INTRODUCTIONIndian Railways (reporting mark IR / भा. रे) is an Indian state-owned enterprise, owned and operated by the 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 65,808 km (40,891 mi) and 7,112 stations.[4] In 2014-15, IR carried 8.397 billion passengers annually or more than 23 million passengers a day (roughly half of whom were suburban passengers) and 1058.81 million tons of freight in the year.[3] In 2014–2015 Indian Railways had revenues of ₹1634.50 billion (US$25 billion) which consists of ₹1069.27 billion (US$16 billion) from freight and ₹402.80 billion (US$6.1 billion) from passengers tickets.

Railways were first introduced to India in the year 1853 from Mumbai to Thane. In 1951 the systems were nationalized as one unit, the Indian Railways, becoming one of the largest networks in the world. IR operates both long distance and suburban rail systems on a multi-gauge network of broad, meter and narrow gauges. It also owns locomotive and coach production facilities at several places in India and are assigned codes identifying their gauge, kind of power and type of operation. Its operations cover twenty nine states and seven union territories and also provides limited international services to Nepal, Bangladesh and Pakistan.

Indian Railways is the world's seventh largest commercial or utility employer, by number of employees, with over 1.334 million employees as of last published figures in 2013. As for rolling stock, IR holds over 245,267 Freight Wagons, 66,392 Passenger Coaches and 10,499 Locomotives (43 steam, 5,633 diesel and 4,823 electric locomotives).The trains have a 5 digit numbering system and runs 12,617 passenger trains and 7421 freight trains daily. As of 31 March 2013, 21,614 km (13,430 mi) (32.8%) of the total 65,808 km (40,891 mi) route length was electrified.[7] Since 1960, almost all electrified sections on IR use 25,000 Volt AC traction through overhead catenary delivery.

Electric Locomotive Story and Working

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Locomotives (popularly called train engines) are the heart and soul of the Railway system. Locomotives give life to coaches and wagons which are otherwise dead hunks of metal which can best qualify as shelters during rains, converting them into trains. Locomotives work based on a really simple principle. Be it diesel or electric, locomotives are actually “run” by a set of electric AC induction motors called  traction motors attached to their axles. These motors need electric power to run, and the source that supplies this power is what differentiates diesel and electric locomotives. Traction motors are electric motors which are a really bigger, extrapolated, enhanced, more complicated and powerful version of the conventional electric induction motor seen in electric fans, pump sets etc. The electric power derived from a source is fed to traction motors which run and turn the wheels of the locomotive, the remaining being only details.

In addition to the power output of the engine, many other factors like Tractive Effort, Gear Ratios, Top Speed Weight of the Locomotive, Axle Load, Adhesion factors etc. also determine the type of service and work the locomotive will be used for, whether for hauling freight, passenger or both (mixed type). This goes for both Diesel and Electric Locomotives. Today’s locomotives are all microprocessor controlled which help them to work efficiently and productively. These computers continuously gather and analyze data to calculate the optimum power required by each axle of the locomotive for its best performance according to the load, grade, speed, adhesion factors etc. They then supply the right amount of power to corresponding traction motors. Supplementing this are all the supporting functions of the loco such as advanced suspension, batteries, Dynamic Brake Resistors, radiators, exhaust and cooling systems, braking and sanding equipment etc.

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How Electric Locomotives WorkAn “Electric Locomotive” is a railway vehicle that can move along rails and push or pull a train attached to it using electric power drawn from an external source, usually from overhead cables or a third rail. Electric Locomotives do not have a conventional “engine” in them, but use the electricity collected from the outside source to power traction motors which turn the wheels. Electric Locomotives in India are of three types: Those which can work on DC (Direct Current), AC (Alternating Current) or on both (AC/DC – Bi-current). Electric Locomotives, though high on electrical engineering, work on the single principle of drawing current from external sources and then after sufficiently “modifying” it, feed it to the traction motors. The process of “modifying” the raw current drawn from outside into “usage” power includes a complicated process of conversion, reconversion, smoothening and transformation of the current to varying values of frequency, Voltage, Current etc. This involves a bank of many components like transformers, rectifiers, inverters, capacitors, thyristors, compressors and other such paraphernalia, housed within the locomotive body or the “shell”, and there is no central “Engine” or prime mover. All this has to be done for optimum performance of the traction motors under different conditions and loads. Bi-Current locomotives work according to the same principles, only they have more equipment packed inside them to enable them to work under both type of currents. Each one the Pantographs are used to collect a specific type of current only. Electric locomotives have this major drawback of being totally dependent on the power which has to be supplied for it to run. Any power outage, short circuit or breaking of Overhead Equipment (OHE) will cause trains to come to a standstill. Hence, even on fully electrified routes, diesel locomotives are kept on standby always. And on partly electrified routes, trains are run on diesel under the wire because it is more efficient than switching locomotives.

The power of the electric locomotive, be it a standalone unit or the power cars of an EMU train set, is generated all by the traction motors attached to the wheels. In fact, one can say that the traction motors are the actual “engines” of the electric locomotive and the remaining are just there to supply optimum power to these motors. The newer three “modern” locomotive classes in India – the WAP5, WAP7 and WAG9 are called three-phase locomotives, since their traction motors run on 3-Phase Alternating Current.

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Electric Locomotives are basically giant electrical transformers on wheels.

Indian Locomotive Classes, Types, Statistics and Explanations

Since its formation in 1948, the Indian Railways has operated 92 different classes of diesel and electric locomotives. Only four types of Steam engines were widely known to be in service, the WP, WG, YG and YP class locomotives, which were all withdrawn from active service by the late 1980s. Today, the scene is dominated by Broad Gauge AC Electric and Diesel Locomotives. Here is a drilldown of the classification of these locos in terms of Gauge, Traction and Load, based on how many are diesel and different types of electric traction. For example, there have been 6 classes of Broad Gauge AC Electric Passenger Locomotives, 11 classes of BG Diesel Mixed locos, 1 class of DC electric Goods loco, total 13 classes of AC electric Goods locos and 9 classes of Meter Gauge locos and 50 types of Diesel locomotives in all and so on. In the next parts, we will check out most of these loco classes one by one, starting with the Diesels.

