15 Days Visit to Howrah Electric Multiple Unit(EMU) Shed......

1st February, 2013

Acknowledgement:-

        My trip, my learning experience,  my understanding of the Electric Multiple Units, my  easy access to all the workshops, and my innumerable questions being  answered and explained to, has all been possible because of the kind help and  encouragement of Mr C.N JHA, Senior Divisional Electrical Engineer,  Howrah, EMU.

Thank You sir, Thank you very much.

I am ever grateful to you.

With Regards

Sundar Mukherjee

An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages. Most EMUs are used for passenger trains, but some have been built or converted for specialized non-passenger roles, such as carrying mail or luggage, or in departmental use, for example as de-icing trains. An EMU is usually formed of two or more semi-permanently coupled carriages, but electrically powered single-unit railcars are also generally classed as EMUs.

EMUs are popular on commuter and suburban rail networks around the world due to their fast acceleration and pollution-free operation.Being quieter than DMUs and locomotive-drawn trains, EMUs can operate later at night and more frequently without disturbing residents living near the railway lines. In addition, tunnel design for EMU trains is simpler as provisions do not need to be made for diesel exhaust fumes, although retrofitting existing tunnels to accommodate the extra equipment needed to transmit the power to the train can be expensive and difficult if the tunnel has limited clearance.

Types

A power car carries the necessary equipment to draw power from the electrified infrastructure, such as pickup shoes for third rail systems and pantographs for over head systems, and transformers.The cars that form a complete EMU set can usually be separated by function into four types: power car, motor car, driving car, and trailer car. Each car can have more than one function, such as a motor-driving car or power-driving car.

The entrance to Howrah Electric Multiple Unit Shed.

A testing car has been kept undergoing maintenance and the other coaches(trailer car+motor car) both undergoing major and minor repair.

The shed is divided into several lines. It comprises of a total of 15 lines where the first line is used for maintenance both for POH(Periodic Overhauling) and IOH(Intermediate Overhauling) purposes whereas the other lines are meant for the rakes to be kept and tested.

An array of spare parts can be seen comprising of springs that form the suspension system and pivots and bogie bolsters.

The wheels are kept for polishing and to be fitted and adjusted with bogies where maintenance is taking place.

An overview of the shed from the top floor.

A line of series of EMU's where maintenance is taking place awaiting both major and minor overhaul.

• Motor cars carry the traction motors to move the train, and are often combined with the power car to avoid high-voltage inter-car connections.
• Driving cars are similar to a cab car, containing a driver's cab for controlling the train. An EMU will usually have two driving cars at its outer ends.
• Trailer cars are any cars that carry little or no traction or power related equipment, and are similar to passenger cars in a locomotive-hauled train. On third rail systems the outer vehicles usually carry the pick up shoes, with the motor vehicles receiving the current via intra-unit connections.

A view of the entire shed.

Many different EMU formations have been used in different areas. In the 1930's, Madras suburban service started with 3-car EMUs which were notable in having coupled bogies across cars, thereby making the entire 3-car formation a rigid unit. Later Madras also got some 4-car (non-rigid) EMUs. They were sometimes operated in pairs at rush hours, leading to 6-car (two rigid) and 8-car (two non-rigid) formations, and rarely 7-car formations (one 3-car rigid and one 4-car).

10-car formations were seen rarely (two 3-car rigid EMUs with a 4-car EMU) in Madras. While the MRTS in Chennai normally runs 9-car EMUs; however, in an effort to increase service frequency 3-car rakes have been introduced. These have two power cars (driving power car at one end, and trailing power car at the other end), unusual for such short trains. New Delhi has seen 6-car and 8-car EMUs, but now up to 12-coach EMU and MEMU rakes are seen. The power cars (motorcoaches) are usually in positions 1, 3, 10, and 12.

In Mumbai, 9-car formations were standard for a long time (from 1963). (Much earlier, 4-car rakes were in use, with 8-car rakes having started on the main line from 1927.) Then in 1988 the 12-car formation became common (having been used on a trial basis from 1986), following increased demand for services and lengthening of platforms. 

