ABSTRACT Control and Instrumentation in any process industry, can be compared to the nervous system in the human being. In industries and Process plants. Instrumentation makes use of various measuring components designed to suit the process and the purpose. As some of the big industries and process plants needs to control different process variables from remote distance control room, the further measuring, the transmitting, indicating, recording, abnormality alarm system are innovated The current project deals with the "Familiarization and Hands-On-experience with the Distributed Digital Control and Monitoring and Information System" by designing and implementing control logics for lube oil mechanism, monitoring and the study of the single element drum level control. The logic is implemented using the Distributed Digital Control System (DDCS using the Procontrol-P language). INTRODUCTION TO NTPC SIMHADRI NTPC was incorporated in 1975. In the last 30 years, it has grown into the largest power utility of India. NTPC is the sixth largest thermal power generator in the World and the Second most efficient utility in terms of capacity utilization based on data of 1998. NTPC delivers power at minimal environment cost, and achieves it. Right from the stage of its project conceptualization, technology selection to operations, care is taken to preserve the natural ecology and minimize environmental impact NTPC comes to the rescue of about 20 million units of power consumed even day in VP. NTPC Simhadri is providing the ever growing power needs of A.P. the total power generation capacity of NTPC has reached to 3600 MW in A.P with NTPC Ramagundam already generating 2600 MW a day. Location of Simhadri project is near Parawada Village, Visakhapatnam District. A.P. I hi plant is developed near Parawada and 3384 acres of land. is used for the construction of I hernial Plant.
Transcript
ABSTRACTControl and Instrumentation in any process industry, can be compared to the nervous
system in the human being. In industries and Process plants. Instrumentation makes use of various measuring components designed to suit the process and the purpose. As some of the big industries and process plants needs to control different process variables from remote distance control room, the further measuring, the transmitting, indicating, recording, abnormality alarm system are innovated
The current project deals with the "Familiarization and Hands-On-experience with the Distributed Digital Control and Monitoring and Information System" by designing and implementing control logics for lube oil mechanism, monitoring and the study of the single element drum level control. The logic is implemented using the Distributed Digital Control System (DDCS using the Procontrol-P language).
INTRODUCTION TO NTPC SIMHADRI
NTPC was incorporated in 1975. In the last 30 years, it has grown into the largest power utility of India. NTPC is the sixth largest thermal power generator in the World and the Second most efficient utility in terms of capacity utilization based on data of 1998. NTPC delivers power at minimal environment cost, and achieves it. Right from the stage of its project conceptualization, technology selection to operations, care is taken to preserve the natural ecology and minimize environmental impact
NTPC comes to the rescue of about 20 million units of power consumed even day in VP. NTPC Simhadri is providing the ever growing power needs of A.P. the total power generation capacity of NTPC has reached to 3600 MW in A.P with NTPC Ramagundam already generating 2600 MW a day. Location of Simhadri project is near Parawada Village, Visakhapatnam District. A.P. I hi plant is developed near Parawada and 3384 acres of land. is used for the construction of I hernial Plant.
Coal is being drawn from Mahanadi Coal Fields in Orissa drawing over 5 million tonnes of coal every year. The Coal comes to the plant with a rail fine. The water intake for the plant for cooling is done by sea water drawn from 8.9 km away from Bay of Bengal through an intake well sized 9100 m3/h. The plant also gets sweet water from the Eluru canal.The power generated at NTPC Simhadri is bought by A.P. Transco- the power distribution arm of the electricity board in the state. The height of chimney is 275 meter-a record in Asia tor being the tallest factory chimney. Near to this there are two 165 meter cooling towers. I he intake well is again the biggest well constructed in the entire India.The National Thermal Power Corporation (NTPC) Simhadri plant has generated 7000 million units so far during the last financial year at a plant load factor of 92.7%. standing 3rd among the N l'P( stations. Inspired by its glorious past and vibrant present, NTPC is well on its way to realize its vision.
VISION OF NTPC:"A World class Integrated power major, powering India's growth, with increasing global presence."
OPERATION OF THERMAL POWER PLANTCoal from the coal wagons is unloaded in the coal handling plant. This coal is transported up to the coal bunkers with the help of conveyor belts. Coal is transported to bowl mills by coal feeders. Here the coal is pulverized in the bowl mill, where it is ground to a powder form. The mill consists of a round metallic table on which the coal particles fall. This table is rotated with the help of a motor. There are three large steel rollers which are spaced 120° apart. When there is no coal, these rollers does not rotate but when the coal is fed to the table it packs up between roller and the table and this lorces the rollers to rotate. Coal is crushed by the crushing action between the rollers and rotating table. This crushed coal is taken away to the furnace through the coal pipes with the help of hot and cold air mixture from primary air (P.A) fan. P.A fan takes atmospheric air. a part of which is sent to air pre heaters for heating while a part goes directly to the mill for temperature control. Atmospheric air from F.D fan is heated in the air heaters and sent to the furnace as combustion air.
Water from the boiler feed pump (BPP) passes through economizer and reaches the boiler drum. Water from the drum passes through the down comers and goes to bottom ring header. Water from the bottom ring header is divided to all the four sides of the furnace. Due to heat and the density difference the water rises up in the water wall tubes. Water is partly converted to steam as it rises up in the furnace. This steam and water mixture is again taken to the boiler drum where the steam is separated from water (water steam separator). Water follows the same path while steam is sent to upper heaters for super heating. The super heaters are located inside the furnace and the steam is super heated (540° C) and finally goes to turbine.
Flue gases from the furnace is extracted by induced draught (I.D) which maintains balanced draught in the furnace (-5 to -10mm of Wcl) with F.D fan. These flue gases emits their heal energy to various super heaters in the pant house and finally passes through air pre-heaters and goes to electro static precipitators (ESP) where the ash particles are extracted. ESP's consists of metal plates which are electrically charged. Ash particles are attracted on to these plates so that they do not pass through the chimney to
pollute the atmosphere. Regular mechanical hammer blows cause the accumulation of ash to fail on to the bottom of the precipitator where they are collected in a hopper for disposal. I Ins ash is mixed with water to form slurry which is pumped to ash pond.
