SUMMER TRAINING REPORT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL AND INSTRUMENTATION ENGINEERING DEPARTMENT OF
THAPAR UNIVERSITY PATIALA (PUNJAB) AS PART OF COURSE WORK OF
B.E. ELECTRONICS (INSTRUMENTATION AND CONTROL)
SUBMITTED BY
Samarth Sidhpuria B.E ( EIC) Roll No.
–
101005048
Preface When I was a small kid, I always used to wonder and fascinate about trains. The sound, vibration of the trains, its environment, to sum up loved everything about trains. As I got older, I came to know that apart from hauling me from one to place other, it transferred goods, also was one of the largest contributors to the Indian economy and many else. So, I decided to go for my 6 weeks (45 days) summer training with an organization called Indian Railways to know that a machine so large, which runs as the bloodlines for this country must have quite a science and engineering involved behind it and that is what we are going to explore in this project report. Basically, which machine is the mastermind behind all these carrying all loads and passengers throughout the mapof our country? LOCOMOTIVES. Locomotives are thebasic machines mind behind a giant organization like the Indian railways and is single most important building block of railways. But how do they work, what are the major components involved in building of superstructure machine like this. So, in this project report, we would be basically discussing about the two important locomotives, namely electric and diesel electric locomotive in detail with theirexplained working of each and every part and how do they contribute into the locomotive. We would also study about the requirement and benefits and working of new microprocessor based control system in Indian railways locomotive in place of conventional locomotive control system. We would also go through some of the standard specifications of some of the components used by the Indian railways. The present report has been done as a summer training of six weeks for the completion of 5th semester of B.E Electronics(Instrumentation and Control) Engineering. During the training I got the exposure to various equipment and machines their maintenance and technology concerning the repairing the Diesel Locomotive and Electric Locomotive and hence was assisted in developing self-confidence. The training helped me in implementing my theoretical knowledge to the actual industrial environment. This training at the“ELECTRIC LOCO SHED (NEW KATNI JUNCTION)” and “DIESEL LOCO SHED(NEW KATNI JUNCTION)”is definitely going to play an important role in developing an aptitude for acquiring knowledge hard work and self confidence necessary for successful future. Every attempt has been sincerely made to keep the report short and interesting and easily understandable but due to various constraints involved, somewhere in the report we might feel that topics are under covered or over explained, but it might be kept in our minds that machine so large with range of equipment so vast, it might have some loops in the report but I expect all of you to enjoy this fantastic creation of science and engineering.
Acknowledgement In these six weeks of industrial training, I wish to my attribute my profound sense of gratitude without whose generous co-operation and co-ordination it would have been highly difficult for me to have such a successful training experience in the organization, in every game of life these are multitude of players whose are the real heroes and this experience there are many loyal and phenomenally selfless friends, co-workers and my mentors in industry, I am overwhelmed. Few tasks are more enjoyable and fulfilling than acknowledging my gratitude to all those, who have helped in this effort in so many ways. I take this opportunity to express my sincere thanks to the management of “ELECTRIC LOCO SHED (NEW KATNI JUNCTION)” and “DIESEL LOCO SHED(NEW KATNI JUNCTION)” of permitting me to observe and study the whole setup of factory. I owe more than a debt of gratitude to Mr. P.S Soni (Chief instructor), Mr. Manish Saxena (ADEE) from Electric loco shed (New katni junction) and Mr. R.K Gupta (Chief instructor), Mr. R.P Khare (ADME), Mr. Suman kumar tanti (Sr. DME) and Mr. Sameer Chaube (Senior Section Engineer ) from Diesel loc shed (New katni junction) & all the staff for theircorporation & guidance made itpossible to complete the work. I am equally thankful to Thapar University for providing me this opportunity to work with such a big organization which happens to be largest employer in the world. I would highly indebted by Sh. A.K Saxena (Retd. Senior Section Engineer ) from Diesel loco shed (NKJ) who helped me out at every single step of this training, helping me with any problem I might ever had and a true guide throughout this memorable journey.
Contents
Organization
Classification & nomenclature of locomotives
Electric Locomotives
Diesel Locomotive
Control systems in Diesel- Electric loco
Organization Introduction Indian Railways (reporting mark IR) is an Indian state-owned enterprise, owned and operated by the government of India through the Ministry of Railways. It is one of the world's largest railway networks comprising 115,000 km (71,000 mi) of track over a route of 65,000 km (40,000 mi) and 7,500 stations. IR carries about 7,500 million passenger annually or more than 20 million passengers daily (more than a half of which are suburban passengers) and 2.8 million tons of freight daily. In 2011-2012 Indian Railways earned 104,278.79 crore (US$19.71 billion) which consists of 69,675.97 crore (US$13.17 billion) from freight and 28,645.52 crore (US$5.41 billion) from passengers tickets. Indian Railways is the world's fourth largest commercial or utility employer, by number of employees, with over 1.4 million employees. As for rolling stock, IR holds over 229,381 Freight Wagons, 59,713 Passenger Coaches and 9,213 Locomotives. The trains have a 5 digit numbering system as the Indian Railways runs about 10,000 trains daily. As of 31 March 2012, 22,224 km (13,809 mi) (34%) of the total 65,000 km (40,000 mi) km route length was electrified. Since 1960, almost all electrified sections on IR use 25,000 Volt AC traction through overhead catenary delivery.
History
The first railway on Indian sub-continent ran over a stretch of 21 miles from Bombay to Thane. The idea of a railway to connect Bombay with Thane, Kalyan and with the Thal and Bhore Ghats inclines first occurred to Mr. George Clark,the Chief Engineer of the Bombay Government, during a visit to
Bhandup in 1843.The formal inauguration ceremony was performed on 16th April 1853, when 14 railway carriages carrying about 400 guests left Bori Bunder at 3.30 pm "amidst the loud applause of a vast multitude and to the salute of 21 guns." The first passenger train steamed out of Howrah station destined for Hooghly, a distance of 24 miles, on 15th August, 1854. Thus the first section of the East Indian Railway was opened to public traffic, inaugurating the beginning of railway transport on the Eastern side of the sub-continent. In south the first line was opened on Ist July, 1856 by the Madras Railway Company. It ran between Veyasarpandy and Walajah Road (Arcot), a distance of 63 miles. In the North a length of 119 miles of line was laid from Allahabad to Kanpur on 3rd March 1859. The first section from Hathras Road to Mathura Cantonment was opened to traffic on 19th October, 1875. These were the small beginnings which is due course developed into a network of railway lines all over the country. By 1880 the Indian Railway system had a route mileage of about 9000 miles.
Structure Indian Railways has one of the largest and busiest rail networks in the world, transporting over 18 million passengers and more than 2 million tones of freight daily. It is the world's largest commercial or utility employer, with more than 1.4 million employees. The railways traverse the length and breadth of the country, covering 6,909 stations over a total route length of more than 63,327 kilometers (39,350 mi). As to rolling stock, IR owns over 200,000 (freight) wagons, 50,000 coaches and 8,000 locomotives. Indian Railways operates about 9,000 passenger trains and transports 18 million passengers daily across twenty-eight states and one union territory. Sikkim, Arunachal Pradesh and Meghalaya are the only states not connected by rail. The passenger division is the most preferred form of long distance transport in most of the country. Indian Railways is divided into zones, which are further sub-divided into divisions. The number of zones in Indian Railways increased from six to eight in 1951, nine in 1952, and finally 16 in 2003. Each zonal railway is made up of a certain number of divisions, each having a divisional headquarters. There are a total of sixty-seven divisions. Each of the sixteen zones, as well as the Kolkata Metro, is headed by a General Manager (GM) who reports directly to the Railway Board. The zones are further divided into divisions under the control of Divisional Railway Managers (DRM). The divisional officers of engineering, mechanical, electrical, signal & telecommunication, accounts, personnel, operating, commercial and safety branches report to the respective Divisional Manager and are in charge of operation and maintenance of assets. Further down the hierarchy tree are the Station Masters who control individual stations and the train movement through the track territory under their stations' administration.
Working site Katni ( used as depot name for locomotive in this case) is the Diesel loco shed which holds WDM-2, WDM- 3A, WDG-3A, and WDG-3C. This is located at New Katni Jn. presently in West central railways (WCR) division, but the diesel locos always carry the marking that says simply 'Katni' (in Devanagari) or 'KTE'. This is one of Indian Railway's biggest diesel sheds. This is a separate shed about 3km from the Katni electric shed (below). It is on the Itarsi-Allahabad line. The shed used to be in CR until 2003. Holds the only WDG-3C ‘Cheetah’. New Katni Jn. ( used as depot name for locomotive in this case) is the electric loco shed which houses Electric locomotive such as WAG-5, WAG-7 Located at New Katni Jn. The shed used to be in CR (Central railways)until 2003. Had WAM-4/WAM-4P until the early 1990s or so. Electric locos are marked 'NKJ' (for New Katni Jn.) in contrast to the diesels (above) that say just 'Katni'. The shed is about 3km east of the diesel shed, near the junction of track going to Singrauli and Bilaspur. It has a large marshalling yard attached. 120+ locos
Location Katni (also known as Murwara (Katni) or Mudwara) is a town on the banks of the Katni River in Madhya Pradesh, India. It is the administrative headquarters of Katni District. It is located in the Mahakoshal Region of Central India. The city is 90 km (56 mi) away from the Divisional Headquarters of the region, Jabalpur. It is one of largest railway junctions in India and has the largest railyard and biggest diesel locomotive shed in India.[2] The city has an abundance of lime and bauxite. It also has Ordinance Factory Katni of the Ordinance Factories Board which maufactures products for the Indian Armed Forces.
Classification & nomenclature of locomotives In India locomotives are classifies according to their track gauge, motive power, the work they are suited for and their power or model number. The class name includes this information about the locomotive. It comprises 4 or 5 letters. The first letter denotes the track gauge. The second letter denotes their motive power (diesel or electric) and the third denotes the kind of traffic for which they are suited (goods, passenger, mixed or shunting). The forth letter used to denotes locomotive model number. However, from 2002 anew classification scheme has been adopted. Under this system, for new diesel locomotives, the forth letter will denotes their horsepower range. A locomotive have a fifth letter is its name which generally denotes a technical variant or subclass or subtype. This fifth letter indicates some insulator variation in the basic model or series, perhaps different motors or a different manufacturer. Track gauge
Broad gauge is the most predominant gauge used by the Indian railway. The total length of track used by Indian railways is about 111559 km while the total route length of the network is 63465km.about 28% of the route –kilometer and 40%of the total track kilometer is electrified. Indian railways use three gauges, the broad gauge which is wider than the 1435mm, standard gauge: the meter gauge and the narrow gauge 762 mm
The first letter (gauge)
W = Broad Gauge Y = Meter Gauge
The second letter (motive power)
D = Diesel C = DC traction A = AC traction
The third letter (job type)
M = Mixed Traffic P = Passenger G = Goods S = Shunting U = Multiple Unit (EMU / DEMU)
Electric Locomotives Types of electric Locomotives and their comparison Comparative features of A.C. locos WAG5 3850
WAG7 5000
WAG9 6000
WAP4 5000
WAP5 6000
80
100
100
140
160
Max. tractive effort at starting
HS 15250 33.5 t
HS 15250 42 t
FRA 6068 47 t
HS 15250 30.8 t
6FXA 7059 30 t
Cont. tractive effort
20.6 t
24 t
33 t
24 t
26 t
Total weight of loco
126 t
123 t
123 t
112.8t
78 t
AIR/ RHEO 3900
AIR/ RHEO 5400
AIR/ REGN 6531
CO-CO
CO-CO
Horsepower Max. service speed Type of TM
Break system Transformer in KVA
CO-CO
Wheel arrangement
AIR 5400
AIR/ REGN 7475
CO-CO
BO-BO
Traction motor o/p voltage current power No. of axles Adhesion Type of bogies
750 840 585 6
750 900 630 6
2180 540 1150 6
750 900 630 6
2180 370 850 4
29 ℅
35.70℅
38 ℅
35 ℅
38 ℅
CAST
FABRI
FABRI
FABRI
FABRI
Gear ratio
18:64
18:64
DIRECT
23:58
DIRECT
Electric traction Voltages used for electric traction in India Voltages used are 1.5kV DC and 25kV AC for mainline trains. Calcutta had an overhead 3kV DC system The 1.5kV DC overhead system (negative earth, positive catenary) is used around Bombay In preparation for this, BHEL has been retrofitting some Alstom EMUs with AC drives to allow them to operate with both DC and AC traction as the system conversion proceeds. The 25kV AC system with overhead supply from a catenary is used throughout the rest of the country. The WCAM series of locomotives are designed to operate with both DC and AC traction as they move towards or away from the Bombay DC section. The new [2003] AC-DC EMU rakes used in Mumbai are also designed to operate with both DC and AC traction as the Bombay area switches over to the 25kV AC system. The Calcutta Metro uses 750V DC traction with a third-rail mechanism for delivering the electricity to the EMUs. The Calcutta trams use 550V DC with an overhead catenary system with underground return conductors. The catenary is at a negative potential. The Delhi Metro uses 25kV AC overhead traction with a catenary system on the ground-level and elevated routes, and uses a rather unusual 'rigid catenary' or overhead power rail in the underground tunnel sections (Line 2).
Electric transmission circuit of electrc locomotive
Specification diagram of an electric locomotive
Pantograph For collecting power from 25 kV ac contact wire pantographs are mounted on the roof of the traction vehicles.. AM 12 pantograph of Faively design has been adopted by Indian Railways for 25 kV ac electric locomotives. These pantographs are provided with steel strips for current collection. The raising and
lowering of the pantograph is by means of a pneumatically operated servo motor. This pantograph is a single pan design having two o-springs mounted on it. For keeping the pantograph in the lowered condition, main springs have been used. The suspension of pan is on plungers.
DJ ( Disc joint) circuit breaker The high voltage circuit breaker DJ is special type of electro pneumatic contactor mounted on the roof of the loco. The electrical equipment of the loco is connected to or disconnected from the OHE by means of the circuit breaker. it is designed to open the circuit rapidly about 0.03 compressed air apart from operating the breaker acts as a means of extinguishing the are also.
