Industrial Training Report

On

NTPC Dadri Thermal Power Plant

Submitted in partial fulfillment of the requirements for the award of the degree

Of

Bachelor of technology

In

Electronics and Communication Engineering

Govind Ballabh Pant Engineering College

Pauri Garhwal, Uttarakhand

Submitted To: Submitted By:

Mr.Diwaker Pant Harshit Tyagi

(Assistant Professor) ECE Final Year

Roll No: 16

Preface

The aim of industrial training during studies is to expose students to the industrial environment,

which cannot be simulated in the classroom. It helps students to make them aware of the rapid

development being made in the industry, as the needs of the industry are changing due to the rapid

change in technology , management practice, competitive quality and productivity etc.

Summer training has helped me to appreciate the theoretical knowledge gained by me in the

classroom .It has taught me the importance of punctuality and the sense of responsibility. It has

helped me to understand the psychology of the employees, their attitude and their approach to the

problem. Apart from that it has given me good exposure to the current technology development

relevant to my subject of studies.

This report has been made by my experience of training at National Thermal Power Corporation

Limited- Dadri.I was assigned to work in Control and Instrumentation-Thermal Department. The

specification and principles are as learned by me from the employees of each division of NTPC. The

training at NTPC helped me enhance my knowledge to a great level. It has made me understand the

problems in a more logical way and deal with them analytically.

Acknowledgment

I would like to express my deep gratitude to Mr. PPS Tomar, DGM CS Department NTPC

limited-Dadri who provided me the opportunity to undergo summer training at this esteemed

establishment.

I am thankful to Er. Amit Sharma(C&I), Er. Vipul Aggarwal (C&I) my guides who inculcated in

me the interest and the inspiration to undertake this summer training with full desire and successfully

complete it. They have been a great source of motivation for me throughout the training especially in

the plant visit stages and for the boundless support that enabled me to complete the work in the

present form. Also, I would like to express my gratitude towards Mr. Tajinder Gupta,DGM C&I-

Thermal Department, for giving us his valuable time and discussing major challenges faced by him

as a manager of whole department.

Finally, I extend my sincere thanks to all members of NTPC limited, Dadri for their help and support

during my training period.

Harshit Tyagi

ECE IV Year

GBPEC, Pauri

Contents

1. Introduction

2. About NTPC

2.1Overview of NTPC

2.2Dadri Station-At a glance

3. Thermal Plant

3.1 Thermal Power Generation

3.2 Coal Based Power Station

3.3 By Products of Power Generation

3.4 Equipments in Thermal Plant

4. Control & Instrumentation Department

4.1 Measurements in Power Plant

4.2 Control Room

4.3Temperature Measurement

4.4 FSSS Logic System

4.5 Pressure Measurement

4.6 Turbine Protection

5. Safety Measures

6. Conclusion

7. References

1. Introduction

In present time we are seeing that industrial training is necessary for every technical &

management student. NTPC organize training programs according to the trade of trainee and

section of interest of the trainee. NTPC Dadri is the only national capital power station to have

both gas and coal based power generation capacity. It also has the capability to run both the units

simultaneously.

This report is based on my industrial visit to NTPC Power Plant at Dadri. Through this report, I

intend to give a detail about NTPC Dadri power plant and its operation. In this modern era, every

area of work say airport, railway, industries, military, shopping malls & even domestic needs

depends completely upon power supply. These area needs continuous supply for there operation,

therefore there is a need of a unit that can provide continuous power supply to large sections of

society.

