Linear Induction Motor based Passenger Conveyor System

Linear Induction Motor based Passenger Conveyor System for Pedestrians along Circular Route Dr. S. N. Mahendra, Professor in Electrical Engineering, Indian Institute of Technology (BHU), Varanasi [email protected] Ayan Das, M.Tech., Dept. of Electrical Engineering, IIT (BHU), Varanasi, [email protected] Shailendra. N Jaiswal, Senior Professor Management, National Academy of Indian Railways, Vadodara [email protected]  Abstract— Traffic Congestion on roads in Indian cities has become the main cause for increase in the rate of accidents, pollution etc. Shopping complexes and several other activity centers, where a noticeable gathering takes place, makes the traffic problem more serious. The main sufferers of this problem are the pedestrians. The paper focuses on providing a solution for the pedestrians of Connaught Place, New Delhi so that they can comfortably move around. Design and techno-economic viability of a moving platform system propelled by Segmented Linear Induction Motor has been included in this paper.

kmph along the outer circle of CP [3] so that people can travel from one point to another along the outer circle with ease and convenience. The proposed People Mover System (PMS) is propelled by segmented Linear Induction Motor (LIM) primary members laid along outer circle of CP. The geometry of the route incidentally helps minimizing the end effects which otherwise generally affect the performances of LIM based systems.

Index Terms— Linear Induction Motor, Urban transportation, Congestion on roads, Passenger Conveyor

I. INTRODUCTION

C

ongestion on roads in Indian cities resulting in accidents [1] and pollution [2] has become a serious problem – particularly in metros like Delhi, Kolkata, Mumbai etc. The problem has not been solved in some metros even by providing a Mass Rapid Transit System because of lack of integration between the rapid transit system provided and the existing modes of transport systems which are still required by a person to complete the journey. Due to these reasons people still prefer to use their personal transport for fulfilling the purpose of their travel comfortably. However if the gap between various travel options available can be filled by a suitable transportation system, persons using their personal cars may find the public transits systems more attractive, thereby avoiding the usage of personal cars. Connaught Place (CP) in New Delhi, India is a distinct example wherein although there are many travel options like Metro (Rajiv Chowk Metro station, shown in the fig 1), Public buses, Taxi etc., the private car passengers still find it convenient to move around & do their job by using their personal cars. It is needless to mention that this along with the presence of shopping-complex in the CP region result in peakhour congestion on roads and hence discomfort particularly for the pedestrians. In the present paper a techno-economic solution for CP has been presented. It consists of a platform moving at about 5-10

Fig 1: Map of the Connaught Place with proper dimension II. PASSENGER CONVEYOR SYSTEM Generally conveyor belt is used for continuous movement of materials from one place to another in industry. In a similar manner people are also moved from one point to another. This type of system is commonly found in airports to carry the passengers and is called Travelator [4]. Figure 2 shows technical details and also the return path at one end of a typical Travelator. Linear motion in these systems is obtained by converting the rotary motor torque into linear force through adhesion between the drum connected to the motor shaft and the moving conveyor belt. Thus in addition to the problem associated with the rotary motors and that with the adhesion between drum connected to the motor shaft and the conveyor belt for power transfer, only 50% of the belt and the associated mechanisms are used in the transfer of man and material between two desired points of transfer – the remaining 50% is used to complete the return path. The case under consideration in this paper is Connaught Place, New Delhi, India which has a very special geometry

with three concentric roads connected by radial roads as shown in figure 1. Salient details of CP region are given in Table 1[5].

IV. ADVANTAGES OF THE PROPOSAL There are distinct advantages of using LIM instead of a rotary motor in the proposed system [3, 7]. From traction point of view the proposed system has distinct features such as: 1. In rotary motor based traction minimum adhesion between the mechanical output member of the rotary motor system and the moving mechanical system is an essential requirement. On the other hand the LIM based traction systems are adhesion-free with only rolling-wheels (no driving–wheels) thus adhesion is no more a controlling factor in the proposed system.

