TRAINING REPORT OF INDUSTRIAL TRAINING
RAJGHAT POWER HOUSE
ASHUTOSH KUMAR MAURYA
B.TECH(EC) 7TH SEMESTER
BHARAT INSTITUTE OF TECHNOLOGY
BY PASS ROAD PARTAPUR,MEERUT
(FROM:-07 JUNE 2010 TO 24 JULY2010)
I would hereby like to express my profound sense of gratitude to G.M. (T)
IPGCL & PPCL, Mr. Y.P. Arora for giving me the opportunity to carry out my
industrial training at Rajghat Power House under their experienced and
highly qualified staff. Equally thankful I am to Mr. Premraj Singh
(Manager,Electrical) for his invaluable guidance during the training period.
Thanks are due to Mr. Surendra Vishwakarma (Asst. Mgr., Electrical), Mr.
Praveen Kumar (Asst. Mgr., Electrical), Mr. H.C. Pandey (Asst. Mgr., Electrical)
and Mr. R.K. Prajapati (Asst. Mgr., Cont. & Inst.) who despite of their busy
schedule and workload, were able to find some time for us and imparted us
the knowledge that paved a way for better understanding of the fundamentals
and their applications alike.
I duly acknowledge the help, direct or indirect of the whole department and
staff members of the organization for providing all the facilities for the
training. The knowledge gained herein and the practical experiences learnt
will be invaluable in the long run.
Conveyor:Ashutosh Kumar Maurya
ELECTRONICS & COMMUNICATION ENGINEERING
BHARAT INSTITUTE OF TECHNOLOGY
BY PASS ROAD PARTAPUR, MEERUT
With day to day advantage of new technology the older machinery are being
replaced by new machinery . Now it has not been the work of semi skilled
persons .It has opened a new horizon for degree holder engineers. But to do
the job properly a suitable training is needed.
The knowledge of entire system is must for an engineer to do the
trouble shooting in the quickest possible way so that the production does not
So for engineering the industrial training is playing a vital role in
developing the practical knowledge. The industrial training is not merely an
academic requirement but a professional necessity too.
With the increasing demand and utilization of electricity an electrical
engineer should be well versed or at least must be familiar with the
generation ,transmission and distribution of electricity, at the same time must
be capable of fault detection and elimination.
It is thus the responsibility of an electrical engineer to deal with the
sophistication and make the maximum possible utilization.
Title of Heading
About the company
Introduction of RAJGHAT POWER STATION
POWER PLANT BASICS
Overview of thermal power plant
Steam Turbine (Prime Over)
The steam & water circuits
Fuel air & Flue Ȃgas circuits
Control & Instrumentation in Power Plant
Combustion and Draught Control
Feed Water Control
Steam Temperature Control
Turbine Control & Monitoring
Title of Heading
Casing & Cylinder Expansion
505 Turbine Control
Automation of Process
About the company
Beholding the grimness of power situation in Delhi and failure of all previous attempts in
restoring the quality of service to the citizens Delhi Electricity Board Regulatory
Commission (DERC) was constituted in May 1999 whose prime responsibility was to look
into the entire gamut of existing activity and search for various ways of power sector
reforms. This was followed with a Tripartite Agreement which was signed by the
government of Delhi, DVB employees to ensure the cooperation of stakeholders in this
reform process. The tripartite agreement sent off very positive vibes to the people in
general as well as to the investor community about the sincere and hassle-free objectives of
The Government of India on July 1, 2002, implemented the reforms by unbundling DVB
into six companies, one holding company, one generation company (GENCO), one
transmission company (TRANSCO) and three distribution companies (DISCOMS). The
government handed over the management of the business of electricity distributions to
there private companies since July 1, 2002 with 51% equity with the private sector.
It was thus that IPGCL (GENCO) came into existence with the aim of meeting the power
demands of a city which is the capital of one of the most populated countries of the world
and whose resources fall much below its demand and since then its contribution to the
power sector has been beyond the expectations as is evident from the current power
situation in the city. The following facts may summarize the success story of a never before
330 MW capacity Pragati Power Station was commissioned in the year 2002-03 and
performing excellently. Achieved 100.4% PLF during the month of Jan.,ǯ05 and
88.27% PLF (Deemed PLF 95%) during the year 2004-05, Pragati Power
Corporation Ltd. paid dividends of Rs.17.5 Cr., for FY 2003-04 & Rs.14 Cr. for FY
2004-05 as well as 2005-06.
The performance of Indraprastha Gas Turbine Power Station which was 47.24% in
2001-02 increased to 70.76% (deemed PLF 75.35%) in 2005-06. This is the best
performance of the station in a year since its commissioning in 1985-86. The station
also achieved highest ever generation in a day, 5.743 MU (84.86% PLF) on 26.12.05
and highest ever generation in a month, 166.227 MU (79.23% PLF) in October,
2005. The forced outages of the station have also reduced from 17.75 % to 5.2 %.
The overall performance of GENCO increased from 45.90% during the year 2001-02
to 64.35% in 2005-06.
RAJGHAT POWER STATION
Two Units of 67.5 MW were installed in 1989-90 at Rajghat Power House as Replacement
of old Units and the present generation capacity of this Station is 135 MW. Further, the
station has acquired the following certifications:
ISO-9001:2000 for Quality Management
ISO-14001:2004 for Environment Management.
OHSAS-18001:2007 for Occupational Health & Safety Management
Rajghat Power House Specifications
Coal based thermal power plant
3. Installed Capacity:
2 x 67.5 MW = 135 MW
4. Land Detail
a. Plant area:
b. Ash dump area:
5. Cooling Water
b. Cooling Method:
Closed cycle with cooling tower
6. Fuel: Coal
b. Linked coal mines:
c. Gross calorific value:
d. Ash content:
e. Sulphur content:
With design coal:
With actual coal:
72000 sq. mt.
b. Nearest service outlet:
Mathura-Shakurbasti oil depot
1. OVERVIEW OF THERMAL POWER
Schematic of a thermal power plant
Power plants generate electrical power by using fuels like coal, oil or natural gas. A simple
power plant consists of a boiler, turbine, condenser and a pump. Fuel, burned in the boiler and
superheater, heats the water to generate steam. The steam is then heated to a superheated state in
the superheater. This steam is used to rotate the turbine which powers the generator. Electrical
energy is generated when the generator windings rotate in a strong magnetic field. After the
steam leaves the turbine it is cooled to its liquid state in the condenser. The liquid is pressurized
by the pump prior to going back to the boiler.
Thus the main inputs required by a plant are:
Coal: Should have high calorific value and low ash content
Water: De-mineralized water for steam generation
In this chapter first steam and its properties are described which are essential to the
understanding of the underlying principle of the thermal plant, the Rankine cycle which is
Steam power is fundamental to what is by far the largest sector of the electricity-generating
industry and without it the face of contemporary society would be dramatically different from its
present one. We would be forced to rely on hydro-electric power plant, windmills, batteries, solar
cells and fuel cells, all of which are capable of producing only a fraction of the electricity we use.
Steam is produced by boiling of water and it is achieved at atmospheric pressure at 100 degree
Celsius. Let us consider a quantity of water that is contained in an open vessel. Here, the air that
blankets the surface exerts a pressure on the surface of the fluid and, as the temperature of the
water is raised, enough energy is eventually gained to overcome the blanketing effect of that
pressure and the water starts to change its state into that of a vapour (steam). If the pressure of
the air blanket on top of the water were to be increased, more energy would have to be
introduced to the water to enable it to break free. In other words, the temperature must be raised
further to make it boil. To illustrate this point, if the pressure is increased by 10% above its
normal atmospheric value, the temperature of the water must be raised to just above 102 °C
before boiling occurs.
The information relating to steam at any combination of temperature, pressure and other factors
may be found in steam tables, which are nowadays available in software as well as in the more
traditional paper form. These tables were originally published in 1915 by Hugh Longbourne
Callendar (1863-1930), a British physicist. Because of advances in knowledge and measurement
technology, and as a result of changing units of measurement, many different variants of steam
tables are today in existence, but they all enable one to look up, for any pressure, the saturation
temperature, the heat per unit mass of fluid, the specific volume etc.
Steam becomes superheated when its temperature is raised above the saturation temperature
corresponding to its pressure. This is achieved by collecting it from the vessel in which the
boiling is occurring, leading it away from the liquid through a pipe, and then adding more heat to
it. This process adds further energy to the fluid, which improves the efficiency of the conversion
of heat to electricity.
