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.

2

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.

3

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

4

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

5

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

6

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

8

specific functions such as logic, sequence, counting, timing and arithmetic

operations to control the processing of machines.

OVERVIEW

9

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

10

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.

11

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.

14

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

16

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:

17

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.

18

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

19

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

20

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

21

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-

22

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.

23

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

24

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.

25

SEQENTIAL CONTROL

SEQUENTIAL CONTROL

INTRODUCTION:

26

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

27

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:-

28

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

29

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.

30

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

31

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

9. Synchronous condenser generator to Generator

10.Generator to Synchronous condenser Generator

11.Stand still to generator(Back to back)

12.Stand still to Spin pump (Back to Back)

13.Stand still to pump (SFC)

14.Stand still to Spin Pump(SFC)

15.Stand still to pump(SFC)

16.Spin pump to pump

START PERMISSIBLE CONDITIONS & BREAK –AWAY CONDITIONSD:

8 Permissible Conditions and 3 Break conditions are considerer for the 6

modes of operation and the change –Over from one mode to another mode.

STRAT PERMISSIBLE CONDITIONS:

32

1. SP1-SD to G or S.G

2. SP2-SD to B-B G

3. SP3-SD to S. Pu

4. SP4 –SD to Sy.C.G

5. SP5-S.Pu to pu

6. SP6-Sy.C.G to G

7. SP7 –S.G or G to Sy.C.G

8. SP8-S.G to G

BREAK - AWAY CONDITIONS:

1. BC1-SD to G or B-B G

2. BC-2 SD to S.Pu

3. BC3-SD to SFC

33

34

CRITERIA:

PROCED CRITERIA:

Each set of the program is assigned with a set of criteria and commands.

The set of criteria required to be fulfilled prior to entering a step are called

‘Proceed Criteria.

SUPERVISION CRITERIA:

To ensure safe operation of the unit, certain important criteria which are

essentially required for safe operation of unit are supervised for several steps

after the initial step to which they are assigned as proceed Criteria. These

Criteria are called ‘Supervision criteria’.

OVER-RUN CRITERIA:

Over-run criteria decided the step from which the program shall be

started and the steps to be bypassed when any program is executed from a

transient state.

CONTROL CONSOLES:

Control consoles are provided both on the Sequence control panel and on

the control desk. The control console of the units consist of all the push buttons

and indicating lamps required for selection/execution/Indication of all the

programmers of the unit is shown in below figure.

35

The following additional push buttons are provided on control consoles of Unit6

to 8:

1. Missing criteria

2. Generator start not ready

3. Synchronous condenser generator start not ready

4. Pump start not ready

36

SELECTION OF CONTROL:

The Unit can be controlled

1. Locally

2. At the control Room

3. From a remote Location

Selection of control can be done with the corresponding push button and

the selection mode is indicated by the lamps in the push buttons.

The unit can be operated only from the control consol selected however,

indications on the both the consoles are operative irrespective of console

selection. While the unit can be operated in all possible modes from either of

console from remote console, the unit can be operated only as a Generator. The

programme to Generator is selected and executed with a single command from

the remote station.

START PERMISSIBLE CONDITION/START NOT READY CONDITION:

The Non- Availability of all the criteria required for the various start

permissible conditions is indicated by the lamps in start not ready push buttons.

The lamp glows when any of the criteria required are missing.

TABLE: START NOT READY INDICATINGS

STATUS OF THE

UNIT

START PERMISSIBLE

CONDITIONS FOR SOME

CRITERIA MISSING

INDICATING LAMP THAT

WILL GLOW

SD

SG

SyCG

SD

SG or G

SD

SPU

SP1 & SP2

SP8

SP6

SP4

SP7

SP3

SP4

Generator start not ready

Sy.C.G.Strat not ready

Pu.start not ready

It may be noted from above table that while all the programmers to

S.G, G, Sy.C.G, S.Pu or Pu required the same start permissible conditions to be

fulfilled, the programme to shunt down does not require any permissible

condition to be fulfilled. To ensure safety of the unit, it is programmed in such

way that the unit can be shut down from any stage whether transient or steady

state without any pre conditions.