ELECTRICAL AUXILIARY EQUIPMENT

IntroductionThis page describes the on-board electrical services required by electric trains and how they are provided on the locomotive and passenger vehicles

Contents

On-Board Services – 

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High Voltage and Low Voltage Systems – Converting HV to LV – Development - Motor Generators - Motor Alternators – Electronic Auxiliaries – Gaps. On-Board ServicesThe modern passenger train provides a number of on-board services, both for passengers and control systems.  They are almost all electrically powered, although some require compressed air and a few designs use hydraulic fluid.  Since the train is virtually a self-contained unit, all the services are powered and used on board.  Their use and features can be summarized as follows:

Compressed air –

Almost always used for brakes and sometimes for powering automatic doors.  Also once popular for powering traction power switches or contactors.  Usually used for raising pantographs on overhead line systems. Always needs drying after compression to avoid moisture getting into valves.  The compressor is normally driven directly from the main power source (the overhead line or third rail on electrified lines or the main generator on diesel powered vehicles).

Battery –

Normally provided on locomotives and trains as a basic, low voltage standby current supply source and for startup purposes when livening up a dead vehicle.  The battery is normally permanently charged from an on-board power supply.

Generator –

The traditional source for on-board low voltage supplies.  The generator is a DC machine driven by the diesel engine or, on electric locomotives, by a motor powered from the traction current supply.  On a coach, the generator was often driven directly off an axle (a dynamo), batteries providing power for lighting when the train was stationary.

Alternator –

The replacement for the generator which provides AC voltages for auxiliary supplies.  AC is better than DC because it is easier to transmit throughout a train, needing smaller cables, and suffering reduced losses.  Needs a rectifier to convert the AC for the battery charging and any other DC circuits.

Converter –

The replacement for the alternator.  This is a solid state version for auxiliary current supplies and can be a rectifier to convert AC to DC or an inverter to convert DC to AC.  Both are used

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according to local requirements and some designs employ both on the same train.  The name converter has become generic to cover both types of current conversion.

This page deals with compressed air supplies.  For details of pneumatic auxiliary equipment, go here.

High Voltage and Low Voltage SystemsA locomotive or multiple unit is provided with two electrical systems, high voltage (HV) and low voltage (LV).  The high voltage system provides power for traction and for the low voltage system.  The low voltage system supplies all the auxiliary systems on the train like lighting, air conditioning, battery charging and control circuits.  The two are separated because the high voltage required for traction is not needed for most of the other systems on the train so it is wasteful and expensive to use the high voltage.

Converting HV to LVThe current drawn by a locomotive from the overhead line or third rail supply can be supplied at voltages ranging from 25,000 volts AC to 600 volts DC.  With the exception of heaters and compressor motors which, on the lower voltage DC railways are normally powered by the line current, all of these supply voltages are really too high to use efficiently with the comparatively small loads required by the on-board services on a train.  The common approach therefore, has been to reduce the line voltage to a suitable level - generally below 450 volts and on some systems as low as 37.5 volts.  Most systems have used a dynamo, a generator, an alternator or a current converter to get the lower voltages required.  Usually, different voltages are used for different applications, the particular conversion system being specially designed to suit.

DevelopmentThe first electric lighting provided on steam hauled trains was supplied from a large capacity battery contained in a box slung under the coach.  The battery was recharged by a dynamo powered by a belt driven off one of the coach axles.  Of course, this meant that the battery was recharged only when the train was moving and it had to have sufficient capacity for prolonged station stops, particularly at terminals.  The voltage varied from system to system but was usually in the 12 to 48 volt range.  Trains were heated by steam piped from the engine.  If the locomotive was electric or diesel, a train heating boiler would be installed on the locomotive.  Some European railways had train equipped with both steam and electric heating.  More recently, all heating has become electric.

Electric trains originally used power obtained directly from the line for lighting and heating.  The lamp voltage was kept to a low level by wiring groups of lamps in series.  Each vehicle had its own switch which had to operate by a member of the crew.  On some railways, where there were tunnels, daytime crews were instructed to switch on all the lights at the station before the tunnel and switch them off at the station after the exit.  Such stations were provided with staff allocated to this job.

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This diagram shows the basics for an early electric train set-up with a DC overhead line power supply system.  The line voltage supplies the lighting, heating and compressor power requirements directly.   The only reduction in voltage is achieved by wiring lamps and heaters in series.  Each circuit has its own switch.  The compressor would also have a governor, not shown here.  This diagram shows a typical arrangement before about 1914.  After that time, trains were equipped with multiple of auxiliary services, where all cars were controlled from one position using separate control wires running along the train.  Multiple unit control of traction equipment arrived in the UK from the US in 1903.

Batteries were still provided on some electric trains, especially those on underground lines, for emergency lighting.  A small number of lamps in each car were connected to the battery so that some illumination was available if the main traction current supply was lost.  The batteries were recharged through a resistance fed from the traction current supply.

Motor GeneratorsIn the mid-1930s, electric multiple units began appearing with on-board, DC generators to supply lights.  This allowed lower voltages and reduced the heavy wiring required for traction current fed lighting.  Outputs from these generators ranged from 37 to 70 volts, depending on the application.  The generator was driven by a small electric motor powered by the traction supply.  For this reason they were often referred to as "motor generators".

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In this diagram (left) of a motor generator system, the train lighting and battery are fed from a generator driven by a motor at the line voltage.  The return circuit is through ground, using the car structure like a road vehicle.  A voltage regulator is provided to reduce the risk of damage through sudden changes in voltage caused by gaps in the current rail or neutral sections in the overhead line.  If the MG stops, the battery is disconnected from the charging circuit and supplies a few emergency lights.  In addition to supplying lighting, the LV circuit was used to supply all the train's control circuits.  See Multiple Unit Operation. 

Motor AlternatorsBy the late 1940s, fluorescent lighting was becoming popular and was recognized as better, brighter and requiring less current that tungsten bulbs.  However, if DC is used, the lighting tubes become blackened at one end, so AC was adopted for lighting circuits on trains.  At first, some systems used a DC generator with an alternator added to the drive shaft, a motor-generator-alternator.  The DC output from the generator was used for control circuits while the AC output from the alternator was used for lighting.  Emergency lighting was still tungsten, fed from the battery. 

In the early 1960s, the motor alternator appeared.  The appearance of silicon rectifiers allowed the AC output of the alternator to be converted to DC for battery charging and control circuits.  The introduction of solid state electronics also saw the old mechanical voltage regulators replaced.