From the boiler a steam pipe conveys steam to the turbine through a stop valve (which can be used to shut off the steam in an emergency) and through control valves which automatically regulate the supply of steam to the turbine. Stop valve and control valves are located in the steam chest tnd a governor, driven from the main turbine shaft, operates the control valve to regulate the amount of steam used which depends on the speed of turbine and the amount of electricity required to generate.
Steam from the control valves enter the high pressure cylinder of the turbine where it passes through a ring of stationary blades fixed to the cylinder wall. These act as nozzles and direct the team into a second ring of moving blades mounted on a disk secured to the turbine shaft. This second ring turns the shaft as a result of the force of the steam. The stationary and the moving blades together constitute a "stage" of the turbine and in practice many stages are necessary, so that the cylinder contains a number of rings of stationary blades with rings of moving blades arranged between them. The steam passes through each stage in turn until it reaches the end of the high pressure cy Under and in its passage some of its heat energy is changed into mechanical energy.
The steam leaving the high pressure cylinder goes back to the boiler for re heating and returns by a further pipe to the intermediate pressure cylinder. Here it passes through another series of stationary and moving blades.
Finally, the steam is taken to the low pressure cylinders, each of which it enters at the centre flowing outwards in opposite directions through the rows of turbine blades-an arrangement known as double flow-to the extremities of the cylinder. As the steam gives up its heat energy to drive the turbine, its temperature and pressure falls and it expands. Because of this expansion the blades are much larger and longer towards the low pressure ends of the turbine.
The turbine shaft usually rotates Kt 3000 RPM. This speed is determined by the frequency of the electrical system used in this country and is the speed at which a 2-pole generator must be driven to generate an alternating current at a frequency of 50 cycles/sec.When as much energy as possible has been extracted from the steam it is exhausted directly to the condenser. This runs the length of the low pressure part of the turbine and may be beneath or on either side of it. The condenser consists of a large vessel containing some 20.000 tubes, each tube-having 25mm diameter. Cold water from the sea. river, estuary or cooling tower is circulated through these tubes and as the steam from the turbine passes through them the steam rapidly gets condensed into water droplets. Because water has a much smaller comparative volume than steam, a vacuum of
0.8mm is created in the condenser. This allows the steam to reduce down to pressure below that of the normal atmosphere and more energy can be utilized.
From the condenser the condensate is pumped through low pressure heaters by the extraction pump (CEP); which after its pressure is raised to boiler pressure using low pressure and high pre sure heaters which is then fed to boiler using boiler feed pumps. It is passed through further feed heaters to the economizer and the boiler for re-conversion into steam.
Where the cooling water for power stations is drawn from large rivers, estuaries or from the coast, it can be returned directly to the source after use. Power stations sit.ialed on small rivers and in land do not have such vast water resources availability, so the cooling water is passed through cooling towers where its heat is removed by evaporation and is re-used.
UNIQUE FEATURES
> First coastal based coal fired Thermal Power Plant of NTPC.
> Biggest sea water intake-well in India.
> Use of sea water for condenser cooling and Ash Disposal. Asia"s tallest natural cooling towers
and 6th in the world.
> Use of fly ash bricks in the construction of all the buildings.
> Coal Based plant of NTPC whose entire power is allocated to home state t A.P i.
> Use of monitors as Man Machine Interface (MMI) for operating the plant.
> Use of process analysis, diagnosis and optimization (PADO) for the first time.
> Flame analysis of boilers by dedicated scanners for all the coal burners.
> Boiler mapping by acoustic pyrometers.
> Use of Distributed Digital Control and management information system.
> Totally spring loaded floating foundation for all major equipment including transformer and
generator.
> Use of INERGEN as fire protection system for the 1st in NTPC.
> Commissioning of 1st unit in record of 39 months.
Control And Instrumentation In A Thermal Power Plant
Control and Instrumentation in any process industry, can be compared to the nervous system in the human being. The way the nervous system is controlling the operation of \ various limbs of human being. Control and Instrumentation, in the same way, is controlling and operating the various motors, pumps, dampers, valves, etc. and helps to achieve the targets.
Control and Instrumentation is a branch of engineering which deals with various measurement, indication, transmission and control in different technical fields. I he latest developments made in the area of instrumentation are so wide that it has become humanly impossible to master the over-all system individually. Even in instrumentation there are further sub groups now. I he term instrumentation means "A device or combination of devices used directly or indirectly to measure and display a variable."
Instrumentation is a measurement if various parameters with comparison have been using for ages different instruments such as weights, yard sticks, scales, measuring tapes, standard container for liquid measurement e.g. Liter, gallons etc. Each of these equipments is an instrument. Similarly, in industries and Process plants, Instrumentation makes use of various measuring components designed to suit the process and the purpose. As some of the big industries and process plants needs to control different process variables from remote distance control room, the further measuring, the transmitting, indicating, recording, abnormality alarm system are innovated. The process of innovation is marching at a fast rate. In near future. Control and Instrumentation would enter into a more sophisticated stream.
Distributed Digital Control Systems
Distributed Control implies that the actual control and management functions are in fact distributed throughout the entire plant in several processing units.
In such configurations, the plant is divided in many small groups and each group is controlled by a dedicated set of processors and other hardware. The task of measurements, control, operation communications, and sequence controls, etc. are distributed amongst a number of processing units, each incorporating a micro-computer.
These micro-computers are linked via a common communication highway and are configured in a hierarchical command structure. Distributed control thus represents the physical distribution of digital controls among the plant processor and functional distribution of risk associated with component failure. This arrangement provides the capability for implementing high level of automations. The major features and advantages of this distributed hierarchical approach are:• If the computational tasks are shared between the processors, the systems capability is gieatly enhanced.• The system is more flexible.
