NTPC LTD. KAHALGAON SUPER THERMAL POWER PROJECT

A major training report by:

Name: Suraj Kumar Roll no.:480/08 College: N.I.T. ,Patna Branch: ECE Training period: 16/05/11 to 15/06/11

Contents: NTPC: An introduction I.T. department @ NTPC KhSTPP

Satellite communication exchange Telephone exchange Computer networks Relational database management system

C & I department @ NTPC KhSTPP Pneumatic lab Electronics lab Data acquisition system(DAS) Process Measurements Process Protections Interlock & Protections of Boiler and Turbine

auxiliaries Selective Control System & Short Sequence

System Auto Control system Annunciation system. Furnace safeguard supervisory system SWAS and its auxiliaries

NTPC LTD : An introduction

NTPC Limited (Formerly National Thermal Power Corporation) is the largest power generation company in India. Forbes Global 2000 for 2009 ranked it 317th, in the world. It is an Indian public sector company listed on the Bombay Stock Exchange although at present the Government of India holds 84.5%(after divestment the stake by Indian government on 19 october2009) of its equity.

With a current generating capacity of 31134 MW, NTPC has embarked on plans to become a 75,000 MW company by 2017. It was founded on November 7, 1975.NTPC's core business is engineering, construction and operation of power generating plants and providing consultancy to power utilities in India and abroad.

The total installed capacity of the company is 31134 MW (including JVs) with 15 coal based and 7 gas based stations, located across the country. In addition under JVs, 3 stations are coal based & another station uses naphtha/LNG as fuel.

By 2017, the power generation portfolio is expected to have a diversified fuel mix with coal based capacity of around 53000 MW, 10000 MW through gas, 9000 MW through Hydro generation, about 2000 MW from nuclear sources and around 1000 MW from Renewable Energy Sources (RES).

NTPC has been operating its plants at high efficiency levels. Although the company has 18.79% of the total national capacity it contributes 28.60% of total power generation due to its focus on high efficiency. NTPC’s share at 31 Mar 2001 of the total installed capacity of the country was 24.51% and it generated 29.68% of the power of the country in 2008-09.

Every fourth home in India is lit by NTPC. 170.88BU of electricity was produced by its stations in the financial year 2005-2006. The Net Profit after Tax on March 31, 2006 was INR 58,202 million. Net Profit after Tax for the quarter ended June 30, 2006 was INR 15528 million, which is 18.65% more than for the same quarter in the previous financial year. 2005).

NTPC Kahalgaon ,super thermal power project(KhSTPP) is the fifth largest power station in the country with installed capacity of 2,340 MW. It has 4 units, each of 210MW capacity resulting in a total of 840MW for stage-1 and 3 units ,each of 500 MW capacity resulting in a total of 1500 MW for stage-2.

SATELLITE COMMUNICATION EXCHANGE

The origins of Satellite Communication can be traced back to an article written by Mr. Arthur C. Clarke in the British Radio magazine Wireless World in 1945. Satellite communication began much later in October 1957 with the launch by U.S.S.R. of small satellite called Sputnik I.The first true communication satellites, Telster I and II, were launched in July 1962 and May 1963.

Satellite communication offers a great number of advantages over terrestrial links, that is why, it is preferred over terrestrial communication, namely :-

High availability – minimal/nil fading No last mile problem Extensive coverage-Hemi/Zonal/Spot Broad cast nature allows easy point to multipoint links Easy scalability and expandability of network Security and secrecy can be adequately addressed Less prone to failure due to natural calamities

The disadvantages being:-

High up- front investment in ground segment High recurring cost on satellite segment.

A Satcom exchange has also been provided at NTPC Kahalgaon, which caters to the communication needs of all its 96 employees. The outdoor unit of the exchange BPL ∑ INOX 250 basically consists of the Antenna. The indoor unit comprises a modem, multiplexer, router, DAMA, DTE, EPBX. The users can connect to the worldwide web or the company’s intarnet using this system. Using a PC the user can connect to the company LAN via a modem and then via server all the outside mails are routed to the Proxy server. From the router the data is routed to the multiplexer from where it goes to the RFT via a modem. The data is transmitted via the antenna and the satellite to the NTPC earth station at Muradnagar (now NOIDA). To connect to the Corporate Center a 2Mbps micro wave link is used. A proxy server is also present in the Corporate Center from where it connects to the Internet world via CGI and BSNL server.

Private Branch Automatic Exchange: The EPBAX connects to the main plant telephone exchange as well as a number of subscribers. It provides the facility

of voice communication via satellite to the users. This is particularly useful in case of terrestrial links, which are much more damage prone. GDAMS data is also sent to the corporate centre using this link. A brief description of the components is given below:-

SATELLITE: The third transponder of INSAT-3E with a bandwidth of 18MHz has been allocated to NTPC to cater to its communication purposes. The bandwidth was updated to 27MHZ on 19th of July, 2005.The Kahalgaon satellite communication plan is given below: Satellite : INSAT 3E Location :55 DEG EAST Transponder No. :3 Transponder bandwidth :27 MHz(6012MHz-6039MHz) Beacon frequency :4190.97 MHz Polarization :E/S U/L LINEAR HORIZONTAL E/S DN/L LINEAR VERTICALMCPC Stn. Spt. Tx. Setting :6025MHzMCPC Stn. Spt. Rx setting :3800 MHZ

ANTENNA:

The antenna is of CASs grain configuration using shaped reflector technique to optimize receive gain to noise ratio and the corrugation technique for primary horn feed to get better symmetry and minimum side lobe of the radiation pattern. The antenna specification is given below:-

Type :LIMITED STEERABLE AZ-EL MOUNT

Feed and reflector :7.5 m dia.CASSEGRAIN WITH SHAPED REFLECTOR

Tracking :MANUAL DRIVE,AUTO STEP TRACK

Sky coverage :EL +5 deg - +90 deg

AZ -20 deg- +20 deg

Frequency range :Tx 5.850-6.425GHz

Rx 3.700-4.200 GHz

Polarization :LINEAR ORTOGONAL AND CIRCULAR

Gain :6GHz band-51+20logf/6 db

4GHz band -47.5+20logf/4 db

Power handling capacity :5KW C W

Antenna weight :9 Tonnes

TRANSCIEVER:

The AAV680 C-Band Single Package Transceiver ODU interfaces with the 70MHz/140MHz Indoor Unit having bandwidths of + 18MHz.

The main function of the SPT is to upconvert the 70 or 140 MHz IF input from the indoor modulator to an RF signal in the C-Band, transmission via the antenna ,and to down convert the L-Band signal (950 – 1450 MHz) to an IF signal of 70/140 MHz. for the demodulator.

