CONTROL AND INSTRUMENTATION OPERATIONS AT NTPC,NEW DELHI

An industrial training report submitted

to

MANIPAL UNIVERSITY

For Partial Fulfillment of the Requirement for the Award of the Degree

of

BACHELOR OF ENGINEERING

in

INSTRUMENTATION AND CONTROL ENGINEERING

by

Abhishek Ranjan

8th semester, B.E. (ICE)

Reg. No. 080921316

DEPARTMENT OF INSTRUMENTATION AND

CONTROL ENGINEERING

MANIPAL INSTITUTE OF TECHNOLOGY

(A constituent Institute of Manipal University)

MANIPAL - 576 104, Karnataka, India

ACKNOWLEDGMENTS

I would like to express my sincere gratitude to Dr. Kumkum Garg, (Director, MIT

Manipal) and Dr. Shreesha C. (HOD,Dept.of ICE, MIT Manipal) for their help and

support which was vital in the completion of this report.

I also want to express my sincere gratitude & respect to the people at NTPC, Badarpur

who always helped & guided me in understanding various concepts, which were

unknown to me.

I am thankful to Mrs. Rachna Singh under whose visionary enlightenment I was able to

complete this report.

Furthermore, I would also like to acknowledge the help and co-operation of Mr.

Manmohan Singh. Without their supervision and assistance at every stage of the

preparation of this project, the completion of this work within the stipulated time would

not have been possible.

LIST OF FIGURES

Figure No Figure Title Page No

1.1 NTPC Contribution 2

1.2 Growth chart 2

1.3 NTPC Logo 6

2.1 Bimetallic strip 9

2.2 Liquid in thermometer 10

2.3 RTD 12

2.4 Thermistor 13

2.5 Thermocouples 14

2.6 Piston 15

2.7 Liquid column 15

2.8 McLeod Gauge 17

2.9 Bourdon 18

2.10 Diaphragm 20

2.11 Bellows 21

2.12 Orifice plates 26

2.13 Venturi meter 27

2.14 Flow nozzle 27

2.15 Pitot Tube 28

2.16 VA meters 29

3.1 DCS System 31

CONTENT

1. About the company

1.1 Introduction 1

1.2 Motivation 1

1.3 Growth chart 2

1.4 Offices 3

1.5 Products 4

1.6 Vision and Values 4

1.7 Organisation 6

2. Measurements in power plants

2.1 Temperature Measurement 8

2.1.1 Solid rode thermometers 8

2.1.2 Bi-metallic strip 8

2.1.3 Liquid in glass thermometer 9

2.1.4 Mercury in steel 10

2.1.5 Thermometer Bulbs 11

2.1.6 Gas Thermometers 12

2.1.7 RTDs 12

2.1.8 Thermistors 13

2.1.9 Thermocouples 14

2.2 Pressure Measurement 15

2.2.1 Hydrostatic 16

2.2.2 Piston 17

2.2.3 Liquid column 18

2.2.4 McLeod gauge 19

2.2.5 Bourdon 20

2.2.6 Diaphragm 21

2.2.7 Bellows 22

2.3 Level Measurement

2.3.1 Floats and liquid displacers 23

2.3.2 Head pressure measurement 24

2.3.3 Electrical Method 25

2.3.4 Ultrasonic Method 26

2.3.5 Nucleonic Method 26

2.4 Flow Measurement

2.4.1 Differential pressure flow meters 27

2.4.2Variableareaflowmeters 28

2.4.3 Electromagnetic flow meters 28

2.4.4 Ultrasonic flowmeters 29

3. Distributed Control Systems

3.1 Distributed control system objectives 31

3.2 DCS Benefits 32

4 Contol and monitoring

4.1 Furnace draft control

4.2 Interlock and protection 33

4.3 Protection and interlock control 34

4.4 Turbine monitoring and control 35

4.5 Automation Lab 35

5. Conclusions 36

1. ABOUT THE COMPANY

1.1 INTRODUCTION

NTPC Limited is the one of the largest energy service providers based in New Delhi. The

Government of India holds 84.5% of its equity. With a current generating capacity of

36,014 MW, NTPC has embarked on plans to become a 75,000 MW company by 2017. It

was founded on November 7, 1975. The Navratna power giant today generates more than

one fourth of the total power in the country. It is the second most efficient in capacity

utilization among the top ten thermal generating companies.