37

SELECTION NOT PERMISSIBLE:

If a selection is not permissible is made the same is indicated by the

indicating lamp ”selection not permissible”.

PROTECTION SHUNT DOWN:

In case of protection shunt down the programme under execution

changes over automatically to shut down and the indicating lamp “protection

shuntdown” flashes.

RELEASE PUSH BUTTONS:

Since all the manual commands are by means of push buttons, to avoid

inadvertent operations all important commands are inter-Locked with the

“Release” push buttons.

The release button is required for the following ON/OFF commands of

drive:

1. Circuit Breakers

2. Isolators

3. Mechanical Brakes

4. Penstock Intake Gate

5. Synchronizing

6. AVR change over Manual/Auto

7. Gate Limiter Raise/Lower

8. Selection of Individual/Joint Governing

9. for the ‘Execute’command to start any programme

38

AUTOMATION OF HYDAL UNIT

39

AUTOMATION OF HYDEL UNIT

40

AUTOMATION:

Automation is basically the delegation of human control functions

equipment aimed towards achieving.

Higher productivity,

Superior quality of end product,

Efficient uses of energy and raw material and

Improved safety in working condition.

HISTORY OF PROCESS CONTROL

There are various methods used in the process control and automation

are as follows and they are

Manuel control

Hard-wire control

Electronic control using logic gates

Programmable logic controller

MANUAL CONTROLLER

In manual control all actions related to process control and automation is

taken by operations. By using this method we can have the following drawbacks.

Major drawback of this method is human errors and consequently effect and

quality of final product.

Mannual control has its own limitations with regard to mass production

techniques and this method cannot provide the consumer with quality goods

at an affordable price.

The safety is efficient use of raw material and energy are all subject to the

correctness and accuracy of human actions.

HARD -WARED LOGIC CONTROL:

This is the first step toward automation. Here contractors and relays

together with timers and counters were used in achieving the desired level of

automation. This method served the purpose for many years. But it also has

certain limitations.

Bulky and complex wiring involving a lot of rework to be implement changes

in control logic.

The work can be started only when the task is fully defined and this leads to

longer project.

ELECTRONICS CONTEROL USING LOGIC GATES:

With the advent of electronics, logic gates started replacing the relays

and auxiliary contractors in control circuits. Electronic timers etc. replaced by

metallic and motorized timers.

41

With within of these changes we got the benefits like.

Reduced space requirements

Energy saving

Less maintains and hence greater reliability

However when with electronics, the implementation of changes in control

logic as well as reducing the project lead-time is not possible.

This method of control and automation was also quite popular for some

time.

It has one limitations that is this method is defined if and only if the task is

fully defined.

PROGRAMMABLE LOGIC CONTROL:

With the coming of microprocessors and associated peripheral clips,

the whole process of control and automation under went a radical change

instead of achieving the desired control and automation through physical

wiring control devices, the PLC it is achieved through PLC’s in recent years

experience an unprecedented growth as universal element in industrial

automation. It can be used effectively from single control like replacing small

number of relay to complex automation problems.

CHARACTERISTICS FUNCTIONS OF PLC:

The national Electric Manufactures Association (NEMA) currently defines

a programmable controller as a “Digital Electronic Device” that uses a

programmable memory to store instructions and to implement specific

functions such as logic, sequence, timing, counting and arithmetic to control

machines and process.

It is field programmable by the user. This characteristic allows the user

to write and change program in the field without rewriting or sending

the unit returns back to the manufactures for this purpose.

It contains preprogrammed functions. PLC features logic, timing,

counting and memory functions so that the user can access through

some type of control orient programming language.

It scans memory, inputs and outputs in a deterministic manner. This

critical Oriented feature allows the control engineer to determine

precisely how the machine or process will respond to the logic.

It provides error checking and diagnostics. A PLC will memory

periodically run internal tests of memory, processor and I/O systems to

ensure that what it is doing to the machine or process and what it was

programmed to do.

It can be monitored. A PLC will provide some from of monitoring

capability either through indicting lights that show the status of inputs

42

and outputs by an external device that can display the program

execution status.

