AUTOMATION CONTROL OF HYDEL POWER STATION A PROJECT REPORT SUBMITTED TO JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY, HYDERABAD SCHOOL OF CONTINUING AND DISTANCE EDUCATION IN PART FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DEGREE OF BATCHELOR OF TECHNOLOGY IN ELECTRICAL & ELECTRONICS ENGINEERING Submitted by Kum T.JAYA Roll. No N5063A2296 Under the esteemed guidance of Sreedevi,B.TECH Assistant Professor Department of Electrical & Electronics Engineering GOKARAJU RANGARAJU COLLEGE OF ENGINEERING & TECHNOLOGY,BACHUPALLY,HYDERABAD 2009 1
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AUTOMATION CONTROL OF HYDEL POWER STATION
A PROJECT REPORT SUBMITTED TO
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY,
HYDERABAD SCHOOL OF CONTINUING AND DISTANCE EDUCATION IN PART FULFILLMENT OF THE REQUIREMENTS FOR
THE AWARD OF DEGREE OF
BATCHELOR OF TECHNOLOGY
IN
ELECTRICAL & ELECTRONICS ENGINEERING
Submitted by Kum T.JAYA
Roll. No N5063A2296
Under the esteemed guidance of
Sreedevi,B.TECH
Assistant Professor
Department of Electrical & Electronics Engineering
GOKARAJU RANGARAJU COLLEGE OF
ENGINEERING & TECHNOLOGY,BACHUPALLY,HYDERABAD
2009
1
GOKARAJU RANGARAJU COLLEGE OF ENGINEERING
& TECHNOLOGY, BACHUPALLY,HYDERABAD
Department of Electrical & Electronics Engineering
CERTIFICATE
This is to certify that the project work entitled
“AUTOMATION CONTROL OF HYDEL POWER STATION”
Is the bonafied work done by
Kum T.JAYA
Roll. No :(N5063A2296)
In the Department of Electrical & Electronics Engineering at Gokaraju
Rangaraju college of Engineering & Technology,Bachupally,Hyderabad And is submitted to JAWAHARLAL NEHRU TECHNOLOGICAL
UNIVERSITY,HYDERABAD SCHOOL OF CONTINUING AND DISTANCE EDUCATION in partial fulfillment of the requirements for the award of degree of bachelor of technology in Electronics Engineering.
This work has been carried out under my guidance
SREEDEVI Prof.T.VijayaRama Raju Assistant Professor HOD
DETP OF EEE GRIET.
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ANDHRAPRADESH POWER GENERATION CORPORATION LIMITED
NSHESCHEME NAGARJUNASAGAR
CERTIFICATE
This is to certify that a project titled “AUTOMATION CONTROL OF
HYDEL POWER STATION” has been carried out by the student of Gokaraju
Rangaraju college of Engineering & Technology,Bachupally,Hyderabad at
N.S.H.E.Scheme,NS Power House,Nagarjunasagar.
Kum.T.Jaya, (N5063A2296)
During the period of the project their conduct and character were found to
be satisfactory.
Mr Y.Mallikarjuna
ASSISTANT ENGINEER
AUTOMATION & CONTROL
N.S.H.E.Schem.
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ACKNOWLEDGEMENT
We owe our profound acknowledgement to all those people who
made this project successfully. We would like to express our most
sincere thanks to all those who are involved in our project, a deep
sense of gratitude to AP POWER GENERATIOM CORPORATION
LIMITED, for permitting us to work in their organization
We take this precious chance to acknowledge to our guide Smt
Sreedevi Assistant professor (GRIET) in the department in electrical
and electronics engineering for her co-operation in completing our
training.
We are also highly thankful to Sri M.MALLIKARJUNA,M.TECH,A.E.
for giving guidance to our training.
We express our gratitude to Head of the department of Electrical
& Electronics Engineering, and to our principal for thir timely advice
and encouragement while pursuing this project as well as through
out the B.Tech couse.
We are also very especially thankful to Sri J.S.V.Uma Maheswara
Sastry, SE, NSHES POWER HOUSE for allowing undergoing training
program.
We also express the over exhilaration and gratitude to all those
who animated our project work and accentuated our stance.