NTPC has its core values as:

B BUSINESS ETHICS

C CONSUMER FOCUS

O ORGANISATION AND PROFESSIONAL

M MUTUAL RESPECT AND TRUST

I INNOVATION AND SPEED

T TOTAL QUALITY FOR EXCELLENCE

2. About NTPC

2.1 Overview Of NTPC

NTPC was set up in the central sector in the 1975 in response to widening demand & supply gap

with the main objective of planning, promoting & organizing an integrated development to

thermal power in India. Ever since its inception, NTPC has never looked back and the

corporation is treading steps of success one after the other. The only PSU to have achieved

excellent rating in respect of MOU targets signed with Govt. of India each year. NTPC is poised

to become a 40,000 MW giant corporation by the end of XI plan i.e. 2012 AD. Lighting up one

fourth of the nation, NTPC has an installed capacity of 29,394 MW from its commitment to

provide quality power; all the operating stations of NTPC located in the National Capital Region

& western have acquired ISO 9002 certification. The service groups like Engineering, Contracts,

materials and operation Services have also bagged the ISO 9001 certification. NTPC Dadri,

Ramagundam, Vindhyachal and Korba station have also bagged ISO 14001 certification.

Today NTPC contributes more than 3 / 5th of the total power generation in India. As per Forbes

global 2000 ranking for the year 2005, NTPC was 463rd biggest company in the world and 5th

biggest Indian company

As per ADB’s memorandum NTPC is 2nd largest Asian power generator.

GLIMPSES OF NTPC

1. 22 installed Plants

2. 15 Thermal and 7 Gas Power plants

3. 30,000 MW installed capacity

4. Generates 20% of total power generated in India

5. Largest power plant is situated in Vindhyachal, U.P

6. Also, some captive power plants are run in collaboration like the one in SAIL

2.2 Dadri Station At a Glance

NTPC Dadri is model project of NTPC. Also it is the best project of NTPC also known as NCPS

(National capital power station). Situated 60 km away from Delhi in the District of Gautama

Budh Nagar, Uttar Pradesh. NTPC’s Dadri plant is the only one in India to house gas-based as

well as coal-based generating units. The station has an installed capacity of 1669 MW of power –

840 MW from Coal based units and 829 MW Gas Based Station. The coal-based station’s boiler

can be fired using 100% furnace oil as well.

NTPC Dadri has a total installed capacity of 1669.78 Mega Watts. The coal plant has 4 units

which were commissioned one by one from 1991 to 1994 .Each unit has a generation capacity of

210 MW.

The Gas plant has 6 units which have a combined capacity of 829.78 MW. It has 4 gas turbine

units which were commissioned in 1992 while the 2 steam turbine units were commissioned in

1994. The gas turbine units have a capacity of 130.19 MW each while the steam turbines have a

capacity of 154.51 MW each. The station has ~1,130 employees, who have been given

accommodation in an integrated township adjacent. The plant is spread over 2,665 acres, making

it one of the largest sites in India.

The coal unit receives coal from North Karanpura mines located in Jharkhand, almost 1,400km

from Dadri. The coal (grade E, calorific value ~4,324-5,089 Kcal/kg) is fed through a rail link.

NTPC has a dedicated railway siding that connects Dadri station and the plant. Gas for the plant is

supplied by GAIL and is sourced through the HBJ pipeline. The plant consumes 4.7m tones of

coal annually, and requires 4.0 mmsmd gases. However, owing to the shortage of gas in India,

actual supplies are only 2.5-2.6mmsmcd. Hence, although the coal plant’s PLF has been well over

90% since FY05, the gas station’s PLF has been much lower, at ~74% for the same period.

The station has the largest switchyard in India, with power-handling capacity of 4,500MW.

The station is excelling in performance ever since it’s commercial operation. It is consistently in

receipts of meritorious project awards, the coal based units of the station stood first in the

country in terms of PLF for the financial year 1999 – 2000 by generating an all time national

high PLF of 96.12 % with the most modern O & M Practices. NTPC – Dadri is committed to

generating clean and green Power. The Station also houses the first HVDC station of the country

(GEP project) in association with centre for power efficiency and Environment protection

(CENEEP) – NTPC & USAUID. The station has bagged ISO 14001 & ISO 9002 certification

during the financial year 1999 – 2000, certified by Agency of International repute M/s DNV

Netherlands M/s DNV Germany respectively.

As a part of the infrastructure for the Commonwealth Games, the station is adding coal-based

capacity of 980MW (Stage II expansion) consisting of two units of 490MW each.

