Summer Training

Report

Electric Locomotive Shed

Kanpur

Summer Training Report

15th June to 14th July

Submitted To- Guided By-

Mr. Ishrar Mohammad Mr. S.K.Pandey

Submitted By-

Ashish Kumar

Gaurav Mishra

Satyendra Kushwaha

ACKNOWLEDGEMENT

I am thankful to the organisation "LOCO SHED KANPUR" for providing necessary facility to carry outmy training successfully.

It is our duty to record our sincere thanks and gratitude towards the institute staff, who helped us in bringing this project to its present form. The valuable guidance and interest taken by them has been a motivator and source of inspiration for me to carry out the necessary proceedings for the project to be completed successfully.

Also, we are highly obliged to the head of our training and placement cell"Mr. Ashutosh Dewedi" who provided us such a great opportunity to do our summer training in a reputed institute like

"ELECTRIC LOCOMOTIVE SHED KANPUR".

CERTIFICATE OF ORIGINALITY

We are the regular student of Bachelor of Technology (B.tech) Programme of Maharana Pratap Engineering College, Kanpur. I hereby certify that this project work carried out by me at ELECTRIC LOCO SHED KANPUR the report submitted inpartial fulfillment of the requirements of the programme is an original work of mine under the guidance of the industry mentor Mr. Israr Mohammad

and guide mentor Mr. S. K. Pandey and is not based or reproduced from any existing work of any other person or on any earlier work undertaken at any other time or for any other purpose, and has not been submitted anywhere else at any time.

Faculty Mentor's Signature Student's Signature

CONTENTS

1- About the company2- Introduction3- Operation of Locomotive4- Different Equipment In Electric

Locomotive 5- Dc Motor Brush Holder 6- Performance Of Carbon Brushes and

Failure of carbon brushes7- Installation of Carbon Brushes8- Causes of failure of Commutation9- Main Cause of Brush Failure10- Conclusion

About The Company

The Electric loco shed, Kanpur was established during the year 1965 for homing 11 locomotives. This shed was commissioned primarily to meet the requirement of passenger and goods traffic over Indian railways. At present the shed has been expended suitably to home 176 loco motives for hauling, passenger and goods traffic.

The shed is responsible for carrying out monthly inspection schedule viz. IA, IB, IC, I0 & ICO in addition to annual and intermediate overhauling schedules.

Further the unscheduled repairs to electric locos of CNB shed & other sheds are being done as per requirements of RDSO organization & HQ’s instructions. All modification & special maintenance instructions, approved by RDSO & N .Rly. Hd. Qtr. are also carried out as per the guide lines being issued from time to time.

ELECTRIC LOCO MAINTENANCE SHED

Electric Loco Shed maintains locomotive for utilization in freight and passenger train. All the miner and major inspection are carried out in the shed on a regular schedule specified by RDSO (Research Design Standard Organization). Monthly schedule are done at an interval of 45 days and major schedule are carried out after 18 months.

OPERATION OF LOCOMOTIVE

The electric locomotive basically works at 25 KV, 50Hz supply. The 25KV AC supply is drawn from overhead catenaries wires. The supply from overhead wires are

drawn through a pantograph inside the loco transformer. This transformer is an autotransformer from which regulated voltage is taken to a rectifier block for conversion from AC to DC .It may be worth mentioning that the final tractive effort is through DC traction motor hence AC is required to be converted to DC. The DC current from rectifier block is then filtered to pure DC and then fed to traction motor.

There are 6 traction motors which works parallel to provide the attractive effort for hauling the train.

All the operations are controlled through control circuit which works at 110 volt DC. Various power equipments during operation gets heated up and hence to cool the same, it is done by various blowers.

Different Equipments in an Electrical

Locomotive

1) Pantograph

It is pneumatically operated equipment mounted on the roof for collection of current from overhead wire.

2) Main Transformer

It is an autotransformer which is utilized for drawing various grades of voltage required for operation of locomotive.

3) Rectifier

This unit consists of rectifier diodes connected in bridge for conversion of AC current to DC current.

4) Traction Motor

The traction motor is one of the most important

equipment in the locomotive which transmits power to wheels for moving the trains.

5) Auxiliary Circuit

This Circuit is three phase 415 volts which supplies current to various three phase induction motors used for driving blowers for forced air cooling of major equipments like transformer, rectifier, smoothing reactor and traction motor. This 3 phase line voltage is supplied by either static converter or Rotary ARNO Converter.