Kum.T.JAYA
Roll.No
N5063A2296
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INDEX
ABSTRACT
1. OVER VIEW OF POWER PLANT 1
1.1 Pumped storage scheme 2
1.2 Right canal electro-Hydraulic station 2
1.3 Left canal power House 2
1.4 Ports of hydel stations 3
2. SPEED GOVERNOR 5
2.1 Speed error sensing unit 6
2.2 Derivative unit 6
2.3 Speed adjusting gear 7
2.4 power output adjusting gear 7
2.5 Speed droop 7
2.6 Isodrome Unit 8
2.7 Summation and amplification unit 8
2.8 Magnetic amplifier 8
2.9 Electro-Hydraulic transducer 9
2.10 Relay section 9
2.11 Synchronous compensator 10
2.12 Joint governor 10
2.13 Follow up circuit 11
3. STATIC EXITATION SYSTEM 13
3.1 Rectifier transformer 15
3.2 SCR output stage 15
3.3 Excitation starter and field discharge equipment 16
3.4 Regulator and operational control circuit 16
3.5 Control electronics 16
3.6 Power supply 19
3.7 Protection 19
4. SEQUENTIAL CONTROL 20
4.1 Westing house PC-700 programmable logic control 22
4.2 Keltron versamac PLC 25
4.3 Modes of operation 25
4.4 Automatic programs 27
4.5 Start permissible & break away condition 29
4.6 Criteria 29
4.7 Control consoles 30
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4.8 Selection of control 32
4.9 Start permissible & start not ready condition 32
4.10 Selection not permissible 33
4.11 Protection shutdown 33
4.12 Release push button 34
5.AUTOMATION OF HYDEL UNIT 35
5.1 Automation 36
5.2 History of process control 36
5.3 Characteristics of PLC 38
5.4 Step by step 39
5.5 Automation operation 39
5.6 Programme selection 39
5.7 Execution 39
5.8 Progression of the programme 40
5.9 Disturbance in status 40
5.10 Auto inactive 41
5.11 Additional facilities 41
5.12 Method of indication of missing criteria 42
5.13 Sorting as S.pu/pu 44
5.14 working of PLC 46
5.15 Applications of PLC 47
5.16 Comparisons 48
7.CONCLUSION 51
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ABSTRACT
7
ABSTRACT
Title: “Automation control of Hydel Power Station”
Nowadays Electrical energy has become one of important daily needs in
human life. It is not only used in house hold appliances and industrial applications
such as transportation purposes. There are different resources of energy from which
electrical energy can be produced are Hydel, Thermal, Solar, Nuclear etc of all this
hydel power station is one of the important means.
A Programmable Logic controller is a digitally operated electronic device that
uses a program memory for intermediate storage of instructions that implement
specific functions such as logic, sequence, counting, timing and arithmetic
operations to control the processing of machines.
In industries there are many productions tasks, which are of highly repetitive
in nature. Although repetitive monotonous, each stage needs careful attention of
operator to ensure good quality of final product. Many of times, close supervisor
process cause high fatigue on operator resulting in loss of task of process control.
Sometimes it is hazardous as in the case of potentially explosive process. Under all
such conditions we can use programmable logic controllers effectively and
efficiently in totally eliminating the possibilities of human error by automating the
process. However with technological development, the programmable logic
controllers are used today in a divers range of industrial and process control
applications. Also they can be designed with communications capabilities that allow
conversing with local and remote
There are many closed loop controls that are used in Hydel power station
keep every process parameters within the limits automatically. In automation
control sequence important and critical element to be monitored and controlled
closely with in the set limits. Otherwise, this may even cause damages to the
turbine or generator.
This project mainly deals with the automation control employed in Hydel
Power station. In this the automation sequential controls equipment furnished for
the reversible turbine generating consists of a control disk, sequential control panel,
drives control and drives protection panels and interfacing the control equipment
with the various field actuators. Each control consists of input, logic and output
section.
A Programmable Logic controller is a digitally operated electronic device that
uses a program memory for intermediate storage of instructions that implement
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specific functions such as logic, sequence, counting, timing and arithmetic
operations to control the processing of machines.
OVERVIEW
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1. OVERVIEW
The Nagarjunasagar reservoir named after Acharaya Nagarjuna, the
great disciple of Lord Buddha, extends up to the toe of the Srisailam dam where
another major hydel project is existing. The Nagarjunasagar dam rising
123.2mt(404) above the Deepest foundation level has a gross storage capacity of
11,310 million cubic meters (400tmc) at the full reservoir level of el+181.051m
(590) and a live storage of about 190tmc. Two canal systems take off from the right
and left bank s of the reservoir providing irrigation for vast areas on both banks of
the river. Water is also let into The River for irrigation lands in the Krishna’s delta
lower down the river. The project commands an area of 3.5 million acres of land and
affords a power potential of 1000MW.
Pumped Storage Scheme:
The first stage of the scheme covers installation of 4Nos reversible types
pump turbine motor/generator units. This equipment was supplied by M/s Hitachis
Mitsubishi. M/s BHEL has also supplied some of the components of field excitation
and pump units.
The second stage of the scheme covers the installation of 3Nos reversible units-8
pen stocks of dia 4.8m(16’) have been embedded in the body of the dam on the left
bank to feed 8 generating units of (1*110+100.8)MW. The ultimate installation
capacity of the power house 815.16MW.
