Professor S. A. Nasar of University of Kentucky, USA. I got encouragement and positive response from all three of them. Now came the problem of choosing a country from these three countries for which I got the guidance from Professor R. J. Galgali, Department of Chemistry, BHU – a God gifted person who helped so many in so many ways during his stay in BHU.Based on his analysis and intuition he said „you go to London, the UK - a country which has the roots of the subject and Professor E. R. Laithwaite is known as the father of Linear Induction Motors‟. My correspondences with Professor E. R. Laithwaite, Professor S. A. Nasar, Professor Sakae Yammauraand Professor A. J. Ellisionfor seeking possibility of doing research under them have been a memorable part of my journey with LIM. It is memorable because these correspondences reflect the nature and seriousness which these professors had for the prospective research scholars – and this is essential even now. Excerpts from the lettersof Professor E. R.

Laithwaite are given below to show how helpful and considerate he has been in his correspondence. “….All these things are indicative of toils and troubles of a professor at Imperial College. If you were to register for Ph. D. you will be supervised by me, as Dr. Eastham is leaving, and I have already so little time for casual visitors, it would not be fair to ask you to work with me at this time.” April 4, 1973 “….May I first offer you my sincere congratulations on being awarded the National Scholarship for Study Abroad. What I said earlier is still true. It would be unfair for someone like yourself to be under my direct supervision, as my outside commitments are so heavy that it could well be that we will talk to each other only twice a year. However, we have very close ties with City University…..there my personal friend Professor A. J. Ellison is working on linear motors……would be willing to accept you…..and it would mean that you still have access to me, probably for longer than if you worked in my department……….. I hope you will do this and I will have the pleasure of meeting you before the end of this year.” May 17, 1973

The net outcome of the correspondence was that I joined The City University (TCU), London, and after meeting my guide Professor A. J. Ellision I visited Imperial College of Science & Technology, London, to report to Professor E. R. Laithwaite and take his advice and direction for my research in TCU. The few hours meeting was a memorable one as every word of his within a short time had enchanted me with the greatness of linear induction motors as experienced by him. He demonstrated so many working systems he had made to understand „what is induction motor‟ (as he had often repeated during his class lectures that he has not been able to understand what induction is). He also demonstrated his famous transverse flux linear induction motor. I was asked to hold a small „vehicle‟ (with secondary aluminum plate underneath) from one end of the transverse flux linear induction motor primary member and leave it when he tells me. To my surprise the vehicle left by me on the track „flew‟ over the entire length of transverse flux linear induction motor primary member without touching the track or falling sideways due to the presence of electromagnetic forces of levitation and lateral guidance produced in what he called the „magneticriver‟ created by him. The vehicle was caught by him at the other end. During this meeting Professor Laithwaite also told me not to rush for a quick degree

MY JOURNEY WITH LINEAR INDUCTION MOTOR but do a good work. He also told me that it took him seven years to obtain his Ph.D. degree. Perhaps he observed some reaction on my face and reacted immediately, „It‟s not that I did not do much during this period. It got delayed because I did not have time to put all my work in a thesis form.‟ After this I met him many times without any problem, attended his inspiring lectures and watched his BBC Christmas Special Lectures. I remember each and every bit of it. My Stay at the City University, London My guide Professor A. J. Ellision right from day one had been very kind to me and gave me time whenever I wanted to discuss my research progress and take his advice. By nature he was also very friendly and kind to everyone and this quality of his benefitted me a lot as whenever (while meeting a person from universities and industriesin and around London) I told that I am working with Professor A. J. Ellision he/she would offer to help me in my research work in whatever way it was possible for him/her. I was thus able to effectively integrate the rich academic and industrial exposure which I received in the UK and also in European citieswhich I visited with IEE and IEEE Students Travel Scholarships. During one of the initial meetings when I told him that I understand the inputs and outputs of an electromagnetic system but not what is happening in the electromagnetic system. He said do you want to go inside this black-box? Do you have the courage? My reply was „yes‟as I wanted to explore the links between the electrical input and mechanical output of an electromagnetic system. I knew that till I do not understand this I will never be able to effectively design these electromagnetic systems by providing a balance between all the five basic circuits of electromagnetic device viz. electrical, magnetic, mechanical, thermal and dielectric circuits of an electromagnetic system. He gave me green signal. In yet another meeting after about six months when I approached him with a proposal to make circular transverse flux induction motor so that one can test transverse flux induction motor under dynamic conditions (as the set-up at Imperial College of Science & Technology, London, was good for standstill tests only). I had located U-shaped stampings in the Department store and had drawn a diagram also. He patiently listened to me and said „OK you play with this till we finalize your research plan‟. This resulted in development of Basic transverse Flux Circular

