study of operation of wagon tippler and side arm charger

CHAPTER 1 INTRODUCTION 1.1 About RTPP During the year 1985 the installed generating capacity of our state was 1963MW of hydel units and 983MW of thermal units. Most of these units were located in the northern half of the state. In view of the predominant hydel installation in the Southern Region of the state, it is considered necessary to increase thermal generation in the area thereby strengthening the base load capacity. Also the need for stable power supply in the Rayalaseema region is considered a must, in view of the rapid industrial growth envisaged in the region. Government of Andhra Pradesh has taken a policy decision of locating a 420MW thermal power station in Rayalaseema region, based on the water from the Mylavaram Dam on the Penneru River. Based on Government Decision A.P.S.E.B has taken up 2 Nos. 210MW thermal units under Rayalaseema Thermal Power Project (Stage-I). The project was approved by the Planning Commission in March, 1988 at an estimated cost of Rs. 503.71 Cr. The project helps improved the voltage profile in Rayalaseema region which is economically backward and drought prone. It is built on a 2500 acre area acquired. Water for the project is drawn from Mylavaram reservoir formed by Mylavaram dam across River Penneru through a 22 KM long steel pipe line laid underground. Rayalaseema Thermal Power Project is one of the major power generation facilities developed in Andhra Pradesh to meet the growing demand for power. The Project envisaged the installation of 5 x 210 MW coal based thermal generation units. The first 210 MW unit came for commercial operation on 25-Nov-1994 and the second 210 MW unit on 30-Mar-1995. 1.2 Location The project is located at a distance of 8 KM from Muddanur Railway Station of South Central Railway on Chennai-Mumbai Railway Line. The site selected is at an adequate distance from the populous towns and the land (2600 acres) is government land not put to any use. The water requirement for the project is envisaged to be supplied from the Mylavaram reservoir and Brahma Sagar reservoir. The project is quite near to the existing railway line and transmission lines of the Andhra Pradesh Grid.

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Stage-I Unit-I is synchronized to grid on 31st of March1994 while the Unit-II is synchronized 25th of February 1995. This stage-I is synchronized to the grid on 29th November of 1995. Stage-II Appreciating the prompt Completion of Rayalaseema Thermal Power Station Stage-I project with the A.D.B. loan in a record time, the Director planning of C.E.A. requested A.P.S.E.B. for preponing the Rayalaseema stage-II to the 8th plan from 9th plan as many other projects planned for completion in 8th plan in the country were not materializing. The A.P.S.E.B. agreed to it and the project was quickly approved by CEA. As an expansion to the existing stage-I A.P.S.E.B has taken up Rayalaseema Thermal Power Project Stage-II by installation of two units of 210 MW thermal units adjacent to the existing 2 units of 210 MW with estimated cost of the Project is Rs. 1640 Crores. PFC & REC has provided financial support for this stage. The annual coal requirement of 2.06 million tones has been linked to Singareni collieries. Unit-III is synchronized to grid on 25th of January 2007 while Unit-IV was synchronized on 20th of November 2007. Stage-III During Dedication Programme of Unit-3, APGENCO has planned to take up one 210MW unit under Stage-III and one 600MW unit under Stage-IV as an expansion to the existing Stage-II which is now under construction. Irrigation Department of AP has allocated 1.4 TMC of water from Sri PothuluriVeeraBrahmam Reservoir via G.O.Rt.No.183, on 29th march, 2010 for both Stage-III & Stage-IV. Stage-IV (Under Construction) APGENCO has taken up one 600MW unit as Stage-IV with an estimated cost of Rs.3525Cr. M/s Power Finance Corporation Ltd. agreed to sanction loan of Rs.2423Cr. on 19th of March 2010. Ministry of Coal allocated 2.31mtpa long term coal linkage from MCL for 600MW Unit. MOC has been addressed for additional quantity of 1.2mtpa required for 600MW.Additional coal linkage is awaited. Purchase Order issued on 14-Oct-2010 to BHEL for BTG package for Rs.1445 Cr. And another P.O. issued on M/s Tech Pro Systems Ltd for executing BOP works.