The total installed capacity of the company is 36,014 MW with 15 coal based and 7 gas

based stations, located across the country. NTPC is committed to the environment,

generating power at minimal environmental cost and preserving the ecology in the

vicinity of the plants.

Its core business is engineering, construction and operation of power generating plants. It

also provides consultancy in the area of power plant constructions and power generation

to companies in India.

Major Achievements of NTPC are:

1) Largest thermal power generating company of India

2) Sixth largest thermal power generator in the world.

3) Second most efficient utility in terms of capacity utilization.

4) One of the nine PSUs to be awarded by the status of Navratna

1.2 MOTIVATION TO UNDERTAKE TRAINING AT NTPC Ltd.

NTPC Limited is the largest thermal power generating company of India and has been

ranked 5th largest power generating utility in the world. With a current generating

capacity of 36,014 MW, NTPC has embarked on plans to become a 75,000 MW company

by 2017.

Fig 1.1 NTPC Contribution

1.3 GROWTH CHART :-

Fig 1.2 Growth chart

1.4 OFFICE LOCATIONS

REGISTERED OFFICE:

NTPC Bhawan

Core-7, Scope Complex,

7, Institutional Area, Lodi Road,

New Delhi – 110003

REGIONAL HEADQUARTERS:

Eastern Region

Loknayak Jaiprakash Bhawan,

2nd floor Dak Bunglow Chowk

Patna-800001,

Bihar

National Capital Region

NTPC, R&D Centre Building

Sector-24, NOIDA - 201301,

Uttar Pradesh

Northern Region

B-1 Block, Picup Bhawan,

Vibhuti Khand

Gomti Nagar, Lucknow - 226001,

Uttar Pradesh

Southern Region

2nd & 5th Floor, M.C.H. Complex,

R.P. Road, Secunderabad -500003,

Andhra Pradesh

Western Region

Samruddhi Trade Centre

2nd Floor, MIDC, Marol

Andheri (East),

Mumbai - 400093

Maharastra

1.5 PRODUCTS

NTPC Limited is one of the largest thermal power generating company of India. Its core

business is engineering, construction and operation of power generating plants, It also

provides consultancy to power utilities in India and abroad. It has adopted a multi-

pronged growth strategy which includes capacity addition through green field projects,

expansion of existing stations, joint ventures, subsidiaries and takeover of stations. NTPC

has set new benchmarks for the power industry both in the area of power plant

construction and operations, hence providing power at the cheapest average tariff in the

country. It is committed to preserving the ecology in the vicinity of the power plants and

has also set up an Ash Utilisation division.

1.6 VISION AND VALUES

NTPC’s long term vision, mission and value statements are as appropriate today as when

they were first drafted and introduced. These will continue to guide it in its future

direction of meeting if not exceeding the expectations of its customers and shareholder.

Vision:

“To be the world’s largest and best power producer, powering India’s growth and to be

regarded as an exceptional utility, up to the challenge of delivering safe, reliable and fair-

priced power through a territory-wide system that is efficient and sustainable.”

Mission:

“Develop and provide reliable power, related products and services at competitive prices,

integrating multiple energy sources with innovative and eco-friendly technologies and

contribute to society.”

Core Values –

BE COMMITTED

B- Business Ethics

E- Environmentally & Economically Sustainable

C- Customer Focus

O- Organisational & Professional Pride

M- Mutual Respect & Trust

M- Motivating self & others

I- Innovation & Speed

T- Total Quality for Excellence

T- Transparent & Respected Organisation

E- Enterprising

D-Devoted

In achieving the Corporation’s Vision and Mission, we will endeavour to:

communicate in an open and timely manner

be cost effective in the utilization of all resources, always remembering that we

are spending the customer’s money

be responsive to our customers and their changing needs

act ethically and honestly treating employees, customers and others with fairness,

dignity and respect

commit to the safety of our employees and the public

respect and protect the environment in all our activities to ensure a sustainable

environment

Strive to increase shareholder value in the long-term.

1.7 ORGANISATION OF THE COMPANY

Fig 1.3 NTPC Logo

1975 - NTPC was set up in 1975 with 100% ownership by the Government of

India. In the last 30 years, NTPC has grown into the largest power utility in India.

