1. INTRODUCTION:

Rajdhani, Shatabdi, Durunto, Double-Deckers and Garib-Rath are the premium fully Air-Conditioned semi-high Speed Passenger Trains on the network of Indian Railways. These Trains are mostly hauled by High Horse-Power Electric Locomotives of the range of 6000 HP on the electrified sections and Diesel-Electric Locomotives on the non-electrified sections. The Power required for the Lighting Equipment, Fans and the Air-Conditioning Units is supplied from the Power Cars which house Diesel-Generator Sets. This method of supplying Power to the Passenger Coaches is called End-On-Generation (EOG). The EOG Power Cars cause a lot of noise and air pollution, are also energy inefficient and cause lot of Vibrations [1].

They also operate with poor power factor of about 0.4 to 0.6 lag requiring a good amount of Reactive Power compensation. To eliminate the use of Power Generator Cars for supplying Power to the Passenger Coaches, the Authors propose a Traction Drives System with Wound Rotor Induction Motors(WRIM) as Traction Motors with a low Voltage Slip-Power Recovery Scheme to deliver Power to the Passenger Coaches.

2. LITERATURE SURVEY:

The Literature Survey undertaken for this Research Paper is described in the following three sub-sections. The Authors made a detailed study of the existing EOG in Indian Railways, the low Voltage Slip-Power Recovery Scheme in Stone Grinding Mills of Australia and the Scope for conservation of Energy in the EOG in Indian Railways to propose this Design of Drive System to generate Power from the Traction Motors to deliver Power to the Passenger Coaches.

2.1 THE END-ON-GENERATION SYSTEM IN INDIAN RAILWAYS:

This scheme of Generation of Power is used in Trains like Rajdhani and Shatabdi. The EOG consists of a Diesel Generator of rating of 500 kW [1], [2]. There are two such Power Cars in each of the Shatabdi/Rajdhani Expresses. The DG sets generate 3-ph, 415 V, 50 Hz AC which is fed to the two roof mounted Air-Conditioning Units in each Air-Conditioned Coach by means of feeders. For Lighting and Fans in the Coaches, a Step-Down Transformer is used in the Power Car itself which is rated at 2.5/5kVA. The Stepped down Voltage of 3-ph, 110 V, 50 Hz AC is directly fed to the Lights and Fans connected between each Phase and Neutral (Balanced Loading). The 3-ph Evaporator Blower Motor is also connected to this Circuit. The Schematic Diagram of EOG system is shown in Fig.1.The Disadvantages of EOG are noise and air pollution, Vibrations, cost of Fuel, Voltage Drop, reduction in Passenger capacity equivalent of two Coaches and requirement of extra Staff for operation. The advantage is that this Power Car can work irrespective of the type of Traction with 100 % reliability of operation.

2.2 WOUND ROTOR INDUCTION MOTOR AND LOW VOLTAGE SLIP-POWER RECOVERY SCHEME:

Wound Rotor Induction Motors are ideally suited for Applications which involve high Inertia Loads, high Starting Torque with low Starting Current on a weak Power System and better Speed Control [4]. The Study of one such Application in a Stone Grinding Plant in Australia has proved that for a 5000 kW WRIM, the savings per annum would be about $500000as the Slip-Power recovered by using low Voltage Slip-Power Recovery Drive was 970 kW per Hour per WRIM. It has also been mentioned that for Applications like Traction where Braking has to be robust and at the same Time when Braking Torque has to be maximum, a WRIM is best option as the introduction of External Resistances in the Rotor Circuit during Braking results in high Slip resulting in high Braking Torque as the Torque developed is proportional to Slip [3]. With modern manufacturing Technology it is possible to manufacture WRIM with either Automatic Brush Lifting Gear such that Slip-Rings are required only during Starting after which the Brushes are lifted or with Permanent Slip-Rings Grooved eliminating the frequent maintenance [5]. Also, the WRIMs are more efficient as compared to Squirrel Cage Induction Motors, have higher Starting Torque with low Starting Current and can be operated in a weak Power System without disturbing it. Hence, if a WRIM is used for Traction, it can deliver the required constant Torque and also help in supplying Power to the Trailing Passenger coaches through the low Voltage Slip-Power Recovery System thus eliminating the use of EOG Power Cars at least partially if not fully.