Principle of operation The opening and closing of the DJ is effected by a servo motor which is supplied with compressed air from the reservoir TDJ minimum pressure 6.5 KG. if the air pressure is less than 6.5 KG it is possible to close DJ but it can not be open if the pressure is very less and the loco may risk an over current. To close DJ it is necessary to admit compressed air on the right side of the piston. This is affected by a closing device, which is operated by the electro valve EFDJ, when EFDJ is energized, the passage opens air is admitted on the right side of the piston and the DJ closes. The air pressure which was admitted close the DJ is automatically exhausted after the DJ closed. At the same time it should be ensured that air pressure does not enter the left side of the piston, otherwise this air pressure will cause the DJ to open and cause a second detonation. To prevent the air pressure from entering the left side the piston, the electro valve MTDJ which controls the opening device must be energized. When MTDJ is energized the opening device passage is closed and air pressure can not enter the left of the piston. The DJ is locked in the closed or open position by a mechanical locking device and prevents it from leaving the position due to vibration etc. For closing DJ, energized EFDJ and MTDJ together. After DJ has closed EFDJ is to be de-energized, and for opening DJ, de-energized MTDJ can be done either of voluntarily by the driver or by the action of the safety relays. DJ can be controlled from the driver cab simply by using the BLDJ switch on the switch panel. The pilot lamp LSDJ gives the indication that DJ is currently open or close. If the lamp is glow it shows the DJ is open.
Transformer Power to the traction vehicles is available at 25 kV ac single phase from the contact wire. In order to step down the voltage as well as to control the same for feeding to the traction motors, the traction power transformers are provided on the traction vehicles. These transformers generally have a primary winding, a regulating winding, traction secondary windings and auxiliary windings. The regulating winding is designed for choosing appropriate voltage for the traction motors. The auxiliary winding is required for feeding the auxiliary motors on the locomotive. In order to increase the horse power of the locomotives, the traction transformers have been up rate. The up ratings have been achieved by using increased copper section of the conductor used, improved insulation scheme and in certain cases adoption of aluminum foil wound construction for minimizing the losses. This is a main transformer of locomotive. The 25 KV single phase AC power supply of OHE is fed to the
winding of regulating transformer through main bushing. The winding is equally divided into 32 taps. These taps are connected to tap changer.
The complete winding of transformer is oil immersed in a tank and oil is cooled through oil cooling system containing MPH and MVRH. Above the transformer there is oil conservator, the pipe leading to it serving as safety valve. Above this safety valve there is an oil overflow chamber with a discharge pipe leading the blown out oil underneath the loco body. The air does not come in to contact with the oil in the conservator direct by having been completely dried before by means of silica gel air gryer. The transformer is fitted with oil level indicator on both the sides. There is a red mark at 15 c. normally the oil should not go below the red mark. The transformer has three lag. Lag one carries the winding of the regulating transformer stepping down the voltage of the overhead system to a value permissible for the equipment. The series winding A-32 ---- A-33 has turns and a cross sectional area of 27.45 mm² The main winding A-0 ----- A-32 has 960 turns and a cross sectional area of 27.45 mm²
Therefore, the total no. of turns in a complete winding of the regulating transformer will be N1= 80 + 960 = 1040 turns According to the actual position of the tap changer i.e. Pos 0, 1, 2, 3…28, 29,30,31,32
The active no. of turns varies from NR = 0, 30, 60, 90, 120 ….840, 870,900,930,960 turns
In addition to the winding of the regulating transformer Leg 1 carries the electrically separated winding a-0 ---- a-1 of the auxiliary circuits also. This winding has 18 turns and cross sectional area of 248 mm². The leg 2 and 3 carries the primary and secondary windings of the main transformer. The indication effect of the winding of leg 3 on the winding of leg 2 varies according to the position of the tap changer. The design of the two legs is similar, the difference being in the cross sectional area only. The primary windings both legs are connected in series and each leg has Np = 288 turns. The beginning of the primary windings led to the terminal A 34 and is connected through the tap changer with the tapping A-0 to A-32 of the regulating transformer. The end of the following is permanently connected to A-0 internally.
Brief specifications of Transformer
Type Supplier Phase Cooling No of taps Voltage Primary
Secondary
HETT 3900 NGEF, CROMPTON GREAVES, BHEL Single OFAF 32 Maximum Nominal Minimum Maximum minimum
27.5 KV 25.0 KV 22.5 KV 1058V in each winding 869 in each winding
Primary input Secondary output Aux. system output System
Rated
4170 KVA 3900 KVA 270 KVA Single phase, 50 c/s oil immersed, air cooled with forced oil circulation primary single winding and secondary with double winding with equal ratings. secondary 2250 amps.
current of winding
each
Tap Changer:
The Tap changer is provided on 25 kV (HT) regulating winding of locomotive transformer for controlling the voltage input to main transformer. The Tap Changer operates with the help of elaborate mechanism using an air driven Servo Motor (SMGR) and a bevel gear arrangement. Through precision adjustment and provision of transition resistance (RGR) it is ensured that there is no break of load current in-side the selector (GR) which is oil filled and the load current is broken by load switches known as CGR1, CGR2 and CGR3.
The tap changer is directly built on to the transformer. The tapings of the transformers are bought out and arranged in circular fashion on an insulated contact plate. There are to rows of contact segments which are aligned on outer and inner circles of the contact plate. An arm which is known as selector arm is driven by shaft at the center of the contact plate. Two rollers are situated at the edge of the selector arm. These rings are provided in front of the contact plate. The center shaft which extends outside the tap changer casing is driven by an air servomotor known as SMGR. The design of the air servo motor is such that once the selector arm begins its movement, it can be stopped only at the required tap (not in between two taps). The connection between the inner or outer ring to the transformer is being established by means of CGR contactor.
Method of operation The selector arm is actuated by the driving shaft through an intermittent gearing comprising of drive wheel, Lantern gear pinion and stopping wheel. This driving shaft also operates the CGR cam shaft in sequence with the operation of contact rollers. The opening and closing sequence of CGR contactors are given below:
Even notches In bet. notches Odd notches
CGR I Open Closed Closed
CGR II closed closed open
CGR III closed open open
Before moving contact roller leaves the zero tap contact segment, it touches the first tap segment. During this the CGR1 contactor closes inserting the diverter resistance RGR inbetween tap ‘0’and tap ‘1’ through RGR. This resistance RGR restricts the short circuit current when the selector arm further moves fully on tap 1, the inner contact roller breaks the contact with zero tap. Meanwhile CGR II contactor opens and cuts off RGR from circuit, Like wise when the selector arm moves from first tap to second tap. The contact roller will continue to make connection between inner segment and inner ring. This is due to over lapping contact segment. At the same time CGR I, CGR II are closed again setting the
resistor RGR in between the short circuited winding. Now the service current flows from the contact ring in the selector through the resistor RGR. When the selector arm further moves, the outer roller leaves the tap 1 segment and breaks the contact. At the same time CGR gets opened and CGRII and CGR III are closed. This again cuts off the resistor RGR. The opening and closing of CGR contacts is carried out by cam shaft which is driven by the main shaft through gear arrangements. This ensures a perfect relationship between the movement of selector arm and the operation of CGR contactors. A high resistor RGR serves as the connection between equal potential, which ensures that branches of the circuit being interrupted at the given potential.
Control of tap changer
The servo motor which drives the graduator is controlled by electro valves VE1 and VE2 for progression and regression respectively. These electro valves are remote controlled from driver desk by the master controller MP. The master controller hand wheel MP has 4 position 0, --, + and N. When MP is placed on ‘+’ VE! Will be energized and progression will take place. When MP is placed on ‘0’ VE2 will be energized and regression will take place. ‘—‘position is used for notch by notch
regression and N shows the neutral position. Position ‘—‘and ‘+’ are unstable position, if the hand wheel is released in such position it is returned to N by spring force. If P is placed on 0 the tap changer regresses to ‘0’ notch at a time.
Traction Motor
Our Indian railways in olden day’s compound motors are used for traction but now a day’s using DC
series motors as traction motors for running locomotives. While comparing with AC motors these DC motors are efficient and high starting torque. The speed control of DC motor is very easy but in AC three phase induction motor it is difficult. For every locomotive there are 6 DC traction motors in which all six are connected in parallel. The speed of the traction motor is controlled by tap changer circuit with 32 notches. The traction motor is a dc series motor four pole or six pole forced ventilated machine arranged for axle mounting on sleeve baring and supported on the opposite by the resilient suspension unit, transverse movement is limited by the flanges of axle. These motors are axle hung, nose suspended type and are provided with grease lubricated roller bearings for armature as well as for suspension. Special provision has been made in design of the motors to ensure the locomotive operates satisfactorily on flooded track, to max. Flood level of 20 cm , above rail level.
The main parts of motors are given below 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Magnet frame armature and shields. Brush holders and brushes. Commutator Armature Stator Armature windings Field windings Inter poles Armature bearings Axle bearing
Technical data
Type Continuous out put Volts Current Speed Number Field Insulation No. of poles Ventilation
HS 15250 A 630 KW 750 V 900 Amp. 895 RPM 6 Per Loco Series field with commutating poles Class H Main 6, commutating 6 90 cu meter/min
Generally in locos there are six traction motors. Three motors per bogies and each motor driving one axle directly through gears. The motors M1 to M6nare supplied jointly by the two silicon rectifiers connected in parallel through contactors L1 an L2. Each rectifier units RSI is connected to separate secondary winding TFP 1, 2 and the smoothing the current thus rectified in carried out by means of two smoothing reactors SL1 and SL2. By increasing the notch of the tap changer using SMGR the we can increasing the speed of the traction motor after applying maximum tension to the traction motor if the required speed can not be attended , the field coils of the traction motors can be shunting is done dead resistance are introduced in parallel to the field coils. Shunting is effected in 3 steps by four electro pneumatic contactors for each motor or pair of motor. These contactors are remote controlled by the shunting controller MPS which has 5 positions. Shunting can only be done if 20 or more notches are taken, as the cam contact of GR on the control circuit of shunting contractors will close only on notches 20 – 30. Shunting should only be done when it is absolutely necessary and only a after having applied the max. Permissible tension to the traction motors. It should be ensured that the max. Permissible limit of intensity is however not exceeded.
Carbon brush arrangements
Arno Converter Arno Converter is a special duty machine for conversion of single phase in-coming supply into 3 phase out- put supply. 3 phase supply is essentially required on most of the electrical locomotives for driving certain auxiliary equipment like blowers and compressors. The function of Arno Converter is to supply 3 phase power required for these auxiliaries. It converts single phase supply from main transformer to 415v three phase supply for auxiliary motors. Arno Converter of horizontal construction was used in WAG 4x\WAG5x\WAG6x\WAG7x locomotives. Indigenously developed Arno Converter however is of vertical construction. The machine has mechanical construction suitable to withstand the severe vibrations encountered on locomotives.
Static Inverter The Arno convertor suffers from various disadvantages chief of which is output voltage imbalance which can cause heating up of the auxiliary motors, varying output voltage because of the variations in OHE voltage, problems related to starting of the Arno, etc. To overcome these shortcomings and to improve loco reliability, the Indian Railways have started providing Static Inverter power supply for auxiliary machines in locomotives. The Static Inverter comprises a force commutated rectifier, a DC link and an Inverter which is usually composed of six IGBT switches. The Static Inverter broadly works in the following manner: The supply from the transformer tertiary winding is fed into the rectifier of the Inverter which is force commutated and is usually composed of IGBTs. The rectified supply is fed into the DC link which is a large capacitor and is charged by the DC supply. The DC link also has an inductor to suppress the AC ripple left over from the rectification cycle and harmonics generated by the inverter. Additionally the DC link maintains the supply to the inverter in case of temporary supply failure and also absorbs transient voltages generated during switching heavy loads. In some models if the Static Inverter, an IGBT type switch is provided which is used to switch the DC link in and out of the circuit as per requirement. The DC from the rectifier/DC link is converted into three phase AC by the Inverter module by switching the IGBTs in proper sequence which creates a near sine wave AC displaced by 120 degrees. Voltage control is achieved by the Pulse Width Control (PWM) method. This ensures that the output voltage of the Static Inverter is near constant irrespective of the input voltage from the transformer. Apart from improving the reliability of the power supply system, one of the most important advantages of the Static Inverter is that it has considerably reduced Auxiliary Motor burnouts due drastic improvement in the power quality in terms of voltage. Additionally the Static Inverter also detects earth faults, single phasing and overloading hence these functions are no longer needed to be monitored by external devices. An electronic control system is provided which monitors the complete functioning of the Static Inverter. The control system gives the gate firing impulses to the various IGBTs and also controls the phase angle of the firing pulse to ensure proper phase sequencing. In addition it monitors the Static Inverter for internal and external faults.
Schematic circuit Diagram of Inverter
Auxiliary Motors and Equipments AUXILIAR Y
MPH
MVRH
MVSI 1&2
MVSL 1&2
STARTS (CONTACTOR NO.)
PROGRA M SWITCH
PROGRA M SWITCH POSITIO N0 OFF
PROGRA M SWITCH POSITIO N1 Normal Running
On DJ being closed (Direct supply from ThreePhase Bus bar via HPH) MPJ in Forward/Rever se or BLVMT ½ being closed (C-107)
HPH (Provided on the Auxiliary panel) HVRH (Provided on the Auxiliary panel)
OFF
Normal Running
On DJ being closed (Direct supply from ThreePhase Bus bar
HVSI 1&2 (Provided on respectiv e RSI
OFF (Traction Motors also isolated)
Normal Running
via HVSI 1&2)
block itself) HVSL 1&2
On DJ being closed
OFF
Normal Running
PROGRA M SWITCH POSITIO N2 Motor isolated and detecting relay in circuit Motor isolated and detecting relay in circuit Motor isolated and detecting relay in
PROGRA M SWITCH POSITIO N3 Motor running and detecting relay isolated Motor running and detecting relay isolated Motor running and detecting relay
circuit
isolated
Motor isolated
Motor running
REMARKS
MVMT 1
(Direct supply from ThreePhase Bus bar via HVSL) Five seconds after MVRH starting (C-105)
HVMT 1 (Provided on the Auxiliary panel)
OFF
MVMT 2
Five seconds after MVMT-1 starting (C-105)
HVMT 2 (Provided on the Auxiliary panel)
OFF
MCP-1, MCP-2, MCP-3
On closing BLCP/BLCPD/R GCP (C-101, C102, C-103)
HCP (Provided on the Auxiliary panel)
OFF
MPV-1, MPV-2
MVRF (In locos provided with internal DBR)
On closing BLPV (C111/C112 for low speed and C121 and C122 for high speed) On the initiation of dynamic braking from master controller (Is in parallel with the DBR
ZPV and other brake interlocks
and and detecting detecting relay in relay circuit isolated Normal Motor Motor Running isolated running and and detecting detecting relay in relay circuit isolated Normal Motor Motor Running isolated running and and detecting detecting relay in relay circuit isolated HCP at position-1 - MCP 1/2/3 running HCP at position-2 - MCP 2/3 running HCP at position-3 - MCP 1/3 running (In dual-brake locos, an interlock is provided wherein only one compressor can be run if the Vacuum Exhauster is running while working vacuum braked
RGCP is the auto pressure switch which normally regulates the running of the compresso
trains. In such cases compressed air is needed only for the loco and one compressor is sufficient for the purpose and also prevents excess load on the power supply system).
rs
Normal Running
New locos being turned out by CLW have a threephase motor to
OFF
Motor isolated and detecting relay in circuit
Motor running and detecting relay isolated
load resistances and also constitutes part of the load on the traction motors)
MVMSR-1- On DS being 4 closed (In dual power locos only)
run the MVRF blower and it takes supply from the Static Convertor. HVMSR 1 and 2 (Provided on the Auxiliary panel)
OFF
Normal Running
Motor isolated and detecting relay in circuit
Motor running and detecting relay isolated
Relays High voltage overload relay QLM:- The relay QLM is fed by means of the high voltage current transformer TFILM (250/5A).This causes the high voltage circuit breaker DJ to trip out, if the current taken in by the main transformer exceed the setting value of the relay 300A. Overload relays for silicon rectifiers (QRSI 1 and QRSI 2):- The relays QRSI 1-2 are fed by means of the rectifier current transformer RSILM 1 and 2(4000/5a) which causes the high voltage circuit breaker to trip, if the current taken in by the rectifiers exceeds the setting value of the relays (3600 A).