1997 - In 1997, Government of India granted NTPC status of ³Navratna being one

of the nine jewels of India, enhancing the powers to the Board of Directors.

2004 - NTPC became a listed company with majority Government ownership of

89.5%. NTPC becomes third largest by Market Capitalization of listed companies.

2005 - The company rechristened as NTPC Limited in line with its changing

business portfolio and transforms itself from a thermal power utility to an

integrated power utility.

2008 - National Thermal Power Corporation is the largest power generation

company in India. Forbes Global 2000 for 2008 ranked it 411th in the world.

2012 - NTPC has also set up a plan to achieve a target of 50,000 MW generation

capacities.

2017 - NTPC has embarked on plans to become a 75,000 MW company by 2017.

2. Measurements in Power Plants

In any process the philosophy of instrumentation should provide a comprehensive

intelligence feedback on the important parameters. In power plants also several important

parameters are required to be measured and controlled for efficient and safe operation.

Such parameters are temperature,pressure,level and flow.

2.1 Temperature Measurement:

The most important parameter in thermal power plant is temperature and its measurement

plays a vital role in safe role operation of the plant. Rise of the temperature in a substance

is due to the resultant increase in molecular activity of the substance on application of

heat which increases the internal energy of the material. Therefore there exists some

property of the substance which changes with its energy content. The change may be

observed with substance itself or in subsidiary system in thermodynamic

equilibrium,which is callerd testing body and the system itself is called hot body. There

are many temperature measuring devices used in plants. They are solid rod

thermometers,bi-metallic strip,liquid in glass thermometers,mercury in steel, thermometer

bulbs, gas thermometer,RTDs,thermistors and thermocouples. Following will be the

description about each type of temperature measuring devices.

2.1.1 Solid Rod Thermometers:-

A temperature sensing – controlling device may be designed incorporating in its

construction,the principle that is used will be some metals expand more than others for

the same temperature range.Such a device is the thermostat used with water heaters.

2.1.2 The Bi-metallic strip:-

Bi-metal strips are composed of two metals as the name implies,whose coefficients of

linear expansion are dissimilar.These two metal plates are welded together as a sandwich.

When heated,both metals expand,but the metal with greatest coefficient of linear

expansion will expand more causing the sandwich to curl up or down depending on the

position of the metal.

Fig 2.1 Bimetallic strip

2.1.3 Liquid in glass thermometer

The coefficient 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 it contains. At a high temperature the mercury will occupy a greater fraction

of the volume of the container than it will be at low temperature.

Under normal atmospheric conditions mercury normally boils at a temperature of 347

degree celsius.To extend the range of mercury in glass thermometer beyond this point the

top end of a thermometer bore opens into a bulb which is many times larger in capacity

than the bore. This bulb plus the bore above the mercury is filled with nitrogen and

carbon dioxide gas at a sufficiently high pressure to prevent boiling at the highest

temperature to which the thermometer may be used.

Fig 2.2 Liquid in thermometer

2.1.4 Mercury in Steel

The range of liquid in glass thermometers although quite large,does not lend itself to all

industrial process. This fact is obvious by the delicate nature of glass. Also the position of

the measuring element is not always the best position to read the result.Types of mercury

in steel thermometers are :-

Bourdon Tube

Spiral Type

Helical type

2.1.5 Thermometer Bulbs:-

The thermometer bulbs may take many forms dependent on the application. For example,

if the temperature of a large enclosure is to be measured the bulb may be in the form of a

U or of a considerable length of small tube into spiral. This type of bulb presents the

surface are necessary for measuring the temperature of a gas and is therefore used in this

application.

2.1.6 Gas Thermometers:-

As already stated,in effect of heat,the volume of a gas at constant pressure will change

with relation to temperature change and that at constant volume the pressure change in

relation to temperature. Therefore if a bulb,capillary and a bourdon tube enclose a certain

volume of gas and the both of that assembly is subjected to heat,or change of the

same,the changes of pressure,affected by the heat,within the system can be directly

related to temperature. The later will be shown through the movement of the free end of

the bourdon tube.