2.3 ENERGY REQUIREMENTS OF PASSENGER CARS:

The Passenger Cars of the Shatabdi/Rajdhani Express Trains are fully Air-Conditioned. The Coaches are constantly cooled by roof mounted Air-Conditioning Units rated at 11.5 kW each. The Power Consumption of the Coaches vary with their configuration. The Various Coach Configuration that are used in the Shatabdi and Rajdhani along with their Weights and the Power Consumed are listed in Table No.1 and 2 respectively. The Lights and Fans in the Coaches consume about 5 kW Power. The average consumption of Energy by the Trains for Air-Conditioning and Lighting is about 400 Units per Hour whereas the Locomotive itself requires only 1400 Units per Hour for Traction. The Energy requirements of the Coaches of the Shatabdi/Rajdhani Expresses are entirely met by EOG.

2.4 ENERGY CONSERVATION:

There is lot of scope of Energy Conservation in these types of Trains. The Diesel consumed by the Power Cars for generating energy is 100 litres/Hour. If part of the Air-Conditioning Load is taken over by the Locomotive, lot of Fuel can be saved. Also if Sun-Films are used for the Windows of the Passenger Coaches, the heat flow through the Windows will considerably reduce bringing down the Load on Air-Conditioners. Also use of individual Cooling control in Cubicles for each Passenger as it is in Aircrafts will also reduce Energy Consumption. Lastly use of LEDs for lighting will considerably reduce the Reactive Power Consumption as the Power Factor in the current Technology used is very poor and is in the range of 0.4 lag to 0.6 lag [1]. By providing an extra Auxiliary Winding in the Traction Transformer to aid the Power Supply from the low Voltage Slip-Power Recovery (SPR) Scheme whenever the Locomotive is Stationary or running at near rated Speed, lot of Costly Fossil Fuel can be saved. Also, the levels of Pollution due to Diesel-Generator Sets can be brought down thus saving the Environment.

3. PROPOSED CIRCUIT, SIMULATIONS AND RESULTS:

The Drive System for Electric Traction with WRIM as Traction Motors with a low Voltage Slip-Power Recovery System to deliver Power to the Trailing Passenger Coaches is proposed and the results of the Simulation Studies are discussed in this Section. The Main Drive System consists of a 10 MVA Traction Transformer with Primary Winding Voltage of 25 kV, 1-ph, 50 Hz, AC. On the Secondary side four Tapings of each with a Voltage of 5000 V are taken for Traction Motors Drive System. Four Tapings of Voltage level of 1000 V are taken for the Auxiliary Loads with the Assumption that the WRIMs are self-Ventilated and hence do not requires separate Blowers for Cooling. The WRIMs are rated at 1.6 MW or 1600 kW each and there are four such Motors to Drive the Axles. Thus for a Six Axle Locomotive, four Axles will be powered and two Axles will be Dead Axles. This Configuration is called Bo1-1Bo according to UIC Classification of Locomotives [8]. The Traction Converter System involves 1-ph to 3-ph conversion by means of Rectifier-Inverter System. The Auxiliary Circuit consists of both 1-ph to 3-ph Conversion and 3-ph to 3-ph Conversion by use of a Rectifier-Inverter Circuit when tapped from Auxiliary Winding of Transformer and low Voltage SPR Drive respectively. The Auxiliary Windings are connected to three individual 4-Pulse Rectifier for conversion to DC. On the Rotor side of the Traction Motors, a 3-ph Diode Bridge Rectifier is connected. Each of the 1-ph and 3-ph Rectifiers are connected to a 3-ph Inverter. These Inverters Drive the Air-Conditioning Units. For the purpose of Lights and Fans Loads, the fourth Auxiliary Tapping is connected to 1-ph to 3-ph Conversion System and the Loads are Balanced on the Ph-Neutral in each of the three-phases after the Voltage has been stepped Down from 800 V to 110 V. The main Circuit Diagram is shown in Fig.2.

The Circuit Shown in Fig. 2 was simulated for a Simulation time of 20 seconds. The Embedded MATLAB Program generated commands for the PWM Generator to deliver Pulses to the Insulated Gate Bi-polar Transistors at the required Frequency of operation depending on the Speed of the Locomotive at the Wheel. The Control Strategy used in this Simulation is constant V/f to maintain the Torque almost Constant [7], [9]. In order to simulate the 1-ph, 25 kV AC delivered by the Over-Head Equipment, a Voltage Source was connected to the Main Transformer. The Main Rectifiers converter 1-ph AC to 5000 V DC. The Harmonics were filtered using LC Filter in the DC Link. The Straight-line DC was fed to 3-ph Inverter. Each Inverter was connected to a Traction Motor. The Inverter delivered a 3-ph Voltage of 5800 V with 180 A Current. The Traction Motors reached their rated Speed after about 0.4 seconds. The commands for Speed reduction, Braking were given at different intervals to simulate the running conditions of Locomotives according to the Trapezoidal Speed-Time Curve for Passenger Services operations which consists of Notching Up, Acceleration, Free running, Coasting and Braking.