In all these formations, the basic unit consists of 3 cars coupled together: a driving trailer ("C"), a motor coach or power car ("B"), and a trailer coach ("A"). The 9-car rake therefore looks like this: YSYL - YSZZ - YSFS - YSYL - YSZZ - YSFS - YSFS - YSZZ - YSYL. (YSYL = trailer coach with vendor's compartment, YSYL = driving trailer coach, YSZZ = motor coach). In the late 1960s, WR introduced a "standees" train with far fewer seats. In this rake (#701-702), one of the unused driving trailer in the middle was replaced by a power car. This 9 coach rake therefore had four power cars. The standard train was changed to run with only 3 power cars. Later [2010] the standees train was taken out of . In the Calcutta area, for a long time AC EMU rakes were made up of 4-car units, consisting of a driving trailer ("A"), a power car ("B"), a trailer ("C") and a driving trailer ("D").

The cranes that move to and fro lifting coaches, bogies and other parts inside the workshop.

An inspection Car kept at Howrah Carshed.

Bogie

The bogies are manufactured at Integral Coach Factory (ICF) Perambur. The design of the bogie was developed by ICF (Integral Coach Factory), Perambur, Chennai, India in collaboration with the Swiss Car & Elevator Manufacturing Co., Schlieren, Switzerland in the 1950s. The design is also called the Schlieren design based on the location of the Swiss company.

The bogie can be divided into various subsections for easy understanding as follows:

Bogie frame

The frame of the ICF bogie is a fabricated structure made up of mild steel. Main sub-assemblies of bogie frame viz. side frames, transoms, headstocks, longitudinal forms the skeleton of the bogie frame. The sub assemblies are fabricated from flanges, webs, channels and Ribs by welding process. Various types of brackets are welded to the frame for the purpose of primary and secondary suspension arrangement, alternator suspension arrangement and brake rigging arrangement. Various brackets viz. brake hanger brackets, brake lever hanger brackets, brake cylinder fixing brackets, anchor link brackets, bolster spring suspension brackets, alternator suspension brackets, belt tensioning bracket/s, axle box guides, suspension straps are welded on the bogie frames. It involves 40 meters (app.) of welding in a single conventional bogie frame. Based on load carrying capacity per axle, the conventional bogie frames are grouped in to two types. They are 13 ton bogie frame and 16 ton bogie frame. 13 ton bogie frames are being used in the bogies of all non-AC mainline coaches and 16 ton bogie frames are being used in bogies of all AC coaches, power cars and diesel multiple unit trailer coaches.

EMU Motor Coach type bogie frames, a different design of bogie frame is being used in all coaches of Electric Multiple Units (EMU) and all self-propelled coaches (motor coaches).

The price of a railway bogie in India is Rs. 60 lakhs.

Bogie bolster

A Bogie-Bolster is the central part of every bogie to which the under-frame of the coach is pivoted through the Center Pivot Pin. A Bogie-Bolster is a floating member takes up the entire weight of the Coach and is coupled to the Bogie frame through the secondary suspension system. In bogie bolster there are 2 metal sections, one upper and one lower section, separated by a web running along the entire length. It also has a center pivot pin housing. The sections and housing are joined by excellent quality welding. The end sections of the bolster are designed to hold the secondary suspension of the Coach. These parts on the bolster act as a female part and matches with the male part (center pivot) welded to the coach under-frame. These are very vital parts for smooth running of a Train.

Center pivot pin

A center pivot pin is bolted to the body bolster. The center pivot pin runs down vertically through the center of the bogie bolster through the center pivot. It allows for rotation of the bogie when the coach is moving on the curves. A silent block, which is cylindrical metal rubber bonded structure, is placed in the central hole of the bogie bolster through which the center pivot pin passes. It provides the cushioning effect.

Wheel set assembly

Wheel arrangement is of Bo-Bo type as per the UIC classification. The wheel set assembly consists of two pairs of wheels and axle. The wheels may be cast wheels or forged wheels. The wheels are manufactured at Durgapur Steel Plant of SAIL( Steel authority of India Ltd.) or at Wheel and Axle Plant of Indian Railways bases at Yelahanka near Banglore in the state of Karnataka. At times, imported wheels are also used. These wheels and axles are machined in the various railway workshops in the wheels shops and pressed together.