While techniques based on thermal expansion provide useful measurements,they lack the

ability to directly transduce temperature into a continuous electrical signal. This limits

their application in automated monitoring and control functions. Fortunately,there are

many measurement techniques that do represent temperature as an electrical quantity.

2.1.7 RTDs :-

Electrical resistance can also be used to determine temperature. The resistance of many

materials (e.g.,iron,copper,aluminium) increases at about 0.3% per degree celcius over a

wide range of temperature. To obtain a significant amount of resistance (e.g., 100

ohms),the metal is either wound on core or patterned as a thin film substrate. The

resulting device is known as resistance temperature detector.

Fig 2.3 RTD

2.1.8 Thermistors

For more pedestrian measurements, requirements and smaller budgets,thermistors offer

another type of temperature to resistance transducer. These devices are made from

various non metallic conductors (e.g.,metal oxides and silicon) and offer the advantage of

much higher thermal coefficients of resistance.

Thermistors are of two types : negative temperature coefficient (NTC) and positive

temperature coefficient (PTC). The resistance of an NTC drops with increasing

temperature ,while that of PTC device rises.

Fig 2.4 Thermistor

2.1.9 Thermocouples

Any junction of dissimilar metals will produce an electric related to temperature. A

thermocouple is a junction between two different metals that produces a voltage related to

a temperature difference. Thermocouples are a widely used temperatire sensor for

measurement and control and can also be used to convert heat into electric power. They

are inexpensive and interchangeable,are supplied fitted with standard connectors, and can

measure a wide range of temperatures. The main limitation is accuracy : system errors of

less than one degree Celsius can be difficult to achieve.

Fig 2.5 Thermocouples

2.2 Pressure Measurement :-

Many instruments have been invented to measure pressure with different advantages and

disadvantages. Pressure range,sensitivity,dynamic response and cost all vary by several

orders of magnitude from one instrument design to the next. The oldest type is the liquid

column (a vertical tube filled with mercury) manometer.

2.2.1 Hydrostatic :-

Hydrostatic gauges (such as the mercury column manometer) compare pressure to the

hydrostatic force per unit area the the base of a column of fluid. Hydrostatic gauge

measurements are independent of the type of gas being measured,and can be designed to

have a very linear calibration. They have poor dynamic responses.

2.2.2 Piston:-

Piston-type gauges counter balance the pressure of fluid with a solid wight or a spring.

Another name for piston gauge is deadweigh tester. For example, dead-weight testers

used for calibration or tire-pressure gauges.

Fig 2.6 Piston

2.2.3 Liquid column

The difference in fluid height in a liquid column manometer is proportional the pressure

difference.

H=P-P0 / ɡδ

Fig 2.7 Liquid column

Liquid column gauges consist of a vertical column of liquid in a tube whose ends are

exposed to different pressures.The column will rise or fall until its weight is in

equilibrium with the pressure differential between the two ends of the tube. A very simple

version is a U-shaped tube half-full of liquid,one side of which is connected to the region

of interest while the reference pressure is applied to the other. The difference in liquid

level represents the applied pressure. If the fluid being measured is significantly

dense,hydrostatic corrections may have to be made for the height between the moving

surface of the manometer working fluid and the location where the pressure measurement

is desired.

Although any fluid can be used,mercury is preferred for its high density (13.534 g/cm3)

and low vapor pressure. For low pressure differences well above the vapour pressures of

water,water is commonly used (and “inches of water” is a common pressure unit).

Liquid-column pressure gauges are independent of the type of gas beinf measured and

have a highly linear calibration. They have poor dynamic response. When measuring

vacuum,the working fluid may evaporate and contaminate the vacuum,if its vapour

pressure is too high. When measuring liquid pressure,a loop filled with gas or a light fluid

must isolate the liquids to prevent them from mixing. Simple hydrostatic gauges can

measure pressures ranging from a few Torr (a few 100 Pa) to a few

atmospheres(approximately 1,000,000 Pa).

A single-limb liquid column manometer has a large reservoir instead of one side of the U-

tube and has a scale beside the narrower column. The column may be inclined to further

amplify the liquid movement. Based on the use and structure following type of

manometers are used.