As stated earlier, heat added once the water has started to boil does not cause any further
detectable change in temperature. Instead it changes the state of the fluid. Once the steam has
formed, heat added to it contributes to the total heat of the vapour. This is the sensible heat plus
the latent heat plus the heat used in increasing the temperature of each kilogram of the fluid
through the number of degrees of superheat to which it has been raised. In a power plant, a major
objective is the conversion of energy locked up in the input fuel into either usable heat or
electricity. In the interests of economics and the environment it is important to obtain the highest
possible level of efficiency in this conversion process.
Rankine Cycle: The Working Principle
The Carnot cycle postulates a cylinder with perfectly insulating walls and a head which can be
switched at will from being a conductor to being an insulator. Even with modifications to enable
it to operate in a world where such things are not obtainable, it would have probably remained a
scientific concept with no practical application, had not a Scottish professor of engineering,
William Rankine, proposed a modification to it at the beginning of the twentieth century. The
concepts that Rankine developed form the basis of all thermal power plants in use today. Even
today¶s combined-cycle power plants use his cycle for one of the two phases of their operation.
The Rankine cycle in a steam-turbine power plant
In the system shown in figure, water is heated in feed heaters (A to B) using steam extracted
from the turbine. Within the boiler itself, heat is used to further pre-warm the water (in the
economiser) before it enters the evaporative stages (C) where it boils. At D superheat is added
until the conditions at E are reached at the turbine inlet. The steam expands in the turbine to the
conditions at point F, after which it is condensed and returned to the feed heater. The energy in
the steam leaving the boiler is converted to mechanical energy in the turbine, which then spins
the generator to produce electricity. The diagram shows that the energy delivered to the turbine is
maximised if point E is at the highest possible value and F is at the lowest possible value.
2. TEAM TURBINE (PRIME MOVER)
A steam turbine at Rajghat Power station
2.1 Raising steam
Steam is mostly raised from fossil fuel sources, mostly coal but also oil and gas, in a combustion
chamber. Recently these fuels have been supplemented by limited amounts of renewable biofuels
and agricultural waste.
The chemical process of burning the fuel releases heat by the chemical transformation
(oxidation) of the fuel. This can never be perfect. There will be losses due to impurities in the
fuel, incomplete combustion and heat and percentage of the available energy in the fuel.
2.2 Working Principles
High pressure steam is fed to the turbine and passes along the machine axis through multiple
rows of alternately fixed and moving blades. From the steam inlet port of the turbine towards the
exhaust point, the blades and the turbine cavity are progressively larger to allow for the
expansion of the steam.
The stationary blades act as nozzles in which the steam expands and emerges at an increased
speed but lower pressure. (Bernoulli's conservation of energy principle - Kinetic energy increases
as pressure energy falls). As the steam impacts on the moving blades it imparts some of its
kinetic energy to the moving blades.
There are two basic steam turbine types, impulse turbines and reaction turbines, whose blades are
designed control the speed, direction and pressure of the steam as is passes through the turbine.
2.2.1 Impulse Turbines
The steam jets are directed at the turbine's bucket shaped rotor blades where the pressure exerted
by the jets causes the rotor to rotate and the velocity of the steam to reduce as it imparts its
kinetic energy to the blades. The blades in turn change the direction of flow of the steam
however its pressure remains constant as it passes through the rotor blades since the cross section
of the chamber between the blades is constant. Impulse turbines are therefore also known as
constant pressure turbines.
The next series of fixed blades reverses the direction of the steam before it passes to the second
row of moving blades.
2.2.2 Reaction Turbines
The rotor blades of the reaction turbine are shaped more like aerofoils, arranged such that the
cross section of the chambers formed between the fixed blades diminishes from the inlet side
towards the exhaust side of the blades. The chambers between the rotor blades essentially form
nozzles so that as the steam progresses through the chambers its velocity increases while at the
same time its pressure decreases, just as in the nozzles formed by the fixed blades. Thus the
pressure decreases in both the fixed and moving blades. As the steam emerges in a jet from
between the rotor blades, it creates a reactive force on the blades which in turn creates the
turning moment on the turbine rotor, just as in Hero's steam engine. (Newton's Third Law - For
every action there is an equal and opposite reaction).
The turbine employed at the station comprises of 47 stages one of which is impulse and the rest
are reaction stages.
2.3 Turbine-Generator arrangement
The plant employs a 2-pole synchronous generator with a synchronous speed of 3000 rpm. The
output frequency is determined by the relation
ܰ ൌ ͳʹͲ כ
where N is the rotor speed in RPM
f is the output frequency of generator
P is the number of poles of generator
The generator is air cooled and the bearings are cooled by oil which is supplied by various oil
pumps EOP, JOP, BOP etc. The detailed description of the generator unit is provided in
Appendix-C. The following figure shows the arrangement of turbine and generator set.
Overall turbine and generator arrangement
Steam turbines are provided with journal bearings and thrust bearings. Journal bearings are at
each end of each rotor to support the weight of the rotor. One thrust bearing is provided for the
entire steam turbine to maintain the axial position of the rotor.
Journal Bearings. The journal bearings are constructed of two halves that enclose the shaft. The
inside of the bearing adjacent to the shaft is lined with babbitt metal. Babbitt is an alloy of tin,
copper, and antimony that has antiseizing qualities and a natural oiliness. The journal bearings
are oil-pressure lubricated. Oil flow is controlled to limit oil temperature rise to a set value.
Thrust Bearings. The thrust bearing consists of babbitt metal lined, stationary shoes that run
against the rotor thrust runner. Shoes on both sides of the runner prevent movement in either
axial direction. The thrust bearing compartment is oil-pressure flooded with the oil introduced
near the shaft and flowing outward by the centrifugal action of the runner. Oil flow is controlled
to limit oil temperature rise to a set value.
Major control valves associated with the steam turbine and their operations are as follows:
Main Steam Stop (Throttle) Valves: The steam from the steam generator flows to the main
steam stop or throttling valves. The primary function of the stop valves is to provide backup
protection for the steam turbine during turbine generator trips in the event the main steam control
valves do not close. The energy in the main steam and steam generator can quickly cause the
turbine to reach destructive overspeed on loss of the generator load. The main steam stop valves
close from full open to full closed in 0.15 to 0.5 s. The stop valves are also closed on unit normal
shutdown after the control valves have closed.
A secondary function of the stop valves is to provide steam throttling control during startup. The
stop valves have internal bypass valves that allow throttling control of the steam from initial
turbine roll to loads of 15% to 25%. During this startup time, the main steam control valves are
wide open and the bypass valves are used to control the steam flow.
Main Steam Control (Governor) Valves: The steam flows from the stop valves to the main
steam control or governor valves. The primary function of the control valves is to regulate the
steam flow to the turbine and thus control the power output of the steam turbine generator. The
control valves also serve as the primary shutoff of the steam to the turbine on unit normal
shutdowns and trips.
3. THE STEAM AND WATER CIRCUITS
3.1 Steam Generation and use
The steam generation occurs in banks of tubes that are exposed to the radiant heat of combustion.
The steam leaves the drum and enters a bank of tubes where more heat is taken from the gases
and added to the steam, superheating it before it is fed to the turbine. The superheater, comprises
a single bank of tubes but in many cases multiple stages of superheater tubes are suspended in
the gas stream, each abstracting additional heat from the exhaust gases. In boilers (rather than
HRSGs), some of these tube banks are exposed to the radiant heat of combustion and are
therefore referred to as the radiant superheater. Others, the convection stages, are shielded from
the radiant energy but extract heat from the hot gases of combustion.
Schematic of a boiler
After the flue gases have left the superheater they pass over a third set of tubes (called the
economizer), where almost all of their remaining heat is extracted to pre-warm the water before
it enters the drum.
Finally the last of the heat in the gases is used to warm the air that is to be used in the process of
burning the fuel. The major moving items of machinery shown in the diagram are the feed pump,
which delivers water to the system, and the fan which provides the air needed for combustion of
the fuel (in most plants each of these is duplicated). In a combined-cycle plant the place of the
combustion-air fan and the fuel firing system is taken by the gas turbine exhaust.
