Contents

1. Introduction                                                                1

1. Details of organizational setup                                2

2. Transformer                                                                

1. Introduction                                                        4

3. Protection                                                                        

1. Introduction                                                        6
2. Relays                                                                7
3. Various Faults                                                        7
4. Types of Relays                                                        8

4. Details of Technical and other Observations

1. Transmission Lines                                                12
2. Conductors Used                                                        12

5. Isolators

1. Introduction                                                        13
2. Operation                                                                13

6. Circuit Breaker

1. Introduction                                                        14
2. Principle                                                                14

7. Lightning Arrester

1. Introduction                                                        16

8. Power Line Carrier Communication

1. Introduction                                                        18
2. Basics                                                                19
3. Major System Component & Equipments                        20
4. Basic Principle of PLCC                                        20
5. Line Traps/Wave Traps                                                22
6. Coupling Capacitors                                                23
7. Drainage Coils                                                        24
8. Advantages & Disadvantages of PLCC                                25
9. Failure Scenarios                                                                26

9. Control Room

1. Introduction                                                                27
2. Announcing Section                                                        28
3. Control and Relay panel                                                28
4. Supervisory Control & Data acquire system                        29
5. Scanning and Indication                                                30
6. CRT Display                                                                30

List of Figures

Fig.1 Switchyard                                                                        3

Fig.2 Transformer                                                                        5

Fig.3 Relays on Panel                                                                9

Fig.4 Buchholz’s relay                                                                11

Fig.5 ABCB Breaker                                                                15

Fig.6 SF6 Breaker                                                                        16

Fig.7 Lightening Arrestor                                                        18

Fig.8 Basic Power Line Carrier Terminal                                        20

Fig.9 Power Line Carrier Communication                                        21

Fig.10 Coupling Capacitor and Drain Coil Combination                        23

Fig.11 Control panels in control room                                                30     

INTRODUCTION

The Rajasthan state as it exist today is the result of integration of 19 former Princely States and was formed in April, 1949.At the formation of Rajasthan in April, 1949 there were 15 state owned Power Houses with a total installed capacity of 13271 KW and an aggregate maximum demand on the stations of approximately 7483 KW.

The Rajasthan State Electricity Board was constituted with effect from July 1, 1957 by Government of Rajasthan Notification No. F.11/OSD (PWD)/57 dated the 28th June, 1957 under the electricity (Supply) Act, 1948

Government of Rajasthan on July 19, 2000 issued a gazette notification unbuilding Rajasthan State Electricity Board into Rajasthan Rajya Vidyut Utpadan Nigam Ltd. which will be generation company; Rajasthan Rajya Vidut Prasarn Nigam Ltd. which will be the transmission Company and three regional distribution companies namely Jaipur Vidyut Vitaran Nigam Ltd., Ajmer Vidyut Vitaran Nigam Ltd. and Jodhpur Vidyut Vitaran Nigam Ltd.

The Generation Company will own and operate the thermal power stations at Kota and Suratghar, Gas based power station at Ramghar, Hydel power station at Mahi and mini Hydel stations in the State.

The Transmission Company will own and operate all the 400kV, 220 kV, 132kV and 66kV electricity lines and system in State and will also be responsible for procuring power.

The three Distribution Companies will operate and maintain the electricity system below 66kV in the state and their respective areas.

1.1 DETAILS OF ORGANISATION SETUP: -

GRID:       Grid is a technical word used for the interconnection of power received from more than one place. It is a network of main power line for transmission of electricity.

Duties:      Following are the duties of R. R. V. P. N. L.:

•  Supply maximum demands and should be prepare to increase it future is asked for.
• Provide the service line to customer, which must carry the consumer load safety.
• The standard value of voltage (400kv) should be maintained.
• Not discriminate between consumers of the same category, i.e. the categories of consumers may be domestic, commercial, industrial and bulk consumers etc.

SWITCH YARD

So including above the yard consists of following equipment

.

1. 315MVA, 250MVA power transformer.
2. Bus bars i.e. main.
3. Instrument transformer i.e. P.T. and C.T.
4. Isolators.
5. Circuit breakers.
6. Battery sets and battery charger.
7. Lighting arrester.
8. Insulator.
9. Carrier current equipment.
10. Control cable and conduct system
11. Synchronous condenser.

Fig 1. Switch yard

TRANSFORMER

INTRODUCTION: -

It is a mutual link in power system, which makes possible to low voltage to be step up to the extra high voltage for long distance transmission and then transferred to voltage for utilization at proper load centre.