It is packed appropriately. PLC is designed to withstand the temperature,

Humidity, vibration, and noise found in most factory environments.

It has general –purpose suitability. Generally a PLC is not designed for a

specific application but it can handle a wide variety of control tasks

effectively.

This unit can be operated in step by step automatic.

STEP BY STEP:

“Step by Step” should be selected before selecting any programmed.

The step by step operation can be selected with the step by step push

buttons and selection is indicated by the built – in lamp push button. The

selection can be reset by using the “preselect Reset” push button before the

execution of program. It is also reset in case of a protection shut down. If step

by step is selected the programmed selected and executed proceeds only

one step at a time. After the criteria required for the next step are fulfilled,

the execute push button glows and till the execute push button is pressed for

the program does not proceed further to next step. This method is mostly

useful during testing and commissioning.

To ensure safety of unit, in the event of a protection shunt done, the step

by step selection is automatically rest and the shut down programme is

executed as and when it becomes necessary.

AUTOMATIC OPERATION:

There is no separate selection as such for automatic operation. If the

step by step mode is not selected the unit under auto-operation as it is the

default mode of operation.

PROGRAMME SELECTION:

The programme selected is indicated by a steady glow of corresponding

arrow. Thus progrmme selected is rest either a new selection in which case

the arrows switch over to correspond to new selection mode or by’ preset

reset’ push button in which case the selection gets rest totally and arrows are

switched off. The selection mode gets reset automatically if the sane is not

executed within 10 seconds.

EXECUTION:

43

The programme selected can be executed by pressing the ‘release’ and

execute’ push buttons simultaneously. The push buttons shall be kept

pressed for at least 2 seconds for the selected programme to start. This in

additional safety precautions to avoid starting of a programme due to

inadvertent operation of the push buttons. The steady light in the arrow now

turns to slow flashing and the steady light in the status push button switched

off.

PROGRESSION OF THE PROGRAMME:

The selected programmed, thus executed, proceeds step after step

ensuring that the commands given out are properly executed by checking the

proceed criteria. The step number of the step executed is indicated in the 4

digital, 7-segment LED display in the two digital 7- segment LED displays in

the LCP only.

PROGRESSION CRITERIA FAILURE:

The time in which the commands of each step are to be executed is

defined, taking into account the time required for the corresponding drives to

operate. So, unless the proceed criteria for the next step are not fulfilled with-

in the predefined time, the same is indicated by the flashing light in the

indication lamp “progression criteria failure”. It will become steady once

accepted. Simultaneously the missing criteria” push buttons also glows. The

programme proceeds further only after the missing criteria are fulfilled.

FREEZE:

Freezing of the programme is useful to change the dirtection of the

program before it is completed.E.G the programme for SD by Sy.c.g. can be

halted at a permissible step and the SD –G programme can be selected and

executed.

The program under execution can be stopped only at any permissible

step using push button “FREEZE”. The programmed is indicated by the

flashing light in “Freeze” push button and will become steady once accepted.

The slow flashing in arrows changes over to fast flashing indicating the

disturbance in running programme.

END OF PROGRAMME:

After the last step is executed the programme comes to an end, and the

unit reaches a steady state, if all the criteria defined for the status are

fulfilled. This is indicated by the steady light in the corresponding mode push

buttons.

44

DISTRUBANCE IN STATUS:

If any of the criteria required for the steady status are lost for the some

reason, the status lamp starts flashing indicating the disturbance in the

status. This disturbance flashing can not be accepted by using the accept

push button. The status lamp will become steady only after the missing

critera are fulfilled. The missing criteria can be found out by the missing

criteria indication system.

AUTO INACTIVE:

Auto inactive is also a selection to be made/reset when the machine is in

a steady state. The selection can be made with the push button’ auto

inactive’ and can be reset by ‘preselect reset ‘push button. The selection is

indicated by the lamp in the push button. When auto inactive is selected, the

commands from the sequence control to the drive control are totally blocked

while all other indications such as arrow display, step display

And missing criteria display is available. In auto inactive the sequence

control will act a guide to the operator while he operated the machine

manually. To ensure safety of the unit when any protection acts, it is

programmed in such away that ‘auto inactive’ selection gets is reset at the

shunt down programme is executed automatically when the protection shunt

down acts.