Braking excitation overload (QE):Thethe relay QE is excitation fed by means of the excitation current transformer ELM (1000/5 A)relay which causes braking contactors C145 to trip out, if the current taken in by the excitation winding of the motor exceeds the setting value of the relays (900 A) Braking overload relay QF-1 and QF-2:- The relays of QF 1-2 areconnected to the shunts SHF 1-2, which cause the braking excitation contactors C145 to trip out, if the current taken in by braking resistance RF 1 and 2 exceeds the setting value of the relays (700A). Slipping device differential relays QD 1-2:- When slip relays of current differential type are provided. When current difference is 125A in between motors 1 and 3 and motors 4 and 6, the relay operates, in case of slipping, it feeds relay Q-48, there by energizing sanding electro valves VESA and sand is applied to corresponding wheels relay Q-51 is also energized causing regression of graduator till the slipping stops. Main circuit earthing relay QOF 1-2:- In case of failure of insulation of traction power circuit to earth. The battery supply available to the relay trips the relay through the earth fault and in turn opens the HV circuit breaker DJ. Traction motor over voltage relay Q-20:- Relay Q-20 which is connected via resistance RQ-20 across rectifier output causes buzzer SON 1-2 to work, if voltage exceeds 865v, when voltage falls to740 v, buzzer stops working.
No voltage relay or low volts relay Q-30:- The relay Q-30 drops out if the single phase auxiliary/winding voltage drops below 215 volts. Its contacts switch off relay Q-44, there by tripping DJ. Relay Q-30 is switched on directly/via the contacts of the relay Q-45 and is fed via resistor RQ-30 after the relay Q-45 opens/drops. Arno starting relay QCVAR:- Relay QCVAR has been put across ‘w’ phase and neutral of arno to ensure its proper starting. This cuts out arno starting contact for C118. This is English electric relay. It picks up at 155-160 volts a.c. Battery charger signaling relayQV-61:- This relay which has been provided acrossthe battery Charging CHBA, indicates the working of the charger. This relay is English electric makes and operates at a voltage of 68-136 v d.c. Q46:- Relay GR protection during regression. When the driver puts the MP to 0 position the tap-changer (GR) starts regressing to 0 notch. However, the driver once having put the MP to 0 may not be monitoring the notch indicator and due to some reason the GR may have stopped midway. In such a case relay Q46 acts. It trips the DJ after a time delay of around 5 seconds. It should be noted that although Q46, by itself is not a Time Delay Relay but it acts through relay Q118 which has a time delay of 5 seconds. Q49:- Relay GR Synchronization during MU working -- In order to ensure that all the Tap-Changers work in tandem during MU working Relay Q49 is provided. Q51:- Auto Regression relay -- This relay is used to give regression impulse to the GR in case of wheelslipping, load-parting, emergency braking, traction supply failure, etc. Q52:- Notch-to-Notch relay -- During progression, this relay ensures that the driver can take only one notch at a time. Even if he keeps the MP at '+' continuously he gets only one notch and must return the MP to 'N' before taking the next notch. QV62 :- Relay to monitor GR reaching '0'position.This relay lights the LSGR lamp on the driver's desk when GR reaches 0 position. Q44 :- this is probably the most important protective relay related to the tap-changer. Also Q44 relay is a not an ordinary relay but it is a time delay relay. It releases after a delay of 0.6 seconds after the supply to its energizing coil is cut off. In older versions the Q44 was a mechanical relay with a clock mechanism used to bring about the time delay. But newer versions are electronic. Older locos are also being retrofitted with electronic Q44 relays. Another important feature of the Q44 is that it can be 'wedged' in the closed position, that is in case the Q44 itself becomes defective it can be temporarily wedged so that the DJ can be closed and the section can be cleared. Coming back to its function with respect to the Tap-Changer, the transition between two notches must be as fast as possible because the shorting of two taps through the RGR gives rise to almost short-circuit level current which can damage the RGR and the Transformer. Hence, during transition if the tap-
changer becomes stuck between notches and the taps remain shorted for a long duration, it can destroy the RGR and the transformer. In order to prevent such an occurrence there is a contact on the ASMGR which opens between notches, that is during transition. This contact is connected in series with relay Q44. Hence, during transition, supply to relay Q44 coil is interrupted which initiates the de-energizing time delay. However, if during such delay the transition is completed successfully, then the ASMGR contact closes, thereby restoring supply to Q44 and keeps it energized but if the tap-changer gets stuck mid-notch then Q44 drops out and trips the DJ. As such the tap-changer must complete its transition in 0.6 second which is the maximum time which Q44 gives it. From the above the importance of Q44 can be judged and it should also be ensured drivers do not indulge in wedging the Q44 lightly. Many drivers, for the sake of expediency may wedge Q44 without verifying that nothing is wrong with the tap-changer or some other equipment that the relay protects such as the RSI blocks.
Rectifier Block In electric loco mainly two silicon rectifier blocks RSI 1 and RSI 2 are provided for converting AC to DC. They are bridge connected. Continuous current retting of each block is 1000 amps.
Each rectifier blocks are provided with set of tells tale fuses. Each rectifier bridge consists of four arms and each arm carries four fuses. In case of puncturing of silicon diode in a particular block, the main fuse melts and the corresponding tell tale fuse also melts which causes the micro switch to operate. By closing of micro switch, the related relay will be energized which make glows respected pilot lamp in cab 1 and cab 2 the defective block or arm can be curtained by visual inspection of rectifier cabinet . The melted tell tale fuse can be identified by the black button projecting out. The maintenance of the rectifier is limited to an inspection every three months to check whether the cell is screwed tightly in to position. Any dirt which may have accumulated in the rectifier must be removed by using a rag and brush. It should be specially observed that the protecting cover of each cell is always clean. If a protecting cover becomes brittle or is no longer tightly fitted to the cell casing, this cap must e replaced.
Energy conservation in Electric traction system
Use of gradients for coasting. Level section can also be used for coasting by following proper driving techniques. Number of scheduled halts/ unscheduled halts and speed restriction should be minimum avoid late lowering of signals control chain pulling. Talk to engg. Dept. for realignment of track for reduction in length of track ,reduction in curves, reduction in speed restrictions, reduction in gradients etc.these measures maybe economical at some locations by taking in to view energy conservation, increased line capacity, reduction in running time and increased availability of rolling stock. Running at booked speed saves sizeable amount of energy but affects line capacity, promote use of long welded rails for low track resistance. Monitor profile of rail and wheel. Lubricate outer flange of curved rail for reduction in resistance between rolling stock wheel flange and rail, power factor correction in locos will reduce line losses Aerodynamic design of loco will reduce air resistance between rolling stock body should be reduced and no projections should be added during maintenance. Reduce the tare weight of coach and wagon. Driver should be trained for good driving techniques. Provide energy meter to monitor. Release brakes fully before starting. Switch off auxiliaries when not required provide coasting boards at all suitable locations. Switch of electric locos when idle more than 45 minutes. Avoid running of trains via loop. Do not run trains without guards as speed Restrictions are to be followed. Control brake binding in rain. Improve brake power of train. Carry goods via shortest route. Avoid use of resistance in locomotives. Use tube lights and FRP fan blades in EMU/coach/locos Use efficient speed control methods. Do not use resistance for speed control. Thyristor control, chopper control and 3 phase technology with frequency control etc can be useful. Use regenerative braking. Avoid running of light locos. Reduce running of dead locos. Repair in nearest loco shed. Reduce running of empty rakes. Reduce running of EMUs on holidays. Power factor : induction motor, welding transformer, florescent tubes, induction furnaces etc, are the main sources of low power factor. Use capacitor to improve power factor. Because this reduce maximum demand charges based on KVA, reduce line losses and improves voltage. Reduce material handling need by proper layout of working section in sheds. Control leakages of water, gas, air, electricity etc. Lubricate motors pumps etc, periodically. Maintain the equipments periodically for running at high efficiency. Dust, grease etc, cause poor heat/light transfer and hence causes poor efficiency of motor, condensers, intercoolers, light sources etc. control idle running of machines. Train and award staff for energy conservation measures. Display energy conservation board. Review existing installation for latest design, location etc. and do energy audit. Measure and monitor energy consumption at different machines, sections, etc. this will help in knowing efficient machines, section etc. appoint energy managers for auditing energy.
Diesel Locomotive Locomotive equipment layout
Schematic diagram of diesel-electric locomotive
Fig. 1 schematic diagram of diesel electric locomotive
Block diagram of diesel-electric locomotive
RADIATOR AFTER
EXPRESSOR OR COMPRESSOR
ENGINE
ROOM
ROOM
DRIVER GENERATOR
CABIN
NOTCH COMPARTM
Fig. 2 Block diagram of diesel locomotive
A Diesel locomotive is a type of railroad locomotive in which theprime mover is a Diesel engine
Diesel Engine The diesel engine was first patented byDr Rudolf Diesel (1858-1913) in Germany in 1892 and he actually got a successful engine working by 1897. By 1913, when he died, his engine was in use on
locomotives and he had set upa facility with Sulzer inSwitzerland to manufacture them. His death was mysterious in that he simply disappeared from a ship taking him to London. The diesel engine is a compression-ignition engine, as opposed to the petrol (or gasoline) engine, which is a spark-ignition engine. The spark ignition engine uses an electrical spark from a "spark plug" to ignite the fuel in the engine's cylinders, whereas the fuel in the diesel engine's cylinders is ignited by the heat causedby air being suddenly compressed in thecylinder. At this stage, the air gets compressed into an area 1/25th ofits srcinal volume. This would be expressed as acompression ratio of 25 to 1. A compression ratio of 16 to 1 will give an air pressure of 500 lbs/in² (35.5 bar) and will increase the air temperature to over 800° F (427° C). The advantage of the diesel engine over the petrol engine is that it has a higher thermal capacity (it gets more work out of the fuel), the fuel is cheaper because it is less refined than petrol and it can do heavy work under extended periods of overload. It can however, in a high speed form, be sensitive to maintenance and noisy, which is why it is still not popular for passenger automobiles.
Diesel-electric control
A Diesel-electric locomotive's power output is independent to road speed, as long as the units generator current and voltage limits are not exceeded. Therefore, the unit's ability to develop tractive effort (also referred to as drawbar pull or tractive force, which is what actually propels the train) will tend to inversely vary with speed within these limits. The diesel engine ideally should operate with maximum fuel economy as long as maximum power is not required. Maintaining acceptable operating parameters was one of the principal design considerations that had to be solved in early Diesel-electric locomotive development, and ultimately led to the complex control systems in place on modern units where all these parameters are solved and regulated by computer modules. The prime mover'spower output is primarily determined by its rotational speed(RPM) and fuel rate, which are regulated by a governor or similar mechanism. The governor is designed to react to both the throttle setting, as determined by the engineer (driver), and the speed at which the prime mover is running. Locomotive power output, and thus speed, is typically controlled by the engineer (driver) using
a stepped or "notched" throttle that produces binary-like electrical signals corresponding to throttle position. This basic design lends itself well to multiple unit (MU) operation by producing discrete conditions that assure that all units in a consist respond in the same way to throttle position. Binary encoding also helps to minimize the number of train lines (electrical connections) that are required to pass signals from unit to unit. For example, only four train lines are required to encode all throttle positions. In older locomotives, the throttle mechanism was ratcheted so that it was not possible to advance more than one power position at a time. The engineer could not, for example, pull the throttle from notch 2 to notch 4 without stopping at notch 3. This feature was intended to prevent rough train handling due to abrupt power increases caused by rapid throttle motion ("throttle stripping," an operating rules violation on many railroads). Modern locomotives no longer have this restriction, as their control systems are able to smoothly modulate power and avoid sudden changes in train loading regardless of how the engineer (driver) operates the controls.