In brief, a transformer is a device that:

1. Transfer electric power from one circuit to another
2. It does so without change of frequency
3. It accomplishes this by electromagnetic induction
4. Where the two electric circuits are in mutual inductive influence of each other

A high voltage is desirable for transmitting large powers in order to decrease the I2r losses and reduce the amount of conductor material.

 A very much lower voltage, on the other hand, is required for distribution, for various reasons connected with safety and convenience. The transformers make this easily and economically.

Transformers are of three types

1. Core type transformer
2. Shell type transformer
3. Berry type transformer

Power transformers are installed with various fittings and devices, which are necessary for their proper functioning. Some of the fittings, which are normally provided depending upon the size of transformer, are as –

4. Dial type oil temperature gauge.
5. Dial type oil winding temperature gauge.
6. Conservator tank.
7. Silica gel Breather.
8. Pressure relief vent.
9. Buchholz relay.
10. Oil filling, drain valves and plugs.
11. Oil filters valves.
12. Terminal kiosk.
13. Earthing terminal, nameplates, radiators, roller etc.

`Fig 2. Transformer

PROTECTION

 3.1 INTRODUCTION:-

        For 400kv GSS protection for transformer, busbar and transmission line has been duplicated for fast and reliable protection. For this two sets of protection systems are used which will isolate the equipment as quickly as possible even in case of defective tripping. Thus, a local back up protection has been introduced in case there occurs a mechanical or electrical failure during isolating equipment.

Transmission line protection

There are 2 methods which uses-

1. Phase comparison carrier current protection.

2. Distance protection.

System ‘A’ (first main protection)

400kv line is an extra high voltage line so phase comparison carrier current protection is used. It has advantage that it operate instantaneously and it does not need potential transformer and not sensitive phase power swings. Thus, fuse failure not occurs.

System ‘B’ (second main protection)

A twelve element scheme is used with the carrier equipment with distance protection as a unit scheme and fault occurring in the end zone of protected line that wound normally cleared in a relatively low zone 2 not greatly in excess of zone 1.

3.2 RELAYS: -

INTRODUCTION: -

In order to generate the electric power and transmit it to consumer millions of rupees must be spent on power system equipment. These equipment are to work under specified normal conditions. However, a short circuit may occur due to failure of insulation called by:

1. Over voltage due to switching.
2. Over voltage due to direct and indirect lightning strokes.
3. Briding of conductors by birds.
4. Break damage of insulation due to decrease of it’s di-electric strength.
5. Mechanical damage of the equipment. The fault takes place in following properties.

3.3 VARIOUS FAULTS:-

        Phase to phase 20-25%

        Single phase short circuit 50-60%

        double phase S.S. 3-5% 20-25%

        Three phase short circuit 3-5%

        Phase to Phase and Phase to guard 10-15%

Fault may be defined as the rise of current in the several times to normal current, resulting the high temperature rise which can damage the equipment.

It reduces the voltage immediately and considerably.

Basic equipment or Requirement of Protective Relays.

Basic Requirement of protective relays are as follows:

Speed 

Protective relaying should do’s connect a faulty element as quickly as possible.

Selectivity 

The ability of the protective relay to determine the point of which have the fault occurs and select the nearest circuit breaker tripping of which will lead the clearing of fault with min-or so damage to the system.

Sensitivity

It is the capacity of the relaying to operate relay under the actual condition that produces the last operating condition tendency.

Depending upon the method of element connected primary relay (series element connect directly on the circuit of protective element) and secondary relay 9sensing element connected through a current and voltage transformer.

3.4 Types of Relays

These are called normally opened, normally closed in GSS control room there is panel in which the relays are set and there are many types of relays.

1. Over voltage relays
2. Over current relays
3. I.D.M.T. fault relay
4. Earth fault relay
5. Bucheloz’s relay
6. Differential relay

Over voltage relay – This protection is required to avoid damage of system in case line becomes open circuited at one end. These fault would trip the local circuit breaker thus block the local and remote ends. This relay is operated i.e., energized by CVT connected to lines.

Fig 3. Relays on panel

• Over Current relay – This relay has the upper electromagnet of non-directional relay connected in series with lower non-directional electromagnet. When the fault current flow through relay current coil which produces flux in lower magnet of directional element. Thus the directional relay has the winding over the electromagnets of non-directional element and produces a flux in lower magnet and thus over current operates.
• Earth fault relay: - when a conductor breaks due to some reason and it is earthen then earth fault occurs. The fault current is very high thus, there is need to of over current relay. This relay has minimum operating time.