The AAV 680 C-Band SPT system is comprised of the following subsystems :

Single package RF transceiver Phase Locked Low Noise Block ( PLLNB) Booster for 16W and above (optional) Accessories

The SPT has two modules:

L- band module comprising of the:1. Synthesizers2. up converter3. down converter4. monitor & control

Power & Block Up Module (PBU) consisting of the:1. Power supply board2. SSPA module ( Solid State Power Amplifier) 3. BUC module ( Block Up Converter)

It is designed as a single PCB. All SSPA configurations are designed as soft boards bounded onto aluminum base plates. For better reliability, two streams of outdoor C-Band and Ex C-Band transceivers have been provided. A low noise

amplifier (LNA) is provided which receives the weak downlink signal (3.625-4.200MHz) and amplifies it to the correct level before sending it to the SPT for frequency down conversion. It uses high electron mobility transistor (HEMT) devices to achieve low noise, high gain and low distortion amplification features. A Booster is provided to boost up the transmit power of the signal from SPT.

Redundancy switching equipment performs the switchover operation when a fault is detected at any one of the streams. Switchover can be auto/manual and results in less than half a second of traffic interruption. Independent path switching between the transceivers is allowed.

BOOSTER is used to boost the transmit power of signal from SPT. It has two parts:

1. Power supply board: This converts AC to DC for SSPA.2. SSPA (Solid State Power Amplifier ): This receives RF power from SPT and

amplifies it to correct power level. REDUNDANCY CONTROL UNIT(RCU):

The redundancy control unit is supplied with +12 or +15 V DC via Agillis transceivers. The unit contains:

Monitor & control (M & C ) module Window access panel (WAP ) IF input power splitter IF output switch

M & C

This module comes with an Intel based microcontroller to link the monitor and control functions from the outdoor RCU to the indoor DTE (usually PC).

To active remote /local mode, toggle the DIP switch at the outdoor RCU window access panel. MODEM:

The word "modem" is a contraction of the words modulator-demodulator. The digital satellite modem serves as an interface between the user’s data terminal equipment and the IF frequency interface with the up/down converter. The UMOD has been configured for full duplex operation. The transmit and receive paths are independent for most application.

In the transmit direction the UMOD accepts user data at the common interface module (CIM) and directs it across the backplane to the transmit portion of the terrestrial data interface which converts the users electrical format to the format used in UMOD. The data is directed to the optional internal framing unit for processing and then to the UMOD motherboard. On the motherboard the data is sent to the channel encoder where scrambling, differential encoding & FEC encoding is performed. The data is then routed to the transmit filter for digital filtering and interpolation; then passed to the modulator where the signal is PSK modulated onto an IF carrier provided by the transmit synthesizer. This modulated carrier is then amplified inn the IF stage, then routed for transmission across the backplane to the IF OUT connector on the IF panel.

In the receive direction the IF signal is input at the IF IN connector on the IF Panel, passed across the backplane and received by the receive IF processor on the UMOD motherboard which performs low noise amplification, automatic gain control and filtering. The signal is then routed to the receive synthesizer and demodulator where the IF carrier is removed by either BPSK or QPSK demodulation. The resulting base band data is then directed to the channel decoder where it is FEC decoded, differentially decoded and descrambled. The data then passes through the optional IFU daughter card where deframing and other processing takes place. The data is then routed to the receive portion of the terrestrial data interface daughter card which converts the receive data and clock to appropriate formats and directs it across the backplane to the CIM where they can be accessed by the user.

MULTIPLEXER:

The Kilomux is an advanced, highly versatile user configurable modular TDM system providing an efficient method for transmitting data, voice and fax over digital data services. Its main functions are:-

Multiplexing/De-multiplexing operation System management Interfacing with the optional external system

management.

The basic Kilomux system consists of two kilomux units interconnected with each other. Two main links are there to provide for standby redundancy for the main link. The Kilomux uses permanent on-demand allocation of main link bandwidth.

The Kilomux is designed for unattended operation. A complete collection of parameters configuring the kilomux system and each of its modules,is determined by a database which is stored in the non-volatile memory of the Kilomux control module. Kilomux can store two different databases and can be configured to switchover automatically between databases as per requirement.

ROUTER: Routers are specialized computers that send our messages and

those of every other Internet user speeding to their destinations along thousands of pathways.. These are crucial devices that let messages flow between networks rather than within networks. A router has two separate but related jobs: (i) The router ensures that information doesn't go where it's not needed. This is crucial for keeping large volumes of data from clogging the connections of "innocent bystanders." (ii) The router makes sure that information does make it to the intended destination. It joins the two networks, passing information from one to the other and, in some cases, performing translations of various protocols between the two networks. It also protects the networks from one another, preventing the traffic on one from unnecessarily spilling over to the other. As the number of networks attached to one another grows, the configuration table for handling traffic among them grows, and the processing power of the router is increased. A configuration table is a collection of information, including:

(i) Information on which connections lead to particular groups of addresses (ii) Priorities for connections to be used (iii) Rules for handling both routine and special cases of traffic.

ROUTING OF PACKETS:-

The office network connects to the router using an Ethernet connection. There are two connections between our router and the ISP. One is via the satcom system and the other via the BSNL ISDN line . This way the ISDN line is held as an “insurance” against a problem with the other faster connection.

In addition to routing packets from one point to another, the router has rules limiting how computers from outside the network can connect to computers inside the network, how the network appears to the outside world, and other security functions. While most companies also have a special piece of hardware or software called a firewall to enforce security, the rules in a router's configuration table are important to keeping a company's (or family's) network secure. One of the crucial tasks for any router knows when a packet of information stays on its local network. For this, it uses a mechanism called a subnet mask. The subnet mask looks like an IP address and usually reads "255.255.255.0." This tells the router that all messages with the sender and receiver having an address sharing the first three groups of numbers are on the same network, and shouldn’t be sent to another network.

Thus knowing where and how to send a message is the most important job of a router. Some simple routers do this and nothing more. Other routers add additional functions to the jobs they perform. Rules about where messages from inside a company may be sent and from which company’s messages are accepted can be applied to some routers. Others may have rules that help minimize the damage from "denial of service" attacks. The one constant is that modern networks, including the Internet, could not exist without the router.

TELEPHONE EXCHANGE

WAYS OF COMMUNICATION :

WIRED WIRELESS

#SIMPLE # COMPLEX

# Ease in maintenance # Complications

# Lesser GOVT obligations # License Req.

# L.F application # V.H.F Application

# Prone to faults # Convenient to User

# Landline ,Broadband etc. # GSM /WLL mobile ,

WI-FI, WI-Max

COMMUNICATION TECHINQUES :

TDMA (TIME DIVISION MULTIPLE ACESS) FDMA ( FREQUENCY DIVISION MULTIPLE ACESS) TDD & FDD (Time Division Duplexing & Frequency Division

Duplexing) CDMA (CODE DIVISION MULTIPLE ACESS) OFDMA ………….upcoming tech.

COMMUNICATION MEANS:

LAND LINE TELEPHONE DIAL UP INTERNET / BROADBAND LEASED / DATA LINES ISDN LINES MPLS GSM MOBILE WLL / CDMA MOBILE SATELLITE PHONE ……..etc.

