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CONTENT

DCSPLCGenerators

TurbinesBolier and its auxiliariesCHP & AHPPlant water systemsSCADA

CCTV

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Distributed Control System

Several processors operate together Different tasks are dedicated to differentmachines

The plant's information and control systems aredetermined based on requirements of mechanical and electrical engineeringControl system functions: Acquisition & Processing of process data.

Open loop and closed loop control. Open loop system is a non feedback type system relying

only on the current and the model of the system

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ConfigurationCentral Cabinet house theprocessors that execute thecontrol functions.These cubicles also containthe attendant interface and

input/output (I/O) cards andthe necessary power supplyunits (PSUs). The latter will usually beduplicated or triplicated, withautomatic changeover fromone to another in the event of the first failing.

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This automatic changeover is often referred to asdiode auctioneering because silicon diodes areused to feed power from each unit onto a commonbus-main

In the event of the operational power-supply unitfailing, its diode prevents a power reversal while theback-up power unit takes over.They may also allow limited control to be performed,but all this will function for only a short period(typically 30 min) and it is therefore usual to providean external uninterruptable power supply (UPS)system which can allow the plant to be operated for alonger time

Instead, it is common to provide a battery capacitythat will allow the plant to be safely shut down in the

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Operator WorkstationsThe operator workstations consist of screens on which plantinformation can be observed, plus keyboards, trackballs or 'mouse' devices allowing the operator to send commands tothe system

Also comprise printers for operational records, logging of

eventsScreen update time: This is the time between the occurrenceof an event and its appearance on the screen. As systemloading is increased, this time can become extended

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Operator Work Station

Alarm MonitoringMimic/graphic displayTrend DisplayOperator guidance displaySystem and diagnosticdisplayControlBar chart

Sequence display

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DCS Components

The typical DCS system shown in above figure canconsists of one or more of the following elements:

Local Control Unit (LCU) Data Acquisition Unit Batch Sequencing Unit Local Display Bulk Memory Unit General Purpose Computer Central Operator Display

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Programmable LogicController A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical

processesthe PLC is designed for multiple inputs andoutput arrangements, extended temperatureranges, immunity to electrical noise, andresistance to vibration and impactDigital or discrete signals behave as binaryswitches, yielding simply an On or Off signal

Analog signals are like volume controls, with a

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enera or o ageRegulation

To maintain the output voltage of a generator at adesired value

As load on an AC generator changes, the voltagewill also tend to change.

The main reason for this change in voltage is the changein the voltage drop across the armature winding causedby a change in load current

Because of changes in voltage, due to changes inload and changes in power factor, AC generatorsrequire some auxiliary means of regulating outputvoltage

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Generator Protection Circuitry and Relaying

Protective relays are designed to cause the promptremoval of any part of a power system that mightcause damage or interfere with the effective andcontinuous operation of the rest of the system.

The relays can be designed to protect generatingequipment and electrical circuits from anyundesirable condition, such as under voltage, under frequency, or interlocking system lineups.

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There are only two operating principles for protective relays:

electromagnetic attraction andelectromagnetic induction.

Electromagnetic attraction relays operate by aplunger being drawn up into a solenoid or anarmature that is attracted to the poles of anelectromagnet. This type of relay can be actuatedby either DC or AC systems.

Electromagnetic induction relays operate on theinduction motor principle whereby torque isdeveloped by induction in a rotor. This type of relay can be used only in AC circuits .

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Need for C&I of turbines

Modern control platforms provide better control of the steamturbine, the flexibility to meet the demands of the market can beobtained.

The control system design is critical to optimize availability andreliability while minimizing impact on maintenance and capitalbudgets.

Recent developments in digital processing faster processingspeeds, lower cost, and smaller sizes

Maintenance of old systems required a certain degree of familiarity and knowledge of the instrumentation of its era

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Turbine control system (TCS)

TCS is designed to control the main steam flow to the steamturbine in all operational conditions by means of the turbinethrottle, governor, admission, and or extraction control valves.

The control functions are conducted through the use of simplexor redundant electronic functions incorporated within the TCSsoftware and hardware

Master controllers automatically engage when required toensure the appropriate rates of change match the mode of operation of the turbine.

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The principle features of the TCSsystem

Speed Control Inlet/Admission Pressure Control

Load Control

Turbine Stress Influence Frequency Influence

ADS (Automatic Dispatch System) Influence

Valve Lift Control

Other functions

The TCS system ensures stable operation throughout allo erational hases, i.e. durin unit start u , shutdown, arallel

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The TCS should provide automatic and manualshutdown.

