ROLE OF CONTROL AND INSTRUMENTATION IN THERMAL POWER PLANT

Summer Training Project Report
“Overview and Role of C & I in Thermal Power Plant”
Submitted by:
GAURAV RAI
IET, BUNDELKHAND UNIVERSITY
JHANSI (UP)

Power plant C&I (IPC) systems
&
Tending to Zero Forced Outage
by
Internalization of Best Practices

1.Some definitions & basics of Pressure, Flow & Temp. measurement
2. Categorization of C&I systems based on location of application
3. Division of power plant C&I systems based on functionality & type of
application
4.Evolution of C&I systems and latest trend in technology
5.Reliance Power at a glance and maintenance practices of C&I systems
6. Some case studies

Outline:
 Some Definitions
 Pressure Units
 Manometers
 Elastic Pressure Sensors
 Electrical Pressure Sensors
 Pressure Switches
 Snubbers & Siphon Tubes

Terminology
 Accuracy : Closeness with which an instrument reading approaches the
true value of the variable being measured.
 Precision : A measure of reproducibility of the measurements; i.e. given
a fixed value of a variable, precision is a measure of the degree which
successive measurements differ from one another.
 Sensitivity : The ratio of output signal or response of the instrument to a
change of input or measured variable.
 Resolution : The smallest change in measured value to which the
instrument will respond.
 Error : Deviation from the true value of the measured variable.

Repeatability refers to the ability of a pressure sensor to provide the
same output with successive applications of the same pressure.
Hysteresis is a sensor's ability to give the same output at a given
pressure while increasing and decreasing the pressure.

Pressure : Definitions
 Definition: Force per unit area
 Absolute pressure
 Atmospheric pressure
 Differential pressure
 Gauge pressure
Importance : Pressure measurement is critical for safe and optimum operation of
processes such as steam generation, hydraulic equipment operation, air
compression, vacuum processing etc.

Zero Reference , Gauge, Absolute, Atmospheric Pressure
 Any pressure above atmosphere is called gauge pressure
 Any pressure below atmosphere is a vacuum (negative gauge pressure)
 Absolute pressure (psia) is measured from a perfect vacuum
Differential Pressure has no reference to either absolute vacuum or atmospheric pressure

Units
 The SI unit for pressure is the Pascal (Pa);1Pa= 1 N·m-2
 Non-SI unit pound (Lb) per square inch (psi) and bar are commonly
used
 Pressure is sometimes expressed in grams-force/cm2or as kgf/cm2
(KSC)
1 atm=1.03 ksc=14.696 psi=760mmHg=10000 mmWC
=101325 Pa
Standard pressure:Pressure of normal (standard) atmosphere is defined as
standard pressure

Pressure Measuring devices
 Manometers
 using water ,mercury and other liquids of known density
 For measuring low pressures.
 Mechanical/Elastic Pressure Sensors
 Electrical Pressure Transducers
 For measuring pressure of all ranges for telemetering purposes.
Manometer:
A simple pressure standard
May be used for gauge, differential, and absolute measurements with a suitable reference.
Useful mainly for lower pressure work because the height of the column of mercury will
otherwise become very high.
The difference in column heights gives the pressure reading

Elastic Pressure Sensors
The basic pressure sensing elements:
A: C-shaped Bourdon tube , B: Helical Bourdon tube , C: flat diaphragm
D: Convoluted diaphragm, E: Capsule , F: Set of bellows

Electrical Pressure Sensors
1. Potentiometer Sensor
2. Inductive
3. Capacitive
4. Piezoelectric
5. Strain Gauge
Usually generate output signals in the mV range (spans of 100 mV to 250
mV).
 In transmitters, these are amplified to the voltage level (1to 5 V) and
converted to current loops, usually 4-20 mA dc

Pressure Switches
Applications
 Alarm (Status)
 Shutdown (Hi/Lo Limits)
 Control (ON/OFF)
A “switch” is an instrument that automatically senses some process variable
(such as pressure) and provides an on/off signal relative to some reference
point.
Sensing
Element
Conditioning
Circuit
Bourdon Tube
Bellows
Diaphragm
Strain Gauge
Mechanical Switch
Transistor
Set Point

High Pressure In High Temperature
* When high process temperatures are present, various methods of
isolating the pressure instrument from the process are used.
* These include siphons, chemical seals with capillary tubing for
remote mounting, and purging.
 Snubbers & its use
 Chemical Seal
 Siphon

Pressure Snubbers
 To filter out pressure spikes, or to average out pressure pulses, snubbers
are installed between the process and the instrument
 Instrument indicates avg pr.
Snubber Before use After use
when one is interested in the measurement of fast, transient pressures
(such as to initiate safety interlocks on rising pressures), snubbers must not be
used, as they delay the response of the safety system.

Chemical Seal or diaphragm Protector
Chemical seals are used when media can falsify the pressure
measurements due to high temperature, high viscosity or their
property to crystallise

Siphon
A siphon is a coiled tube. This coil provides a large cooling surface and the trap
created prevents the condensate from draining away.
A siphon is required for hot condensing. fluids, such as steam, to assure a
liquid trap.
It is used to prevent live steam from entering and damaging the device.
It is used to protect the instrument from hydraulic or thermal shocks.
The two most common forms of siphon tube are the 'U' and Pigtail types.

Types of flow meters:
1. Orifice Flow meter
2. Vortex flow meter
3. Ultrasonics flow meter
4. Coriolis Mass Flow meter
5. Major issues for selecting flow meters
Orifice Flow-meters
Several sensors rely on the pressure drop
or head occurring as a fluid flows by a
resistance. The relationship between flow
rate and pressure difference is determined
by the Bernoulli equation.