WIRED SYSTEM COMPONENTS

o TELEPHONE EXCHANGE (TELECOM SWITCH )

COPPER CABLES UNAROMORED CABLES

ARMORED CABLES

o TELEPHONE DP BOXES o TELEPHONE SET

TELEPHONE EXCHANGES

POWER SYSTEM OF EXCHANGE

FCBC / SMPS

BATTERY BANK (24 Cells of 2 Volt)

ROSSET

AC Supply 220 volt / 440 volt

- 48 volt DC supply

(2-10 mA / 80 mA )

STROWSER TYPE CROSS BAR ESS EXCHANGES SEMI DIGITAL EXCHANGES DIGITAL EXCHANGES IP / VOIP EXCHANGES

GSM – MOBILE SYSTEM

The Global System for Mobile Communications, GSM is the most popular standard for mobile phones in the world

GSM networks operate in four different frequency ranges Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including the United States and Canada)

use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated.

What is IPPBX ?

An IPPBX is a complete telephony system that provides telephone calls over IP data networks. All conversations are sent as data packets over the network.The technology includes advanced communication features but also provides a significant dose of worry-free scalability and robustness that all enterprises seek.

How IPPBX Works?

The Top Benefits:

Benefit #1: Much easier to install and configure than a proprietary phone system:

Benefit #2: Significant cost savings using VOIP providers:

Benefit #3 Eliminate phone wiring!

Benefit #4: Eliminate vendor lock in!

Benefit #5: Allow hot desking & roamimg

COMPUTER NETWORKS

To fecilitate communication, we deploy networks OSI(open systems interconnection) network reference model is divided

into seven layers: Layer 7: application

Layer 6: presentation Layer 5: session Layer 4: transport Layer 3: network Layer 2: data link Layer 1: physicalThis seven layer model consists of categories(layers) that represent functions required to communicate.the purpose of layering is to make functions as discrete and independent as possible

In this model individual layers are said to provide services to the layers above them and to consume data from the layers beneath them.

Application layer: it provides a consistent interface to the network for all computer software.these are often called application programming interfaces(API) and they allow a program to be written once without regard to the network involved and then used on any network(e.g.TCP/IP,Ethernet etc)

Presentation layer:it is responsible for data translation into a standard format. Examples are ASCII texts,JPEG images,MP3 music formats.this layer is also responsible for encryption and decryption for security purposes, as well asa compression.

Session layer:it is responsible for establishing ,maintaining and ending sessions across the network.this layer manages name recognition ,synchronisation and some access features.e.g.when a device can transmit and how long it can transmit

Transport layer:it is responsible for preparing data to be transported.the transport layer manages flow control,error correction and divides chunks of data into segments appropriately sized for the layers below it.TCP & UDP are the examples of layer 4 protocols

Network layer:it is responsible for assigning a globally unique address to every device and provoding directions from any point on the network to any other pointthe devices that operate at this layer are called routers

Data-link layer:it packages the data from the upper layers into frames and then transmits them onto the media.bridges and switches operate at layer

Physical layer:it is the bottom layer which is responsible for defining a bit.the physical layer includes the media types ,including the minimum and maximum cable lengths,the connecting interfaces e.g.cable jacks.

RELATIONAL DATABASE MANAGEMENT SYSTEMS

Introduction

A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, and the use of a database. A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different user application programs to easily access the same database. DBMSs may use any of a variety of database models, such as the network model or relational model. In large systems, a DBMS allows users and other software to store and retrieve data in a structured way. Instead of having to write computer programs to extract information, user can ask simple questions in a query language. It helps to specify the logical organization for a database and access and use the information within a database. It provides facilities for controlling data access, enforcing data integrity, managing concurrency, and restoring the database from backups. A DBMS also provides the ability to logically present database information to users.

Overview

A DBMS is a set of software programs that controls the organization, storage, management, and retrieval of data in a database. DBMSs are categorized according to their data structures or types. The DBMS accepts requests for data from an application program and instructs the operating system to transfer the appropriate data. The queries and responses must be submitted and received according to a format that conforms to one or more applicable protocols. When a DBMS is used, information systems can be changed muchmore easily as the organization's information requirements change.

C&I SYSTEMS @ NTPC KAHALGAON

The control & instrumentation package of Kahalgaon project (4x210 MW) is supplied by Russia with the Main package by M/s. TPE, USSR. In addition to the original Russian supplied system there are Furnace Safeguard Supervisory System (Make Forney, USA), Data Acquisition System (Make Westinghouse, USA), Steam Water Analysis System & uninterrupted Power Supply system (supplied by Keltron).

The C&I package can be broadly classified into the following categories:

1. Process Measurements2. Process Protections3. Interlock & Protections of Boiler and Turbine auxiliaries4. Selective Control System & Short Sequence System5. Auto Control system6. Annunciation system.7. Furnace safeguard supervisory system 8. Data acquisition system 9. SWAS and its auxiliaries

1. PROCESS MEASUREMENT The process parameter measurement is realized by means of Transmitters, Thermocouples, RTDs and other primary instruments. The signals received from these primary instruments are utilized for Control /Record /Indication of the process parameter and protection of the process. In the process where mass monitoring is required like Boiler metal temperatures, Turbine metal temperatures, Turbine bearing temperatures and Generator slot temperatures in these cases either multipoint recorders or indicators with a manual switch for point selection is provided. For remote indications of level, pressure and flow, transmitters are providing. Explosion proof Transmitters are provided for explosion prone areas like Fuel oil pump house and Hydrogen plant. All transmitters are of strain gauge type, which gives an output of 4 – 20mA when the pressure across the diaphragm varies from minimum range to maximum range.

For some process parameters the signal for DAS & Measurement is shared from a single transmitter. This sharing is done through Zener diode isolation circuit. Generally for Auto Control System dedicated transmitters are provided with 100% redundancy. All the secondary instruments are powered from UPS including Recorders, Indicators, TSI equipment & all process variation measuring transmitters.

Unit Control Board (UCB) is distinctly divided into two parts. One is operative area which contain Desk panels, Annunciation panels, Recorder & Indicator panels, Transmitter power supply panels & Mimic panels .The other is the Non- operative area consisting of Interlock and Protection panels, Auto Control panels, Selective and Short sequence panels, RC feeder & FSSS panels.

There is facility to control the operation of all drives, valves & dampers from operator desk panel. Status of the same is indicated through mimic just above the operating panel in the operator desk .

The recorders & indicators are of three different types depending upon the inputs i.e. milliampere, potentimetric and bridge type. These are utilised for measurement of transmitter signal, thermocouple signal and resistance thermal detector signal respectively.

For the measurement of excess Oxygen in flue gas, an insitu zirconia probe (Make Westinghouse, supplied by I.L.Kota) is installed at 41 meter in second pass of Boiler. The output of the probe is in mV, which is converted to mA through converter. The cell constant and cell slope is adjustable. Auto calibration facility is also available.

In Air preheater system, which is of tubular type, differential temperature of air & gas is measured in a recorder. This gives annunciation when it crosses the alarm value. In case of fire the differential temperature increases and when it crosses a pre-set value alarm is obtained at UCB.

For Drum level protection as per the original design, level switches are provided at different levels. However presently protection of drum level is of two out of three logic rooted through Hydrastep (Keyston Make) both left and right side and the pressure compensated signal from drum level compensation package (supplied by M/s Bells control). Bearing temperature, winding temperature PA Fans & Mills are shared by DAS and

measurement from dual RTD. Coal pipe temperatures of furnace inlet are exclusively provided in DAS only.