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Motor. When it was shown to the professors of Imperial College of Science & Technology, London, one of them - Professor Freeman - remarked „Oh God this is a missing link between all the electric motors made so far‟. Later BTFCM was placed as an exhibit during IEEE INTERMAG-75 at Imperial College of Science & Technology, London, - the only exhibit from a research scholar as all other exhibits were of senior professors. Through research a link between the electrical inputs and mechanical outputs via magnetic circuit was thoroughly analyzed using the Maxwell‟s equations and Maxwell‟s Second Stress Tensor. The predicted 3components of flux densities, forces and the performance closely matched with the experimental results obtained from BTFCM under dynamic conditions. The work was appreciated by IEE (UK) through “IEE Student Premium Award‟.

Back in BHU1978 onwards – activities & milestones On return I had planned to integrate the knowledge gathered in London to remove the weaknesses of the working system developed before going to London. In achieving this objective the encouragement and support received from Professor G. Rajsekar needs special mention. He, after looking at my thesis, asked me „Can you translate your research into working systems to demonstrate the principle?‟ My reply was in affirmative. I told him that the main difficulty was in the laying of track along which the system has to move. He took this as a challenge and in his own dynamic way persuaded his friend Mr. K. P. Jairam, the then General Manger, DLW, Varanasi, to extend support for making the working system. I am grateful to DLW, its Officers and workers who whole heartedly extended help to make the whole system as it was unconventional in many ways. The 1:15 scale LIM based BHU-DLW surface transport model moving along 33-m oval track was later exhibited number of times in the Railway Pavelion of India International Fairs at Pragati Maidan, New Delhi. Being the only working system of its type in the country, it attracted attention of the visitors including the then Prime Minister of India Shri Rajeev Gandhi who remarked to ShriMadhaoRaoScindia, the then Railway minister that „this could be the future transport system for India‟. Since then a large number of LIM based working systems including a full-scale system carrying

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about 20-adults moving along 65-m meter-gauge track has been made with the help of UG/PG students and financial support from organizations like AICTE. To cut the long story short I willnarrate my journey through photographs and brief description of some of the working systems developed along withtheir usefulness. (a) 1:15 scale LIM based BHU-DLW Surface Transport working System moving along 33m oval track [1981, 2001]

demonstrated the indigenous capabilities developed in the design/fabrication of LIM based systems as per specifications.

Fig 5 Trolley with LIM Primary lifted-up to show the underside arrangement

Fig 4 ShriDigvijay Singh, Min of State for Railways, Professor YC Simadhari, VC-BHU &Shri O. P. Gupta, GM, DLW, inspecting 15:1 BHU-DLW LIM Surface Transport System [2001]

The trolley safely moves along very sharp curves (with about 6-m diameter even at 16kmph) due to the presence of force of attraction between the moving primary iron & the secondary reaction rail. A unique feature of LIM based system in contrast to any other conventional wheel-rail/road systems wherein (with increase in speed) the wheel-rail/road grip becomes poor leading to accidents. The working system effectively bridges the gap between the technology & decision makers as it explains the principle of operation and the inherent advantages easily. (b) LIM based surface transport system for underground metro moving along 65-m meter-gauge track at Malaviya Center for Development of LIM Propelled Rail Metro System: [1997, 1998, 2001] Working system was primarily made to verify the developed design methodology. It also