Electronic AuxiliariesModern auxiliary services on electrified railways are now mostly solid state systems, using power and control electronics, as shown in the diagram below:

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The output from the DC to AC auxiliary converter is 3-phase AC at about 380 volts and is used for train lighting and the AC motors of air conditioning fans and compressors.  The 3-phase is also converted to DC by the rectifier which provides current for battery charging and control circuits.  The diagram on the left shows the set-up for a DC overhead system but it is similar for AC systems except for the addition of the transformer and rectifier as shown below.

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On a locomotive hauled train, the individual coaches are provided with an on-board converter supplied from a train line carrying a 3-phase supply generated on the locomotive.  On a diesel locomotive, this supply would come from an on-board alternator driven by the diesel engine.

GapsA feature of electric railway operation is the gap or neutral section.  Gaps occur in third rail systems and neutral sections in overhead line systems.  See also Electric Traction Pages Power Supplies.  The gap in a current rail is necessary at junctions to allow the continuity of the wheel/rail contact and at substations to allow the line to be divided into separate sections for current feeding purposes.  Neutral sections in the overhead line are also used for this purpose.

Although they are always kept as short as possible, gaps will sometimes cause loss of current to the train.  The train will usually coast over the gap but there will be a momentary loss of current to the on-board equipment - lights will go off for a second or two and ventilation fans will slow down or stop.  On trains provided with generators or alternators, the momentum in the machine would often be sufficient to maintain some generation over the gap and lighting often remained unaffected.  The only difference noticeable to the passenger was the change in the sound of the generator as it lost power and then regained it a second or two later.

Modern electronics has given us static inverters to supply on-board inverters but they have no inertia and stop output as soon as a gap is encountered.  To prevent the lights going off at every little gap, all lights are connected through the battery.  To prevent the battery becoming discharged too quickly, the inverter starts a "load shed" at about a 60 second delay.  After this time, the main lighting is switched out and only emergency lights remain.  Battery current is also used for emergency ventilation, essential controls and communications

Generation alternatorsThe KEL 4.5KW Train Lighting System consists of a three-phase homopolar inductor type alternator and a static Regulator-cum-Rectifier Unit. Such brushless alternators render a trouble free long service without practically any maintenance, as it is completely free for many moving contacts or winding on rotor. The regulator has been designed for a reliable performance in any operational conditions by eliminating transistors and thyristors, which are comparatively less reliable.

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Brushless Alternator type KELA 45135-D is of totally enclosed construction capable of developing a constant voltage of 120V at a load current of 37.5A from minimum speed for full output to maximum speed. The machines are used for:

Charging the coach battery Operation of fans, lights etc. in the coach

Principle of operation

The alternator consists of two sets of winding namely AC winding and field winding, both accommodated in the stator. The AC windings are distributed in the small slots and field windings are concentrated into two slots. Each field coil spans half the total number of stator slots. AC coils are connected in star and field coils are connected in series. The rotor consisting of stacked stampings resembles a cogged wheel having eight sets of teeth and slots, uniformly distributed on the rotor surface skewing the rotor axis. The core of the stator, which is completely enclosed by field coils, will retain a residual magnetism if excited by battery once. The flux produced by the field coils find its path through the rotor. When the rotor is rotated, the passage of the rotor teeth and teeth alternately under the field offers a varying reluctance path for the flux produced by the field coils. This flux, which varies periodically links with the AC, coils and induces an alternating voltage in the AC coil. The frequency of the induced voltage depends upon the speed of the rotor. The magnitude depends on the speed of rotation and level of excitation. The field is strengthened by a positive feedback system in the regulator to attain the desired output voltage.

Regulator-rectifier unitThe regulator rectifier unit has mainly following functions:Rectifying the three phase AC output of the alternator to DC using full wave Rectifier BridgeRegulating the voltage generated by the alternator at the set value.Regulating the output current at the set value.Power rectifier PR

This consists of six numbers of silicon diodes, connected in three-phase full wave bridge. The three phase AC output of the alternator is rectified by these diodes to obtain DC output terminals +DC and –DC of the regulator-rectifier Unit. Each diode is protected against transient surge voltage by capacitor C1. The whole bridge is protected against high frequency surges by capacitor C3 and DC output is filtered by capacitor C2.

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Voltage regulation

The voltage induced in the AC winding of the alternator is dependent on the speed of the alternator, the excitation current and the load current. In the absence of a voltage regulator, the output voltage will rise indefinitely due to positive feedback to the field. The voltage regulator monitors the voltage and passes a command to the control circuit to reduce the excitation current to reduce the excitation current as soon as the output voltage reaches the set value.

The control circuit is wired in a rack consisting of the following parts:  

Excitation transformer

This is a double winding transformer with tapings for input and output. The transformer steps down the voltage for the field coils. The transformer has five sets of terminals brought to a terminal strip.Terminal 14 and 15 – Input from the two phases of AlternatorTerminal 19 – Center tapping of the transformer going to the negative terminal of field supplyTerminal 18 and 161 – Output of the transformer going to the respective terminals of Magnetic Amplifier. Voltage detector – DT

The voltage detector serves the function of providing necessary ‘error signal’ for voltage regulation. It consists of a network of sneer diode, potential divider and rheostat.

When the output voltage of the alternator exceeds the set value, the voltage drop across the resistance R1 reaches sufficient value to cause the sneer break breakdown and this will sent a current through the control winding of Magnetic Amplifier, which causes in the impedance of load winding decreasing the field current, maintaining the output voltage of alternator at set value. The sneer diode starts conducting only at a designated voltage (sneer voltage). The voltage across sneer will be maintained even if the voltage input to the circuit is increased. Thus it serves as a base for comparison. A rotary switch is provided for setting the voltage at 120, 122 and 124V.

Magnetic amplifier – MA 

The Magnetic Amplifier forms the nucleus of the regulator circuit. It works on the principle of saturation of Magnetic core.

It has 6 sets of winding designated as follows:

Load windings – Two sets (18-162 and 17-161)Control windings – Four sets (10-11, 26-27, 29-30 and 20-40)Of these four sets of control windings only three sets are used in the circuit for voltage control, current control and gain control. The load winding is connected in the field circuit and the field current passes through this winding. Subject to the command from the

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voltage and current sensing circuits, manifested through control windings, load winding offers a variable impedance to the field thereby regulating the voltage and current at set value. 