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1.3 Coal to Power Steam power plants basically operate on the Rankin cycle shown in Fig1.1. Rankin cycle is a model that is used to predict the performance of steam turbine systems. It is an idealized thermodynamic cycle of heating engine that converts heat into mechanical energy. The heat is

Fig.1.1 Rankin cycle

usually supplied to a closed loop which uses water as working fluid. Coal is burnt in a boiler which turns water into steam. The steam that produced form boiler is enfettered into super heater which is heated at a temperature of 510°. From the super heater the steam is utilized for driving the turbines and the output of the turbines which is Mechanical energy is given to the generator as the input and the power is delivered from the Generator. It is given to the bus bars and transmitted over the transmission lines to the load centers. 1.4 Description of coal plant In the marshalling yard of Rayalaseema Thermal Power Station, coal loaded Broad Gauge open wagons will be unloaded in to hoppers by two nose side discharge wagon tipplers working on the main track. Side arm charges have been provided for each of the wagon tipplers to work as a wagon–marshalling machine. The charger is mounted alongside the main rail-track and runs on its own track parallel to main track to prevent the roll-track of wagons on to tippler platform during tipping cycle. Clickingstops are provided both on inhaul and out haul side of main rail track .Wagon tipplers have integral type-weighbridges for weighing wagons. From R.C.C. made hoppers beneath tippler, coal will be replaced by two Vibrating feeders VF-1 to VF-2 and will discharged to conveyor nos. 3A, 3B from the hoppers. Table 1.1 Wagon Tippler Types Type of Wagon BOX BOXN.MKD.II BOXN BOXNHA BOZ OZ O

Height 3161 3225 3735 3450 3154 3037 2836

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Width 3136 3200 3136 3200 2926 3136 3055

Length 14082 10715 10715 10713 13192 14740(PAIR) 14428(PAIR)

1.5 Wagon Tippler Wagon tipplers are used to discharge broad gauge open rail wagons. They have a rail table mounted on a rotary support structures which can lift and tilt wagons to an angle of about 135° at various processing plants such as power, steel, cement and for relocating the bulk material like core,

Fig.1.2 Wagon tippler

Iron- ore, lime. A Rota side wagon tippler has a variable size domain, ranging from 90 to 110 tones shown in Fig1.2. These are different kinds of wagons of variable height, width and length. However they can be handled skillfully by the Rota side wagon tippler manufacture by TRF. Over 60 wagon tipplers manufacture by the company provide trouble free service to customers across India. These tipplers have the capability to unload 20wagons per hour, making this machine sought after and dependable equipment for handling bulk material. 1.6 Side Arm Charger The side Arm charger runs on its own set of rails beside the tippler rail track and is parallel to it. It is fitted with an extended arm at its outer end which is an automatic coupler. It couples to the front of the wagon to draw a single loaded one to position on to tippler platform, or to

Fig.1.3 Side arm charger

Draw the entire rake of loaded wagons. It also has got a pusher pad mounted on forward face of its arm by which it can push on the rear of an empty wagon already being unloaded by the wagon tippler. The arm is capable of being raised retracted to clear the tipper structure with wagon on to it during tipping operation and can move in to position between tipping cycles. 1.7 Dust Suppression System The dust suppression system at wagon tippler employs the principle of spraying chemical solution on the dust generation points – either side of hopper and top of wagon. The sprays at these locations start at different points of time with the help of 4

solenoid valves which are controlled by timers. Water is received in a 4.5m³ capacity RCC tank near wagon Tippler Complex. MST compound is mixed with water at the

outlet of feed water pump

in the ratio of 1:3750(chemical: water by weight). This solutions thus formed is Fig.1.4 Dust Suppression system

stored in a solution tank of capacity 470lts.

Solution pumps deliver this solution to respective wagon tipplers for spraying on either side of the hopper. 1.8 Programmable Logic Controllers A programmable logic controller is a digital computer used for electromechanical processes, such as control of machinery on factory assembly lines, amusement lights, or lighting fixtures and in many industrial machines such as packaging and semiconductor machines. Unlike general-purpose computers, these are designed for multiple inputs and output arrangement, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. 1.8.1 Inputs and outputs of PLC Inputs:  Auxiliaries.  On and off Push Buttons. Outputs:  Lamps & Machines 1.8.2 Advantages of PLC 

Reduced space.



Energy saving and easy of maintenances.



Modular replacement.