Right canal Hydro-Electric station:
The canal taking off from the side of Nagarjunsagar dam is named
“JAWAHAR CANAL” In affectionate memory of late Sri Jawaharlal Nehru, the prime
minister of independent India. Right canal power House has an installed capacity of
3Units of 30MW each.
Left Canal Power House:
The left canal is called Lal Bahadur canal in every loving memory of the
second Prime Minister of India Late Sri Lal Bhadur Sastry. Left canal power House
has and installation capacity of 2 Units of 30MW.
Parts of hydel Station:
In hydroelectric power station, water kinetic energy and potential energy
is used to generate electrical energy. The main parts of the station are.
1.Reservoir
2.Dam
3.Trach rack
4.Penstock-Ingate
5.Pensotck
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6.Turbain
7.Generator
8.Transformer&Switch gear etc
Reservoir:
The place where the water is stored used to generate electricity is called
“Reservoir”. Electrical generation capacity depends upon the water level this known
as “water head”
Dam :
On river, barrages are constructed corresponding to the water head for
the generation of electricity. According to dam’s height, reservoir storage capacity
is increased.
Trash Rack:
This is used to resistance wastage in the reservoir through the wicket
gates in to the turbine runner. This is constructed with steel bats.
Penstock Intake Gate:
This is the gate placed at the entrance of Penstock at the reservoir. It
controls the water entering into the penstock.
Penstock:
The steel pipes that are used to supply water to turbine from the
reservoir through Penstock intake gate is known as penstock. In medium head and
above medium head power stations, steel penstocks are used. In low head power
stations, concrete penstocks are used.
Turbine:
It converts potential energy of water into kinetic energy. In
Nagarjunasagar power plant, modern Francis turbines are used.
Generator:
It converts kinetic energy (mechanical) that is given by the prime mover
to electrical energy. In Nagarjunasagar power plant, salient pole alternator is used.
Transformers:
Power transformer is used to step up the voltage from 13.8KV to 220KV.
Here in excitation unit, unit auxiliary transformer and rectifier transformer are used.
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SPEED GOVERNOR
12
2. SPEED GOVERNOR
SPEED ERROR SENCING UNIT:
Operation of this unit is based upon variation in impedance caused by
the alternating current in a LC circuit fed from tachogenerator(Parallel coupled
capacitor and chock coil) since the tacho generator is coupled to the turbine shaft.
Its voltage and frequency is proportional to the speed of the turbine. Values of
choke and capacitor are so selected that the Resonance occurs at a frequency of
50c/s which corresponds tot the rated speed of turbain under the resonance
condition, the circuit resistant increases and current flowing through the circuit is
practically nil.
With the speed of rotation increasing and decreasing, leading or lagging
current flows through the circuit respectively. The value of this current being
proportional to the amount of speed change.
DERIVATIVE UNIT:
The derivative signal is incorporated by switching on the switch. The
output of speed error sensing unit is fed to series R.C. Circuit and this current which
is derivative signal is Fed to the control winding it stage magnetic amplifiers.
The derivative signal provides stabilizing effect on the speed loop and improves
governor transient response. Time constant is adjustable in 10 discrete steps
through the selector switch.
SPEED ADJUSTING GEAR(SAG):
Speed adjusting gear consists of a motor coupled ten turn
potentiometer enabling to generate a signal for adjusting of speed of the set before
synchronization. This signal is fed to the transformer, secondary of which is
connected to the control signal summation circuit. The motor is remote controlled
through key mounted on hydro mechanical cabinet of governor and a duplicator key
in main control room.
13
POWER OUTPUT ADJUSTING GEAR (OAG):
Power output changer of a motor coupled ten turn potentiometer
enabling to generate a signal for changing the output of set. This signal through
speed droop is fed to the transformer, secondary of which is connected to the
control signal summation circuit. New balanced position is obtained when
potentiometer under the effect of feed back comes to the position corresponding to
(OAG) effect and the effect of gate position changing. Therefore isodrome signal
practically remains unchangeable. The governor made according to such diagram
ensures high speed of signal response to output change irrespective of isodrome
settings.
SPEED DROOP:
A ten potentiometer with indicating digital is used to provide step less
variation of speed droop up to 10% voltage is supplied to this potentiometer
servomotor position feedback potentiometer and Output adjusting potentiometer. It
contributes to the servomotor position VS speed characteristic of the system Slope
of which is determined by the value of the speed droop setting.
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ISODROME UNIT:
The operation of the electrical isodrome gear is based upon the property
of R.C Circuit coupled resistant box and capacitor box to pass charging or
discharging current that gradually drops to zero in accordance with the exponential
law owing to variations in applied voltage.