Field rectifier unit – D2-D3 

Silicon diodes D2 and D3 act as a full wave rectifier for the field supply. These diodes conduct alternately as the terminals 18 and 161 become positive with respective to the center tapping. The rectified current from the diodes is taken through the feedback winding of Magnetic Amplifier to the terminals, 20 and 19 the positive and negative terminals for the field supply.

Free – wheeling diode – D4

In case there is a voltage surge from the field circuit, which will have a polarity opposite to that of excitation, the freewheeling diode will conduct avoiding creepage of surge voltage to important components like Magnetic Amplifier.

Rectifier Bridge – RT

It consists of three silicon diodes connected for three phase full wave rectification with the negative terminal taken from the Power Rectifier Bridge Pruitt rectify the AC output of the alternator and supplies DC voltage to the voltage detector for voltage sensing.

Current regulation 

Current regulation circuit consists of a variable shunt (SHR) connected in series with the load circuit and a diode D1.When the load current exceeds the set value, the drop across the shunt will be sufficient to drive the diode D1 into conduction and pass a current through the control winding of Magnetic Amplifier. The effect of this control current is to retain the current at the limited value reducing the output voltage on further loading. The current limiting circuit prevents the alternator from over loading.

Mounting

Alternator

The alternator is provided with two cast nylon suspension bushes to accommodate a suspension pin of 31.75 + 0.1mm die as per the RSDO specification. The tension mechanism should also be mounted accordingly. 

Rectifier – Regulator

The rectifier – regulator box is designed for under frame mounting. It can also be mounted inside the coach, provided, sufficient ventilation is provided. Care must be taken to fix the box firmly to the underframe. It should be ensured that all enclosures are water tight, before mounting.

Air Conditioning Unit

Air conditioning unit classified on the basis of

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1. AC GENERATION

2. TYPE OF AC PLANT

According to generation, it is again classified as:

1. End on generation

2. Self-generation 

End on generation  

As the name suggests, in this type generators are at the end of the coaches. There are two generators of rating 250kvA, 750V, 3phase.

In RAJADHANI EXPRESS&SHATABTI EXPRESS, they are using this type of AC unit. In these trains, the provision of dedicated rakes lows the use of a separate ‘power-car’ to supply electricity for all the coaches. There are usually 2 generators in each power car; each generator (an ‘end-on generator’ (EOG)) generates 3-phase 750V AC power, which is then distributed across the train, and stepped down to 415V AC (3-phase) for the air-conditioning, or 110V (single-phase) for other appliances. The elimination of generation equipment also allows the coach bogies to be designed with higher speeds in mind. The power car capacity is 250kVA.

These 250kVA power cars were introduced in 1992. Before that the power cars in use had a capacity of 125kVA and used 440V as the AC distribution voltage. With these, most Rajdhanis and Shatabdis needed three power cars — one at either end, or one in the middle of the rake, which split the rake into two portions (termed ‘Unit I’ and ‘Unit II’). As the power cars are (were) not equipped for anyone to walk through, there was no way to get from one portion of the rake to the other while the train was in motion.

A very small number of other trains also use such EOG cars for power; these EOG cars tend to be different from the ones used for Rajdhani and Shatabdi trains.

Self-generation

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Here there are three power supply arrangements. Axle driven brushless alternator Battery Precooling Arrangement In axle driven brushless alternator, practically 98-103V is generated. The capacity of this alternator is 25KW or 18KW.There is one Regulation cum rectifier unit. Here also there is magnetic amplifier, which senses the variation in voltage and current and accordingly regulates the field excitation. There is also an Over voltage protection circuit to prevent the damage due to over voltages.

Battery unit: 

Some years back, they were using Lead acid cell batteries of 800AH capacity. But due to its severe drawbacks like frequent addition of distilled water, sulphonation etc. now they are using Valve regulated lead acid battery popularly known as Maintenance free battery of capacity 1100AH.Its lifetime is around 4years.

Pre cooling Arrangement: 

This is essential because when the train happens to halt in a station for more than say half an hour it is not economical to switch on the air conditioning unit by the battery. So in this condition, we tap the 440V ac supply from the station itself using an arrangement. Then there is a step down transformer, which step down 440V to 110V.

According to type of plant they are again classified into

Under Slung

Roof Mounted Ac Package Unit

Under Slung Unit:

 This type used before 1995.

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Roof mounted ac package unit

The roof mounted package unit is factory assembled, gas charged and hermetically sealed refrigerant system. It has two Hermetically sealed, 3phase reciprocating compressors, two vertical flow condenser fans and one blower motor with two forward curved blowers. Condenser fan motors are 3 phase motors whereas the blower motor is double shaft 3-phase motor. There are two independent refrigerant circuits in each roof mounted package units having a compressor, condenser coil and evaporator (cooling) coil .The condenser fans and evaporator blower motor are common to both the circuits.

Each circuit has its own fresh air and return air filters, condensate drain pan and drain outlet. The condenser fans and compressors can be accessed from the top of the unit whereas the return air filters can be pulled out from under the unit by opening the access door, in the corridor of the coach .The blower, heaters and safety controls can be accessed by opening the access door at the center of corridor of the coach .The blower motor can be opened without disconnection, by opening the central access door .The blower assembly is hinged and opens to hang vertically

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down. This provide access to heaters, blower motors and blowers .To open this access this access door remove all bolts while supporting the motor disengage the safety leych and gradually lower the central access door. Care should be taken while doing this, as the weight of blower motor and blower are supported on the central access door.The terminals for connecting cables are located below the evaporator area and are accessible directly once the coach access door in the false ceiling is opened. As the roof mounted package unit is modular Hermetically sealed type, it requires minimum maintenance .The refrigerant system is Hermetically sealed and has no fittings or gauge ports .The safety devices are provided to protect against abnormal operating refrigerant pressures, loss of air and overheating of heating elements, low voltage and high voltage.

