Light Weight Individually Powered Railway Freight Wagons Modified to Utilize Lost Energy during Braking

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ISSN : 2319 – 3182, Volume-2, Issue-3, 2013

78

Modified to Utilize Lost Energy during Braking

Gaurab Bhowmick & Gunjan De

Mechanical Engineering, Dr. Sudhir Ch. Sur Degree Engineering College, Kolkata, India E-mail : [email protected], [email protected]

Abstract – EMU or the Electric Multiple Units are those type of trains consisting of self-propelled carriages using electricity as the motive power. An EMU requires no separate locomotives, as electric traction motors are incorporated within one or a number of carriages.

Generally EMUs are used for passenger train but the same technology can be implemented in freight carriages also.

These EMU based freight cars will reduce the line congestion mainly in India due to its rapid acceleration and high speeds.In this study, the purpose of the carriage is to be self-propelled using highly efficient traction motors powering each carriage made of high strength Aluminum having individual and independent wheel set. Also, the wagon will harness the waste braking energy using regenerative braking technique to power the traction motors partially. This study addresses the problem of severe line congestion, unwanted holding of freight trains to make passageway for passenger trains, light weight wagons, harnessing the wastage braking energy which are generally removed as heat. Therefore, study of the methodologies suggested has to be done in order to determine the feasibility and effectiveness of the methods both in terms of technology and financially. To achieve this detailed analysis is carried out to understand the modification of normal freight wagon to self-propelled EMU type wagon.

Keywords – EMU, Regenerative, aluminum, self-propelled.

I. INTRODUCTION

Generally, in India freight trains are conventionally pulled by a locomotive either electric or diesel.[1] In the conventional method of hauling the locomotive has tractions motors fitted only in its wheel.[2] So, in the entire rake only the locomotive wheels are powered which in turn provides the necessary force and torque required for moving the train. The conventional freight carriages have connected wheels sets with an axle,[3]

which in turn adds for some extra weight and restricts operation for high speed resulting in line congestion.

Even though the technology of dynamic braking is implemented in almost all locomotives of Indian

Railway.[4] But, the advanced form of dynamic braking i.e. the regenerative braking is not being used here in India and the entire energy obtained from dynamic braking is released in the form of heat.[5] Another shortcoming is the use of steel, iron and its corresponding alloys to make the wagons instead of using light weight, robust material having same & better properties as of steel & its derivatives.[6]The above mentioned shortcomings results in some disadvantages, which are discussed in the following sections.

II. DISADVANTAGESOFSOMEOFTHE IMPLEMENTEDTECHNIQUES:

 Locomotive pulling the entire rake results in very slow acceleration, highly inefficient operation, more load on the engine , low avg. running speeds results in line congestion.

 The use of dynamic braking and releasing the energy as heat result for huge loss.

 Using heavy weight materials adds more weight to the carriage and needs more power from the engine.

The disadvantages can be overcome by the technique discussed in details below taking each case separately.

III. NOMENCLATURE r - Radius of wheel

m – Mass of wheel I – Moment of inertia

N – Newton, Angular Velocity in r.p.m.

T – Torque

α – Angular acceleration V – Linear Velocity

ω – Angular velocity in rad/s t – time , s

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79 IV. ANALYSIS

4.1 Self-propelled carriages

Indian Railways has a wide range of locomotives both diesel and electric type varying from 2500HP to 7000HP (approx.). These locos provide a variable range of tractive forces to pull the rake. As these locos are the only power source for the entire rake, it results in a very slow rate of acceleration.

 Case I (WAG 9 IR)

Fig. 1 ^[i]

Table i (Technical Specs.)^[ii]

Manufacturers ABB Swiss Locomotive Works, CLW

Traction Motors

ABB's 6FRA 6068 (850 kW, 2180V, 1283/2484 rpm, 270/310A. Weight 2100 kg) Axle-hung, nose-suspended.

Gear Ratio 77:15 / 64:18

Transformer ABB's LOT 6500, 4x1450kVA.

Power Drive Power converter from ABB, type UW-2423-2810 with SG 3000G X H24 GTO thyristors (D 921S45 T diodes), 14 thyristors per unit (two units). Line converter rated at 2 x 1269V @ 50 Hz, with DC link voltage of 2800V. Motor/drive converter rated at 2180V phase to phase, 971A output current per phase, motor frequency from 0 to 132 Hz.