• If any microprocessor should tail, implications are not catastrophic, only a portion of s stem will not be available.• It is easier to make software change in distributed systems• The units in the system can become standardized• The interlinking of distributed units by a data highway means they can be distributed over a wide area• The availability of color CRT based operator control centers provide more information and guidance of operation for these actions• Control rooms are simplified as all information is available on CRT's
Unit Operation Philosophy with DDCMIS:The unit operation philosophy envisaged calls for the control and monitoring of team
generators and turbine generator and their auxiliaries and ancillary units in all regions of operation i.e start up, normal and shut down operations through color CRT/KBD mounted on the unit control desk(UCD) in the unit control room. In addition, all required conventional hardwired push button stations, hand-auto stations, status indication lamps, indicators, recorders are also being provided as a backup on unit control board(desk-cum- panel) for important drives and parameters to achieve unit control and monitoring in the event of failure/non -availability of CRI s/KBD s redundant system bus controllers etc.
The normal mode of operation for centralized keyboard operation can be entered through CRT/KBD with microprocessor based hardware. The system shall be provided with redundant data bus for communication from CRT/KBD to control system. However, in case of failure of data bus or CR T. the control system shall remain unaffected and same shall be operated through hardwired baek-up conventional push buttons. The operator shall be provided with the indication of some permissive conditions for the major auxiliary such as ID, FD fans etc., through suitable means on the unit control desk. Only critical drives of closed and open loop, both dedicated drive control push-buttons shall be provided with operation enable push button to avoid unauthorized operation of drive/sequence..
Distributed Digital Control and Monitoring and Information Systems
The DDCMIS provides all functions required for the automation of the power plant process like Acquisition and Processing of process data ,Open loop and Closed loop Control, Calculation and optimization of plant performance. Monitoring, signaling, operation and visualization of the process in interactive mode on a monitor or via a conventional push buttons/indicators.
These functions of DDCMIS can be achieved in 2 ways:
• By geographically distributing the hardware.• By functionally distributing the hardware
Geographical Distribution:
In this concept, the hardware is distributed geographically in the plant, i.c the electronics modules are not placed in a central location but segregated in small groups and kept near the respective systems being controlled.( These systems have the advantage of saving a lot of cabling costs as the signals need not be routed to the central control equipment: room). However, this systems concept is not-used in NTPC because of the environmental conditions present in Indian power plants due to which it is difficult to maintain required environment for microprocessor based hardware at many places in the plant.
Functional Distribution:
In this concept, the hardware is kept in a centralized control equipment room but the electronics hardware is functionally divided to perform-the functions independently, i.e failure of one functional group/sub-group does not affect another group/sub-group. This is the concept adopted by NTPC as this needs only one centrally air conditioned room for the electronics modules.
Sub-Systems of DDCMIS:
There are different functional blocks in DDCMIS . They are Measurement System(for CI.CS, OLCS, IS), Control System(CLCS. OLCS), Information Systems, System Bus. Man - Machine Interface, Sequence of events recording systems, Master and Slave Clock Systems.The three systems Closed Loop Control System (CLCS), Open Loop Control System (01 CS) and Information System (IS) are connected to the system Bus. However, all the three systems are independent of each other in all respects like functional independence, hardware independence and cabinet location independence.
Measurement System of DDCMIS:
The measurement system shall perform the functions of signal acquisition conditioning and signal distribution. Three measurement systems have been envisaged, one for Closed Loop Control System (CLCS), one for Open Loop Control System (OLCS) and one for Information System (IS) through Signal Acquisition System (SAS).The measurement system accepts the following inputs: a. Analog Inputs:i. 4-20 mA, DC input
Maximum input resistance to be 50 ohm . 24 V DC loop power for 4-20 mA 2wire/4-wire transmitters shall also be on part of the system.
ii. RTD Input:The system shall be capable of recurring 100 ohms 3wire/4w ire platinum RTD's and 53
ohm 3wire or copper RTD's
iii Thermocouple InputsThe system accepts thermocouple of the type E.J.K.. R and I cither directlywired to it or through JC boxes mounted locally.
b. Binary InputsThe system accepts binary inputs in the form of Normally Open/Normally Closed
/Change Over Contacts. The contact interrogation voltage is 48V which will also be supplied by the system.
c. Pulse InputsThe system accepts servo based pulse or rectangular wave or sinusoidal wave form or
potential free contacts.
Redundant Transmitters For Control System:Multiple transmitters with monitoring circuits are used to ensure thai the failure of a
single transmitter does not lead to malfunction of reduced availability of the related control system.
Dual Measurement System:
Two independent transmitters preferably connected to separate tapping are employed. The outputs of these transmitters are continuously monitored for excessive deviation. Such a deviation is logged by DDCMIS and alarmed on Unit Control Panel. Automatic change over provision is made available from unhealthy transmitter to healthy transmitter during normal operation of control loops without affecting the status of control loops. If other transmitters are not in working order, the control loop is transferred from auto to manual mode. Facility is provided for selecting the output of any transmitter for control purpose from the control desk. Facility is provided for defeating monitoring circuit.
Triple Measurement System:
Triple measurement system is provided for critical measurement systems like furnace drafts, feed water flow, throttle pressure, turbine first stage pressure, etc.Three independent transmitters connected to separate tapping point arc employed. The system auctioneers the three signals to determine the median value signal which is used for control purpose. The control loop trips to manual when any two of the three transmitter signals fails. Appropriate messages/indications is displayed/logged at DDCMIS. The conditioning, high deviation
between any transmitters, any value and the median value and any transmitter failure is displayed/logged at DDC MIS. Adequate signaling indications are provided to immediately nn.\ which of the three transmitters are working. Facility is provided to select an> of the transmitters or the median value of the control from control desk. Facility is provided to \defeal the deviation monitoring circuit.
Types of Controllers:
Generally there are two types of controllers available.• Single Loop Controller• Multi Loop Controller
Single Loop Controller:
In case of single loop controller, dedicated controller hardware is envisaged for each loop of CLCS and OLCS. Here all the Signal Conditioning and processing functions are implemented in separate hardware, independent of controller availability. Further this alternative drive control modules are used for all power operated drives covered and OLCS (one for each drive) to get the advantages of built in monitoring, detailed status information, easy trouble shooting, etc.. and enable the use of miniaturized control room tiles independent of controller availability with equipment protection available for remote manual operation.