Voltage from feed-back potentiometer proportional to gate apparatus
servo motor position is supplied to R.C circuit through the phase sensitive rectifier
which comprises inlet transformer, reference voltage transformer, rectifier diodes
and filter. At turbine no load operation isodrome time is adjusted by switch and
intensity by switch. Switches are meant by adjusting isdrome parameters on load.
Isodrome signal is passed to control windings of magnetic amplifiers. Condensers
which are not connected to R.C Circuit are charged through resistant.
SUMMATION & AMPLIFICATION UNIT:
Signals from transformer T 101,T102 and T103 are fed into the primary
of T104, then into the phase sensitive rectifiers, consisting of rectifying diodes’
D113 to D120 and reference voltage transformer T 105. from the phase sensitive
rectifier-Output Signal is passed through resistance R120; R 121 series connected
control windings of first stage magnetic amplifier.
MAGNETIC AMPLIFIER:
The amplifier is intended to obtain sufficiently strong electric signals
applied over the coli an electro hydraulic transducer. In order to get higher gain
coefficient, the amplifier incorporated two push-pull stages. The first stage
comprises three individual input windings one designed to feed separate
governing. In the second stage just one control windings is made use of Bias
windings in both stages are fed with stabilized voltage. The second stage has
proportional feedback adjustment of total gain coefficient is archived by changing
resistant R116,C101,R206,to R213,R217 to R 224), its value being altered at a time
if the change in isodrome intercity takes place.
ELECTRO-HYDRALIC TRANSDUCER:
The electro-Hydraulic transducer consists of electric and hydro-
Mechanical sections. The electrical part of the transducers is essentially a magneto
electric system the action of which is based on pushing of energized coil out
magnet. A spring suspension keeps the coil in medium position. When current is
flow through the coil winding, magneto electric forces cause the coil to shift, the
amount and direction of this shift being in compliance with those of coil ampere
turns reduced by current flowing through the coil Alternating current is supplied to
the coil through capacitors and to create vibration.
15
RELAY SECTION:
The relay section is intended for switching on the governor circuit
when changing governor operating conditions. Shutdown of the hydraulic turbine is
performed by means of gate limiter “OLG through relay when starting the hydraulic
turbine the relay section switches on the electric Motor of gate limiter “OLG” and
shifts the limiter up to its opening for starting. The extent of opening for starting
can be varied by turning a cam in track contact which actuates relay closes when
the gate limiter beings to remove in the direction of opening. Signal for opening is
passed to the coil of electro-hydraulic transducer which results in gate servomotor
displacement to the position adjusted by the gate limiter. After the hydraulic turbine
speed reaches to automatic control.
Synchronization to the turbine is carried out with the aid of frequency
changer its electric motor being controlled by mean of key “ICS”. After connection
to the network the unit control is automatically shifted to the power output changer
“OAG” is also operated with key is contact and relay are provided in the governor
for the purpose of increasing turbine output when frequency of the power system
drops down.
In case of Hydro set load row off relay gets energized through the
contacts of relay the contacts of relay turns on the during motor and brings the
output setter to no load setting. Motor is switched off by limit switch.
In case of, turbine speed rises to 112% of its rated value, relay energies-
resulting into faster closing action of the turbine through electro-hydraulic
transducer. As the normal rotational speed is archived relay drops off and the unit is
shifted to normal automation control rotation.
Emergency shutdown of the turbine is affected by means of
electromagnet actuated vale provided in the emergency protection system. This
closes the guide apparatus through an emergency closure slide value, by passing
the governor pulse is initiated from over speed protection device to the
electromagnet.
Over speed protection device consist device consist of an electric speed
relay set for operation at 115% of the rated value and contact opening only when
the main slide value shifted sufficiently towards closer. Also a contact of master
controller is connected in series which closes only when the guide apparatus
opening exceeds that for no load operation.
SYNCHRONOUS COMPENSATOR:
A change over to synchronous compensator operation is achieved by
means of a key SCS. Relay comes into action there with removes current from
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magnetic amplifier and feeds signal for closing to the coil of electro hydraulically
transducer.
Adjustment according to head is carried out with the aid of two phases
electrical control motor fed through a transistors amplifier which is provided in this
module. A signal from head sensor is fed into the transistorized amplifier. A
feedback release signal from potentiometer coupled to the gear for adjusting
according to thread is fed into the same input.
Provision is made in the governor for installation of remote indicator of
gate opening and gate opening and gate opening limited. Pickups of the indicator
R708 and R709 are located in hydro mechanical cabinet and should be electrically
connected with their associated meters in the control room.
JOINT GOVERNING:
The change over to the joint governing operation is carried out by means
of key. Relay gets energized which in turn energies relay and power to the joint
governing system is supplied from power station network through a transformer of
the out put setter.
According to both the schemes provided, the joint governing signals are
summed up with separate governing signal in the windings of d.c magnetic
amplifiers.