3. Thermal Plant

Thermal power plants convert the heat energy of coal into electrical energy. Coal is burnt in a boiler

which converts water into steam. The expansion of steam in turbine produces mechanical power

which drives the alternator. To achieve efficient conversion of heat energy into electric energy, a

variety of auxiliary equipments are needed. The auxiliary equipments in a thermal plant are so much

that they overshadow the main equipments.

The coal handling plant supplies coal to the boiler. The ash formed in the boiler is disposed by the ash

handling plant. Air taken from the atmosphere by the action of force induced or draft fan is heated in

the preheater before being fed to the boiler. The flue gases pass through dust collector, air preheater

and economizer before being discharged to the atmosphere through the chimney. The boiler vaporizes

water into steam; steam is further heated in the super heater and fed to the high pressure turbine. After

expanding in high pressure turbine, steam is heated again in a boiler and fed to the low pressure

turbine. The exhaust steam from the low pressure turbine is condensed by the condenser and the

condensate, along with makeup water, is passed through economizer before being fed to the boiler

The coal plant produces a total power of 840MW. The coal-based station’s boiler can be fired using

100% furnace oil as well. The gas station has two modules, each consisting of four 130.2MW gas

turbines, with a waste-heat recovery boiler and two 154.5MW steam turbines. The station has the

largest switchyard in India, with power-handling capacity of 4,500MW. As a part of the

infrastructure for the Commonwealth Games, the station is adding coal-based capacity of 980MW

(Stage II expansion) consisting of two units of 490MW each. The Dadri plant is 50km away from

Delhi, in the state of Uttar Pradesh. Road connectivity to the plant has improved of late, thanks in

large part to NTPC’s efforts Dadri coal plant has the highest PLFs among all of NTPC’s units . The

coal unit receives coal from North Karanpura mines located in Jharkhand, almost 1,400km from

Dadri. The coal (grade E, calorific value ~ 4,324-5,089 Kcal/kg) is fed through a rail link. NTPC has

a dedicated railway siding that connects Dadri station and the plant. Gas for the plant is supplied by

GAIL and is sourced through the HBJ pipeline. The plant consumes 4.7m tones of coal annually, and

requires 4.0mmsmd gas. However, owing to the shortage of gas in India, actual supplies are only 2.5-

2.6mmsmcd. Hence, although the coal plant’s PLF has been well over 90% since FY05, the gas

station’s PLF has been much lower, at ~ 74% for the same period. Environment-friendly unit. The

plant operates the country’s largest fly-ash disposal facility, with 53m m3 storage capacity.

Additionally, Ambuja and Grasim have announced plans to set up cement units near the plant, to use

the fly-ash generated from the plant. As an incentive, NTPC will supply fly-ash to these plants free of

cost for the first few months. The thermal station currently produces 1.5m tones of fly-ash daily and

some of this is sold in auctions by NTPC’s subsidiary NTPC Vidyut Vyapar Nigam. This generates

an additional ~ Rs350m income for NTPC annually. The unsold ash has been used to create a

flourishing nature park around the plant. The 550-acre ash mound acts as an ecosystem for both flora

and fauna. However, churn is evident at the corporate level, where such amenities are not provided

and the operating structure is more bureaucratic.

Dadri is a benchmark for the best operation practices .Dadri has adopted the best practices for safety,

environment protection and maintenance. This is evident from its ISO 9001-2000, ISO 14001 and

OSAS 18001 certifications. Additionally, to improve infrastructure around the plant, the company is

laying a cement access road. 35% of material used would be fly-ash generated by the plant. The

Rs250m-300m expenditure incurred would be capitalized by NTPC. As a part of supply-chain

management, the station also assists coals mines in their operations and maintenance. Dadri can add a

further 500MW capacity through Brownfield expansion. The existing campus has enough land

available to allow an additional Brownfield expansion by 500MW. Even for the Stage II expansion,

only 200 acres additional land for the reservoir was required.