Hauling capacity

4250t

Bogies Co-Co,

Fabricated Flexicoil Mark IV bogies (Design later used

for IORE and China Railways HXD3B; bogie wheelbase 1850mm + 1850mm

Wheelbase 15700mm Unsprung mass

per axle

3.984t Body width 3152mmn Cab length 2434mm

From the above technical specification it is seen that the tractions motors (850KW) each are being used in the loco. It takes around 10-15Km of track to reach an optimum speed of 80-100kmph with a rake of 42 BCN carriages. If instead of using the loco, each around 60KW high torque traction motors for powering each independent wheel can be used, which will result in a better acceleration.

Traction motor considered has the following specification –

Table II : (HVH250 HT)^[iii]

Overall Length (mm) 180

Stator Outside Diameter (mm) 242 Rotor Inside Diameter (mm) 132 Mass – Complete Motor (kg) 43 Continuous Power Output (kW) 60 Peak Power Output (kW) 87 Continuous Torque Output (N-m) 243 Peak Torque Output (N-m) 440

Max. Input Current Peak/

Continuous (Amps) 200/300

Peak Efficiency (%)

93 @ 1,500-8,000 rpm Max. Operating Speed (rpm) 10,600

Base Speed (rpm) 1,400

Operating Voltage (VDC nom.) 320

Temperature Limits 160° C

Conductor Type High Voltage

Hairpin Estimated calculations for this case are as follows : 4.1.1 Sample calculation –

(Assuming wheels are directly driven by the motor shaft with gears of ratio 1:1 in between and the calculation is based on theoretical aspect and is just an estimation) Power of each traction motor = 60KW

No. of wheel in each carriage = 8

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80 Total power (each carriage) = 60x8 = 480KW

Starting torque each motor = 440Nm

Total starting torque (each carriage) = 440x8 = 3520Nm No. of carriages in a rake = 42 (generally)

So, Total starting torque for entire rake = 3520x42

= 147840Nm Now, for BCN wagons radius of each wheel, r = 0.5m Axle load = 20.32tonnes

Therefore, load on each wheel (assuming equal distribution), m = 20.32/2 = 10.16x1000 = 10160kg Moment of Inertia, I = ½ x mr²

Or, I = ½ x 10160 x 0.5 x 0.5 Or, I = 1270kg/m²

Torque, T = Iα Or, α = T/I Or, α = 3520/1270 Or, α = 2.77 rad/s²

Now, suppose we require reaching the speed of 100km/h, then

Velocity, V = ω x r Or, ω = V/r Or, ω = 27.78/0.5 Or, ω = 55.56 rad/s We know, ω = α x t or, t = ω/α or, t = 55.56/2.77 or t = 20.05sec 4.1.2 Result Analysis Under Analysis

4.2 Harnessing the energy from Dynamic Braking

Conventional loco in India has the provision for dynamic braking i.e. using the motors as generator to slow down the train. But, the energy obtained from dynamic braking is totally wasted as heat through the network of resistors to the atmosphere. This is a total waste of energy thus reducing the efficiency of the train.

There is a provision of feeding back the generated current from dynamic braking to the grid lines using the

same pantograph used to receive power. But, in India there is no provision for adequate transfer of current back to the grid lines.

This problem can be solved by harnessing the energy within the train itself. As already discussed that each wheel will have its own traction motor to power the rake. So, placing a battery next to each traction motor and the battery can be used for additional supply of current and power when required. Now, the battery needs to be charged. The charging voltage will come from the motor itself when used as a generator during dynamic braking. The generated voltage will be used up by the battery instead of losing it as heat to the atmosphere. According to various studies done across the globe, it is found that dynamic braking energy accounts for up to 40% of the energy used to drive the train. So, if this energy is harnessed and used again to drive the train, the efficiency of the whole system will increase. Since, these individual traction motors gives a tremendous acceleration, similarly these motors when used as generators will give almost same amount of braking effort.

Flow Chart for utilizing the lost braking energy

4.2.1 Result Analysis

Under Analysis and experimentation 4.3 Use of light weight material

Typically the freight wagons are made of steel and sometimes stainless steel to reduce corrosion. Earlier

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81 iron was used to build the wagons, but due to the corrosive nature of iron , stainless steel was adopted to manufacture the wagons. But, due to the tremendous rise in price of steel, railway started to initiate production of aluminum wagons on a trial basis. Since aluminum is lighter than steel it reduced the tare by 4.2tonnes. Aluminum wagons besides being of a lower cost and having a lower tare weight, also have the advantage of suffering less corrosion in many circumstances. A typical rake with aluminum wagons instead of steel ones would carry almost 240t more goods.