Multi Loop Controller:
In case of multi loop controller more than one loop of CLCS or OLCS can be implemented in a controller. Here all signal processing are performed in the controller and remote manual operation through miniaturized control room tiles is routed through the controllers. However, in certain systems a drive level card is used as in the case of single loop controller to get the advantage of built in monitoring detailed status information, easy trouble shooting, etc.. This will also enable the use of miniaturized control room tiles independent of controller availability with equipment protection available for remote manual operation. As many loops are clubbed into one controller, a controller failure will lead to the failure or non-operability for many loops and these controllers are implemented in redundant configuration.
PROCONTROL-P"Pro control-P" — Distributed Digital Control is a microprocessor based intelligent
remote multiplexing system which allows complete plant automation and provides the operating personnel with the necessary tools to increase plant availability and efficiency. This is based on modular electronics with programmable processors, data acquisition and remote multiplexing.
The control system is configured in a geographically centralized but functional distributed architecture to enable plant operation from a central control room.
System Overview and Control Philosophy:
The system allows to tighten the scope of control hardware to the particular control strategy and operating requirements of the process. Also, the Procontrol-P provides system uniformity arid integrity for:• Signal Conditioning and transmission• Modulating controls• On/Off logic / Sequential Controls• Individual and process protection• Overall Man-Process interface
The controllers, binary / analog input /output modules are housed in local buses / local stations permitting the realization of self contained automation islands. These local stations are connected to the data bus system (interplant bus) which serves as a transport medium for signals between various local stations and the upstream-connected Man Machine Interface System (MMI).
System configuration:This configuration drawing represents all the constituents of the control and monitoring
system.
Signal conditioning system:The hardware equipment in this system represents the front end interlace to the plant. I he
tasks involved are signal acquisition, monitoring and conditioning. The automation stations accept automatic commands from either the level controllers or manual commands from either hardwired A/M stations or from VDC consoles via data bus.
Data transmission system:
The data transmission of PROCONTROL-P is performed with two level serial bus systems with time division multiplexing.• Local bus• Intra plant busThe local bus plant is a back plane serial bus interconnected to all inputs, outputs and processing electronic modules, which is a part of a local stationThe intra-plant bus interconnects its related local buses via co-axial cables. This interconnection provides galvanic separation and dynamic data transfer. The local buses can be grouped together at the same location or geographically distributed over a large distance.
Hardware:
The PROCONTROL-P has two basic types of processing modules.• Individual control module.• Universal processing module.
These modules are connected to the local bus. whereby one or several of 'hem can be connected to the same bus or to various ones.
Individual control modules:
The individual control module is implemented to control, supervise, monitor and protect individual final control element of any type (ON / OFF or Modulating), such as salves, pumps, fans etc. This module is equipped with a microprocessor and forms with its built in inputs / outputs a compact and dedicated control entity to control each final control element. The inputs allow gather data on the position and status of final control element as well as the status of its related power amplifier.
The outputs allow to provide positioning or ON /OFF orders either with a 4-20 mA or contact signal. A serial input / output interface to the local bus is available to receive process signals and to interface with the control room operator station.
Universal processing module:
The universal processing module is implemented for two different types of application, a> Automation unit, functionally super imposed on the individual control module.> Processing unit, performing combined individual control and automation functions.The universal-processing module has a large fast programming capability, which allows performing long and complex control functions. This universal processing module can perform all kinds of control algorithms either binary (AND, OR, flip flop, etc.) or analog control function (ADD, SUBTRACT, PID etc.) or any macro function, which is a combination of various basic functions.
Input / output modules:
PROCONTROL-P has various modules for input / output capability which can be connected to any local bus. These modules can handle any type of signal, such as single, double throw contacts, thermocouples, RTD's, Milliamps signal etc. or to provide milliamp. voltage, electronic or contact output signals.
The input modules provide for a wide range of functions such as 1 ms sequence of events, supply of individual power to contacts, transmitters. These modules also have an extended and integrated monitoring capability to detect disturbances that may occur at the module, transmitter level (e.g. out of range) or in the field cabling.
Man machine interface:
The man machine interface comprehensively caters to the function ot CRT based VIMi and data acquisition system (DAS) for the complete plant. It is the actual interlace between the plant management, operating / maintenance, personnel and the process as well as control system The functions of these interface includes:■ Operators station■ Plant monitoring systems■ Engineering station
The MM I is realized in redundant 3-bit workstation environment. The MMI resides on lie data bus system and serves as a pool for co1 lection of process and processed data for control purposes.
Operator station:
The operator station consists of two techniques. Conventional station with push buttons, I imps and indicators and CRT based stations.
The conventional station as well as the CRT based station provides the operator with the possibilities to give orders to the individual control loop and automation loops as well as to supervise each loop in regard to the control on disturbance status.
The CRT-based stations provide the possibility to tune individual control loops and to also perform interface-monitoring functions. Such simple indications functions, as tabulation, bar charts, trends, mimic displays or single protocols.
Plant monitoring system:
This plant monitoring system informs the plant personnel of over all plant behavioi and historical data. It provides via CRT, printer, hard copy unit or plotter plant real and non-real time data or calculated data, such as:■ Plant efficiency■ Life time calculation and monitoring■ Early detection of beginning deterioration of process components■ These data are indicated either in tabulation, bar chart, curve or mimic display form.
Engineering station:
The engineering station allows to dialogue and record control system internal disturbances. This station also allows to develop programs, control schemes directly via CRT / keyboard.
TROUBLESHOOTING:
The basic trouble shooting procedures in PROCONTROL P consists of replacing disturbed modules or programs with corresponding new ones, since disturbances are limited to the board level. This procedure can be executed on a 24hrs basis without the need to switch off the control system or shut down the corresponding process/plant. The application of this procedure is the result 01 the implementation of the following techniques:• Extended partitioning• Extended use of firmware• Use of standard modules• Hot repair capability• Active 'One’
These techniques guarantee Active control, protection of functions’ loops, to remain operational during the entire trouble shooting procedure.
To trouble shoot process safety functions without loosing the proper functioning ot the corresponding safety function or tripping the related process, e.g. boiler, turbine.