In automatic shutdown, the system must lower theload until the generator breaker opens on reversecurrent.

On manual shutdown, the operator will open thegenerator breaker manually once the turbine is atminimum load.

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Inlet/Admission PressureController

The inlet/admission pressure control provides twochannel selection which facilitates initial pressure(boiler follow mode) and limit pressure (turbinefollow mode) functions.

This automatic control function is activated whenthe inlet-steam pressure drops to a pre-determinedconfigurable set point.

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Load Control

Once the turbine is on the grid, the TCS can either be transferredautomatically or manually into the load control mode of operation.

The load control function produces steam flow demand signals via theposition controller of the associated servo valve actuators.

Logic signals derived from the units load control system (ULCS)indicate operating conditions, such as power load imbalance.

Standard turbine runback features designed within the system are

Loss of boiler feed water pump

Loss of condenser vacuum

Loss of primary coolant/pump (generator H2 coolant circulatingwater pump

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Turbine Stress Influence

Limiting the acceleration and load ramp gradients

This value would limit the acceleration and or deceleration limit applied to the turbine via themaster controllers

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Frequency Influence

When the generator is on the grid and the turbine controller is in the load control mode, the speed control functioncontinues to provide a speed error (influence) input for usein frequency regulation.

Comparing the speed reference with the actual speedderives the speed error signal.

The frequency detection accuracy is within 10 MHz, withtunable variables controlling dead band and droopcharacteristics.

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ADS (Automatic Dispatch System)Influence

The TCS system is designed to accept influencingfrom an ADS controller, facilitating the remotedispatch loading and unloading of the machinealong predetermined ramp gradients.

The load limit gradients are configurable throughthe entire range of operation

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Valve Lift Control

The valve lift controller integrates the min-gatedvalve demand reference versus valve actual(setpoint) functions.

Rates of greater than 20 samples per cyclic eventthroughout the stroke of the valve to achieve thefastest possible response time.

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Field Device Parameter SensingAssemblies

The following items are installed in place of the tripblock assembly and provide inputs to the TPS.

Vacuum Pressure

Bearing Lube Oil Pressure.Turbine Thrust Pressure Sensing.

Turbine Trip Solenoids.

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Electrical Auxiliaries

Vibration monitoring equipment should be added or upgraded to monitor the health of the rotor and associatedbearings.

Adding more sensors to monitor bearing lube oil and metaltemperatures, valve metal temperatures, steam chesttemperatures and any other temperatures as applicableshould enhance temperature monitoring.

These indications should be added to the TCS graphics.

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Instrumentation and controls in a boiler plant encompass an enormousrange of equipment from simple in the small industrial plant to the

complex in the large utility station.It consists of several control loops to control various systems related toa boiler.

The main control of boilers include combination control and feed-water control.

Virtually any boiler-old or new, industrial or utility can benefit from or several control system modifications available today either byintroducing advanced control schemes adding to existing controlschemes

The boiler control system is the means by which the balance of energy& mass into and out of the boiler are achieved.

Inputs are fuel, combustion air, atomizing air or steam &feed water.

Of these, fuel is the major energy input.

Combustion air is the major mass input, outputs are steam, flue gas,-

Boiler and its Auxiliaries

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Boiler control systems contain several variable

with interaction occurring among the control loopsfor fuel, combustion air, & feed-water .The overall system generally can be treated as a

series of basic control loops connected together.for safety purposes, fuel addition should be limitedby the amount of combustion air and it may needminimum limiting for flame stability.

Combustion controls

Amounts of fuel and air must be carefully

CONTROL LOOPS

l k i

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The output from the boiler i.e., thesteam outputs and the level of water is given to transmitters.

The output of transmitter is given tothe controller which act as levelindicator controller and flowindicator controller.If there is any error corresponding

to desired set point, the signal from

Block Diagram

BOILER DRUM TRANSMITTER CONTROLLER CONVERTER VALVE

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A combustion control system is broken down into

(a) Fuel control(b) Combustion air control subsystems.

The interrelationship between these two subsystems necessitatethe use of fuel air ration controls.