There are many important parameters, which are measured locally through pressure gauges & switches. In Boiler Feed Pumps the bearing temperature recorders & winding temperature indicators are located at local which helps the operator for easy monitoring of the temp regularly.

For safe operation of Turbine the following Turbo Supervisory measurements are carried out in continuous basis. .

01. Axial shift.02. HPC / IPC differential expansion.03. Eccentricity04. HPC/IPC thermal expansion05. Turbine speed measurement06. Turbine vibration of Bearing 1 to 7.07. Seal Noise device for Bearing 1 to 7.08. Control valve servo meter position measurement.

Axial Shift, HPC / IPC/ LPC differential expansion measurement are realised by a instrument based on the principle of Linear voltage differential transducer principle. Axial shift pick up is fixed near brg-2 i.e. the pivot point of the turbine rotor.

For Turbine speed measurement a permanent magnet pick up is mounted above a wheel of 60 teeth attached to turbine shaft located at MOP. This pick up is having a coil which is induces an A.C current which is processed by a pre amplifier to get a square pulse. This square pulse is finally counted by the counter located in NOP area which gives three Analogue & three digital output used for local / UCB analogue / digital measurement.

For Turbine vibration measurement in each bearing there are two pick-ups. One is for vertical vibration & other one for axial & cross sectional vibration. Vibration signal is measured by piezoelectric crystal, which induces a millivoltage as per the vibration, which is subsequently amplified by preamplifier at local. At UCB the signal is processed & integrated to get velocity measurement output in the range of 0 – 12 mm/sec or 0 – 30mm/sec. The signal is converted into analogue output of 0 – 5 mA who is shared DAS & measurement. In each pick up there is a facility of on line checking of healthiness by injection of A.C voltage another piezoelectric crystal placed near to the measuring crystal. There is a provision of two-alarm contact for alarm & warning setting for the measurement of each vibration.

In offsite areas including Fly Ash, Bottom Ash, FOPH, UPH, H2 & chlorine plant, for easy monitoring and operation of the equipment in addition to local Pressure gauge, pressure switch, Recorders and instruments indication the temperature & current etc. are also provided near the equipment itself. The ON/OFF status of the major offsite drives are available in UCB # 1. In case of emergency i.e. when any local annunciation is generated a parallel contact goes to UCB and ‘control board faulty ‘ annunciation appears. This helps the UCB personnel to maintain & monitor the offsite area.

In Fuel Oil Pump House there are three receiving tanks, each consisting of two oil transfer pumps. There are four oil storage tanks in which level and temperature are measured. There are two sets of lift pumps. Each set consists of two stages. Suction and discharge pressure is measured through local gauges. Fuel oil flow to boiler and return oil flow from boiler is measured through transmitters.

There are two Bottom Ash pump house. Each Bottom Ash pump house consists of three sets of pumps. In each set there are two pumps connected in series. This arrangement is done to give more discharge Pressure to the slurry. In each pump Bearing temperature is measured & dedicated recorders are provided in local panel. Pneumatic valves are provided in the discharge of the pumps. Gland sealing is required for each stage of pump. In Air Compressor house, there are four compressors common to all four units. The Compressor has got two independent motors winding for two independent speeds (Low speed and High speed). For each stage air temperature before cooler is measured and independent tripping is initiated when it rises beyond the alarmed value. Compressor trips when lubrication oil pressure falls below the set limit and cooling water flow is absent.

A detailed description of various instruments used for various process measurements is listed below:

<A>.Temperature measurement

### Expansion thermometers

(a)Solid rod thermometers: It is a temperature sensing and controlling device. It incorporates in its construction the principle that some metals expand more than the others for the same temperature range. Such a device is the thermostat used with water heaters.

(b)Bi-metallic strip: Bi-metals strips are composed of two metals, whose coefficients of linear expansion are dissimilar. These two metal plates are either welded or riveted together as a sandwitch. When heated , both the metals expand but the metal with greatest coefficients of linear expansion will expand more causing the sandwitch to curl up or down depending on the position of this metal. This bending action can be sensed by a displacement transducer, but it is mostly used to operate switch contacts, usually with the strip itself carrying one contact. for greater sensitivity ,the strip is arranged into a spiral because the sensitivity depends upon the length of the strip. The amount of deflection can be fairly precisely proportional to change if the temperature range is small. A simple bimetallic strip composed of a layer of brass (high expanding material) and a layer of invar (low expanding material) will deflect when subjected to a change of temperature and if the strip is coiled its angular motion will be given by (C.T.L/t);where C is the length of the strip and t is the thickness of the strip.

(c)Liquid in glass thermometers: changes in volume of a liquid by the application of heat enclosed in a test body is utilized to measure the quantity of temperature .the liquids normally used are:

Mercury and ethyl alcohol-----------------------for low temperature measurement

Metaxylene------------------------------------------for medium range temperature

Tetrahydrochloro naphthalene (tetralene)---for higher temperature measurement

The test bodies are either glass or of steel material. The liquid filled system consists of an element sensitive to temperature change,an element sensitive to volume change(bourdon, bellow of diaphragm) , means of connecting these two and a device for measuring and indicating. the liquids are filled in a bulb from which a capillary is drawn, which ends in a bourdon or bellow or a diaphragm. When the temperature rises the volume of the liquid increases thereby tending to enlarge the enclosure. As a result a mechanical motion is achieved , which is transmitted to the dial indication by lever arrangement ora rack and pinion arrangement.

There is a possibility that the metal enclosed also may increase in volume due to thermal expansion which will add error to the system. To remove this error a compensation means is provided.

The co-efficient of cubical expansion of mercury is about eight times greater than that of glass. Therefore ,a glass container holding mercury when heated will expand far less than the mercury. At a higher temperature , the mercury will occupy a greater fraction of the volume of the container than it will have at a low temperature.

(d)Liquid in steel thermometers: it is used when relatively higher temperature measuring is required. types of mercury in steel thermometers are –

Bourdon tube---------------------------------most common and simplest

Spiral tube--------------------------------------more sensitive and compact

Helical type-------------------------------------most sensitive and compact

The thermometer bulb may take many forms dependent upon the application.

(e)Gas thermometers: in this case change in pressure of the gas filled in test body is utilized to measure the temperature. the gas used normally is nitrogen. The bulb is evacuated and filled by the gas at a required pressure and then the system is sealed. Rest of the system is same as that of the liquid filled system and here the bourdon becomes sensitive to temperature changes.

(f)Vapour thermometers: it works on the basic principle that all enclosed liquids at a given temperature will create a definite vapour pressure if the liquid is only partially filled. This vapour pressure will increase with temperature and this property is utilized in measurement.

###Thermo electricity

According to Seebeck effect ,”when two junction made up of two dissimilar metals is kept at a different temperature, then an emf is generated which is proportional to the temperature difference between the two junctions.”

According to Seebeck effect, e=a +bƟ+cƟ2 ; where a,b,c are constants for the types of metal used and Ɵ is the temperature difference between them. If the cold junction is held at 00C, then e=αT+βT2 ;where α & β are measured constants for the pair of metals and T is the temperature of the hot junction.

