c&i_report for vts

7/27/2019 C&I_report for VTS

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C&I system at NTPC KAHALGAON

The control & instrumentation package of Kahalgaon project (4x210 MW) is

supplied by Russian with the Main package by M/s. TPE, USSR. In addition to the

original Russian supplied system there are Furnace Safeguard Supervisory System

(Make Forney, USA), Data Acquisition System (Make Westinghouse, USA), SteamWater Analysis System & uninterrupted Power Supply system (supplied by Keltron).

The C&I package can be broadly classified into the following categories.

1. Process Measurements

2. Process Protections

3. Interlock & Protections of Boiler and Turbine auxiliaries

4. Selective Control System & Short Sequence System

5. Auto Control system

6. Annunciation system.

7. Furnace safeguard supervisory system8. Data acquisition system

9. SWAS and its auxiliaries

1. PROCESS MEASUREMENT

The process parameter measurement is realized by means of Transmitters,

Thermocouples, RTDs and other primary instruments. The signals received from these

primary instruments are utilized for Control /Record /Indication of the process

parameter and protection of the process. In the process where mass monitoring is

required like Boiler metal temperatures, Turbine metal temperatures, Turbine bearing

temperatures and Generator slot temperatures in these cases either multipoint recorders

or indicators with a manual switch for point selection is provided. For remote

indications of level, pressure and flow, transmitters are providing. Explosion proof

Transmitters are provided for explosion prone areas like Fuel oil pump house and

Hydrogen plant. All transmitters are of strain gauge type, which gives an output of 4

20mA when the pressure across the diaphragm varies from minimum range to

maximum range.

For some process parameters the signal for DAS & Measurement is sharedfrom a single transmitter. This sharing is done through Zener diode isolation circuit.

Generally for Auto Control System dedicated transmitters are provided with 100%

redundancy.All the secondary instruments are powered from UPS including Recorders,

Indicators, TSI equipment & all process variation measuring transmitters.

Unit Control Board (UCB) is distinctly divided into two parts. One is operative

area which contain Desk panels, Annunciation panels, Recorder & Indicator panels,

Transmitter power supply panels & Mimic panels .The other is the Non- operative area

consisting of Interlock and Protection panels, Auto Control panels, Selective and Short

sequence panels, RC feeder & FSSS panels.


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There is facility to control the operation of all drives, valves & dampers from

operator desk panel. Status of the same is indicated through mimic just above the

operating panel. In the operator desk

The recorders & indicators are of three different types depending upon the

inputs i.e. milliampere, potentimetric and bridge type. These are utilised formeasurement of transmitter signal, thermocouple signal and resistance thermal detector

signal receptively.

For the measurement of excess Oxygen in flue gas, an insitu zirconia probe

(Make Westinghouse, supplied by I.L.Kota) is installed at 41 meter in second pass of

Boiler. The output of the probe is mv, which is converted to mA through converter. The

cell constant and cell slope is adjustable. Auto calibration facility is also available.

In Air preheater system, which is of tubular type, differential temperature of air & gas

is measured in a recorder. This gives annunciation when it crosses the alarm value. In

case of fire the differential temperature increases and when it crosses a pre-set value

alarm is obtained at UCB. For cleaning these tubular type

For Drum level protection as per the original design, level switches are provided at

different levels. However presently protection of drum level is of two out of three logic

rooted through Hydrastep (Keyston Make) both left and right side and the pressure

compensated signal from drum level compensation package (supplied by M/s Bells

control). Bearing temperature, winding temperature PA Fans & Mills are shared by

DAS and measurement from dual RTD. Coal pipe temperatures of furnace inlet are

exclusively provided in DAS only.

There are many important parameters, which are measured locally through

pressure gauges & switches. In Boiler Feed Pumps the bearing temperature recorders &

winding temperature indicators are located at local which helps the operator for easy

monitoring of the temp regularly.

For safe operation of Turbine the following Turbo Supervisory measurements

are carried out in continuous basis. .

1. Axial shift.

2. HPC / IPC differential expansion.

3. Eccentricity

4. HPC/IPC thermal expansion

5. Turbine speed measurement6. Turbine vibration of Bearing 1 to 7.

7. Seal Noise device for Bearing 1 to 7.

8. Control valve servo meter position measurement.

Axial Shift, HPC / IPC/ LPC differential expansion measurement are realised by a

instrument based on the principle of Linear voltage differential transducer principle.

Axial shift pick up is fixed near brg-2 i.e. the pivot point of the turbine rotor.