The primary boiler fuels are coal, oil and gas.The control of gas and oil fuels requires simplest controls- i.e., a

control valve in the fuel line.The steam drum pressure is an indication of balance between theinflow and outflow of heat. Therefore by controlling the steam supplyone can establish balance between the demand for steam (processload ) and supply of water.

COMBUSTION CONTROL

DIFFERENT TYPES OF COMBUSTION

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There are three general types of combustion control schemes used today:

Series,In series control, variations in steam header pressure(the master controlsignal) cause a change in combustion air flow which in turn results in asequential change in fuel flow. This type of control is limited to smallboilers having relatively constant steam load & burning fuel.

Parallel

In parallel control, variation in steam pressure simultaneously adjustsboth fuel & air flows. This method is common to any size boilers.

Series-parallel

In series-parallel, variation in steam pressure set points are used toadjust the fuel. Flow to the above boiler since steam flow is directlyrelated to heat release of the fuel and hence the air flow, the steam flowcan be used as an index of the required combustion air .

DIFFERENT TYPES OF COMBUSTIONCONTROLS

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The control hardware used to carryout the above schemes include:

ON/OFF controls:

Are still used in many industries but are generally used in small water tubeboilers. When the pressure drops to a present value, fuel & air are automaticallyfed into the boiler at predetermined rate until pressure has risen to its upper limit.

Positioning systems:

Respond to changes in header pressure by simultaneously positioning the forceddraft damper and fuel valve to a predetermined alignment. This is not used inliquid , gaseous fuel fired boilers.

Metering control system:

In this system control is regulated in accordance with the measured fuel and air

flows. This maintains combustion efficiency over a wide load ranges & over longperiod of time.

Both metering & positioning control systems use steam header pressure as their primarymeasured variable & as a basis for firing rate demand. A master pressure controller responds to changes on header pressure & positions the dampers to control air flow andfuel valve to regulate fuel supply

CONTROL

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Feed-water control is the regulation of water

to the boiler drum. It provide a massaccounting system for steam leading andfeed-water entering the boiler.

Proper boiler operation requires that the levelof water in the steam drum should bemaintained within certain band.

It is important to made that the water level inthe boiler drum must be above 50% all thetime.

The water level in the boiler drum is relatedto, but is not a direct indicator of , the quantityof water in the drum. At each boiler load,there is different volume in the water that isoccupied by steam bubbles. So if load isincreased there are more steam bubbles andthis cause water to rise, rather than fallbecause of added water usage

FEED-WATER CONTROL

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Control system complexity is based on number of measured variables usedto initiate control action and include single element ,two element,3 elementand advanced control schemes to improve accuracy of final control action.

SINGLE ELEMENT CONTROL SYSTEMS

Used for small boilers having relatively high storage volumes and slowchanging loads ,single element control system is used

Controls feed water flow based on drum level.

Response is very slow

TWO ELEMENT CONTROL SYSTEMSUses steam flow changes as a feed forward signal

Used in intermediate boilers as well as large boilers

Flow and level transmitters are summed by a computing relay and will bethe set point for feed-water

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Required for wide and rapid loadchangesSimilar to two element except for theclosed water flow loop

Control action, the third elementbased on feed-water flow.The level and steam flow signals aresummed and used as an index or setpoint to the feed-water flow.

The feed-water flow measurementprovides corrective action for variation in feed-water pressure.

Three Element Control

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Additional elements can be added to a feed-water control systemto improve response accuracy

Five Element Control

Steam flow measurement is temperature compensated

Drum level measurement is pressure compensated

Five Element ControlTransmitters for blow down flow

Soot-blower flow could be added

Advanced Element Controls

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ADVANTAGES

Multiple element feed-water control can help:

Faster response of systems.

More accurate control.

Maximum system stability.

Metering control system maintains combustion efficiency over wide.

load changes and over long period of time.Parallel combustion control can be used in any size of boilers

DISADVANTAGES

Boilers require quick responding controls.

Level of the water in the boiler must be kept above 50% of height.

CONTROL OF COAL HANDLING

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CONTROL OF COAL HANDLINGPLANT

Control & instrumentation through microprocessor based PLCsystem for the entire Coal handling plant

It should cover the total functional requirement of sequencecontrol, interlock and protection, monitoring, alarm , datalogging etc.

Design of the control system shall adhere to the principleof Fail safe operation of all system levels

The system shall provide an integrated control & monitoringof coal handling plant equipment from a Main CHP ControlRoom.