In case of scheme number two. Setting signal is passed through control
winding 4H- 4K magnetic amplifier MA 101 and MA 102. Feed back signal is passed
through the transformer to the winding 3H-3K of the same amplifier.
The distinctive characteristics of this scheme is that total output
generated by a group of hydro sets depends on number of operating units and is
adjustable by output potentiometer.
FOLLOWING-UP CIRCUIT:
To ensure smooth change over from joint to separate governing. One
transistorized power switch is used for controlling motor. This rings the output
changer potentiometer in step with the gate feedback potentiometer.
DESCRIPTION OF ELECTRONICS CABINET:
Electrical equipment are placed in metal cabinet 600* 610*2110. two
single fold doors at the front and at the rear of the cabinet provided access to
cabinet internal equipment internal equipment.
To facilitate cable lying to an outside terminal block adjustment of the
electrical equipment. There is fluorescent lamp lighting the cabinet inside. Socket
for connecting a soldering iron is also provided in the cabinet. The components of
the electrical equipment are mounted inside the cabinet on nine modules. The
modules have the following names.
TERMINAL MODULE:
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Comprising of rows of terminal that connect the electrical components of
the cabinet to other devices of the governor circuit outside the cabinet and sources
of power supply. All modules mounted inside the cabinet have their own row of
material is used to connect the panels to a bunch of conductors thus setting up and
internal circuit of the electrical equipment cabinet. Units of adjustment according to
head is not connected with the terminal box of electrical equipment cabinet
transformer and automatic switch of tacho generator supply are also located on
terminal module.
DETECTOR MODULE:
This comprise of
1. Turbine speed error sensing device and electric pendulum
2. Phase sensitive rectifier
3. D.C High gain magnetic amplifier
4. Transformers to feed and sum up electric signals.
GOVERNER ADJUSTING MODULE
This comprises of
1. Electrical isodrome gear
2. Speed droop potentiometer
3. Components of follow up drive
4. Relay for switching the governor operating conditions whenever a
necessity to do so arises
JOINT GOVERNING MODULE:
Comprises of the rectifiers, potentiometers and relays necessary for joint
governing operation. A set of plug to change over from one type of scheme of joint
governing to another is also provided in this module.
Relay module comprises relays which are necessary for switching over
with in the governor circuit when the turbine is started shutdown or operating
conditions are changed.
PROTECTION MODULE:
Comprises rectifiers, capacitors, semiconductors, transistors and relays
providing for unit protection under emergency condition. Protection unit is located
at the rear part of electrical equipment cabinet.
UNIT OF ADJUSTMENT ACCORDING TO HEAD:
For limiting the gate opening according to head in EH governors. This
module a comprises transistorized amplifiers and a number of auxiliary devices and
components necessary for amplification and summation of signal fed from the
actual head pickup and feed back loop over the position of a mechanism under
control.
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The module has a terminal block for external cable connections and is
located n the rear part of the cabinet housing the electric equipment. The output
setter consists of a stabilized power supply and one transformer to supply the two
phase A.C motor along with two ten turn servo potentiometer with clutch these
potentiometers are mounted with their indicating diagram.
STATIC EXITATION SYSTEM
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STATIC EXITATION
In static excitation system, the ac power is tapped off from the generator
terminals stepped and ratified by fully controlled thyristors bridges and then fed to
the generator field thereby controlling the generator voltage output. A high
controlled is achieved by using an inertial free control and power electronic system.
Any deviation in thr generator terminal voltage is sensed by an error detector and
causes the voltage regulator to advance or retard the firing angle of the thyristors
thereby controlling the field excitation of the alternator. The below figure shows the
block diagram of static excitation system.
It can be designed with out any difficulty to provide high response ratio,
which is required by the system. The response ratio of the order 3 to 5 can be
archived by this system. This equipment controls the generator terminal voltage
and hence the reactive load flow by adjusting the excitation current. The rotating
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exciter is dispensed with and silicon controlled rectifiers are used which directly
feed the field of alternator.
The static excitation system consists of:
1) Rectifier transformer
2) SCR output stage
3) Excitation starter and field discharge equipment
4) Regulator and operational control circuit.
Rectifier transformer:
The excitation power is taken from generator output and fed through the
excitation(rectifier) transformer, which steps down to the required voltage, for
the SCR Bridge and then through field breaker to the generator field. The
rectifier transformer used in the static excitation system should have high
reliability, as failure if this will cause shunt down of power station.
Dry type cast oil transformer is suitable for static excitation applications.
The transformer is selected such it supplies rated excitation current at rated
voltage continuously and is cable of supplying ceiling current at the ceiling
excitation for a short time of 10 seconds.