(a)Thermocouple: it consists of two wires of suitable materials which are joined together at the ends by twisting together and then joining the tip by welding. This combination is capable of producing an emf the magnitude of which is related to the temperature. the ranges covered are a few degrees to 30000C. the output from a thermocouple is small, of the order of mV for a 100C temperature difference. Copper/constantan type thermocouple is used mainly for the lower range of temperature and Pt/Rh type for the higher temperatures. One particular advantage of thermocouples is that the sensing elements themselves are very small, allowing thermocouples to be inserted into very small spaces and to respond rapidly changing temperatures.

Of many possible combinations of metals that could be used for thermocouples , only a few are practical from the consideration of a reasonably linear scale and good resistance to high temperatures. Table below shows most commonly used metals:-

Code Metals Temp. Range

mV@1000C Remarks

S PtRh/Pt 0-14000C 0.645 needs ceramic sheath R PtRh/Pt 0 14000C 0.647 Needs ceramic sheath J Fe/CuNi 0-8000C 5.268 Attacked by O2 or acids K NiCr/NiAl 0-11000C 4.095 Avoid reducing agents T Cu/CuNi -200-+4000C 4.277 Low temperature use E NiCr/CuNi 0-8000C 6.137 High output

S type thermocouples are required for the higher temperatures, but have lower output levels and require ceramic sheathing to avoid oxidation damage. J type thermocouples require protection against rusting and aginst oxidizing atmosphere generally.

(b)Resistance temperature detectors(RTDs): Its operation is based on the fact that as a wire is heated its electrical resistance increases in proportion to the temperature. All metallic conductors exhibit a change of

resistivity when their temperature changes according to the relation RƟ=R0(1+αƟ); R0 is the resistance at 00C. the change of resistance is a more linear quantity over a large range of temperature than the output from a thermocouple. RTDs employ mainly three metals as Ni, Cu &Pt. for comparatively small temperature ranges (upto 4000C), Ni or Ni alloys can be used, because its characteristics is not linear throughout the range. For higher temp. ranges, Pt & its alloys are more suitable because of their much greater resistance to oxidation. For measurement purposes , RTDs can be connected to a measuring bridge. Although Ni & Cu can be used for some purposes in the lower ranges of temp., Pt has the advantage that it can be prepared in a very pure state, is highly resistant to corrosion and has a resistance –temperature relationship which is almost perfectly linear over a wide range of temperature. Also Pt is a very stable material, both electrically and mechanically , so that drift of resistance value as material ages and with use is negligibly small.RTDs can be used in one of the arms of WSB and the unbalance is directly fed to galvanometer whose deflection is proportional to the change of temp. and calibrated in terms of temperature.

(c)Thermistors: These are non metallic resistors(semiconductor), made by sintering mixtures of metallic oxides such as Mn, Ni, Co, Cu and U. the thermistors with a positive temperature co-efficient are very non linear but the more common negative temperature co-efficient types follow a roughly logarithmic law with no violent changes in resistance.NTC thermistors are used for temperature control applications such as low temperature oven controllers, deep freezer thermostats , room temperature sensors and process controllers. PTC are used mainly for protection circuits for temperature sensing or control. The over- temperature protection type of PTC has a switchover point at a reference temp. or trip temperature Tr. at temperatures lower than the trip temp. , the resistance of the PTC is fairly constant, but around the trip temperature the PTC characteristics takes over and their resistance rises very sharply as the temperature rises. The sudden change in resistance can be used to operate an indicator or to switch other circuits for purposes such as motor protection or for preventing overheating of transformers. Thermistors due to their thermoresistive characteristics , stability and high sensitivity have become more versatile tool for temperature measurement.

(d)Optical pyrometer: the radiant energy is measured by photometric comparison of the relative brightness of the object of unknown temperature with a source of standard brightness such as tungsten filament of an electric lamp.

(e)Radiation pyrometer: the radiation from a portion of the target object, whose temperature is being measured is focused by lens arrangement on thermopile(a number of small thermocouples connected in series) . this thermopile generates an emf proportional to the amount of energy falling upon it. This emf is fed to a galvanometer with an indicator which indicates the temperature. The radiation pyrometer is ideally suited for very high temp. measurement , beyond the practical range of thermocouple measurement.

### Change of state of testing bodies

For pure chemical elements or compounds , change of state viz from solid to liquid to gaseous etc. takes place at a fixed temp. and this property thus gives a method to measure the temp.

(a)Fusion method: fusion of different metals takes place at different temperature. Pyrometric comes are made for different temp. and are placed inside the furnace which will indicate the temp. when the rated fusion temp. is attained.

(b)Vapourisation method: vapourisation temp. of different volatile liquids are different. This property is utilized to measure the temperature.

<B>.Pressure measurement

The commonly used pressure measuring devices in a power plant are as follows:-

(a)Manometers using water, mercury and other liquids of known density for low pressure measurement

(b)Diaphragm ,capsule, bellows for measuring medium pressures.

(c)Bourdon tube gauges for measuring medium and high pressures.

(d)Transducers of different types for measuring pressures of all ranges for telemetering purposes.

The manometers are mostly used in laboratory for calibration purposes. At site they are mainly used for test purposes , in the low ranges 0-1000mm with Hg as manometers liquid in maximum cases.

Currently low pressure to medium pressure applications are met with diaphragms. They help in remote measurement and control of pressures even of very low range. The various types of diaphragm and bellow elements are made of steel of special composition, phosphor bronze , nickel silver and beryllium copper. For very low pressures , the diaphragms are required to be extremely flexible. For these applications ,materials like colon leather , gold beater skin, nylon rubberized fabric are used. these groups of sensors are used for the measurement of very low pressures upto 20-25 kg/m2.

(a )Bourdon tube gauges: Initially these instruments were used to measure pressures from medium to high ranges . But , currently these instruments are used for almost every range of pressure measurement . however , their application is limited to measure ”Guge pressures” only.

It consists of a metal tube approximately elliptical in cross section formed into ‘C’ shape. The tube is closed and sealed at one of the ends and the opposite end is left open and terminated to a block where the pressure is applied. If the pressure inside the tube is more than that existing outside , the elliptical section changes its shape and it begins to straighten out, with free end deflecting in an arc. The deflection is proportional to the pressure difference between inside and outside pressures. Since the outside pressure is atmospheric , these gauges measure “Gauge pressure”.

Bourdon tube gauges are in use from the range 0-0.5kg/cm2 to 6,000 kg/cm2 and even higher occasionally. the practical range of each type of tube is listed below:

Helical bourdon--------------------0-0.5kg/cm2 upto 0-6,000kg/cm2

‘C ’ type bourdon------------------upto 700 kg/cm2

Flat spiral bourdon---------------low ranges upto 0-70 kg/cm2

Materials like phosphor bronze, steel, beryllium copper etc. are used depending upon the pressure range and media’s corrosiveness. Hydraulic calibrator is used for calibrating the pressure gauges. Hydraulic units use oil for application of pressure.