Air-conditioning unit specifications

1. Unit type             : Roof Mounted Package Unit

2. Unit Model Name     : FLC-RAC-04

3. Cooling Capacity         : 84000 BTU/Hr Temperature and relative     : 25.0ºC at 50% RH Humidity at evaporator Inlet Outside Temperature: 50º C DBT for

Dry Summer 

4. Power Supply         : 415V±5%AC, 3Ø, 50Hz 

5. Power Consumption     : 13.5kW 

6. Current             : 22 Amps

7. Conditioned Air flow rate: 4000M³ /Hr at 20mm W.G. Ext. Static

8. Refrigerant         : R-22, 2.4 kg per circuit

9. Dimensions         : Length * Width * Height 2150mm 2250mm 600mm

10. Weight             : Approx.580kg

11. Outline Drawing No.     : CC-90012 (alt d) 

12. Compressor         : Hermetic reciprocating type Kirloskar MG52/Maneurop MT57HL4

13. Condenser Fan         : Direct drive propeller fan 2 Nos. per unit

14. Condenser Fan Motor     : 6 pole (2 Nos. per unit) 0.55kW 415 VAC 3Ø, 50Hz15. Evaporator Fan         : Direct driven centrifugal fan 0.75kW 2 Nos. per Unit

16. Evaporator Fan Motor     : 4 pole, 415 VAC, 3Ø, 50 Hz, 1 No. per unit

17. Heaters             : 3kW 2 Nos. per unit 415 VAC 3Ø, 50Hz.

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Control and Power Circuitry

  The electrical circuit of ac package unit is divided into two sections: Three phase ac power circuit at 415 V, 50Hz

Single phase control circuit at 110 V, 50 Hz

Power Circuit

The 3 phase 415 V, 50 Hz power supply is used to operate two Hermetically Sealed Compressors, One double shaft blower motor , two heaters and two condenser motor through 6 contactors .The equipment’s are protected by using MCBs and Overload relays

Control Circuit

    A step down transformer of 415/110 V is used to provide 110 V, single phase to control circuit. The thermostats ,PCBs and other interlocking devices operate on control voltage for protection of various equipment’s .However ,the Crank Case Heaters of both compressors are operated on 415 V and are kept energized all the time and are not switched off even when it is switched off .This is to ensure that the crank case lubricating of the compressor is kept warm during Off cycle and machine shut down so that refrigerant does not migrate into the compressor crank case .This will ensure that during compressor start up ,no liquid refrigerant is present in the compressor crank case to cause foaming of the oil and consequent compressor damage due to absence of lubricant .Three stage thermostats are provided for cooling and heating to maintain 24 to 26 deck during summer (for cooling) and 19 to 21 deck during winter (for heating) at Low, Medium and High positions of rotary switch respectively. The control circuit is designed such that in case of power failure the machine shuts down and when the power is restored the machine restarts automatically. The incoming power is indicated by three lights, Red, Yellow, and Green .A normally ON status of each equipment is indicated by Green lights. Red lights indicate overload tripping in case of the heaters .In addition for the compressors Red Indicators are provided for low and high pressure trip. Green lights indicate the manual/auto and heating/cooling status of the unit. 

Rotary switchthere are mainly five types of rotary switches.

RSW1 to switch on/off mains supply.

RSW2 to switch on blower.

RSW3 to select auto / manual heat /manual cool /vent mode as per requirement of inside condition.

RSW4 to select the three stage of temperature low/ medium/ high by operating thermostat.

RSW5 to select the working of compressors on/ bypass.

Control/protection components in electrical power and control circuit.

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Overload protection used for blower motor, condenser motor and compressor.

Time delay relay (TDR) used for compressor motor.

Contactors used for blower motor, condenser motor, compressor and heater.

Overheat protection used for heater.

Cooling relay

Heating relay

PCB with LEDs for status indication.

Vane relay used for air proving SPDT switches.

Transformer for control circuit. 

Safety protections in the control panel

     Temperature Protective Thermostats (OHP) set at 200 Deck. Are provided on each heating element to switch OFF power to the Heater element in case the surface temperature of the heater reaches 200.Deg.C.  Electro-Pneumatic Time Delay Relay are provided on each compressor to ensure delay in starting of each compressor when power is switched “ON” and to prevent both compressors starting at once. Two Vane Relays are provided to ensure operation of condenser fans, compressors or heaters only when the air flow is present across the cooling coils and the heating elements. High Pressure Safety Cut-out (HP) and Low Pressure Safety Cut-out (LP) are provided to switch OFF compressor when the high pressure exceeds 420 PSIG or suction pressure drops below 35 PSIG. The LP cutout is auto reset whereas HP cutout is manual reset Overload Relays with built in single phasing protection are provided to protect Compressor, condenser fan and blower motors against single phasing and over load.

Electric Traction

Functioning of various equipment

Power supply

25 kV, ac 50Hz single phase power supply for electric traction is derived from grid system of State Electricity Boards through traction substations located along the route of the electrified sections at distances of 35-50 km apart. The distance between adjacent substations may however be even less depending on intensity of traffic and load of trains.

At present there are broadly four different arrangements in existence as under:

1. The Supply Authorities supply power at 220/132/110/66 kV EHV at each traction sub-station, which is under the control of the Railway.

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2. The Railways receives three phase power supply from Supply Authority at a single point near the grid sub-station from where the Railway runs its own transmission lines providing its own traction sub-station.

3. All EHV and 25kV equipment is under the control of the Supply Authority except 25Kv feeder circuit breaker which are the under the control of the Railway.

4. All EHV and 25kV equipment is under the control of the Supply Authority but 25kV feeder circuit breakers alone are operated on remote control by the Traction Power Controller (TPC).

Duplicate supply

    To ensure continuity of supply under all condition, the high voltage feed to the traction sub-station is invariably arranged either from two sources of power or by a double circuit transmission line, so that even if one source fails, the other remains in service. Suitable protective equipment is installed at the sub-stations to ensure rapid isolation of any fault in transmission lines and sub-station equipment, so that the power supply for electric traction is maintained under all conditions. At each traction sub-station, normally 2 single-phase transformers are installed one of which is in service and the other is 100% stand by. The present standard capacity is 21.6MVA. These transformers step down the grid voltage to 25kV for feeding the traction OHE. 25kV feeders carry the power from sub-stations to feeding posts

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located near the tracks. Each feeder is controlled by a single pole circuit breaker equipped with protective devices. 