SCR OUTPUT STAGE:
The SCR output stage consists of a suitable number of bridges connected in parallel. Each thyristor bridge comprises of 6 thyristors, working as a six pulse fully controlled bridge. Current carrying capacity of each bridge depends on the rating of individual thyristors. Thyristors are designed such that their junction temperature rise is well with in these specified rating. By changing the firing angle of the thyrtistors. Variable output is obtained. Each bridge is controlled by one final pulse stage and is cooled by a fan.
These bridge are equipped with protection devices and failure of one
brige causes alarm. If there is a failure of one or more thyristor bridge excitation
current will be limited to a pre-determined value lesser than the normal current.
However, failure of the third bridge results in tripping and rapid de-excitation of
the generator.
EXCITATION START UP AND FIELD DISCHARGE EQUIPMENT:
For the initial build up of the generator voltage, a field flashing
equipment is required. The rating of this equipment depends on the no load
excitation requirement and field time constant of the generator. From the
reliability point of view, provision for both AC and DC field flashing is provided.
The field breaker is selected such that it carries full load excitation current
continuously and also it breaks the maximum field current when the three-Phase
short circuit occurs at generator terminals. The field discharge is normally of
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non-Linear type for medium and large machines i.e., voltage dependent resistor.
To protect the field winding of the generator against over voltages, an over
voltage protector along with a current limiting resistor is used to limit the over
voltage across the field winding. The OVP operates on the insulation break over
principle. The voltage level at which the OVP should operate is selected based on
the insulation level of field winding of the generator.
CONTROL ELECTRONICS:
Regulator is the heart of the system. This regulates the generator
voltage by controlling the firing pulses to the thyristors.
ERROR DETECTOR & AMPLIFIER:
The generator terminal voltage is stepped down by the three-Phase
power transformer and fed to the AVR. The AC input thus obtained is rectified,
filtered and compared against a highly stabilized reference value and the
difference is amplified in different stages of amplification. The AVR is designed
with highly stable elements so that variation in ambient temperature dose not
cause any drift or change in the output level. Three current transformers sensing
the output current of the generator feed proportional current across variable
resistors in the AVR. The voltage thus obtained across the resistors and be
added vectorially either for compounding or for transformer drop compensation.
GRID CONTROL UNIT:
The output of the AVR is fed to a grid control unit, it gets its synchronous
AC reference through a filter circuit and generates a double pulse spaced 60
elec. Apart whose position depends on the output of the AVR,i.e, the pulse
position varies continuously as a function of control voltage. The two relays are
provided, by energizing, which, the pulses can be either blocked completely or
shifted to inverter mode of operation.
PULSE AMPLIFIER
The pulse output of the grid control unit is amplified further at
intermediate stage amplification. This is known as pulse intermediate stage, the
unit has a DC power supply, which operates from a three phase 380 volts supply
and delivers+15Volts, -15 volts, +5V and a course stabilized voltage V. A built in
relay is provided which can be used for blocking the six pulse channels. In a two-
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channel system, the changeover is affected by energizing/de-energizing the
relay.
PULSE FINAL STAGE:
This unit receives input pulses from the pulse amplifier and transmits
them through pulse transformers through the gates of the thyristors. A built in
power supply provided the required DC supply to the final pulse amplifier. Each
thyristor bridge has its own final pulse stage. Therefore, even if a thyristor bridge
fails with its final puls stage,the remaining thyristor bridges can continue to
cater to full load requirement of the machine/and thereby ensure(n-1) operation.
MANUAL CONTROL CHANNEL:
A separate manual control channel is provided where the controlling D.C
signal is taken from a stabilized D.C voltage through a motor operated
potentiometer ,i.e., the signal is fed to a separate grid control unit whose output
pulses after being amplified at an intermediate stage can be fed to he final pulse
stage. When one channel is working, generating the required pulses, the other
remains blocked Therefore, blocking or releasing the pulses of the corresponding
intermediate stage affects a change over from auto to manual channel or vice-
versa.
A pulse supervision unit detects spurious pulses or loss of pulses at the
pulses bus bar and transfers control from auto channel to manual channel.
FOLLOW UP UNIT:
To ensure a smooth switch over from auto to manual control, it is
necessary that the position of pulses on the both channels should be identical a
comparison unit detects any deference in position of pulses and with a help of
follow up unit activities the motor operated potentiometer on the manual
channel to turn in a direction so as to eliminate the difference. However, while
transferring control from manual to auto mode any difference in control levels
can be visually checked on a balanced meter and adjusted to obtained null
before change over.
LIMIT CONTROLLERS:
When a generator is running in parallel with the power network, it its
essential to maintain it in synchronism without exceeding the rating of the
machine and also without the protection system tripping. The automatic voltage
regulator by itself cannot ensure this. It is necessary to supplement the basic
voltage regulators by limiters to limit over excitation and under excitation.
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Limiters don’t replace the protection system but only prevent the protection
system from tripping unnecessarily under extreme transient conditions.