For Turbine speed measurement a permanent magnet pick up is mounted above a

wheel of 60 teeth attached to turbine shaft located at MOP. This pick up is having a coil

which is induces an A.C current which is processed by a pre amplifier to get a squarepulse. This square pulse is finally counted by the counter located in NOP area which


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gives three Analogue & three digital output used for local / UCB analogue / digital

measurement.

For Turbine vibration measurement in each bearing there are two pick-ups. One is

for vertical vibration & other one for axial & cross sectional vibration. Vibration signal

is measured by piezoelectric crystal, which induces a millivoltage as per the vibration,which is subsequently amplified by preamplifier at local. At UCB the signal is

processed & integrated to get velocity measurement output in the range of 0 12

mm/sec or 0 30mm/sec. The signal is converted into analogue output of 0 5 mA

who is shared DAS & measurement. In each pick up there is a facility of on line

checking of healthiness by injection of A.C voltage another piezoelectric crystal placed

near to the measuring crystal. There is a provision of two-alarm contact for alarm &

warning setting for the measurement of each vibration.

In offsite areas including Fly Ash, Bottom Ash, FOPH, UPH, H 2 & chlorine plant,

for easy monitoring and operation of the equipment in addition to local Pressure gauge,

pressure switch, Recorders and instruments indication the temperature & current etc.are also provided near the equipment itself. The ON/OFF status of the major offsite

drives are available in UCB # 1. In case of emergency i.e. when any local annunciation

is generated a parallel contact goes to UCB and control board faulty annunciation

appears. This helps the UCB personnel to maintain & monitor the offsite area.

In Fuel Oil Pump House their three receiving tanks, each consisting of two oil

transfer pumps. There are four oil storage tanks in which level and temperature are

measured. There are two sets of lift pumps. Each set consists of two stages. Suction and

discharge pressure is measured through local gauges. Fuel oil flow to boiler and return

oil flow from boiler is measured through transmitters.

There are two BottomAsh a pump house. Each Bottom Ash pump house consists of

three sets of pumps. In each set there are two pumps connected in series. This

arrangement is done to give more discharge Pressure to the slurry. In each pump

Bearing temperature is measured & dedicated recorders are provided in local panel.

Pneumatic valves are provided in the discharge of the pumps. Gland sealing is required

for each stage of pump. In Air Compressor house, there are four compressors common

to all four units. The Compressor has got two independent motors winding for two

independent speeds (Low speed and High speed). For each stage air temperature before

cooler is measured and independent tripping is initiated when it rises beyond the

alarmed value. Compressor trips when lubrication oil pressure falls below the set limitand cooling water flow is absent.

2. PROCESS PROTECTION

Protection intended to prevent the damage of the equipment under the alarm

conditions can be broadly divided into the following categories.

1. Unit protection.

2. Turbine protection

3. BFP protection

4. Boiler trip protection5. Boiler load drop protection


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6. QPRDS protection

7. Turbine local protection (HPH,LPH,D/A)

4. AUTO CONTROL SYSTEM

The Auto Control system is intended to maintain process variables within a

predetermined range and to ensure the reception of process data. The system produces

control instructions & actions which helps in achieving the predetermined state.

The system is based on a split architecture. Controllers comprises of two separate

units i.e regulating unit and operative unit.

The Controllers actions are processed through different blocks which are used

for different purposes .Some of the important blocks are mentioned below.

1.Signal input block.2.Signal converter block,

3.Integration block

4.Summator block

5.Pulse output block

6.Annunciation block

The input to the system is of 4 20 mA , millivolts or resistance depending upon

the type of transducer used which in-turn converted to 0 10v for block operation

through input signal block. This also optically isolates the input & output signals.

The pulse output block compare the process parameter set point , process

parameter measurements and control valve position and gives output accordingly for

the control valve.There is a signaling unit, which compares the parameter value with a

predetermined set point. Deviation beyond that gives alarm & changes the Auto

operation into Manual Mode. In the event of abrupt failure such as open circuit or short

circuit in transmitters controller trip action takes place through this block. Parallel

command goes to annunciation blocks also.

For some important controllers redundant transmitters are provided. Provisions

are there for manual change over to the standby in case of failure of the working

transmitter .Provisions are there for bumpless transfer of actuator from auto mode tomanual mode.

The main automatic controllers are as detailed below.

A. UNIT CAPACITY CONTROL

This controller is for maintaining a controlled TG power output and mainsteam

inlet pressure to turbine. This controller incorporate Load change limiter, Boiler capacity

control and Turbine capacity control. Boiler capacity controller will receive unit preset

capacity signals from unit load rate of change limiter and the actual power output. Itgenerates a demand signal to a coal flow controller & total air flow controller. Turbine


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capacity controller will receive signal from actual power output , rate of feed forward

signals of the preset output, the error signal representing the discrepancy between the

demand and actual main steam inlet pressure to for time . Turbine capacity control

initiates command to operate the speeder gear motor.