3.2 Feed water-condensate cycle
Inside the plant, the steam and water system forms a closed loop, with the water leaving the
condenser being fed back to the feed pumps for reuse in the boiler. However, certain other items
of plant now become involved, because the water leaving the condenser is cold and contains
entrained air which must be removed.
Air becomes entrained in the water system at start-up (when the various vessels are initially
empty), and it will appear during normal operation when it leaks in at those parts of the cycle
which operate below atmospheric pressure, such as the condenser, extraction pumps and low
pressure feed heaters. Leakage can occur in these areas at flanges and at the sealing glands of the
rotating shafts of pumps. Air entrainment is aided by two facts: one is that cold water can hold
greater amounts of oxygen (and other dissolved gases) than can warm water; and the other is that
the low-pressure parts of the cycle must necessarily correspond with the low temperature phases.
3.3 The Deareator
The deaerator removes dissolved gases by vigorously boiling the water and agitating it, a process
referred to as 'stripping'. The water entering at the top is mixed with steam which is rising
upwards. The steam, taken directly from the boiler or from an extraction point on the turbine,
heats a stack of metal trays and as the water cascades down past these it mixes with the steam
and becomes agitated, releasing the entrained gases. The steam pressurizes the deaerator and its
contents so that the dissolved gases are vented to the atmosphere.
Minimizing corrosion requires the feed-water oxygen concentration to be maintained below
0.005 ppm or less and although the deaerator provides an effective method of removing the bulk
of entrained gases it cannot reduce the concentration below about 0.007 ppm. For this reason,
scavenging chemicals are added to remove the last traces of oxygen.
Principle of a deaerator
4. THE FUEL, AIR AND FLUE-GAS
4.1 Corner Fired Boiler: The plant employs corner fired (tangential) boilers in which the
burning fuel circulates around the furnace, forming a large swirling ball of burning fuel at the
centre. The burners are placed at five equidistant levels (named A, B, C, D and E) along the
height of boiler on all four corners. A certain degree of tilt can be provided to the burners to
direct the fireball to a higher or lower position within the furnace, and this has a significant effect
on the temperature of the various banks of superheater tubes, and therefore on steam
4.2 Air Heater: It works as a heat exchanger and transfers the heat remaining in the exhaust
gases to the air being fed to the furnace. The reuse of heat in the exhaust gases results in
improvement of efficiency of the plant. However, the exchanger suffers from leakage of heat and
perfect transfer of heat cannot be obtained.
4.3 Pressurized Bowl Mill: The coal that is discharged from the storage hoppers is fed down a
central chute onto a table where it is crushed by a grinding rotor assembly and is ground down to
a very fine powder (called pulverized fuel (PF)). Air is blown into the crushed coal and carries it,
via adjustable classifier blades, to the PF pipes that transport it to the burners. The air that carries
the fine particles of coal to the burners is supplied from a fan called a 'primary-air fan'. This
delivers air to the mill, which therefore operates under a pressure which is slightly positive with
respect to the atmosphere outside.
Pressurized bowl mill
For supplying the air to the mill, cool air and heated air are mixed to achieve the desired
temperature. This temperature has to be high enough to partially dry the coal, but it must not be
so high that the coal could overheat (with the risk of the coal/air mixture igniting inside the mill
or even exploding while it is being crushed). The warm air is then fed to the mill (or a group of
mills) by means of yet another fan, called a 'primary air fan'. It should be noted that the cooler of
the two air streams is commonly referred to as 'tempering air' since, because it is obtained from
the FD fan exhaust it may already be slightly warm, and its function is to temper the mixture.
A steam turbine generator
In electricity generation, an electrical generator is a device that converts mechanical energy
to electrical energy, generally using electromagnetic induction. The reverse conversion of electrical
energy into mechanical energy is done by a motor, and motors and generators have many similarities. A
generator forces electric charges to move through an external electrical circuit, but it does not create
electricity or charge, which is already present in the wire of its windings. It is somewhat analogous to a
water pump, which creates a flow of water but does not create the water inside. The source of mechanical
energy may be a reciprocating engine, a steam or gas turbine, water falling through a turbine or
waterwheel, an internal combustion engine, a wind turbine, a hand crank, the sun or solar energy,
compressed air or any other source of mechanical energy.
Control & instrumentation in Power Plant
For the power plant to run and produce electricity, the equipment in each category must be
placed into operation to perform its intended function. The operation of the equipment must be
coordinated to meet the demand of the electricity production process, and the production process
must be regulated so that the cycle and the equipment are operated within design conditions. The
plant control systems provide the necessary tools to enable the operators to orchestrate plant
operation for the reliable and efficient production of electricity. This section provides an
overview of the plant control system, its functions, and the type of control equipment used in the
Rajghat Power House.
5. COMBUSTION AND DRAUGHT
In a fired boiler the control of combustion is extremely critical. In order to maximize operational
efficiency combustion must be accurate, so that the fuel is consumed at a rate that exactly
matches the demand for steam, and it must be executed safely, so that the energy is released
without risk to plant, personnel or environment keeping in mind that the amount of energy
involved in a power plant is considerable: in each second of its operation a large boiler releases
around a billion joules, and in a process of this scale the results of an error can be catastrophic.
5.1 Load control strategy for pressurized mills
The approach is to provide closed-loop control of the primary-air flow, as shown. Here, because
the system detects and immediately reacts to changes in PA flow, and adjusts the flow-control
damper to compensate, disturbances to steam production are minimized. Again, a feeder-speed
signal, representing fuel flow, is fed back to the master system to provide closed-loop correction
of speed changes, which would otherwise introduce disturbances to the steam pressure.
Closed loop control of PA flow
5.2 Mill temperature control
Control objective: It is very important that the temperature of the air in the mill should be
maintained within close limits. For many reasons, including inadequate drying of the coal,
combustion efficiency will be reduced if the temperature is too low, while too high a temperature
can result in fires or explosions occurring in the mill.
Control Technique: The control technique involves mixing hot and cold air streams to achieve
the correct temperature. Pressurized coal mills require the use of two dampers for this purpose
one controlling the flow of hot air, the other the cold air.
Mill Temperature Control
5.3 Draught control
In a fired boiler, the air required for combustion is provided by one or more fans and the exhaust
gases are drawn out of the combustion chamber by an additional fan or set of fans. The control of
all these fans must ensure that an adequate supply of air is available for the combustion of the
fuel and that the combustion chamber operates at the pressure determined by the boiler designer.
All of the fans also have to contribute to the provision of another important function--purging of
the furnace in all conditions when a collection of unburned fuel or combustible gases could
otherwise be accidentally ignited. Such operations are required prior to light-off of the first
burner when the boiler is being started, or after a trip.
5.3.1 Maintaining the furnace draught
Apart from supplying air to support combustion, the FD fans have to operate in concert with the
ID fans to maintain the furnace pressure at a certain value. The heavy solid line of figure below
shows the pressure profile through the various sections of a typical balanced-draught boiler
system. It shows the pressure from the point where air is drawn in, to the point where the flue
gases are exhausted to the chimney, and demonstrates how the combustion chamber operates at a
slightly negative pressure, which is maintained by keeping the FD and ID fans in balance with
each other. If that balance is disturbed the results can be extremely serious. Such an imbalance
can be brought about by the accidental closure of a damper or by the sudden loss of all flames. It
can also be caused by mal-operation of the FD and ID fans. The dashed line on the diagram
shows the pressure profile under such a condition, which known as an 'implosion'. The results of
an implosion are extremely serious because, even though the pressures involved may be small,
the surfaces over which they are applied are very large and the forces exerted become enormous.
Such an event would almost certainly result in major structural damage to the plant.
Draught profile of a boiler and its auxiliary plant
5.3.2 Fan control
The throughput of two fans operating together can be regulated by a common controller or by
individual controllers for each fan. Although a single controller cannot ensure that each fan
delivers the same flow as its partner, this configuration is much simpler to tune than the
alternative, where the two controllers can interact with each other and make optimization
Controlling the windbox pressure
5.4 Binary control of the combustion system
So far, we have considered only the modulating systems involved with the combustion plant. In
practice, these systems have to operate in concert with binary control systems such as interlocks
The purpose of an interlock is to co-ordinate the operation of different, but interrelated plant
items: tripping one set of fans if another set trips, and so on. The purpose of a sequence system is
to provide automatic start-up or shutdown of the plant, or of some part of it.