Roller bearing assembly

Roller bearings are used on the ICF bogies. These bearings are press fitted on the axle journal by heating the bearings at a temperature of 80 to 100 °C in an induction furnace. Before fitting the roller bearing, an axle collar is press fitted. The collar ensures that the bearing does not move towards the center of the axle. After pressing the collar, a rear cover for the axle box is fitted. The rear cover has two main grooves. In one of the grooves, a nitrile rubber sealing ring is placed. The sealing ring ensures that the grease in the axle box housing does not seep out during the running of the wheels. A woolen felt ring is placed in another groove. After the rear cover, a retaining ring is placed. The retaining ring is made of steel and is a press fit. The retaining ring ensures that the rear cover assembly is secured tightly between the axle collar and the retaining ring and stays at one place. The roller bearing is pressed after the retraining ring. Earlier, the collar and the bearings were heated in an oil bath. But now the practices has been discontinued and an induction furnace is used to heat them before fitting on the axle. The axle box housing, which is a steel casting, is then placed on the axle. The bearing is housed in the axle box housing. Axle box grease is filled in the axle box housing. Each axle box housing is filled with approximately 2.5 kg. of grease. The front cover for the axle box is placed on a housing which closes the axle box. The front cover is bolted by using torque wrench.

Brake levers

Various type of levers are used on the ICF Bogie . The typical levers being the "Z" lever, floating lever and the connecting lever. Theses levers are used to connect the brake beam with the piston of the brake cylinder. The location of the brake cylinders decides whether the bogie shall be a BMBC Bogie or a non BMBC Bogie. Conventional bogies are those ICF bogies in which the brake cylinder is mounted on the body of the coach and not placed on the bogie frame itself.

Brake cylinder

In an ICF BMBC Bogie, the brake cylinder is mounted on the bogie frame itself. Traditionally, the ICF Bogies were conventional type i.e. the brake cylinder was mounted on the body of the coach. However, in the later modification, the new bogies are being manufactured with the BMBC designs only. Even the old type bogies are being converted into BMBC Bogies. The BMBC bogie has many advantages over the conventional ICF bogie. The foremost being that, since the brake cylinder is mounted on the bogie frame itself and is nearer to the brake beam, the brake application time is reduced. Moreover, a small brake cylinder is adequate for braking purpose. This also reduces the overall weight of the ICF bogie apart from the advantage of quick brake application.

The springs have been kept to be retrofitted to the existing EMU's after getting overhauled.

Primary suspension

The primary suspension in an ICF Bogie is through a dashpot arrangement. The dashpot arrangement consists of a cylinder (lower spring seat) and the piston (axle box guide). Axle box springs are placed on the lower spring seat placed on the axle box wing of the axle box housing assembly. A rubber or a Hytrel washer is placed below the lower spring seat for cushioning effect. The axle box guide is welded to the bogie frame. The axle box guide acts as a piston. A homopolymer acetyle washer is placed on the lower end of the axle box guide. The end portion of the axle box guide is covered with a guide cap, which has holes in it. A sealing ring is placed near the washer and performs the function of a piston ring. The axle box guide moves in the lower spring seat filled with dashpot oil. This arrangement provides the dampening effect during the running of the coach.

Dashpot arrangement

The dashpot arrangement is mainly a cylinder piston arrangement used on the primary suspension of Indian Railway coaches of ICF design. The lower spring seat acts as a cylinder and the axle box guide acts as a piston.

The dashpot guide arrangement has the following main components:

Lower Spring Seat Lower Rubber Washer Compensating Ring. Guide Bush Helical Spring Dust Shield. Circlip. Dust Shield Spring. Protective Tube Upper Rubber Washer. Axle Box Guide Screw with sealing washer The axle box guide (piston) is welded to the bottom flange of the bogie side frame. Similarly, the lower Spring seat (cylinder) is placed on the axle box housing wings forms a complete dashpot guide arrangement of the ICF design coaches.

Axle box guides traditionally had a guide cap with 9 holes of 5mm diameter each; however, in the latest design, the guide cap is made an integral part of the guide. Approximately 1.5 liters of dashpot oil is required per guide arrangement.

Air vent screws are fitted on the dashpot for topping of oil so that the minimum oil level is maintained at 40mm.