Orifice Flow-meters
• An orifice plate is a restriction with an opening smaller than the pipe
diameter which is inserted in the pipe; the typical orifice plate has a
concentric, sharp edged opening.
• Because of the smaller area the fluid velocity increases, causing a
corresponding decrease in pressure.
• The flow rate can be calculated from the measured pressure drop across
the orifice plate, P1-P3.
• The orifice plate is the most commonly used flow sensor, but it creates a
rather large non-recoverable pressure due to the turbulence around the plate,
leading to high energy consumption.

Venturi Tube
The change in cross-sectional area in the venturi tube causes a pressure
change between the convergent section and the throat, and the flow rate can
be determined from this pressure drop. Although more expensive that an
orifice plate; the venturi tube introduces substantially lower non-
recoverable pressure drops

Pitot Tubes
Pitot tubes were invented by Henri Pitot in 1732 to measure the
flowing velocity of fluids. Basically a differential pressure (dp) flow meter,
a pitot tube measures two pressures: the static and the total impact
pressure.
 Pitot tubes are used to measure air flow in pipes, ducts, stacks, and
liquid flow in pipes, open channels.
 While accuracy and rangeability are relatively low, pitot tubes are simple,
reliable, inexpensive, and suited for a variety of environmental
conditions, including extremely high temperatures and a wide range of
pressures.

Pitot Tubes
 A single-port pitot tube can measure the flow velocity at only a single point in the
cross-section of a flowing stream.
 The probe must be inserted to a point in the flowing stream where the flow
velocity is the average of the velocities across the cross-section, and its impact
port must face directly into the fluid flow.

Pitot Tubes
The point velocity of approach (VP) can be calculated by taking the square root
of the difference between the total impact pressure (PT) and the static pressure
(P) and multiplying that by the C/D ratio, where C is a dimensional constant and
D is density:
 The pitot tube measures the static and dynamic (or impact) pressures of the fluid
at one point in the pipe.
 The flow rate can be determined from the difference between the static and
dynamic pressures which is the velocity head of the fluid flow.

Vortex Flow-meters
 This measuring principle is based on the fact that vortices are
formed downstream of an obstacle in a fluid flow, e.g. behind a
bridge pillar.
 This phenomenon is commonly known as the Kármán vortex street.

Vortex Flow-meters
This is detected by a sensor, such as capacitive sensor and fed to
the electronic processor as a primary, digitized, linear signal.
Capacitive sensors with integrated temperature measurement can
directly register the mass flow of saturated steam as well.
 Universally suitable for measuring liquids, gases and steam
 Largely unaffected by changes in pressure, temperature and
viscosity
 High long-term stability (lifetime K factor), no zero-point drift
 No moving parts
 Marginal pressure loss

Ultrasonic flow-meters
Swimming against the flow requires more power and more time than
swimming with the flow. Ultrasonic flow measurement is based on this
elementary transit time difference effect.
 Two sensors mounted on the pipe simultaneously send and receive ultrasonic
pulses.
 At zero flow, both sensors receive the transmitted ultrasonic wave at the same
time, i.e. without transit time delay.
 When the fluid is in motion, the waves of ultrasonic sound do not reach the two
sensors at the same time.

 This measured "transit time difference" is directly proportional to the flow
velocity and therefore to flow volume.
 By using the absolute transit times both the averaged fluid velocity and the
speed of sound can be calculated.
 Ultrasonic flow meters measure the difference of the propagation time (transit
time) of ultrasonic pulses propagating in (normally an inclination angle around
30 to 45° is used) flow direction and against the flow direction.
 This time difference is a measure for the averaged velocity of the fluid along
the path of the ultrasonic beam

Advantages:
 With homogeneous fluids, the principle is independent of pressure,
temperature, conductivity and viscosity
 Usable for a wide range of nominal diameters Direct meter
installation on existing pipes
 Non-invasive measurement
 No pipe constrictions, no pressure losses
 No moving parts. Minimum outlay for maintenance and upkeep

Coriolis Mass Flow-meters
 If a moving mass is subjected to an oscillation perpendicular to its
direction of movement, Coriolis forces occur depending on the
mass flow.
 A Coriolis mass flow meter has oscillation measuring tubes to
precisely achieve this effect.
Coriolis forces are generated when a fluid (= mass) flows through
these oscillating tubes. Sensors at the inlet and outlet ends register
the resultant phase shift in the tube's oscillation geometry.

Coriolis Mass Flow-meters
The processor analyzes this information and uses it to compute
the rate of mass flow.
Advantage
This principle is used in a huge range of industry sectors,
including pharmaceuticals, chemicals and petrochemicals, oil and
gas, food etc.

Major issues for selecting flow-meters
Accuracy
Repeatability
Linearity
Reliability
Range/Span
Dynamics(Response time)
Safety
Maintenance
Cost

Measurement Devices
 Thermocouples
 Resistance Thermometers
 Thermistors
 Bimetallic Thermometers
 Acoustic Pyrometers
 Local Instruments

Thermocouple
IT IS BASED ON ‘SEEBECK’ EFFECT WHICH SAYS THAT
WHEN HEAT IS APPLIED TO A JUNCTION OF TWO
DISSIMILAR METALS AN ‘EMF’ IS GENERATED WHICH CAN
BE MEASURED AT THE OTHER JUNCTION
T/C Connection
COMPENSATING CABLE
HOT JUNCTION
TO DDC CARDS
TERMINAL END CJC BOX

Thermocouple
Types of T/C:E,J,K,T,R,S,B
K (Chromel & Alumel; Ni-Cr &Ni-Al) Type: mostly used in power plant for low
temp. application )
R (Platinum & Platinum-Rhodium) Type: Used for high temp. application. Highly
resistant to oxidation & corrosion
Advantages: - Disadvantages: -
- Low Cost - Sensitivity low & low voltage output
- No moving parts, less likely to be broken. susceptible to noise
-Wide temperature range. - Accuracy not better than 0.5 °C
-Reasonably short response time. - Requires a known temperature
- Reasonable repeatability and accuracy. reference