Fig.2: Typical Travelator showing speed, dimensions & return path at one end [4]

2. The stationary primary member produces the tractive force directly in the moving secondary member fixed to the platform without any intermediary transmission. This reduces noise level, wear and tear and minimizes maintenance. The loss is zero between force producer and the tractive effort receiver, so the system has 100 % transmission efficiency.

Table 1: Dimension of Connaught Place, New Delhi Parameter Outer circle Inner circle Diameter 700 m 250 m Perimeter 2.2 km 785 m Right of way 35 m 55 m Carriage way 17 m 25 m Footpath 6 m 11 m

3. The two features discussed above greatly reduce the mass of the people conveyor system. Further since propulsion force is produced uniformly along the entire circle of the people-conveyor plate, there is virtually no longitudinal tension and hence thickness of the conveyor belt can be kept low by incorporating this aspect. Thus the pay-load-to-dead-load ratio will increase considerably.

The visitors coming to the CP region for work, shopping or tourism have two options: Use metro to reach CP and then move around or reach their destination by using taxi, bus or by walking.  Use a taxi or a personal car to reach CP region and also to their work places. Whereas in the former it takes care of parking problem at the cost of the visitor’s discomfort, that in the latter (though convenient for the visitor) it adds to the problem of car parking, wastage of energy with noise and environmental pollution. The present paper proposes a solution which will bridge the gap between the existing public/private transport systems so as to make the visit of the visitor to the CP area comfortable, convenient and economical while at the same time reducing air and noise-pollution, traffic-congestion with substantial saving in energy consumption.

4. There will be no frequent start-and-stop of the conveyor and the speed of the conveyor belt will remain almost constant. The specific energy consumption will therefore become low.

III. THE PROPOSAL The passenger conveyor system proposed for Connaught Place has a moving circular platform below which is attached a circular reaction-rail made-up of aluminum and backing iron. This reaction rail is propelled by segments of LIM primary members laid along a circle. Since both the primary and the secondary members of the linear induction motor and also the moving platform for the users will be used continuously, the material utilization in this case will be 100%.

5. The operation will be smooth and riding will be comfortable. 6. The construction of LIM propelled system will be simple and therefore the civil and mechanical engineering costs will not be very high. 7. The system is environmental-friendly as it produces no pollution. 8. The people mover can be suitably subsidized to attract users. The subsidy will pay back many times by attracting more customers to the city centre reducing accidents, pollution and convenience to CP visitors. V. DESCRIPTION OF THE SYSTEM The people mover system has been proposed for outer circle as it is feasible and has distinct benefits from usage point of view and it will provide better integration of CP with rest of Delhi. In principle the arrangement for primary and secondary members of the motor will be similar to as shown in Fig.3. The bottom most layer consists of stationary circular primary

member with distributed 3-phase winding which will be connected to 3-phase supply. Above this primary member will be a circular reaction-rail consisting of aluminum plate backed by iron.

Among these Steel-wheel-on-Steel-rail has been proposed as it is convenient to make, maintain and operate. It is also the most energy efficient system till now. VI. SEGMENTED LIM OPTION The perimeter of the circular primary member is very large and making a single LIM primary is not feasible. Therefore from fabrication and implementation point of view the 2.2 km perimeter of the outer circle will be made up of about 900 LIM segments each about 2.44m long and 50mm wide so as to cover the entire perimeter of the outer circle. Fig. 4 shows the arrangement along the circle and an enlarged view of few segments. Fig.5 shows one segmented of LIM.

Fig 3: Circular longitudinal-flux induction motor The moving platform for carrying the people will be suitably fixed to the top of the reaction-rail assembly consisting of conducting secondary and mild steel plate. The whole system will be inside a steel cage with a shade to protect the passenger from sun and rain. There will be railing on both sides of the moving platform for the people to hold.