The Circuit Breakers on the Input side of the Auxiliary Rectifier were initially kept in Closed Position as there would be no Slip-Power Recovery when the Locomotive starts. After the Traction Motors reached the required Speed, the Circuit Breakers were Reset to Open position. The Auxiliary Loads were now entirely fed from the low Voltage SPR Scheme. Again when the Coasting and Braking mode of operation was underway, the Circuit Breakers in the Auxiliary Power Circuit Closed so as to deliver Power to the Loads from the Over-Head Power Lines through the Auxiliary Winding of the Transformer. Thus, the opening and Closing of the Circuit Breakers is decided by the Voltage sensed from the Main Traction Inverter.

The Speed of the Traction Motors was controlled by means of an Embedded MATLAB program. The Speed required at the Wheel in kmph was given as input to the Program. This Speed was in turn converted into Speed in rpm and matched with the Speed of the Traction Motors measured. If the Speeds were same no Error was generated. If the Speeds were different, the required new Frequency of the Inverter was calculated and the output was fed to the PWM Controller to calculate the required Boost in Inverter Voltage to develop Constant Torque. The PI Controller was used for the purpose of delivering the required Gain in Voltage. Thus even though the Speed of the Traction Motors was varied according to the needs of the Speed of the Locomotive at Wheel, the Torque was maintained near constant by the V/f method[8]. The various Graphs of the 3-ph Main Inverter Output Voltage, Auxiliary Inverter Output Voltage, Speed developed by Traction Motors, Speed developed by Air-Conditioner Compressor Motors are shown in Figures 3, 4, 5, 6 respectively. The parameters of the WRIMs used are shown in Table No. 3.The detailed Calculations of Power delivered to Traction Motors, Slip-Power recovered, Tractive Effort developed at different Speeds, savings in Fuel are presented in the next section with necessary Equations and Assumptions.

4. EQUATIONS AND CALCULATIONS:

The Equations and Calculations related to the proposed Traction Drive systems are presented in this section in brief.

4.1 Calculation of Tractive Effort Required:

The various Tractive Efforts required by a Locomotive are [1, 6]:

Tractive Effort for Acceleration ( F_a):

---------------------- -Eq. (1)

Tractive Effort to overcome Gravitational Pull ( F_g ):

-----------------------Eq. (2)

Tractive Effort required to overcome Train Resistance for a Locomotive ( F_r ):

-------------------------------Eq. (3)

Tractive Effort required to overcome Curve Resistance

( F_c ):

-----------------------Eq. (4)

Total Tractive Effort = F_t = ------------------------------------------------------------Eq. (5)

4.2 Assumptions for Calculations:

It is assumed that the Locomotive starts on a plane surface without Gradient and Curvature hence, the Tractive Effort required would be only Tractive Effort for Acceleration. The Calculations shown in this section are for (i) Shatabdi Expresses and (ii) Rajdhani Expresses. Let us assume that the Locomotive has to accelerate a trailing Load to 120 Kmph in 304 seconds.

(a) Calculation of Tractive Effort:

Acceleration, α in Kmphps will be given as,

Weight of the Locomotive = W_l = 90 tonnes

(i) For Shatabdi Expresses:

These Trains normally have 12 coaches. The Coach Composition is given in the Table No.1.

Weight of the Trailing Load = W_t = = 599 Tonnes

Total Weight = W = ( W_l + W_t ) = 689 tonnes

Effective weight of Locomotive and Trailing Load = = W_e = 757.9 tonnes

Tractive Effort required for Acceleration = F_a =

(ii) For Rajdhani/Duranto Expresses:

These Trains normally have 19 coaches. The Coach Composition is given in the Table No.2.