Working of a locomotives When the throttle is in the idle position, the prime mover will be receiving minimal fuel, causing it to idle at low RPM. Also, the traction motors will not be connected to the main generator and the —the generator will not produce electricity generator's field windings will not be excited (energized)
with no excitation. Therefore, the locomotive will be in "neutral." Conceptually, this is the same as placing an automobile's transmission into neutral while the engine is running. To set the locomotive in motion, the reverser control handle is placed into the correct position (forward or reverse), the brake is released and the throttle is moved to the run 1 position (the first power notch). An experienced engineer (driver) can accomplish these steps in a coordinated fashion that will result in a nearly imperceptible start. The positioning of the reverser and movement of the throttle together is conceptually like shifting an automobile's automatic transmission into gear while the engine is idling Placing the throttle into the first power position will cause the traction motors to be connected to the main generator and the latter's field coils to be excited. It will not, however, increase prime mover RPM. With excitation applied, the main generator will deliver electricity to the traction motors, resulting in motion. If the locomotive is running "light" (that is, not coupled to a train) and is not on an ascending
grade it will easily accelerate. On the other hand, if a long train is being started, the locomotive may stall as soon as some of the slack has been taken up, as the drag imposed by the train will exceed the tractive force being developed. An experienced engineer (driver) will be able to recognize an incipient stall and will gradually advance the throttle as required to maintain the pace of acceleration. As the throttle is moved to higher power notches, the fuel rate to the prime mover will increase, resulting in a corresponding increase in RPM and horsepower output. At the same time, main generator field excitation will be proportionally increased to absorb the higher power. This will translate into increased electrical output to the traction motors, with a corresponding increase in tractive force. Eventually, depending on the requirements of the train's schedule, the engineer (driver) will have moved the throttle to the position of maximum power and will maintain it there until the train has accelerated to the desired speed. As will be seen in the following discussion, the propulsion system is designed to produce maximum traction motor torque at start-up, which explains why modern locomotives are capable of starting trains weighing in excess of 15,000 tons, even on ascending grades. Current technology allows a locomotive to develop as much as 30 percent of its loaded driver weight in tractive force, amounting to some 120,000 pounds of drawbar pull for a large, six-axle freight (goods) unit. In fact, a consist of such units can produce more than enough drawbar pull at start-up to damage or derail cars (if on a curve), or break couplers (the latter being referred to in North American railroad slang as "jerking a lung"). Therefore, it is incumbent upon the engineer (driver) to carefully monitor the amount of power being applied at start-up to avoid damage. In particular, "jerking a lung" could be a calamitous matter if it were to occur on an ascending grade. As previously explained, the locomotive's control system is designed so that the main generator electrical power output is matched to any given engine speed. Due to the innate characteristics of traction motors, as well as the way in which the motors are connected to the main generator, the generator will produce high current and low voltage at low locomotive speeds, gradually changing to low current and high voltage as the locomotive accelerates. Therefore the net power produced by the locomotive will remain constant for any given throttle setting.
In older designs, the prime mover's governor and a companion device, the load regulator, play a central role in the control system. The governor has two external inputs: requested engine speed, determined by the engineer's throttle setting, and actual engine speed (feedback). The governor has
two external control outputs:fuel injector setting, which determines the engine fuel rate, and load regulator position, which affects main generator excitation. The governor also incorporates a separate over speed protective mechanism that will immediately cut off the fuel supply to the injectors and sound an alarm in the cab in the event the prime mover exceeds a defined RPM. It should be noted that not all of these inputs and outputs are necessarily electrical. The load regulator is essentially a large potentiometer that controls the main generator power output by varying its field excitation and hence the degree of loading applied to the engine. The load regulator's job is relatively complex, because although the prime mover's power output is proportional to RPM and fuel rate, the main generator's output is not (which characteristic was not correctly handled by the Ward Leonard elevator drive system that was initially tried in early locomotives). As the load on the engine changes, its rotational speed will also change. This is detected by the governor via a change in the engine speed feedback signal. The net effect is to adjust both the fuel rate and the load regulator position. Therefore, engine RPM and torque will remain constant for any given throttle setting, regardless of actual road speed. In newer designs controlled by a “traction computer,” each engine speed step is allotted an appropriate power output, or “kW reference”, in software. The computer compares this value with actual main generator power output, or “kW feedback”, calculated from traction motor current and
main generator voltage feedback values. The computer adjusts the feedback value to match the reference value by controlling the excitation of the main generator, as described above. The governor still has control of engine speed, but the load regulator no longer plays a central role in this type of control system. However, the load regulator is retained as a “back-up” in case of engine overload.
Modern locomotives fitted with electronic fuel injection (EFI) may have no mechanical governor, however a “virtual” load regulator and governor are retained with computer modules.
Fig.4 3200Hp Diesel Locomotive Engine
Traction motor performance is controlled either by varying the DC voltage output of the main
generator, for DC motors, or by varying the frequency and voltage output of the VVVF for AC motors. With DC motors, various connection combinations are utilized to adapt the drive to varying operating conditions.
Fig. 5 Top View of Diesel Locomotive Engine
Here are some of the specifications of this engine:
Number of cylinders: 12
Compression ratio: 16:1
Displacement per cylinder: 11.6 L (710 in3)
Cylinder bore: 230 mm (9.2 inches) Cylinder stroke: 279 mm (11.1 inches)
Full speed: 904 rpm
Normal idle speed: 269 rpm
At standstill, main generator output is initially low voltage/high current, often in excess of 1000 amperes per motor at full power. When the locomotive is at or near standstill, current flow will be limited only by the DC resistance of the motor windings and interconnecting circuitry, as well as the capacity of the main generator itself. Torque in a series-wound motor is approximately proportional to the square of the current. Hence, the traction motors will produce their highest torque, causing the locomotive to develop maximum tractive effort, enabling it to overcome the inertia of the train. This effect is analogous to what happens in an automobile automatic transmission at start-up, where it is in first gear and thus producing maximum torque multiplication. As the locomotive accelerates, the now-rotating motor armatures will start to generate a counter-electromotive force (back EMF, meaning the motors are also trying to act as generators), which will oppose the output of the main generator and cause traction motor current to decrease. Main generator voltage will correspondingly increase in an attempt to maintain motor power, but will eventually reach a plateau. At this point, the locomotive will essentially cease to accelerate, unless on a downgrade. Since this plateau will usually be reached at a speed substantially less than the maximum that may be desired, something must be done to change the drive characteristics to allow continued acceleration. This change is referred to as "transition," a process that is analogous to shifting gears in an automobile.
Starting A diesel engine is started (like an automobile) by turning over the crankshaft until the cylinders "fire" or begin combustion. The starting can be done electrically or pneumatically. Pneumatic starting was used for some engines. Compressed air was pumped into the cylinders of the engine until it gained sufficient speed to allow ignition, then fuel was applied to fire the engine. The compressed air was supplied by a small auxiliary engine or by high pressure air cylinders carried by the locomotive. Electric starting is now standard. It works the same way as for an automobile, with batteries providing the power to turna starter motor which turns over the main engine. In older locomotives
fitted with DC generators instead of AC alternators, the generator was used as a starter motor by applying battery power to it.
Tractive Effort, Pull and Power Before going too much further, we need to understand the definitions of tractive effort, drawbar pull and power. The definition of tractive effort (TE) is simply the force exerted at the wheel rim of the locomotive and is usually expressed in pounds (lbs) or kilo Newtons (KN). By the time the tractive effort is transmitted to the coupling between the locomotive and the train, the drawbar pull, as it is called will have reduced because of the friction of the mechanical parts of the drive and some wind resistance. Power is expressed as horsepower (hp) or kilo Watts (kW) and is actually a rate of doing work. A unit of horsepower is defined as the work involved by a horse lifting 33,000 lbs one foot in one minute. In the metric system it is calculated as the power (Watts) needed when one Newton of force is moved one metre in one second. The formula is P = (F*d)/t where P is power, Fis force, d is distance and t is time. One horsepower equals 746Watts. The relationship between power and drawbar pull is that a low speed and a high drawbar pull can produce the same power as high speed and low drawbar pull. If you need to increase higher tractive effort and high speed, you need to increase the power. To get the variations needed by a locomotive to operate on the railway, you need to have a suitable means of transmission between the diesel engine and the wheels. One thing worth remembering is that the power produced by the diesel engine is not all available for traction. In a 2,580 hp diesel electric locomotive, some 450 hp is lost to on-board equipment like blowers, radiator fans, air compressors and "hotel power" for the train.
Main parts of a diesel-electric locomotive Main Alternator
The diesel engine drives the main alternator which provides the power to move the train. The alternator generates AC electricity which is used to provide power for the traction motors mounted on the trucks (bogies). In older locomotives, the alternator was a DC machine, called a generator. It produced direct current which was used to provide power for DC traction motors. Many of these machines are still in regular use. The next development was the replacement of the generator by the alternator but still using DC traction motors. The AC output is rectified to give the DC required for the motors.
Auxiliary Alternator Locomotives used to operate passenger trains are equipped with an auxiliary alternator. This provides AC power for lighting, heating, air conditioning, dining facilities etc. on the train. The output is transmitted along the train through an auxiliary power line. In the US, it is known as "head end power" or "hotel power". In the UK, air conditioned passenger coaches get what is called electric train supply (ETS) from the auxiliary alternator.
Motor Blower The diesel engine also drives a motor blower. As its name suggests, the motor blower provides air which is blown over the traction motors to keep them cool during periods of heavy work. The blower is mounted inside the locomotive body but the motors are on the trucks, so the blower output is connected to each of the motors through flexible ducting. The blower output also cools the alternators. Some designs have separate blowers for the group of motors on each truck and others for the alternators. Whatever the arrangement, amodern locomotive has a complexair management system which monitors the temperature of the various rotating machines in the locomotive and adjusts the flow of air accordingly.
Rectifiers/Inverters
The output from the main alternator is AC but it can be used in a locomotive with either DC or AC traction motors. DC motors were the traditional type used for many years but, inthe last 10 years, AC motors have become standard for new locomotives.They are cheaper to build andcost less to maintain and, with electronic management can be very finely controlled. To convert the AC output from the main alternator to DC, rectifiers are required. If the motors are DC, the output from the rectifiers is used directly. If the motors are AC, the DC output from the rectifiers is converted to 3-phase AC for the traction motors. In the US, there are some variations in how the inverters are configured. GM EMD relies on one inverter per truck, whileGE uses one inverter per axle - both systems have their merits. EMD's system links the axles within each truck in parallel, ensuring wheel slip control is maximized among the axles equally.
Parallel control also means even wheel wear even between axles. However, if one inverter
(i.e. one truck) fails then the unit is only able to produce 50 per cent of its tractive effort. One inverter per axle is more complicated, but the GE view is that individual axle control can provide the best tractive effort. If an inverter fails, the tractive effort for that axle is lost, but full tractive effort is still available through the other five inverters. By controlling each axle individually, keeping wheel diameters closely matched for optimum performance is no longer necessary.
Control Stand This is the principal man-machine interface, known as a control desk in the India. The common India type of stand is positioned at an angle on the left side of the driving position and, it is said, is much preferred by drivers to the modern desk type of control layout usual in Europe and now being offered on some locomotives in the US.
Batteries Just like an automobile, the diesel engine needs a battery to start it and to provide electrical power for lights and controls when the engine is switched off and the alternator is not running. The locomotive operates on a nominal 64-volt electrical system. The locomotive has eight 8-volt batteries; each weighing over 300 pounds (136 kg). These batteries provide the power needed to start
the engine (it has a huge starter motor), as well as to run the electronics in the locomotive. Once the main engine is running, an alternator supplies power to the electronics and the batteries.
Traction Motor Since the diesel-electric locomotive uses electric transmission, traction motors are provided on the axles to give the final drive. These motors were traditionally DC but the development of modern power and control electronics has led to the introduction of 3-phase AC motors. There are between four and six motors on most diesel-electric locomotives. A modern AC motor with air blowing can provide up to 1,000 hp. Propulsion: The traction motors provide propulsion power to the wheels. There is one on each axle.
Each motor drives a small gear, which meshes with a larger gear on the axle shaft. This provides the gear reduction that allows the motor to drive the train at speeds of up to 110 mph. these have been discussed in previous topic of electric locomotive.
Fig. 10 Traction Motor
Each motor weighs 6,000 pounds (2,722 kg) and can draw up to 1,170 amps of electrical current.
Fuel Tank
A diesel locomotive has to carry its own fuel around with it and there has to be enough for a reasonable length of trip. The fuel tank is normally under the loco frame and will have a capacity of say 5,000 liters in a WDM2 2200 hp locomotive. Air reservoirs are also required for the train braking and some other systems on the locomotive. These are often mounted next to the fuel tank under the floor of the locomotive.
Governor Once a diesel engine is running, the engine speed is monitored and controlled through a governor. The governor ensures that the engine speed stays high enough to idle at the right speed and that the engine speed will not rise too high when full power is demanded. The governor is a simple mechanical device which first appeared on steam engines. It operates on a diesel engine as shown in the diagram below. The governor consists of a rotating shaft, which is driven by the diesel engine. A pair of flyweights is linked to the shaft and they rotate as it rotates. The centrifugal force caused by the rotation causes the weights to be thrown outwards as the speed of the shaft rises. If the speed falls the weights move inwards. The flyweights are linked to a collar fitted around the shaft by a pair of arms. As the weights move out, so the collar rises on the shaft. If the weights move inwards, the collar moves down the shaft. The movement of the collar is used to operatethe fuel rack lever controlling the amount offuel supplied to the engine by the injectors.
Fig. 11 Principle of Governor
Fuel Control In an automobile engine, the power is controlled by the amount of fuel/air mixture applied to the cylinder. The mixture is mixed outside the cylinder and then applied by a throttle valve. In a diesel engine the amount of air applied to the cylinder is constant so power is regulated by varying the fuel input. The fine spray of fuel injected into each cylinder has to be regulated to achieve the amount of power required. Regulation is achieved by varying the fuel sent by the fuelpumps to the injectors.
Fig. 17 Fuel System
The amount of fuel being applied to the cylinders is varied by altering the effective delivery rate of the piston in the injector pumps. Each injector has its own pump, operated by an engine-driven cam, and the pumps are aligned in a row so that they can all be adjusted together. The adjustment is done by a toothed rack (called the "fuel rack") acting on a toothed section of the pump mechanism. As the fuel rack moves, so the toothed section of the pump rotates and provides a drive to move the pump piston round inside the pump. The fuel rack can be moved either by the driver operating the power controller in the cab or by the governor. If the driver asks for more power, the control rod moves the fuel rack to set the pump pistons to allow more fuel to the injectors. The engine will increase power and the governor will monitor engine speed to ensure it does not go above the predetermined limit. The limits are fixed by springs limiting the weight movement.
Fig.18 Fuel Supply system
Radiators They are used for cooling internal combustion engines, chiefly in automobiles but also in pistonengined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine. They operate by passing a liquid coolant through the engine block, where it is heated, then through the radiator itself where it loses this heat to the atmosphere. This coolant is usually water-based, but may also be oil. It's usual for the coolant flow to be pumped, also for a fan to blow air through the radiator. In railway with a liquid-cooled internal combustion engine a radiator is connected to channels running through the engine and cylinder head, through which a liquid (coolant) is pumped. This liquid may be water (in climates where water is unlikely to freeze), but is more commonly a mixture of water and antifreeze in proportions appropriate to the climate. Antifreeze itself is usually ethylene glycol or propylene glycol (with a small amount of corrosion inhibitor). The radiator transfers the heat from the fluid inside to the air outside, thereby cooling the engine. Radiators are also often used to cool automatic transmissions, air conditioners, and sometimes to cool engine oil. Radiators are typically mounted in a position where they receive airflow from the forward movement of the vehicle, such as behind a front grill. Where engines are mid- or rear-mounted, it is
common to mount the radiator behind a front grill to achieve sufficient airflow, even though this requires long coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is most common for engine and transmission cooling and top airflow most common for air conditioner cooling.