Easy trouble shooting. 5

CHAPTER 2 WAGON TIPPLER AND SIDE ARM CHARGER OPERATION 2.1 Description of Wagon Tippler and Side Arm Charger Side discharge wagon tippler is suitable to handle BOXN MARK-II, BOXN, BOX/BOX C, ‘O’ TYPE IN PAIR wagons. The weigh bridge is equipped with an indicator, recorder for printing gross & tare weights on internal paper roll. The angle of tip achieved by the tippler is approximately 1500 & 00angle of the side of the wagon if operates automatically at the following time cycle. Table 2.1 Wagon Tippler timing cycle -

Placement of Wagon Weighing of wagon Tippling operation Pause Return Weighing Total

59 seconds 46 seconds 5 seconds 5 seconds 29 seconds 10 seconds 144 seconds

2.2 Tippling operation The wagon is pushed on to the tippler platform ejecting any emptied wagon previously occupying it & is then weighed. There after the rotation commences, the rail platform is lifted from its supports and as a result of the offset pivot, the wagon tilts slowly until it rests against the longitudinal side beam. The rotation continues & before the platform has attained 900 the tippler top clamp beams clamp the top of the wagon with the help of a hydraulic cylinder, thus holding the wagon. When the platform has rotated by approximately 1500 the fully tipped position is reached, and the tippler halts. After a short pause to allow the contents of the wagon to be discharged the tippler rotates in the opposite direction &returns the now empty wagon which is then weighed & waits ejecting by the arrival of the nextwagon. The equipment is designed to operate on 415V, 3phase, 50Hz supply. 2.3 Tippler parts The tippler arrangement mainly comprises of the platform, end frames & pedestal bearings, tippler drive, side beam and limit switches.

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Platform: The platform is a bridge shaped structure which carries a section of the rail track through the installation. It has a length sufficient to accommodate the wagons to be tipped. At rail level, the platform rests directly on the tippler foundations but it is lifted off by the weigh bridge structure, for weighing operation or rail table supports and the end frame toe rollers for the tipping operation. End Frames and Pedestal bearings: The end frames are heavy steel structures, roughly semicircular in shape, which rotate on pedestal bearings located at above & frame side of the platform. When rotated they pick up the platform with the wagon on it, which is inverted over the concrete hoppers so that the contents are discharged. Reversal of the rotation then returns the platform& wagon to rail level. The end frames are counter-weighed to balance part of the weight of the wagon & platform. End Frame drive: The drive shaft carries a rack pinion, which engages with racks mounted to the periphery of both the end frames. The shaft is driven by an electric motor, through helical gear box & spurs gearing. The arrangement provides a means of rotating the end frames, as described above. The drive assembly incorporates electromagnetic brake automatic in operation, which holds the end frames against any movement except that provided by the electric motor. Side beam: This is an arrangement of transverse & longitudinal beams, which support the weight of the wagon during the tipping operation & so prevent it from falling off the platform. The side beam is directly supported on the end frames. Tippler Drive: It should be required to disconnect the tippler-driving shaft, first it need to bring the tippler to a state of balance, otherwise the machine will swing rapidly upon its pivots as soon as the coupling bolts are removed. To balance the tippler, release the tippler-

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drive brake by hand and let the machine turn until it is in equilibrium, where upon the shaft may safely be disconnected. 2.4 Necessary working conditions of wagon tippler a. Overrun limit switch The operating leveler of this switch is activated by twin-strikers mounted on an extension of the tippler pivot shaft. Operation of the switch 

Rotate the tippler to its normal “TIPPED” position.



Set one striker so that any further rotation of the tippler in the “TIPPED” direction will trip the switch.



Rotate the tippler to its normal “DOWN” position.



Set remaining striker so that any further rotation in the “DOWN” direction will trip the switch.

To reset manually 

Release the hydraulic brake of the tippler drive-unit & let the tippler rotate by gravity to within the limit of the auxiliary current gear limit switch.