(b)Differential pressure gauge: It is a dual bourdon system. The two tubs are connected to the single pointer. Both the tubes form two ports which are connected to the process whose differential pressure is to be measured. The deformation of first tube causes the pointer to rotate anticlockwise while that of the second tube causes the pointer to rotate clockwise. The movement of pointer is opposite for the individual pressures and hence gauge reads the differential pressure.

(c)Pressure gauge cum switch: These types of gauges are used to give alarm when the pressure reaches a set level. In this instrument , there is a pressure setting needle . this needle is set via a knob through the centre of the glass of the gauge. The needle has a projection where contact will be made. The needle is connected to a wire.

The pointer is also connected to a wire . when it touches the projection on the setting indicator , a contact is made. When the pressure reaches the set value then the gauge pointer touches the projection on the setting needle. The pointer and the setting needle behave like an open switch till the set limit is reached . the gauge can be connected to a relay for alarm or control .

In a similar manner alarm controls can be made at two points , one for low pressure limit and the other for a higher pressure limit.

(d) Pressure transmitters: a pressure transmitter has pressure as its input and an electric or pneumatic signal as its output . the basic function of the transmitter is to proportionally modulate an electric / pneumatic signal in response to the process parameters.

These transmitters may contain transducers to convert pressure to corresponding electrical signals. They sense the change in pressure within a

certain range and produce output current within a range. The output range is standardized to bring uniformity in the construction of secondary instruments as well as to fecilitate the test and calibration work. The output signal ranges are :

(a)4-20 mA dc (b)0-20 mA dc (c)10-50 mA dc

Transmitters are generally connected in a measurement loop according to one of the following methods :

(1)four wire transmitters :in this method , four conductors are led to the transmitter. One pair is used to carry the power supply (220V ac or 24V dc). The other pair is used for signal transmission.

(2)two wire transmitters : this is presently the most widely used method for transmitter connections .there are three basic elements in this loop , namely ac power supply, transmitter and receiving instrument . they are connected in series and the transmitter acts as a current regulator in series circuit. In this case cabling and erection costs are reduced.

<C>.Level measurement

Level can be defined as “the height of a liquid or solid above a reference line “ .if the dimensions of the vessel are known then the volume or mass of its contents can be determined by measuring the level. There are many methods of measuring level , the selection of a particular system is largely determined by the practical consideration together with the capital cost , reliability, maintenance etc. following are the methods for level measurement:-

(a) Floats and liquid displacers (b) Head pressure measurement(c) Electrical/electronic(d) Ultrasonic (e) Nucleonic (f) Direct

viewing

### Electrical/electronic methods of level measurement

These methods are very useful especially where the transmission distance between the transducer and display or control devices is minimum. Their speed of response is often better than those of pneumatic systems and they are very useful while measuring the level of vessels containing the solids.

(a)Conductivity method level measurement : This system consists of a number of conductors of different lengths connected together by a series of resistors .As the level increases more and more conductors are shorted together , thus shorting out the resistors joining them and the overall resistance will decrease. In such systems, ac voltage supply prevents electrolytic action.

If a constant voltage is applied across the terminals , then as the level increases , resistance decreases , hence the current flowing in the circuit will increase . therefore, current will be proportional to the level . since the current is proportional to level , hence an ammeter placed in series with the circuit can be calibrated directly in terms of level.

This system is probably the most common system used for boiler drum level measurement. This system has the main advantage of digital output which can be readily provided for computer or microprocessor control.-

(b)Capacitance method: this method involves the use of an electrode which extends the full length of the tank and forms a capacitance between itself and earth. A variation of capacitance occurs when the depth of the substance in the vessel alters giving a capacitance change proportional to the level. This capacitance change gives us a proportionate voltage change which may be read by proper measuring device.

By this method the level of liquids, powders or granular solids may be measured. When the medium is a good conductor of electricity then the system works as a variable area capacitance. The electrode is one plate of the capacitor and is insulated with a material that is compatible with the medium, the insulation forming the dielectric. The medium in the vessel forms the other plate of the capacitor. Thus, as the level changes the area of the capacitor plates varies. if level falls then area decreases and capacitance decreases.

On the other hand, when the medium is non conducting the electrode is not insulated and the system works as a variable dielectric capacitance transducer. This dielectric is made up of two materials(say liq. In the tank and the air or gas in the space above the liquid)having diff. dielectric constants. As the liq. Level varies then the overall capacitance will change due to change in dielectric constants. A rise in level will increase capacitance and fall in level will decrease capacitance.

###Ultrasonic method

Ultrasonic beams are a form of energy transmitted by means of mechanical vibrations. These beams have a frequency greater than 20 kHz. For level switching a range b/w 36 & 40 kHz is used.

For level measurement, the time taken by the ultrasonic beam to leave the antenna, travel to the substance and return back to the antenna is calculated. Since we know the value of speed of the beam we can calculate the level.

This technique is mainly used in level measurement of toxic, corrosive, highly viscous slurries, heavy or irregular bulk material. The principle of operation of ultrasonic sensors is that, when certain materials eg.Ni,Fe,Co are placed within a magnetic field, their lengths will vary by an amount dependent on the strength of the magnetic field.

An ultrasonic transmitter consists of a Ni tube which carries the coil and bias magnet. Application of ac through the coil either weakens or strengthens the field, causing increase or decrease of the length of the tube at the supply freq. owing to mechanical properties of the tube it will tend to oscillate longitudinally as a half wave resonator.

Similarly in case of receiver, a sound wave impinging on the diaphragm will cause a relatively large amount of movement in the Ni tube. Changing the length of the tube will cause a change in the magnetic strength of the bias magnet, thereby generating an emf within the coil.

These sensors are temp. sensitive; the resonant freq. falls as the temp. rises but there is no effect if both the sensors are at the same temp.

### Nucleonic method

These type of instruments involve a radioactive source, a radiation detector and an electronic measuring circuit. The advantage of nuclear gauges is that they can operate entirely from outside the process containing vessel. They may be designed to provide on/off control at the fixed level in the vessel, or to provide continuous indication of level over a given range.

A typical system consisting of radioactive source emits gamma rays which propagates towards radiation detector on other side of the vessel. As the process level inside the vessel rises, energy reaching the radiation detector will decrease. Thus energy reaching the radiation detector is inversely proportional to the process level. Electronic measuring circuit processes the detector signal and transmits the process variable as 4-20 mA analog or digital signal.

### Direct viewing(CCTV remote display)

Using a special type of side glass (water gauge) with an associated CCTV, allows us to display level of a vessel remotely in the control room.

The water gauge works on the principle that diff. substances have diff. R.I.,that’s why they bend light by diff. degrees. The gauge is vertical tube of triangular wedge cross section. Illumination is projected through the gauge and the light is bent by the medium. The degree of bend depends on whether the medium is water or steam. CCTV camera mounted a few feet away from the gauge is used for remote display of the level.

<D>.Flow measurement

Flow-meters measure either the quantity of flow or rate of flow. Quantity of flow refers to the quantity of fluid passing a given point in a given time i.e. gallons or pounds. Rate of flow is the speed of the fluid passing a given point at a given instant and is proportional to quantity passing at a given instant i.e. gallons/min.