Voltage regulation

     The permissible variation of the bus bar voltage on the bus bars at the grid sub-stations is +10% and-5% i.e. between 27500V and 23750V. The tapings on the transformer are on the secondary winding and are set to ensure that the voltage is maintained as high as possible but not exceeding 27.5kv at the feeding post at any time.

25kV SUPPLY AT TRACTION SUB-STATIONS

On the secondary side, one transformer circuit breaker and one feeder circuit breaker are installed with associated double pole isolator, the bus bar connections being such that full flexibility of operation is assured.        

The traction substation is designed for remote operations.

The facilities exist to change over from one feeder to the other by means of isolator/bus coupler.

One end of the secondary winding of transformer is solidly earthed at the sub-station and is connected to track/return feeder through buried rail.

FEEDING AND SECTIONING ARRANGEMENTSThe generation and transmission systems of Supply Authorities are three phase systems. The single-phase traction load causes unbalance in the supply system. This unbalance has undesirable effects on the generators of the Supply Authorities and equipment of other consumers, if its value becomes excessive. To keep the unbalance on the three-phase grid system within limits, power for ac single-phase traction is tapped off the grid system across the different phases of adjacent sub-stations in cyclic order. Thus it becomes necessary to separate electrically the OHE systems fed by adjacent sub-stations. This is done by providing a “Neutral Section “between two sub-stations on the OHE ensure that the two phases are not bridged by the pantographs of passing electric locomotives/EMU’s.

To ensure rapid isolation of poles on the OHE and to facilitate maintenance work, the OHE is sectioned at intervals of 10-15kms along the route. At each such point a “Switching station interrupters” usually rated at 600amps are provided. The shortest section of the OHE, which can be isolated by opening interrupters alone, is called sub-sector. Each sub-sector is further sub-divided into smaller “elementary sections” by provision of off-load type manually operated isolator switches. At some stations with large yards, alternative feeding arrangements are provided so that the power for feeding and yards may be drawn from alternative routes. Normally the switch is locked in one position, being changed to the other when required after taking necessary precautions.

Feeding post 

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Each feeder supplies the OHE on one side of the feeding post through interrupters controlling supply to the individual lines. Thus, for a two-track line, there will be four interrupters at each feeding post.

Sectioning and paralleling post (SP)

These posts are situated approximately midway between feeding posts marking the demarcating point of two zones fed from different phases from adjacent sub-stations. At these posts, a neutral section is provided to make it impossible for the pantograph of an electric locomotive or EMU train to bridge the different phases of 25 kV supply, while passing from the zone fed from one sub-station to the next one. Since the neutral section remains ‘dead’, warning boards are provided in advance to warn and remind the driver of an approaching electric locomotive/EMU to open locomotive circuit breaker before approaching the neutral section, to coast through it and then switch ‘on’ the other side. Special care is taken in fixing the location of neutral sections, on level tangent tracks far away from signals, level crossing gates etc. to ensure that the train coasts through the neutral section at a sufficiently high speed, to obviate the possibility of its stopping and getting stuck within the neutral section.

    A paralleling interrupter is provided at each ‘SP’ to parallel the OHE of the up and down tracks of a double track section. ‘Bridging interrupters’ are also provided to permit one feeding post to feed beyond the sectioning post up to the next FP if its 25 kV supply is interrupted for some reasons. These bridging interrupters are normally kept open and should only be closed after taking special precautions

Sub-sectioning and paralleling post (SSP)  

One or more SSPs are provided between each FP and adjacent SP depending upon the distance between them. In a double traction section, normally three interrupters are provided at each SSP i.e. two connecting the adjacent sub-sectors of up and down tracks and one for paralleling the up and down tracks.

Certain equipment at switching substations

Certain equipment are installed at various points to protect the lines, to monitor the availability of power supply and provide other facilities. These are generally as under:- 

1. Lightning arresters are provided to protect every sub-sector against voltage surges. 

2. Auxiliary transformers are provided at all the posts and also at certain intermediate points to supply ac at 240V, 50Hz required for signaling and operationally essential Lighting installations. To ensure a fairly steady voltage, automatic voltage regulators are also provided where required. 

3. Potential transformers are provided at the various switching stations for monitoring supply to each sub-sector. 

4. A small masonry cubicle is provided to accommodate remote control equipment, control panel, telephone and batteries and battery chargers required for the control of interrupters and other similar equipments.

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SRR-ERS SECTION DIAGRAM

Fig. SRR-ERS SECTION DIAGRAM

 

TSS-Traction sub-station                    AFK-Angamali

SSP-Sub-Sectioning and Paralleling Post            CKI-Chalakudi

SP-Sectioning and Paralleling Post                PUK-Puthukkadu

ERS-Ernakulam                         PNQ-Poonkunnam

ERN-Ernakulam North                     WKI-Wadakancherry

AWY-Alwaye                         SRR-Shorenoor

OVERHEAD EQUIPMENTThe fundamental aim of design overhead equipment is to install the contact wire at the requisite height and to keep it within the working range of the pantograph under all circumstances.

Catenary and contact wires

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The overhead equipments above the tracks comprises of the following:A stranded cadmium copper wire of about 65 mm² section or stranded aluminium alloy wire of about 116 mm² section for catenary. A grooved hard drawn copper contact wire of 107 mm² cross-section (when new) supported from the catenary by means of droppers of 5 mm diameter spaced not more than 9 m apart. The catenary and contact wire together have an equivalent copper section of 157 mm². The current normally permissible on single track is 600 A approximately, because of cross-sectional area of OHE. This current limit is based on the temperature limit of 85ºC in contact wire. Certain sections in Waltair-Kirandul section have the catenary and contact wires together having an equivalent copper section of 200 mm².For loop lines, sidings, yards and spur lines excluding the main running lines and first loop or lines taking off from main running line, tramway type OHE having only grooved hard drawn copper contact wire of 107 mm² section is provided. 

Fig. internal parts of AC coach

Height of contact wire

    The normal height of contact wire for regulated OHE is 5.60 m (with 10 cm presage for 72 m span) above rail level. For unregulated OHE in areas with a temperature range of 4ºC to 65ºC, this figure is 5.75 m and in areas with a temperature range of 15ºC to 65ºC, it is 5.65 m. in certain cases, such as under over-line structures, the height may be as low as 4.65 m on BG and

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4.02 m on MG. For passing oversize consignments on such lines, special precautions have to be taken.