• Directional relay: - It allows to flow the current only in one direction then only this relay operates. It has a winding connected through the voltage coil of relay to lower magnet winding called current coil. Which is energized by C.T. if fault occurs. This relay operates when v/I is less than theoretical value. The v/I is normally constant.

• Differential relay:- This relay operates when phase difference of two electrical quantities exceeds the predetermined value. It has always two electrical quantities; hence in 400kv GSS for transformer differential relay is used.

• Inverse time characteristics relay:- The relay using here having the inverse time characteristics having the time delays dependent upon current value. This characteristic is being available in relay of special design. There are:-

1. Electromagnetic Induction type
2. Permanent magnetic moving coil type
3. Static type

• Buchholz’s relay: - It is the protective device of the transformer. When any fault occurs in the transformer then it indicates about fault and we disconnect the transformer from the circuit. It is used in the power transformer. It is connected between the tank and conservator. It has two floats on which two mercury switch are attached. One float is used for the bell indication and other float is used for the tripping. In the normal position the relay is filled with the oil and contacts of the mercury switch are opened. When the earth fault occurs in the transformer then it increases the temperature of oil and oil flows into the conservator through relay. On the way it makes the contacts of the tripping circuit short. So in the we can say that this relay works as circuit breaker.

Fig 4. Buchholz’s relay

DETAILS OF TECHNICAL AND OTHER OBSERVATIONS

4.1 TRANSMISSION LINES

In this category the extra high voltage lines of 400kV, 220kV, 132kV and 66kV are considered/are used voltage from one grid sub-station to other through six various types conductors.

4.2 THE CONDUCTORS USED FOR

(i)  For 400kV line       : Taran Tulla and Marculla conductor.

(ii) For 220kV line        : Zebra conductor is used composite of Aluminium strands and Steel wires.

(iii) For 132kV line      : Panther conductor is used composite of Aluminium strands and Steel wires.

The material used in these conductors is generally Aluminium Conductor Steel Reinforced (ACSR). The conductors run over the towers cross arms of sufficient height with the consideration to keep safe clearance of sagged conductors from ground level and from the objects (trees, buildings etc.) either side also.

ISOLATOR

5.1 INTRODUCTION: -

          When to carry out inspection or repair in the substation installation a disconnection switch is used called isolator. Its work is to disconnect the unit or section from all other line parts on installation in order to insure the complete safety of staff working. The isolator works at no load condition. They do not have any making or breaking capacity.

  On fundamental basis the isolating switches can broadly divided into following categories: -

1. Bus isolator
2. Line isolator cum earthing switch
3. Transformer isolating switch.

5.2 OPERATION: -

           The operation of an isolator may be hand operated without using any supply or may be power operated which uses externally supplied energy switch which is in the form of electrical energy or energy stored in spring or counter weight.

           In a horizontal break, center rotating double break isolator, 3 strokes are found. Poles are provided on each phase. The two strokes on side are fixed and center one is rotating. The center position can rotate about its vertical axis at an angle of 90. In closed position, the isolating stroke mounts on galvanized steel rolled frame. The three poles corresponding to 3 phases are connected by means of steel shaft.

Isolators are of two types -

1. Single pole isolator
2. Three pole isolator

CIRCUIT BREAKER

6.1 INTRODUCTION:-

        The circuit breaker is one of the important equipment in power system. It protects the system by isolating the faulty section while the healthy one is keep on working. Every system is susceptible to fault or damages while can be caused due to overloading, short-circuiting, earth fault etc. thus to protect the system and isolate the faulty section C.B. are required. Apart from breaking and making contacts, a C.B. should be capable of doing.

1. Continuously carry the maximum current at point of installation.

2. Make and break the circuit under abnormal and normal condition.

3. Close or open the faulty section only where fault exists.

6.2 PRINCIPLE:-

        During making and breaking an arc is struck between the separating contacts which play an important role in interruption process as it provides for the gradual transition from current carrying to voltage withstanding states of contacts, but it is dangerous on account of energy generated in the form of heat which may results in explosive forces. This should be extinguished shortly.

Method of interruption are current:-

1. High resistance interruption

2. Current Zero interruption

In high resistance interruption arc is controlled by subsequently increasing resistance is brought into circuit and are cooled simultaneously so that current is quickly reduced to a value insufficient to maintain the arc.

