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1 
Chapter-1 
INTRODUCTION 
1.1 AN OVERVIEW OF R.S.E.B. 
“Rajasthan State Electricity Board” started working form 1 July, ...
-> Distribution authority for Jodhpur - JVVNL 
-> Distribution authority for Ajmer - AVVNL 
Power obtain from these statio...
3 
Chapter-2 
GRID SUBSTATION 
A substation is a part of an electrical generation, transmission, and distribution system. ...
For economic transmission the voltage should be high so it is necessary to step up the 
generated voltage for transmission...
5 
2. 33 KV Yard 
Fig.2.4 33 KV yard 
There are two bus bars in 132 KV yard and also two bus-bars in 33KV yard. The incomi...
Fig. 2.5 Single Line Diagram of GSS, Sitapura 
6
7 
Chapter-3 
EQUIPMENTS USED IN G.S.S. 
Some equipments are used in the GSS for successful operational breaker & a half s...
8 
Chapter-4 
LIGHTNING ARRESTER 
Lightning arrestor is a device, which protects the overhead lines and other electrical a...
9 
Clearances 
These are given on the drawings. These are the maximum recommended. The term 
‘clearance’ means the actual ...
10 
WORKING 
Lightning, is a form of visible discharge of electricity between rain clouds or between a rain 
cloud and the...
11 
Chapter-5 
CAPACITIVE VOLTAGE TRANSFORMER (C.V.T.) 
CVTs are special king of PTs using capacitors to step down the vol...
12 
Application: 
1) Capacitive voltage transformer can be effectively as potential sources for measuring, 
metering prote...
13 
Chapter-6 
POTENTIAL TRANSFORMER 
Potential Transformer is designed for monitoring single-phase and three-phase power ...
14 
Chapter-7 
ISOLATOR 
Fig.7.1 Isolator 
An isolator switch is part of an electrical circuit and is most often found in ...
Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent 
operation is not possibl...
16 
Chapter-8 
WAVE TRAP 
To communicate between two G.S.S. we use power line itself. Power line carrying 50Hz 
power supp...
Figure-8.1 Wave Trap 
17
18 
Chapter-9 
CIRCUIT BREAKER 
A circuit breaker is an automatically operated electrical switch designed to protect an 
e...
19 
Construction & working: 
The physical size of such units, which contain large arc chutes, quickly makes them 
uneconom...
cooling surface in close proximity to the arc.(iv)The oil used such as transformer oil is a very 
good insulator and allow...
Fig.9.1 SF6 Circuit Breaker 
Rating of SF6 breaker: 
Type: pneumatic operated 
Make: ABB 
Rated Voltage 145KV 
21
Rated normal current 2000A 
Rated Lightning withstand impulse voltage: 650KV 
Rated short circuit breaking current: 31.5KA...
23 
Chapter-10 
CURRENT TRANSFORMER 
When current in a circuit is too high to directly apply to measuring instruments, a c...
The current transformer is mounted one of the power transformer leads; it can be associated 
with an Lv or Hv lead; depend...
25 
Chapter-11 
BUS BAR SYSTEM 
The conductors used 
(i) For 400KV line : Taran Tulla and Marculla conductor. 
(ii) For 13...
26 
Chapter-12 
POWER TRANSFORMER 
A transformer is a device that transfers electrical energy from one circuit to another ...
27 
CORE 
Core is the main part of the transformer It is subjected to magnetic flux For efficient 
operation, it is essent...
layer side parallel to the core axis. The winding using rectangular conductors may be 
simultaneously wound from or more p...
The CT secondary current is chosen to the max ‘hot spot’ winding gradient occurring in 
either Hv or Lv windings of the po...
(c) Terminal block for alarm and contacts of buchholz relay 
(d) Terminal block for oil level alarm and contacts of Magnet...
banks and duplicate oil pumps may be specified. In the larger ODAF cooling designs there 
may be four independent unit coo...
32 
Chapter-13 
RELAY 
A relay is an electrically operated switch Current flowing through the coil of the relay 
creates a...
electromagnets of non-directional element and produces a flux in lower magnet and 
thus over current operates. 