1. Simple Manometer

2. Micro Manometer

3. Differential Manometer

4. Inverted differential Manometer

2.2.4 McLeod Gauge :-

Fig 2.8 McLeod Gauge

A McLeod gauge isolates a sample of gas and compresses it in a modified mercury

manometer until the pressure is a few mmHg. The gas must be well-behaved during its

compression(it must not condense, for example) . The technique is slow and unsuited to

continual monitoring,but is capable of good accuracy.

USEFUL RANGE :Above 10-2 Pa as high as 0.1 mPa

0.1 mPa is the lowest direct measurement of pressure that is possible with current

technology. Other vacuum gauges can measure lower pressures,but only indirectly by

measurement of other pressure-controlled properties. These indirect measurements must

be calibrated to SI units via a direct measurement,most commonly a McLeod gauge.

2.2.5 Bourdon:-

A bourdon gauge uses a coiled tube,which,as it expands due to pressure increases causes

a rotation of an arm connected to the tube. In 1849 the Bourdon tube pressure gauge was

patented in France by Eudgene Bourdon.

The pressure sensing element is a closed coiled tube connected to the chamber or pipe in

which pressure is to be sensed. As the gauge pressure increases the tube will tend to

uncoil,while a reduced gauge pressure will cause the tube to coil more tightly. This

motion is transferred through a linkage to a gear train connected to an indicating

needle.The needle is presented in front of a card face inscribed with the pressure

indications associated with particular needle deflections. In a barometer,the bourdon tube

is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed.

Differential Bourdon gauges use two Bourdon tubes and a mechanical linkage that

compares the readings.

In the following illustration we have the bourdon tube through which we can easily

measure pressure.

Fig 2.9 Bourdon

2.2.6 Diaphragm:-

This uses the deflections of a flexible membrane that separates regions of different

pressure. The amount of deflection is repeatable for known pressures so the pressure can

be determined by using calibration. The deformation of a thin diaphragm is dependent on

the difference in pressure between its two faces. The reference face can be open to

atmosphere to measure gauge pressure,open to a second port to measure differential

pressure,or can be sealed against a vacuum or other fixed reference pressure to measure

absolute pressure. The deformation can be measured using mechanical,optical or

capacitive techniques. Ceramic and metallic diaphragm are used.

Useful range: roughly 1 Pa

For absolute measurements,welded pressure capsules with diaphragms on either side are

often used.

Shape:

Flat

Corrugated

Flattened tube

Capsule

Fig 2.10 Diaphragm

2.2.7 Bellows :-

In gauges intended to sense small pressure or pressure differences, or require that an

absolute pressure be measured,the gear train and needle may be driven by an enclosed

and sealed bellows chamber,called an aneroid which means “without liquid”.(Early

barometers used a column of liquid such as water or the lquid metal mercury suspended

by vacuum.) This bellows configuration is used in aneroid barometers (barometers with

an indicating needle and dial card),altimeters,altitude recording barographs,and the

altitude telemetry instruments used in weather balloon radiosondes.These devices use the

sealed chamber as a reference pressure and are driven by external pressure. Other

sensitive aircraft instruments such as air speed indicators and rate of climb indicators

(variometers) have connections both to the internal part of aneroid chamber and to an

external enclosing chamber.

Following is the diagram for bellows.

Fig 2.11 Bellows

2.3 Level Measurement:-

The most important reason for making measurement of solid particles or liquid level is

the safety of the personnel and the power plant. Level is mostly measured in terms of

“height of a liquid above a reference line”. If the dimensions of a vessel are 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),volume (liters) or

mass,(kilograms).

There are many methods of measuring level,the selection of a particular system is largely

determined by the practical consideration with capital cost (equipment and

installation),reliablity,maintenance cost and degree of expertise required by the

maintenance personnel.

The methods can be classified as follows:-

1. Floats and Liquid Displacers

2. Head Pressure Measurement

3. Electrical/Electronics

4. Ultrasonic

5. Nucleonic

2.3.1 Floats and Liquid Displacers

Floats:

The use of floats enables the level of liquid to be measured when direct viewing is

impossible. The float material may be of a hollow metal, a plastic material or molded

rubber.

The Floast And Counterweight method consists of a large area float connected by a chain

type or cable to a counterweight which passes in front of a scale and acts as index.