B. COMBUSTION CONTROL

Combustion control is done by means of Coal flow controller , Mill loading

controller, Total Air flow , Furnace draught controller & F.O pr. controller. Summation

of Coal flow & Fuel Oil flow are used for Total air flow controller which maintain a

predetermined value of free oxygen in flue gas. The loop actuates individual actuate of

FD fans dampers for maintaing the specified free oxygen in flue gas. Mill loading

controller regulates feeding of coal to the pulverizes. Furnace draught is controlled

through controlling the inlet vanes of ID fans.

5. ANNUNCIATION SYSTEM

The Annunciation system is intended to make available the information about

the equipment under control, deviation of measured parameters from the normal

(preset) value and interlock action. Alarm is provided with each annunciation block.

Visual status indication of equipment under control i.e Devices and Stop valves

Audio-visual alarm annunciation of emergency tripping and autostart of equipments

Audio-visual process annunciation.

Audio-visual preventive alarm annunciation of parameter deviation from normal

values.

There are three major section in the annunciation circuit. Section I controls

the Boiler & off site annunciations, section II controls the turbine related

annunciations and section III looks after the generator related annunciation. The

circuit is powered by 110v DC which is generated by 3 phase 415v AC rooted through

a transformer and diode rectifier circuit.

Operating status of important drives protection status and alarm conditions,

when arises actuate the annunciation system. Once the alarmed value is reached by any

signal, it flashes & hooter circuit is energizes. Flashing takes place till the resetting is

not done. If the alarmed condition stillexist then it glows steadily. Each annunciation

section will be provided with test push buttons to check the audio annunciation signaland with the panel switches for lamp healthiness checking.

6. FURNACE SAFEGUARD SUPERVISORY SYSTEM

The Furnace safeguard supervisory system supplied by Forney, USA i.e of

Model AFS 1000 is a 16 bit 80186 microprocessor based system. The main task of

FSSS is to control the fuel system equipments i.e. oil guns, igniters, PA Fans, Mills,

seal air fans and their associated dampers etc. so as to ensure safe operation of the

Boiler under start up, transient and normal conditions. Besides, one of the most

important FSSS task is to implement process protections with provision for a first up

annunciation facility on operating console with respect to the first actuated protections.


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AFS 1000 Burner management system employs plug in printed circuit board

assemblies.This permits maintenance by replacing board without causing the total

shutdown. The Burner Managent System logic comprises of ten nos. of subsystems

(Excluding Maintenance subsystem II) per each unit each responsible for predefined

portion of the overall system. There are two CRT master subsystem ,one purge and fuelsafety subsystem, one oil burner subsystem & six mill subsystems. Each subsystem is

responsible for a portion of overall control.

A subsystem consist of a single - board control card (80186 up based ) , solid state

input / output printed circuit board assemblies, starburst keyboard with

intercommunication through fiber optic Assembly and a shared operation interface

through fiber of the cable assembly and having touch screen facility. There are also

some logic derived inputs that got transmitted from one subsystem from another and all

subsystem operate independently of other subsystem.

1. CRT master subsystem:

The primary function of each CRT master subsystem is to act as controller ofthe intercommunication bus (ICB) used to pass data back and forth between the

master and the other subsystem. It also decodes commands that it receives from

CRT screen. In the CRT screen the last acknowledged alarm, Printer ON/OFF

status and Command elements appear of which print out can be taken if

required. For depicting valves ,dampers and drives different symbols were used

and when status changes the colour changes.

2. Purge and fuel safety subsystem :

The purge and fuel safety subsystem comprises of the following logic.

Purge logic has the major responsibility for insuring that the furnace is purged

thoroughly with air to remove any combustible before the fuel is released into

the headers & into the furnace. For starting the purge the following conditions

should be met.

a). All burner oil valves closed.

b). Oil trip valve closed.

c). Oil re-circulation valve closed

d). No flame detected

e). Scanner Air fan on.

f). Any Induced Draught & Furnace Draught running,

g). All primary fans , pulverizers & Raw coal feeders off.

h). All hot air damper closed.

i). Igniter trip valve closed.j). No trip (Boiler) present

k). Air flow >30%

After all these conditions are satisfied PURGING takes place for 10Minutes.

03. Pre light Logic: When furnace purging is completed pre light logic is responsible

for the safe release of fuel into the headers. Pre light logic is also responsible for

communicating to the banners subsystem that furnace conditions are satisfactory for

banner operation.