The AVR also has a built in frequency circuit so the when the machine is
running below the rated frequency, the regulated voltage should be proportional
to frequency. With the help of a potentiometer in the AVR, the circuit can be
made to respond proportionally to voltage above a certain frequency. The range
of adjustment of this cut-off frequency lies between 40 and 60HZ
The static excitation system is equipped with three limiters, which act in
conjunction with AVR.
ROTOR CURRTENT LIMITER:
This avoids the thermal overloading of the rotor winding and is provided
to protect the generator rotor against excessively long duration over loads. The
ceiling excitation is limited to a predetermined limit and is allowed to flow for a
time, which is dependent upon the rate of rise of Field current before limited to
the thermal unit value.
ROTOR ANGLE LIMITER:
The unit comprehends the rotor and DC signal proportional to the load or
rotor angle by means of a simple analog circuit. When the rotor angle exceeds
the limit settable with the differential potentiometer the excitation is increased
immediately to reduce the load angle to the limit value. The rotor angle limiter
takes over control de-coupling the output of the AVR.
STATOR CURRTENT LIMITER:
This avoids thermal over loading of the stator windings. Stator current
limiter is provided to protect the generator against long duration of large stator
currents. For excessive inductive current it acts over the AVR after a certain time
lag and decreases the excitation current to limit the inductive current to the limit
value. But for excessive capacitive current it acts on the AVR without time delay
to increase the excitation and thereby reduce the capacitive current it acts on
the AVR without time delay to increase the excitation and thereby reduce the
capacitive loading. This is necessary, as there is a risk for the machine falling out
of step in under excited mode of operation.
SLIP STABILIZING UNITS:
The slip-stabilizing unit is used for the suppression of rotor oscillations of
the alternator through the additional influence of excitation. The slip as well as
the acceleration signals needed for the stabilization is derived from the active
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power delivered by the alternator. Both the sign ALS, which are correspondingly
amplified and assumed up, influence the excitation of the synchronous machine
through AVR in a manner as to suppress the rotor oscillations.
POWER SUPPLY:
The voltage regulating equipment needs an AC supply 380V, 3Phase for
its power supply units, which is derived from the secondary side of the rectifier
transformer through an auxiliary transformer. This voltage is reduced to different
levels required for the power packs by means of multi wingding transformers.
A separate transformer supplies the synchronous voltage 3X380V for the
filter circuit of each channel and the voltage relay. During testing and pre-
commissioning activities when the generator voltage is not available, the step
down transformer is used for testing purpose with the help of a regulator
test/service switch.
The supply for the thyristor bridge fan is taken from an independent
transformer, which gets its input supply from the secondary of the excitation
transformer. The control & protection relays need 48V & 24V DC which are
delivered from the station battery by means of DC/DC converters, which are
internally protected against overload.
PROTECTIONS:
The following protections are provided in the static excitation equipment.
1) Rectifier transformer over current instantaneous and delayed.
2) Rectifier transformer over temperature
3) Rotor over voltage
4) Fuse failure monitoring circuit for thyristors
5) Loss of control voltage (48V & 24V)
6) DV/DT protection of SCR by snubber network.
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SEQENTIAL CONTROL
SEQUENTIAL CONTROL
INTRODUCTION:
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The automatic sequential control equipment furnished for the reversible
turbine drive generators, units 6,7&8, consists of a control desk, sequence control
panel, drive control and protection panels and interfacing relays which interfacing
the control equipment with the various field actuators which is shown in below fig.
the sequential control panel of unit 6 is made of wasting house while 7 & 8 is made
of keltron. The drive control & drive protection panels consist of hard-wired wasting
house numa –logic 300 series solid state controls, while the interfacing relays are of
ASEA make for all the three units. A Westinghouse makes type X solid state auto
synchronizer and auto synchronizing relays are provided for each unit. Facilities for
transformer tap indication are provided at the control desk. Facilities for alarm
annunciations system is furnished separately by others.
To facilities random coupling of all the 8 Units for B-B start/SFC start a
microprocessor based interface panel is provided. This interface panel is of wasting
house make.
The main tasks of the equipment supplied are to provided for automation
start/Stop of this units as
a) Spin generator
b) Generator
c) Synchronous condenser generator
d) Spin pump
e) Pump
f) Back to back generator
Functionally, the overall system supplied by M/s BBC for Units 2 to 5 to
avoid any confusion to the operating personnel. Hence through the technology
and the equipment inside the panels is completely different from that M/s BBC,
as far as the operator is concerned there is no difference in the system including
control consoles and control desks. However, some additional facilities are
provided, viz.
a) Missing criteria indication for
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i) disturbance in start permissible condition
ii) progress criteria failure
iii) disturbance in status criteria
b) Digital display of commands are given out at each step
c) Digital step display on the control desk, in addition to the local control panel
d) Manual control start, to start the generator and run it up to 100% speed with
all the inter locks required and to stop the machine if need be.
