This document provides an overview of instrumentation and control systems used in a thermal power plant. It discusses the key components measured including pressure, temperature, flow, level, vibration and flue gas analysis. It describes the various sensors and instruments used to measure these variables, including bourdon tubes, diaphragms, bellows, thermocouples, RTDs, orifice plates, and analyzers. It also discusses the control and monitoring systems, laboratories, and pollution control systems used in thermal power plants.

1. Instrumentation Scheme of
Thermal Power Plant
By:
Shilpa Mishra
ME, IC, Panjab

2. There are basically three main units of a thermal power plant:
1. Steam Generator or Boiler
2. Steam Turbine
3. Electric Generator

3. Electricity From Coal
Basic Principle

4. Objectives of Instrumentation & Control
Efficient Operation of the plant.
Economic Operation of the plant.
Safe operation of the plant.
Pollution control

5. This entire task is often taken up by control &
instrumentation or simply instrumentation system which
has following functions:-
a) Measurement
b) Control
c) Operation
d) Monitoring
e) Protection

6. Quantities To Be Measured:
For a Plant Measurement system needs to be:
 Very accurate
 Reliable
 Delays should be as small as possible
 Should be switched on manually when a overall control
system fails.
 Pressure
 Temperature
 Flow
 Level
 Expansion/ Contraction
 Analysis of (1) Water (2) Steam (3) Flue Gases
And Others

7. Measurement Points & Variables
Variables/ Measuring Points Types Of Sensors/ Approx. number
Parameters Instruments in the plant
(1)Pressure (a) Boiler Bourdon Tube,
(b) Turbine Diaphragm,
(c) Turbine Throttle Bellows 375-400
(d) Furnace Bell Gauges
(2)Tempera (a Steam at superheater Thermocouple
ture inlet & outlet
(b Feed Water at
economiser inlet
(c Water at condenser RTD 700-750
inlet
(d Air Preheater
(e Flue Gases Thermocouple

8. (e Bearing of turbine & Thermocouple
generator
(f feed pump, condensate RTD
pump
(3) Flow (a High Pressure Steam Orifice, Venturi, 75-100
(b Feed water inlet Flow Nozzle,etc.
(c Condensate
(4) Level (a Boiler Drum
(b condensate tank Differential 75-100
(c Water line pressure methods
(5) Expansion (a Turbine Shaft Relative 6-8
(b Turbine casing Displacement
(6) Vibration (a turbine & generator Mass spring with
shafts & bearing shells Potentiometric
Capacitive, eddy 30-50
current, piezo
electric & optical
types are used

9. (7) Analysis
(i) WATER (a feed water at econ-
-omiser inlet
(b Boiler inlet Conductive cell 8-12
(c Condenser with meter
(d Condensate pump
discharge
(ii) STEAM (a Saturated steam Conductive cell 4-6
(b Main line steam with meter
(c Super heater inlet Na Analyser 1-2
(iii) FLUE
GASES (a O2 – Economiser to air Zirconia cell 2-4
heater
(b CO2 – Air heater inlet CO2 analyser 2-4
& outlet
(c CO – stack CO analyser 2-4
(d SO2 - Stack SO2 analyser 1-2
(e Nitrogen Oxide- stack N- Oxide Analysesr 1-2
(f Dust concn.- stack Optical method 2-3

10. Measurement of Pressure
Pressure measuring devices are divided into two groups:
 Liquid Columns
 Expansion Elements
Liquid columns:
.
Low range pressure measurement
May be of U-Tube type or well-Type.
Unknown
Pressure

11. These are not favoured in modern power plant but are still used in older
power plants.
Expansion Elements:
Used in modern power plants.
Usually metallic & its movement indicates the pressure.
Either directly coupled with mechanical linkages or indirectly by an
electrical transducer connected to a read out device .
Main Expansion Elements are:
Diaphragms.
Bellows
Bourden tube

12. Diaphragms
 Commonly corrugated diaphragms are used because large deflection can
be produced without nonlinearity compared with flat type.
 In order to increase the deflection capabilities two or more corrugated
diaphragms are welded at the circumferences--- Capsule element.

13. Bellows:
Manufactured from
Brass, Brass alloys,
Stainless steel.
Used for low pressure
measurement.
For high pressure
measurement bellows
are connected with
spring.

14. Bourden Tube
 C shaped and made into an
arc of about 270
0
 Material from which it made
depends upon the pressure range
of the device
 Bourdon tubes are also used
in forms other than C type:-
 Spiral element: large
movement than C tube.
Helical element: produce more
or less circular movement which
is useful for driving a recorder
pen directly.