5.4.1 Flame monitoring
Monitoring the status of a flame is not easy. The detector must be able to discriminate between
the flame that it is meant to observe and any other in the vicinity, and between that flame and the
hot surfaces within the furnace. The detector must also be able to provide reliable detection in
the presence of the smoke and steam that may be swirling around the flame. To add to the
problems, the detector will be required to operate in the hot and dirty environment of the burner
front, and it will be subjected to additional heat radiated from the furnace into which it is
With their attendant BMS¶s, flame scanners of a boiler are vital to the safety and protection of
the plant. If insufficient attention is paid to their selection, or if they are badly installed or
commissioned, or if their maintenance is neglected, the results can be, at best, annoying. The
problems will include nuisance trips, protracted start-up of the boiler and the creation of
hazardous conditions that could have serious safety implications.
A flame scanner is a complex opto-electronic assembly, and modern scanners incorporate
sophisticated technologies to improve flame recognition and discrimination. Although the
electronics assembly will be designed to operate at a high temperature (typically 65 °C), unless
great care is taken this value could easily be exceeded and it is therefore important to take all
possible precautions to reduce heat conduction and radiation onto the electronic components.
Typical flame scanner
5.4.2 The requirements for purge air
The purge air that is supplied to the scanner serves two purposes:
1. it provides a degree of cooling and
2. it prevents dust, oil and soot from being deposited on the optical parts of the unit.
The air should be available at each burner, even if the burner itself is not operating. It should
therefore be obvious that the air used for purging should be cool, dry and clean, and that it should
be available at all times. Purge air can be obtained from the instrument-air supply, or it can be
provided by dedicated blowers. In some cases it is taken from the FD fan discharge. Each of
these is viable, provided the requirements outlined above have been thoroughly considered. It is
also important that the presence of the purge-air supply should be monitored and its loss
transmitted to the DCS, because failure of the air supply could result in expensive and possibly
irreparable damage to the scanners. Modern scanners include self-monitoring circuits that will
warn of overheating. The scanner system should be fail-safe, as a failed system represents the
loss of a critical link in the plant's safety chain. If it is overridden, the operator can become used
to operating without it in place, and such lapses can eventually create a severe hazard.
6. FEED-WATER CONTROL
6.1 Controlling the flow
Control Objective: To supply enough water to the boiler to match the evaporation rate for the
widest practical range of operation in a safe and cost-effective manner.
1. Measurements of drum level cannot be made easily.
2. Interactions in the boiler system and uneven nature of these interactions.
Control requirement: The purpose of the drum is not only to separate the steam from the water
but also to provide a storage reservoir that allows short-term imbalances between feed-water
supply and steam production to be handled without risk to the plant. As the level of water in the
drum rises, the risk increases of water being carried over into the steam circuits. The results of
such 'carry-over' can be catastrophic: cool water impinging on hot pipework will cause extreme
and localized stresses in the metal and, conversely, if the level of water falls there is a possibility
of the boiler being damaged, partly because of the loss of essential cooling of the furnace waterwalls.
Therefore, the target of the feed-water control system is to keep the level of water in the drum at
approximately the midpoint of the vessel. Given this objective, it would appear that the simplest
solution would appear to be to measure the level of water in the drum and to adjust the delivery
of water to keep this at the desired value--feeding more water into the drum if the level is falling,
and less if the level is rising. Unfortunately, the level of water is affected by transient changes of
the pressure within the drum and the sense in which the level varies is not necessarily related to
the sense in which the feed flow must be adjusted. In other words, it is not sufficient to assume
that simply because the level is increasing the feed-water flow must be decreased, and vice versa.
This strange situation is due to effects known as 'swell' and 'shrinkage'. Boiling water comprises
a turbulent mass of fluid containing many steam bubbles, and as the boiling rate increases the
quantity of bubbles that is generated also increases. The mixture of water and bubbles resembles
foam, and the volume it occupies is dictated both by the quantity of water and by the amount of
the steam bubbles within it. If the pressure within the system is decreased, the saturation
temperature is also lowered and the boiling rate therefore increases (because the temperature of
the mixture is now higher in relation to the saturation temperature than it was before the pressure
change occurred). As the boiling rate increases, the density of the, water decreases, but since the
mass of steam and water has not changed the decrease in density must be accompanied by an
increase in the volume of the mixture.
By this mechanism the level of water in the drum appears to rise, a phenomenon referred to as
'swell'. The rise of level is misleading: it is not indicative of a real increase in the mass of water
in the system, which would require the supply of water to be cut back to maintain the status quo.
In fact, if the drop in pressure is the result of the steam demand suddenly increasing, the water
supply will need to be increased to match the increased steam flow. 'Shrinkage' is the opposite of
swell: it occurs when the pressure rises. The mechanism is exactly the same as that for swell, but
in the reverse direction. Shrinkage causes the level of water in the drum to fall when the steam
flow decreases, and once again the delivery of water to the boiler must be related to the actual
need rather than to the possibly misleading indication provided by the drum-level transmitter.
If a slow change of steam flow occurs, all is well because the pressure within the system can be
controlled. It is when rapid steam-flow changes happen that problems occur since, due to swell
or shrinkage, the drum level indication provides a contrary indication of the water demand.
Following a sudden increase in steam demand, which causes the pressure to drop (and therefore
the drum level to rise), a simple level controller would respond by reducing the flow of feed
water. Equally, a sudden decrease in steam flow, which would be accompanied by a rise in
pressure and an attendant fall in the drum level, would cause a level controller to increase the
flow of water. Both actions are, of course, in the incorrect sense.
The effects of swell and shrinkage, in addition to being determined by the rate of change of
pressure, also depend on the relative size of the drum and the pressure at which it operates. If the
volume of the drum is large in relation to the volume of the whole system the effect will be
smaller than otherwise. If the system pressure is low the effect will be larger than with a boiler
operating at a higher pressure, since the effect of a given pressure change on the density of the
water will be greater in the low-pressure boiler than it would if the same pressure change were to
occur in a boiler operating at a higher pressure.
Control technique: Remembering that the basic requirement of a feed-water control system is to
maintain a constant quantity of water in the boiler, it is apparent that one way of addressing the
problem would be to maintain the flow of water into the system at a value which matches the
flow of steam out of it. The flow is controlled using a valve which maintains the rate of water
flowing through the valve at a figure which is directly proportional to the demand signal from the
controller (i.e. if the demand signal varies linearly from 0 to 100%, the flow rate also changes
linearly between 0 and 100%). Such a valve is said to have a 'linear characteristic' and is
employed in conjunction with a transmitter that produces a signal proportional to steam flow.
Used together, these two devices keep the parameters in step. If the transmitter produces a signal
which is equal to the steam flow at all loads and if the flow through the valve is matched with
this signal at every point in the flow range, a controller gain of unity will ensure that, throughout
the dynamic range of the system, the flow of water will always be equal to the flow of steam.
However, the flow through a valve depends both on its opening and on the pressure drop across
it. In a feed-water system, the pressure drop across the valve varies from instant to instant, and
the flow through it at any given opening will therefore vary. One method of correcting for the
error produced by the feed valve is the addition of a third element to the system-a measurement
of feedwater flow.
Three-element feed-water control system
Here a cascade control technique is applied. The blocks are described below:
Item 1: Flow Transmitter for feed water flow rate
Item 2: Flow transmitter for steam flow rate
Item 3: Level transmitter for drum level
Item 4: A gain block to adjust for any range difference between the steam-flow and feed-flow
Item 5: Drum-level controller (proportional only)
Item 6: Error generator
Item 7: Closed-loop feed-water controller
A control valve consists of many components which may conveniently be considered as falling
into one of two groups: the valve body and the actuator. The former is the part through which the
water flows and this flow is controlled by adjusting the resistance offered to the water. This is
done by moving the position of a plug in relation to its seat. The position of the plug is controlled
by an actuator which acts via the stem.
Figure shows a small-bore feed-water control valve body with a contoured trim (the 'trim' being
the part of the valve which is in flowing contact with the water). The contour determines the
relationship between the position of the plug and the flow of water past it. The type of trim will
be dictated by the application, such as the need to minimize acoustic noise or cavitation, the
rangeability needed etc. In addition the trim design will determine the valve characteristic, which
is the curve relating the stem position to the rate of flow of water through the valve. This is an
important feature, since the characteristic determines the gain of the valve system, which forms
part of the overall loop gain.