Fig 6 Trolley fitted with LIM Primary operating on 65m meter-gauge track &Shri. S.K.Khanna, MEL, IR Board, Shri O. P. Gupta, GM, DLW, &Shri J. Upadhyay, ExMEL, IR Board doing foot-plate inspection of the LIM Propelled Rail Metro System

Fig 7 ShriDigvijay Singh, Min of State for Railways, Professor Y.C. Simadhari, VC-BHU & Prof. P. C. Upadhyay, Registrar BHU, doing foot-plate inspection [2001]

MY JOURNEY WITH LINEAR INDUCTION MOTOR The working system attracted attention of decision makers like the then Minister of State for Railways, present & former Indian Railway Board Members (Elect.).

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The proposal can be implemented in regions where other modes of transport are neither feasible nor economical and the ropeways are the only choice.

The system also attracted attention of press & TV media and its working along with the Institute R&D has been widely reported by many TV channels including „Imaging Sciences‟ programme of national DD TV. The working system has acted as an effective bridge between the technology and prototype stage for adoption. (c) LIM Powered People Mover system for closedloop circular track for Connaught Place people transport system. (The moving platform at 5-10 kmph can complete one circle in 15-30 min) [1986, 2013]

Fig 9 LIM based ropeways in which the rope is stationery

Concluding remarks & suggestion for further work Fig 8 LIM Powered People Mover system for closed-loop circular track for Connaught Place people transport system

The model demonstrates feasibility of integration between metro terminals and other public transport modes as well as the shopping points in city-centers like Connaught Place. The cost analysis has been done and the proposal has been recently presented in two international conferences. International reactions are being received (d) LIM based ropeways in which the rope is stationery [2010, 2011] Made primarily to demonstrate the principle of ropeways in which the rope is stationery and the trolley moves due to linear force produced by LIM mounted on the trolley. Since moving parts are only the wheels on bearings (with no drum/gears connecting to the electric motor or the moving-ropes) the maintenance will be bare minimum. It has provision for remote monitoring and control.

One important thing brought out in this article needs special mention again. The role of teachers like Professor M. Bhattacharrya, Professor G. Rajsekar, Professor E. R. Laithwaite, Professor A. J. Ellison, who had so coolly played their role in shaping me and my work on LIM needs to be appreciated for the fact that the role of a good teacher is the most essentialfactor in shaping the „future-components‟ of the society viz. the Man. The technological developments may assist a teacher but these shall never be able to become a substitute for the qualities of a good teacher. Another point which I would like to highlight here is the international interest shown in LIM activities by countries like Japan. In February 2007 Mr. Masahiro Ando, P.E. Professional Engineer as Authorized by the Japanese Government &Dr. Vijay Kumar Jatiya Funakawa Information & Environment Technology Co. Ltd., Tokyo, and Manager dealing in Business Planning & International Business Operations, visited for discussions for providing an effective solution to the ever-growing

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urban transportation problem in the Indian cities. In Japan the technology has been adopted through a consortium (Japanese Subway Association) approach which included people from Academic/Associations, Subway Operators, Development Components and Administration [13] (supportive organizations). Figures below show the usage up to 2006 and distinct advantages observed by JSA.

Merit of Linear Metro

Compact ＆ Comfort ◆Lower than a conventional subway car floor height by 30 cm, the Linear Metro uses limited space more effectively. Conventional subway

Linear Metro

Comfortable interior Diameter Interior height

Number of passengers in Japan

Linear motor Small-diameter wheels

◆ Up to March 2006 since the first introduction in 1990 in Osaka, Japan the Linear Metro systems carried safely more than around 2.2 billion passengers in total. 400

Copyright © Japan

Subway

Association. 2007. All rights reserved

18

On the basis of experiences gathered from linear metros operating in Japan the Japanese have taken a blanket decision to make all future metros in the country Linear Motor based only. Two typical metros in operation in Japan are shown below.