In current, zero interruption the arc resistance is kept low until the current becomes zero, where the arc extinguishes itself and is prevented from restricting in spite of high restricting voltage.

                                                Fig 5. ABCB breaker

           Fig 6.SF6 Circuit breaker

Lighting Arrestor

7.1 INTRODUCTION:-

        Every instrument must be protected from the damage of lighting stroke. The three protection sin a substation is essential:

• Protection for transmission line from direct strokes.

• Protections of power station or substation from direct strokes.

• Protection of electrical apparatus against traveling waves.

Effective protection of equipment against direct strokes requires a shield to prevent lighting from striking the electrical conductor together with adequate drainage facilities over insulated structure.

Lighting Arrestors: - Lighting arrestor is a device, which protects the overhead lines and other electrical apparatus viz., transformer from overhead voltages and lighting. When the positively charged cloud produce negative charge on the overhead line by electrostatic induction then the negative charge is however presented right under the cloud and portion of the line away from the cloud becomes positively charged. This charge on the line does not flow.

The positive charge on the far and flows to the earth through insulators, thus leaving the negative charge on the line directly under the cloud. Now assume due to the direct discharge occurring between this clouds and passing by negative charge cloud the charge in the cloud becomes neutralized, then the charge on the line is no more bound charge and is free to travel on the both directions in the form of waves. These traveling waves will be of light magnitude and have steep wave front, which can damage the unprotected equipment connected to the line. These waves are passed to the earth through the lighting arrestors.

        It consist of a isolator in series and connected in such a way that long isolator is in upward and short isolator is in downward so that initially large potential up to earth is decreased to zero.

An ideal arrestor must therefore have the following properties:

1. It should be able to drain the surge energy from the line in a minimum time.
2. Should offer high resistance to the flow of power current.
3. Performance of the arresters should be such that no system disturbances are introduced by its operation.
4. Should be always in perfect from to perform the function assigned to it.
5. After allowing the surge to pass, it should close up so as not to permit power current to flow to ground.

                            Fig 7. Lightening Arrestor

POWER LINE CARRIER COMMUNICATION (PLCC)

8.1 Introduction

Power line communication or power line carrier (PLC), also known as Power line Digital Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor also used for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving information bearing signals over power lines.

Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage, and used inside buildings at lower voltages. Powerline communications can be applied at each stage. Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically the transformer prevents propagating the signal so multiple PLC technologies are bridged to form very large networks.

8.2 Basics

All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of powerline communications use different frequency bands, depending on the signal transmission characteristics of the power wiring used. Since the power wiring system was originally intended for transmission of AC power, in conventional use, the power wire circuits have only a limited ability to carry higher frequencies. The propagation problem is a limiting factor for each type of power line communications. A new discovery called E-Line that allows a single power conductor on an overhead power line to operate as a waveguide to provide low attenuation propagation of RF through microwave energy lines while providing information rate of multiple Gbps is an exception to this limitation.

Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz) carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, or telemetry and control circuits with an equivalent data rate of a few hundred bits per second; however, these circuits may be many miles long. Higher data rates generally imply shorter ranges; a local area network operating at millions of bits per second may only cover one floor of an office building, but eliminates installation of dedicated network cabling.

8.3 MAJOR SYSTEM COMPONENTS EQUIPMENT        

 The major components of a PLC channel are shown in Figure. The problem associated with the PLC channel is the requirement to put the carrier signal onto the high voltage line without damaging the carrier equipment. Once the signal is on the power line it must be directed in the proper direction in order for it to be received at the remote line terminal.

                           Fig 8. Basic Power Line Carrier Terminal         

8.4 BASIC PRINCIPLE OF PLCC

 In PLCC the higher mechanical strength and insulation level of high voltage power lines result in increased reliability of communication and lower attenuation over long distances.

 Since telephone communication system cannot be directly connected to the high voltage lines, suitably designed coupling devices have therefore to be employed. These usually consist of high voltage capacitors or capacitor with potential devices used in conjunction with suitable line matching units (LMU’s) for matching the impedance of line to that of the coaxial cable connecting the unit to the PLC transmit-receive equipment.

 Also the carrier currents used for communication have to be prevented from entering the power equipment used in G.S.S as this would result in high attenuation or even complete loss of communication signals when earthed at isolator.. Wave traps usually have one or more suitably designed capacitors connected in parallel with the choke coils so as to resonate at carrier frequencies and thus offers even high impedance to the flow of RF currents.