Electrical components used in diesel electric locomotive Relays
A relay is essentially, a switch which is operated by an electromagnet instead of manually. A relay may open or close one or more circuits when energised or it may open one circuit and close another. When the requirements of one circuit depend on the function of another a relay used, is In other words, it may be essential for current to flow or cease to flow in a certain circuit when the current starts or ceases to flow in another circuit. Further-more a relay may be calibrated in such a way that it will only operate when the current passing through its own operating coil has risen or fallen to a certain value. A relay is shown in a circuit as a coil and a pair of contacts.
When the operating coil is energised a normally open contact is closed, whereas a normally RELAY closed contact is opened. Circuit diagrams always show relays in de-energised position.
Relay of ALCO locomotive General Purpose Relays :
ESR1, ESR2, ESR3 & ESR4 (Engine Speed Relays) – These relays get operated in different
combination depending on throttle handle positions. Combination of relays vary the speed signal to GE governor and thereby the RPM of diesel engine.
BKR (Braking Relay) – This relay gets operated during dynamic brake application to re-organise
and re-calibrate the excitation control, which is required to have control on excitation according to SH position and limit the excitation in order to limit the Generator output at a lower voltage.
FSR (Field Shunting Relay) – This relay helps in operating the FS Contactors and thereby
introducing the Field Weakening process of Traction Motors.
TR (Transition Relay) – Transition Relay helps in disconnecting the Traction Motors from Series
Parallel combination and connecting them in parallel.
DMR (Demagnetising Relay commonly known as Dead Man's Relay) – This relay gets operated
after MCB(A+B) are put on. However, if there is a train parting or chain pulling, DMR gets de-
energised through PCS and bring the engine to IDLE, irrespective to the TH position. This relay ensures that the TH is brought back to IDLE for notching up, after restoration from train parting / chain pulling.
ERR (Engine Run Relay) – This relay is fitted only in Woodward governor type locomotives. This
relay gets operated with ECS in RUN and remains energised all the time during locomotive operation. Operation of safety devices forces the ERR to drop, which brings the engine to IDLE in the event of GR and ETS operation and brings the engine to halt in the event of MUSD, LWS, EOA (in WDS6 & YDM4) and OPS operation.
LOR (Low Oil Relay) – This relay is fitted in some of the Woodward Governor type locomotives
and gets operated on operation of Low Lube Oil Shut down device for audio-visual indication to driver. Special purpose relays:
SR (Signal Relay) – This relay gets energized in the event of operation of safety devices and
operates the Alarm Gong for providing Audio Signal.
GR (Ground Relay) – This relay gets operated when there is a ground fault, whether in Control
Circuit or in Power Circuit. Operation of GR during starting of the diesel engine indicates ground fault in Control Circuit, which is commonly known as Starting Ground and that to during locomotive operation, when the power is ON, indicates ground fault in the Power Circuit, which is commonly known as Power Ground.
WSR1, WSR2 & WSR3 (Wheel Slip Relays) – Each WSR is connected across a pair of motor to
monitor the potential difference across them. The potential difference beyond a limit indicates either unequal speed of the motors or an unhealthy motor in the pair. This causes operation of the concerned WSR resulting power reduction and audio-visual indication (lamp and Buzzer) to the driver.
SAR (Safety Auxiliary Relay) – This relay is fitted only in GE governor type locomotive. The relay
brings the engine to halt by avoiding over-speeding, when there is loss of electrical speed signal.
Contactors Contactors are switches which handle heavy current and operate as a result of the action of other switches or relays. They fall into two main classes electromagnetic (EM) and Electro pneumatic (EP). The exposed surfaces which actually make contact and complete the circuit are called contact tips. They get mechanical wear and electrical burning. They are usually made to copper and bolted in place. If these bolts get loose the tips will overheat. The heat will carry out to surrounding parts and cause warping and bending. These are small contact fingers that work at the same time as the main contacts, They are usually connected in the low voltage or battery circuit and give a signal when the main contacts operate. Two kinds are common. One is normally open, that is the interlocks are opened when the main contacts are closed. The other is normally closed. That is, the inter lock
circuits are closed when the main contacts are open and open when the main contacts are closed. Interlocks, being in low voltage circuits usually have silver contact tips to reduce electrical resistance.
Electromagnetic Contactors Magnetic contactors are operated directly by electricity. When the current flows through the operating coil, the core becomes a magnet and pulls the armature against the core. This is the force that closes the contact tips and completes the circuit. As the armature moves, it also stretches the armature spring. When the current flow to the coil is stopped the core ceases to be a magnet. The armature spring pulls the armature away from the core and back against the stop. This is the force that opens the contact tips. The knife edge on the armature may become worn and may cause faulty operation. All contactors have a flexible lead called a shunt. It is made by a woven strands of very fine copper wire. It is expected to last several hundred thousands operations of the contactor. But since copper strands are very fine, the shunt can be easily damaged on large contactors. This may happen through misdirected arcs. If an arc strike the shunt it may weld together a large number of strands. Then this part of the shunt is no longer flexible. The result is usually a broken shunt. While a damaged shunt may last to the next inspection, it is good idea to replace it as soon as possible. Loose connection also shorten shunt life. If the bolts that fasten the ends of the shunt to the contactor get loose, there is a poor connection andthe shunt terminals will over heat. This makes the copper strands brittle and dis-coloured such a shunt will break in a little while. Some examples of such type of contactors are:
CK1 &CK2 (Cranking Contactors) – These contactors are operated to connect the battery to the
Main Generator to crank the diesel engine. CK1 is at the +ve side and CK2 is at the –ve side of the battery.
FPC (Fuel Pump Contactor) – This contactor connects the Fuel Pump Motor and Crank Case
Motor circuit to the Battery / aux. Gen.
GFC (Generator Field Contactor) – This contactor connects the Exciter output to the Main
Generator field.
FS21 – FS26 (Field Shunting Contactors) – These contactors introduce the Field Shunting
Resistors to the Traction Motor Fields in order to have the field weakening process. There may not be any FS Contactor, if the locomotive does not have the provision of Field Weakening.
R1 & R2 (Radiator Fan Contactors) – These two contactors supply the ECC to clutch the Radiator
Fan of the Diesel Engine. R1 & R2 are operated by T1 and T2 thermostats respectively, at two pre-set temperatures.
`Air operated contactor In the main traction circuits, that carry heavy currents, contactors operated by air pressure are commonly used. Such contactor has a piston, piston rod, spring and cylinder. The piston packing is of some flexible material usually rubber or leather. The other end of the rod is connected to a lever which moves one of the contact tip commonly called the movable tip. The cylinder is a casting with the walls honed to a very smooth finish. All air operated contactors have some means of lubricating the cylinder. This lubricant does three things. First, it reduces wear and prolongs the life of the piston packing. Second, piston moves freely. Thirdly, it helps the packing to fit closely and form an airtight seal. If the cylinder walls get sticky the operation of the contactors becomes sluggish. The control air available at 70 psi or 5 kg/cm2 is used for operation of the contactors. If the pressure is below normal the operation of the contactors is sluggish. Air entering the cylinder, builds up pressure and pushes the piston away from the contactor base. This is the force that closes the contact tips. At the same time the piston return spring is compressed. When the air supply is cut off, the spring forces the piston back. This is the force that opens the contact tips. Some examples of Electropneumatic contactors of locomotives are:
S1, S21, S31 (Series Contactors) & P1, P21, P31, P2, P22, P32 (Parallel Contactors) – These are 9 Power Contactors for connecting the Traction Motors to the Main Generator, which are known as Traction Motor Contactors too. The Series Contactors connect the Traction Motors in Series-
Parallel combination and the Parallel Contactors connect the Traction Motors in parallel. If the
locomotive does not have the Series-Parallel combination, the there can be only six power contactors.
D.C Generator Introduction A machine, which convertsmechanical energy into electrical energy, is called aGenerator. This energy conversion is based on the dynamically induced emf. According to the Faraday's law of electromagnetic Induction, an induced emf is produced in the conductor which cuts the magnetic flux. This emf causes a current to flow in the conductor if its circuit is closed. Hence the basic essentials for an electrical generator are: (i) Magnetic field; (ii) Conductor or conductors and; (iii) Relative motion between magnetic field and conductors.
Constructional Details Here we are dealing with a DC generator. But there is a good similarity with a DC motor also as far as construction is concerned. The following are the main parts of a DC generator:
Yoke
Pole core or pole shoes
Field coils
Armature core
Armature winding
Commutator
Brushes and bearings
Yoke This is the outer part of the DC generator. It provides the mechanical supports for the poles and acts as a protecting cover for the whole machine. It carries the magnetic flux produced by the poles. Yokes are made out of cast iron or cast steel. The modern process of forming the yoke consists of rolling a steel
slab round a cylindrical mandrel and then welding it at the bottom. The feet and the terminal box etc. are welded to the frame afterwards. Such yokes possess sufficient mechanical strength and have high permeability.
Pole core The field magnet consists of pole cores and pole shoes. The pole shoes serve two purposes. (i) They spread out the flux in the air gap and also being the larger cross section reduced the reluctance of the magnetic path. (ii) They support the exciting coils.
Field Coils The field coils or pole coils, which consist of copper wire, are former-wound for the current dimension. Then the former is removed and the wound coil is put into place over the core.
Armature core It houses the armature conductors or coils and causes them to rotate and hence cut the magnetic flux of the field magnets. Its most important function is to provide a path of very low reluctance to the flux through the armature from North Pole to South Pole. It is laminated to reduce the loss due to eddy currents. Thinner the lamination, greater will be resistance offered to the induced emf and hence smaller the current. And thus the loss is also small.
Armature Windings It is generally former wound. These are first wound in the form of flat rectangular coils and then are pulled into their proper shape in a coil puller. Two types of windings are mainly used - namely lap winding & Wave winding. Lap winding
In lap winding finish end of one coil is connected to a commutator segment and to the start end of the adjacent coil situated under the same pole and similarly all coils are connected. Since the successive coils overlap each other and hence the name (Ref. fig.1).
Fig 1
Wave winding
It is also called as series winding. In this winding, the coil side is not connected back but progresses forward to another coil sides. In this way the winding progresses, passing successively every N pole and S pole till it returns to coil side from where it was started. As the winding shape is wavy, the winding is, therefore, called wave winding (Ref. fig.2).
Fig 2
Commutator The commutator, whose function is to facilitate the collection of current from the armature, is cylindrical in structure, built up of segments of high conductivity, hard drawn copper insulated from one another by mica sheets. It also converts alternating current into unidirectional current (DC). Brushes and bearing
The function of brushes is to collect current from the commutator. These are rectangular in shape, made of carbon normally. These brushes are housed in brush holder usually of the box type variety.
Generally ball bearings are employed due to their reliability but for heavy duty, roller bearings are also used. The balls and rollers are generally packed in hard oil for quieter operation. Sleeve bearings are also used where low wear is required.
E.M.F. Equation of generator Generated E.M.F, E =
PZN 60 A
Volts
Where, P = No. of poles, = Flux per pole in Wb (Weber), Z =Total nos. of conductors, N = r.p.m, A = nos. of parallel paths in Armature, (A = 2for wave winding & A = P for lap winding)
DC Motors Introduction A motor is a mechanism by which electrical energy is converted into mechanical energy. Its operating principle is the reverse of a DC generator. When a coil, carrying current, is placed in a magnetic field, it experiences forces, which turn it about in a direction perpendicular to both the field and current. Thus the motor armature placed inside the magnetic field gets motion, converting electrical energy to mechanical.
DC MOTORS – Principle of operation A motor is a mechanism by which electrical energy is converted into mechanical energy. Both in principle and design, a DC motor is the reverse of a DC generator. A steady current is passed through the armature coil from the commutator and the brushes are so arranged as to reverse the current every half revolution. When a coil, carrying a current, is placed in a magnetic field, it experiences forces, which turn it about in a direction perpendicular to both the field and the current. Due to the rotating torque the motion of rotation will not be continuous, unless the direction of the current is reversed each half revolution with the help of a split ring commutator (in a 2pole machine). The electric motor is fundamentally similar to the primitive form of D.C. generator described earlier and is based on the fact that, if a "loop of wire". If it is supplied, through its commutator, with electric current from a battery or any other source of direct current (D.C.) supply, the loop will rotate. If the brushes of the machine were connected to the terminals of a primary cell, instead of being connected to load R, the "loop of wire "would rotate. A greatly enhanced performance would be obtained by having an iron core on this loop, a further improvement would be to have many loops,
another to have increased pole area, and a still further improvement would be obtained by having electromagnets instead of permanent magnets. When used for traction, the direct current electric motor is usually of the series wound type, that is, the current, which passes through the armature also, passes through the field coils. The reason for this is that a motor having this particular type of winding has characteristics eminently desirable for traction work, its torque being proportional to the current flow, multiplied by the magnetic strength of the field system. The series wound motor is capable; therefore, of producing a high torque when the vehicle is started, and also has the advantage that as the load increases its speed drops. The direct current traction motor can be considered as having the following major parts;
1. The electro-magnetic system consisting of the frame with pole pieces, the field windings and brush gear. 2. The reduction gears between the armature shaft and the road wheels, together with the gear case, which protects the gear wheels and holds the gear lubricant. 3. The axle bearing where the traction motor frame rests on the axle of the vehicle, this arrangement maintains a constant. 4. The nose suspension arrangement prevents the frame of the motor from rotating round the axle of the vehicle, The nose is spring borne on a bogie cross member.
Back Emf Due to the rotation of the armature coil (i.e. a conductor) in the magnetic field, the motor works as a DC generator and induced e.m.f acts in the circuit, which opposes the current. This induced e.m.f is called back e.m.f.
Heating and cooling
Every electrical machine is a power (or energy) conversion device. During these power conversion some of the energy is wasted. In electrical machines the loss in energy occurs in electrical circuits and in portions of magnetic circuits also. There are also frictional losses in the dynamic parts of the machines. These losses are converted in the form of heat energy, which increases, or tends to increase the temperature of iron and copper above that of the ambient temperature, which in turn effects the winding insulation. In addition to the effect it has on the insulation, an excessive temperature rise may also adversely influence the mechanical operating conditions of a given machine part. Thus, for example the srcinal dimension of the commutator may change. Solder between the commutator and windings may get washed out. So to avoid all these, it is very essential to provide a cooling system on machines.