ADDITIONAL FACILITIES PROVIDED IN THE CONTROL SYSTEM OF

UNITS:

The following additional facilities are provided in the control system

supplied by SANAG for units 6 to 8

MISSING CRITERIA INDICATION:

A facility to indicate criteria numbers of the missing criteria on demand,

directly in the digital display is provided in the following cases:

a) START NO READY

b) PROGRESSION CRITERIA FAILURE,

c) STATUS DISTRIBUTED

1.Digital step display on the control desk in addition to the display on the

LCP.

2. Digital display of the commands given out at each step in the LPC.

3. Manual control start.

45

MISSING CRITERIA:

For the indication of missing criteria, the same digital display in which

the step number is indicated is made use of for recalling the missing criteria,

a push button with built in signal lamp is provided in both the control

consoles.

METHOD OF INDICATION OF MISSING CRITERIA:

FOR START NOT READY:

In the control consoles of units 6 to 8, the 3 Nos. start not ready

indicating lamps are replaced by push buttons with built in signal lamps.

To find out the missing criteria corresponding to any of the start not ready

lamps, the “START NOT RADY” push button should be depressed until the

lamp in the missing criteria push button glows. Now if the missing criteria

push down is pressed, the criteria number of the first missing criteria is

indicated in both the digital displays. If there are more missing criteria the

lamp continues to glow. By pressing the missing criteria push button

repeatedly, all the missing criteria are indicated in the as sending order.

When the last missing criteria is indicated on the digital display, the

missing criteria lamp will switch off and after a small delay the digital

display will display what it was showing before the missing criteria were

indicated.

FOR PROGRESSION CRITERIA:

During the execution of any programme, if any of the criteria required

for the progression of any step are not fulfilled within the specified time,

the progression criteria failure lamp glows and simultaneously the lamp in

the mission criteria push buttons also glows. Now by pressing the mission

criteria push button, the missing criteria indicated in the digital display.

FOR THE STATUS CRITERIA INDICATION:

After reaching any steady status, the corresponding status lamp glows

with a steady light. If for any reason any reason any of the status criteria

changes state, the status lamp will start flickering.

To find out the missing criteria, the push button with the flickering

status lamp shall be kept pressed till the lamp in the missing criteria push

button glow. Now by pressing the missing criteria push buttons the missing

criteria are indicated in the digital display

DIGITAL DISPLAY COMMANDS:

In addition to the digital display of step numbers, commands given out in

the last step executed are indicted in the digital displays mounted inside the

local control panel. These displays are not provided in the control desk.

46

MANUAL CONTROL START:

While the first two additional facilities are provided in the sequence

control, another important additional facility manual control start is provided

in the control.

To facilities starting the unit and taking it up to 100% speed, with all

the necessary interlocks taken care of in case of any failure in the sequence

control start is provided in the drive control. The control console for this

purpose is provided on the door of the drive control panel housing the

mechanical drive cards and machine input cards.

To manual control start operation is carried out in four steps starting

the unit up to 100% speed, viz.0301,3002,0401 and 0402 and two steps for

stopping the unit from 100% speed, viz 0105 and 0201.

This is mainly useful to run the unit as generator/Spin generator. After

starting the unit, using this console on the drive control panel, voltage

building up and synchronizing shall be done from the control desk. Similarly

only after the main breaker and field breaker are switched off from the

manual control start control console.

Each step is provided with a push button release, lamp test and

manual control start buttons are also provided in addition to the start not

ready indication lamp.

Manual control start can be selected only when the sequence control

panel is switched off or when the control is kept under “AUTO INACTIVE”

manual control can be selected by using the manual control push buttons.

The release push button is provided to avoided inadvertent operations as in

the case of sequence control. Separate commands are to be given at each

step. It is interlocked in such a way that commands to the next step can be

given only after the previous step is complete, which is indicated by the

steady light in the corresponding step button. The step under execution is

indicated by a flashing lamp in the corresponding push button. The

commands and the criteria interlocked for each step are identical to the

automatic sequence control. For detailed manual control start scheme.