6) ARNO Converter

Arno converter , is specific-duty machine for conversion of a single-phase supply into a three-phase supply. While the electric traction supply is standardized as single-phase A.C. supply, a three-phase supply is needed on locomotives for driving certain auxiliary equipments. The function of the Arno converter is to convert the incoming single-phase supply in to a three-phase supply for the auxiliaries.

ARNO Converter is of vertical construction and has a flexible mounting .The machine is of robust mechanical construction to withstand the several vibrations encountered on locomotives.

TECHNICAL DATA

Single-phase input Three-phase output KVA 150 KVA 120Volts 380 Volts 380Amps 395 Amps 190Frame VA-330

Class ’F’

Connection: Star RPM 1490 Cycle 50

OPERATIONAL PRINCIPLE

The single-phase supply of 380 volts AC is fed ‘direct’ to the ‘U’ & ‘V’ phases of the Arno converter. Since the

ARNO Converter is connected to single-phase supply, no starting torque is developed. For starting the ‘ARNO’ split phase starting method has been employed. The W phase winding is connected to the supply phase U through a starting resistor R-118 and starting contactor C-118 for a short duration to start the Arno. Thus unbalanced three-phase voltage is impressed to each phase winding of Arno converter and the starting torque is developed .the Arno Converter picks up speed within five seconds. After the Arno has gained sufficient speed, the phase W is opened from the starting circuit by starting contactor C-118.

The Arno converts the single phase input into 3 phase output as 380 volt ± 22.5%. The three-phase output of the Arno converter is connected to the auxiliary motors.

7) Control Circuit

The control circuit is purely 110 volt DC and the most important network for handling various operational feature of the locomotive. All the power equipment and auxiliary circuit equipment are controlled through

various switches in 110 volt circuit provided in the driving cab. All the circuit and equipment in the high voltage power side & auxiliary circuit equipment and the control circuit is protected against overloading, short circuiting and earth fault. For this purpose various relays have been used as protection device so as to protect the circuit from any mal functioning.

8) Asynchronous MotorModern traction motor type using three phase AC electrical supply and now the favoured design for modern train traction systems. Can be used on DC and AC electrified railways with suitable control electronics and on diesel-electric locomotives.9) Axle BrushThe means by which the power supply circuit is completed with the substation once power has been drawn on the locomotive. Current collected from the overhead line or third rail is returned via the axle brush and one of the running rails. 10) BatteryAll trains are provided with a battery to provide start up current and for supplying essential circuits, such as

emergency lighting, when the line supply fails. The battery is usually connected across the DC control supply circuit.11) Bucholz RelayA device inserted in the oil cooling circuits of electric locomotive transformers to detect low oil pressure. In this event the relay trips out the power system. Often a source of spurious circuit breaker trips if not carefully calibrated.12) CamshaftMost DC electric traction power circuits use a camshaft to open or close the contactors controlling the resistances of the traction motor power circuit. The camshaft is driven by an electric motor or pneumatic cylinder. The cams on the shaft are arranged to ensure that the contactors open and close in the correct sequence. It is controlled by commands from the driver's cab and regulated by the fall of current in the motor circuit as each section of resistance is cut out in steps. The sound of this camshaft stepping can be heard under many older (pre electronics) trains as they accelerates.13) Cannon BoxSleeve used to mount a traction motor on axle in electric

power bogies and sometimes including an axle brush.14) Chopper ControlA development in electric traction control which eliminates the need for power resistors by causing the voltage to the traction motors to be switched on and off (chopped) very rapidly during acceleration. It is accomplished by the use of thyristors and will give up to 20% improvement in efficiency over conventional resistance control.

15) Circuit BreakerAn electric train is almost always provided with some sort of circuit breaker to isolate the power supply when there is a fault, or for maintenance. On AC systems they are usually on the roof near the pantograph. There are of two types - the air blast circuit breaker and the vacuum circuit breaker or VCB. The air or vacuum part is used to extinguish the arc which occurs as the two tips of the circuit breaker are opened. The VCB is popular in the UK and the air blast circuit breaker is more often seen on the continent of Europe.16) ContactorSimilar to a relay in that it is a remotely operated switch