3.1. Thermal Power Generation

In a conventional thermal power station, a fuel is used to heat water, which gives off steam at high

pressure. This in turn drives turbines to create electricity. At the heart of power stations is a generator,

a rotating machine that converts mechanical energy into electrical energy by creating relative motion

between a magnetic field and a conductor. The energy source harnessed to turn the generator varies

widely. It depends chiefly on which fuels are easily available and on the types of technology used.

Thermal power plants are classified by the type of fuel used

Nuclear power plants use a nuclear reactor’s heat to operate a steam turbine generator

Fossil fuelled power plants may also use a steam turbine generator or in the case of

natural gas fired plants may use a combustion turbine.

Geothermal power plants use steam extracted from hot underground rocks

Renewable energy plants may be fuelled by waste from sugar cane, municipal solid

waste, landfill methane, or other forms of biomass

In integrated steel mills, blast furnace exhaust gas is a low-cost, although low-energy-

density, fuel

Waste heat from industrial processes is occasionally concentrated enough to use for

power generation, usually in a steam boiler and turbine

Solar thermal electric plants use sunlight to boil water, which turns the generator

3.2. Coal Based Power Stations

When coal is used for electricity generation, it is usually pulverised and then burned in a furnace with

a boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines which

turn generators and create electricity.

The thermodynamic efficiency of this process has been improved over time. ‘Standard’ steam

turbines have topped out with some of the most advanced reaching about 35% thermodynamic

efficiency for the entire process, which means 65% of the coal energy is waste heat released into the

surrounding environment. Old coal power plants, especially ‘grandfathered’ plants, are significantly

less efficient and produce higher levels of waste heat. About 40% of the world's electricity comes

from coal.

3.3 By Products of Power Generation

Byproducts of power plant operation need to be considered in both the design and operation. Waste

heat due to the finite efficiency of the power cycle must be released to the atmosphere, often using a

cooling tower, or river or lake water as a cooling medium. The fuel gas from combustion of the fossil

fuels is discharged to the air; this contains carbon dioxide and water vapor, as well as other

substances such as nitrogen, nitrous oxides, sulfur oxides, and (in the case of coal-fired plants) fly ash

and mercury. Solid waste ash from coal-fired boilers is removed. Ash generated can be re-used for

building materials.

3.4 Equipments in Thermal Plant

3.4.1Coal Handling Plant

The function of coal handling plant is automatic feeding of coal to the boiler furnace. A grate at

the bottom of the furnace holds the fuel bed. Coal is weighed and led to a hopper through a

conveyer mechanism. From the hopper it is fed to the gate through some form of stoker

mechanism. The stoker may be an overfeed stoker or underfeed stoker depending on whether

coal entry is above or below the air entry. It require around 8,400 tons of coal daily. In NTPC

there is enough storage of coal to last for 15 days or so.

3.4.2 Pulverizing Plant

In modern thermal power plants, coal is pulverized i.e. ground to dust like and carried to the

furnace in a stream of hot air. Pulverization is a means of exposing a large surface area to the

action of oxygen and consequently helping the combustion.

ADVANTAGES

1. The rate of combustion can be controlled and changed quickly to meet the varying load.

2. The banking losses are reduced.

3. The percentage of excess air required is low.

4. Automatic combustion control can be used.

5. A wide variety of even low grade coals can be used.

6. The boiler can be started from cold conditions very rapidly.

DISADVANTAGES

1. Investment cost of plant is increased.

2. Explosion hazards exist. Therefore, skilled personnel are required.

3. Auxiliary power consumption of the plant is increased.

4. A lot of extra equipments, mills, burners are needed.

3.4.3 Draft System

The combustion in the boiler requires a supply of sufficient quantity of air and removal of

exhaust gases.

The circulation of air is caused by a difference in pressure, known as draft. Thus draft is the

differential in pressure between the two points i.e. Atmosphere and inside the boiler. A

differential in draft is needed to cause flow of gases through the boiler setting. This required

differential is proportional to square of the rate of flow. It may be natural or mechanical.