Span of supporting mast/structures

The span normally used for supporting the OHE from masts/structure using the cantilever type bracket assembly varies from maximum 72 m on straight track to 27 m on curved track, the spans depending upon the degree of curvature. The catenary system is normally supported on straight tracks at maximum intervals of 72 m (63 m on MG) by cantilever type arms fixed to galvanized broad flange or I section steel masts or fabricated steel structures. On curves the catenary is supported at closer intervals, the spans adopted depending upon the degree of curvature. 

Stagger

    The contact wire is staggered so that as the pantograph glides along, the contact wire sweeps across the current collecting strips of the pantograph up to a distance of 200 mm on either side of the centerline on straight runs and 300 mm on one side on curves. This ensures a uniform wear of the current collecting strips of the pantographs. 

Overlaps 

    The OHE conductors are terminated at intervals of about 1.5 km with an overlap, the conductor height being so adjusted that the pantograph glides from one conductor to the other smoothly.

There are two types of overlap spans as under:

Uninsulated overlap spans where the distance of separation between two contact wires is 200 mm Insulated overlaps, where the two OHE systems are kept apart at a distance of 500mm.Normally the electrical discontinuity at insulated overlaps is bridged by interrupters or isolator except at neutral sections.

Neutral sections

When successive sections of the AC catenary are supplied by different phases from the 3-phase power grid, there is a short, electrically neutral (un-energized) section (dead zone or neutral section) of catenary that comes between them. The loco has to coast through this ‘phase break’ with a brief interruption in the supply of power. Sometimes different sections of the catenary are connected to different phases at different times and the neutral sections may be a switched neutral section. (The term also refers to neutral sections at AC-DC switchover points where the neutral section can be switched to either the AC or the DC supply, and is also known as the dynamic neutral section.

In DC catenaries, there are similar breaks (power gaps) with neutral sections at points where adjacent sections of catenary are supplied by different substations. Neutral sections used to be quite long (41m was a common length) but now many neutral sections corresponding to phase

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breaks in the AC power supply are as short as 5m. Some locomotives are also being provided with modifications to keep their headlights and some auxiliary equipment turned on while traversing the neutral section.

Regulated and unregulated OHE 

OHE with automatic tensioning called “regulated OHE” is generally provided for all main lines, but for large isolated yard and unimportant lines, automatic tensioning is dispensed with in the interest of economy and only unregulated OHE is used. 

Section insulator assembly

Section insulators are provided to insulate the OHE of one elementary section from the OHE of the adjacent elementary section such as at cross-overs. When the pantograph of a locomotive passes from one track to another along a cross-over /turnout, current collection changes from one OHE to other and therefore the runners of the section insulators overlap with contact wire so that there is no arcing. On double line sections with runners trailing, the section insulator assembly using porcelain insulators are fit for speeds up to 120kmph provide it is installed between the first one-tenth and one-third of the span. In case the runners of the section insulator assembly are in the facing direction or it is not installed within the first one third of the span, the speed should be restricted to 80kmph.

Mechanical independence of OHE track-structures 

By providing independent structures for supporting the OHE of each track, complete mechanical independence of each OHE is secured. Any irregularity or damage or maladjustment of the OHE of one track will not, therefore, affect the performance of the other.

Flexible head-span and rigid portals

In large yards, where difficulty is experienced in locating individual supporting structures between the tracks, a catenary wire system called flexible head-span is provided to maintain two or more catenaries and their contact wires at the appropriate heights and locations. Where the OHE has to be regulated, rigid portal structures are used.

Maximum speed 

The OHE with maximum span of 72m and with presage of that span of 10mm and with tension of 1000kgf in contact and catenary wire is designed for a speed potential of up to 160kmph.The existing system is generally at for 140kmph with AM-12 pantographs now in use on ac locomotives.

Droppers

The contact or trolley wire is supported from the catenary or messenger wire by means of droppers. The droppers are made of solid copper of usual cross section of 5 sq. mm and are

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spaced closely along the contact wire at 9m distance from one another. The lengths are so adjusted so that although there is a sag in the messenger wire, contact wire is practically level.

Booster transformer (BT) system:

 In the simple AC system, there can be severe inductive interference in telecom lines and other equipment because of the large loop area between the catenary and the rails which carry the return current. Some of the return current also flows in the earth causing conductive interference and corrosion problems in buried cables, pipes, etc. Such earth currents are higher if the conductive path in the rails is degraded because of rail joint problems. In booster transformer (BT) feeding system there is now a return conductor, a wire that is close to and parallel to the catenary wire. The return conductor is connected to the rails and earthed. Periodically, there are breaks in the catenary where the supply current is forced to flow through one winding of a booster transformer; the other winding is in series with the return conductor. The 1:1 turn’s ratio of the BT means that the current in the catenary will be very nearly the same as the current in the return conductor. The current that flows through the loco goes to the rails but then up through a connecting wire to the return conductor, and through it back to the substation. Insulated rail joints are also provided — this ensures that current flows in the rails only in the particular section where the loco is present. At all other places, the inductive interference from the catenary current is nearly cancelled by that from the return current, thus minimizing the interference effects. The problem of stray earth currents is also reduced. One disadvantages in this system is that as a loco passes a booster transformer, there is a momentary interruption in the supply (because of the break in the catenary) with the attendant problems of arcing and transients on the line, as well as radio frequency interference.

IMPORTANT EQUIPMENTS OF ELECTRIC LOCO / EMU

Pantograph 

For collecting power from 25kv ac contact wire pantographs are mounted on the roof of the traction vehicles. AM12 pantograph of naively design has been adopted by Indian Railways for 25kv ac electric locomotives and EMUs. These pantographs are provided with steel strips for current collection. The raising and lowering of a 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.This pantograph is suitable for operation up to 140km/h. For increasing the speed potential, improved pantograph with lower dynamic mass and independent pan heads have been used. Further, in order to increase the life of contact wire, use of carbon strips have also been tried.

Transformer

Power to traction vehicles is available at 25kv 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

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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. With the introduction of thyristorised convertors, the design of the traction transformer has undergone simplification with the deletion of regulating winding. The transformer for thyristorised convertor becomes a two limb construction and a traction secondary winding split into 4 windings for two step sequence control. The traction transformer necessarily has to have forced oil circulation and forced air cooling. For this purpose oil pump, oil cooler and blower form an integral part of the traction transformer.