The sequencer for Unit -6 is a Westinghouse 700 series programmable controller
technical feature of westing house PC-700PLC.
WESTINH HOUSE PC-700 PROGRAMMABLE LOGIC CONTROL:
It consists of compact 16 bit microprocessor based programmable
controller. The control system comprising of the this unit can be broadly into
three sections.
INPUT SECTION:-
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Which provided the input information required to keep track of status of
operation The input section consist of two type of input cards, viz. NL708M,24V
DC input module used for monitoring the input from control desk and NL 701,5V
DC input module are used for monitoring the inputs from drive control.
LOGIC SECTION:-
Which analyses and processes the input information from the input
section to determine the output commands to be generated the logic section
consists of a controller or central processing unit and memory to store
information programs. The CPU is used to process and analyze input information
and to generate the output commands based on the instructions given to it by
the software programs. All components are solid state devices. A program loader
feeds the memory with the necessary program to perform a given operation.
OUTPUT SECTION:-
Which activates field actuators based on the information given to it by
the logic section the output section of 4 types of out put cards viz.NL753H
type,5V DC out put cards with signal output compatible to the driver control
system for output to input modules are provided with built in leds to inside the
availability of inputs/Outputs these leds are visible. The drive control NL728
type,24V DC out put modules for output to the control desk, NL753H type
register output cards for the command/step digital displays and NL-735 type 24V
output modules with relay contacts for annunciation purpose.
The I/O modules are provided with built-in LEDs to indicate the
availability of the I/Os these LED are visible when they glow through the
translucent plates mounted in front of the cards.
NLR 704 vertical racks are used to house the modules. As well as for
inter connection between the modules.
The processor co-ordinates all the various operations of the PC-700
memory-user memory, is to store the ladder diagram instructions programmed
from the program loader and for calculation/processing data and I/O image
memory containing status of various input/output circuits at the beginning of a
sampling, and which is updated with each pass. The user memory is in RAM
backed by a Ni-Cd battery. The programme can be retained for a maximum
period of 30 days without input supply to the processed.
The NLTL-783 tape loader allows the storage of programs developed for
the PC-700 on digital cassettes. The provides a safety against accidental erasure
of program memory and also a back up for the software programs. The tape
loader is connected to the processor through the program loader, which initiates
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the loading of a programmed from tape, at the storage of a programme to tape
on-line programming is possible. As such therefore, extra care should be taken
before attempting this on-line programming.
The PC-700 is built up of the following modules(PCB cards);
3Nos, Nl 708 M, 24V DC input module.
26 Nos nl 701,5V DC input signal module.
8 Nos Nl 753H,5V DC output signal module
4 Nos Nl 728,24V DC output module.
Keltron versamac PLC:
Versamac is also modular in design and layout, and supports a leader
diagram program with capabilities for sequence generation through sequence
tables. The over –all structure is broadly similar to the westing-house unit.
Each PLC unit utilizes three 6u height 19” racks, one which is for an 8 bit
microprocessor functioning as the CPU and a few I/O modules. LEDs are given on
a separate local panel for indicating criteria input and output command outputs.
Random access memory is provided for storing/updating I/O status information
and erasable programmable read only memory is provided for storage of
programs. Programming of the sequencer is done through a CRT terminal and
key board, using the relay ladder diagram and symbols.
OPERATION OF SEQUENCER
INTRODUCTION:
As explained earlier, operationally, the system is made identical to that
of the sequence control system of NSPSS stage –I The function of each push
button in control console is identical to that of stage –I i.e. except in case of the
additional push buttons provided for missing criteria & manual control start.
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MODES OF OPERATION:
There are six modes of operation.
1. Stand still
2. Spin generator
3. Generator
4. Synchronous condenser generator
5. Spin pump
6. Pump
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In addition to these steady state modes of operation the units can be run
as back to back generators also, which is a transient mode of operation, i.e any
unit as back generator will take another unit connected to it as spin pump up to
100% speed and after the other unit is synchronized as spin pump the B-B
generator comes back to stand still. Provision is also made in the control circuit
to start the units in the pump direction using static frequency control equipment.
AUTOMATIC PROGRAMS:
1. The Automatic operation of the unit is possible only through the following
programs
a) Generator to stand still
b) Spin generator to stand still
c) Synchronous condenser Generator to stand still
d) Pump to stand still
e) Spin pump to stand still
f) Transient to stand still
2. Stand still to spin generator
3. Stand still to generator
4. Stand still to synchrous condenser Generator
5. Spin generator to generator
6. generator to Spin generator
7. Spin generator to synchronous condenser generator.
8. Synchrous condenser generator to spin generator