RESISTANCE THERMOMETER (RTD)
THE RESISTANCE OF A CONDUCTOR CHANGES WHEN ITS
TEMPERATURE IS CHANGED .THIS PROPERTY IS UTILISED TO
MEASURE THE TEMPERATURE.
Rt = Ro (1+βdT)
WHERE β = TEMP CO- EFFICIENT OF RESISTANCE ; dT = TEMPERATURE DIFFERENCE
When discussing RTDs, following must be considered:
• Wiring configuration (2, 3 or 4-wire)
• Self-heating
• Accuracy RTD types:
• Stability 1. Platinum (Range -200 °C to 600 °C )
• Repeatability 2. Copper (Range -100 °C to 100 °C )
• Response time 3. Nickel (Range -60 °C to 180 °C )

THERMISTORS
THERMISTORS ARE GENERALLY COMPOSED OF SEMICONDUCTOR
MATERIALS.THEY HAVE A NEGATIVE COEFFICIENT OF TEMPERATURE SO
RESISTANCE DECREASES WITH INCREASE IN TEMP.
Making use of Negative Temperature Coefficient characteristics,
thermistor and can be applied in temperature compensation, inrush current
limit, precision temp. control (temp. coefficient very large compared to RTC
& T/C) etc.
BIMETALLIC THERMOMETERS
 ALL METALS EXPAND OR CONTRACT WITH TEMPERATURE
 THE TEMPERATURE COEFFICIENT OF EXPANSION IS NOT THE SAME FOR
ALL METALS AND SO THEIR RATES OF EXPANSION AND CONTRACTION
ARE DIFFERENT
USAGE: IN PROCESS INDUSTRIES FOR LOCAL TEMPERATURE MEASUREMENTS
OVERLOAD CUTOUT SWITCH IN ELECTRICAL APPARATUS

ACOUSTIC PYROMETER
 Acoustic Pyrometer is a non-contact measurement device that obtains
highly accurate instantaneous gas temperature data in any area of the
boiler, helping improve combustion efficiency.
 For measurement of temperatures across large spaces of known distance in
a noisy, dirty and corrosive environment such as a coal-fired utility boiler, or
a chemical recovery boiler.
 The Velocity of Sound in a medium is proportional to the Temperature.
LOCAL INDICATION
 LIQUID IN GLASS THERMOMETER
 MERCURY IN STEEL THERMOMETER
 BIMETALLIC THERMOMETER

1.Field instruments/ input & output instruments
a) Various measuring instruments like Transmitters, RTD,
Thermocouples, Pr. & temp. gauges, speed & vibration pick
ups etc. (Analog inputs)
b) Various Pr., Temp. & limit switches, for Interlock , protections
& feedback of control element (Binary inputs)
c) Output devices like solenoids, EP converters, Positioners
etc. for controlling final control element
d) Final control elements like Power cylinder, Pneumatic/
motorized actuators etc.

2. Control Systems
a) Various control cabinets for acquiring field signal (both analog &
binary inputs), processing the signals as per control logic and
issuing output command to output devices (Binary & analog).
b) Various control desk devices like command consoles, Push button
modules, indicators, recorders, CRTs, PC based Operator Work
Stations (OWS) etc. for human machine interface for monitoring &
control of the plant
c) Power supply system(UPS)/ chargers with battery backups to
ensure uninterrupted power supply of desired quality for the
control system

3. Analyzers
The availability, reliability & efficiency of boiler unit hinge around the
close control of chemical regimes of working fluid i.e. water/steam as well
as combustion in the boiler. The instruments monitoring the chemical
regimes and combustion are generally called analytical instruments. These
instruments fall under three category
i) Water/ Steam Analyzers
ii) Gas analyzers
iii) Smoke monitors
HIGH PURITY WATER IS ESSENTIAL TO MINIMISE
 SCALING
 CORROSION
 CARRY OVER
 EMBRITTLEMENT

ANALYZERS AND MEASURMENT LOCATION
a) ON LINE gas analyzers for measurement of flue gas oxygen, carbon
mono-oxides, carbon di-oxides, oxides of sulpher & nitrogen at various
location of boiler.
b) ON LINE analyzers for measurement of conductivity, pH, silica, dissolved
oxygen, phosphate, hydrazine, chloride, sodium etc. at various points in
the water & steam cycle of boiler & turbine area (SWAS-steam & water
analysis system).
c) ON-LINE opacity monitors for measurement of dust concentration in flue
gas
d) ON LINE analyzers for measurement of conductivity, pH, silica, dissolved
oxygen etc. at various ION exchangers of DM plant .

TYPICAL VALUES OF CHEMICAL PARAMETERS BEING MEASURED (SWAS)
SAMPLE PARAMETER UNIT LIMIT
DM WATER a) Conductivity
b) Cation Conductivity
µS/cm <0.3
Condensat
e pump
discharge
(CEP)
a) Conductivity
b) Cation Conductivity µS/cm <5
<0.3
c) pH 9.0-9.2
d) Na+
ppb <5ppb
e) Dissolve oxygen (DO) ppb <10
Economize
r Inlet
a) Conductivity
b) Cation Conductivity
µS/cm <5
<0.3
c) Hydrazine
ppb
10-20
Boiler
water
a) Conductivity
µS/cm 100
b) pH 9.1-9.4
c) Silica ppb 100
Sat & Main steam a) Conductivity
b) Cation Conductivity µS/cm <5
<0.3

4. Laboratory Instruments & Setup
Activities of C&I Lab
 CALIBRATION
 REPAIR
 TESTING with proper documentation & records
CALIBRATION:
 Pressure switch , Transmitter , Gauge
 Temperature switch , Transmitter , Gauge
 Flow Transmitter
 Level Switch

REPAIR:
1. ELECTRONIC CARDS
3. POWER SUPPLY MODULES
TESTING:
1. ELECTRONIC MODULES
2. RELAYS
3. POWER SUPPLY MODULES

a) Different standard instruments with traceability up to national standard .
These insts. include Standard Gauges, Multimeters, Resistance boxes,
mA sources, oscilloscope, signal generator etc. for calibration of
measuring instruments.
b) Dead Weight tester, Comparator, Temperature bath, Vacuum pump,
manometer, soldering stations etc.
c) Test benches with standard power supply sockets (e.g. 24VDC, 48VDC,
220VDC, 110VAC, 230VAC etc.) in each bench depending on
requirement.
d) Laboratory should be air-conditioned with monitoring of temp., humidity
and barometric pressure. Also, proper provision for handling electronic
cards (floor mats, ESD protective bags/ anti static bags etc.)