used to control a higher power local circuit. The difference is that contactors normally latch or lock closed and have to be opened by a separate action. A lighting contactor will have two, low voltage operating coils, one to "set" the contactor closed to switch on the lights; the other to "trip" off the lights.17) ConverterGeneric term for any solid state electronic system for converting alternating current to direct current or vice versa. Where an AC supply has to be converted to DC it is called a rectifier and where DC is converted to AC it is called an inverter. The word originated in the US but is now common elsewhere.18) Cooling FansTo keep the thyristors and other electronic power systems cool, the interior of a modern locomotive is equipped with an air management system, electronically controlled to keep all systems operating at the correct temperature. The fans are powered by an auxiliary inverter producing 3-phase AC at about 400 volts.19) Creep ControlA form of electronically monitored acceleration control used very effectively on some modern drive systems

which permits a certain degree of wheel slip to develop under maximum power application. The GM Class 59 diesel-electric locomotive built for the UK has this system. A locomotive can develop maximum slow speed tractive effort if its wheels are turning between 5% and 15% faster than actually required by the train speed.20) DC Link FilterUsed on modern electronic power systems between the single phase rectifier and the 3-phase inverter. It is easier to convert the single phase AC from the overhead line to the 3-phase required for the motors by rectifying it to DC and then inverting the DC to 3-phase AC.21) Dynamic BrakingA train braking system using the traction motors of the power vehicle(s) to act as generators which provide the braking effort. The power generated during braking is dissipated either as heat through on-board resistors (rheostatic braking) or by return to the traction supply line (regenerative braking). Most regenerative systems include on board resistors to allow rheostatic braking if the traction supply system is not receptive. The choice is automatically selected by the traction

control system. .22) GridTrain or locomotive mounted expanded steel resistor used to absorb excess electrical energy during motor or braking power control. Often seen on the roofs of diesel electric locomotives where they are used to dissipate heat during dynamic braking.23) Ground RelayAn electrical relay provided in diesel and electric traction systems to protect the equipment against damage from earths and so-called "grounds". The result of such a relay operating is usually a shut-down of the electrical drive. Also sometimes called an Earth Fault Relay.24) GTO ThyristorGate Turn Off thyristor, a thyristor which does not require a commutation (reverse flow circuit) circuit to switch it off .

25) IGBT(Insulated Gate Bipolar Transistor)Most recent power electronics development. It is replacing the GTO thyristor as it is smaller and requires less current to operate the switching sequences.

26) InverterElectronic power device mounted on trains to provide alternating current from direct current. Popular nowadays for DC railways to allow three phase drive or for auxiliary supplies which need an AC supply.27) Jerk LimitA means by which starting is smoothed by adjusting the rate of acceleration of a train by limiting the initial acceleration rate upon starting. It could be described as limiting the initial rate of change of acceleration. Also used in dynamic braking.28) Line BreakerElectro-mechanical switch in a traction motor power circuit used to activate or disable the circuit. It is normally closed to start the train and remains closed all the time power is required. It is opened by a command from the driving controller, no-volts detected, overload detected and (were required) wheel spin or slide detected. It is linked to the overload and no-volt control circuits so that it actually functions as a protective circuit breaker. 29) Master ControllerDriver's power control device located in the cab. The

driver moves the handle of the master controller to apply or reduce power to the locomotive or train.30) Motor BlowersTraction motors on electric locomotives get very hot and, to keep their temperature at a reasonable level for long periods of hard work, they are usually fitted with electric fans called motor blowers. On a modern locomotive, they are powered by an auxiliary 3-phase AC supply of around 400 volts supplied by an auxiliary inverter.

31) Notching RelayA DC motor power circuit relay which detects the rise and fall of current in the circuit and inhibits the operation of the resistance contactors during the acceleration sequence of automatically controlled motors. The relay operates a contactor stepping circuit so that, during acceleration of the motor, when the current falls, the relay detects the fall and calls for the next step of resistance to be switched out of the circuit.32) No-Volt RelayA power circuit relay which detected if power was lost for any reason and made sure that the control sequence was returned to the starting point before power could be

re-applied. 33) Overload RelayA power circuit relay which detected excessive current in the circuit and switched off the power to avoid damage to the motors. 34) RectifierA converter consisting of thyristors and diodes which is used to convert AC to DC. A modern locomotive will usually have at least two, one for the power circuits and one or more for the auxiliary circuits.35) RelayA remotely controlled switch which uses a low voltage control circuit. It will close (or open) a switch in a local circuit, usually of higher power.36) Resistance ControlMethod of traction motor control formerly almost universal on DC electric railways whereby the power to the motors was gradually increased from start up by removing resistances from the power circuit in steps Originally this step control was done manually but it was later automatic, a relay in the circuit monitoring the rise and fall of current as the steps were removed. Many examples of this system still exist but new builds now use

solid state control with power electronics.37) SEPEXShort form of SEParate EXcitement of traction motors where the armature and field coils of an electric motor are fed with independently controlled current. This has been made much more useful since the introduction of thyristor control where motor control can be much more precise. SEPEX control also allows a degree of automatic wheel slip control during acceleration.38) ShoegearEquipment carried by a train and used for current collection on track mounted (third rail) power supply systems. Shoegear is usually mounted on the bogies close to the third rail. It is often equipped with devices to enable it to be retracted if required to isolate the car or on-board system which it supplies.