(million passengers / year)

330 million 300

2.2 Billion Passengers (1990~2006)

200

Floor height

Reaction plate

Application example１

100

Osaka City 0 1990

2000

2006

Copyright © Japan

2010 (year)

Subway Association. 2007. All rights reserved

6


Steep gradient Non-adhesion drive allows even inclines of over 60‰ to be negotiated .

Copyright © Japan

Subway


25

Subway


29

Application example2

Tokyo Metropolitan

Copyright © Japan

Subway


10


Sharp curve The Linear Metro handles sharp curves effortlessly.

Quiet，smooth operation，with no squealing.

Copyright © Japan

Subway


Copyright © Japan

My presentation in February 2007 was followed by that of Mr. Ando [13]and the two presentations received lot of interest followed by discussion from the audience in the lecture hall as well from the media. Prof. G Rajsekhar, former Dean Faculty of 11

MY JOURNEY WITH LINEAR INDUCTION MOTOR Engineering and Technology and Professor Department Electrical Engineering IT–BHU, traced the history of LIM R&D activities in the Department. He wondered that if the country had implemented the Departmental proposal made in early 80‟s, India would have been leaders in this field by now. He was hopeful that now thevisit of Mr. Ando and Dr. Jatiya will lead to an effective integration of the „rich experience of Japanese Subway Association (JSA) in the implementation of Linear Metro in Japan‟ with the „fundamental LIM based R&D achievements of IT– BHU‟.He was optimistic and confident that jointly the two organizations can provide a solution for the urban transportation problem in India and all over the world. Mr. Ando who is „father of linear metro in Japan‟ appreciated the R&D in BHU and felt a need for exploring the possibility of solving the urban transportation problem in Indian cities through linear metro. There was a general consensus that the Government of India and the Government of Japan may be requested to initiate steps for joint ventures/participation in making Linear Metro based joint project proposals for Indian cities. To start with the first Linear Metro may be made operational in Varanasi as it would be a fitting tribute to Mahamana Pandit Madan Mohan Malaviyaji – the founder of Banaras Hindu University. The other reasons being that: Due to Sarnath many Japanese visit Varanasi and this will help them in moving around comfortably Any activity in Varanasi catches attention the world-over, and The R&D at BHU can be easily integrated. Since then efforts were made at many levels to initiate the activity between Japan and Varanasi but with no success so far. It is expected that with renewed efforts being made with the new ministry at the center wherein Varanasi happens to be the Prime Minister‟s constituency, the proposal may come through. During the years a large number of technologies/working-systems have been developed and are ready for adoption by the user industries. These are: a. LIM powered systems for: (i) Overhead/Underground/Surface transportation, (ii) Material Handling, (iii) Ropeways in which the rope does not move, (iv) Vertical elevators for vehicle parking,

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(v) People mover system for Connaught Place b. Control strategies for energy saving in LIM based systems including independent control of propulsion & attraction forces produced c. Handloom for visually handicapped. Journey with a subject never ends. People/researchers may change but so far as the R&D in the subject is concerned it continues and I have all hope that this will happen in our Department also. In this regard it is worthwhile now to explore the possibility of industry/academic-institution participation for further development and effective absorption of Linear Induction Motor (LIM) based systems which have been developed & tested in the Department.

Acknowledgement Following individuals & Agencies support is gratefully acknowledged: MHRD/AICTE 1994-2000: For R&D Grants to develop LIM propelled transport system operating with 15-adult load on a 65-m meter-gauge track for demonstrating the technical feasibility Prof. Hari Gautam 1996(the then later Chairman UGC): For supporting Malaviya Centre for “Development and of Low Cost LIM Propelled Rail Metro IT-BHU.