Essential Tools/ Infrastructure for Repairing & testing
1. IN-CITCUIT IC TESTER
2. ESD WORK STATION
3. ULTRASONIC CARD CLEANER
4. STORRAGE OSCILLOSCOPE
5. LOGIC ANALYSER
6. THERMOCOUPLE SIMULATOR
7. VIDEO PATTERN GENERATOR
8. EPROM PROGRAMMER

C&I systems of Boiler
- FSSS (Furnace safeguard supervisory system)
- Open loop control system (interlock & protections) of
boiler auxiliaries
- Secondary Air Damper control system (SADC)
- Hydrastep for drum level measurement
- Measurements, Protection & Control of Coal Feeders

FSSS
FUNCTIONS OF F.S.S.S
1. FURNACE PURGE SUPERVISION
2. OIL GUNS ON/OFF CONTROL
3. PULVERISERS/FEEDERS ON/OFF CONTROL
4. SECONDARY AIR DAMPERS CONTROL
5. FLAME SCANNER INTELLIGENCE
6. BOILER TRIP PROTECTIONS

FSSS
WHY AT ALL A PROTECTIVE SYSTEM IS REQUIRED FOR THE
BOILER?
THE BOILER’S FURNACE IS CONTINUOUSLY FED WITH HIGH
CALORIFIC VALUE ATOMISED FUEL WHICH IS IN THE PROCESS OF
CONTINUOUS BUT CONTROLLED COMBUSTION.
COMBUSTION-THE PROCESS
COMBUSTION IS A RAPID BURNING OF OXYGEN WITH FUEL RESULTING
IN RELEASE OF HEAT. AIR IS ABOUT 21% OXYGEN AND 78% NITROGEN BY
VOLUME. MOST FUELS CONTAIN CARBON, HYDROGEN AND SULPHUR. A
SIMPLIFIED COMBUSTION PROCESS COULD BE
CARBON+OXYGEN=CARBONDIOXIDE+ HEAT
HYDROGEN+DO =WATER VAPOUR + HEAT
SULPHUR +DO =SULPHURDIOXIDE+ HEAT
WHICH MEANS THAT THE FINAL DESIRED PRODUCT OF THE PROCESS
IS HEAT WHICH WE REQUIRE TO BOIL THE WATER

FSSS
COMBUSTION-THE PROBLEM : WHEN THIS CONTROLLED BURNING
GOES OUT OF CONTROL DUE TO AN IMBALANCE IN THE FUEL/AIR RATIO,
THERE IS EITHER A FUEL RICH MIXTURE OR A FUEL LEAN MIXTURE. IN
BOTH CASES THE FLAME QUALITY BECOMES POOR. THERE IS A CHANCE
OF FUEL ACCUMULATION WHICH CAN LATER ON IGNITE SUDDENLY AND
CAUSE EXPLOSIONS.
SO FSSS IS USED FOR SAFE AND ORDERLY STARTUP AND
SHUTDOWN OF BOILER THROUGH VARIOUS INTERLOCKS AND
PROTECTIONS
THE PROTECTIVE SYSTEM IN THE BOILER IS DESIGNED
BASICALLY TO PREVENT OCCURRENCE OF SUCH SITUATIONS BY
TAKING ADVANCE ACTIONS.

N.F.P.A Guide line & Boiler Protection
 N.F.P.A- National Furnace Protection Association, USA
 Deals with protection for various types of furnace
 Protection of Pulverized fuel fired boiler is governed by Section-85c
 Different categories of protection:
 a) Mandatory, b)Mandatory & automatically generated, c) Optional
but alarm has to be there

BOILER FLAME & FLAME SCANNERS
It looks rather static, but in reality
the fire energy fluctuates rapidly. The Fuel and
Oxygen in the uncontrolled fire constantly
burn as in small explosions and
then sucks new Fuel & Oxygen to the
flames. This process causes the flame
flicker.
Flicker frequency for oil
flame is more than that of coal flame.

INTENSITY RELATIVE TO WAVELENGTH

FLAME SCANNERS
-UV Scanners
-Visible Range Scanners (Safe scan-1&2)-Used for both Oil & Coal Flame
-IR Scanners (UR600 of ABB)
SAFE FLAME SCANNER

C&I systems of Turbine
- ATRS (Automatic Turbine Runup system)
- Turbine Governing System
- Turbovisory Instruments & turbine protections
- Interlock, Protection & Control of HPBP system
- Open loop control system (interlock & protections) of
turbine auxiliaries
- Interlock & protections of Seal Oil & Stator water system

C&I systems for control & MIS
-Automatic Control System (ACS)
-DATA Acquisition system(DAS)
-Distributed Digital Control Monitoring
and Information System

AUTOMATIC CONTROL SYSTEM & POWER PLANT CONTROL LOOP
PROCESS: Process refers to the method of changing or refining raw
materials to create the desired end product. The raw materials may
undergo physical, chemical, or thermal state changes during the Process.
 Process is of Two Types :
A) Continuous and B) Batch
Continuous Process is one where the change of state of Input into Output
occurs continuously.
Ex.: Power Plant Process, Petroleum Industry etc.
Batch Process is one where a Batch of the Product is produced and the
Process stops till production of next Batch is started.
Ex.: Automobile Production