STARTING AS S. Pu/Pu:

BACK To BACK METHOD:

In this method another generator is utilized as back to back generator to

start the required unit as s.pu/pu. Both will be connected to the starting bus

through their starting isolators.

SELECTION OF EXECUTION:

To start one of the unit in the pump direction, the selection of s.pu/pu

shall be done through its control consoles and one of the other 7 units shall

47

be selected as back to back generator. Now the programmed shall be

executed from the control console of the units selected as s.pu/pu. The back

to back generator programme in the selected as back to back generators also

start simultaneously with the s.pu/pu. The back to back generator does not

need a separate execute command.

STATIC FREQUENCY CONVERTER:

All the controls required to start any of the 7 reversible units in the

pumping direction using SFC equipment have also provided.

SELECTION AND EXECUTION:

The selection of the required units as S.pu/pu and the SFC mode

of starting are to be selected from its own control consoles using the

respective push buttons. The programme also to be executed from the same

control console. All the commands required to be given to the SFC equipment

are generated in the interface panel of stage-1.

RANDOM COUPLING – INTERLOCKING:

Logic required for the interlocking to operated the units as back

to back generator /pump is programmed in the microprocessor provided in

the inter facing panel. It co-ordinates with the interface logic required for unit

1 to 5. The interface logic in the interface panel provided in stage 1 takes

care of the total logic required for random coupling of all the 8 units as back

to back generator/s.pu/pu.

WORKING OF PLC:

The process of working of PLC can be easily explained in four stages.

BREAKING INPUT SIGNAL STATUS TO THE INTERNAL MEMORY OF THE

CPU:

The field signals are connected to the input modules. At the

output of input modules, the filed status converted into the voltage level

required by the CPU is always available. At the beginning if each cycle the

CPU brings all field input signals from input module and stores into it’s

internal memory as process image input.

PROCESSING OF SIGNAL USING USER PROGRAM:

Once the field input status is brought into the memory of CPU,

the execution of user program, statement by statement begins. Based on the

user program the CPU performs logic and arithmetic operations on the date

from pore diagram. It also process times and counts as well as flag states.

48

STORING THE RESULT OF THE PROCESSING IN THE INTERNAL

MEMORY:

The result of the use program scan are than stored in the

internal memory of CPU. This internal memory is called PROCESS OUT PUT

IMAGE.

SENDING PROCESS OUPUT IMAGE TO OUTPUT MODULE:

At the end of the program run, at the end of scanning cycle the

CPU transfers the signal states in the process image output to the module

and further to field controls.

INPUT AND OUTPUT MODULE:

INPUT MODULE:

The input modules act as an interface between the field input and the

CPU. It converts the field signals generated by the sensors, transducers, limit

switches, push buttons etc.. to a standard control signal for processing by

PLC. The standard control signal delivered by input module could be 5v or 9v

where as the field signal received by it could be the 24v Dc or 230v AC. It

requires isolates the field signal from CPU. It sends one input at a time to CPU

by multiplexing action.

Depending upon the nature of the input signal coming from the

field input module could be analog or digital input module. The typical analog

current input modules are 4 – 20ma, and analog voltage input modules are 0-

50mv, s5135 U programmable controllers employs digital input and out put

modules.

As shown in the block diagram the process signal s are conditioned in

the input circuit of the module for processing at the internal level of the

module. Most digital input modules supply isolated signals to the date

register. An external signal at the enable input can disable processing of the

input and disconnected the module from the bus system.

The module address is set on an addressing switch, the controller issues

a DRY acknowledgement signal to the CPU, if the address on the system bus

recognized by the address decoder is identical with the address set. Then the

data will be transferred to the CPU from the data register through the bus

driver.

ADVANTAGES OF PLC:

PLC has a lot of advantages and some of them are explained below.

REDUCE SPACE:

49

PLC is fully solid-state devices and hence extremely compact as

compared to hard-wired controller where in electromechanical devices are

used.

ENEGY SAVING:

Average power consumption is just on e tenth of power consumed by

an equivalent relay logic control.