The flaot should have the largest possible area in order to reduce the errors owing to

friction and out of balance forces of the cable or chain. If the surface of the liquid under

measurement is turbulent, a guide will have to set up to stop the float moving around in

the tank and causing errors.

Liquid Displacers:-

This gauge embodying a displacer,relies on Archimedes principle for its

operation.According to this principle if an object is weighted in air and then in liquid

there is apparent loss of weight which is equal to weight of the displaced liquid. The

displacer is a long hollow cylinder loaded to remain partially submerged,and is suspended

in the liquid in the vessel or in an adjacent small diameter chamber connected to the

vessel. The apparent weight of the displacer will decrease as the level of the liquid rises.

2.3.2 Head Pressure Measurement:-

These systems use the principle that a column of liquid will exert pressure whose value

depends only on the weight of liquid, density of liquid and acceleration due to gravity and

is totally independent of the cross-sectional area.

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 that datum point. Thus

a pressure measuring device such as bourdon tube,U tube,manometers can be used scaled

in units of level.

2.3.3 Electrical Method:-

Electrical methods for level measurement are very useful as generally where is the

minimum limitation on transmission distance between transducer and display or control

devices. Their speed of response is often better than pneumatic systems and they are very

useful when measuring the levels of vessels containing the solids.There are basically two

ways of level measurement using electrical method. They are :-

Conductivity Method :-

The system consists of a number of conductors of different legths connected

together by a series of resistors. As the level increases more and more

conductors are shorted together,so shorting out the resistors joining them,thus

the overall resistance will decrease. If a constant value is applied acroos the

terminals,then as level increases,resistance decrease,hence the current flowng

in the circuit increase.Therefore current will be proposrtional to level.

Capacitance Method :-

It involves the use of an electrode which extends the full length of the tank

and forms a capacitance between itself and the earth where earth may be

vessel,the contents or a concentric cylinder around the elctrode,depending on

the type of electrode involved.A variation of capacitance will occur when the

depth of the medium in the vessel alters therefore the capacitance change will

be proportional to level.

2.3.4 Ultrasonic Method :-

When certain materials,mainly nickel,iron and cobalt,are placed within a magnetic

field,their lengths will vary by an amount dependent on the strength of the magnetic field.

The fundamental generator is a nickel tube which carries the coil and bias magnet.

The current through the coil either weakens or strengthens the field,depending on the

direction of the current. Application of an alternating current causes the length of the tube

to increase and decrease at the supply frequency. Owing to the mechanical properties of

the tube it will tend to oscillate longitudnally as a half wave resistor.

Similarly with the reciever, a sound wave impinging on the diaphragm will cause a

relatively large amount of movement in the nickel tube,if within the band paths

frequency,virtually non if outside. Changing the length of the tube will cause a change in

the magnetic strength of the bias magnet,thereby generating an e.m.f. within the coil.

Hence the same can’t be used as either a transmitter or a receiver.

The system is unaffected by dirt,vapor,moisture etc. The sensors are temperature

sensitive; the resonant frequency falls as the temperature rises but there is no effect if

both sensors are at the same temperature. Its another advantage is that the maintenance

required is very less.

2.3.5 Nucleonic Method:-

The nucleonic type level instruments involve a radioactive source, a radiation detector

and electronic measuring circuits.

Since the advent of nuclear reactors and the ready availability of radioactive

materials,nuclear techniques have been employed for the extension of some of the more

conventional methods of level measurement,as well as the invention of the new methods.

The special advantage of nuclear gauge is that they can operate entirely from outside the

containing vessel, or to provide continuous indication of level over a given range.

2.4 Flow Measurement :-

Fluid flow in industrial undertakings occur in two general form : either as a flow in pipe

or as a flow in open channel (in case of liquids only). In both cases,the rate of flow is of

primary importance.

Both gas and liquid flow can be measured in volumetric or mass flow rates,such as litres

per second or kilograms per second. These measurements can be converted between one

another if the material’s density is know. The density for a liquid is almost independent

of the liquid conditions; however,this is not the case for a gas,the density of which

depends greatly upon pressure,temperature and to a lesser extent, the gas composition.