NATURAL DRAFT

A natural draft is provided by a chimney or stack. Chimney serves two purposes i.e. it produces a

draft so that can flow into the boiler and products of combustion are discharged to the

atmosphere and it delivers the product of combustion and fly ash to a high altitude so that air

pollution is reduced. The gases within the chimney are at higher temperature than that of the

surrounding air.

MECHANICAL DRAFT

Modern large size plants use very huge size boilers of capacity above 1000,000 kg per hour.

Such boilers need tremendous volume of air. A chimney cannot provide enough draft for this

amount of air. Therefore mechanical draft is necessary. Of course a chimney is always provided.

3.4.4. Boiler

A boiler is a closed vessel in which water, under pressure, is converted into steam. It is one of the

major components of a thermal power plant. A boiler is always designed to absorb maximum

amount of heat released in the process of combustion. This heat is transferred to the boiler by all

the three modes of heat transfer i.e. conduction, convection and radiation. They are classified as

fire tube boiler and water tube boiler.

FIRE TUBE BOILER

This boiler is so named because the product of the combustion passes through the tubes which

are surrounded by the water. Depending upon whether the tubes are horizontal or vertical, they

are further classified as horizontal or vertical tube boilers. They may be internally fed or

externally fed.

WATER TUBE BOILER

In this boiler, water flows inside the tubes and hot gases flow outside the tubes .The tubes are

interconnected to common water channels and to steam outlet. Water tube boilers are classified

as vertical, horizontal and inclined tubes depending upon whether the tubes are vertical,

horizontal or inclined. The number of drums may be one or more.

3.4.5. Steam Turbine

A steam turbine converts heat energy of steam into mechanical energy and drives the generator.

It uses the principle that a steam when issuing from a small opening attains a high velocity. This

velocity attained during expansion depends on the initial and final heat content represents the

heat energy converted to kinetic energy. They are of two types impulse and reaction turbine.

3.4.6. Ash Handling Plant

Coal contains a considerable amount of ash. The percentage of ash in the coal varies from about

5% in good quality coal to about 40% of poor quality coal. Power plants generally use average or

poor quality coal .As a result of this the ash produced by a plant is pretty large. A modern 2000

MW plant produces 5000 tons of ash daily. Of this about 25% is furnace bottom ash and

remaining 75% is pulverized fuel ash or dust or fly ash .The small stations use some conveyer

arrangement to carry ash to dump sites directly or for carrying and loading it to trucks and

wagons which transport it to the site of disposal.. Large stations use more elaborate

arrangements and separate systems for the furnace bottom or fly ash.

3.4.7. Condenser

Condenser does the job of condensing the steam exhausted from turbine. Thus it helps in

maintaining low pressure at the exhaust, thereby permitting expansion of steam in the turbine to

a very low pressure. This improves the plant efficiency .The exhaust steam is condensed and

used as feed water to the boiler. Maintenance of high vacuum in the condenser is essential for

efficient operation. Any leakage of air in the condenser is essential for efficient operation. Any

leakage of air into the condenser destroys the vacuum. As it is impossible to eliminate air

leakage completely, a vacuum pump is necessary to remove the air leaking into condenser.

3.4.8. Cooling Towers

The condenser needs huge quantity of water to condense the steam. Roughly one kg of steam

needs 100 kg of cooling water for the condenser. Such large requirement of water can be met if

the plant is situated by the side of a big river with sufficient flow. Water is led into the plant by

means of circulating water pumps and, after passing through the condenser, is discharged back

into the river. It is necessary to establish the correct relative position of the intake and outfall.

A cooling tower is a steel or concrete hyperbolic structure having a reservoir at the bottom for

storage of cooled water. Warm water is led to the top. Air flows from the bottom to top. The

water drops falling from the top come in contact with air, lose heat to the air and get cooled.

3.4.9 Economizer

Flue gases coming out of the boilers carry lot of heat. An economizer extracts a part of this heat

from the flue gases and uses it for heating feed water. The use of an economizer results in saving

the coal consumption and higher boiling efficiency, but need extra investment and increase in

maintenance costs and flour area required for the plant. Economizer is used in all modern power

plants.