Weight of the Trailing Load = W_t =

= 984 Tonnes

Total Weight = W = ( W_l + W_t ) = 1074 tonnes

Effective weight of Locomotive and Trailing Load = = W_e = 1182 tonnes

Tractive Effort required for Acceleration = F_a =

(b) Calculation of Power, Torque developed:

Voltage per phase = 5800 V

Current per phase = 180 A

Power Factor = 0.9 (Assumed)

Efficiency of the Machine = 95% (Assumed)

Frequency = 50 Hz, No. Of Poles = 2, Diameter of the Wheel = 1092 mm

Efficiency of the Gear = 0.9

Gear Ratio for Passenger Locomotive = G_r = 3.6

Power input to the WRIM = Watts

= Watts

= 1627435 Watts (per Motor)

Power Output per Motor = 0.95 x 1627435 = 1546 kW

Rated Speed of the Traction Motors = N_s = rpm = = 3900 rpm

If the Speed of the Locomotive is 150 Kmph, then the Speed of the Traction Motors will be N_tm.

Rpm

= Rpm = 2623.433 Rpm

Torque developed per Machine = Nm = Nm =5627.44 Nm

Total Torque developed by 4 Traction Motors = T_d = 22509.76 Nm

Tractive Effort Developed (at Speed of 150 kmph) = = = 134 kN

Speed of the Locomotive at Wheel =

= = 223 kmph (at rated Speed of the Traction Motor)

= = 85.76 kmph (During Deceleration)

Starting Torque of the Traction Motor = Nm = Nm = 84361.2 Nm

Total Torque developed by 4 Traction Motors = T_d = 337444.8 Nm

Tractive Effort Developed at starting (at Speed of 10 kmph) = = = 200 kN

(c) Power Required by the Air-conditioned Coaches:

(i) For Shatabdi Coaches:

The Total Connected Load and the number of Coaches of each type is given in Table No.1. Hence, from the Table,

The Total Connected Load for a Train comprising of 12 Coaches is given as,

= 498 kW

Assuming a Diversity Factor of 0.7, the Maximum Demand =

= = 348.6 kW

(ii) For Rajdhani Coaches:

The Total Connected Load and the number of Coaches of each type is given in Table No.2. Hence, from the Table,

The Total Connected Load for a Train comprising of 19 Coaches is given as,

= 795.75 kW

Assuming a Diversity Factor of 0.7, the Maximum Demand =

= = 557.025 kW

(d) Calculation of Slip-Power and Total Power Delivered to Air-conditioned Coaches

Air-Gap Power of one Traction Motor = 1546 kW

Slip (at 150 kmph) = = =

Theoretical Slip – Power Recoverable of one Traction Motor when Locomotive Speed is 150 Kmph

= = 505.5 kW

Slip-Power Recoverable from four Traction Motors = 2022 kW

Output Voltage of Auxiliary Winding of Transformer = 1000 V

Output Current of Auxiliary Converter = 75 A

Output Power at each Auxiliary Inverter terminals fed from Auxiliary Windings of Transformer when Traction Motors are at standstill = = = 130 kW

Total Output Power from four Auxiliary Inverters = = 520 kW

Slip-Power Recovered per Traction Motor (at 150kmph) = (from Graph of Voltage in Aux. Ckt)

= = 70 kW

Slip-Power Recovered from four Traction Motors = (from Graph of Voltage in Aux. Ckt) = 280 kW

Diesel consumption per Hour by the two 500 kW EOG Cars = 100 litres.

If at least one EOG Car is switched off and Power is taken from the Slip-Power recovered, the Savings in Diesel for a Shatabdi Express that run for approximately 14 Hours on one round Trip would be,

= = 700 litres.

With Diesel costing about Rs. 48/- in India, the Amount of money saved per Trip = = Rs. 33600/-

For the Whole year, if the Shatabdi is run for 300 days, the total savings would be

For a Rajdhani Express which on an average runs for 30 Hours in one Direction, the savings in Diesel would be 1500 litres. Amount of Money saved per Trip would be = Rs. 72000/- for one way Journey per Day.

For the Whole year, if Rajdhani runs on all days, the total savings would be

5. ADVANTAGES OF THE PROPOSED CIRCUIT:

The following are the advantages of the proposed Circuit:

· Noise and Air Pollution due to EOG is reduced.

· Costly Fossil Fuel is saved.

· Energy is conserved as the low Voltage Slip-Power Recovery is used instead of drawing Power from the EOG set to aid the Power delivered by Transformer Auxiliary Windings.

· This circuit along with Efficient heat management system inside the coaches by using Sun-Films on Windows will save lot of Energy and Fuel.

· The elimination of one EOG Power Car will be helpful to attach another Passenger Car for the same Tractive Effort required to haul the Train thereby enhancing the capacity of the Train and also earn more revenue per Trip.