A typical feed-water control valve body
For a given opening, the flow through the valve will be determined by the delivery pressure of
the feed pump and the resistance that the boiler pipework offers to the flow. To simplify the task
of selecting the correct valve size and characteristic, it is necessary to relate everything to a
definable set of conditions. This is achieved by determining what the flow through the valve
would be if a fixed differential pressure were to be maintained across it. This is termed the
inherent characteristic of the valve.
Once the valve is operating on the actual plant, the position/flow relationship achieved in
practice will not match the inherent characteristic, because in the real world the inlet pressure
and system resistance will vary, producing a pressure drop which is different from the value that
was used to define the inherent characteristic. The pressure/flow relationship achieved in actual
operation is called the installed characteristic.
Inherent characteristics of valves
6.3 Deareater control
Steam admitted to the deaerator rises upwards past metal trays over which the water is
simultaneously cascading downwards. As the water and steam mix and become agitated,
entrained gases are released. The dissolved gases are vented to the atmosphere because the vessel
is pressurised by the steam. The deaerator is situated in the water circuit between the discharge
of the condenser extraction pump and the inlet of the feed pumps. It will be evident that two
control functions are required by the deaerator:
y to maintain the steam pressure at the optimum value
y to keep the storage vessel roughly half full of water.
6.3.1 Steam pressure control
The pressure of the steam entering the deaerator is maintained by a simple controller whose
measured-value signal is obtained from a transmitter measuring the steam pressure in the
deaerator. The set value of the controller is fixed.
6.3.2 Level control
The storage vessel provides a measure of reserve capacity for the plant. To achieve this function
the level of water in it must be maintained at roughly the midpoint. This is achieved by means of
a level controller whose measured-value signal is obtained from a differential-pressure
transmitter or from capacitive probes which would normally be connected to tappings of an
external water column which is in turn connected to the top and bottom of the deaerator storage
vessel. If there were no losses in the system, the amount of water would be constant and the level
in the deaerator storage vessel would remain at the correct value set during commissioning.
However, losses are inevitable (for example, due to leakages at pump glands or during sootblowing or blowdown operations), and a supply of treated water must therefore be made
available. The deaerator level controller output adjusts the opening of a valve that admits this
make-up water to the condenser, as shown.
The make-up supply is conventionally fed into the system at the condenser. Figure shows that
interaction between the level controllers of the deaerator and condenser is inevitable. The
situation is made more complex because the condenser extraction pump has to be provided with
a bypass arrangement to maintain a minimum flow through the pump at all times.
In fact, the conditions which cause the deaerator level controller to call for more water to be
added to the system will also cause the condenser level to fall, and so the two systems do not act
in opposite senses. Nevertheless they do interact, and care must be taken to minimise the
instability that is likely to arise.
Principle of deaerator level control system
a. Single element water level control, Only single sensor i.e. level sensor is used to
control the level
b. Double Element water level control
This uses two sensors level and flow sensors. It is better and precise than single element
Other Temperature, Flow and Pressure control is done by Feedback loop- This uses a single
feedback loop which finds out error from the set point and finds out controller output.
Cascaded Feedback loop control
This uses two controller:
The set point of slave controller is decided by the controller output of the master.
7. STEAM TEMPERATURE CONTROL
7.1 Temperature control
Control Objective: To maintain the temperature of steam at a precise value over the entire load
Control Requirement: The steam turbine requires the steam temperature to remain at a precise
value over the entire load range, and it is mainly for this reason that some dedicated means of
regulating the temperature must be provided. Since different banks of tubes are affected in
different ways by the radiation from the burners and the flow of hot gases, an additional
requirement is to provide some means of adjusting the temperature of the steam within different
parts of the circuit, to prevent any one section from becoming overheated.
Difficulties: The long time constants associated with the superheater do not permit a simple
control strategy based on measuring the temperature of the steam leaving the final superheater,
and modulating the flow of cooling water to the spray attemperator so as to keep the temperature
constant at all flow conditions. This form of control would produce excessive deviations in
temperature, and a more complex arrangement is required.
Two time constants are associated with the superheater. One represents the time taken for
changes in the firing rate to affect the steam temperature, the other is the time taken for the steam
and water mixture leaving the attemperator to appear at the outlet of the final superheater. In
terms of temperature control it is the latter effect which predominates because, although changes
in heat input will affect the temperature of the steam, a fast-responding temperature-control loop
will be able to compensate for the alterations and keep the temperature constant. It is the reaction
time between a change occurring in the spray-water flow and the effects being observed in the
final temperature that determines the extent of the temperature variations that will occur.
Control technique: Another problem with a simple system is that it does not permit any
monitoring and control of the temperature to occur within the steam circuit--only at the exit from
the boiler. These difficulties are addressed by the use of a cascade control system as shown.
Since it is the temperature of the steam leaving the secondary superheater that is important, this
parameter is measured and a corresponding signal fed to a three-term controller (proportionalplus-integral-plus-derivative). In this controller the measured-value signal is compared with a
fixed desired-value signal and the controller's output forms the desired-value input for a
secondary controller. (Because the output from one controller 'cascades' into the input of another,
this type of control system is commonly termed 'cascade control'.) The secondary controller
compares this desired-value signal with a measurement representing the temperature of the steam
immediately after the spray-water attemperator.
Because the steam temperature sensors used are subjected to the high pressures and temperatures
of the superheater, they have to be enclosed in substantial steel pockets. Even with the best
designs, pockets are usually slow-responding, with the result that any high-speed fluctuations in
the measured-value signal will be smoothed out and the resultant signal will be fairly stable. The
use of a derivative term is therefore easier than in, say, flow measurement applications where
small-scale but sudden changes in flow can occur. When rapid input changes are differentiated,
the controller output changes by a large amount, and for this reason tuning three-term flow
controllers for optimum response can become difficult. This is not a problem with the
temperature controllers used here, and the application of derivative action is viable.
Steam-temperature control with a single interstage spray attemperator
7.2 Spray Water Attemperator: The high-pressure cooling water is mechanically atomized into
small droplets at a nozzle, thereby maximizing the area of contact between the steam and the
water. With this type of attemperator the water droplets leave the nozzle at a high velocity and
therefore travel for some distance before they mix with the steam and are absorbed. To avoid
stress-inducing impingement of cold droplets on hot pipework, the length of straight pipe in
which this type of attemperator needs to be installed is quite long, typically 6 m or more.
With spray attemperators, the flow of cooling water is related to the flow rate and the
temperature of the steam, and this leads to a further limitation of a fixed-nozzle attemperator.
Successful break-up of the water into atomized droplets requires the spray water to be at a
pressure which exceeds the steam pressure at the nozzle by a certain amount (typically 4 bar).
Because the nozzle presents a fixed-area orifice to the spray water, the pressure/flow
characteristic has a square-law shape, resulting in a restricted range of flows over which it can be
used (this is referred to as limited turn-down or rangeability). The turn-down of the mechanically
atomized type of attemperator is around 1.5:1.
The temperature of the steam is adjusted by modulating a separate spray-water control valve to
admit more or less coolant into the steam.
Mechanically atomised desuperheater
7.3 Temperature control with tilting burners
The burning fuel in a corner-fired boiler forms a large swirling fireball which can be moved to a
higher or lower level in the furnace by tilting the burners upwards or downwards with respect to
a mid-position. The repositioning of the fireball changes the pattern of heat transfer to the
various banks of superheater tubes and this provides an efficient method of controlling the steam
temperature, since it enables the use of spray water to be reserved for fine-tuning purposes and
for emergencies. In addition, the tilting process provides a method of controlling furnace exit
8. TURBINE CONTROL AND
The steam turbine generator is controlled and monitored by several interrelated systems:
1. Turbine governor system: automatically controls turbine speed, acceleration, and load;
2. Trip system: provides protection through trips and ranbacks;
3. Supervisory instrumentation system: provides past and present operating data through
parameter sensing, indicating, and recording; and
4. Excitation system: controls generator voltage
8.1 Turbine Governor: The turbine governor system is a hybrid electrical-hydraulic system.
This type of control system is significantly more advanced and preferable to the older
mechanical-hydraulic designs in that the linkages and cams of the mechanical designs have been
replaced with electrical logic and fast-acting hydraulic servomotors. The hydraulic fluid is
supplied to the stop and control valve servomotors by a high-pressure power pumping unit. The
fluid is flame retardant to minimize fire hazards in the event of a leak. The system also includes
controls and instrumentation.