3.4.10 Relay

A relay is n electrical switch that opens and closes under the control of another electrical circuit.

In the original form, the switch is operated by an electromagnet to open or close one or many

sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an

output circuit of higher power than the input circuit, it can be considered to be, in a broad sense,

a form of an electrical amplifier.

Since relays are switches the terminology applied to switches is also applied to relays. A relay

will switch one or more poles, each of whose contacts can be thrown by energizing the coil in

one of three ways:

Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit

is disconnected when the relay is inactive. It is also called a Form A contact or "make"

contact.

Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the

circuit is connected when the relay is inactive. It is also called a Form B contact or

"break" contact.

Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-

open contact and one normally-closed contact with a common terminal. It is also called a

Form C contact or "transfer" contact ("break before make"). If this type of contact

utilizes” make before break" functionality, then it is called a Form D contact.

Motor Protection Relay This relay detects how much is the positive sequence component, how

much is negative sequence component and how much is zero sequence component. In case

negative sequence component and zero sequence component (earth fault) goes above a certain

value, it trips the Circuit Breaker.

Fig 2.2 Relays

3.4.11. Feed Water Heater

A feed water heater is a power plant component used to pre-heat water delivered to a steam

generating boiler. Preheating the feed water reduces the irreversibility involved in steam

generation and therefore improves the thermodynamic efficiency of the system. This reduces

plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed

water is introduced back into the steam cycle.

In a steam power plant, feed water heaters allow the feed water to be brought up to the saturation

temperature very gradually. This minimizes the inevitable irreversibility associated with heat

transfer to the working fluid (water).

3.4.12. Super heater and re heater

Fossil fuel power plants can have a super heater or re heater section in the steam generating

furnace. Nuclear-powered steam plants do not have such sections but produce steam at

essentially saturated conditions. In a fossil fuel plant, after the steam is conditioned by the drying

equipment inside the steam drum, it is piped from the upper drum area into tubes inside an area

of the furnace known as the super heater, which has an elaborate set up of tubing where the

steam vapor picks up more energy from hot flue gases outside the tubing and its temperature is

now superheated above the saturation temperature. The superheated steam is then piped through

the main steam lines to the valves before the high pressure turbine.

Power plant furnaces may have a re heater section containing tubes heated by hot flue gases

outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the re

heater tubes to pickup more energy to go drive intermediate or lower pressure turbines.

3.4.13. Air Preheater

An air preheater (APH) is a general term to describe any device designed to heat air before

another process (for example, combustion in a boiler) with the primary objective of increasing

the thermal efficiency of the process. They may be used alone or to replace a recuperative heat

system or to replace a steam coil. The purpose of the air preheater is to recover the heat from the

boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat

lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas stack (or

chimney) at a lower temperature, allowing simplified design of the ducting and the flue gas

stack. It also allows control over the temperature of gases leaving the stack (to meet emissions

regulations, for example).

There are two types of air preheater for use in steam generators in thermal power stations: One is

a tubular type built into the boiler flue gas ducting, and the other is a regenerative air preheater.

These may be arranged so the gas flows horizontally or vertically across the axis of rotation.

3.4.14. Protection and control Equipment

In the thermal power plant, protection and control equipments controls and protects all the

equipments of power generation process from emergency or unexpected conditions. Devices

protected are such as Boiler, turbine etc. Control devices measure and maintain other parameters

such as temperature, pressure etc.

The turbine protection system can be actuated by two methods-Hydraulic trip system and

Electrical Trip System. Both the systems, when initiated, act on hydraulic control system and

cause trip oil pressure to collapse which in turn closes the emergency stop valves, Interceptor

valves and control valves.

4. Control & Instrumentation Department

Control and Instrumentation department plays the most significant role in a thermal power plant.

It consists of engineers from Electronics and Communication Branch. This department is further

divided into

1. Operations Department and

2. Maintenance Department

Operations Department looks after the successful operation and running of power plant.

This department takes care of plant running conditions. They are responsible for

providing data at control room regarding the plant conditions and parameters such as

temperature etc.