Traditionally, rubber washers have been used at the seating arrangement of the primary springs of the axle box housing in the ICF design passenger coaches on the Indian Railways. The rubber washer is used directly on the axle box seating area. the lower spring seat sits on the washers. The lower spring seat is a tubular structure and 3/4 section is partitioned by using a circular ring which is welded at the 3/4 section. On the top of spring seat, a polymer ring called NFTC ring sits. The primary spring sits on the NFTC ring. The lower spring seat plays the role of a cylinder in the dashpot arrangement and is filled with oil. In the dashpot arrangement, the top portion is called the axle box guide. The axle box guide is welded to the bogie frame. The axle box guide works as a piston in the Lower spring seat filled with oil. This helps in damping the vibrations caused during running train operation.

The axle box guide, which is welded to the bogie frame has a polymer washer (homopolymer acetal guide) bush fixed at the head. A polymer packing ring and a guide ring is attached with the Acetal guide bush. These two components act as piston rings for the axle box guide. In order to ensure that the packing ring and the guide ring retain their respective place, a dashpot spring is fixed which applies continuous pressure on the piston ring.

The bottom of the axle box guide has a guide cap with perforations so that during the downward movement of the axle guide in the lower spring seat, the oil in the dashpot rushes in the axle box guide. This provides the dampening of vibration in a running coach.

The guide cap is fixed with the help of a steel circlip. However in the new design of Axle box guide, the guide cap is welded with the guide assembly and hence the need of a guide cap has been eliminated. The complete guide and lower spring arrangement is covered with a dashpot cover also known as protective tube. The protective tube has a circular ring over it called the dust shield which prevents the ingress of the dust in the cylinder piston arrangement of the dashpot.

Spring seating

As described above, the rubber washers sit directly on the axle box spring sitting area. Earlier,wooden washers were used. However, with the development of technology, rubber washers replaced wooden washers. Presently, RDSO, Lucknow which is a Research, Design & Standardization organization for the Indian Railways developed a new design for washers made from a polymer commonly known as HYTREL. Hytrel polymer is a product of M/s DuPont .

The reason for replacement of the rubber washers with the hytrel washers was that the rubber washers were not lasting for the full Periodic overhaul cycle of the Railway Coaches which was one year. The washers also had to be replaced in the coaching maintenance depots leading to lifting and lowering of coaches.

Introduction of Hytrel washers was considered a breakthrough in the ICF dashpot design. However, the mass scale replacement of the rubber washers by Hytrel washers without adequate trials lead to massive failure of the axle Box housing.

The hardness of the washers as per the specified limits was to be 63+- 5 Shore D hardness. Another parameters was the load deflection characteristics of the washers.

A study was carried out on a major workshop on Indian Railways and it was found that the washers were having a hardness more than the specified limits. Moreover, the load deflection characteristic of the washers were also not found to be in line with the desired specification.

Within 6 months of provision of Hytrel washers on all the main line coaches, the failure of Axle box housing increased. The reason was the axle box wing cracks. Hence on examination of the failed axle boxes, it was noticed that the Hytrel washers were forming a deep groove of 4 to 8mm on the seating area of the axle box spring seating. They washers were also increasing the diameter of the spring seating due to continuous hitting of the raised section of the sitting area.

The coaches come to the workshop once in a year. During examination of these coaches, it was noticed that the Hytrel washers have not only damaged the axle box housing but also the lower spring seat as well as the Protective tube.

To prevent such damage, RDSO, Lucknow issued a guideline asking the Railways to provide a delrin liner below the Hytrel washers. However, it was indicated that these liners are to be provided only on new coaches and in coaches in which new wheels are fitted.

A look at the drawing of the dashpot arrangement will suggest that this problem is universal for all the coaches, whether a new coach or an old coach. Moreover, the provision of the liners below the Hytrel washers will not stop the damage to the lower spring seat and the protective tube.

Problem of oil spillage

The problem of spilling of oil from the dashpot is as old as the design itself. Numerous design changes have been implemented in the last many years however, the problem of oil spillage is still a challenge.