6. CONCLUSIONS:

From the Simulation Studies carried out with Air-Conditioner Blower Motors rated at 11.5 kW as the Loads on the low Voltage Slip-Power Recovery Drive, it can be concluded that the Slip-Power generated at Speed range of the Locomotives below 170 Kmph can be fully utilised to Drive the Air-Conditioning Units and also deliver Power to the Lighting Loads inside the Coaches of the Trailing Passenger Coaches. In case of Speed of the Traction Motors being almost the rated Speed, the Power delivered by the Auxiliary Winding of the Traction Transformer can be utilised to aid the Slip-Power recovered as the Slip-Power at near rated Speed would be lesser as compared to at lower Speeds of the Traction Motors. This means that the need of End-On-Generation with the help of Diesel Generators can be either partially or totally eliminated in these Trains depending on the Power delivered by SPR Scheme. The elimination of EOG Power Cars would enable Railways to add at least three more Passenger Coaches thereby increasing the Revenue per Train. The elimination of EOG Power Car would also reduce the money spent on Diesel Oil used for running the Generators. It would also lead to reduction in noise, air pollution due to emitted smoke and vibration levels in the Train Sets. Hence, it can be concluded that Head-On-Generation aided by low Voltage Slip-Power Recovery scheme would lead to Profit making by bringing down the running Costs involved in buying Diesel Oil and also help in reducing Pollution in the long run with a very comfortable ride for the Rail Passengers. Therefore, Traction Drive System with low Voltage Slip Power-Recovery Scheme to Drive the Locomotive and also deliver Power to Trailing Passenger Coaches is a viable cost saving option that can be implemented in the Future.

Table No 1.: Details of Coaches of Shatabdi/Durunto Express Trains (Chair Car Type)

S. No	Type of Coach	Weight in Tonnes	Total Connected Load kW	No. Of Coaches
1	First AC Chair Car	45.30	40	2
2	Second AC Chair Car	47.3	40	8
3	EOG – Diesel Generator Cars	65	49	2

Table No 2.: Details of Coaches of Rajdhani/Duranto Express Trains (Sleeper Type)

S. No	Type of Coach	Weight in Tonnes	Total Connected Load in kW	No. Of Coaches
1	First AC 2-Tier Sleeper	46.60	15.75	1
2	AC 2-Tier Sleeper	48.8	34.75	6
3	AC 3-Tier Sleeper	51.36	40	8
4	Pantry Car	51.90	76.75	2
5	EOG – Diesel Generator Cars	65	49	2

Table 3: Traction Motors Parameters:

S. No	Parameter	Traction Motors
1.	Rated Voltage	5000 V
2.	Rated Power	1600 kW
3.	Operating Frequency	50 Hz
4.	Efficiency	95 %
5.	Power factor	0.9 lag
6.	No. Of poles	2 poles

7. REFERENCES:

[1] Anula Khare, Saroj Rangnekar "Hotel Load in Indian Railways: Energy Conservation in EOG Scheme", International Journal of Emerging Trends - 2011.

[2] Ministry of Railways, Government of India, “General Services- Train Lighting”, IRIEEN, Nashik, India

[3] H. Partab “Modern Electric Traction” Publisher: Dhanpat Rai and Sons, India – 2012.

[4] Paul Blaiklock, William Horvath “Saving Energy” TMEIC GE, USA – Motor Technology September-2009

[5] ABB Motors and Generators – “Brochure on Slip Ring Motors for heavy-duty and critical Applications”-

2011.

[6] J. Upadhyaya and S.N. Mahendra “Electric Traction”, Allied Publishers India – 2000.

[7] S. S. Chirmurkar, M. V. Palandurkar and S. G. Tarnekar “Torque Control of Induction motor using V/f Method” International Journal of Advances in Engineering Sciences, Vol.1, Issue 1, Jan 2011.

[8] Toby J Nicholson “DC and AC Traction Motors”. IET Professional Development Course in Traction Systems 3-7 Nov 2008, Manchester Pages34-44.

[9] Rupesh Kumar “Course on Three Phase Technology in TRS Applications” IRIEEN, Nasik, India – Aug.2010.

Received on 25.05.2015 Accepted on 25.07.2015

Research J. Engineering and Tech. 6(4): Oct. - Dec., 2015 page 399-407

DOI: 10.5958/2321-581X.2015.00062.8