Traction motor

Traction motors power the driving wheels which actually move the locomotive. In case of traction motors great emphasis is being given to improve power to weight ratio, keeping in view the limited space available on locomotive for mounting the same. There is a continuous effort to improve the performance of traction motors by making them lighter/compact, at the same time more reliable. Improvements in the basic design of traction motors have become possible due to availability of new insulating materials with high thermal margins. Instead of dealing with individual insulating material, the specification now covers the combination and system as a whole. The new feature is added because of thermal Endurance of the system which may not be directly related to the thermal capability of individual materials.

PROTECTIVE RELAYS

A protective scheme includes circuit breakers and protective relays to isolate the faulty sections of the system from the healthy sections. A circuit breaker can disconnect the faulty element of the system when it is called upon to do so by the protective relay. The function of the protective relay is to detect and locate the fault and issue a command to the circuit breaker to disconnect the faulty element. Protective relays can be classified into the following categories depending on the duty they are required to perform.

Over current relays Under voltage relays Impedance relays Under frequency relays Directional relays

These are some important relays. Many other relays specifying their duty they perform can be put under this type of classification. The duty which a relay performs is evident from its name. For example, an overcurrent relay operates when the current exceeds a certain limit, an impedance relay measures the line impedance between the relay location and the point of fault and operates if the point of fault lies within the protected section. Directional relays check whether the point of fault lies in the forward or reverse direction. The above relays may be electromagnetic, static or microprocessor-based relays. 

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Remote Control SystemTo maintain continuity of electric supply to track is of utmost importance. In order to ensure this it becomes necessary to have a comprehensive picture of supply conditions and arrangement to operate switchgear with minimum delay. This is the purpose of a remote control Centre (RCC). The in charge of a remote control station is called traction power controller (TPC).The TPC monitors the remote control Centre around the clock He is responsible for carrying out all switching operations on the electric supply system. Each remote control Centre is connected to grid substations, feeding posts, sectioning and sub sectioning post, station masters offices, important signaling cabins, divisional office and traffic control office. Made by Ravi Kant All the interrupters at various control posts and circuit breakers at various substations are controlled by what is called a remote control system which operates on transmission of voice frequency signals.

Fig. railway controlling system

This system of signaling, used to avoid magnetically induced disturbances from transient currents of switching operations, is carried out by pilot wires with one pair for taking the

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operating signal and another for incoming indicating signal. Potential transformers at switching stations monitor the availability of supply to each and every section of the overhead equipment (OHE). By this arrangement the entire electrical supply system is placed under the control of a single entity i.e. the TPC who is fully equipped with facilities for instantaneous control of any switching operations to ensure quick isolation of the faulty sections and restoration of supply to the adjoining healthy sections as also for the isolation of sections for maintenance work anywhere on the system which for the Thiruvananthapuram division extends from Thirunelveli to Shornur (excluding these Stations). Electrification has been carried out only of the section between Ernakulam and Shornur. Control and Monitoring: A Remote Control Center (RCC) is located at or near the divisional traffic control Centre. The RCC has the control and monitoring equipment for the electric traction in the areas controlled by the traffic control Centre. Earlier Indian Railways used an electromechanical control system, Frequency Modulated Voice Frequency Telegraph (FMVFT). These are still in use in some places. Now, IR has been installing a microprocessor-based system Called ‘SCADA’ (Supervisory Remote Control and Data Acquisition System) for remote control of electric substations and switchgear. A central SCADA facility (the division control Centre) can control a region extending to about 200-300km around it. SCADA allows remote monitoring of electrical parameters (voltage, current, power factor, etc.) in real time and remote operation of switchgear, as well as automatic fault detection and isolation, allowing better control of maximum demand, trouble-shooting, etc. SCADA replaces an older system that used electromechanical remote control apparatus 

SCADAThe term SCADA is an acronym for Supervisory Control and Data Acquisition. It is a system that provides a real time diagrammatic representation of the entire traction system. Its predecessor was a mimic diagram installed at every remote control system.

A remote terminal unit is installed at every switching station this unit relays data to the remote control Centre regarding various station parameters. Data is relayed through a network of optical fibers to a master server placed at the RCC. A front end processor (FEP) analyses the acquired data.

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Fig. SCADA working

The data is not received continuously but at predetermined intervals from each station. The receipt of valid data is noted on a counter as is the receipt of invalid data. Three consecutive error messages trigger a warning indicating that the system is malfunctioning. The processed data is displayed at a number of computer nodes or workstations. The display is in the form of a diagram showing the complete traction system. Different symbols are used to represent equipment such as interrupters, circuit breakers, transformers etc. Colour coding is used to represent the status of the equipment. For e.g. green lines may indicate a healthy section of track while red would indicate a fault. Relevant data such as the voltage and current output of a substation is also displayed alongside.This kind of a display allows easy analysis of the situation at any given instant. Operations such as closing an interrupter or isolating a faulty section can be done by clicking on the concerned symbol. The program is protected by authorization codes which ensure that only authorized personnel can carry out switching operations or access data.  For an ordinary power system supplying domestic needs failure is undesirable but does not have very serious consequences. This is not so for an electric traction system. A major failure would have a domino effect throwing the entire train schedule into disarray. This would not only cause inconvenience for passengers but would also cause economic losses. So the monitoring system must be foolproof. Hence the server, FEP, workstations, all have 100% standby facilities. The advantages of using the SCADA system are ease of operation, fast response and greater

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coordination and control over the entire system. If a fault occurs immediate isolation of the faulty section and rerouting of power to healthy sections can be carried out. Thus the system allows smooth, uninterrupted operation

CONCLUSION

In conclusion to all the mentioned design aspects of the AC COACH and ELECTRICAL LOCO of Train there are several other factors that are needed to be considered. This includes socio-economic factor of the surrounding locality, political developments, union of workers and contractors. Economic factors become chief aspect in any project which can take a prolonged period to complete. An assumption of price hike of all the materials to a higher precision is needed to be made in order to estimate the budget of this project. The mechanical and civil designs are also an essential part of any electrical substation design. Thus a lot of other engineering brains in those fields are also employed for the construction. Experts in the field of commerce and law are also employed to meet the various challenges that may rise up.

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