The cylinder piston arrangement of the dashpot, i.e. the Lower Spring seat and the axle box guide is not fully sealed due to the limitation of the design and practical applicability. Its design provides that when a vertical vibration occurs during the movement of the railway coach, the axle box guide moves down. The downward movement of the Axle box guide puts pressure on the oil in the lower spring seat. The oil rushes up. However, since there are holes in the guide cap, the oil passes through these holes into the hollow body of the axle box guide. This helps in dampening the vertical vibrations. The axle box guide displaces the oil in the lower spring seat and pushes it upwards. Since, only part quantity of oil is able to move up in the hollow portion of the axle box guide, the balance displaced oil moves up.

As per correct maintenance practice, it is to be ensured that the hole in the guide are in alignment with corresponding holes in the guide bush. However, this is practically difficult to maintain in the shop floor of bogie shop.

As the top portion of the lower spring seat is not sealed and only covered with the help of a protective tube also called the dashpot cover, the rising oil has a tendency to shoot above the top rim of the lower spring seat and spill out.

Oil spillage can be prevented by the following actions:

a. Change the dashpot design from the cylinder piston arrangement to hydraulic shock absorbers.

b. Increase the hole diameter from 5mm in the guide cap to more than the existing diameter. However, it must be ensured that the increased diameter of the holes of the guide cap does not lead to less dampening effect.

c. Provide a conical arrangement above the rim of the lower spring seat up to half the height of the dashpot cover. However, the clearances of the protective tube and the outer dia of the proposed conical section at the top of the lower spring seat needs to be taken care of

d. Modify the dust shield ring by incorporating a rubber component in it in such a manner that it also acts as an oil seal

e. Ensure that the hole in the guide are in alignment with corresponding holes in the guide bush

Some of these proposed modifications have already been tried out on the Indian Railways, however, the trials have not yielded a consistent positive feedback.

Secondary suspension 

The secondary suspension arrangement of the ICF bogies is through bolster springs. The bogie bolster is not bolted or welded anywhere to the bogie frame. It is attached to the bogie frame through the anchor link. The anchor link is a tubular structure with cylindrical housing on both the ends. The cylindrical housings have silent blocks placed in them. The anchor link is fixed to the bogie bolster and the bogie frame with the help of steel brackets welded to the bogie bolster and the bogie frame. Both the ends of the anchor link act as a hinge and allow movement of the bogie bolster when the coach is moving on a curved track.

Lower spring beam 

The bolster springs are supported on a lower spring beam. The lower spring beam is a fabricated structure made of steel plates. It is trapezoidal in shape with small steel tubes on each end. The location of the bolster spring seating is marked by two circular grooves in the center. A rubber washer is placed at the grooved section. The bolster spring sits on the rubber washer. The lower spring beam is also a free-floating structure. It is not bolted or welded either to the bogie frame or the bogie bolster. It is attached to the bogie frame on the outside with the help of a steel hanger. They are traditionally called the BSS Hangers (Bogie Secondary Suspension Hangers). A BSS pin is placed in the tubular section in the end portion of the lower spring beam. A hanger block is placed below the BSS pin. The BSS hanger in turn supports the hanger. This arrangement is done on all the four corners of the lower spring beam. The top end of the hanger also has a similar arrangement. However, instead of the BSS pin, steel brackets are welded on the lower side of the bogie frame of which the BSS hanger hangs with the help of hanger block. This arrangement is same for all the four top corners of the hangers. Hence, the lower spring beam also become a floating member hinged to the bogie frame with the help of hangers on the top and the bottom. This allows for the longitudinal movement of the lower spring beam.

Buffer Height adjustment

The wheel diameter(tread) reduces due to brake application as the brake blocks rub against the wheel tread. Over a period of time, the wheel diameter reduces up to 819 mm. 819mm is the condemnation diameter for the wheels. This diameter is also not sacrosanct and is changed depending upon the supply position of the wheels. The maximum variation in the wheels on the same axle is permitted up to 0.5 mm, between two wheels of the same bogie up to 5 mm and among the four wheel sets of the same coach up to 13 mm. The diameter of a new wheel is 915 mm. Hence maximum wheel tread wear allowed is (915 mm - 819mm) = 96 mm. In order to adjust for the difference in the wheel tread, a packing is placed under the flange of the lower spring seat. This packing ring is generally made up of NFTC(Natural Fiber Thermosetting COMPOSITE) or UHMWPE (Ultra-high molecular weight polyethylene) material. The thickness of the NFTC packing ring is equal to 50% of the difference between the dia of a new wheel and the wheel in question.