Maintenance department is responsible for all the maintenance related tasks of plant and

control systems. Thermal power plant consists of control systems used for controlling the

plant devices. These control systems are maintained by C&I Department.

4.1. MEASUREMENTS IN POWER PLANTS

In a power plant number of measurements is made. These can be divided into

Electrical measurements – current, voltage, power, frequency, power-factor etc.,

Non-Electrical parameters – flow of feed water, fuel, air and steam with correction factor

for temperature – steam pressure and steam temperature-drum level measurement –

radiation detector – smoke density measurement – dust monitor.

4.2. Control Room

From the control room, the plant operators monitor and operate the facility, via the

plant’s “Distributed Control System”, with the click of a mouse, viewing graphic

representations of all MEC systems on various screens.

The system gives operators both audible and visual signals to keep them informed of

plant conditions at all times and to determine when preventative maintenance is required.

Control Rooms are connected to plant via optical fibers.

They receive real time data regarding the plant conditions such as boiler temperature,

pressure, fan speed etc.

They are used to control and monitor all the plant conditions and various parameters.

They are used to trip boiler, primary fan, turbine and other power plant equipments in

case of their regarding parameters crossing the safe limits.

4.3. Temperature Measurement

Temperature Measurements in a power plant is a very important task. If temperature of any of

the plant equipments rises above its safe limits, it would cause serious security problems and can

be a threat to plant and its workers.

4.3.1. Temperature Measurement Devices

For the purpose of temperature measurement, various devices are used depending on the

suitability and applicability of measuring devices. Some of them are thermocouples, resistance

thermometers, thermistors, bimetallic thermometers and acoustic pyrometers.

Thermocouple

Thermocouple is based on seeback effect which states that when heat is applied to a junction of

two dissimilar metals an emf is generated which can be measured at the other junction.

Fig. A thermocouple junction

Resistance Thermometer

The resistance of a conductor changes when its temperature is changed. This property is utilized

to measure the temperature.

Rt = Ro (1+βdT)

WHERE β = Temperature co-efficient of resistance

dT = Temperature difference

HOT JUNCTION

TERMINAL ENDCJC BOX

COMPENSATING CABLE

TO DDC CARDS

Fig. Resistance Temperature Detector

Thermistors

Thermistors are generally composed of semiconductor materials. They have a negative

coefficient of temperature, so resistance decreases with increase in temperature.

The coefficient is as large as several % per degree Celsius. This allows the thermistors to detect

small changes in temperature which could not be observed with thermocouples or RTDs. So

these are used for precision temperature measurements control and compensation.

Bimetallic Thermometers

Bimetallic Thermometers works on the principle that all metals expand or contract with

temperature and the temperature coefficient is not the same for all metals and so their rate of

expansion or contraction are different.

ELEMENT

SHEATH

LEAD SUPPORT

MOUNTING THREADS

CONNECTING LEADS

Fig. Bimetallic Thermometer

Bimetallic devices are extensively used in process industries for local temperature

measurements. These are also used as cut out switch in electrical apparatus by monitoring

current flow.

Acoustic Pyrometer

Acoustic pyrometers work on the principle that the velocity of sound in a medium is proportional

to the temperature.

Gas Temperature = [ Distance / (Time * B) ]^2

Where, B=constant

4.4. FSSS Logic System

FSSS stands for Furnace Safeguard Supervisory System. It has the following major tasks to

perform:

Satisfactory Boiler Startup

Startup Of Individual Oil Systems

Operation Of fuel firing subject to certain conditions

Protection and interlock of oil/coal system

FIXED

END

FREE END

DEFLECTION

4.5 Pressure Measurement

Pressure is defined as force per unit area. Pressure measurement is very important as high

pressure may cause accidents. For example, if pressure inside a boiler rises above the safe limits

then it may cause bursting of boiler.