The turbine governor facilitates control of the turbine over the full operational range by
positioning the turbine control valves and the interceptor valves to control turbine speed, load,
and throttle pressure.
8.2 Trip System: The trip system initiates protective tripping of the turbine by sensing
potentially damaging operating conditions. Typical parameters sensed for initiation of turbine
protective functions include the following:
Over speed governor trip
Manual trip device
Generator protection trips (loss of coolant, high stator temperature, etc.)
High differential expansion
Turbine over speed
Thrust bearing failure
Low lubricating oil or hydraulic fluid pressure
Operator manual trip
Governor system protective trips
Condenser low vacuum trip
High exhaust temperature trip
High vibration trip
8.3 Supervisory Instrumentation System: The supervisory instrumentation system includes
devices to sense, indicate, and record parameters necessary to monitor the operation of the
machine. The following parameters are monitored along with others:
Governor or control valve position;
Radial (X-Y) shaft vibration at all turbine, generator, and
Shell, rotor, and differential expansion;
Shell and valve chest temperatures;
Water induction thermocouple temperatures;
Vibration phase angles;
Bearing metal temperature, including the thrust bearing;
Generator winding temperatures;
Generator gas temperatures;
Generator cooling water temperatures; and
These parameters are measured, recorded, displayed, and alarmed by hard-wired monitors in the
system cabinets. High differential expansion, turbine over speed, and thrust bearing wear alarms
are provided to the trip system. Rotor vibration alarms are displayed in the main control room.
Turbine Supervisory Equipment Application
8.4 Sensors and Measurement Techniques
Turbine supervision is an essential part of the day-to-day running of any power plant. There are
many potential faults such as cracked rotors and damaged shafts, which result from vibration and
expansion. When this expansion and vibration is apparent in its early stages the problem can
usually be resolved without any of the disruption caused when a turbine has to be shut down. By
appropriate trending of the various measurement points and the identification of excessive
vibration or movement, scheduled equipment stoppages or outages can often be utilised to
investigate and resolve the failure mechanism.
8.4.1 The Eddy Current Proximity Probe
The principle of operation, as the name implies, depends upon the eddy currents set up in the
surface of the target material - shaft, collar, etc. adjacent to the probe tip.
The Eddy probe tip is made of a dielectric material and the probe coil is encapsulated within the
tip. The coil is supplied with a constant RF current from a separate Eddy Probe Driver connected
via a cable, which sets up an electromagnetic field between the tip and the observed surface.
Any electrically conductive material within this electromagnetic field, i.e. the target material,
will have eddy currents induced in its surface. The energy absorbed from the electromagnetic
field to produce these eddy currents will vary the strength of the field and hence the energizing
current, in proportion to the probe target distance. Such changes are sensed in the driver where
they are converted to a varying voltage signal.
The whole probe, extension cable and driver system relies for its operation on being a tuned
circuit and as such is dependent on the system¶s natural frequency. Thus each system is set up for
a fixed electrical/cable length. Eddy probe systems are usually supplied with 2, 5, 9 or 14 metre
total cable lengths.
The probe types available are generally according to the API670 standard. Three main variants
are straight mount, reverse mount and disc type probes. The main difference between the straight
and reverse mount is the location of the thread on the probe body and the fixing nut. Reverse
mount tend to be used exclusively with probe holders, while straight mount are the more
common and are used on simple bracketry or mounting threads where adjustment to the target is
achieved through use of the thread on the probe body in conjunction with a moveable lock nut.
The maximum measurement range available on this type of probe is typically 8mm.
The disc probe mounts the encapsulated coil on a metal plate with fixed mounting holes, making
a very low profile assembly with a side exit cable. Larger coils can be mounted on this plate; for
example, the 50mm diameter tip probe can provide a measurement range of beyond 25mm.
However, care must be taken to ensure the target area is sufficient to obtain the required linear
response. Note the relationship opposite ± between linear range, probe tip and target area.
Application: In rotating plant, the variations in shaft/bearing distance created by vibration,
eccentricity, ovality etc. are measured by probes mounted radially to the shaft. When the target is
stationary the measured voltage can be used to set the probe/target static distance. Shaft speed
can also be measured by placing the probe viewing a machined slot or a toothed wheel.
8.4.2 LVDT (Linear Variable Differential Transformer)
The LVDT is an electromechanical device that produces an electrical signal whose amplitude is
proportional to the displacement of the transducer core. The LVDT consists of a primary coil and
two secondary coils symmetrically spaced on a cylindrical former.
Schematic of an LVDT
Core displacement characteristics
A magnetic core inside the coil assembly provides a path for the magnetic flux linking the coils.
The electrical circuit is configured as above with the secondary coils in series opposition.
When an alternating voltage is introduced into the primary coil and the core is centrally located,
then an alternating voltage is mutually induced in both secondary coils. The resultant output is
zero, as the voltages are equal in amplitude and in 180º opposition to each other. When the core
is moved away from the null position the voltage in the coil, towards which the core is moved,
increases due to the greater flux linkage and the voltage in the other primary coil decreases due
to the lesser flux linkage. The net result is that a differential voltage is produced across the
secondary tappings, which varies linearly with change in core position. An equal effect is
produced when the core is moved from a null in the other direction but the voltage is 180º
different in phase.
Application: The LVDT can be operated where there is no contact between the core and
extension rod assembly with the main body of the LVDT housing the transformer coils. This
makes it ideal for measurements where friction loading cannot be tolerated but the addition of a
low mass core can. Examples of this are fluid level detection with the core mounted on a float
and creep tests on elastic materials. This frictionless movement also benefits the mechanical life
of the transducer, making the LVDT particularly valuable in applications such as fatigue life
testing of materials or structures.This is a distinct advantage over potentiometers which are prone
to wear and vibration.
The principle of operation of the LVDT, based on mutual inductance between primary and
secondary coils, provides the characteristic of infinite resolution. The limitations lie within the
signal processing circuitry in combination with the background noise.
Commercially available LVDT¶s
8.4.3 The Accelerometer
The accelerometer is based on the electrical properties of piezoelectric crystal. In operation, the
crystal is stressed by the inertia of a mass. The variable force exerted by the mass on the crystal
produces an electrical output proportional to acceleration. Two common methods of constructing
the device to generate a residual force are compression mode and shear mode respectively. A
residual force is of course required to enable the crystal to generate the appropriate response,
moving in either direction on a single axis.
An accelerometer operates below its first natural frequency. The rapid rise in sensitivity
approaching resonance is characteristic of an accelerometer, which is an un-damped singledegree-of-freedom spring mass system. Generally speaking, the sensitivity of an accelerometer
and the ratio between its electrical output and the input acceleration is acceptably constant to
approximately 1/5 to 1/3 of its natural frequency. For this reason, natural frequencies above
30KHz tend to be used.
Typical frequency response of an accelerometer
Although the piezoelectric accelerometer is a self-generating device, its output is at a very high
impedance and is therefore unsuited for direct use with most display, analysis, or monitoring
equipment. Thus, electronics must be utilised to convert the high impedance crystal output to a
low impedance capable of driving such devices. The impedance conversion electronics may be
located within the accelerometer, outside of but near the accelerometer, or in the monitoring or
analysis device itself.
8.4.4 Velocity Transducer
The velocity transducer is inherently different to the accelerometer with a conditioned velocity
output. This device operates on the spring-mass-damper principle, is usually of low natural
frequency and actually operates above its natural frequency. The transducing element is either a
moving coil with a stationary magnet, or a stationary coil with a moving magnet. A voltage is
produced in a conductor when the conductor cuts a magnetic field and the voltage is proportional
to the rate at which the magnetic lines are cut. Thus, a voltage is developed across the coil, which
is proportional to velocity.
8.4.5 Absolute vibration
Absolute vibration monitoring is perhaps the primary method of machine health monitoring on
steam turbines. The type of transducer used is seismic (ie vibration of turbine relative to earth)
and can either be a velocity transducer or an accelerometer.