Actuate by hand the operating –leveler of the overrun limit switch.

b. Auxiliary current gear limit switch Auxiliary current gear limit switch is coupled with pinion shaft. It consists of various cams, which not only dictates the limit positions of the drive, but also carries out switching duties at points between the extreme positions. These cams are adjustable and shall be set manually considering end points of the operation. This limit switch consists of gears, which in turn operates cams. The ratio gears are selected such that it fulfills total travel of drive well within limits. c. Photo cell It consists of two components mainly transmitter and receiver. Transmitter at the rail track and receiver at the top line. If there is any interruption in signal between transmitter and receiver the operation haults .The interrupt may be due solid particles

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or dust particles. So even small dust particles may cause interruption of the signal and leads to tippling failure. d. Weighing the loaded wagon If weigh bridged is installed with the tippler, weighment of loaded wagon is to be carried out as described in the weighbridge manual separately. e. Tippling the wagon After weighment of the loaded wagon, press & release the “TIP” push button. The tippler along with loaded wagon rotates empties & wagon at its full tipping angle and returns automatically to its normal rail level & stops. f. Weighing the tippled wagon Weighment of empty wagon has to be done as described in the weighbridge manual separately. 2.5 Emergency condition a. Making an emergency stop: Press & release the “STOP” push button, during cycle of operations of wagon tippler to stop the tippler operation during emergency. While tippler is rotating either in tip direction or return direction, the tippler stops immediately. b. Completing an interrupted cycle: The wagon tippler stops in between during its cycle of operation, if emergency stops push button is operated or due to power failure. Such incomplete cycle has to be completed first to continue further continuous operations. If the tippler was stopped during its return cycle, press & release its “RETURN”, push button. The tippler returns to rail level & stop. If the tippler was stopped in forward “TIP” direction or while the wagon was getting emptied, press & release the “RETURN” push button. The tippler returns to rail level & stops. Next, press the “TIP” push button for normal automatic tipping cycle. The tippler should not be operated with inching motion as it can cause damage to motor.

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2.6 Charger Drive Variable displacement A4VG180 pump is used for hydro motor and control through amplifier and potentiometer to obtained desired flow from the system. For coupler released system, oil flow is available from boost pump of A4VG180 pump. System is equipped with hand pump, float switches, return line filters, air oil cooler etc., for safety and proper operate of the system. Charger drive System: As soon as electric motor TP No.5 is switched on, boost pump of A4VG180 will start delivering oil. Boost pump will fill up complete pipe lines, pump housing and maintain 25 bar pressured in the line. Excess oil will return to the tank through boost pressure relief valve through air oil cooler TP No.26 and return line filter TP No.28. Boost pump filling oil through filter to ensure supply of cleaned oil into the main pump. Charger Drive Operation: A rake (train) of 20 nos. of eight wheeler loaded wagons is pushed by locomotives on tippler track on inhaul side such that first wheel of leading wagon is placed at inhaul waiting position. Now locomotive is un-coupled from rake and goes back to bring another rake of wagons. The side arm charger arm is lowered in front of leading wagon through hydraulic cylinder about 2 meters away from the leading wagon. The charger moves with fast acceleration up to slow speed towards leading wagon, till charger coupler engages with coupler of leading wagon automatically and stops in position. Mechanical stopper provided on inhaul side of wagon tippler are normally in applied condition. Before the rake of wagons is pulled further, the mechanical stoppers on inhaul side are opened automatically. The whole rake is pulled by side arm charger with slow accelerations up to forward top speed. Also the whole rake is stopped by side arm charger with slow deceleration & after stopping the rake of wagons the leading wagon is decoupled manually from rake. Mechanical stoppers on incoming side of wagon tippler closes automatically after wagon passes through stopper. For central location indication, wagon on table limit switch & groove is provided on rail at tippler table.

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Also, during placement of loaded wagon the charger pushes previous empty wagon on rail table through buffer provided exactly opposite to coupler. The centre placement of loaded wagon tippler table is governed by fourth wheel position from centre line of tippler at 5400mm for Box wagon and at 4262mm for Box ”N” wagons. After placement of wagon on tippler table, the sidearm charger arm coupler is uncoupled by hydraulic cylinder & wagon is disconnected from arm coupler. The side arm charger moves further with fast acceleration up to forward top speed, after a pause with arm in lowered position, pushing empty wagon or rake of previous empty wagons by buffer up to outhaul “RETURN POSITION” of side arm charger, clearing rail table area for tippler to tip. As soon as wagon is uncoupled from side arm charger coupler, gross weighing of loaded wagon is carried out by weighbridge provided underneath rail table and recorded automatically. As soon as weighing is over and side arm charger reaches outhaul “RETURN POSITION”, the rotation of tippler rail table starts. The hydraulic clamps start clamping at different angle for different wagons and holds wagon firmly on tippler table. Before wagon is clamped the rail table starts tilting towards side beam in the direction of rotation and resets on the side beam pads. After the wagon is tipped at 1500 max & brought back to its initial position with empty wagon, tear weight of wagon is recorded through load cell weighing bridge which in turn gives net content discharged to hopper[1]. During this period the arm of the side arm charger at out haul “RETURN POSITION” gets raised to 800 from horizontal position by hydraulic cylinder & charger travels back with fast acceleration up to return top speed towards inhaul “WAITING POSITION” stopping with fast deceleration about 2mtrs. Distance away from next leading wagon coupler. Here arm gets lowered to horizontal & travel further towards next leading wagon tip engage & pull further for next cycle of operation.