 EARTH FA...
34 
Chapter-14 
INSULATORS 
In order to avoid current leakage to the Earth, through the supporting structure provide to th...
2. Suspension Type:-These insulators hang from the cross arm, there by forming a 
string. For voltages greater than 33 kV,...
Figure-14.4 Shackle Type Insulator 
36
37 
Chapter-15 
POWER LINE CARRIER COMMUNICATION 
15.1 INTRODUCTION 
Power line communication or power line carrier (PLC),...
Also the carrier currents used for communication have to be prevented from entering the 
power equipment used in G.S.S as ...
39 
15.6 DRAINAGE COILS:- 
The drainage coil has a pondered iron core that serves to ground the power frequency 
charging ...
40 
Chapter-16 
CONTROL ROOM 
To remote control of power switch gear requires the provision of suitable control plates 
lo...
Fig.16.1: panel of control room 
 ENERGY METER: - These are fitted on different panel to record transmitted energy 
and r...
42 
Chapter-17 
BATTERY ROOM 
In a GSS, Separate dc supply is maintained for signaling remote position control, alarm 
cir...
43 
 CHARGING OF BATTERIES:- 
It is the first charging given to batteries by which the positive plates are converted to 
...
44 
Chapter-18 
CAPACITOR BANK 
Capacitor banks are used to improve the quality of the electrical supply and the efficient...
45 
Chapter-19 
CONCLUSION 
It was a very good experience of taking vocational training at 132KV GSS Sitapura, Jaipur. 
Al...
46 
Chapter-20 
REFERENCES 
1. Electrical Technology By B.L.Theraja & A.K.Theraja 
2. Power System Protection And Switchge...
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  1. 1. 1 Chapter-1 INTRODUCTION 1.1 AN OVERVIEW OF R.S.E.B. “Rajasthan State Electricity Board” started working form 1 July, 1957. When India becomes independent its overall installed capacity was hardly 1900 mw. During first year plan (1951-1956) this capacity was only 2300 MW. The contribution of Rajasthan state was negligible during 1 & 2 year plans the emphasis was on industrialization for that end it was considered to make the system of the country reliable. Therefore Rajasthan state electricity board came into existence in July 1957. In 1957 RSEB (Rajasthan State Electric Board) is comes in to existence and it satisfactorily work from 1 July 1957 at that time energy level in Rajasthan is very low . The 1st survey for energy capacity in Rajasthan is held in 1989 at that time the total electric energy capacity of Rajasthan is 20116 MW. At that time the main aim of RSEB is to supply electricity to entire Rajasthan in the most economical way. The aim of RSEB is to supply electricity to entire Rajasthan state in the most economical way. Government of Rajasthan on 19th July 2000, issued a gazette notification unbundling Rajasthan State Electricity Board into Rajasthan Rajya Vidyut Utpadan Nigam Ltd (RRVUNL), the generation Company; Rajasthan Rajya Vidyut Prasaran Nigam Ltd, (RRVPNL), the transmission Company and the three regional distribution companies namely Jaipur Vidyut Vitran Nigam Ltd, (JVVNL) Ajmer Vidyut Vitran Nigam Ltd (AVVNL) and Jodhpur Vidyut Vitran Nigam Ltd (JVVNL) The Generation Company owns and operates the thermal power stations at Kota and Suratgarh, Gas based power station at Ramgarh, Hydel power station at Mahi and mini hydel stations in the State The Transmission Company operates all the 400KV, 220 KV, 132 KV and 33KV electricity lines and system in the State. The three distribution Companies operate and maintain the electricity system below 66KV in the State in their respective areas Rajasthan State Electricity Board has been divided in five main parts are:- -> Electricity production authority - RRVUNL -> Electricity transmission authority - RRVPNL -> Distribution authority for Jaipur - JVVNL