In most cases, the cooling is done by air currents. The cooling of machines by air streams is called ventilation. The ventilation employed depends on the environmental conditions of the place where the machine is to operate. According to the method of ventilation employed, the following types of machines are distinguished: (i) Machines with natural ventilation. (ii) Machines with internal self-ventilation. (iii) Machines with external self-ventilation. (iv) Machines with independent ventilation.
Ratings There are three types of ratings as specified. (i) Continuous Rating: This is an output, which a machine delivers continuously without exceeding the
permissible temperature. It can deliver 25% overload for two hours. (ii)Continuous maximum Rating: This is similar to continuous rating but not allowing overload. (iii) Short time ratings: This is an output which a machine can deliver for a specified period (say 1 hr 1/2
hr, 1/4 hr etc) without exceeding the maximum temperature rise limit.
Transition Introduction The purpose of transition is to keep the diesel engine working on the full horsepower part of the generator curve for the maximum possible period of locomotive operation- from its low speed to the maximum speed. In this we change the traction motor circuits, so that they draw value of current that falls on horsepower curve, as the locomotive speed changes. This change of motor circuits is called transition. For better understanding of the transition let us review our knowledge of traction motor, traction generator and diesel engine characteristics.
Traction Motors We use series type D.C. motors for traction purposes. This type of motor draws a high current at low speed and a low current at high speed. If its load is heavy, it runs at low speed if light it runs at high speed. The way such a motor acts is shown in Fig.E4.1. While doing Foot-plating, this can be noticed on the load meter.
Traction generators The
traction
generator
is
a
d-c
generator. It takes mechanical power from the diesel engine and converts it to electrical power for the traction motors. We have seen in the chapter on Excitation system how the generator is controlled so that it delivers power as shown Fig.E4.2. When the load resistance is low the amperes are high. When the load resistance is high the amperes are low. The generator characteristic can be obtained from the load test.
Diesel Engine The diesel engine converts the energy of burning fuel into mechanical power. With the throttle at 8th: notch and full fuel the engine will run at its rated speed and produce its rated horsepower. If we try to get more power it will stall. If we try to get less power, the racks will back 'off' (the engine will take less fuel). To get the most out engine we must stay on the full horsepower part of the generator curve
Fig.e.4.2. The purpose of transition is to obtain higher speed of the locomotive and still utilize the constant horsepower of the engine at a speed setting. The out put characteristic of the traction generator, as determined by the excitation system, is such that it holds the diesel engine at approximately constant horse power at a particular speed setting.
When the locomotive is starting, and at low locomotive speeds, the main generator supplies a high current to the traction motors. As the traction motor armatures begin turning, they generate a voltage commonly called back EMF. This back EMF, as if increases the effective resistance to the current flow. Therefore, as the locomotive speed increases, the generator voltage must increase to maintain the traction motor current. The traction motor current will decrease however because of the constant power characteristic of the generator (Fig.E4.1). With further increase in locomotive speed, if the back EMF reaches the voltage limit of generator, the generator current starts falling and the horsepower reduces (Fig.E4. 2). However, by changing the generator motor connections, the back voltage is reduced and the generator can force more current to the motors to enable acceleration. To achieve higher starting torque, sometimes, two traction motors are connected in series during starting of the locomotive. In these locomotives, changing their connections from series to parallel can reduce the back emf. Weakening the motor fields can also reduce back emf. The change in the motor connections, or weakening of fields is known as an event of transition. The number of events is decided from the generator characteristic and the number of motors.
Process of field weakening and paralleling Forward transition We want to keep the engine working on the constant horsepower part of the generator curve as much of the times as possible. To do this we use what is called transition. That is, as the locomotive speed changes, we change the traction motor circuits so that they will draw a value of current that falls on the horsepower curve. Let us see how transition
is used to accelerate a train.
Fig.E4.3
At the start the traction motors are connected to the generator as shown Fig.E4.3 (This connection is called 2S-3PFF i.e. two traction motors in series and three parallel paths with full field). This means the generator supplies current through three paths to run six traction motors. So it has to supply only three times the signal motor current in starting. Even though the current drawn by each motor is very high, by using such a circuit the generator is kept to a reasonable size. In Fig.E4.3 we can see how the current drops off as the train moves out. This is shown by the arrows on the horsepower curve .At about 10 miles an hour we get on the full horse power portion of the curve. From this point it is necessary to stay on this part of the curve to get constant power from the engine. If we have a locomotive with 75 MPH gearing and 40 inch wheels, when we reach about 19.2 MPH (30.8 KMPH) point C in Fig.E4.3 is reached, the motor current will have dropped so much that continued acceleration would be at reduced horsepower along the field limit line.
To prevent this, the motor fields are shunted as shown in Fig.E4.4 (this is called 2S-3P WF, i.e. two motors in series three parallel paths with weak field). Part of the motor current then flows around the field) through the shunting contractors (FS21, FS22 etc.), and the shunting resistors. This causes motors to draw more current from the generator, because of fall in counter emf. With this, operating point moves back down toward the bottom of horsepower curve as show n in Fig.
E4.4. On some locomotives field shunting is done in two or more steps. This is done to keep the motor current to safe value.
Fig.E4.4
When voltage is reduced, torque remaining the same, I has to increase so we slide down from point 3 to point 2 in Fig.E4.4. As the train continues to accelerate, the generator current, will again decrease as shown by the arrows in Fig. E4.4 (the generator current decreases as with the locomotive speed the back EMF of traction motors goes on increasing). At 30 M.P.H. (48 km/h), it will be back at the top of horsepower curve again. To prevent unloading, the motor current must be again increased by 2nd.transition. This time we do this differently. We change the motor connections from series parallel to parallel as shown in Fig.E4.5. Instead of three paths for the generator current there are now six. This causes generator current to increase. The operating point is now back at the bottom of the horsepower curve again as shown in
Fig.E4.5 (We call this 6P-FF i.e. six traction motors in parallel with full field).
In making second transition the shunting contractors (FS21, 22 etc)
Fig.E4.4 are first opened. This unshunts the motor fields. Then the series contactors S1, S2, S3 in Fig.E4.4 are opened and finally the parallel contactors, P1, P22, P31, P2, P22 and P32 in Fig.E4.5 pick up. This may happen in different sequence on various locomotives, but the end result is the same. Since the generator is at
Fig.E4.5
high voltage when this sequence begins its voltage must be reduced before switching of motors can be safely accomplished. This is done by opening the generator field contactor- G.F. This transition should take place at the right time. If it occurs too late, or at a too high a speed locomotive will loose power before transition. If it occurs too soon, there will be a loss of power after transition. In either case the operating point will not fall on the full horsepower curve.
Fi .E4.6
Fi . E4.7 - Onward Transitions
As the train continues to accelerate, the generator current again drops off. By the time speed reaches 50.8 M.P.H. (81.7 kmph), the generator will again be operating at the top of the horsepower curve, point C in Fig.E4.5. Now we go for parallel field shunting (transition 3). As in series field shunting, part of the motor current bypasses the motor field through the shunting resistor. The increased generator current moves the operating point down the horsepower curve as shown in Fig.E4.6, permitting further acceleration at full horsepower.
Backward transition If the train hits sufficiently steep grade, it will begin to slow down. As the speed drops, motor current increase as shown in Fig.E4.8. Suppose the train is travelling at 49 m.p.h. when it hits the grade. This point P is shown near the top of the curve. As the train slows down, generator current increases.
At a speed of ground 30 m.p.h. the locomotive will be operating at the bottom of the full horsepower curve, point B. Something must be done or the operating point will go below B on locomotives without current limits this could mean overheating the generator. With current
limit the locomotive will operate at reduced power, which reduces engine efficiency. The current that the generator must supply can be reduced by making a backward transition. This will transfer the operating point back to the top of the horsepower curve point as shown. If the speed continues to drop unshunting is done. There is one little difference in backward transition 3 to 2 from forward transition 2 to 3 on some locomotives, which at times is confusing. The generator field is left on in backward transition, but not in forward transition. There is a reason for it. If we look at the horsepower curve Fig.E4.8 we will see that backward transition takes place at point B where the generator current is high and the voltage is low. At this low voltage there is little chances of generator flashing ever when switching is done. Also during switching, this provides for the quickest rise to full voltage after the switching is completed so, we are still operating at full horsepower, but not at top of the horsepower curve. From the above, we can understand that transition takes place back and forth as train speed and load change. Its purpose is to hold operating point on the generator horsepower curve. This keeps the engine delivering full horsepower at all times. Let us now see how transition is done.
Automatic transition We have seen that transition is made at a definite train speed and also at a definite point on the generator horsepower curve. This makes possible two methods of bringing about transition automatically, e.g. (i) (ii)
Train speed based transition. Generator volts and amps based transition.
Generator volts and ampere based transition The second method of controlling automatic transition is based on generator volts and amperes. Relays that pick up on generator voltage at the top of the generator horsepower curve, point C in Fig.E4.2 bring about forward transition. Usually one relay is used for field shunting in series parallel and parallel. Another relay is used for series-parallel to parallel transition. One or more additional relays, that operate in generator current at the bottom of the horsepower curve, point B in Fig.E4.2 are also required for backward transition. For satisfactory operation, these relays should be accurately calibrated on the bench.
What is excited and why The voltage output of a generator depends on the speed of the armature and the amount of field excitation. The current, on the other hand, depends on the circuit connected to the generator (usually called "load"). In a diesel electric locomotive, the load is the combination of traction motors connected with their cables and switches. These motors should have the right voltage at all the times. To get the right voltage, the current in the generator field must be varied to suit the locomotive operating conditions. This is known as excitation control.
Job of a excitation system A diesel engine gives maximum fuel efficiency if it is loaded in such a way so that it develops constant HP with each throttle setting. In a diesel electric locomotive, load is the combination of traction motors, and the current through them varies with their change in speed. So to keep main generator power constant, the output voltage must be varied accordingly. Excitation system controls the output voltage of the main generator to (1) maintain constant horse power (2) limit the current at stand still condition of the locomotive (being the series motor, they draw excessive current at stand still. (3) Limit the voltage to avoid flash over at higher speed of the locomotive. For these jobs it must respond automatically to any movement of the throttle handle, to any change in load on the generator, or to any combination of both.
Where does excitation comes from Excitation systems can be roughly classified in two groups, internal and external. In internal system, the main generator and exciter is built to operate in such a way that without interference of any other control device, main generator develops constant power at different load condition. In an external system, control apparatus outside the main generator and exciter is used to get these results. The whole problem is to properly vary the current in the field of main generator. This current may come from a storage battery, the generator's own armature, another dc generator, or a combination of the above. A good excitation system produces a generator characteristic curve of constant power. A typical main generator characteristic curve produced by a good excitation system is shown in Figure E-3.1. Power output at any point on this curve is equal to the voltage multiplied by the current. This is kept constant for each throttle setting by the excitation system.
Electronics Excitation system Introduction
In a locomotive, the load on the main generator at any fixed engine speed varies as locomotive track speed increases due to the counter EMF created by the rotating armatures of the traction motors. The load is also changed by shunting the traction motor fields or changing connections from series to parallel. Therefore, the excitation control must act to keep generator horsepower demand constant over a wide variation of terminal voltage to run the diesel engine with maximum fuel efficiency.
The "electronics excitation system" is a
system
using semiconductor components. The
system controls exciter generator field current; i.e. the exciter output. The system provides the function of current limit, voltage limit on the generator and keeps the generator power constant at eight different levels as far as possible at each of the eight engine speeds available.
Generator Load Curve The required performance is illustrated by the "Typical Generator characteristics" curve, Fig.1. The curve is drawn for 8th notch (full power) operation.
The portion of the curve denoted by line BC is the current limit for the generator. Currents in excess of the values shown by this line would produce excessive slippage when starting a train and also may cause damage to the main generator and traction motors. The slightly rising line from the srcin of the curve at O volts and O amperes to the point B is known as the IR line. This represents the voltage obtained at various generator currents with the motors connected, but with the train not yet moving. The current in the motors at stand still is equal to the voltage across each motor divided by the motor resistance. The current and voltage combinations represented by points along the line CF indicate a constant rated engine horsepower, expressed in electrical terms. Voltage and current to the right of this line would represent a higher load on the diesel engine. If the excitation system were allowed to load the engine in such a manner, the engine speed would drop, because of limit in fuel, resulting in loss of power and controlled operation could not be obtained. The dotted lines represent the characteristic provided by the excitation system to approximate constant engine horsepower. System tolerances (+ 2.1/2%) are such that actual generator characteristic may fall anywhere in the band shown, meaning that it may, in some instances, slightly exceed the normal. When this occurs, generator characteristic may be trimmed to meet the desired constant H.P curve by the load control potentiometer actuatedby the engine governor.
Family of notches curve Fig.2 shows the family curves representing generator characteristic from first notch through eight notch as developed by the excitation system. The actual position of each curve is determined by an engine speed signal continually fed to the excitation control. When the engine accelerates from one notch value to the next higher one, the generator current increases smoothly until it reaches a new notch value as the engine gets to the corresponding speed for that notch.
Basic excitation system
Fig.3 shows a basic block diagram of the Electronics Excitation System. The exciter shunt field is fed from the locomotive battery through a network of resistors and exciter field transistor EFT1. The power transistor functions as a switch and is turned "ON" and "OFF" 800 times per second by pulses generated by the oscillator. The pulse width modulator (PWM) controls the duration of "ON" time as compared to "OFF" time during each pulse, thus regulating the average current in the exciter field PWM responds to several "feed-back" signals as shown in the block diagram, Fig.3 and described in detail below. Generator armature current is measured by a special reactor called armature currentcontrol reactor (ACCR). Generator voltage is measured by a reactor called voltage control Reactor (VCR). The outputs of these reactors are fedto the reference mixer network. Only the greater of the two outputs is used at any one time. When the output of either ACCR or VCR is greater than the reference current, a current is put through the main winding of the pulse width modulator to limit generator excitation. The function generator circuit modifies the output of ACCR in relation to generator voltage to produce the constant horsepower portion of the generator characteristic curve for notch 8. In the lower notches, the function generator also responds to engine speed to prodvide the proper separation of the notch curves.
System components Exciter generator The exciter - generator is a shunt wound d-c machine. The generator is mounted on the traction generator gear box and gear driven from it at a speed proportional to engine speed.