The control Room operator shall be provided with color graphic displays of the Coal handling plant and with sufficientdetails to allow proper control and monitoring of the plantfunction.

The entire Coal handling plant ill be controlled from the follo ing

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The entire Coal handling plant will be controlled from the followingcontrol points

The overall operation and control of the entire Coal Handling Plant,with a control desk and suitable control panel will be provided at theMain CHP Control Room .The traveling Tippler and its associated drives shall be controlled fromlocal panel located near the bunker floor MCC roomSimilarly Coal unloading operation for wagon rakes near track hopper area shall be controlled from control panel located in the control roomwith in building near track hopper.

Stacker reclaimer shall be provided with PLC system.Following Equipment will come under sequential interlock scheme andcan be started / stopped from control desk in the main CHP control room:

All belt conveyors.

Vibrating feeders.ScreensCrushersFlap Gates.

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Following equipment will not generally come under interlockscheme and can be started / stopped / controlled from its local

Belt Weigher Bunker Level Indicator Paddle Feeder Stacker/Reclaimer

Coal Sampling System Mobile Tippler Magnetic Separator in line Ventilation system Dust extraction System Dust suppression System Vibration monitoring system( for coal crushers)

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Following equipment will be operated from its local panelswithout any indication in control desk

Electric Hoist.

Sump pump Suspended magnets

All equipment systems and accessories supplied shall be fromthe latest proven product range of a manufacturer

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HANDLING SYSTEM The control & instrumentation shall be through microprocessor based

PLC system for the entire Ash handling plant covering the totalfunctional requirement of sequence control, interlock & protection,monitoring, alarm data logging etc.

The entire Ash Handling plant will be controlled from the followingcontrol points:

For overall operation and control of entire Ash Handling Plant withfly ash system, bottom ash system, ash water and slurry pumpingsystem and ash disposal system, a control desk along with controlpanels mimic will be provided at the Main AHP Control Room.

System cabinet associated with local controls shall be located near the local control panels.

Suitable alarm system will be provided to warn any mal-functioning of ash handling system

Following Equipment will come under interlock scheme and can be started/stopped

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from control desk with indication on CRT and mimic panel with fault correction facility:

All Pumps/Blowers and Compressors .

Bottom Ash system.

Fly ash system, comprising of ash extraction from ESPs & duct hopper to buffer hopper located near ESPs and fly ash transportation system from buffer hopper to storage silos.

Ash slurry disposal system.

Bottom ash over flow system comprising of bottom ash over flow water storagetanks, settling tank, ash over flow water pumps, sludge pumps etc.

Silo system.

All Motorized valves

All pneumatic operated valves.

For local operation in the Bottom Ash area one Bottom ash control panel/cubical isprovided for each unit .this panel shall provide control for clinker grinders, bottomash discharge valves, jet pumps for ash slurry transport etc.

A control panel/cubicle shall also be provided in MCC room near silo area for flyash collection system. The panel shall provide control for dry pneumatic ashextraction transportation and unloading system.

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Plant Water system

C&I shall be through microprocessor based PLC system for the entire Plant water system covering the total functionalrequirement of sequence control, interlock & protection,monitoring, alarm data logging.

Overall operation and control of entire Plant water system i.e.raw water system, Chlorination plant for raw water system andDM plant system, a control desk along with control panelsmimic will be provided at the DM plant Control Room.

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The following local control panels are envisaged which

are located near their associated systemRaw water system local control panel

Chlorination plant local control panel for raw water treatmentand CW water treatment

Chlorination plant local control panel for potable water system.CW treatment plant local control panel

Transfer of acid/Alkali local control panel for DM plant

Any other control recommended by contractor

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SCADA SystemSupervisory control and data acquisition systems (SCADA) are widelyused in industry for supervisory control and data acquisition of industrial processes.

The SCADA system usually consists of the following subsystems:

A Man-Machine Interface (MMI) is the apparatus which presentsprocess data to a human operator, and through this, the humanoperator, monitors and controls the process.

A supervisory system, acquiring data on the process and sendingcommands to the process.

Remote Terminal Units (RTUs) connecting to sensors in theprocess, converting sensor signals to digital data and sending digitaldata to the supervisory system.

Communication infrastructure connecting the supervisory system tothe RTUs.