EASY OF MAINTENANCE:

Modular replacement, Easy trouble shooting, Error diagnostics with

programmer

ECONOMICAL:

Considering one time investment in PLC is most economical system. Cost

of PLC recovers with in short period.

GREATER LIFE AND RELIABILITY:

These are static devices. Hence lesser number of moving parts, reducing

wears and tears.

TERMEDOUS FLEXIBILITY:

To implement changes in control logic, no wiring is required. So

considerable time is saved. It can carry out complex functions such as

generation of time delays, counting, comparing arithmetic and logical

operations etc. Also online(without disturbing process) and offline

programming is possible.

SHORTER PROJECT TIME:

The hard wired control system can be constructed only after the task is

fully defined. In PLC, however the construction of the controller and wiring are

independent of control program definition.

APPLICATIONS OF PLC:

In industry, there are many production tasks, which are highly

repetitive nature. Although repetitive and monotonous, each stage needs

careful attention of operator to ensure good quality of final product. Many a

times, close supervision of processes cause high fatigue on operator resulting

in loss of task of process control. Sometimes it is hazardous as in the case of

potentially explosive chemical processes. Under all such conditions we can use

PLC effectively in totally eliminating the possibilities of human errors.

Few examples in industries where PLC are used for control purpose

are:

50

Tire industry

Ship unloaded

Wagon loaders

Steel plants

Pulp factory

Printing industry

Dairy automation

Coal handling section etc

COMPARISON

51

COMPARISION:

HARD WARE CONTROLS Vs PROGRAMMABLE CONTROLS

HARDWARE CONTROL CIRCUIT:

It is a conventional circuit. It consist of auxiliary contactor, timers and

coils. Hardware has to be drawn through the circuit and terminal blocks have to the

arranged for connection at different places.

ADVANTAGES:

1. Initial cost is less

2. Less qualified persons are required

DISADVANTAGES:

1. Regular maintenance is required

2. Trouble shooting is difficult

3. Actual wiring has to be for any change in logic

4. Less accurate in operation.

PROGRAMMABLE CONTROLLER:

Programmable controller are introduced to eliminate above problems

and for following reasons.

1. Relay had limitations has control devices.

2. Manufacturing and process equipment were becoming more sophisticated

ADVANTAGES:

1. A number of control programs can be run on the same PLC for different

applications.

2. Fast implementation of changes in control program.

3. Large quantities of contacts are available.

4. High speed operation.

52

5. PLC operation status can be seen on the video display unit in minute display

details step by step that makes trouble shooting easier

6. More reliable than relays

DISADVANTAGES:

1. High initial cost.

2. Qualified persons are required to maintained system.

CONCLUSION

53

CONCLUSION

The programmable Logic controllers used for Automation & control at

NSPH are versatile and simple and simple. This PLC system gained more popularity

due to the advent of LSI/VLSI technology. This replaced the old version of

complicated relay logic that were normally slow in operation, prone to frequent

troubles due to mal operation of relays. This is totally avoided in digital logic

controls. Because of the advantage of flash memories. The software programs could

easily be altered as per necessarily even after years of commissioning. Facilitating

easy updating of plant logic. The PLC’S are highly adaptable and can easily be

coupled to the stand alone system like Excitation system and Governor System etc.,

there by opening the possibility of pre fabricated logics and easy coordination

resulting in smaller commissioning periods.

The high speed Digital controls are capable of accurately controlling

the plant operation. Every control viz. proportional, integral & differential controls

and their combination is possible to be realized. The usage of digital soft ware

programs rules out the ageing effects caused by employing inductor, capacitors

incorporated in Analog controls.

The modular design of PLC’S reduced the size of control panels,

brought in cost reduction and plant esthetics this modular designer also reduced

the cost of inventory and hence the cost of spares. In case of fault, the operation of

entire power station can easily be diagnosed and the fault be located and attended

quickly and accurately, thereby reducing the down time of the machines.

FUTURE SCOPE:

The latest developments in Digital Communication Technology High

Speed data transfer are now opening new frontiers to more sophisticated controllers

called Distributed Digital Controllers like Max DNA controller which are more

powerful versatile, fast and even more flexible and economical

54