When gases or liquids are transferred for their energy content, such as the sale of natural

gas, the flow rates may also be expressed in terms of energy flow,such as GJ/hour or

BTU/day. The energy flow rate is the volume flow rate multiplied by the energy content

per unit volume or mass flow rate multiplied by the energy content per unit mass. Where

accurate energy flow rate is desired,most flow meters will be used to calcilate the volume

or mass flow rate which is then adjusted to the energy flow rate by the use of a flow

computer.

Rate of flow measuring instrument :-

This class may be broadly divided into :-

1 Differential Pressure flow meters

Orifice pattern

Venturi and nozzle pattern

Pitot tube pattern

2 Variable Area Flow meters

3 Electromagnetic Flow meters

4 Ultrasonic Flow meters

2.4.1 Differential Pressure flow meters

2.4.1.1 Orifice Plate

An orifice plate is a plate with a hole through it,placed in the flow; it constricts the flow,

and measuring the pressure differential across the constriction gives the flow rate. It is

basically a crude form of Venturi meter,but with higher energy losses. There are three

types of orifice : concentric, eccentric, and segmental.

Fig 2.12 Orifice plates

2.4.1.2 Venturi Meter:-

A venturi meter constricts the flow in same fashion, and pressure sensors measure the

differential pressure before and within the constriction. This method is widely used to

measure flow rate in the transmission of gas through pipelines, and has been used since

Roman Empire times. The coefficient of discharge of Venturi meter ranges from 0.93 to

0.97.

Fig 2.13 Venturi meter

2.4.1.3 Nozzle

The nozzle falls between the venture tube and the orifice plate as a means of flow

measurement. It approximates to a venturi tube with the curved form of approach, giving

a gradual change of sectional area and has the same order of discharge coefficient. But

the absence of a downstream expansion core brings the pressure loss in to the same

region as that for an orifice plate. It is cheaper than a venturi tube,and at a high velocity

flow it is used in place of an orifice plate.

Fig 2.14 Flow nozzle

2.4.1.4 Pitot Tube

A pitot tube is a pressure measuring instrument used to measure fluid flow velocity by

determining the stagnation pressure. Bernoulli’s equation is used to calculate the dynamic

pressure and hence fluid velocity.

Fig 2.15 Pitot Tube

2.4.2 Variable Area Flow Meters

The variable area (VA) meter, also commonly called a rotameter, consists of a tapered

tube,typically made of glass, with a float inside that is pushed up by fluid flow and pulled

down by gravity. As flow rate increases,greater viscous and pressure forces on the float

cause it to rise until it becomes stationary at a location in the tube that is wide enough for

the forces to balance. Floats are made in many different shapes,with spheres and spherical

ellipses being the most common. Some are designed to spin visibly in the fluid stream to

aid the user in determiningwhether the float is stuck or not. Rotameters are available for a

wide range of liquids but are most commonly used with water or air. They can be made to

reliably measure flow down to 1% accuracy.

Fig 2.16 VA meters

2.4.3 Electromagnetic Flow Meters

The most common flow meter apart from mechanical flow meters is the magnetic flow

meter,commonly referred to as a “mag meter” or an “electromag”. A magnetic field is

applied to the metering tube,which results in a potential difference proportional to the

flow velocity perpendicular to the flux lines. The physical principle at work is Faraday’s

law of electromagnetic induction. The magnetic flow meter requires a conducting fluid,

e.g. water,and an electrical insulating pipe surface,e.g. a rubber lined nonmagnetic steel

tube.

2.4.4 Ultrasonic Flow Meters

Ultrasonic flow meters measure the difference of the transit time of ultrasonic pulses

propagating in and against flow direction. This time difference is a measure for the

average velocity of the fluid along the path of the ultrasonic beam. By using the absolute

transit times both the averaged fluid velocity and the speed of sound can be calculated.

3. Distributed Control System

A distributed control system (DCS) refers to a control system usually of a manufacturing

system,process or any kind of dynamic system, in which the controller elements are not

central in the location but are distributed throughout the system with each component sub

system controlled by one or more controllers. The entire system of controllers is

connected by networks for communicating and monitoring.