VC BHU & creation of Evaluation System” in

Shri Jagdish Upadhyay 1994-2000(Former Member Electrical Railway Board, Visiting Professor & Advisor AICTE project entitled LIM Propelled Rail Metro System): For giving a practical shape to LIM traction R&D activities and projecting it for its adoption in India. Professor M. Bhattacharrya (since 1973) for starting my journey with LIM and Professor G. Rajsekar (since 1977) for providing the necessary thrust which was a great helped in making of BHUDLW model that helped in bridging the gap between the technology and the decision makers. „Government of India‟s National Scholarship for Study Abroad‟ (1973-77) that helped in acquiring advanced knowledge related to LIM technology from abroad.

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Graduate, Post-graduate & Research Scholars 1977 till date: For assistance in fabricating LIM powered working models of various applications to demonstrate principle of LIM propulsion.

References [1] S. N. Mahendra: Linear oscillating induction motors, M. Tech. Project under Professor M. Bhattacharry submitted in Dept of Elect. Engg., IT-BHU, 1982 [2] Mahendra, S.N. &Upadhyay, J.:Low-Cost LIM Propelled Metro System for Indian Cities, Urban Railways, v 2, Issue II, Nov. 1999, p 15-21. [3] S.N. Mahendra, and J. Upadhyay, R&D Project at IT-BHU for Development of LIM Propelled Rail Metro for Medium Size Indian Cities,8th World Conference on Transport Research (WCTR-98), Antwerp, Belgium, July 12-17, 1998. Special Interest Group (SIG-1): Urban Development Problems. [4] S. N. Mahendra, Ayan Das, Shailendra. N Jaiswal:„Segmented LIM based Passenger Conveyor System for Circular Route: A Case Study‟, Research SymposiumUrban Mobility India (UMI) Conference and Expo, New Delhi, 2013http://www.scribd.com/doc/189741371/Linea r-Induction-Motor-based-Passenger-ConveyorSystem [5] S N Mahendra & S Jaiswal,“Linear Induction Motor Propelled Pms For Closed Loop Circular Track”, International Conference on Transportation system studies, IIT Delhi, 1986 [6] Raj Kumar Sinha& Naidu VenkatramanaRao: „LIM based ropeways‟, B. Tech. Project submitted under Professor S. N. Mahendra in Dept of Elect. Engg., IIT (BHU), 2010

[7] Anuj Kumar:„Design and Analysis of Traction Elevators‟,M. Tech. dissertation submitted under Professor S. N. Mahendra in Dept of Elect. Engg., IIT (BHU), 2013 [8] LakshmareddyDondeti:„Performance analysis of LIM based ropeway system operating under various supply conditions‟, M. Tech. dissertation submitted under Professor S. N. Mahendra in Dept of Elect. Engg., IIT (BHU), 2011 [9] S. N. Mahendra, LakshmareddyDondeti, U. Ram GopalVarma: Linear Induction Motor Based Material Handling Systems for Saving Clean Energy, IEI International Conference on “Green Power Generation: Vision 2020”, IEI Anpara Local Centre, Sonebhadra, Renusagar, 10th to 12th December, 2010 [10] S. N. Mahendra: Current & flux distributions, forces &stiffnesses in Linear Induction Machines Ph. D. thesis submitted under AJ Ellision at The City University, London, 1977. [11] S.N. Mahendra: LIM Based Traction: Philosophy, Selection, Design-aspects & Application to Transport Sector, International Workshop on „LIM Propelled Rail Metro System‟ Department of Electrical Engineering, IT-BHU, January 8-9, 1999, pA-1 to A21. [12] S. N. Mahendra, SrihariVelisetti, Kunwar Aditya: „Implementation of VVVF, CVVF &CFVV Control Strategies for Control of LIM‟,IEEE 3rd International Conference on Sustainable Energy Technologies (ICSET 2004), Kathmandu, Nepal, pp 141-145. [13] Power point presentation of Mr. Masahiro Ando, P.E. Professional Engineer as Authorized by the Japanese Government in February 2007 in Department of Electrical Engineering, IT-BHU, Varanasi.