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CHAPTER 3 PLC AND ELECTRONIC CARDS 3.1 Programmable Logic Control Control engineering has evolved over time. In the past, humans were controlling the systems. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most recent revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls. PLCs have been gaining popularity on the factory floor and will probably remain Predominant for some time to come. They are used mostly because of the advantages they offer. 

Cost effective for controlling complex systems.



Flexible and can be reapplied to control other systems quickly and easily.



Computational abilities allow more sophisticated control.



Trouble shooting aids make programming easier and reduce downtime.



Reliable components make these likely to operate for years before failure.

3.2 Ladder Logic Ladder logic is the main programming method used for PLC’s. As mentioned before, ladder logic has been developed to mimic relay logic. The decision to use the relay logic diagrams was a strategic one. By selecting ladder logic as the main Programming method, the amount of retraining needed for engineers and trades people was greatly reduced. Modern control systems still include relays, but these are rarely used for logic. A relay is a simple device that uses a magnetic field to control a switch, as pictured in Fig. 3.1. When a voltage is applied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch. The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized. Relays are normally drawn in schematic form using a circle to represent 12

the input coil. The output contacts are shown with two parallel lines. Normally open contacts are shown as two lines, and will be open (non-conducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting).

Fig.3.1 A simple relay controller Relays are used to let one power source close a switch for another (often high current) Power source, while keeping them isolated. An example of a relay in a simple control application is shown in Fig 3.2. In this system the first relay on the left is used as normally closed, and will allow current to flow until a voltage is applied to the input A. The second relay is normally open and will not allow current to flow until a voltage is applied to the input B. If current is flowing through the first two relays then current will flow through the coil in the third relay, and close the switch for output C. This circuit would normally be drawn in the ladder logic form. This can be read logically as C will be on if A is off and B is on. The example in Fig 3.1 does not show the entire control system, but only the logic. When we consider a PLC there are inputs, outputs, and the logic. Fig 3.2 shows a more complete representation of the PLC. Here there are two inputs from push buttons. We can imagine the inputs as activating 24V DC relay coils in the PLC. This in turn drives an output relay that Fig.3.2 A PLC illustrated with relays 13

switches 115V AC, which will turn on a light. Note, in actual PLCs inputs are never relays, but outputs are often relays. The ladder logic in the PLC is actually a computer program that the user can enter and change. Notice that both of the input pushbuttons are normally open, but the ladder logic inside the PLC has one normally open contact, and one normally closed contact. Do not think that the ladder logic in the PLC needs to match the inputs or outputs. Many beginners will get caught trying to make the ladder logic match the input types. Many relays also have multiple outputs (throws) and this allows an output relay to also be an input simultaneously. The circuit shown in Fig 3.3 is an example of this, it is called a seal in circuit. In this circuit the current can flow through either branch of the circuit, through the contacts lapelled A or B. The input B will only be on when the output B is on. If B is off, and A is energized, then B will turn on. If B turns on then the input B will turn on and keep output B on even if input A goes off. After B is turned on the output B will not turned off.

Fig.3.3 A seal-in circuit 3.3 Programming The first PLCs were programmed with a technique that was based on relay logic wiring schematics. This eliminated the need to teach the electricians, technicians and engineer

how

to

program

a

computer, but this method has stuck and it is the most common technique for programming PLCs today. An example of ladder logic can be seen in Fig3.4. To interpret this diagram imagine that the power is on the vertical line on the left hand side.