Excitation panel The excitation panel is a steel fabricated housing with component parts mounted on seven plug in type cards, which slide out of the housing for easy inspection. Three rheostats are mounted on the face of one card. One adjusts main generator characteristic and two adjust dynamic braking efforts .
Oscillator
The oscillator is an a-c power supply used to supply power for various control functions. It operates from a d-c input voltage from the locomotive battery. The oscillator transformer (OST) has number of secondaries to supply a-c power to various circuits as follows: WINDING
FUNCTIONS
1. 2. 3. 4.
Excitation Transistor (EFT1) Oscillator Feed Back. Pulse Width Modulator (PWM) Spare
5. 6.
A C C R. V C R.
The power supply consists of a saturating transformer alternately energised in opposite directions. Transistors which function as switch, causes flux reversal in the transformer core. The oscillator changes d-c input to a 400 CPS (cycles per second) square wave output.
Armature current control reactor The armature current control reactor is a measuring device which when powered by an a.c. source produces a signal proportional to main generator current. A reactor offers the advantage of isolating the output circuit from the main or high voltage input circuit. The a.c. input is fed to the a.c. winding from a secondary of the oscillator. The reactor consists of a large busbar, two cores, two a.c. windings single turn d.c. winding and a 1740 turn d.c. winding. The large busbar is made to encompass the d.c. and a.c. windings. Fig. 5 shows a cross sectional view of the reactor. The one turn d.c. winding is copper wire connected to the large busbar, and forming a parallel path for current in the busbar. The cores, with the a.c. and d.c. windings, are assembled around the one turn d.c. winding. The reactor is calibrated and the complete magnetic structureis sealed in epoxy. The ACCR is connected in series with themain generator. The majority of the main generator current passes through the busbar with only a small fraction of the generator current passing through the single turn d.c. winding. Since the current in the single turn winding is directly proportional to the main generator current, it may be measured by the reactor to obtain a signal proportional to main generator current. The more d.c. input in the one turn winding, the more a.c. output. If current is also passed through the 1740 turn winding, the a.c. output will increase. Further discussion of theuse of 1740 turn
winding is contained under the heading "Function Generator". The a.c. output of the reactor is rectified and fed to the mixer circuit.
Pulse width modulator (PWM) The pulse width modulator (PWM), mounted in the excitation panel, is a small self-saturating reactor with five d.c. control windings and two a.c. windings fed by one of the oscillator transformer secondaries. The function of the pulse width modulator is to control the time that the exciter generator shunt field is excited thus controlling the maingenerator output. This reactor is used in the excitation system tocontrol rather than to measure. The pulse width modulator contains two cores. There is an a.c. winding on each core; the five d.c. windings are wound about both cores. Refer to Fig.6 for simplified circuit. The output of each a.c winding is rectified and half of the input cycle is used from each coil. Since the oscillator frequency is 400 Hz, there will be 800 times ON pulses per second fed tothe base emitter circuit of transistor EFT1. This causes the transistor to be fully turned on.
Mixer reference The mixer network is where the signals from ACCR and VCR are compared against each other and the reference signal. Two outputs are in such a way that only whichever is larger actually supplies the circuit and as if the other one has no effect in the external circuit. Current goes out from the mixer circuit is the amount equal to the largest of these three. The adjustments are so made that at point F, VCR output exceeds that of ACCR and the line FG on the generator characteristic is determined.
Engine speed reference The tachometer generator on the diesel engine generates alternating voltage, with the frequency proportional to the engine RPM. This is fed into a saturable core transformer (ESST) whose secondary voltage is proportional to the frequency with minimum error either due to temperature or variations in flux of the core (due to change in voltage). One function of the tachometer generator is to control the generator characteristic on the basis of engine speed such that characteristic shrinks as lower speeds are set. This provides a smooth change in level of power, when throttle handle is moved.
Engine load control
The governor load controlpotentiometer (LCP) is connected in to the network of resistor LCR1 and LCR2 so that with the LCP in inactive zone, the brush arm is at 24.4 volts above 4 wire potential, with the engine running and auxiliary generator at 75volts. If the governor goes in to load control, more than 24.4 volts appear at the LCP brush arm and the current flowing in the mixer circuit will be less and excitation is reduced to restore the proper loadon the diesel engine.
Control Systems in Diesel- Electric Loco The Diesel Electric Locomotives of Indian Railways, driven by DC traction motors, employ AC/DC Power Transmission System. The basic Block Diagram of the Locomotive Control System is shown in Figure 1. Traction Alternator is directly coupled with Diesel Engine. The three-phase output of the Alternator with variable frequency and voltage, depending on RPM of Diesel Engine and Excitation level of the Alternator, is fed to a Rectifier Panel. The Rectified DC output is fed to the Traction Motors, mounted on individual axles, through electro pneumatic Power Contactors. At starting the motors are connected in series-parallel (e.g. in WDG series locomotive with 6 motors locomotive starts in 2 series-3 parallel mode). When a specified Locomotive speed is achieved, Motor Transition takes place by changing the connection configuration of Traction Motors to series to series weak field or series weak field to parallel (6P) and vice versa when the speed is reduced as per setting done in the configuration parameters. For ⇔ series weak field ⇔ example, in WDM2 series locomotives, three Transitions are provided viz. series parallel ⇔ parallel Weak field at specified speeds. The Locomotive has a Master Controller on the Control Stand for control actions such as Forward or Reverse movement, Traction or braking mode of operation, setting the Engine RPM and power level through eight Notches, etc. Control Equipment on the Locomotive works on a Regulated Power Supply generated by a DC Auxiliary Generator. Field current of the Auxiliary Generator is controlled by an AG Control Circuit to regulate its output voltage. Another DC Machine called Exciter supplies power to the Field Winding of the Alternator. Field winding of Exciter is controlled by an Exciter Control Circuit to maintain the required power level to Traction Motors. To reduce speed of a moving locomotive, in addition to mechanical braking, an electrical Dynamic braking system is used on these locomotives. In Dynamic braking system, the DC Traction motors work as Generators and dissipate the power generated in a resistance grid. Thus, for operating a locomotive, the following control systems are required
Excitation Control to run locomotive at different power levels as per requirement Propulsion Control to run the locomotive in Traction/ Braking mode, Forward/Reverse direction, etc Wheel Slip Control to detect the slipping of wheels and taking corrective action
Dynamic Braking Control during the Dynamic braking
Auxiliary Generator Control for charging the on board batteries and supplying power to other equipments
E-type Diesel locomotive control system The Diesel Electric Locomotives (WDG3A/WDM3A) of Indian Railways driven by DC traction motors employs AC/DC transmission system. The basic block diagram of the locomotive control system is shown in Fig. 1.
The power generated in the diesel Engine is converted to electrical energy through the traction alternator directly coupled to the diesel engine. The 3-phase AC output from Traction Alternator is rectified to DC voltage by rectifier panel. The rectified DC output is fed to the traction motors through BKT, REV and power contactors. The following control systems are required for operating a locomotive.
Engine cranking and propulsion control system: a. This control system cranks the engine through governor when START button is pressed. It controls the engine RPM in 8 different notches based on the signals received either from control desk operated by the driver or leading locomotive while working in multiple unit (MU) operation. The engine generates 8 different levels of power as per the selected notch. b. It also shutdown the engine as requested by driver or when any safety device is operated.
Auxiliary generator control system: All the control equipments on a Diesel electric locomotive work on 72V DC. Aux. Generator basically a shunt generator produces this low voltage control supply. The VRP regulates the Aux. Gen. Field current and maintains it voltage at 72V. The same regulated voltage is used for charging batteries that are initially used for cranking the engine.
Loco propulsion control system:
a. The loco propulsion control system changes direction of loco movement by energizing reverser to the
required direction. b. The loco propulsion control system manipulates the traction motor connections based on the signals
received from the driver / MU consists and the locomotive speed. E.g. in WDG3A class of locomotives, the six traction motors are connected in 2 series – 3 parallel (2S-3P) by energizing series power contactors while the locomotive speed is below 42 KMPH. Above 42 KMPH of speed all the six traction motors are connected in 6 parallel (6P) combination by energizing parallel power contactors. c. During dynamic brake operation, the BKT is operated to braking side and required power contactors
are energized. The traction motor fields are separated from armatures and all the six fields of traction motors are connected in series across the rectifier output and the armatures are connected to dynamic brake grids with two armatures in series across one set of grids by energizing BKT and associated power contactors. The propulsion control system also recalibrates the excitation controls to achieve lower level of traction alternator outputs during D.B. d. It detects wheel slip and sends a signal to excitation control system to reduce power. e. It also detects engine cooling water temperature and operates radiator fan when engine requires
cooling. f. All the above operations are carried out through a series of sequentially connected mechanical
interlocking to ensure safety and smooth operation from one mode stage to another.
Excitation control system: Excitation control system regulates the exciter field current through a transistor switch operated by the Pulse Width Modulator basically a magnetic amplifier. The average current is decided by the ON to OFF ratio of the PWM which is controlled by the mixer reference net work basically a resistor network with two reactors and rectifiers. The mixer reference network receives proportionate feedback signals from T.A. voltage, T.A. current and engine speed. Based on the input signal levels it sends a controlling signal to the PWM, which controls the exciter field current, and it’s output. The exciter output is directly
connected to alternator field through GF contactor, which is again controlled by propulsion control system. Thus traction alternator power is controlled to the required constant HP at each notch.
Demerits in existing locomotive control system The present locomotive control system consists of different panels having analog control circuits to achieve the desired operation. The control system being analog type, has following inherent limitations: A. Setting of power levels during motoring, dynamic braking, transition speeds etc. needs to be done
with potentiometers, which makes the adjustment cumbersome, time consuming and inaccurate. Also
these potentiometers are prone to failures due to wear and tear of the movable brush arms and cause malfunction. B. Various time delays for smooth loading and unloading of power either in starting or during transition
are achieved through RC (resistor capacitor) network. These capacitors are bulky and electrolytic in nature. They are prone to leakage in service and cause variation in timings unless they are closely monitored and replaced in time. C. The engine and loco propulsion control logic uses number of interlocking relays and auxiliary contacts
of contactors for sequential operation. Being a mechanical interlocking system, all these interlocks wear in service and require periodical attention to ensure proper timing and sufficient interlock pressures. D. Because of too many interlocks, wiring is complicated and being analog control system
troubleshooting is tedious. E. Additional safety interlocking if required cannot be added without additional hardware like relays.
Interlocks etc., which mean lot of manpower and material, is required to implement. F. In case of any failure in thesystem, three is no assistance to driver / maintenancestaff regarding
exact fault and its remedies. G. In case of locomotive operating on the short term rating of traction motors, the operating timings in
that band are to be observed invariably by the driver. During dynamic brake operation also, driver should limit the load meter to 600 Amps (Yellow dot on the load meter) above 85 KMPH. Otherwise traction motors are damaged due to commutation problems. H. The wheel slip detection is by difference in currents of traction motors and the control is not proportional to the amount of wheel slip. The excitation reduces drastically to zero and the driver has to
reduce the notch till the wheel slip stops. I. In case a defective traction motor is isolated, there is no automatic limitation of power to safeguard
the remaining traction motors.
Microprocessor system- MEP 660 based locomotive control system A. The MEP – 660, microprocessor based loco control system developed for Diesel Electric
locomotives takes over the entire locomotive control replacing the above discussed 4 control systems, available in the conventional E-Type loco control system with a microprocessor control as shown in fig.2.
B. In the Microprocessor based Locomotive control system MEP-660, has got a centralized
control system through microprocessor. The MEP-660 receives various digital input signals either from control desk or MU wires. It also receives feedback signals from individual output devices indicating their status (energized / de-energized). All the analog parameters like voltages, currents, pressures and temperatures are sensed through various sensors and are connected to MEP-660 for monitoring. All the speed signals from traction motors and engine are connected as frequency input signals to MEP-660. The MEP-660 continuously monitors status of these digital, analog and frequency signals in a cyclic manner and performs the following tasks. a. It receives operational requests/commands either from driver or leading loco in the form of digital inputs. b. It computes them as per the input vs output matrix stored as set of instructions and decides
which output devices to be energized. c. It ensures the associated safety devices are in normal status. d. It energizes the required output devices. e. It verifies the status of all output devices through their respective feedback signals. C. The MEP-660 has got two programmable PWM outputs to perform the activities of auxiliary
generator field control and excitation control systems. Here the On to OFF ratio of these PWMs can be controlled through a set of instructions written in the form of algorithm and stored in the microprocessor. These variable / programmable PWMs are connected to two IGBTs. One IGBT is connected in the exciter field circuit to control traction alternator excitation and the second is connected in the Auxiliary generator field circuit to control Auxiliary generator output. The MEP-660 dynamically computes the output power that can be generated bythe engine at any instance of operation based onvarious inputs like site altitude, Ambient Air Temperature and engine RPM. Then MEP-660 calculates the Voltage to be generated at that instance based
on the Traction alternator current and alternator efficiency. Accordingly the microcontroller in MEP-660 generates a PWM output signal, which drives the IGBT connected in Exciter field circuit. Accordingly the exciter field current varies based on the duty cycle of PWM. Thus the exciter armature current varies, which in turn drives the traction alternator field current and hence its output power. Thus the traction alternator output power is controlled by the microcontroller to the required constant HP at each notch. During dynamic brake operation also, the micro-controller in MEP-550 generates a proportionate PWM signal based on master handle position in the Dynamic brake Zone, and the speed of locomotive. The traction motor field current is regulated in such a way to limit the traction motor armature currents with in safe limits whatever may be the master handle position. In this way the maximum braking effort can be achieved even at higher speeds, which is not possible with conventional system. The 2nd microcontroller in the MEP-660 generates another PWM signal to drive the 2nd IGBT connected in Aux. Gen. field circuit. The auxiliary generator armature current, battery charging current, Auxiliary generator voltage and battery voltage are continuously monitored by MEP660 through appropriate Voltage and current sensors. The auxiliary generator field current is controlled in such a way that the set constant voltage output is maintained at Auxiliary generator armature terminals. However when the Aux. Gen. Current or battery charging current exceed safe limit, the Aux. Gen. Field current is limited to safe guard the machine by changing the duty cycle of the PWM signal. All these parameters– A.G. Voltage, A.G. current and battery charging current are made user programmable so that MEP-660 is suitable for different types of Aux. Generators and batteries used on the locomotive which is not possible in the conventional system without changing hardware components like shunts, VRP etc.