Positive or volumetric type instruments measure flow by measuring the quantity of fluid transferred from the inlet to the outlet in a given interval of time.

Inferential type instruments measure the velocity of the flow and the volume passed is equal to the velocity times the cross-sectional area of the flow. This type of instrument is the most widely used. Following are the flow measuring instruments:-

(a)differential pressure flow-meters

Orifice plate ventury tube and nozzle

Pitot tube dall tube

(b) variable area flow-meters

(c) electromagnetic flow-meters

(d) ultrasonic flow-meters

(e) positive displacement flow-meters

### Differential pressure flow-meters

It works on the principle of Bernoulli’s theorem, which states that total energy of the fluid is constant at every point. These flow-meters are simple in construction.

<a> Orifice plate

It is a circular metal plate with a central hole or orifice concentric with the circumstance of the place. It is fixed between the pipe flanges and is located by the flanges bolts. The orifice is then concentric with the internal bore of the pipe. Just before the orifice, there is a slight increase in pressure. The stream is then constrained to flow through the smaller size of the orifice, from which it issues a jet. At points just after the plate there are lower pressures than that at the up stream position. Due to decrease in pressure, the velocity increases. The stream or jet cross-section decreases in area after leaving the orifice until it reaches a point, where it is minimum and the velocity is maximum. This is

mainly due to the inertia effects, persisting in the direction of flow for a distance after it leaves the orifice. The static pressure reaches its minimum value at this position, which is known as Vena-contracta . the distance from the orifice varies with the ratio of orifice diameter to pipe diameter but an avg. value may be about ½ of the pipe diameter.

For obtaining the differential pressure, there has to be a variety of positions for tapping. By measuring the differential pressure b/w the normal pipe-section and at the Vena-contracta, the volumetric flow-rate can be obtained by using Bernoulli’s equation. Materials used for orifice plates include mild steel, stainless steel, monel, phosphor bronze, gun metal etc. depending on the application.

<b> Ventury tube

It consist of a local contraction in the cross-section of flow through a channel in the shape of a ventury. The qty. of fluid or gas flowing is prop. to the sq. root of the differential pressure. This type of instrument is generally used for medium and high qty. fluid-flow.

The ventury tube has relatively lesser pressure loss than orifice plate. In addition to it, ventury tube offers the flexibility of using sq. or rectangular shape for measuring large volumes of fluid-flow. The non-circular section lends itself to constructional materials other than metal and even concrete can be used for the purpose. Construction of the ventury tube depends on the application . for normal uses the section will be of gun-metal, cast iron or mechanite etc.

<c> Flow-nozzle

This is in fact a very short venture, the entrance cone is bell-shaped and there is no exit cone. A gradual change of cross-sectional area exists similar to that of a ventury tube, but the absence of the down-stream expansions core brings the pressure loss into the same region as that for an orifice plate. It is cheaper than a ventury tube and at high velocity flow it is used in place of an orifice plate.

<d> Pitot tube

It consists of a tube placed with its open end facing into a stream of fluid and fluid impinging on the open end is brought to rest and its energy of motion is converted to pressure energy.

This is used mainly for experimental work to determine the flow in pipes or ducts prior to making a permanent installation.

### Variable area flow-meters

These are used to meter all types and rates of flow. It consists of a tapered tube forming and upward passage with its smallest diameter at the bottom containing a tapered float having an outside diameter which just clears the bore of the tube to its lowest position where it rests on stop. As the flow increases the float rises to a position of equilibrium b/w the pressure loss across the orifice and the weight of the float. The distance of the float from the stop is a measure of the rate of flow.

2. PROCESS PROTECTION Protection intended to prevent the damage of the equipment under the alarm conditions can be broadly divided into the following categories.

1. Unit protection.2. Turbine protection3. BFP protection4. Boiler trip protection5. Boiler load drop protection6. QPRDS protection7. Turbine local protection (HPH,LPH,D/A)

3. AUTO CONTROL SYSTEM The Auto Control system is intended to maintain process variables within a predetermined range and to ensure the reception of process data. The system produces control instructions & actions which helps in achieving the predetermined state.

The system is based on a split architecture. Controllers comprises of two separate units i.e regulating unit and operative unit.

The Controllers actions are processed through different blocks which are used for different purposes .Some of the important blocks are mentioned below.

Signal input block. Signal converter block, Integration block Summator block Pulse output block Annunciation block

The input to the system is of 4 – 20 mA , millivolts or resistance depending upon the type of transducer used which in-turn converted to 0 – 10v for block operation through input signal block. This also optically isolates the input & output signals.

The pulse output block compare the process parameter set point , process parameter measurements and control valve position and gives output accordingly for the control valve.There is a signaling unit, which compares the parameter value with a predetermined set point. Deviation beyond that gives alarm & changes the Auto operation into Manual Mode. In the event of abrupt failure such as open circuit or short circuit in transmitters controller trip action takes place through this block. Parallel command goes to annunciation blocks also.

For some important controllers redundant transmitters are provided. Provisions are there for manual change over to the standby in case of failure of the working transmitter .Provisions are there for bumpless transfer of actuator from auto mode to manual mode.

The main automatic controllers are as detailed below:

A. UNIT CAPACITY CONTROL

This controller is for maintaining a controlled TG power output and mainsteam inlet pressure to turbine. This controller incorporate Load change limiter, Boiler capacity control and Turbine capacity control. Boiler capacity controller will receive unit preset capacity signals from unit load rate of change limiter and the actual power output. It generates a demand signal to a coal flow controller & total air flow controller. Turbine capacity controller will receive signal from actual power output , rate of feed forward signals of the preset output, the error signal representing the discrepancy between the demand and actual main steam inlet pressure to for time . Turbine capacity control initiates command to operate the speeder gear motor.

B. COMBUSTION CONTROL Combustion control is done by means of Coal flow controller , Mill loading controller, Total Air flow , Furnace draught controller & F.O pr. controller. Summation of Coal flow & Fuel Oil flow are used for Total air flow controller which maintain a predetermined value of free oxygen in flue gas. The loop actuates individual actuate of FD fans dampers for maintaing the specified free oxygen in flue gas. Mill loading controller regulates feeding of coal to the pulverizes. Furnace draught is controlled through controlling the inlet vanes of ID fans.

4 . ANNUNCIATION SYSTEM The Annunciation system is intended to make available the information about the equipment under control, deviation of measured parameters from the normal (preset) value and interlock action. Alarm is provided with each annunciation block.

Visual status indication of equipment under control i.e Devices and Stop valves

Audio-visual alarm annunciation of emergency tripping and autostart of equipments

Audio-visual process annunciation. Audio-visual preventive alarm annunciation of parameter deviation from

normal value.There are three major section in the annunciation circuit. Section – I controls the Boiler & off site annunciations, section – II controls the turbine related

annunciations and section – III looks after the generator related annunciation. The circuit is powered by 110v DC which is generated by 3 phase 415v AC rooted through a transformer and diode rectifier circuit. Operating status of important drives protection status and alarm conditions, when arises actuate the annunciation system. Once the alarmed value is reached by any signal, it flashes & hooter circuit is energizes. Flashing takes place till the resetting is not done. If the alarmed condition still exist then it glows steadily. Each annunciation section will be provided with test push buttons to check the audio annunciation signal and with the panel switches for lamp healthiness checking.