39) Synchronous MotorTraction motor where the field coils are mounted on the drive shaft and the armature coils in the housing, the inverse of normal practice. Favoured by the French and used on the high speed TGV Atlantique trains, this is a single-phase machine controlled by simple inverter. Now

superseded by the asynchronous motor.40) Tap ChangerCamshaft operated set of switches used on AC electric locomotives to control the voltage taken off the main transformer for traction motor power. Superseded by thyristor control.41) ThyristorA type of diode with a controlling gate which allows current to pass through it when the gate is energised. The gate is closed by the current being applied to the thyristor in the reverse direction. Thyristors (also referred to as choppers) are used for traction power control in place of resistance control systems. A GTO (Gate Turn Off) thyristor is a development in which current is turned off is by applying a pulse of current to the gate.

42) TransformerA set of windings with a magnetic core used to step down or step up a voltage from one level to another. The voltage differences are determined by the proportion of windings on the input side compared with the proportion

on the output side. An essential requirement for locomotives and trains using AC power, where the line voltage has to be stepped down before use on the train.43) TransistorThe original electronic solid state device capable of controlling the amount of current flowing as well as switching it on and off. In the last few years, a powerful version has been applied to railway traction in the form of the Insulated Gate Bipolar Transistor (IGBT). Its principle advantage over the GTO Thyristor is its speed of switching and that its controls require much smaller current levels.44) Wheel SpinOn a steam locomotive, the driver must reduce the steam admission to the cylinders by easing closed (or partially closed) the throttle/regulator when he hears the wheels start to spin. On diesel or electric locomotives, the current drawn by individual or groups of traction motors are compared - the motor (or group) which draws proportionally less amps than the others is deemed to be in a state of slip - and the power is reduced. Some systems - EMD Super Series for one - measure

known wheel speed against ground speed as registered on a Doppler Radar. Many locomotives additionally use sand, which is applied to the wheel/rail contact point to improve adhesion - this is either controlled automatically, or manually by the driver.45)Wheel Spin Relay (WSR)A relay in older traction motor control circuits used to detect wheel spin or slide by measuring the current levels in a pair of motors on a bogie and comparing them. The idea is to prevent motor damage by preventing an over-speeding motor causing an unacceptable rise in current in the other motor of the pair. If detected, the imbalance causes the control circuits to open the line breakers and reset the power control to the start position like a "no-volt" relay.

The Block Diagram of Modern AC Electric Locomotive describing the various parts, can be given as:

DC MOTOR BRUSH HOLDERS AND THE PERFORMANCE OF CARBON BRUSHES

Introduction

A DC Motor carbon brush is an electrical contact which makes a connection with a moving surface. Optimal performance on motors, generators and other types of moving contact applications will be attained only when the carbon brush, the brushholder and the contact surface are properly designed and maintained. All three components are critical factors in a complex electro-mechanical system. The DC Motor brushholder, as the name suggests, holds the brush so that the brush can perform properly. Holders provide stable support in the proper position in relation to the contact surface and often provide the means for application of the contact force on the brush.For many decades brushholders had received little attention. New rotating equipment was supplied with copies of the same old brushholder designs. Typically, when performance problems occurred the focus had been on the brush as this was the part exhibiting rapid wear. In the early 1980’s Helwig Carbon led the industry towards the consideration of brushholders and particularly spring pressure as a common cause of many brush problems. Further, recent holder developments and the coordination

of the designs of constant pressure holders with Red Top brushes have resulted in significant advancements in performance and life.The purpose of this paper is to review the critical areas of consideration for brushholders in relation to the proper functioning of brushes. The most important factors are 1) maximum stability of the carbon in the holder, 2) proper positioning of the brush on the contact surface, and 3) minimum resistance through the brush and holder portion of the electrical circuit.Return to top of page.