15. Measurement of Temperature
Temperature can be measured only by using indirect methods.

16. The most important parameter in thermal power plant is temperature and its
measurement plays a vital role in safe operation of the plant.
Rise of 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 .
The efficiency of generation also depend on the temperature measurement
T2 = Tempreture inside the condenser.
T1= Superheater temperature.
1T
2T
1

17. Measurement of Temperature
Expansion Thermometer
In this type of measurement two dissimilar metal tube having different
expansion coefficient are attached end to end.
For same temperature change difference in the lengths are compared and
calibrated for unknown temperature measurement.
Variation in length is slight and has to be magnified for detection.

18. THERMOELECTRIC THERMOMETRY
This device is based on SEEBACK and PELTIER effect. It comprises of
two junctions at different temperature. Then the emf is induced in the
circuit due to the flow of electrons. This is an important part in the plant.
The actual value depend upon the material used and on temperature
difference between the junctions.

19. RESISTANCE THERMOMETRY
Suggested by Siemens in 1871- but not satisfactory used for high
temperature .
Today RTD is given by H.L.Calender in 1891
PROPERTY-The resistance of the conductor changes when its temperature
is changed.
Copper is occasionally used.
Platinum, nickel or nickel alloys are commonly used .
Tungsten is used for high temperature applications
METAL MIN. TEMP. MAX.TEMP. MELTING
POINT
PLATINUM -260
0
C 110
0
C 1773
0
C
COPPER 0
0
C 180
0
C 1083
0
C
NICKEL -220
0
C 300
0
C 1435
0
C
TUNGSTEN -200
0
C 1000
0
C 3370
0
C

20. RTDs
ULTRA VIOLET SENSOR
This device is used in furnace and it measures the intensity of
ultra violet rays there and according to the wave generated
which directly indicates the temperature in the furnace.

21. Measurement of Flow
A universal flow meter for all applications in power station is not
available.
Infect there are more ways of measuring flow than measuring
pressure & temperature.
Dual function meters usually measure flow rate with linear output &
minimum error.
Vortex & Ultrasonic meters have become available in recent years
(1986) & their full potential is not still fully developed.
Two principle measurements are made by flow meters viz. quantity
of flow and rate of flow.
 'Quantity of flow' is the quantity of fluid passing a given point in a
given time, i.e. gallons or pounds.
 ‘Rate of flow' is the speed of a fluid passing a given point at a given
instant and is proportional to quantity passing at a given instant, i.e.
gallons per minute or pounds per hour.

22. There are two groups of measuring devices:-
1. POSITIVE, OR VOLUMETRIC, which measure flow by
transferring a measured quantity of fluid from the inlet to the
outlet.
2. INFERENTIAL, which measures the velocity of the flow and the
volume passed is inferred, it being equal to the velocity times the
cross sectional area of the flow. The inferential type is the most
widely used.

23. Analysis
pH, DO,TURBIDITY & HYDRAZINE:
 Need to be checked for acidity (pH), Dissolved oxygen(DO)
 Turbidity arising out of contamination by suspended
particles .
 Hydrazine which is added from outside to the feed water but
the excess should be monitored.
 Oxygen reacts with thallium to form thallium oxide which in
aqueous solution show good conductivity.

25. Functions
Control and instrumentation in any process industry, can be compared
to the nerve system in the human being.
The way the nerve system controls the operation of various limbs of
human beings, C&I in the same way controls and operates various
motors, pumps, etc and thus helps us to achieve our targets.
C&I, as the name indicates, is a branch in engineering which deals
with various measurement, indication, transmission and control in
different technical field.
The main work of C&I department is to observe, control and
manipulate electrical as well as non-electrical quantities like
temperature, pressure, vibrations.

26. C&I department governs the whole functioning and operation of
power plant through the Central Control System (DDC-MIS)
“Distributed Digital Control Monitoring and Information System”.