Fig 9. Power Line Carrier Communication

1. WAVE TRAP                                        5. GROUND SWITCH        
2. COUPLINGCAPACITOR                        6.MATCHINGTRANSFORMER        
3. DRAINAGE COIL                                           7. TUNING CAPACITOR
4. VOLTAGE ARRESTER                              8. VACUUM ARRESTER

8.5 LINE TRAPS or WAVE TRAPS:-

The carrier energy on the transmission line must be directed toward the remote line terminal and not toward the station bus, and it must be isolated from bus impedance variations. This task is performed by the line trap. The line trap is usually a form of a parallel resonant circuit which is tuned to the carrier energy frequency. A parallel resonant circuit has high impedance at its tuned frequency, and it then causes most of the carrier energy to flow toward the remote line terminal. The coil of the line trap provides a low impedance path for the flow of the power frequency energy. Since the power flow is rather large at times, the coil used in a line trap must be large in terms of physical size.

Once the carrier energy is on the power line, any control of the signal has been given over to nature until it reaches the other end. During the process of traveling to the other end the signal is attenuated, and also noise from the environment is added to the signal. At the receiving terminal the signal is decoupled from the power line in much the same way that it was coupled at the transmitting terminal. The signal is then sent to the receivers in the control house via the coaxial cable.

8.6 COUPLING CAPACITORS:-

The coupling capacitor is used as part of the tuning circuit. The coupling capacitor is the device which provides a low

impedance path for the carrier energy to the high voltage line and at the same time, it blocks the power frequency current by being a high impedance path at those frequencies. It can perform its function of dropping line voltage across its capacitance if the low voltage end is at ground potential. Since it is desirable to connect the line tuner output to this low voltage point a device must be used to provide a high impedance path to ground for the carrier signal and a low impedance path for the power frequency current. This device is an inductor and is called a drain coil. The coupling capacitor and drain coil circuit are shown in Figure.

Fig 10.        Coupling Capacitor and Drain Coil Combination

 It is desirable to have the coupling capacitor value as large as possible in order to lower the loss of carrier energy and keep the bandwidth of the coupling system as wide as possible. However, due to the high voltage that must be handled and financial budget limitations, the coupling capacitor values are not as high as one might desire. Technology has enabled suppliers to continually increase the capacitance of the coupling capacitor for the same price thus improving performance.

8.7 DRAINAGE COILS:-

The drainage coil has a pondered iron core that serves to ground the power frequency charging to appear in the output of the unit. The coarse voltage arrester consists of an air gap, which sparks over at about 2 KV and protects the matching unit against line surges. The grounding switch is kept open during normal operation and is closed if anything is to be done on the communication equipment without interruption to power flow on the line. The matching transformer is isolated for 7 to 10 KV between the two winding and former two functions. Firstly it isolates the communication equipment for the power line. Secondly it serves to match the characteristic impedance of the power line 400-600 ohms to that of the co-axial vacuum arrester (which sparks) is over at about 250 V is provided for giving additional protection to the communication equipment.

        The LMU which consists of the matching transformer and tuning capacitors indicated above is tailor-made to suit the individual requirements of the coupling equipment and is generally tuned to a wide band of carrier frequencies-(100-450 KHz typical).

8.8 ADVANTAGES & DISADVANTAGES OF PLCC

ADVANTAGES

1. No separate wires are needed for communication purposes as the power lines themselves carry power as well as the communication signals. Hence the cost of constructing separate telephone lines is saved.

2. When compared with ordinary lines the power lines have appreciably higher mechanical strength. They would normally remain unaffected under the condition which might seriously damage telephone lines.

3. Power lines usually provide the shortest route between the power stations.

4. Power lines have large cross-sectional area resulting in very low resisntanc3 per unit length. Consequently the carrier signal suffers lesser attenuation than when travel on usual telephone lines of equal lengths.

 5. Power lines are well insulated to provide negligible leakage between conductors and ground even in adverse weather conditions.

6. Largest spacing between conductors reduces capacitance which results in smaller attenuation at high frequencies. The large spacing also reduces the cross talk to a considerable extent.

DISADVANTAGES

1. Proper care has to be taken to guard carrier equipment and persons using them against high voltage and currents on the line.

2. Reflections are produced on spur lines connected to high voltage lines. This increases attenuation and create other problems.

3. High voltage lines have transformer connections, which attenuate carrier currents. Sub-station equipments adversely affect the carrier currents.