PROCESS CONTROL: Process control techniques are developed over the
years to have
 Quality of the end product
 Economy of production
 Ability to cater to emergencies and bring the process to safe shutdown.
CONTROLLED CONDITION: The physical quantity or condition of a
process or machine which is to be controlled
CONTROL SYSTEM: An arrangement of elements interconnected and
interacting in such a way that it can maintain some condition of a
process or machine in a prescribed manner

OPEN AND CLOSED LOOP CONTROL:
A Closed Loop Control (CLCS) is one where a Process
Variable is measured, compared to a Set Value and action is
taken to correct any Deviation or Error from Set Value. The
continuous Measurement of PV and its’ comparison to Set Point
closes the Loop.
An Open Loop Control(OLCS) is one where the PV is not
compared with Set Value and action taken, but action is taken
without regard to conditions of PV.

OPEN LOOP CONTROL:
Open Loop Control is accomplished by the following means:
 Group Control
 Sub-Group Control
 Sub-Loop Control
 Drive Level Control
 Programmable Logic Control(PLC)
 Group Control : Start and Stoppage of a Group of equipment is
accomplished by Group Control(GC).
Ex. :CEP GC, Equipment Cooling GC etc.

OPEN LOOP CONTROL:
Sub-Group Control : Start and Stoppage of an equipment with its’
associated auxiliaries in Step-Sequence manner is done by Sub-Group
Control. Operator intervention is not required in Sub-Group Control(SGC).
Sub-Loop Control: Start and Stoppage of auxiliaries of an equipment is
carried out by Sub-Loop Control(SLC)
Drive Level Control : Start and Stop or Opening and Closure of a Drive is
carried out by Drive Control. The Drive logic shall have Protection, release
,auto and manual commands and these are executed as per pre-determined
logic.

CLCS TERMINOLOGY:
Desired Value or Set Point : The value of the variable/parameter which needs
to be controlled at the required condition.
Process Variable(PV) : The present value of the Parameter of Process at that
particular instant. This is sometimes referred as Measured Value.
Error/Deviation : It is the Difference between Set Point and Process Variable,
and can be +ve or –ve. It has three components: a) Magnitude b) Duration and
c) Rate of change.
Controller : A Controller is a device that receives data from a Measurement
Instrument, compares the data with the Set Point and if necessary, signals a
Control element to take Corrective action. This Corrective action ensures that
the PV shall always be maintained at the Set Value.
The Controller can be a) Electronic, b) Pneumatic and c) Hydraulic type.

 Controller types: Functionally, Controllers can be
a) Continuous and b) Step Controllers.
Depending on the control loop; controller action can be adjusted as (i)
Direct acting:-Increase of process value increases controller output
(ii) Reverse acting:- Increase of process value decreases controller
output
 Control Element : The Control or Correcting Element is the part of the
Control System that acts to physically change the Manipulated Variable.
Ex. : Control Valves, Louvers or Dampers, Solenoids, Pump Motors
etc.

 Bump less Transfer : The arrangement where the transfer from auto to
manual mode does not affect the process.
 Proportional Control : The Proportional (P) action responds only to a
change in the magnitude of Error(e) i.e. controller output changes by an
amount which is proportional to error.
Output change of Controller in % = (Error change in %)(Gain), where
Gain is called the Controller gain. The reciprocal of Gain is termed as
Proportional Band(PB) and is expressed in %.
Proportional Band(PB): The change in deviation required to cause the
output of the controller to change from one extreme to the other.
 Integral Control : In Integral Control, the Controller output is a function of
the Duration of Error(e).

Hence, the Controller output is the time Integral of Error and the time set is
Integral Action Time(IAT) i.e. IAT can be defined as time taken for the integral
action to change output by the same amount as the proportion action .
Usually, both P and I Controls are combined and the Controllers are tuned to
minimize Error(e) and controller is termed as PI controller.
Derivative Control : Derivative or Rate Controller’s output is Proportional to the
rate of change of Error(e). The Control action is termed as D. The action is to
apply an immediate response that is equal to the P+I action that would have
occurred some time in the future.

Important Closed Loop Controls in a Thermal Power Plant:
a) Furnace Draft Control
b) Boiler Drum Level Control
c) HOT well & D/A level control
d) Main Steam Temperature Control
e) Air and Fuel Flow to Boiler Control
f) SH & RH spray control
g) Coordinated Master Control(CMC)
h) Turbine Speed, Pressure and Load Control

Coordinated Master Control
This is an integrated automatic control of unit operation. There is a
continuous co ordination between boiler and turbine control to maintain a
balance between steam generation and steam consumption.
• Boiler Follow Mode (BFM)
• Turbine Follow Mode (TFM)
• Co-ordinated Master Control (CMC)
• Runback Mode

Boiler Follow Mode (BFM)
• Unit load control from turbine local load set point
• Change in turbine load set point will modulate turbine CVs
• Boiler master output gets corrected to maintain throttle pr dev.
• Boiler control will follow turbine control
• BLI signal as feed forward signal for boiler firing rate control
• Result - Boiler acts as throttle pr controller where turbine is in load controller mode

Turbine Follow Mode (TFM)
• Unit target load set point goes to boiler master
• Change in BLI will modulate turbine CVs
• Boiler master output gets corrected to maintain Unit load dev.
• Turbine control will follow boiler control
• Load deviation as feed orward signal for boiler firing rate control
• Result - Boiler acts as load controller where turbine is in pressure controller mode