Fig.3.4 A simple ladder logic 14

On the right hand side is the neutral rail. In the Fig there are two rungs, and on each rung there are combinations of inputs (two vertical lines) and outputs (circles). If the inputs are opened or closed in the right combination the power can flow from the hot rail, through the inputs, to power the outputs, and finally to the neutral rail. An input can come from a sensor, switch, or any other type of sensor. An output will be some device outside the PLC that is switched on or off, such as lights or motors. In the top rung the contacts are normally open and normally closed. This means if input A is on and input B is off, then power will flow through the output and activate it. Any other combination of input values will result in the output X being off. The second rung of Fig 3.4 is more complex, there are actually multiple combinations of inputs that will result in the output Y turning on. On the left most part of the rung, power could flow through the top if C is off and D is on. Power could also (and simultaneously) flow through the bottom if both E and F are true. This would get power half way across the rung, and then if G or H is true the power will be delivered to output Y. Structured Text programming has been developed as a more modern programming Language. It is quite similar to languages such as BASIC[2].

Fig.3.5 An example of sequential function chart 3.4 PLC connections When a process is controlled by a PLC it uses inputs from sensors to make decisions and update outputs to drive actuators, as shown in Fig 3.5. The process is a real process that will change over time. Actuators will drive the system to new states (or modes of operation). This means that the controller is limited by the sensors available, if an input is not available, the controller will have no way to detect a condition. The control loop is a continuous cycle of the PLC reading inputs, solving the ladder logic and then changing the outputs. Like any computer this does not happen instantly. Fig

15

3.6 shows the basic operation cycle of a PLC. When power is turned on initially the PLC does a quick sanity check to ensure that the hardware is working properly. If there is a problem the PLC will halt and indicate there is an error. For example, if the PLC backup battery is low and power was lost, the memory will be corrupt and this will result in a fault. If the PLC passes the sanity checks it will then scan (read) all the inputs. After the inputs values are stored in memory the ladder logic will be scanned (solved) using the stored values - not the current values. This is done to prevent logic problems when inputs change during the ladder logic scan. When the ladder logic scan is complete the outputs will be scanned (the output values will be changed). After this process the system goes back to do a sanity check, and the loop continues indefinitely. Unlike normal computers, the entire program will be run every scan. Typical times for each of the stages are in the order of milliseconds

Fig.3.6. A separation of controller and process

Fig.3.7 The scan cycle of a PLC 3.5 Ladder Logic Inputs Inputs are easily represented in ladder logic. In Fig 3.7 there are three types of inputs shown. The first two are normally open and normally closed inputs, discussed previously. The IIT (Immediate Input) function allows inputs to be read after the input scan, while the ladder logic is being scanned. This allows ladder logic to examine input values more often than once every cycle 16

Fig.3.8 Ladder logic inputs for PLC 3.6 Ladder Logic Outputs In ladder logic there are multiple types of outputs, but these are not consistently available on all PLCs. Some of the outputs will be externally connected to devices outside the PLC, but it is also possible to use internal memory locations in the PLC. Six types of outputs are shown in Fig 3.8. The first is a normal output, when energized the output will turn on, and energize an output. The circle with a diagonal line through is a

normally on

Fig.3.9 Ladder logic outputs When energized the output will turn off. This type of output is not available on all PLC types. When initially energized the OSR (One Shot Relay) instruction will turn on for one scan, but then be off for all scans after, until it is turned off. The L (latch) and U (unlatch) instructions can be used to lock outputs on. When an L output is energized the output will turn on indefinitely, even when the output coil is deenergized. The output can only be turned off using a U output. The last instruction is the IOT (Immediate Output) that will allow outputs to be updated without having to wait for the ladder logic scan to be completed. 17