4. Noise introduced by power lines is much more than in case of telephone lines. This due to the noise generated by discharge across insulators, corona and switching processes.

8.9 Failure Scenarios

There are many ways in which the communication signal may have error introduced into it. Interference, cross chatter, some active devices, and some passive devices all introduce noise or attenuation into the signal. When error becomes significant the devices controlled by the unreliable signal may fail, become inoperative, or operate in an undesirable fashion.

1. Interference: Interference from nearby systems can cause signal degradation as the modem may not be able to determine a specific frequency among many signals in the same bandwidth.

2. Signal Attenuation by Active Devices: Devices such as relays, transistors, and rectifiers create noise in their respective systems, increasing the likelihood of signal degradation.

3. Signal Attenuation by Passive Devices: Transformers and DC-DC converters attenuate the input frequency signal almost completely. "Bypass" devices become necessary for the signal to be passed on to the receiving node. A bypass device may consist of three stages, a filter in series with a protection stage and coupler, placed in parallel with the passive device.

CONTROL ROOM

9.1 Introduction

At NPH not only remote control carry the appropriate means by which circuit breaker may be open or close but also necessary indicating devices, indicating lamps, isolating switching, protective relays, secondary circuit and wires are located here and most important “No load tap changer” for transformer is available. There is a panel for synchronizing. Different panels are located at different stages and on each panel control switch is provided on the board. The control switches for each circuit breaker and isolators are provided on control panel. Colors of signals are synchronized as follows: -

Red      - For circuit breaker or isolator is in closed position.

Green - For circuit breaker is in open position.

Amber - Indicates abnormal condition requiring action.

There are different relays located.

9.2 Announcing section: -This section is always checked by the shift incharge. If any fault or any relay moves from L.T., alarm swings and type of fault is indicated on the announcing box. The most important section is transformer control section, winding temperature indicator. Tap position selector is situated on control panel. A control engineer controls the loading of various lines, outgoing feeders, synchronizing the incoming lines with bus bars.

9.3 Control and relay panel: -The arrangement of control and relay power is such that the indicating apparatus is clearly visible from control place. These respective panels are provided-

• Control and indicating equipment.
• Relay and recording equipment.

 The synchronization switch is put to auto position when condition of synchronizing is satisfied. The white lamp on the top indicating ”synchronizing relay operated” glow and Circuit Breaker is automatically closed. When bus bar is dead there is no need of synchronizing in that case line is connected directly to bus bar by pulling a switch bar dead bus to on position.

Event Logger- to work in control room contain work are automated with computer based control system. By facilitate the operator locating identification and reporting fault, information is received.

 9.4 Supervisory Control and Data Acquire System- for power system operation and control includes-

• Data collection system
• Data transmission telemetric equipment
• Data monitoring equipment
• Man/machine interface

Data collection equipment as data logger collects the primary data from source converts it into suitable form of information and then transmitting and processing data. Logger records the rating from different location in the plant. Data logger is designed for plant performance computation for logical analysis of alarm condition.

 The input scanner is automatic sequence switches, which select each, signal in turn transducers are used to convert original signal in the suitable electrical form for the input of scanner.. Data logger supplies the digitalized data of microprocessor. The signal is fed to the input scanner. The input scanner selects each signal in turn.

9.5 Scanning And Indication- The automatic control necessities a series and checks at regular interval, which provide indication whether and when appropriate action is to be indicated. The scanning gives necessary data regarding the value of various input variables. The decision regarding follow up section is taken according to the program. The logic operation and calculation are performed readily by microprocessor.

                Fig 11. Control panels in control room

9.6 CRT Display- The operation in the control room needs information regarding parameters and configuration according to feeders. It is divided in many parts-

• Indicating system
• Control switches
• Relay section
• Meter section
• Announcing section
• D.C supply system
• Transformer control unit.

             Indicating system is used to indicate total load, bus bar voltage indication of circuit breaker, isolator position. Lever type arrangement for opening and closing of circuit breaker close or open.

                Relay section indicates the position of different relay at different feeder. Fault in any feeder is denoted by corresponding relay that gives alarm signal.

               Master relay gives the signal to the trip coil of circuit breaker and thus faulty feeder is disconnected from supply. Meter section includes different types of meter.

One network CRT display provides operator with following information whenever he works-

Two types of display includes

• Tabulated values of parameter
• Measured values and computed characteristics.

Symbolic representation of equipment states usually in the form of diagram of substation.