Coordinated Master Control
• Unit load is set from unit master.
• Unit master demand is limited by unit capability , TSE margins and unit max/min load
set points.
• Unit target load is derived from unit master after the limitations.
• Unit target load is used as feed forward signal to the boiler firing rate control.
• Turbine control utilises the unit load as turbine load set point after adapting the same
by steam generation delay.
• In TG throttle pressure is maintained by correcting the BMD output depending on the
throttle pr dev.
• Result: Balance is achieved between steam generation and steam consumption
PROPER COORDINATION BETWEEN BOILER CONTROL AND TURBINE
CONTROL

DATA ACQUISITION SYSYTEM-DAS
WHY DAS IS REQUIRED IN THERMAL POWER PLANTS ?
 SAFE & RELIABLE OPERATION OF THE UNIT OR EQUIPMENTS
 ASSIST CONTROL ROOM OPERATORS BY PROVIDING TIMELY
ANNUNCIATION OF ALL ABNORMAL CONDITIONS
 PROVIDE DETAILED INFORMATION ON THE PLANT PERFORMANCE
 PROVIDE MANAGEMENT WITH ACCURATE RECORDS ON THE PAST
PLANT PERFORMANCE FOR ANALYSIS

DATA ACQUISITION SYSYTEM
3 MAJOR FUNCTIONS OF DAS:
 DATA ACQUISITION
 DATA PROCESSING
 DATA REPRESENTATION
The Major Parts
 Process Control Units ( PCU )
 Computer Interface Unit ( CIU )
 Termination Units ( TU )
 Buffer Terminal Cabinets ( BTC )

TYPES OF DATA (Input): Analog & Digital
Analog inputs:
1. Thermocouple Input ( mV )
 K-Type T/C ( Cr-Al ) : For temp < 600 Deg C& used in Flue Gas path
after FSH outlet.
 R-Type T/C ( Pt-Pt-Rh ) : For temp > 600 Deg C used in PSH & FSH
region of FG path.
2. RTD Input ( Resistance )
 Pt-100 RTD : For Brg. Temp measurement.
 Cu-53 RTD : For HT motor & Generator Stator winding temp.
measurement.

Analog inputs:
3. 4 – 20 Ma Input
 Coming from Pr. / Flow Transmitters.
 Coming from Signal Distribution Cards of automatic control system
4. 0 – 10 Volt Input
 Coming from ATRS cabinets
 Used for Turbine Brg. Temp. /Vibration measurement.
DIGITAL INPUTS
These are coming directly from switches or relay contacts of other
systems (FSSS, ATRS, ACS etc.)

DIGITAL INPUTS (TYPES)
 LOW RESOLUTION : The scanning time of inputs is 1
second.
 HIGH RESOLUTION : The scanning time is 1
millisecond. These are called
Sequence Of Events ( SOE )
Inputs.
 PULSE INPUT : For calculation of Total Coal
Flow, Total Air Flow etc.

FUNCTIONS OF DAS:
 Alarm Management.
 Production of hardcopy print outs in different printers.
 Operator Guidance Messages.
 Graphic Displays of plant sub-systems.
 Trending of analog variables on recorders.
 Sequence Of Events ( SOE ) recording following unit /
equipment trip conditions.
 Efficiency calculations

DATA PROCESSING: It has the following parts
 COMPUTER PROCESSING UNIT ( CPU )
 BULK ( SOLID STATE ) MEMORY WITH BATTERY BACKUP
 MAGTAPE UNIT
 COMMUNICATION CABINET & MODEM
 MOVING HEAD DISC DRIVE
 VIDEO HARD COPIER
 TREND RECORDER
 UNIT CONTROL DESK & PROG. ROOM CRT
 PRINTERS

Features:
 REAL TIME VARIABLE CALCULATION
Summing, Subtraction, Maximum , Minimum, Averaging,
Hourly & Daily integration, rate of changes & comparison
of limits etc.
 ON-LINE DATABASE EDITION
1. Assign points to any process parameter
2. Scan, Off-scan , Delete , Activate , inactivate a
process parameters , calculated points when reqd.
3. Change the Engg. Unit
4. Change the range , alarm limits & dead bands
5. Change the scan frequency
6. Review total analog and digital points depending on its
quality flag like alarm , channel failure , off-scan etc.

ALARM MANAGEMENT:
 All the analog points which cross their normal limits or all the digital points
which go into their alarm state come on the alarm CRT with associated time
& blink as long as the alarms remain unacknowledged.
 Alarm will come in RED colour
 If all the pages are full (normally no. of alarm pages & alarm per page is
predefined) and any new alarm comes , then oldest alarm will disappear
from the alarm page as FIFO basis
 Alarm print out will be available in alarm printer

DATA REPRESENTATION:
 Printed outputs of displays /collection of data in different formats
like :
1. Copy Screen
2 Alarm Print out
3. Log Print out
 CRT Displays
1. Alarm CRT display
2. Utility CRT display

DATA REPRESENTATION:
TYPES OF TREND LOG PRINOUTS
 TIME ACTIVATED
 EVENT ACTIVATED
 DEMAND LOGS
 SOE PRINTOUT
TIME ACTIVATED LOG:
 Automatic Triggered Logs
 Sample frequency is 1 Hour.(Normally)
 Time of trigger can be specified

TIME ACTIVATED LOG:
 Max. 15 nos. of points can be assigned
 Normally printed in the logging printer in UCB
 Examples :
1. Shift Log
2. Efficiency Log
3. Boiler Drum / Tube Metal Temp. Log
4. FSH / RH Metal temp. excursion Log
EVENT ACTIVATED LOG:
 Automatic Triggered Logs
 Used for Unit or Equipment Outage Analysis
 Minimum Sample frequency is 10 seconds.