Traditionally, 13mm, 26mm, 38mm, 48 mm packing rings are used. They correspond to wheel diameter of 899-864, 862-840, 839-820 and 819 mm. The correct buffer height is obtained by measuring the height of the bolster top surface from the rail level. In case the buffer height is still not obtained even after placement of the packing ring, then compensation rings are to be inserted below the axle box spring ensuring that the bogie frame height is within 686 + - 5 mm.

The picture shows how the primary gear is attached to the secondary gear of the traction motor thus providing power to the wheels which make the EMU (Electric Multiple Unit) move.

Equalizing stay rod 

The inner section of the lower spring beam is connected to the bogie bolster with the help of an equalizing stay rod. It is a double Y-shaped member fabricated using steel tubes and sheets. The equalizing stay rod is also hinged on both the ends with the lower spring beam as well as the bogie bolster with the help of brackets welded to the bogie bolster. They are connected through a pin making it a hinged arrangement.

Motor (DC Series)

Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. The DC motor was the mainstay of electric traction drives on both electric and diesel-electric locomotives, street-cars/trams and diesel electric drilling rigs for many years.

The end points of the wire of a motor.

Windings

It consists of two parts, a rotating armature and fixed field windings surrounding the rotating armature mounted around a shaft. The fixed field windings consist of tightly wound coils of wire fitted inside the motor case. The armature is another set of coils wound round a central shaft and is connected to the field windings through "brushes" which are spring-loaded contacts pressing against an extension of the armature called the commutator. The commutator collects all the terminations of the armature coils and distributes them in a circular pattern to allow the correct sequence of current flow. When the armature and the field windings are connected in series, the whole motor is referred to as "series-wound". A series-wound DC motor has a low resistance field and armature circuit. Because of this, when voltage is applied to it, the current is high due to Ohm's law. The advantage of high current is that the magnetic fields inside the motor are strong, producing high torque (turning force), so it is ideal for starting a train. The disadvantage is that the current flowing into the motor has to be limited, otherwise the supply could be overloaded or the motor and its cabling could be damaged. At best, the torque would exceed the adhesion and the driving wheels would slip. Traditionally, resistors were used to limit the initial current.

Power control

As the DC motor starts to turn,interaction of the magnetic fields inside causes it to generate a voltage internally. This back EMF (electromagnetic force) opposes the applied voltage and the current that flows is governed by the difference between the two. As the motor speeds up, the internally generated voltage rises, the resultant EMF falls, less current passes through the motor and the torque drops. The motor naturally stops accelerating when the drag of the train matches the torque produced by the motors. To continue accelerating the train, series resistors are switched out step by step, each step increasing the effective voltage and thus the current and torque for a little bit longer until the motor catches up. This can be heard and felt in older DC trains as a series of clunks under the floor, each accompanied by a jerk of acceleration as the torque suddenly increases in response to the new surge of current. When no resistors are left in the circuit, full line voltage is applied directly to the motor. The train's speed remains constant at the point where the torque of the motor, governed by the effective voltage, equals the drag - sometimes referred to as balancing speed. If the train starts to climb an incline, the speed reduces because drag is greater than torque and the reduction in speed causes the back-EMF to fall and thus the effective voltage to rise - until the current through the motor produces enough torque to match the new drag. The use of series resistance was wasteful because a lot of energy was lost as heat. To reduce these losses, electric locomotives and trains (before the advent of power electronics) were normally equipped for series-parallel control as well.

Automatic acceleration[

On an electric train, the train driver originally had to control the cutting out of resistance manually, but by 1914, automatic acceleration was being used. This was achieved by an accelerating relay (often called a "notching relay") in the motor circuit which monitored the fall of current as each step of resistance was cut out. All the driver had to do was select low, medium or full speed (called "shunt", "series" and "parallel" from the way the motors were connected in the resistance circuit) and the automatic equipment would do the rest.

DC motor starters

The counter-emf aids the armature resistance to limit the current through the armature. When power is first applied to a motor, the armature does not rotate. At that instant the counter-emf is zero and the only factor limiting the armature current is the armature resistance and inductance. Usually the armature resistance of a motor is less than 1 Ω; therefore the current through the armature would be very large when the power is applied. This current can make an excessive voltage drop affecting other equipment in the circuit and even trip overload protective devices.