To ensure operation and functional control system integrity during the entire lite of the control system with maintenance personnel having no education on microprocessor or computer techniques.
Benefits of ProControl-P:• Degree and extent of automation can be exactly adapted to the process and operating requirements• Automation islands can be started up one after the other from the lower level up to the highest level• Process redundancy requirements can be exactly duplicated in the control system providing control system transparency• Processing capability is not limited since the control functions requiring more processing capability as available in one universal processing module can be programmed and simultaneously processed by various modules at the same time• Extended partitioning replaces many applications redundancy of control components. In most cases this extended partitioning results in even better plant availability than redundancy.
Description of programming unit:
The programming procedure is described as below: 1. Generation and storage of all instructions in the programming module. Instructions alreadywritten can then be erased, moved or modified individually or in sets if necessary.
2. By pressing the relevant function button on the programming unit, its memory content, are transferred to the test memory inserted on the processing module.According to the selection, the processing module now operates in conjunction with the test memory or with its own EPROMs.
3. If the function read into the test memory is proven in operation, the corresponding instructions can be transferred to the EPROMs of the processing modules. For this purpose the EPROMs may first have to be erased and then inserted in the base provided in the programming unit for program acceptance
4. For return documentation or program modification the contents of the EPROMs can be transferred from the processing module to the test memory, from there to the programming unit and then via a bidirectional, serial interface(RS 232) to a magnetic tape unit or printer.
The EPROMs can however also be inserted in the programming unit and their contents transferred to the memory of the programming unit for copying or documental ion purpose 5. The return documentation of a memory content is made in each case via a printer or a magnetic tape unit connected to the programming unit
Structure of Language:The graphical symbols used in functional control diagrams form the basis lor Procontrol
language. These symbols define a function element in each case, which links the various signal inputs to the outputs.
The instructions for every function element must be given in the following sequence:1. Call-in for the desired function element.2. Allocation of signal addresses to the inputs of the function element if required.3. Allocation of numeric values to the inputs of function element required.4. Allocation of outputs of the function element to signal addresses.
Each instruction consists of instruction line number and instruction code. 1 he instruction code consists of four hexadecimal characters. The first hexadecimal character on the left is called the prefix; it determines the significance of the instruction and the three following digits. The
Significance of the three digits is as follows:
> When calling the function element they identify the element.> For allocation of input and output signals the two digits on the right represent the signal address. The second digit from left is always zero(O) for analog signals: for binary signals it denotes the required bit(O-F) within the word.> For allocation of numeric values these three digits represent the numeric value as a hexadecimal value.
The programming language covers the range from simple, binary operations to the complex, analog function. Basic function elements are the basic elements the control systems, eg. AND. OR, Memory, Multiplier rooter etc.
Multifunction elements are frequently recurring, complex circuits consisting of basic function elements, eg. Drive control function, Pi-controller with/without manual station, etc. In contrast to the basic function elements user can create and use any multifunction elements.
Processing of binary and analog signals for logic control, modulating control and computing functions according to instructions in the programs memory) (EPROM). Parameters can be changed online without program modification.
DESCRIPTION:
Contains:o 2 sockets on the front for the operation with simulation and programming units,o 1 code switch on the front for setting the module address.o EPROM's for definition of basic functions specified in the programming language PROCONTROL PI3.o EPROM's for 2k or 4k instruction lines for definition of multi-functions specified in the Programming language PROCONTROL P13. o EPROM's for 2k or 4k application-specific instruction lines for definition of processing of selected local bus signals, o RAM for storage of 256 parameters values retained in the event of voltage failure.
Conversion of digital local bus signals into binary signals. 0/24V. All module circuits are galvanically connected to the supply voltage. Also serves the purpose of controlling electronic module inputs, relays and lamps. DESCRIPTION: Contains:o It consists of 16 functional units. Consequently 16 different binary signals may be issued at the same time, o 2 code switches on the front for setting the module address.
3. MODULE DESCRIPTION: ANALOG INPUT FOR VOLTAGE AND CURRENT SIGNALS.
MODULE NO: 659IA1AA/659IA1BA
FAMILY: PROCONTROL P13
CROSS REF: 70EA01
APPLICATION:
Conversion of load independent currents. -20mA to 0 to +20mA or of voltages.- 10V to 0 to + 10V into digital local bus signals. All module circuits arc galvanically connected to the supply voltage.
DESCRIPTION:
Contains:
o 4 identical functional units.o 4 binary inputs 24V d.e. for the signal 'measured value disturbed'.o 2 code switches on the front for setting the module address.o 4 wire jumpers on the module for selection between 20mA and 10V.
4. MODULE DESCRIPTION: 16 CHANNEL BINARY INPUT MODULE FOR CONTACTS
Conversion of signals from 8 double throw contacts or 16 single throw contacts into digital local bus signals. The module generates an auxiliary voltage ol 48V dc for contact interrogation. All module circuits are galvanically connected to supply voltage. DESCRIPTION: Contains:
o 16 identical functional units.o Short circuit proof supply to contacts.o 2 code switches on the front for setting the module address.
Conversion of digital local bus signals into outputs with potential free contacts. This serves the purpose of controlling electronic module inputs, relays and lamps.
DESCRIPTION:CONTAINS:
o 16 identical functional units.o 2 code switches on the front for setting the module address.
6. MODULE DESCRIPTION: TEST MODULE FOR SIGNALS.MODULE NO: 659TS5AA FAMILY: PROCONTROL P13 CROSS REF: 70SL05 APPLICATION:
For. indicating either 1 analog or 16 binary signals being transmitted on the local bus. 2 code switches are used to select the desired signal. The test module can also be used as an input module, in that any required signal can be generated (simulated) under the set address The module can be inserted in any desired location in the sub-rack.
DESCRIPTION: Contains:
2 code switches on the front for setting the module address, 16 switches for simulating 1 analog or 16 binary signals, 16 LED's for indicating 1 analog or 16 binary signals, Key for transmit/receive change over, LED for indicating transmit mode of operation.