Advantages of MEP-660 microprocessor based control system over the existing E-type locomotive control system The MEP 660 has overcome all the limitations discussed under ‘Disadvantages of existing loco control system’. MEP-660 also provide the following additional advantages:
A. Adaptability: The same control system can be adoptable to various class of diesel electric
locomotives. B. Flexibility: System parameters can be configured to different types of locomotive under same class of locomotive like WDG3A, WDG3D and WDM3D having different types of sub components. C. Superior control mechanism: MEP – 660 closely monitors various voltages, currents, temperatures, etc. of various equipments through non-contact type DC current sensors, hall effect type Voltage sensors etc. and control them in such a way that they always operate with in
the set specified limits. This enhances the life of the traction equipments and improves the reliability and availability of the locomotive. D. Optimum utilization of power : a. The MEP-660 continuously monitors the site altitude and ambient temperature. Necessary HP corrections are made to the GHP to calculate site HP. Reference HP which ensures that the engine is optimally loaded. b. The exact power consumed by the auxiliaries like compressor, radiator fan, auxiliary
generator and exciter is computed continuously and is deducted from the site HP to arrive TA input HP. set gross HP and the balance HP is provided as traction input. Thus the HP not consumed by the auxiliaries is utilized to traction input. c. Traction alternator efficiency is computed continuously at every current level and necessary correction is made on TA input HP to arrive the HP that can be loaded on the diesel engine at every instance. Accordingly the engine is loaded. d. Thus always the engine is optimally loaded without any over load due to varying conditions like site, ambient temperature etc. e. The unused HP by the Auxiliaries is added to the Traction input without under loading the engine. E. Fault diagnostics : Being a microprocessor-based system the MEP 660 has Fault Diagnostic capabilities. The system continuously monitors various operational parameters and checks for abnormalities in the functioning of various traction equipments. In case a fault is identified, an appropriate action by way of isolating a sub system or limiting the power, etc is taken to prevent further damage to the equipment and other connected equipments. This fault is also displayed on the Display Unit along with restrictions imposed because of the fault, for information of the driver. The fault code along with Real Time and date stamp is logged in the Error Log Memory. F. Data Packs: In addition to fault recording, eight data packs consisting of various locomotive parameters are recorded from five seconds prior to the declaration of fault to three seconds after the declaration of fault. G. Self Diagnostics: In addition to monitoring locomotive equipment, the MEP 660 system keeps on monitoring its own modules and sensors, continually for their healthiness. In case of any failure, appropriate action is taken and the fault is registered in the error log and also displayed to the driver on the display unit. H. Fault tolerance: Fault tolerance capabilities are also built in the MEP-660 control system, for certain faults. In such cases the operation of the locomotive continues in the normal way and the fault is logged in the error log with data packs for later analysis and corrective action by the maintenance staff. Detailed fault tolerance is discussed in system manual – Item 8. I. Automatic fault recovery: For most of the faults, the recovery conditions are identified and whenever the fault ceases to exist, the fault recovery is recognized and displayed to the driver on the display unit, and at the same time all the restrictions imposed by that fault on the loco operation are removed and the event is registered in the error log. There is no need of manual resetting for these faults. J. Short term rating of Traction Motors: The equipment automatically takes care of, short-term traction motor current ratings and does not depend upon the driver, for protection of the
equipment, unlike the conventional E-type excitation system. The system also takes care of commutation limits of traction motor at high speeds for armature currents of traction motor and restricts the same to the desired levels without depending on the driver. K. Digital setting of parameters : Any parameter can be set digitally in the system. There is no need of adjusting any potentiometer by trial & error method. Hence practically no calibration time is required as in the case of conventional system. Any set parameter in MEP-660 does not change in service unless and until somebody changes. L. Low maintenance cost : The MEP-660 eliminated various general-purpose interlocking relays and sequential interlocks from both existing engine and loco propulsion system. Hence maintenance / replacement for these relays and interlocks is eliminated reducing the maintenance cost. Also Failures due to malfunctioning of these items is eliminated. M. Proportionate power reduction / smart control over wheel slip : The MEP-660 provides a
superior wheel slip control, which improves the adhesion substantially. The speed sensors mounted on TM end shield measure all the six Traction Motors RPMs. In case of any one or more wheels are tending to slip, the amount of wheel slip / wheel creep is precisely calculated and the excitation is controlled through a Proportional and Integral Control loop in such a way as to control the wheel slip and at the same time deliver maximum possible tractive effort with the available adhesion at that point of time. P. Self-Load Box Test: (Applicable to locos fitted with MEP-660 control system along with Self load box feature). A simple load test can be carried out to know the performance of the engine and entire control system. During this test, the dynamic brake grids are connected as a resistive load to alternator. Engine can be loaded up to 90%. Q.Event Recorders: (Applicable to locos fitted with MEP-660 control system along with event recorder) The Microprocessor based Locomotive Control System MEP 660 provides built in data log of various locomotive parameters for the benefit of railways. The system records the data on a compact nonvolatile Flash Memory Unit that does not need any electrical power to retain the data in the memory. The data is recorded both in internal memory, and in external memory card. The memory is divided into three categories. 1. Short term 2. Long term 3. Configuration In the short-term memory, the following data is recorded in one-second interval. Latest 45 hours data is available at any time to down load. a. Date b. Time c. Locomotive speed in KMPH d. Distance traveled from previous record in meters e. Train Brake Pipe Pressure (BP) in Kg/cm² f. Loco Brake Cylinder Pressure (BCP) in Kg/cm² g. Notch Position h. T E Limit Current i. Status of Loco Motoring– MOT (ON/OFF)
j. Status of Loco Dy. Brake – BRK (ON/OFF) k. Status of Penalty Brake application - PLT (ON/OFF) l. Loco movement Forward direction– FOR (ON/OFF) m. Loco movement Reverse direction– REV (ON/OFF) n. Status of Flasher Light – FL (ON/OFF) o. Status of Head Light - HL (ON/OFF) p. Status of Head light brightness– HL (Dim/Brt) q. TE LIMIT switch status– TE (ON/OFF) r. VCD time cycles (T2, T3, ACK, Fail & ISO) s. Remarks R. Multi Reset Vigilance Control Device / Alerter: The Microprocessor based Locomotive
Control System MEP is equipped with vigilance control to enhance the safety of the locomotive operation. a. In the conventional loco control system, a vigilance control device had been provided in which a separate vigilance control push button is provided. The driver has to operate this button once in 60 seconds in addition to his regular locomotive operations to inform the control system that he is vigilant. Drivers are not happy with this system and the vigilance device slowly disappeared from the loco control system. b. The multi reset vigilance control device provided in MEP 660 Microprocessor Control System acts very smart. It recognizes the following loco operations performed by the driver and assumes he is vigilant. 1. Change of notch position 2. Application / release of Dynamic brake 3. Application / release of brakes through A9 4. Operation of sand buttons 5. Operation of Elec. Horn buttons 6. Change of locomotive direction through RH 7. Operation of GF switches 8. Sufficient increase / decrease of Dy.Brake level (20%) through master handle 9. Operation of VCD reset switch. S. Auto Flasher: The MEP 660 Control System switches ON the train’s Flasher light automatically
during Train Parting or driver applies fireman emergency brake. T. Auto Emergency Brake system: Automatic emergency braking has been introduced on make microprocessor based control system to avoid run away train.
Control philosophy The Microprocessor based Locomotive Control System MEP 660 functioning is totally controlled by built-in software program using various parameter values stored in a non-volatile data memory. Various functions of the system are described below
Excitation control Depending upon the operating requests of the driver through master controller settings, the out put power of the locomotive is computed by the microprocessor from various inputs. The microprocessor generates a PWM output signal, which drives the field winding of the Exciter. The armature current of the exciter varies accordingly, which in turn drives the Traction Alternator field. Hence the Traction Alternator output power is controlled by the microprocessor to the required constant HP at each notch. Traction Alternator efficiency is computed continuously at every current level and the excitation is controlled in such a way that the gross HP generated by the engine is always maintained constant. Similarly, the auxiliary power utilized by air compressor, radiator fan, auxiliaries, etc. are computed and they are deducted from the input power to traction motors so that the gross HP generated by the engine is always maintained constant. The current limit and voltage limit of the Traction Alternator are computed continuously and the same are not exceeded by proper control of excitation. Various other limits of traction equipment like Exciter Field current Limit, Traction Alternator Field Current Limit etc. are observed in the excitation control so as to protect traction equipment. All these parameters i.e. HP, current limit, voltage limit, and RPM at each notch can be programmed by the user through the user programmable parameters for the installed engine and traction equipment on the locomotive. The engine over loading is sensed by the microprocessor control system by measuring the Load Control Potentiometer Voltage (LCPV) generated by Wood Ward Governor/Electronic Governor and the excitation is controlled in such a way that the Diesel Engine is not over loaded.
Dynamic Braking In this mode of operation, the Traction Motors act as generators and convert the mechanical energy in the form of train’s kinetic energy (proportional to the speed and weight of the train)
into electrical energy and dissipate it in the grid resistors. During dynamic braking, all the traction motor fields are connected in series and are powered by the Traction Alternator. Armatures of individual Traction Motors are connected to the grid resistors independently. The grid resistors are cooled by blowers, which also work on the electrical power generated by the traction motors. Braking level requested by the driver through master controller handle is measured through a potentiometer (BKCP) by the micro computer and the field winding of the exciter is controlled in such a way as to provide traction motor field current proportional to the master controller setting. The armature currents of the individual traction motors are limited to a pre-set maximum level by reducing the excitation if required. This is conventional control methodology used in E-type excitation system. By selecting an alternative control methodology, the microcomputer also controls the traction motor field currents in such a way as to limit the traction motor armature currents proportional
to the master controller setting. In this way the braking effort can be varied widely even at higher speeds, which is not possible with conventional system described above. In both the methods, the traction motor armature currents are limited to a low level at higher speeds to protect the motors against commutation limits. All these parameters such as traction motor field current, armature current at low speed and high speed, and commutating speed limit etc. are made user programmable so that the Microprocessor Based Locomotive Control System MEP 660 system can work with various types of traction motors, braking grid resistors etc.
Propulsion control All the intermediate relays used in the conventional propulsion control system are eliminated by the Microprocessor based Locomotive Control System MEP 660 system. Also various interlocks of relays that are used for sequencing of operations as well as safety requirements are eliminated. The software logic available with microprocessor takes care of all the sequencing requirements and safety interlocks. The microprocessor control system senses the master controller setting and controls various power contactors like GF, Parallel contactors, Series contactors, BKT, REV etc. The microprocessor control system measures the speed of the locomotive and configures the traction motors in series-parallel / series – parallel with weak field /parallel with full field through the control of S-contactors, P-Contactors and field shunting contactors, depending upon the locomotive speed. Based on the notch setting, the AV, BV, CV, and DV solenoids of Wood Ward Governor (signals in case of Electronic Governor) are driven by the micro controller system to attain the required Diesel Engine speed. The Diesel Engine cooling water temperature is measured by the microprocessor control system and the radiator fan drive is controlled accordingly. At low temperature, the radiator fan drive is OFF. At medium temperature the radiator fan is driven at low speed. At higher temperature, the radiator fan is driven at high speed. A still higher level of temperature provides an audio-visual alarm to the driver along with a warning on the display and at extremely high temperature the Diesel Engine is brought to idle speed and prevents further motoring till the temperature decreases down, with appropriate display message being displayed on the display unit. Once the temperature is decreased, automatically the engine is permitted to run at higher notches and traction is permitted. The temperature levels at which all these activities take place are made user programmable, so that the system can function with different types of equipment on the locomotive / different locomotives and at set parameters. The cooling water level is sensed through existing low water switch (LWS) and if it is low, the engine is shut down with appropriate message on the display and the ALG is energized. The power ground leakage current is measured through a current sensor and when it exceeds the set level, the Diesel Engine is brought down to idle RPM and traction is prohibited. The fault
is logged in the error log. If the ground leakage current is reduced to below the set level, after the master controller is brought to idle and after specified time has elapsed, the Diesel Engine is permitted to rise again and traction is permitted automatically.
Wheel slip control The Microprocessor based Locomotive Control System MEP 660 provides a superior wheel slip control, which improves the adhesion substantially. The speed sensors mounted on the traction motors measure all six individual Tr. Motor’s RPMs and MEP-660 computes corresponding wheel RPMs. In case any one or more wheels are tending to slip, the amount of wheel slip/wheel creep is precisely calculated and the excitation is controlled through a proportional and integral control loop in such a way as to control the wheel slip and at the same time deliver maximum possible tractive effort with the available adhesion at that point of time. The adhesion varies depending upon the environmental conditions and the conditions of wheel profile and rail profile of that track section. In the conventional system the wheel slip is identified through a set of differential relays and the excitation is brought down drastically in case of a wheel slip. This is because there are no means of measuring the amount of wheel slip/creep precisely. In the absence of this information, it is not known, whether it is a major wheel slip or a minor wheel slip. In order to protect the rail and wheels and traction motors, the excitation is cut drastically. Because of this philosophy, full adhesion available cannot be utilized. Whereas in the improved wheel slip control system of Microprocessor based Control System MEP 660 the amount of wheel slip/wheel creep is precisely known and excitation is precisely controlled through a PI control algorithm to utilize the full adhesion available at that point of time. For this system to function effectively, the ratios of all the wheel diameters should be known precisely. The Microprocessor based Locomotive Control System MEP 660 provides an automatic wheel diameter calibration system. When the locomotive is in coasting and neither dynamic brake nor air brake is applied and the speed of the locomotive is in specified band, the system calibrates the wheel diameters automatically at preset periodical intervals. This takes care of wheel wear and avoids false wheel slip identification. Sanding is done automatically when wheel slip occurs if the effective traction power delivered is less than 85% of requested power and the loco is working in notch 3 or above. This philosophy conserves sand and at the same time effectively utilizes sand. However, manual sanding by pressing the push button is always permitted, which over rides the Microprocessor based Locomotive Control System MEP 660.
Auxiliary generator control The microprocessor control system generates a PWM signal to drive the field winding of auxiliary generator. The auxiliary generator armature current, battery charging current, auxiliary generator output voltage and battery voltage are continuously measured by the MEP-660
system, through appropriate current and voltage sensors. The excitation of auxiliary generator field is controlled in such a way that the set constant voltage output is maintained at the auxiliary generator armature, irrespective of the RPM of the diesel engine. However, when the auxiliary generator current or battery charging current exceeds the limit, the excitation to Auxiliary generator is reduced to prevent damage to the equipment. All these parameters are made user programmable so that different types of auxiliary generators and batteries can be used with the same Microprocessor based Locomotive Control System MEP 660.
MEP Block Diagram