Along with Aluminum, fiber glass sheet can be used to manufacture the wagons, which will further reduce the weight of the wagon and thus increasing efficiency. An indicative comparison follows –

Table III : (Properties of steel)^[iv]

Properties Carbon Steels

Alloy Steels

Stainless Steels Density (1000 kg/m³) 7.85 7.85 7.75-8.1 Elastic Modulus

(GPa) 190-210 190-

210 190-210 Poisson's Ratio 0.27-0.3 0.27-

0.3 0.27-0.3 Thermal Expansion

(10^-6/K) 11-16.6 9.0-15 9.0-20.7

Melting Point (°C) 1371-

1454 Thermal

Conductivity (W/m-K)

24.3-

65.2 26-48.6 11.2- 36.7 Specific Heat

(J/kg-K)

450- 2081

452-

1499 420-500 Electrical Resistivity

(10^-9W-m)

130- 1250

210- 1251

75.7- 1020 Tensile Strength

(MPa)

276- 1882

758-

1882 515-827 Yield Strength (MPa) 186-758 366-

1793 207-552 Percent Elongation

(%) 10-32 4-31 12-40

Hardness (Brinell

3000kg) 86-388 149-

627 137-595

Table IV : (Properties of Aluminum Alloys)^[v]

Density 2600-2800 kg/m³

Melting Point 660 °C

Elastic Modulus 70-79 GPa

Poisson's Ratio 0.33

Tensile Strength 230-570 MPa Yield Strength 215-505 MPa Percent Elongation 10-25%

Thermal Expansion

Coefficient 20.4-25.0 × 10^-6/K

Chart I

Chart II

Table V : (Fiber Glass Properties)^[vi]

Material Specific gravity

Tensile strength MPa (ksi)

Compressive strength MPa

(ksi) Polyester resin

(Not reinforced) 1.28 55 (7.98) 140 (20.3) Polyester and

Chopped Strand Mat Laminate 30% E-glass

1.4 100 (14.5) 150 (21.8)

Polyester and Woven Rovings Laminate 45%

E-glass

1.6 250 (36.3) 150 (21.8)

Polyester and Satin Weave Cloth Laminate 55% E-glass

1.7 300 (43.5) 250 (36.3)

Polyester and Continuous Rovings

Laminate 70%

E-glass

1.9 800 (116) 350 (50.8)

E-Glass Epoxy

composite 1.99 1770 (257) 410 S-Glass Epoxy

composite 1.95 2358 (342) 1912

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82 4.3.1 Proposed Modifications

As seen above, physical properties chart of three types of materials has been provided along with a graph comparing the Tensile strength & Density of the materials.

 It is seen that out of Stainless Steel, Aluminum &

fiber Glass, stainless steel has the tensile strength a little bit higher than that of aluminum but less than that of fiber glass.

 Similarly, from the density graph it is seen that the density of Fiber glass is the lowest than that of the other two materials.

 If the wagons are manufactured using aluminum alloys or fiber glass, the weight of the wagons will be much less than those made of stainless steel or steel alloys.

 If weight is less , then the efficiency of the engine increases, it requires less energy .

 Fiber glass is totally non-corrosive.

 Cost of making fiber glass is very less as compared to aluminum and stainless steel.

 Less weight means more rapid acceleration.

 Energy required to manufacture fiber glass is far less than the energy wasted in obtaining aluminum and steel from its ores, thus reducing carbon footprint.

4.3.2 Sample Calculation (Approx. Estimation) From the fig. it is seen that length, l = 12800mm Width of the wagon, w = 3136mm

Height of wagon (above floor height), h = 1880mm Surface area for the entire carriage with top open is given by, A = (2xlxh) + (2xwxh) + (lxw)

Or, A = (2x12800x1880) + (2x3136x1880) + (12800x3136),

Or, A = 48128000 + 11791360 + 40140800 Or, A = 100060160 mm²

Or, A = 100.06m²

Now, Cost of stainless steel = 2965US$ / tonne For a sheet of Gauge = 5 and Thickness = 5.314mm Weight per unit area = 41.668kg/m²

Therefore, Total steel required (approx.) is given by N = Weight X Area (A)

Or, N = 41.668 x 100.06

Or, N = 4169.3 kg of stainless steel reqd. (approx.) Cost = 4.1693 x 2965 $

Or, Cost = 12361.97 $

Now, Cost of Fiber glass ((FRP) Corrugated Sheet) of thickness 5mm/5ply = 3$ per sq. ft.