Local Bus:
The local bus mainly contains the bus traffic director 70BV01 and the bus circuit board 70BL01. The bus traffic director controls the signal transmission sequence while the bus circuit board provides the means by which the transmission takes place.The local bus is designed as a PCB type 70BL01 and transmits the binar\ signals and digitaliz.ed 16 bit analog signals in serial and cyclic mode between the modules connected to the local bus.
APPLICATION:Controls exchange of signals between modules connected to the local bus. Two modules
70BV01 are necessary for local bus systems with redundant bus traffic directors
DESCRIPTION: Contains:o Plug-in jumpers for selecting the cycle period and therefore the number of addresses.
— 5ms 064 addresses— 10ms 128 addresses— 20ms 256 addresses o Supply for bus lines
o LED for indication of operationo Jacks for forced, brief interruption of address transmission
Description of Functional Elements:
❖ TAZK: Push button selection with Target Value. This multi-function is used for selection of push-button and/or selection of a target value
❖ BEG: Limiter—This basic function is used in cases where the signal of the input is required to appear at the analog output as long as it is within the limits.
❖ MUL: Multiplier - This basic function is used for the product of the two input signals to appear at the output
❖ TBT: Insert Element for Disturbance Bit -This basic function is used for the output of analog signal to the local bus. Disturbance bit is added to the signal at input to be available .it the output.
❖ MOK: 1-Shot Constant — This basic function is used to result in a logic puise output of length when a change from logic 0 to logic "1 state occurs at the input signal.❖ SWV5: Set Point Station—This is used to create and vary manual!) and automatically an analog value, which can serve as set point, target value, gradient, limit value, etc. on a! control levels. The analog signal will thus be a non-volatile signal.❖ WSP: Non-Volatile Storage — This basic function is used for the storage of a bit or a data— word in the non-volatile parameter memory.♦> L'MS: Change-Over Element — This function can route either the signal at input ' V or at input *2' to the output depending on the value of selector input SI 1.2'❖ ADS: Adder/Subtracter — The sum of all signals of the inputs I to N appears at the output. Subtraction is obtained by negating the corresponding input signal❖ PIR: PI Controller — This multifunction is used in automatic control systems functioning on the process, group, and individual control level. Also, it is capable of adjusting the output value, to use an auxiliary control valve and to limit the output signal❖ GUS: Threshold Element to trip below threshold, with zero setting by disturbance bit.❖ GOS: Threshold Element to trip above threshold, with zero setting by disturbance bit.❖ ABS: Absolute Value Converter — The absolute value of the input signal appears at the output.❖ ESVK: Switch-On-Delay -— A change from logic 0 to logic 1 state of the input signa! will result in an output signal with a delay of time T\❖ AS67: Drive Control Proportiona1 Operative — This function is used to drive control drives with proportional action.
Significance of Prefix when used with Instruction List:
0 nnn Prefix exclusionNotice of nnn prefix-free lines at an input of a special function element. Special cases nnn=000 means dummy statement (no operation)
1 nnn Element numberA dummy statement to serve for identification purposes with a consecutive number nnn: 000 to FFF.
2 paa Input, InternalAllocation of an internal signal to an input of a function clement. Internal means that the signal is only generated and re-used within a processor,
aa: address 00-FF under which the signal is filed in the internal memoryp: not used for analog signals and is set to zero. Bit position 0-1 within the word for binary signals.
3 paa Input, Internal, Negated
Negated allocations of an internal signal same as prefix 2. but here the allocated signal issimultaneously negated:For binary signals logic '0" — logic "1".For analog signals positive - negative.
4 paa Input, Local busAllocation of a local bus signal to an input of a functional element.aa: Address 00-FF under which the signal is tiled in the memorj For bus datap: not used for analog signals and is set to zero. Bit position 0-F within the word forbinary signals.
5 paa Input, Local bus, negatedNegated allocation of a local bus signals same as prefix 4. but here the allocated signal is simultaneously negated.
6 paa Input, parameterAllocation of a parameter value to an input of a function element. Parameter values are the data stored in a non-volatile memory and can be allocated to inputs, aa: Addresses 00-FF under which the signal is filed in the memory) for. parameters p: not used for analog signals and is set to zero. Bit position 0-1 within the word for binary signal's.
7 paa ReservedFor allocation of a signal from a further signal range to an input of a function element
8 paa Output, Local bus, MultiplicationAllocation of an output signal from a function element to several local bus addresses. This instruction can be performed several times in succession. The last instruction (if the relevant output signal must bear the prefix A or B.
9 paa ReservedFor the negated allocation of a signal from a further signal range to an input of a function element, same as prefix 7. but here the allocated signal is simultaneously negated.
A paa Output, InternalAllocation of an output signal from a function element to an internal memory range The same memory range is called with prefix 2 & 3.aa: address 00-FF under which the signal is filed in the internal memory p:not used for analog signals and is set to zero.. Bit position 0-F within the word for binary signals.
B paa Output, Local busAllocation of an output signal from a function element to a local bus address. The samesignal ranger of a local bus is called with prefix 4 <!t 5.aa: Address 00-FF under which the signal is tiled in the memory for bus data.
p:not used for analog signals and is set to zero. Bit position 0-F within the word tor binary signals.
C nn Function Code
Call for a function element, distributed according to the follow ing types:C= (): basic functionc=l-F : multi functionnn: numbering
D abc Input, DirectAllocation of a constant to an input of a function element, i lie constant abc is interpreted in the format of the corresponding function element.
E paa ReservedFor the allocation of an output signal from a function clement to a memory location of a further signal range. The same memory range is culled with prefix 7 & 9.
F nnn Dummy InstructionFor nnn=FFF this instruction is interpreted as dummy instruction. Other functions oi nnn are reserved.
HANDS-ON-EXPERIENCE WITH DDCMIS
Control logics for various control and test processes have been designed and implemented using the Distributed Digital Control System (DDCS using the Procontrol-P language).