EVENT ACTIVATED LOG:
 Max. 36 points can be assigned in a log
 Logs are triggered by a Trip flag
 Normally printed on Logging Printer in UCB
 Pre & Post triggered points can be specified
 Examples :
1. Post Trip Analysis Log ( PTL )
2. TG. Shutdown Analysis Log
3. Boiler Startup Log.
4. Turbine / Generator Diagnostic Logs

DEMAND LOG:
 Not Automatic Triggered Logs
 Logs can be printed on operator’s demand
 Sample frequency is generally 1 Hour.
 Logs are printed in Logging Printer in UCB

SEQUENCE OF EVENTS ( SOE )
THE MAIN FEATURES ARE:
 Determines First Cause Of Trip
 Determines sequence of events or alarms
 Scanning Time is 1 millisecond.
 It is a Stand Alone System
 Max. 256 nos. of Protection related digital points can be assigned
 Automatic Triggered when any point in alarm

DDCMIS
WHAT IS DDCMIS ?
DISTRIBUTED DIGITAL CONTROL MONITORING & INFORMATION
SYSTEM
 Distributed means there is no centralized control and control is spread
across multiple units
 Digital means processing of process information is done in digital form using
micro-processor based hardware
 MIS interfaces the human with process using computers

DDCMIS
TECHNOLOGICAL BACKGROUND
PROGRESS OF INSTRUMENTATION USED TO IMPLEMENT AUTOMATIC
PROCESS CONTROL
 LOCAL PNEUMATIC CONTROLLERS
 MINIATURIZED AND CENTRALIZED PNEUMATIC CONTROLLERS AT
CONTROL PANELS AND CONSOLES
 SOLID-STATE CONTROLLERS
 COMPUTERISED CONTROLS
 DISTRIBUTED MICROPROCESSOR BASED CONTROL

DDCMIS
Components
MAN MACHINE INTERFACE & PROCESS
INFORMATION SYSTEM
DATA COMMUNICATION SYSTEM (DATA HIGH WAY)
CONTROL SYSTEM

DDCMIS
MAN-MACHINE INTERFACE AND PLANT INFORMATION SYSTEM (MMIPS)
 LATEST STATE-OF-THE-ART WORKSTATIONS AND SERVERS BASED ON OPEN-
ARCHITECTURE AND INDUSTRY STANDARD HARDWARE AND SOFTWARE TO
ENSURE BETTER CONNECTIVITY.
e.g. HARDWARE FROM COMPAQ/DIGITAL, HP, SUN MICRO-SYSTEM OR OTHER
MAJOR SUPPLIERS (LESS DEPENDENCE ON THE C&I SYSTEM SUPPLIER IN
THE LONG RUN)
 OPERATING SYSTEM WINDOWS-NT, OPEN-VMS OR UNIX.
 PROVISION OF LVS
 CONNECTION TO OTHER SYSTEM THROUGH STATIONWIDE WAN

DDCMIS
MMIPIS FUNCTIONALITIES
 VARIOUS PLANT EQUIPMENT OPERATION
 OPERATOR INFORMATIONS THROUGH VARIOUS DISPLAYS
 ALARMS, LOGS, HISTORICAL AND LONG TERM STORAGE.
 PERFORMANCE AND OTHER CALCULATIONS

DDCMIS
DATA COMMUNICATION SYSTEM
 LOCAL SYSTEM BUS – It is just lines on the backplane of control panel to
which all the modules are connected directly. It serves as communication
medium between the modules.
 INTRAPLANT BUS(IPB) – It is a coaxial cable which runs through all the
panels of control system and interconnects them.
 LOCAL AREA NETWORK(LAN) – It is a network of computers which are
connected to a single point (HUB).
FOR ALL BUSES REDUNDANCY IS PRESENT

DDCMIS
CONTROL SYSTEM
FUNCTIONAL DIVISION
 SG-C&I SYSTEM
 TG-C&I SYSTEM
 BOP-C&I SYSTEM
HARDWARE COMPONENTS
 POWER SUPPLY
 CONTROL PANEL
 ELECTRONIC MODULES

DDCMIS
PROGRAMMING & MMIPIS M & S
CONFIGURATION SYSTEM CLOCK
SG- C&I BOP- C&I TG- C&I
SYSTEM SYSTEM SYSTEM
DCS
CONTROL SYSTEM

DDCMIS
SG-C&I SYSTEM
 BURNER MANAGEMENT SYSTEM (BMS)
 SOOT BLOWER CONTROL SYSTEM (SBC)
 SECONDARY AIR DAMPER CONTROL SYSTEM (SADC)
 AUXILIARY PRDS CONTROLS (APRDS)
TG-C&I SYSTEM
 ELECTRONIC TURBINE PROTECTION (ETP)
 AUTOMATIC TURBINE RUN-UP SYSTEM (ATRS)
 AUTOMATIC TURBINE TESTING SYSTEM (ATT)
 ELECTRO- HYDRAULIC TURBINE CONTROL SYSTEM (EHTC)
 TURBINE STRESS CONTROL SYSTEM (TSC)
 LP BYPASS SYSTEM (LPBP)
 HP BYPASS SYSTEM(HPBP)
 GLAND STEAM PRESSURE CONTROL
 GENERATOR AUXILIARY MONITORING PANEL (GAMP)

DDCMIS
BOP-C&I SYSTEM
CONSISTS OF OPEN LOOP CONTROL SYSTEM (OLCS) AND CLOSED LOOP
CONTROL SYSTEM (CLCS)
 OLCS - THE SEQUENCE CONTROL, INTERLOCK OF ALL THE PLANT SYSTEMS WHICH
ARE NOT COVERED IN THE SG-C&I AND TG-C&I. THIS INCLUDES MAJOR AUXILIARIES
LIKE FD/ID/PA FANS, AIR-PREHEATER, BFP/CEP/CWP/ BCWP , DMCWP/CLCWP AND
ELECTRICAL BREAKERS.
 CLCS - THE MODULATING CONTROL FOR VARIOUS IMPORTANT PLANT PARAMETERS,
LIKE FW FLOW (DRUM LEVEL), FURNACE DRAFT, COMBUSTION CONTROL (FUEL FLOW
AND AIR FLOW), PA HDR PRESSURE CONTROL, DEAERATOR/HOTWELL/HEATER LEVEL
CONTROLS ETC.