3.7 Applications of PLC Systems In Industry, there are many production tasks which are of highly repetitive nature although repetitive and monotonous, each stage needs careful attention of operator to ensure good quality of final product. Many times, a close supervision of process causes high fatigue on operator resulting in loss of track of process control. Under all such conditions we can use PLCs effectively in totally eliminating the possibilities of human errors. 3.8 Energy Savings In traditional pumping and HVAC applications, the flow of a system was reduced or increased by the opening or closing of valves and dampers. This method of flow control was reliable and worked well, however significant energy was required for the system. In these systems, although demand decreased, the electric motor remained at full speed requiring excessive energy costs. With the addition of a variable frequency drive, flow control is reached by slowing the electric motor’s speed rather than closing dampers and valves. This method of control often saves significant amounts of energy where the VFD will be paid for in six – twelve months alone on saved energy! The annual cost of energy in an AC motor is as follows: Energy Cost = HP * .746 * (hours used) *(cost of power)/motor efficiency In a pumping or HVAC system, the flow of a system is reduced linearly as the speed is reduced. However, the power is reduced by the cube as shown in the following curves. Since most systems are designed for worst case scenarios and very rarely operate at peak levels, the addition of a VFD can result in substantial energy savings. Notice that a small reduction in speed equates to a large reduction in the power requirement of the variable torque load. From the graphs above it can be shown that a 20% reduction in speed can result in 50% less power consumption. This can result in tremendous energy savings for the typical system.

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Fig.3.10 Flow Vs speed

Fig.3.11 Power Vs speed

3.9 Electronic Card The electronic card is an electrical amplifier for the control of proportional valves without electrical feedback. The amplifier VT3600 is suitable for the control of pilot operated proportional directional valves & direct operated proportional pressure valves without electrical position feedback[3]. Characteristics: 

Four command values adjustable with potentiometers.



Four command value call-ups with LED display.



Differential input,Step function generator



Ramp generator with five ramp times.



Two pulsed current output stages.



Polarity protection for the voltage supply. F

Fig.3.12 An electronic card

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3.9.1 Functional Description With the command value inputs 1to4 command values can be called up by operating the corresponding relays (k1 to k4). The command value voltage is either given directly through the controlled voltage ±9V of the power supply or via an external command value potentiometer. For this inputs ±9V = ± 100% is valid. If these four command value inputs are directly connected to the controlled voltage ±9V four different command values can be set at potentiometer R1 to R4. When using external command value potentiometers at these inputs the internal potentiometers also function as weakness or limiters when these are not set to maximum.Which command value is momentarily called up is indicated by the LEDs H1 to H4. if more than one command value is called up simultaneously the input with the highest number has priority. Examples  If command value 1 & command value 3 are activated simultaneously the command value 3 becomes effective. 

A further output of the card provides a supply voltage for the command value call-ups which can be switched over from +9V to -9V with the relay K6.



Each one of the four commands call-up values has an adjustable ramp time allocated. If no command value is called up the ramp time t5 becomes effective.



All relays on the card are switched with 24V DC.



Additionally, the direct command value input 5 is available for the input voltage 0 to ±6V. Valid is±6V.

The command value input 6 is a differential input (0 to ±10V).If the command value is presented by a separate electronics with a different reference potential this input must be taken care that both signal lines are either separated from or connected to the input. All command values are summated with the correct value and sign before they are connected further. The added ramp generator produces a ramp like output signal. The time constant can be set with the potentiometers “t1” to “t5”. The ramp type given refers to command value jump of 100% & can be according to setting through the selection via jumpers approximately 1s to 5s, if a command value jump smaller than 100% is switched to the input of the ramp generator the ramp time shortens approximately.

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By switching the relay K5 or through an external bridge the ramp time is set to its minimum value (approx. 30 ms).The output signal of the ramp generator runs parallel to the summator & the step function generator produces a polarity dependent constant step signal with the command value voltage which is added to the output signal of the ramp generator. This step function causes the rapid traveling across the overlapping area of the valve. The output signal of the summator is command current value and is led to two current output stages & to the test point “w” on the front plate of the card. A voltage of 6V at current valve test points corresponds to the command valve 100%. A positive command valve signal at the input of the amplifier controls the output states of the solenoid “B”, a negative command value signal the output stage for solenoid “A”. If the command value signal is smaller than +-1% a pilot current of 20ma flows through both solenoids. The actual values of current through the two solenoids can be measured separately at the test point IA (‘solinoid1”) IB (solenoid “B”). Here a current of 800ma corresponds to a voltage of 800V. LED H11 lights up when the syste4m is powered up. LED H12 (ready for operation”) lights up to indicate trouble free operation as long as the internal power supply (9V) is functio0ning properly. There is no short-circuit in the solenoid lines. In the event of a fault, both output stages are immediately de-energized & the signal “ready for operation” 9lED H12 is cancelled. Once the fault has been cleared, the amplifier card is immediately operable & LED H13 lights up again.