The following are the various control and test processes.> LUBE OIL MECHANISM> MONITORING AND RECORDING MINIMUM MAXIM IIM VALl JES FOR AN ANA LOG VARYING SIGNAL> TESTING FOR CONTACT INTERROGATION OF INPUT/OUTPUI MODULES
LUBE OIL MECHANISM
Lubrication of bearings of rotating machinery, is a major concern in the process industries. The surfaces of bearing & rotating parts are separated b\ a thin lilm of lubrication oil. so that the friction between them is minimal. Good Lubrication aims at retaining the oil film between the surfaces. Friction produces heat and so lubricating oil is not only required to prevent the surfaces from coming into direct contact but also to dissipate the heat from the pans being lubricated. In case of turbine plant, the heat transmitted along the shafts from the steam cylinders also has to be removed and this is another requirement of the lubricating oil.
Thus there is a continuous requirement of lubrication of the surfaces, bearings and the machinery involved. The lube oils generally used are mineral oils obtained from petroleum The lubricating oil should allow trouble free operation of the plant in which it is used.
To get familiarized with DDC Systems and providing automation using the DDC Systems, the logic for the lubrication mechanism in which two pumps arc provided for pumping the oil iron the tank to various bearings and a return path is provided for the oil to be collected into the lank The automation required for above scheme such that a healthy oil film is maintained, lias been designed and implemented.
Conditions for the Lube Oil Mechanism:
• The pumps can be turned 'ON' at the "start pulse signal'.• The second pump should start on Auto in the event of failure of the first pump.• The pumps should start only if there is sufficient lc\ el of oil in the tank.• There should be a continuous monitoring of pressure in the lube oil lines and when there is not sufficient pressure, the second pump should take start on Auto to maintain the required pressure.• If sufficient level is not available at any point of the system functioning, indication should be given and the pumps should automatically turn wOI I '.• The system should show status of the system performance, i.e Success/failure indication. 'Success' is the event where lube oil pump/pumps running and required pressure ;Neing maintained.
0039 4380 003A 4280 003B B080003C COB 1 ODR OR GATE003D 5080003E B180003F COED END END Of PROGRAM0040 FFFF0041 FFFF0042 FFFF 0036 FFFF
Result:
The logic has been implemented on the SK06 Service Kit and the code has been found to satisfy all the conditions and provide a perfect simulation of lube oil mechanism.STUDY OF SINGLE ELEMENT DRUM LEVEL CONTROL
Introduction to Drum Level Control:
Water tube boilers a,-e used industrially as both a source of power and lor process heating. They consist of furnace and the design uses tubes to directly heat the boiler water using the hot gases from the combustion process. The tubes are connected to the steam drum where the generated water/steam mixture is withdrawn. The mixture is then passed through die furnace in tubes where it is heated to produce superheated steam.
Level Measurement:
In most power station applications, level can be defined as "tire height of a liquid or solid above a reference line".
If the dimensions of a vessel arc known, then the volume or mass of its contents can be determined by measuring the level. Hence the vessel contents can be directly displayed in units of level (meters), volumes (liters) or mass (kilograms).
There are many methods of measuring level, the selection of a particular system is largely determined by the practical considerations such as capital cost( equipment and installation), reliability, maintenance cost and degree of expertise required . The methods can be classified as:• Floats and liquid displacers• Head pressure measurement
• Electrical / electronic• Ultrasonic• Nucleonic .• Direct viewing
Head Pressure Measurement System is discussed herein as it is primarily used in drum level measurement. • . •
These systems use the principle that a column of" liquid will exert pressure whose alue depends only on the weight of liquid, density of liquid and acceleration due to gravity and is totally independent of the cross sectional area of the column .
If the density of the liquid remains constant then the height of the liquid above a datum (tapping) point is directly proportional to the pressure measured at the datum point. Thus a pressure measurement device can be used scaled in units of level.
Measurement of Liquid in Closed Vessels:In most cases, the vessel is closed because the system is pressurized, or to operate at
conditions other than the atmospheric conditions.In these cases, it is necessary to see that the same conditions exist on the reference side of
the indicator as inside the container, so the reference limb is fed back into the top of the vessel.
Control Elements of Drum Level:
Single Element Drum Level Control:
The drum collects water and distributes it through down-comers to lower water wall headers which then channel the water in equal proportion to a large number of water wall tube (risers) in which heat is transferred from the burning fuel to the water to generate steam. The drum level is measured and controlled. It is maintained at a near half level by balancing the iced water into the boiler with the steam flow out of the boiler and accommodating for shrink and swell upon load changes.
2-Element Drum Level Control
The two-element drum level controller can best be applied to a single drum boiler where the feed water is at a constant pressure.The two elements are made up of the following:Level Element : a proportional signal or process variable (I'V) coming from the drum level transmitter.This signal is compared to a set point and the resultant is a deviation value. I his signal is acted upon bythe controller which generates corrective action in the form of a proportional value.Steam Flow Element: a mass (low rate signal (corrected or density) is used to control the teed vatcrflow, giving immediate corrections to feed water demand in response to load changesAny imbalance between steam mass flow out and feed water mass flow into the drum is corrected bythe level controller.This imbalance can arise from*Blow down variations due to changes in dissolved solids "Variations in feed water supply pressure* Leaks in the steam circuits. Notes:* Tighter control of drum level than with only one element*Steam flow act as feed forward signal to allow faster level adjustments*Can best be applied to single-boiler / single feed pump configurations with a constant fe
3-Element Drum Level Control:
In 3-element control the process is controlled by considering steam flow and feed water flow in addition to drum level. Generally, this is adapted to avoid the unwanted results that arise during the process. When there is pressure fluctuation in the steam,-water level m the drum shows volume changes as transients resulting in swelling and shrinking which will initiate control action which is not really needed. To avoid false changes 3-element control is adapted.
The set point for the process is set in the auto/manual station Two control valves such as high and low range feed water control valves are installed on feed water pumping down streams
of the outlets of high pressure feed water heaters. There are 3 boiler feed pumps each equipped with aHydraulic coupling. The control system is of 3-element type that shall produce a Iced water demand signal to regulate feed water control valve.Drum level will be measured by two redundant transmitters provisions arc made in each case for selecting either of the two redundant transmitters or the average of the two signals to he us*. 1 for controlling. Steam flow is computed through appropriate summation of steam How to turbine and auxiliary steam flow. Critical signals are through redundant primaries duly compensated for pressure and temperature as required.