Fig 3.1 DCS

3.1 Objectives

Safe operation of the plant

Lowest cost of generation

Longest equipment life

Minimum environmental effect

Maximum efficiency

Energy conservation

3.2 Benefits :-

High reliability

Improved response time

Improved operator interface to plant

Improved accessibility of plant data to engineering and management personals

4. Control and Monitoring

4.1 Furnace Draft Control

FSSS (FURNACE SAFEGUARD SUPERVISORY SYSTEM) is also called as Burner

Management System (BMS). It is a microprocessor based programmable logic controller

of proven design incorporating all protection facilities required for such system. Main

objective of FSSS is to ensure safety of the bolier.

Furnace draft control system has the responsibility of starting fire in the furnace to enable

the burning of coal. Un-burnt coal is removed using forced draft or induced draft fan. The

temperature inside the boiler is 1100 degree celsius and its height is 18 to 40 m. It is

made up of mild steel. An ultra violet sensor is employed in furnace to measure the

intensity of ultra violet rays inside the furnace and according to it a signal in the same

order of same mV is generated which directly indicates the temperature of the furnace.

For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray of

diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six feeder

mills each separated by warm air pipes fed from forced draft fans. In first stage indirect

firing is employed that is feeder mills are not fed directly from coal but are fed from three

feeders but are fed from pulverized coalbunkers. The furnace can operate on the

minimum feed from three feeders but under no circumstances should anyone left under

operation,to prevent creation of pressure different within the furnace,which threatens to

blasti it.

4.2 Interlock and Protection

4.2.1 Interlocking :-

It is basically interconnecting two or more equipments so that if one equipments fails

other one can perform tha tasks. This type of interdependence is also created so that

equipments connected together are started and shut down in the specific sequence to

avoid damage.

For protection of equipments tripping are provided for all the equipments. Tripping can

be considered as the series of instructions connected through OR gate. When the main

equipments used in this control system are relay and circuit breakers.

Relays:-

These are the protective devices. It can detect wrong condition in electrical circuits by

constantly measuring the electrical quantities flowing under normal and faulty

connections. Some of the electrical quantities are voltage,current,phase angle and

velocity.

Fuses:-

It is a short piece of metal inserted in the circuit,which melts when heavy current flows

through it and thus breaks the circuit. Usually silver is used as a fuse material because of

low coefficient of expansion.

Miniature circuit breaker:-

They are used with combination of the control circuits to:-

Enable the staring of plants and distributors

Protect the circuit in case of a fault

When a fault occurs the contacts separate and are is stuck between them. These are

three types of a) Manual strip, b)Thermal strip & c) Short circuit trip.

4.3 Protection and interlock system circuit :-

4.3.1 HIGH TENSION Control Circuit

For high tension system the control system are excited by separate D.C. supply. For

starting the circuit conditions should be in series with the starting coil of the equipment to

energize it. Because if even a single condition is not true then system will not start.

4.3.2 LOW TENSION Control Circuit

For low tension system the control circuits are directly excited from the 0.415 KV A.C.

supply. The same circuit achieves both excitation and tripping. Hence the tripping coil is

provided for emergency tripping if the intercoection fails.

4.4 Turbine Monitoring and Control

The turbine supervisory instrument system is an aid which enables processing of

information regarding various parameters of the turbine for its safe and proper operation.

The main parameters which are processed under this system are:

Speed of turbine motor

Axial shaft of rotor

Differential expansion of rotor and cylinder

Shaft eccentricity

Casing expansion

Bearing vibration

Seal interference

Turbine metal temperature

4.2 Automation Lab

This lab deals with automating the existing equipments and feeding routes. Earlier the old

technology dealt only with DAS( Data Acquisition System) and came to known as

primary systems. The modern technology or secondary systems are coupled with (MIS)

Management Information Systems.But this lab universally applies the pressure measuring

instruments as the controlling force. However, the relays are also provided but they are

used only for protection and interlocks.

5. CONCLUSIONS

The industrial training exposure at NTPC,Badarpur was a very new kind of experience

for me.For the first time,I saw a very big power plant. I got training in control and

instrumentation department of NTPC.

I saw various kinds of industrial instruments which were used for measuring

temperature,pressure,level and flow parameters in industries.These instruments provided

a practical approach to all the theories that we have studied in college.

Also I was shown the control labs which acted as the brain of the power plant. All

activities were monitored from here at regular basis. The errors that may occur were well

taken care of.

Overall,the industrial visit to NTPC was highly educational experience.