Holder Size Dimensions

The fit of the carbon portion of the brush in the holder is critical for stable electrical contact. If there is inadequate space between the holder walls and the thickness and width of the brush, there is potential for binding of the brush in the holder particularly with increased temperature and contamination. On the other hand, an excess amount of space between the holder and the carbon will result in an unstable electrical contact as the brush face can move tangentially or axially within the holder. The holder and brush tolerances on the thickness and width therefore must be well coordinated. Brushes are machined undersize per NEMA tolerances or per drawing specifications while brushholders are made oversize. As a

general guideline for brushholders, industrial sizes typically should be held oversize to a tolerance of +.002/+.008". Smaller frame units with a brush thickness less than .500" and greater than .125" should have holders with a tolerance of +.001/+.005". Micro size units with brushes of thickness .125" or less should have holders held to a tolerance of +.001/+.003".Over a long period of usage the thickness dimension on a holder can become worn from brush movement or distorted from heat. Therefore, it is important to periodically measure the thickness and width dimensions on the top and bottom of the holders to ensure they are within tolerance and that the brush will have adequate support for a stable electrical contact. When motor and generator brushholders are subjected to high temperatures, it may be necessary to provide extra compensation for thermal expansion depending on the temperature rise and the degree of heat dissipation. In these cases it is easier to reduce the brush thickness and width dimensions slightly to avoid sticking in the holder rather than adjusting holder dimensions. Metal graphite brushes with over 50% metal content by weight are manufactured with an increased undersize tolerance per NEMA standards as they usually carry higher current, generate more heat, and have a higher coefficient of thermal expansion than non-metal grades.Brush and holder length can also have a significant effect on the stability and performance of the brush. Most often

the length is limited due to the space available within the frame. There are, however, also practical length limitations due to the excess resistance of a long piece of carbon. As the carbon length is increased the resistance of the current path from the shunt to the contact surface is increased. At the same time the amount of contact area between the carbon and the longer holder is increased and the corresponding contact resistance is decreased. This then creates the potential for distorted current flow directly between the holder and the carbon rather than through the shunting. On the other hand, short brush and holder designs are more susceptible to instability at the contact surface. There is potential for a higher degree of brush tilt in the holder since the length of support is less in relation to the brush thickness.In addition to dimensional concerns the insides of the holder must be smooth and free of all obstructions including burrs. If a used brush has any straight scratches down the sides of the carbon then there are protrusions inside the brush box, which will restrict the brush from making proper electrical contact. Rough handling of brushholders can cause distortion of the metal and effect the critical inside dimensions of the brush cavity. Holders made from metal stampings are particularly susceptible to irregularities on the inside dimensions and on squareness. Broaching is generally accepted as the best manufacturing method for assurance of consistent inside dimensions and

a smooth finish.Return to top of page.

Holder Position

The holder position will determine the location of the brush on the moving contact surface. For slip ring applications the holders are usually located around the top portion of the ring for ease of access. In this position the weight of the brush contributes to the contact force. If holders are mounted on the underside of a contact surface then additional spring force may be necessary to compensate for the weight of the brush. On DC machines with commutators proper positioning of the holders in relation to the field poles is critical. The brushes should be equally spaced around the commutator. This spacing can be checked by wrapping a paper tape around the commutator, marking the location of the same edge of each brush, and then measuring the distance between marks on the paper. The brushes must also contact the commutator within the neutral zone where voltage levels are near zero. When the holder position allows the brush to make contact outside the neutral zone there will be higher bar to bar voltages under the brush, circulating currents, bar edge burning, and damage from arcing.Return to top of page.

Holder Angle

The most common angle for holder mounting is 0 degrees, i.e. perpendicular to the contact surface. Most slip rings and reversing commutator applications make use of this so-called radial mount. The advantages are ease of holder installation, maximum spring force transferred to the contact surface, and fair stability of brush contact upon reversal of direction. Any brush face movement within the holder will result in a change in the contact surface. The most stable surface contact will occur when the top and bottom of the brush are always held to the same side of the holder regardless of the direction of rotation. Angle holder mountings were developed to increase this stability and the effective area of the brush contact. However stability will occur only when the correct angles are used in relation to the direction of rotation.When the entering edge is the short side of the brush or a trailing position the face angle should be 20 degrees or less. At greater angles the action of the rotation and the spring force wedges the brush into the bottom corner of the holder and causes high friction and an unstable contact. Normally trailing brushes also have a shallow top bevel. When the entering edge is the long side of the brush or a leading position the face angle should be 25 degrees or more. At angles of 20 degrees and less the action of the

rotation pulls the bottom of the brush to the opposite side of the holder from the top of the brush. Leading brushes should have a top bevel of 20 to 30 degrees. A stable contact can be maintained in either or both directions of rotation with brush face angles between 20 and 25 degrees. The potential disadvantage of holder angles is the loss of effective downward force of the spring. A portion of the spring force is dissipated in holding the brush stable to one side for the holder. The loss in downward contact force for various angles are as follows:

Angle Degrees Loss in Downward Force

5 0.4% 0.4% 10 1.5% 15 3.4% 20 6.0% 25 9.4% 30 13.4% 35 18.1% 40 23.4% 45 29.3% The spring force should be increased to compensate for the loss of effective downward force from the action of the brush angle in holding the brush to the side of the holder. If a brush has bevels of 20 degrees on the top and

30 degrees on the bottom then the spring force should be increased 6.0% + 13.4% or about 20% to maintain the proper level of effective downward contact force at the brush face.In the special case of post mounted double holders commonly used on slip rings, the best design would allow both brushes to make contact at zero degrees or perpendicular to the ring. Any angle will result in one brush in the pair operating with less contact stability.Return to top of page.

Holder Mounting Height

The vertical position of the holders above the contact surface is very important in assuring proper brush support throughout the wearable length of the rush and for proper positioning on the contact surface. When a brushholder is mounted too high above the contact surface or when the surface has been turned down to a significantly smaller diameter, there will not be adequate support for the carbon as the brush wears to a short length. This will contribute to increased electrical wear due to the instability of the contact. The holder mounting height should be proportional to the size of the unit. On the large frame sizes the holders should be mounted a maximum of .125" above the contact surface. In a few cases units operated with intentional runout of the contact surface which must be taken into

consideration. The small micro frame sizes should have a holder mounting height of approximately .032". During holder mounting a flexible mounting pad of the appropriate thickness can be placed on the contact surface to ensure consistent height and spacing. This pad also helps protect the commutator from damage during mounting.There are several common problems related to excess height of the holder. When a commutator has been turned down several times angled brushes will make contact in a different position. With steep bottom bevels and significant decreases in diameter the location of the brush contact could even move outside the neutral zone. There will be a significant increase in wear unless the holder is moved closer to the commutator or the neutral is adjusted.Although single post mounted holders can be rotated to move the holder closer to the commutator, the position of brush contact will change. As above it is very likely that adjustment of the neutral position will be required to avoid edge arcing.On V-shaped toe-to-toe holders which are mounted too high above the commutator the brushes can interfere at the toes. This will result in one or both brushes not making contact with the commutator. It is especially important that these old style holders are mounted sufficiently close to the commutator to avoid this problem.Return to top of page.

Spring Force

Many inventive methods have been used for the application of the contact force on brushes. These included clock type springs, torsion bars, lever springs, helical coil springs, and constant force negator springs. As noted in the graph shown below the brush wear rate will change as the spring pressure changes. This is one of the most important concepts in understanding brush performance. There has always been a problem with an accelerating rate of wear as the brush gets shorter due to the declining spring force and the dramatic increase in electrical wear. The most consistent brush performance will be attained when the spring force is virtually constant at the correct level throughout the wear length of the brush. The use of the proper constant force springs can be a significant advantage with consistent minimal wear rate of the brushes, reduced wear of the contact surface, less carbon dust, and much lower overall maintenance costs on the unit.Testing and application experience have resulted in the following recommended ranges of spring pressure:Return to top of page.

Spring Pressure Recommendation

Application Spring Pressure General Industrial

4.0-6.0 PSI Fractional HP Motors 4.0-7.0 PSI Traction 5.0-8.0 PSI Induction & Sync Motors 3.5-4.5 PSI High Speed Slip Rings 2.25-2.75 PSI Elevator Generators 3.5-4.0 PSI 35 18.1% 40 23.4% 45 29.3% When operating conditions vary from the standard then some adjustment in spring force can improve performance. If the current density is very low, the humidity is very low, or the speed is extremely high then a slightly lower spring force than above can be an advantage. However if the current loads are high, the speed low, there is contamination causing over filming, or where external vibration and roughness of the contact surface are affecting the brush, then a spring force near the high end of each range is recommended. The unique set of conditions on each application will result in its own specific graph and numbers for the ideal spring force to obtain minimum wear of the brushes and the contact surface. Often times a change in spring force will have a far more dramatic effect than a change in brush grade. Several original equipment manufacturers test for the ideal spring force prior to testing different brush materials.The springs on all holders should be checked every 2 or 3

brush changes to ensure the pressure is still within the recommended tolerance and the that the force is consistent on all holders. The force of the spring must first be measured with an accurate scale. This value is then used to calculate spring pressure as shown below.If the spring pressure value is below the recommended range then the springs should be replaced to avoid accelerated wear of the brush and the contact surface.Return to top of page.