Therefore the need arises for an additional resistance in series with the armature to limit the current until the motor rotation can build up the counter-emf. As the motor rotation builds up, the resistance is gradually cut out.

Speed control

Generally, the rotational speed of a DC motor is proportional to the EMF in its coil (= the voltage applied to it minus voltage lost on its resistance), and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers.

Relays and other parts

A pantograph (or "pan") is an apparatus mounted on the roof of an electric train or tram to collect power through contact with an overhead catenary wire. It is a common type of current collector. Typically, a single wire is used, with the return current running through the track. 

A lathe rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation, facing,turning, with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.

Lathes are used in woodturning, metalworking, metal spinning, thermal spraying, parts reclamation, and glass-working. Lathes can be used to shape pottery, the best-known design being the potter's wheel. Most suitably equipped metalworking lathes can also be used to produce most solids of revolution, plane surfaces and screw threads or helices. Ornamental lathes can produce three-dimensional solids of incredible complexity. The workpiece is usually held in place by either one or two centers, at least one of which can typically be moved horizontally to accommodate varying workpiece lengths. Other work-holding methods include clamping the work about the axis of rotation using a chuck or collet, or to a faceplate, using clamps or dogs.

Schaku Coupler:

Originally designed by M/s Scharfenburgkupplung, GmbH, Germany , Semi-Permanent Couplers are used on the EMU stock of  Indian Railways.

In Semi permanent couplers the coupling is done manually and the two couplers after being aligned are secured by means of an adjustable cup sleeve joint. During the process of manual coupling the air pipe connections between the two coaches are also established automatically. The pivoted joints between the coupler and the coaches is designed and constructed in such a way that even in case of maximum difference in level, the coaches are capable of negotiating all track curves and of passing through points of change of gradient occurring during service. This coupler fulfills all other operational requirements.

 SALIENT FEATURES OF ESCORTS SEMI-PERMANENT

·         Semi-permanent coupler can take up a compressed load of 100 tons and tensile load of 70 tons.

·         The dynamic absorption capacity of the rubber draft gear of these couplers is 800 m-kg.

·         Due to rigid connection of this coupler there exists negligible play between them in coupling position and hence no appreciable wear and tear during train operation.

·         Due to rigid and stress transmitting mechanical connection between the coaches by fitting semi-permanent couplers, protection to the coach and the load against undue impacts is secured.

·         Due to high draft capacity incorporated in semi-permanent couplers, it allows coaches to buffer at higher speeds (from 3 km/hr to 15 km/hr) without any damage to the coach and the load.

·         The interlocking arrangement of these couplers prevents to some extent the mounting or telescoping of the coaches when involved in accidents.

·         As the fulcrum of these couplers is located far in the rear of the coach, coupler side displacements in curves and consequently the transverse forces acting on the wheel flanges are kept minimum .This reduces the wear of the wheel flanges and minimizes the chances of derailment.

·         As the coupling links of semi-permanent couplers form a parallelogram with equilibrium of forces, unintentional disengagement of coaches due to shocks is rendered impossible.

·         The design and construction of the pivoted joint between these couplers and coach permits vertical deflection of ±75mm and horizontal deflection of 284 mm or 13º on either side and as a consequence enables the coaches to couple up at all track curves and also on points of change of gradient even at maximum height difference between the two coaches.

Tap Changer

A tap changer is a connection point selection mechanism along a power transformer winding that allows a variable number of turns to be selected in discrete steps. A transformer with a variable turns ratio is produced, enabling stepped voltage regulation of the output. The tap selection may be made via an automatic or manual tap changer mechanism.

The output voltage of a transformer varies according to the turns ratio of the primary and the secondary windings of the transformer. It can appreciated that at any point of the primary or the secondary winding the voltage is different from any other point on the same winding because these points are at different ratios with respect to the other winding.

Hence each and every tap brought out from the winding gives a different voltage.

Broadly tap-changers can be divided into two categories-namely off-load and on-load.

Off-load tap-changers cannot be operated while current is flowing in the circuit. Off-load tap-changers are used mainly for non-critical applications where a momentary interruption in the current can be tolerated. Hence, such tap-changers have no use in traction duty.