5. FURNACE SAFEGUARD SUPERVISORY SYSTEM The Furnace safeguard supervisory system supplied by Forney, USA i.e of Model AFS – 1000 is a 16 bit 80186 microprocessor based system. The main task of FSSS is to control the fuel system equipments i.e. oil guns, igniters, PA Fans, Mills, seal air fans and their associated dampers etc. so as to ensure safe operation of the Boiler under start up, transient and normal conditions. Besides, one of the most important FSSS task is to implement process protections with provision for a first up annunciation facility on operating console with respect to the first actuated protections.

AFS – 1000 Burner management system employs plug in printed circuit board assemblies.This permits maintenance by replacing board without causing the total shutdown. The Burner Managent System logic comprises of ten nos. of subsystems (Excluding Maintenance subsystem – II) per each unit each responsible for predefined portion of the overall system. There are two CRT master subsystem ,one purge and fuel safety subsystem, one oil burner subsystem & six mill subsystems. Each subsystem is responsible for a portion of overall control.

A subsystem consist of a single - board control card (80186 up based ) , solid state input / output printed circuit board assemblies, starburst keyboard with intercommunication through fiber optic Assembly and a shared operation interface through fiber of the cable assembly and having touch screen facility. There are also some logic derived inputs that got transmitted

from one subsystem from another and all subsystem operate independently of other subsystem.

A .CRT master subsystem:The primary function of each CRT master subsystem is to act as controller of the intercommunication bus (ICB) used to pass data back and forth between the master and the other subsystem. It also decodes commands that it receives from CRT screen. In the CRT screen the last acknowledged alarm, Printer ON/OFF status and Command elements appear of which print out can be taken if required. For depicting valves ,dampers and drives different symbols were used and when status changes the colour changes.

B .Purge and fuel safety subsystem :The purge and fuel safety subsystem comprises of the following logic.

Purge logic has the major responsibility for insuring that the furnace is purged thoroughly with air to remove any combustible before the fuel is released into the headers & into the furnace. For starting the purge the following conditions should be met.

a). All burner oil valves closed.

b). Oil trip valve closed.

c). Oil re-circulation valve closed

d). No flame detected

e). Scanner Air fan on.

f). Any Induced Draught & Furnace Draught running,

g). All primary fans , pulverizers & Raw coal feeders off.

h). All hot air damper closed.

i). Igniter trip valve closed.

j). No trip (Boiler) present

k). Air flow >30%

After all these conditions are satisfied PURGING takes place for 10Minutes.

I. Pre light Logic: When furnace purging is completed pre light logic is responsible for the safe release of fuel into the headers. Pre light logic is also responsible for communicating to the banners subsystem that furnace conditions are satisfactory for banner operation.

II. Fuel Safety logic :Fuel safety logic is responsible for overall boiler safety. It monitors the potential danger points throughout the boiler. If the predetermined limits are crossed, the fuel safety logic shuts off some or all fuel to the furnace depending upon the conditions. The cause of first out alarm function indicators the cause of the tripping. The MFT 1 and MFT 2 relays get trip command when any of the following conditions is / are initiated.

Both the ID fans off. Both the FD fans off. Operator trip Drum level high / low Loss of all fuel Loss of all flame Unit trip from BPS Furnace pressure high/ low Delayed light off (10 min after purging) Air flow (< 30%) low.

C .Burner control sub system :

It is responsible for following a predetermined programme in safety placing burners in service, removal from service, purging of burners that have been removed from service and for monitoring burner operations.

D.Mill control subsystem: Milling subsystem is responsible for controlling the coal burners and associated pulverizer, primary Air fans, feeders and associated program in safety taking burners in service, removal from service and monitoring burner operation.E .Maintenance subsystem-II.

The MS-II is an equipment helping for fault finding or trouble shooting of the systems input as well as to change the program logic. It comprises of on operation console, a control unit, interfacing cable assembly, graphic CRT / KBD and menu driver software.

6. DATA ACQUISITION SYSTEM The Data Acquisition System of 4x210 Mw KhSTPP was supplied by M/S ESPL ,Chandigarh. This is a WDPF family of system manufactured by Westinghouse with software level version 6.4. This system is a microprocessor based distributed modular type with independent system, drops connected to each other through high speed standard Westnet data highway having 100% redundancy. The drops talk to each other directly over the data highway, which eliminate the need of host computer. The system caters 900 analog points and 1400 digital points in each unit Each system supports two units. The standard WDPF drops and products perform specific functions, which allows a custom system to be configured by determining required functions and selecting the appropriate standard equipment.

7. UPS PACKAGE UPS system of capacity 75 KVA has been supplied by M/S KELTRON ,Trivendrum for each of the four units which caters the power supply for all C&I system including Data Acquisition system. FSSS, Instrument supply, ACS etc. The system consists of 2 nos. chargers, 2 nos. inverters, and one paralleling unit, one servo controlled voltage stabiliser (SVCS) and one set of Battery (550AH) for one-hour backup at 75KVA load. The two inverters, each of which is rated at 75KVA, are connected together to the O/P busbar to share 50% of the load. In case of failure of one inverter the other one takes up the full load automatically. The two chargers, which are meant for feeding the inverters and changing the battery, also work in parallel and each one can take the load if needed. The set of battery is connected at the output of the chargers and input of the inverters. In case of failure of both the chargers the battery automatically takes up the load and starts feeding to the inverters without any interruption. The SCVS is also connected to the output busbar. In case of failure of both the inverters the SCVS gets connected to the output busbar through the static switch with a maximum time delay of 20millisec.

8. ANALYSER AND MISC. C&I EQUIPMENT PACKAGE

The package was awarded to M/S Keltron, Aroor. The package contents of supply of the below mentioned instruments.

1. Analyser for steam and water. Analyse system and Flue gas oxygen analyser. 2. Miscellaneous C&I equipment such as switch drivers etc. and maintenance and Calibration equipment for plant.

The supply and erection and commissioning were in the scope of M/S Keltron.

Only the supply was in the scope of M/S Keltron.

Part (1) is consisting of the following major equipment.a) Flue gas oxygen Analyser.b) Secondary coolers.c) Silica Analyser.d) Hydrogen Analyser.e) PH analyser.f) Conductivity.g) Phosphate Analysers.h) Dissolved oxygen.

Part (2) consists of the following major Equipments.a) Temperature gauges.b) Temperature switch.c) D.P switch.d) Level switch.e) Flow switch.f) Thermocouplesg) Flow elem

Maintenance and calibration equipment:a) Pneumatic test benchb) Vaccum testerc) Thermocouple test furnaced) Flowmeter calibratore) Coil winding machinef) Soldering irong) Radial drilling machine

h) Solder suckeri) Variacj) RLC bridgek) Logic probesl) Portable vibration meterm) Portable pneumatic callibrator