Vibration monitoring is nearly always in terms of velocity or displacement and can therefore be
obtained by an accelerometer or a velocity transducer. Particular care needs to be taken when
double integrating an accelerometer signal to provide a displacement measurement. Problems
usually occur below 10Hz when double integrating and 5Hz when single integrating. In the
frequency ranges normally monitored on steam turbines this is not a problem. These
measurement issues can be reduced by integrating the signal at source rather than after running
the signal through long cables (ie having picked up noise on route).
Pedestal vibration is measured in the two axes perpendicular to the shaft direction where the
bearing is under load, providing complete measurement coverage. In some instances the thrust
direction is also monitored depending on turbine configuration.
8.4.6 Eccentricity & shaft vibration
Eccentricity monitoring can be subdivided into shaft vibration and bent shaft monitoring. Bent
shafts normally result when the turbine is stationary and thermal arching or bowing of the shaft
occurs or the shaft sags under its own weight. The Turbine is rotated slowly (barring) to prevent
this happening or to straighten the shaft after it has occurred.
One of the difficulties encountered when using shaft displacement transducers be they the eddy
current probe or the older inductive probes, is the problem of ³runout´. Runout is the error signal
generated by mechanical, electrical or metallurgical irregularities of the shaft surface.These error
signals are generally of a low magnitude in comparison to the vibration signal and are often at a
much higher frequency.
8.4.7 Rotor differential expansion & shaft position
The eddy current probe, as well as providing ac vibratory information, also provides dc
information of the probe to target gap. This makes it ideal for measuring rotor to casing
differential expansion via a non-contact method.
Two probes monitoring expansion by observing a tapered collar
8.4.8 Speed - overspeed - zero speed monitoring
The eddy current probe as well as being used for shaft vibration and differential expansion can
also be used as a speed monitoring transducer. The eddy current probe gives a large voltage
output, which is independent of shaft speed.
8.4.9 Casing & cylinder expansion
These techniques require a larger measurement range than can be offered through standard
proximity probe equipment, the necessary probe target is also not easy to achieve. This is where
LVDTs are used to provide the expansion measurements required. A total range of 50mm
usually suffices and the various mounting options available with LVDTs makes installation
straightforward. The movement of the turbine pedestals on the cylinder sole plates is a relatively
easy measurement to make requiring an LVDT mounted on the turbine and the extension rod
fixed or sprung onto the slides. The environment is not hostile although care must be taken to
prevent mechanical damage to the transducer.
LVDT monitoring cylinder casing expansion
8.4.10 Valve position monitoring
The Linear Variable Differential Transformer (LVDT) is ideally suited for valve position
monitoring. In this type of application the LVDT is used to provide positional feedback to the
governor control system to effect a closed loop system. The electrical properties of the LVDT
therefore play a key role in determining the system response. Linearity is obviously key as well
as a robust construction with flexible mounting options. AC type devices (as opposed to DC) are
exclusively used for this type of application, which permit long cable runs and offset adjustment
with gain control.
8.5 Woodward 505 Enhanced Digital Control for Steam Turbines
The 505 Enhanced controller is designed to operate industrial steam turbines of all sizes and
applications. This steam turbine controller includes specifically designed algorithms and logic to
start, stop, control, and protect industrial steam turbines or turbo-expanders, driving generators,
compressors, pumps, or industrial fans. The 505 control¶s unique PID structure makes it ideal for
applications where it is required to control steam plant parameters like turbine speed, turbine
load, turbine inlet or exhaust header pressure, or tie-line power.
The control¶s special PID-to-PID logic allows stable control during normal turbine operation and
bumpless control mode transfers during plant upsets, minimizing process over- or undershoot
conditions. The 505 controller senses turbine speed via passive or active speed probes and
controls the steam turbine through one or two (split-range) actuators connected to the turbine
inlet steam valves. The plant employs one controller for each turbine.
The 505 control is packaged in an industrial hardened enclosure designed to be mounted within a
system control panel located in a plant control room or next to the turbine. The control¶s front
panel serves as both a programming station and operator control panel (OCP). This user-friendly
front panel allows engineers to access and program the unit to the specific plant¶s requirements,
and plant operators to easily start/stop the turbine and enable/disable any control mode. Password
security is used to protect all unit program mode settings. The unit¶s two-line display allows
operators to view actual and setpoint values from the same screen, simplifying turbine operation.
Turbine interface input and output wiring access is located on the controller¶s lower back panel.
Unpluggable terminal blocks allow for easy system installation, troubleshooting, and
Integral Overspeed Protection Logic
First-out Indication (10 individual shutdown inputs)
Bumpless transfer between control modes if a transducer failure is detected
Local/Remote Control priority and selection
Fail-safe Shutdown Logic
The following PIDs are available to perform as process controllers or limiters:
Speed/Load PID (with Dual Dynamics)
Auxiliary PID (limiter or control)
Cascade PID (Header Pressure or Tie-Line Control)
y Power: 18±32 Vdc, 90±150 Vdc, 88±132 Vac (47±63 Hz), 180±264 Vac (47±63 Hz)
y Speed: 2 MPUs (1±30 Vrms) or proximity probes (24 Vdc provided), 0.5 to 15 kHz
y Discrete Inputs: 16 Contact Inputs (4 dedicated, 12 programmable)
y Analog Inputs: 6 Programmable Current Inputs (4±20 mA)
y Valve/Actuator Drivers: 2 Actuator Outputs (4±20 mA or 20±160 mA)
y Discrete Outputs: 8 Relay Outputs (2 dedicated, 6 programmable)
y Analog Outputs: 6 Programmable Current Outputs (4±20 mA)
y Serial: 2 Modbus (ASCII or RTU) Comm Ports (RS-232, RS-422, or RS-485 compatible)
The hotness or coldness of a piece of plastic, wood, metal, or other material depends upon the
molecular activity of the material. Kinetic energy is a measure of the activity of the atoms which
make up the molecules of any material. Therefore, temperature is a measure of the kinetic
energy of the material in question.
1. RTD ( Resistance temperature detector )
- The resistance of an RTD varies directly with temperature:
- As temperature increases, resistance increases.
- As temperature decreases, resistance decreases.
· RTDs are constructed using a fine, pure, metallic, spring-like wire surrounded by an insulator
and enclosed in a metal sheath.
· A change in temperature will cause an RTD to heat or cool, producing aproportional change in
resistance. The change in resistance is measured by a precision device that is calibrated to give
the proper temperature reading.
The RTD used in RPH is Pt-100.
Thermocouples will cause an electric current to flow in the attached circuit when
subjected to changes in temperature.The amount of current that will be produced is dependent
on the temperature difference between the measurement and reference junction; the
characteristics of the two metals used; and the characteristics of the attached circuit.
Heating the measuring junction of the thermocouple produces a voltage which is greater than
the voltage across the reference junction. The difference between the two voltages is
proportional to the difference in temperature and can be measured on the voltmeter (in mill
volts). For ease of operator use, some voltmeters are set up to read out directly in temperature
through use of electronic circuitry.
Only J and K type of thermocouple is used in RPH.
The need for a pressure sensing element that was extremely sensitive to low pressures and
provided power for activating recording and indicating mechanisms resulted in the development
of the metallic bellows pressure sensing element. The metallic bellows is most accurate when
measuring pressures from 0.5 to 75 psig. However, when used in conjunction with a heavy
range spring, some bellows can be used to measure pressures of over 1000 psig.
The bourdon tube consists of a thin-walled tube that is flattened diametrically on opposite sides
to produce a cross-sectional area elliptical in shape, having two long flat sides and two short
round sides. The tube is bent lengthwise into an arc of a circle of 270 to 300 degrees. Pressure
applied to the inside of the tube causes distention of the flat sections and tends to restore its
original round cross-section. This change in cross-section causes the tube to straighten slightly.
Since the tube is permanently fastened at one end, the tip of the tube traces a curve that is the
result of the change in angular position with respect to the center. Within limits, the movement of
the tip of the tube can then be used to position a pointer or to develop an equivalent electrical
signal to indicate value of the applied internal pressure.
The operation of the ball float is simple. The ball floats on top of the liquid in the tank. If the
liquid level changes, the float will follow and change the position of the pointer attached to the
Pressure head method
The differential pressure (_P) detector method of liquid level measurement uses a _P detector
connected to the bottom of the tank being monitored. The higher pressure, caused by the fluid
in the tank, is compared to a lower reference pressure (usually atmospheric). This comparison
takes place in the _P detector. Figure illustrates a typical differential pressure detector attached
to an open tank.