The drum level signal is compared to the set value and the resulting error is summed with the steam flow signal to establish a feed water demand signal for the feed water flow and the resulting error is applied to the controller to produce a feed water flow control signal to position the high range feed water flow control valve.
At no load and low load, only drum level is used to establish the feed water demand signal that can be used to position the low range control Valve. Provisions are made for automatic transfer between single element and 3-element control and vice-versa. In single clement control the process is controlled by using only the drum level as control parameter.
Objective of Drum Level Control System
The objective is to maintain the drum level at normal water at all low loads. Ai lower oatls (<30% MCR), the start up feed control valve is used and at higher loads, speed control of boiler feed pumps will be used.
Control Mechanism:Drum level is measured by 3 level transmitters on left and right side respective!} through
temperature compensated constant head unit. Mean value signal of level is compensated for pressure on left and right side respectively. The minimum value of left and right drum level is taken for control
LOW LOAD:
The drum level measured signal is compared with the drum level set point. I he error signal will have a proportional and integral action in the single element controller. This
controller output will be the position demand signal for the start up feed control valve, FD-14. Auto; Manual station is provided for Auto/Manual selection and operation.
HIGH LOAD:At higher load, the start up control valve shall be closed. The steam How is calculated
Tom steam turbine 1st stage pressure and boiler auxiliary steam Ilow is also added to yet the total steam How.
In order to prevent sudden response due to drum water level swell and shrink on load change, a derivative signal of actual drum pressure compensates the 3-element error signal. 1 he temperature compensated feed water flow signal is computed by adding feed water ilow at economizer inlet and super heater spray flow.
The error signal produced between drum level measured signal and drum level set point shall have a proportional and integral action in the 3-eiemenl-drum level controller. I his will be added with the steam signal which is the feed water flow demand signalt set point for feed water flow). This will be compared with the feed water flow in the feed water controller. Deviation if an) will have a proportional and integral action in the feed water controller. This controller output will be the dc-ured speed signal for the individual boiler BFP speed control system. The change over from low load to full load control is automatic.
The control system maintains the DP across the feed control valves to a constant set value. This is required to be maintained to supply feed water according to the requirement of the boiler at various loads.
Differential Pressure across the feed control station is measured and mean value of the two is taken for control. The measured signal is compared with the DP set point. I he selection is inhibited .1 for load >30%. The DP error of the 3-element error is selected and fed to the controller. Controller output is the demand signal for the feed pump speed regulator.
The pump discharge "pressure is compared with the calculated pressure as per I l-Q cure of pump and minimum deviation of the pressure and DP deviation is selected for control of pump speed.
Separate Auto/Manual station is provided for each feed pump spec J regulating device. Biasing of one pump with another is provided from the VPC.
COMPARISION
In all the NTPC projects all the systems were treated as separate independent, systems, utilizing their own dedicated conventional hardware, using conventional display devices like indicators and recorders and conventional push button and hand/auto stations for manual control. NTPC has until now employed conventional, hardwired systems for the modulating controls (closed loop control) whereas the short-sequence control & protection system (open loop system) for various auxiliaries were realized with electromagnetic relays. Regarding monitoring, information and & recorders ha\e been employed with conventional display devices acting as back-up.
As stated above, hardwired solid state Analog Control Systems with split architecture has been adopted by NTPC for its various super thermal power plants so far. fi.ough the same are working satisfactorily they have got certain limitations. For example, in conventional Control System the necessity of assigning functions and distributing information by hardware results in considerable
Problems especially cost during engineering and installation. In the hardwired system any addition or modification in the plant often results in difficult problem if the modification work is to be performed late in the installation phases or possibly during the operation.
In the last few years however, number of important development have been taken place in the field of electronics the most important being the introduction of microprocessor.
The microprocessor has completely revolutionized the basic Configuration, both in terms of hardware as well as in terms of Configuration, operation etc. in the field 01 control and Instrumentation. The microprocessor-based systems do offer number of advantages over 'he conventional system like self-diagnostic and monitoring facilities, centralized operation & monitoring facilities, flexibility etc.-* Hence, it is considered that these microprocessor based systems are technical) much superior i > the conventional hardwired system and are also considered to be more reliable due to their self-diagnostic features. Moreover, their availability and price now-a-days have made it possible to employ set irate micro-processors for different functions thus avoiding the catastrophic failure i.e. complete collapse of the system due to the failure of one of these microprocessors, which can happen in the ca c of centralized computer control system.
Modern power plants are employing the microprocessor based distributed digital control system for modulating control and logic function due to the various advantages built in such system .. Numbers of manufacturers in the different parts of the world have come up with DDC System and these s>stems have been in service for many years thus establishing satisfactorily performance records. Moreover, because more and more power authorities are going in for DDC. the sales of conventional systems are decreasing and hence the long term support b> the manufacturers for the conventional systems is doubted. Hence, the DDC systems are now being adopted for NTPC's projects.
CONCLUSION
India is a developing country with rain-based water system I his makes the use ol thermal power plants inevitable. The heart of the STPP is the boiler. The report thus begins with the introduction of various forms of power followed by and attempt to explain boiler and its various auxiliaries. Then we proceed to look over the steam turbine where the thermal energy in the form of steam is converted to mechanical energy. There an attempt is made to explain its various auxiliaries. Then, we proceed with generator; where much has to be discussed about its cooling system. In the auxiliaries of turbine and boiler, we have covered the various aspects of the coal and ash circuit as well as water and steam circuit like CHP, water treatment plant, air handling as well as Hue gases handbag.
Finally, the current project thus familiarizes with the Distributed Digital Control and Monitoring and Information Systems (DDCMIS) and the automation of vinous control and testing processes. The software implementation of an analog control loop, single element drum level control, also has been studied.
We hereby conclude that, several control and test logics have been designed innovative!;-, and implemented successfully using the DDCMIS (using the Procontrol" p language), these logics have given us a hands-on-experience with the working of the DDCMIS.