Area , A = 1077 ft²

Cost of Fiber glass = 1077 x 3$

Or, Cost = 3231$

Fig. BCXT Wagon^[vii]

[ This figure is used as the for section 4.3.2]

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83 Cost Comparison

4.3.3 Analysis of Result Under Analysis

V. CONCLUSION

 After analyzing the above cases, it is found that implementing the suggested technique will have various advantages over the initial disadvantages stated using the conventional locos and carriages.

 Designing and manufacturing considering the methodologies suggested will result in less manufacturing cost, more efficiency and will reduce the carbon foot print by a huge margin.

 The above aspects are just an theoretical imagination and can be implemented after some research and experimentation.

 The calculations performed in this paper are based on basic equations neglecting many additional effects.

 Detailed calculations can be done after initial practical implementation.

 So, the entire motive of this paper is to clear out the line congestion caused by slow moving goods train along with proper utilization of energy by Indian Railways.

VI. REFERENCES [1] Image source www.en.wikipedia.org [2] CLW loco Driver’s Manual and handbook [3] Remy International Inc. motor specs. Chart [4] www.efunda.com

[5] www.efunda.com/materials/alloys/aluminum/pro perties.cfm

[6] www.en.wikipedia.org

[7] Govt. of India/Ministry of Railways Maintenance Manual

[8] “Indian Railway : The backbone of service sector , “by Sarika Sharma (Research Scholar, Faculty of Commerce, B.H.U., Varanasi-221005)

[9] “Electric Railway Traction, Electric Traction &

DC traction motor drives “ by Hill, Roland John, UK, IEEE.

[10] “Indian Railway axle manufacturing &

maintenance guide”.

[11] “Studies of Regenerative braking in electric vehicle “, by Yoong, M.K., IEEE.

[12] “Transportation: Dynamic braking: The kinetic energy of rapid transit trains that is normally dissipated as heat during braking can be converted to potential energy”, by Kalra, P., IEEE.

[13] “Fiberglass & Glass Technology”, Wallenberger, Frederick T.; Bingham, Paul A. (Eds.)

[14] “FREIGHT TRAIN ROUTING AND

SCHEDULING IN A PASSENGER RAIL

NETWORK: COMPUTATIONAL

COMPLEXITY AND THE STEPWISE

DISPATCHING HEURISTIC”, T. GODWIN ,Marketing and Planning Systems,

RAM GOPALAN, Fox School of Business and Management, Temple University, Philadelphia, PA 19122, USA

T. T. NARENDRAN, Department of Management Studies, Indian Institute of Technology, Madras, Chennai 600036, India.

[15] S.J. Clegg (1996), A review of regenerative braking systems. Institute of Transport Studies, Univ. of Leeds.”

[16] “Govt. of India, Traction Rolling Stock, Maintenance manual”

[17] Maintenance Chart for Wagons by Indian Railway

[18] Ministry of Railways / Engineer’s handbook [19] Ministry of Railways Wagon Specification Chart [20] Theory of Machines – R.K. Bansal, Lakshmi

Publication

[21] http://www.realfibre.com/price_list.html

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84 [22] http://www.worldsteelprices.com/

[23] http://www.custompartnet.com/sheet-metal-gauge [24] http://irdindia.in/Journal_IJTARME/PDF/Vol1_I

ss2/4.pdf

[25] Electrical Technology II – B.L Theraja, S.Chand Publication.

[26] “MECHANICAL PROPERTIES OF G10 GLASS-EPOXY COMPOSITE”, K. Ravi- Chandar, S. Satapathy, The University of Texas at Austin, USA.

[27] ”MECHANICAL PROPERTIES OF

POLYMERIC COMPOSITES REINFORCED WITH HIGH STRENGTH GLASS FIBERS”, Michael Kinsella, Dennis Murray, David Crane, John Mancinelli, Mark Kranjc, Advanced Glass fiber Yarns LLC, Aiken, South Carolina 29802, Advanced Glass fiber Yarns LLC, Huntingdon plant, Pennsylvania 16652, Bell Helicopter Textron Inc., Fort Worth, Texas 76101.

[28] ”Composite Materials: Fatigue and Fracture, Issue 1285”, By ASTM Committee D-30 on High Modulus Fibers and Their Composite.

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