Differential Flow Transmitter
· Flat plates 1/16 to 1/4 in. thick
· Mounted between a pair of flanges
· Installed in a straight run of smooth pipe to avoid disturbance of flow patterns
due to fittings and valves.
· Converging conical inlet, a cylindrical throat, and a diverging recovery cone
· No projections into the fluid, no sharp corners, and no sudden changes in
Dall flow tube
· Consists of a short, straight inlet section followed by an abrupt decrease in the
inside diameter of the tube
· Inlet shoulder followed by the converging inlet cone and a diverging exit cone
· Two cones separated by a slot or gap between the two cones.
Electromagnetic flow meter
The electromagnetic flow meter is similar in principle to the generator. The rotor of the
generator is replaced by a pipe placed between the poles of a magnet so that the flow of
the fluid in the pipe is normal to the magnetic field. As the fluid flows through this
magnetic field, an electromotive force is induced in it that will be mutually normal
(perpendicular) to both the magnetic field and the motion of the fluid. This electromotive
force may be measured with the aid of electrodes attached to the pipe and connected to a
galvanometer or an equivalent. For a given magnetic field, the induced voltage will be
proportional to the average velocity of the fluid. However, the fluid should have some
degree of electrical conductivity.
Ratio control is used to ensure that two flows are kept at the same ratio even if the flows are
changing. E.g. Air-Fuel Ratio where the proper ratio between air and fuel i.e. pulverized coal
has to be maintained.
Controller feed is adjusted according to the ratio of wild feed. The implementation is
utomation of Processes
The main purpose of automation is to minimize human intervention to reduce the errors. Large
processes like power plant has large scope for errors.
The automation of industrial processes is carried by PLCs and SCADA.
The above figure shows the hierarchy setup of industrial automation.
The field devices are connected to the PLC and all the PLCs are connected to the SCADA
server based in control room.
The SCADA server is connected via LAN to ERP (Enterprise Resource Planning) and the data
can be accessed from any where on internet.
PLC (Programmable Logic Controller)
Digital electronic device that uses a programmable memory to store instructions and to
implement specific functions such as logic , sequencing , timing etc to control machine and
Cost effective for controlling complex systems.
Flexible and can be reapplied to control other systems quickly and easily.
Computational abilities allow more sophisticated control.
Trouble shooting aids make programming easier and reduce downtime.
Reliable components make these likely to operate for years before failure.
Many PLC configurations are available, even from a single vendor. But, in each of these there
are common components and concepts. The most essential components are:
Power Supply ±
This can be built into the PLC or be an external unit.
Common voltage levels required by the PLC (with and without the power
supply) are 24Vdc, 120Vac, 220Vac.
CPU (Central Processing Unit) ±
This is a computer where ladder logic is stored and processed.
I/O (Input/Output) ±
A number of input/output terminals must be
provided so that the PLC can monitor the process and initiate actions.
Indicator lights ±
These indicate the status of the PLC including power on, program running, and a fault. These
are essential when diagnosing problems.
The configuration of the PLC refers to the packaging of the components.
Rack - A rack is often large (up to 18´ by 30´ by 10´) and can hold multiple cards.
When necessary, multiple racks can be connected together. These tend to
be the highest cost, but also the most flexible and easy to maintain.
INPUTS AND OUTPUTS
Inputs to, and outputs from, a PLC are necessary to monitor and control a process. Both inputs
and outputs can be categorized into two basic types:
logical or continuous.
Consider the example of a light bulb. If it can only be turned on or off, it is logical control. If the
light can be dimmed to different levels, it is continuous. Continuous values seem more intuitive,
but logical values are preferred because they allow more certainty, and simplify control. As a
result most controls applications (and PLCs) use logical inputs and outputs for most
applications. Hence, we will discuss logical I/O and leave continuous I/O for later. Outputs to
actuators allow a PLC to cause something to happen in a process. A short list of popular
actuators is given below in order of relative popularity.
· Solenoid Valves - logical outputs that can switch a hydraulic or pneumatic flow.
· Lights - logical outputs that can often be powered directly from PLC output boards.
· Motor Starters - motors often draw a large amount of current when started, so they require
motor starters, which are basically large relays.
· Servo Motors - a continuous output from the PLC can command a variable speed or position.
Outputs from PLCs are often relays, but they can also be solid state electronics such as
transistors for DC outputs or Triacs for AC outputs. Continuous outputs require special output
cards with digital to analog converters. Inputs come from sensors that translate physical
phenomena into electrical signals. Typical examples of sensors are listed below in relative order
· Proximity Switches - use inductance, capacitance or light to detect an object logically.
· Switches - mechanical mechanisms will open or close electrical contacts for a logical signal.
· Potentiometer - measures angular positions continuously, using resistance.
· LVDT (linear variable differential transformer) - measures linear Displacement
Step 1-CHECK INPUT STATUS-First the PLC takes a look at each input to determine if it is on
or off. In other words, is the sensor connected to the first input on? How about the second
input? How about the third... It records this data into its memory to be used during the next step.
Step 2-EXECUTE PROGRAM-Next the PLC executes your program one instruction at a time.
Maybe your program said that if the first input was on then it should turn on the first output.
Since it already knows which inputs are on/off from the previous step it will be able to decide
whether the first output should be turned on based on the state of the first input. It will store the
execution results for use later during the next step.
Step 3-UPDATE OUTPUT STATUS-Finally the PLC updates the status of the outputs. It
updates the outputs based on which inputs were on during the first step and the results of
executing your program during the second step. Based on the example in step 2 it would now
turn on the first output because the first input was on and your program said to turn on the first
output when this condition is true.
A motor will be controlled by two switches. The Go switch will start the
motor and the Stop switch will stop it. If the Stop switch was used to stop
the motor, the Go switch must be thrown twice to start the motor. When
the motor is active a light should be turned on. The Stop switch will be
wired as normally closed.
3. Boiler steam pressure:
1.62 (MU) max.
67.5 (MU) max.
4. Boiler steam temperature:
6. Unburnt carbon in fly ash:
7. Unburnt carbon in bottom ash:
8. Feed water temperature after HPH:
9. Steam temp. at throttle valve before ESV:
10. Steam pressure ESV (kg/cm2):
12. Exhaust hood temp.:
13. Circulating water rise of temp.:
14. Fuel oil pressure (LSHS):
15. Generator stator temp.:
16. Steam flow before ESV:
17. Steam consumption per MW:
18. Turbine heat rate:
19. DM water conductivity:
20. DM water silica:
21. Clarifier water outlet turbidity:
22. Feed water conductivity:
23. Feed water silica:
24. Boiler water conductivity:
25. Boiler water silica:
26. Moisture in turbine oil (at filter point):
27. Auxiliary consumption:
28. Make-up water consumption:
29. Clarifier water inlet conductivity:
540 deg C
< 1.0 %
< 3.5 %
236.85 deg C
535 deg C
44.25 deg C
8 deg C
100 deg C
< 1.0 mho/cm
< 20 ppb
6 m mho/cm
< 1 ppm
11.2 % per day (both units)
624 kl/day (both units)
600-1700 m mho/cm
Details of Fans and Pumps used in the plant
Radial Double Suc.
Radial Double Suc.
Radial Double Suc.
Radial Single Suc.
Squirrel cage I.M.
Squirrel cage I.M.
Squirrel cage I.M.
Squirrel cage I.M.
Squirrel cage I.M.
Squirrel cage I.M.
Actual heat consumption:
44.25 deg C
Rotor S.C. ratio:
Type of Cooling:
673.5 MW/ 84.375 MVA
10.5 KV, 4639 A
303 V (max.), 601 A
CONCLUSION:During our visit to power plant station from June 07,2010 to July 24,2010.
The modernization of world as we see today would not become possible
if electrical power do not come into picture. Today each area of Science &
technology is highly affected by the use of electrical energy. Electrical energy is
the only reliable form of Energy which is easily converted into any form of energy
whether it is Mechanical, Chemical, Light, and Sound etc.
The electrical energy has been used not only in industrial areas but also
in residential and commercial application as well. The reason behind the popularity
of this form of energy is because it can be easily transferred to one place to another
So at the outset I would like to conclude that there is no doubt without
the development of this form of energy, we would never achieved the faster pace
of growth rate as today the world is growing and this has become possible only due
to the development of power system.