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In fact, most control actions are performed automatically by RTU or byprogrammable logic controllers (PLC). Host control functions are

usually restricted to basic overriding or supervisory level intervention.Example: a PLC may control the flow of cooling water through part of an industrial process, but the SCADA system may allow operators tochange the set points for the flow, and enable alarm conditions, suchas loss of flow and high temperature, to be displayed and recorded.The feedback control loop passes through the RTU or PLC, while theSCADA system monitors the overall performance of the loop

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Components of SCADA system:Field data interface devices

Communication networks

Central host computers

O erator station and software com onents

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Field Data Interface Devices:

Form the "eyes and ears" of a SCADA system

Devices such as reservoir level meters, water flow meters, valve positiontransmitters, temperature transmitters, power consumption meters, andressure meters all provide information that can tell an experienced operator how well a water distribution system is performing. In addition, equipmentsuch as electric valve actuators, motor control switchboards, and electronicchemical dosing facilities can be used to form the "hands" of the SCADAsystem and assist in automating the process of distributing water.

Information from data interface devices must be converted to a form that iscompatible with the language of the SCADA system

So electronic field data interface is required and RTUs (Remote TelemetryUnits) provide this interface

They are primarily used to convert electronic signals received from fieldinterface devices into the language (known as the communication protocol)used to transmit the data over a communication channel.

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Communications Network

Provide the means by which data can be transferred between the central

host computer servers and the field-based RTUsThe Communication Network refers to the equipment needed to transfer data to and from different sites. The medium used can either be cable,telephone or radio.

The use of telephone lines (leased or dial-up) is a more economical solutionfor systems with large coverage.

Remote sites are usually not accessible by telephone lines. The use of radio offers an economical solution. Radio modems are used to connect theremote sites to the host.

Central Host Computer

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Central Host Computer

Most often a single computer or a network of computer servers that provide

a man-machine operator interface to the SCADA system.It processes the information received from and sent to the RTU sites andpresent it to human operators in a form that the operators can work with.

Operator terminals are connected to the central host computer by aLAN/WAN so that the viewing screens and associated data can bedisplayed for the operators

Recent SCADA systems are able to offer high resolution computer graphicsto display a graphical user interface

With the increased use of the personal computer, computer networking has

become commonplace in the office and as a result, SCADA systems arenow available that can network with office-based personal computers

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Operator Workstations and Software Components

Operator workstations are most often computer terminals

that are networked with the SCADA central host computer The central host computer acts as a server for the SCADAapplication, and the operator terminals are clients thatrequest and send information to the central host computer based on the request and action of the operators.The most obvious software component is the operator interface or Man Machine Interface/Human MachineInterface (MMI/HMI) package

Depending on the size and nature of the SCADAapplication, software can be a significant cost item whendeveloping, maintaining, and expanding a SCADA system

When software is well defined, designed, written, checked,

CCTV

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CCTVCCTV equipment can provide instant alerts when problematic troubleoccurs ensuring crime against people, theft and vandalism are allsubstantially reduced and covered

These systems can facilitate round-the-clock monitoring of the power plant

CCTV system security technology can be used in both internal and externalenvironment to watch over and protect people, property vehicles andvaluables

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Energy Storage systems in thermal power plants

An electrical battery is a combination of one or more electrochemicalcells, used to convert stored chemical energy into electrical energy

The prime function of the Battery Energy Storage System (BESS) is toprovide spinning reserve in the event of power plant or transmissionline equipment failure. For these systems rechargeable batteries areused to store electricity in the form of chemical energy.

These systems can take energy from the grid when either thefrequency or voltage is too high and return that energy to the gridwhen the frequency or voltage begins to sag.

Much like a hybrid electric vehicle incorporates a battery componentto improve efficiency; combining battery storage with a traditionalpower plant allows the plant to more effectively use its own generatedpower while continuing to provide essential spinning reserve

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Referencehttp://specinstrumentationbop.wordpress.com/2008/10/30/154control-philosphy/

http://www.avantgarde-india.com/techpapers/Essential%20Boiler %20Instrumentation%20and%20Controls.pdf

http://provecta.com.au/liddell-coal-handling-plant-systems-controls-and-instrumentation-upgrade/

http://www05.abb.com/global/scot/scot244.nsf/veritydisplay/18ef94c51a2548d1c1257958002ef13e/$file/abb_optimized_coal_handling_article.pdf

www.wikipedia.com

http://www.heinzmann.com/heinzmannuk/steamturbines.php?getfile=Steam_Turbine_Controls_e.pdf