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CHAPTER 4 TIPPLING OPERATION 4.1 Tipping operation As soon as the loaded wagon is kept on the main central position by the SAC, the tippling process starts with weighing the loaded wagon which is on the platform by the weighing bridge. The relays or the Bits that are to be energized to release the breaks of the hydraulic motor to start the tipping process is B3:10(0) which is energized only when the enough pressure is applied to the clamps of the tippler & along with this the relays that are to be energized to start the process. The tip push button in the control desk is operated by the operator with which the process starts, i.e. the inputs to the PLC are auxiliary gear limit switch SNRL limit switch and system stop Bit B3:9(2) is to be energized and all the photo cell placed at either ends of the tippler should be cleared and it should be seen that the wagon is at central position exactly without any over traveling which is examined by the O.T.L.S & this also should be energized with which the tippler return interposing relay i.e. output relay 0:8(2) is energized as shown in Fig 4.1.

Fig.4.1 Ladder diagram for tippling

One the motor are to be started i.e. all the three rotors used for the tipping which are also handled by the relays and along with this the motor should be slowed down (or) 22

change its speed automatically at some conditions which is controlled by the LRSC B3:9(14) Bit this also energized with all these relays energized the wagon tippler tipping Bit B3:10(0) is energized and the process goes on. All the above relays are energized at a time if any one of the relay is not energized Emergency stop push button B3:1(0) series with the wagon tippler interposing relays 0:8(1) will energized & the tippling. During the tippling the motor will run at high speed from 10º to 150º but after the 150º the motor automatically slows down and the tippling is done without any accidents taking place. 4.2 Tippler reverse operation After the tippling of the wagon which is lifted by the empty wagon is to be returned and placed at the normal central position which is called the tippler reverse operation. For the tippler reverse operation to start the BIT B3:10(1) should be energized. To the BIT B3:10(1) get energized, firstly the return Push Button on the control desk is energized i.e. (I:3(15) ), TIP-1 manual mode BIT (B3:9(13)) is to be energized along with the Auxiliary Gear Limit RTL (Rail Level Tippler) BIT I:3(0) is energized as soon as all these Input Bits get energized the output bits i.e., the Interposing relay O:8(1) 3R(2) (return interposing relay) &the tippler motor relay I:3(8) are energized & also the motor break I:3(7) is released and the electromagnetic relay is operated are energized with the tip stop P.B&C.D I:4(0) and the Bit B3:10(1) which is the main Bit that is to be energized to continue the tippler return operation is energized. The Auxiliary Gear Limit Switches energized above are for the variations of the speed of the motor during return process at 10º angle the tippler returns with the same speed at the 180º at10º and slows down after 10º to place the wagon slowly on the plat. As soon as the return process is completed & wagon is in the normal position then the emptied wagon is weighted by the weighing bridge to find the resultant weight of the coal transported or tippled for the further applications. The main purpose of tippling the coal in to the hoppers is completed with the above operations of the tippler using advanced technology with cost effective & less duration of the process are given in table4.1.

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Table 4.1 Operation time OPERATION PLACEMENT OF WAGON WEIGHING TIPPLING OPERATION PAUSE RETURN WEIGHING TOTAL

TIME DURATION 59 seconds 3 seconds 39 seconds 5 seconds 35 seconds 3 seconds 144 seconds

Fig.4.2 Ladder diagram for tippling reverse

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CHAPTER 5 CONCLUSIONS This study is carried at RTTP, Kadapa to understand the operation of wagon tippler and side arm charger based on PLC. Most of the wagon tipplers contain electromechanical and electronic gears indicating the control system. Side arm charger couples to the front of the wagon to draw a single loaded one to proper position on tippler platform. The wagon tippler operation is done by using PLC which monitors various parameters of a wagon tippler such as hydraulic motors, drives etc... By using PLC’s faults occurred during the wagon tippler operation can be determined accurately within a fraction of seconds. But in case of relays it takes some time to find where the fault has occurred and for fault clearance so it is a time consuming process, which is eliminated by using the PLC based operations. The total time consumed by the tippler to tipple the coal in to the hoppers is 75 seconds which is a fast process, also the installation cost is less when compared to the relays and power consumed is less. This technology is the advanced version of RELAYS.

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