27. Labs in Control and Instrumentation
Department of Thermal Plant
Control and Instrumentation Department has following labs:
1. Manometry Lab
2. Protection and Interlocks Lab
3. Automation Lab
4. Electronics Lab
5. Water Treatment Plant
6. Furnaces Safety Supervisory System Lab

28. Manometry Lab
1. TRANSMITTERS
It is used for pressure measurements of gases and liquids, its working
principle is that the input pressure is converted into electrostatic
capacitance and from there it is conditioned and amplified. It gives an
output of 4-20 ma DC. It can be mounted on a pipe or a wall. For liquid or
steam measurement transmitters is mounted below main process piping
and for gas measurement transmitter is placed above pipe.
2. MANOMETER
It’s a tube which is bent, in U shape. It is filled with a liquid. This device
corresponds to a difference in pressure across the two limbs.
3. BOURDEN PRESSURE GAUGE
It’s an oval section tube. Its one end is fixed. It is provided with a pointer
to indicate the pressure on a calibrated scale. It is of 2 types:
(a) Spiral type: for Low pressure measurement.
(b) Helical Type: for High pressure measurement.

29. Protection and Interlocking Lab
INTERLOCKING
It is basically interconnecting two or more equipments so that if one
equipments fails other one can perform the 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 Gates.
 When a fault occurs and any one of the tripping is satisfied a signal is
sent to the relay, which trips the circuit. The main equipments of this
lab are relay and circuit breakers

30.  Some of instrument used for protection are:
1. RELAY
It is a protective device. It can detect wrong condition in electrical
circuits by constantly measuring the electrical quantities flowing under
normal and faulty conditions. Some of the electrical quantities are
voltage, current, phase angle and velocity.
2. 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 .
3. MINIATURE CIRCUIT BREAKER
They are used with combination of the control circuits to-
a) Enable the staring of plant and distributors.
b) Protect the circuit in case of a fault.
In consists of current carrying contacts, one movable and other fixed.
When a fault occurs the contacts separate and are is stuck between
them.

31. Automation Lab
This lab deals in automating the existing equipment and feeding
routes.
Earlier, the old technology dealt with only (DAS) Data
Acquisition System known as primary systems.
The modern technology or the secondary systems are coupled
with (MIS) Management Information System.
All the control instruments are excited by 24V supply (4-20mA)
because voltage can be mathematically handled with ease
therefore all control systems use voltage system for
computation.

32. FURNACE SAFETY AND SUPERVISORY
SYSTEM LAB
This lab has the responsibility of starting fire in the furnace to
enable the burning of coal..
Unburnt 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.

33. Electronics Lab
This lab undertakes the calibration and testing of various cards. It
houses various types of analytical instruments like oscilloscopes,
integrated circuits, cards auto analyzers etc.
Various processes undertaken in this lab are:
1. Transmitter converts mV to mA.
2. Auto analyzer purifies the sample before it is sent to electrodes

34. Operation and Maintenance Lab

35. Electrical Maintenance Division:
It is responsible for maintenance of:
1. Boiler side motors
2. Turbine side motors
3. Outside motors
4. Switchgear
 Protection By switch gear It makes or breaks an electrical
circuit.

36. Pollution Control systems:
In order to ensure that NTPC comply with all the stipulated environment
norms, various pollution control systems / devices as discussed below have
been installed to control air and water pollution.
1. Electrostatic Precipitators:
The ash left behind after combustion of coal is arrested in high efficiency
Electrostatic Precipitators (ESP’s) and particulate emission is controlled well within
the stipulated norms. The ash collected in the ESP’s is disposed to Ash Ponds in
slurry form.
2. Flue Gas Stacks:
Tall Flue Gas Stacks have been provided for wide dispersion of the gaseous
emissions (SOX, NOX etc) into the atmosphere.
3. Neutralisation Pits:
Neutralisation pits have been provided in the Water Treatment Plant (WTP) for
pH correction of the effluents nbefore discharge into Effluent Treatment Plant
(ETP) for further treatment and use.

37. 5. Cooling Towers
Cooling Towers have been provided for cooling the hot Condenser cooling
water in closed cycle Condenser Cooling Water (CCW) Systems. This helps
in reduction in thermal pollution and conservation of fresh water.
6. Ash Water Recycling System:
In the AWRS, the effluent from ash pond is circulated back to the station for
further ash sluicing to the ash pond. This helps in savings of fresh water
requirements for transportation of ash from the plant.

38. Liquid Waste Water/Effluents Treatment
Plants & Management System:
1. The objective of industrial liquid effluent treatment plant (ETP) is
to discharge lesser and cleaner effluent from the power plants to
meet environmental regulations.
2. After primary treatment at the source of their generation, the
effluents are sent to the ETP for further treatment.
3. The scheme involves collection of various effluents and their
appropriate treatment centrally and re-circulation of the treated
effluent for various plant uses.