In traction only on-load tap-changers (OLTC) are used. They are capable of changing the taps rapidly without interrupting the flow of current.

Inside View of Motor Coach:

1. Compressor
2.Transformer oil tank
3.Air pressure switches

Few resistances, potential transformers, speedometers, relays kept to be replaced during failures. The name of the suppliers are provided below.

Speedometers provided by Laxven.

A diode used for the rectifier used in EMU's.

A modern cab. The controls and the various meters (Ammeter, Voltmeter, Battery Voltmeter) and Dead man's switch have been shown.

Air pressure indicators, cab light switches and panto selection switches are shown.

The 10 relays used in an EMU. Few of their functions in an Indian Locomotive (WAP 4/WAM 4/WAG 7) are given below.

The main relays associated with the tap-changer are Q46, Q49, Q51, Q52, Q44 and QV62.

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 wheel-slipping, 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 -- 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 energised 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.

The motor connection switches to isolate, check and to test the DC series motor used in the motor coaches respectively.

Various MCB's, resistors, capacitors have been installed for perfect working of the Electric Multiple Unit and the other parts of it.

A temperature sensor thermometer to check the condition of the traction motors to detect failures if the TM gets overheated.

The machine room consisting of an oil tank which circulates the transformer oil and also other equipment's to check the air pressure and movement of pantographs.

The compressor chamber for generating/storing air.

The pedal to drive the train.

Tap Changers tested and kept.

The memory card which is kept inside the speedometer to check and record the speed of the EMU.

A potential transformer.

Circuit Diagrams

A pocket circuit diagram of the bridge rectifier used by supervisors and engineers in the shed.
Some technical data's.

Different types of relay's and its function.

The circuit diagram of the speedometer and how it works.

New Car

The motor connection switches to isolate, check and to test the DC series motor used in the motor coaches respectively.

Supervisor testing the tap changer.

Switches for cab/coach lights and fans.

Digital board to display the destination station.

Speedometer.

Switches to switch on various relays/ up and down of pantographs and other functions.

Old Car

The brake. It is divided into four parts.
1. EP LAP
2. SELF LAP
3. AUTO
4. EMERGENCY

The horn and emergency brake switch.

A view of the knob and other parts of the EMU.

MCB's being displayed.

The sensor which is used for contacting the guard at the extreme end of the train.

The relays and motor isolation/testing switches.

New Generation EMU

Traditional Screw coupler at both ends of the rake.

Tap changer.

The compressor used to generate air. It has been supplied by Elgi.

• Designed for energy saving and long life.
• Occupies less space and generates less heat
• Intelligent and fail proof instrumentation and control system, hooked up to DCS.
• Wide range of compressor with indigenised air end variety optimised.
• Variants / custom made for individuals markets (multiple electrical inputs)
• Air cooled/ Water cooled, low pressure and high pressure version covering wide range of applications.
• Delivery of high quality air.

Schaku coupler used to attach two coach together and air pressur and eletrical connections can be seen.

The couplers used for connecting two trains/coaches together.

Me and Howrah EMU

A sub station inside Howrah EMU.

Switches to distribute electricity to various parts.

A WAP 7 going to the Locomotive Shed.

The battery box inside driver's cabin.

Brake beam assembly

ICF bogie uses two types of brake beams. 13 ton and 16 ton. Both of the brake beams are fabricated structures. The brake beam is made from steel pipes and welded at the ends. The brake beam has a typical isosceles triangle shape. The two ends of the brake beam have a provision for fixing a brake head. The brake head in turn receives the brake block. The material of the brake block is non-asbestos and non-metallic in nature.

Brake head

Two types of brake heads are used. ICF brake head and the IGP brake head. A brake head is a fabricated structure made up of steel plates welded together.

Brake blocks

Brake blocks are also of two types. ICF brake head uses the "L" type brake block and the "K" type brake block is used on the IGP type brake head. "L" & "K" types are so called since the shape of the brake blocks resembles the corresponding English alphabet letter. The third end of the brake beam has a bracket for connecting the "Z" & the floating lever. These levers are connected to the main frame of the bogie with the help of steel brackets. These brackets are welded to the bogie frame.

The permission given by Senior Divisional Electric Engineer, Howrah, Carshed.

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