Electrical Connections

The primary function of the brush involves conducting current. In many cases the brush holder is also a part of this electrical circuit. Therefore it is necessary that all electrical connections are of minimal resistance to provide the best path for current flow from the main lead connection to the contact surface. Corrosion, contamination, or electrolytic action over a period of time can cause dramatic increases in resistance which then requires cleaning. Careless installation of the brushes or the holders can lead to loose connections. Any high resistance in the brush circuit will result in excess heat or an undesirable path of current flow and unequal loading of the brushes. On fractional horsepower cartridge style brushholders with captive coil spring type brushes the current should flow from the clip connector at the bottom of the holder

up the brass insert to the cap on the end of the brush and then down through the shunt to the carbon. The brushes fail very quickly if the round or eared cap on the end of the brush does not make proper contact with the brass holder insert. When this condition exists current will flow directly from the brass insert to the spring or to the carbon. In either case there will be extreme heat, loss of brush contact, commutator wear, and eventually motor failure.Another problem with larger frame sizes can occur when the holder mounting is part of the electric circuit. If the holder mounting surface becomes dirty, corroded, or even painted over then current will again need to follow another path and thereby cause problems.Return to top of page.

Summary

The general knowledge and experience in the field on rotating equipment has been slowly declining for many years. In addition brushholders have seldom ever received proper attention during trouble shooting or as part of a maintenance program. Therefore it is hoped that the above information will be helpful in creating awareness of the potential problems with brushholders as a very critical component in the satisfactory performance of carbon brushes on motors, generators, and other types of sliding contacts. The important factors to check for proper functioning of the holder and brush are: 1. Inside holder dimensions2. Holder spacing3. Holder angle4. Holder height5. Spring force6. Electrical connectionsWhen there is an opportunity to implement new holders, the use of the principles mentioned above along with the coordination of the latest constant pressure holder .

Installation Steps

Carbon Brush1-Disconnect the power to the machine using approved lock-out procedures.

2. Remove all old brushes from the holders. MakeNote of any unusual conditions of the brushes including roughness or burning of the contact face,Polished sides on the carbon, excess heat on the wires, or frayed shunt wires. Unusual brush conditions are indications of the need for and improved brush design or for maintenance on the machine.

3. Inspect the commutator for unusual conditions for high bars and mica. Make note for requiredmaintenance.

4. Check the inside holder cavity for dust, dirt, oil,

deposits, carbon buildup,corrosion, or burned areasand clean as needed.

5. Check the terminal connection area and clean, as needed.

6. Brush holders should be secured to their mount and checked that none have become loosened or are out of alignment.

7. Measure spring forces to ensure there is consistent contact force at the recommended level. Use the measured force to calculate the spring pressure for comparison with recommended level of 4.0+ PSI.

8. Remove the old film from the brush tracks, if the new brushes are made from a different grade. Dry untreated canvas applied with a pressure block or a rubber abrasive. Seater stone can be used as an alternative.However, the remaining dust must be vacuumed orblown out of the machine.

9. Install new brushes in all holders with attention to the orientation on angled designs.Ensure that thebrushes can move freely in the radial direction and that there is a relatively close fit in the tangential and axial directions.

10. Apply the pressure spring to the top of the brush.

11. Pull up on the brush and allow to gently return to contact with the commutator or ring to ensurethere is no binding of the brush and spring.

12. Connect the terminals. Be sure all terminal connections are tight and secure.

13. Seat the brushes to the contour of the commutator using non-metal bearing sandpaper or garnet paper. Do NOT use emery. Medium coarse grade paper pulled under the brush face in the direction of rotation improves the quality of the brush contact surface and speeds the process. There should be at least 90% of the brush face seated to

the contour of the contact sur face prior to operatingthe machine at load. Once this level has beenachieved, then the resulting dust in the machine around the brushes, holders, and commutator should be vacuumed or blown out.

14. Operate the machine at no load for the final wear-in contour of the contact surfaces in order to ensure complete electrical contact of the brushes. This procedure allows the brush to make intimate contact in its operating position in the holder.

15. The machine is ready for use. The film process on the contact sur face can be enhanced with the use of an untreated hardwood burnishing block or a rubber polishing stone. This procedure can reduce the high friction and brush dust developedduring the initial film forming period.