There are three options for implementing the people mover system in CP: 1. At ground level: The civil engineering cost may be minimum but this will restrict free movement of vehicle entering the middle or inner circles as the primary member will be kept on the ground around the periphery of the outer circle. 2. At underground level: it can be a better choice as this arrangement will not prevent the cars entering the inside and the outer circles. But the civil engineering cost will be very high. In addition several other issues will need attention like the ventilation, air-conditioning and movement of people between the road levels to the moving platform level. 3. At overhead: it will be an elevated system raised at a height around the periphery of the outer circle. The cost of this system will be in between the previous two cases but with no hindrance for the moving vehicles on the road. From the above discussion the obvious choice will be an elevated system in which the moving platform will be supported on pillars and will be suitably guided against any unwanted lateral forces. Various options for Suspension cum Guidance system can be:  Roller and Plate  Ball and Plate  Wheel and Rail  Air cushion  Permanent Magnet  Electromagnetic Levitation

Fig 4: Circular primary & LIM segments along an arc

Fig.5: Primary and secondary members of segmented LIM The LIM segments are identical hence only one LIM primary member segment has been considered for detail design and analysis. Along the circle there will be negligibly small gap between adjacent LIM segments. Ideally this should not be there to avoid magnetic discontinuity between the segments but weighing the pros and cons of the two options i.e. primary continuous circular core and segmented linear core, the latter option has been chosen. The electrical discontinuity has been avoided as the end coils occupy end slots of the adjacent LIM segments. Due to this arrangement the end effects due to discontinuities in the magnetic and electric circuits (otherwise present in an LIM) have been minimized. Each LIM primary member segment has been designed [6, 8, 9] so that all the segments when placed along the perimeter of the circle can meet the desired specification of the people mover system given in Table 2.

Table 2: Desired Specifications of people mover system for designing LIM Parameter Value Operating speed (Vr) 5 kmph or 10 kmph Maximum Slip (s) for LIM 30% No. of LIM segments of length 2.4m 900 Dead weight Wd of moving platform 600ton Weight per passenger considered Wp 60 kg Maximum number of passengers 32000 Pay load (maximum) 2000 ton Total maximum Force required at 200*10^3 Newton starting with crush load Ft Force required per LIM segment 225 Newton Maximum power required for all LIM 280 kW segments Maximum power required per LIM 312 W segment Selection of frequency of operation along with the polepitch and the slot-pitch is a critical step in the design of LIM to meet the operating requirements given in Table 2. Possible combinations of pole-pitch and slot-pitch corresponding to synchronous speed and frequency of operation are given in Table 3. It is to be noted that a compromise between τp and f is required to meet Table 2 specifications. The selected values have been highlighted.

Table 4: Design Sheet of Segment LIM Parameters Designed value Slip (s) 30% Synchronous speed (Vs) 2 m/s Slot per pole per pitch (spp) 1 Air gap flux density (Bg) 0.4 T Total number slots per primary 174 segment Phase current 1.9 A Voltage rating line to line 410 V Flux per pole φp 0.8 mWb Width of segment 50 mm Tooth width 5 mm Slot width 9 mm Depth of slot 23 mm Core Depth 17 mm Wire SWG 19 Secondary thickness 6 mm Secondary width 80 mm Mechanical clearance 5 mm Table 5: Approximate dimensions of the mechanical system

S. No. 1. 2. 3. 4. 5. 6.

Item Platform width Platform thickness Wheel diameter Height of moving handrail Thickness of moving handrail Height of shade from the platform

Approximate dimensions in mm 1800 10-20 250 1000 100 2500

VIII. CONCLUSION

Thus the most suitable combination is frequency = 25 Hz, pole pitch = 40 mm and the slot pitch = 13.3 mm for SPP = 1 and Vs = 2m/s. With these specification inputs a segment LIM has been designed and the design sheet is given in Table 4. VII. MECHANICAL SYSTEM Using the dimensional details of the designed segment LIM approximate dimension of the mechanical system have been decided as given in Table 5. The mechanical parts of the people mover system are:  wheels with non rotating axle,  platform on which the passenger will stand,  moving railing etc [10]