DDCMIS
WHY DDCMIS ?
 VERY HIGH FLEXIBILITY FOR MODIFICATION IN CONTROL STRATEGY
 VERY HIGH SELF-DIAGNOSTIC
 VERY LOW DRIFT (ONLY IN I/O CARDS) , HENCE NO NEED OF FREQUENT
RE-CALIBRATION
 MUCH HIGHER RELIABILITY (BASED ON MTBF)
 BETTER LONG TERM SUPPORT DUE TO CHANGING TECHNOLOGY
 MUCH BETTER OPERATOR INTERFACE

DDCMIS
SALIENT FEATURES OF DDCMIS
 INTEGRATED PLANT CONTROL FOR SG, TG AND BALANCE OF PLANT
CONTROL
IT MAY BE REMEMBERED THAT HISTORICALLY THE TERM DDCMIS USED
REFER TO THE SO-CALLED “BOP-C&I” . THE SG-C&I, i.e. FSSS etc. TG-C&I i.e.
ATRS, TURBINE PROTECTION etc. ORIGINALLY WERE NOT CONSIDERED
UNDER DDCMIS OR DCS AS PER MANY SUPPLIERS. ONLY RECENTLY THE
TYPE OF SYSTEMS FOR ALL THE SYSTEMS HAVE BECOME SIMILAR (WITH
SOME DIFFERENCE WHICH WILL BE DISCUSSED LATER), WE TEND TO
CONSIDER THESE SYSTEMS UNDER DDCMIS.

DDCMIS
SALIENT FEATURES OF DDCMIS
 INTEGRATED PLANT OPERATION THROUGH FULLY INTERCHANGEABLE
OPERTAOR WORK STATIONS (OWS) FOR SG, TG AND BALANCE OF PLANT
 PROVISION OF EXTENSIVE SELF-DIAGNOSTICS
 USE OF LARGE VIDEO SCREENS FOR PROJECTIONS OF VARIOUS PLANT
MIMICS ETC.
 PROVISION OF FAULT ALARM ANALYSIS TO GUIDE THE OPERATOR TO THE
MOST LIKELY EVENT
 PROVISION OF ADEQUATE RELIABILITY AND AVAILABILITY WITH PROPER
REDUNDANCY IN SENSOR, I/O AND CONTROLLER LEVELS.

Global & National Power Scenario
Global:
Global electricity consumption 69% higher in 2020 than 2003
80% of energy provided from thermal sources
Emerging trend from Thermal to Hydel and Renewable Energy sources
Indian:
Total installed capacity only 1362 MW in 1947
Per Capita consumption 631 units (2005-06) only with installed capacity of 1,77,000
MW
GDP growth of 8%, power growth required 10%
To add 1,00,000MW capacity by 2017
Liberalizations of the sector

KEY THRUST AREAS
Zero Human Error
Implementation of trip committee recommendations judiciously / rigoro
Identification of trip committee recommendations of other stations
which are relevant and implement them
Implementation of operation memorandum wherever applicable
Dissemination of information about best practices followed across
Reliance Power and other Power Stations
Providing proper environment for C&I equipment to reduce probability
card and equipment failure

9%
22%
28%
2%
9%
17%
7% 2% 4%
Coal09-10
Relay Malfunction
Tx / Sw /Fld Dev
Control System
EHC / ATRS
Power Supply /
Cable
Software / Card
failure
Human Error
UPS
RTD / Tc

Major factors contributing to C&I outage in 2009-10:
1. Control System related failure
2. Field Device Failure
3. Soft ware/Card Failure
4. Power Supply/Relay failure
5. Human error

All ‘unit protections’ are provided with 2/3 logic and audio visual
alarm is provided on 1/3 to operator on actuation of any one sensor
wherever possible with proper approval.
Use of headless RTD in tripping circuit of ID/PA/FD fans & BFPs.
Resistance mapping of critical solenoids including cable during
overhauls and monitoring trend to identify any defects.
Marking of trip related devices and Junction Boxes marked in RED
color.
Regular calibration of all important instruments which have a bearing
on unit safety, reliability and efficiency. Instruments are calibrated
against standard instruments with traceability to NABL.

BEST PRACTICES COMPILED/ADOPTED IN Reliance Power C&I
For handling of electrostatic sensitive electronic hardware, electrostatic
bags, wrist straps and other ESD handling devices are employed in control
panels and lab. All Laboratories are provided with ESD proof workstations.
Disable removable drives of servers and workstations.
Single source responsibility for software backup of DCS and storage in fire
proof cabinets in two different locations.
Detailed work instruction are prepared and followed for working on all trip
related devices.

A single source responsibility is fixed for the generation and maintenance
of system passwords so as to maintain system security
Internal quality inspection for critical checks during overhauls to ensure
quality in overhaul works
Near miss situations are monitored and analyzed. The learning from this
area used to formulate strategies to avoid spurious outages.
All power supply voltages are monitored with a fixed periodicity and
maintained within /- 10% of the rated value.

Other important actions taken for forced outage
reduction
Rerouting of control & power cables in hot zones
Panel power supply monitoring in regular intervals.
CER/UCB temperature and humidity monitoring online. Insisting for
performance of the A/C system
Checking and tightening power supply cables during overhaul
Ensuring healthiness of cabinet cooling fans.

Panel cooling fans supply segregation from system supply with MCB /
fuse.
Cleaning of air filters on panels periodically
Servo valve replacement/ servicing in hydraulic drives.
Individual fuse protection in 220VDC MFT for HOTV, LOTV, HORV,
Scanner emergency air damper solenoids

ROLE OF CONTROL AND INSTRUMENTATION IN THERMAL POWER PLANT

ROLE OF CONTROL AND INSTRUMENTATION IN THERMAL POWER PLANT

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