NOTE: In some cases time allotment, operating conditions, or performance issues may require the replacement of less than a

full set of brushes without normal seating. Then, it is especially important toadhere to step 11 with extended operation at no-load. Shortcuts on procedures for brush installation will result in excess electrical damage to the brush face and the contact surface.

Causes of Commutation Failure

1- Streaking

2- Threading

3- Bar Edge Burning

4- Grooving

5- Slot Bar Marking

6- Photographing

7- Copper Streaking

Causes• Low or unequal spring pressure• Low current loads• Contaminated atmosphere• High humidity• Copper particle pickup from commutator

(streaking)

THREADING

Causes

• Low or unequal spring pressure• Low current loads• Contaminated atmosphere• High humidity• Uneven current distribution• Conditions have been maintained for a long periodof time and caused commutator damage

BAR EDGE BURNING

Causes

• Low or unequal spring pressure• Incorrect brush alignment / off neutral• Wrong brush grade• Sparking caused by commutation problems• Incorrect interpole strength

Grooving

Causes

• Low or unequal spring pressure• Contaminated atmosphere• Low humidity and temperature• Abrasive brush grade

SLOT BAR MARKING

Causes

• Low or unequal spring pressure• Excess vibration• Wrong brush grade• Commutator becomes overheated and softened• High Friction

Copper Drag

Causes

• Uneven current distribution in armature windings• Unequal number of windings in adjacent slots• Inconsistency in armature windings related to number of coils, slots, and commutator bars.

Carbon Brush Failure

The most common cause of carbon brush failure is incorrect spring tension. Once the proper force is applied, grade selection can be fine-tuned to ensure optimum brush and machine performance. For reference, the chart below indicates the recommended ranges of spring pressure for various applications and the method of calculating spring pressure from the measured spring force.

Spring PressureIndustrial D.C Applications 4-6 psi 280-420 g/cm2 WRIM & Sync. Rings 3.5-4.5 psi 240-310 g/cm2High Speed Turbine RingsSoft Graphite Grades 2.5-3.5 psi 170-240 g/cm2Metal Graphite Brushes 4.5-5.5 psi 310-390 g/cm2FHP Brushes 4-7 psi 280-490 g/cm2Traction Brushes 5-8 psi 350-560 g/cm2For brushes with top and bottom angles greater than25 degrees, add an extra .5-1 psi = 35-70 g/cm2

Spring (P.S.I.) = Measured Force (lbs.)

Pressure Brush Thickness (in.) X BrushWidth (in.)

CONCLUSION

A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine,[1] first used in the early 19th century to distinguish between mobile and stationary steam engines.

A locomotive has no payload capacity of its own, and its sole purpose is to move the train along the tracks. In contrast, some trains have self-propelled payload-carrying vehicles. These are not normally considered locomotives, and may be referred to as multiple units, motor coaches or railcars. The use of these self-propelled vehicles is increasingly common for passenger trains, but rare for freight . Vehicles which provide motive power to haul an unpowered train, but are not generally considered locomotives because they have payload space or are rarely detached from their trains, are known as power cars.

Traditionally, locomotives pull trains from the front. Increasingly common is push-pull operation, where a locomotive pulls the train in one direction and pushes it in the other, and can be controlled from a control cab at the other end of the train.

Like great books, no project is created entirely by an individual. There are many people involved in this project too and have helped a lot right from the beginning till the completion of our project. Any bouquets for the merits in this project should go to our door. Any brickbats we are ready to catch ourselves.

It is with a great sincerity, we convey our heartfull gratitude to our Mr. Mohammad Israr, Supervisor, Electric Loco Shed, Kanpur, for his excellent guidance, valuable advice and ample co-operation throughout the training. It is a proud privilege to have availed of the opportunity of guidance.

We are thankful to Mr.S .K. PANDEY too, for their excellent cooperation during our training for the proper response of the machine. We are grateful to all the railway employees.

REFERENCES

1- educateandrapradesh.blogspot.com/2011/01/engineering-projects

2- http://www.ereplacementparts.com/ article/942/Tool_Diagnosis_Is_it_the_Brushes_or_the_Switch.html

3- http://www.swigercoil.com/traction- motor-repair.asp

4- http://electronics.howstuffworks.com/ motor5.htm

5- http://en.wikipedia.org/wiki/ Commutator_%28electric%29

6- http://www.ncr.indianrailways.gov.in/ view_section.jsp?lang=0&id=0,1,513

7- http://www.indiastudychannel.com/projects/5210-Static-Convertor-for-Railway.aspx