Pressure of one normal(standard) atmosphere is known as standard pressure. Mathematically it

can be expressed as:

– 101325 Pa / 101.325 kPa

– 1013.25 mbars

– 14.696 psia

– 29.921 in.Hg / 760 mmHg @ 0oC (32oF)

– 407.5 in.H2O / 33.958 ft.water @ 20oC (68oF)

4.4.1. Pressure Sensors

Fig. Various Pressure Sensing Devices

In the above figure,

The basic pressure sensing element

(A): C-shaped Bourdon tube

(B): a helical Bourdon tube

(C): flat diaphragm

(D): convoluted diaphragm

(E): capsule

(F): a set of bellows

Bourdon Tube

Bourdon tube is a sealed tube that reflects in response to applied pressure. It provides fairly large

displacements (except diaphragms).It is useful in mechanical gauges and for electrical sensors

that require a significant movement.

4.6 Turbine Protection

The turbine protection system, as the name suggests protects the turbine from any hazardous

conditions. The turbine protection system can be actuated by any of the following trip systems:

Hydraulic Trip System

Electrical Trip System

Both the trip systems, when initiated, act on the hydraulic control system and cause trip oil

pressure to collapse which in turn closes the Emergency stop valves, Interceptor valves and

control valves.

In a turbine protection system, two trip solenoids are provided in the hydraulic circuit, which get

trip signals from the electrical system. Actuation of any one solenoid is sufficient to trip the

turbine. The electrical system is configured as a 2-channel system. Each channel is realized in a

Processing Unit. Both the processor units are completely independent of each other and input

modules, processor module and output modules reside on each. Each channel having two

processors Unit with one processor in hot standby mode. Realization of 2 out of 3 trip logic is

carried out in the processor. Both the channels are tested periodically even while the turbine is

running. Cyclic testing is done automatically at preset intervals

Fig. Turbine protection system

ELECTRICAL TRIP

CONDITIONS

ELECTRICAL TRIP

CONDITIONS

TRIP RELAY 1

TRIP RELAY 1

TRIP SOLENOID 1

TRIP SOLENOID 2

TURBINE TRIP VALVE

STOP VALVE

HYDRAULIC TRIP DEVICES

5. Safety Measures

In a thermal power plant, care is taken regarding the safety of the workers in the plant. All

measures are to taken to ensure that there is no accident or any sort of mishappening takes place.

It is very important to maintain the plant safety so as to maintain a good workable atmosphere

among the employees.

History gives us many examples where hundreds of lives have been lost and loss of millions of

money has occurred due to industrial accidents. Accidents like Bhopal Gas Leakage; Mexico etc

have not only destroyed people’s lives but also impacted the future generations in the area.

Effects of these accidents can be still seen in such areas. Children born in these areas are

generally born with some sort of genetic disorder.

For the individual safety of workers, following steps are taken:

They are given helmets to wear before entering the plant.

They are supposed to enter the plant only if wearing shoes.

They are given special training for lifting heavy loads.

Annual training is given to workers for emergency cases such as gas leakage etc.

On the plant level, following steps are taken for safety:

Regular maintenance of plant equipments.

Carrying on pseudo tests on all equipments such as boiler, turbine etc.

Educating labors about what to do in case of emergency such as gas leakage.

Ensuring the quality and durability of devices used.

Taking extra care in handling and maintenance of volatile materials such as chlorine gas.

6. Conclusion

NTPC plays a very vital role in total power supply in our nation. It is one of the largest PSUs in

our country.

As a trainee, when I first went there I wasn’t sure about what I will get to learn considering my

branch of engineering. But, when I went there all my doubts were removed. It was a great

experience working at NTPC with one of the finest engineers in our country. I got to learn a lot

from them regarding the plant operation and maintenance. I learned about control systems and

high speed data communication from plant sites to control room. Also, got to learn about

management skills from department managers. We had interactive sessions with the engineers as

well as labors working in the plant.

This industrial visit helped me to familiarize with industrial environment. It helped me to

visualize many of the concepts that were only available in theoretical form in books. Overall it

was a great experience at NTPC.

7. References

Device Manuals provided at NTPC

http://www.ntpc.co.in

http://www.wikipedia.com