The solution in this paper has been proposed for Connaught Place, New Delhi, because it has circular roads to provide a closed loop operation thereby avoiding wastage of material and energy required in alternative people mover systems. The idea with minor modifications can be implemented with advantage along closed loop routes (not necessarily in circular form as in CP region) which are crowded due to pedestrians and are subjected to traffic congestion. The proposal will certainly benefit the pedestrians as this will make their movement in the city center shopping area safe. The proposal will also reduce accidents, pollution and will provide an effective integration between the pedestrians and the private and public modes of transport. Feasibility of the proposal is due to linear induction motor which is capable of producing propulsion force in the moving parts directly without any physical contact. The propulsion force is produced in the moving platform along the entire length and not at the common surface between the portion of the moving platform and the force-transmitter attached to the rotary electric motor which provides the necessary torque to a

drum or chain type arrangement. This difference between the LIM and RIM system must be appreciated. In the LIM based system the total force required is provided by the entire length of the reaction-rail fixed to the moving-platform. However, in the rotary motor based system the force required will be provided by a small common-contact surface between the moving member and the rotary motor shaft. Thus the stresses in the LIM based system will be small as compared to that in the rotary motor based system. There is yet another feature of LIM based system which needs special attention. In LIM based systems there are only rolling wheels and therefore the system is free from problems associated with meeting minimum requirement of adhesion. This aspect can be gainfully exploited while designing the wheel-rail system. Fig. 6 gives a photograph of a model of the working system made by students in 1988 based on reference 7 and Table 6 gives a break-up of estimates [9] of approximate capital and operating costs of the system proposed. Table 6: Approximate capital and operating costs Capital Cost (in crores INR) Civil Mechanical Elect. cost cost cost

15

26

9 Total capital cost 50

Running Cost per year (in crores INR) Energy Management Maintenance cost cost cost

0.20

3.6 Total operating cost

2 6

IX. Acknowledgement Authors acknowledge with thanks the assistance received on Civil engineering aspects from Dr. Virendra Kumar, Professor, Civil Engg Deptt, IIT (BHU), Varanasi, & Er. Kanhaiya Jha, PWD, Varanasi. Efforts of Mr. Sanjiv Agarwal and his team (in making a model of the working system shown in Fig.6) are also acknowledged.

Fig.6 LIM Powered People Mover for closed-loop circular track

X. REFERENCES 1. “Road Accidents In India”, Government Of Indian Ministry Of Road Transport And Highways Transport Research Wing New Delhi, 2010, page no:1-5 2. Vinish Kathuria: “Vehicular Pollution Control In Delhi”, Transportation Research Part D: Transport and Environment, Volume 7, Issue 5, September 2002, Pages 373–387 3. S N Mahendra & S Jaiswal, “Linear Induction Motor Propelled Pms For Closed Loop Circular Track”, International Conference on Transportation system studies, IIT Delhi, 1986 4. “Walkway Propels Paris Metro into Future” - By Alexandra Fouché BBC News Online, Paris 5. “Annual Report Of National Transport Planning And Automation Centre” Traivandam, 1983-84 6. G. F. Nix, & E. R. Laithwaite: “Linear Induction Motor For Low Speed And Standstill Application”, PROC. IEE, v13, n6, June 1966, pp 1044-1056 7. S. N. Mahendra, M Bharrachariya, G Rajsekhar, “Prospects Of Linear Induction Motor Propelled Traction System For Surface, Under Ground And Overhead Urban Transportation System”, Seminar on Railway Electrification, Vol 1, MT- 15 to MT-29, 1981 8. K. Rahul. Digvijay: “Design & Analysis Of Linear Induction Motor”, M. Tech Dissertation supervised by Prof. S. N. Mahendra, Department of Electrical Engineering, Indian Institute of Technology (BHU), Varanasi, India, 2009 9. Ayan Das: “Design & Analysis of Linear Induction Motor Based People Mover System for Connaught Place, New Delhi”, M. Tech Dissertation supervised by Prof. S. N. Mahendra, Department of Electrical Engineering, Indian Institute of Technology (BHU), Varanasi, India, 2013 10. “Indian Standard Specification For Wheels And Castors (First Edition)”, IS: 7369-1983