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04. Fuel Safety logic Fuel safety logic is responsible for overall boiler safety. It

monitors the potential danger points throughout the boiler. If the predetermined limits

are crossed, the fuel safety logic shuts off some or all fuel to the furnace depending

upon the conditions. The cause of first out alarm function indicators the cause of the

tripping. The MFT 1 and MFT 2 relays get trip command when any of the following

conditions is / are initiated.

1. Both the ID fans off.

2. Both the FD fans off.

3. Operator trip

4. Drum level high / low

5. Loss of all fuel

6. Loss of all flame

7. Unit trip from BPS

8. Furnace pressure high/ low

9. Delayed light off (10 min after purging)

10. Air flow (< 30%) low.

05. Burner control sub system It is responsible for following a predetermined

programme in safety placing burners in service, removal from service, purging of

burners that have been removed from service and for monitoring burner operations.

1. Mill control subsystem- Milling subsystem is responsible for controlling the

coal burners and associated pulverizer, primary Air fans, feeders and

associated program in safety taking burners in service, removal from service

and monitoring burner operation.

2. Maintenance subsystem-II.

The MS-II is an equipment helping for fault finding or trouble shooting of the

systems input as well as to change the program logic. It comprises of on operation

console, a control unit, interfacing cable assembly, graphic CRT / KBD and menu

driver software.

7. DATA ACQUISITION SYSTEM

The Data Acquisition System of 4x210 Mw KhSTPP was supplied by M/S

ESPL ,Chandigarh. This is a WDPF family of system manufactured by Westinghouse

with software level version 6.4. This system is a microprocessor based distributed

modular type with independent system, drops connected to each other through high

speed standard Westnet data highway having 100% redundancy. The drops talk to eachother directly over the data highway, which eliminate the need of host computer. The

system caters 900 analog points and 1400 digital points in each unit Each system

supports two units. The standard WDPF drops and products perform specific functions,

which allows a custom system to be configured by determining required functions and

selecting the appropriate standard equipment.

8. UPS PACKAGE

UPS system of capacity 75 KVA has been supplied by M/S KELTRON

,Trivendrum for each of the four units which caters the power supply for all C&I

system including Data Acquisition system. FSSS, Instrument supply, ACS etc. The

system consists of 2 nos. chargers, 2 nos. inverters, and one paralleling unit, one servo


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controlled voltage stabiliser (SVCS) and one set of Battery (550AH) for one-hour

backup at 75KVA load. The two inverters, each of which is rated at 75KVA, are

connected together to the O/P busbar to share 50% of the load. In case of failure of one

inverter the other one takes up the full load automatically. The two chargers, which are

meant for feeding the inverters and changing the battery, also work in parallel and each

one can take the load if needed. The set of battery is connected at the output of thechargers and input of the inverters. In case of failure of both the chargers the battery

automatically takes up the load and starts feeding to the inverters without any

interruption. The SCVS is also connected to the output busbar. In case of failure of both

the inverters the SCVS gets connected to the output busbar through the static switch

with a maximum time delay of 20millisec.

9. ANALYSER AND MISC. C&I EQUIPMENT PACKAGE:

The package was awarded to M/S Keltron, Aroor. The package contents of supply

of the below mentioned instruments.

(1) Analyser for steam and water. Analyse system and Flue gas oxygen analyser.

(2) Miscellaneous C&I equipment such as switch drivers etc. and maintenance and

Calibration equipment for plant.

(i) The supply and erection and commissioning were in the scope of M/S Keltron.

(i) Only the supply was in the scope of M/S Keltron.

Part (1) is consisting of the following major equipment.

(a) Flue gas oxygen Analyser.

(b) Secondary coolers.

(c) Silica Analyser.

(d) Hydrogen Analyser.

(e) PH analyser.

(f) Conductivity.

(g) Phosphate Analysers.

(h) Dissolved oxygen.

Part (2) consists of the following major. Equipment's.

(a) Temperature gauges.

(b) Temperature switch.

(c) D.P switch.

(d) Level switch.

(e) Flow switch.

(f) Thermocouples

(g) Flow elements.

Maintenance and calibration equipment.

(a) Pneumatic test bunch.

(b) Vacuum tester.

c. Thermocouple test furnace.

d. Flowmeter calibrator.

e. Coil winding machine.

f. Soldering iron

g. Radial drilling machine.

h. Solder sucker.

i. Variac.

j. Rheostat/Potentiometer.

k. RCL Bridge.

l. Logic Probs.

m. Portable pneumatic calibrator.

n. Portable vibration meter.

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