  2. 2. -> Distribution authority for Jodhpur - JVVNL -> Distribution authority for Ajmer - AVVNL Power obtain from these stations is transmitted all over Rajasthan with the help of grid stations. Depending on the purpose, substations may be classified as:- 2 1. Step up substation 2. Primary grid substation 3. Secondary substation 4. Distribution substation 5. Bulky supply and industrial substation 6. Mining substation 7. Mobile substation 8. Cinematograph substation Depending on constructional feature substation are classified as:- 1. Outdoor type 2. Indoor type 3. Basement or Underground type 4. Pole mounting open or kilos type
  3. 3. 3 Chapter-2 GRID SUBSTATION A substation is a part of an electrical generation, transmission, and distribution system. A substation is an assembly of apparatus, which transform the characteristics of electrical energy from one form to another say from one voltage level to another level. Hence a substation is an intermediate link between the generating station and consumer. Fig. 2.1: 132 KV GSS Sitapura, Jaipur Fig. 2.2: 132 KV GSS Sitapura, Jaipur
  4. 4. For economic transmission the voltage should be high so it is necessary to step up the generated voltage for transmission and step down transmitted voltage for distribution. For this purpose substations are installed. The normal voltages for transmission are 400KV, 220KV, 132KV and for distribution 33KV, 11KV etc. 2.1 CONSTRUCTIONAL FEATURES OF 132KV GSS SITAPURA, JAIPUR In this substation the power is coming from two lines namely 4 1. 220 KV INDIRA GANDHI NAGAR 2. 220 KV SANGANER Outgoing feeders are 1. 33 KV NRI 2. 33 KV SITAPURA 3. 33 KV PRATAP NAGAR 4. 33 KV MICO 5. 33 KV TIJARIA 6. 33 KV STONE MART 7. 33 KV SEZ I 8. 33 KV SEZ II 9. 33 KV RAMCHANDRAPURA 10. 33 KV GONER 11. 33 KV PRATAP APARTMENT In this substation there are two yards 1. 132 KV Yard Fig.2.3 132 KV yard
  5. 5. 5 2. 33 KV Yard Fig.2.4 33 KV yard There are two bus bars in 132 KV yard and also two bus-bars in 33KV yard. The incoming feeders are connected to bus-bar through circuit breakers, Isolators, LIGHTNING arrestors, current-transformers etc. The bus-bars are to have an arrangement of auxiliary bus So that when some repairing work is to be done an main bus the whole load can be transferred to the auxiliary bus through bus-coupler. In this 132 KV GSS the incoming 132 KV supply is stepped down to 33 KV with the help of transformers which is further supplied to different sub-station according to the load. 132 KV GSS has a large layout consisting of 2 Nos of 40/50 MVA transformers having voltage ratio respectively 132/33 KV in addition to these transformers. And a 250KVA, 33KV/415V Station Transformer gives the supply to the control room and electrical equipment of GSS.
  6. 6. Fig. 2.5 Single Line Diagram of GSS, Sitapura 6
  7. 7. 7 Chapter-3 EQUIPMENTS USED IN G.S.S. Some equipments are used in the GSS for successful operational breaker & a half scheme two buses, they are: 1. LIGHTNING ARRESTER 2. CVT 3. LINE ISOLATOR 4. WAVE TRAP 5. CIRCUIT BREAKER 6. POTENTIAL TRANSFORMER 7. CURRENT TRANSFORMER 8. BUS BARS 9. POWER TRANSFORMER 10. CONTROL AND RELAY PANEL 11. BATTERY CHARGER
  8. 8. 8 Chapter-4 LIGHTNING ARRESTER Lightning arrestor is a device, which protects the overhead lines and other electrical apparatus viz transformer from overhead voltages and Lightning. An electric discharge between cloud and earth, between cloud and the charge centers of the same cloud is known as lightning. The earthing screens and the ground wires can well protect the electrical system against direct lightening strokes but they fail to provide protection against travelling waves which may reach the terminal apparatus. The lightening arrestors or the surge diverters provide protection against such surges. Every instrument must be protected from the damage of Lightning 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 Lightning from striking the electrical conductor together with adequate drainage facilities over insulated structure. Description The Thyrite Alugard Lightning arrester consists of a stack of one or more units connected in series depending on the voltage and the operating condition of the circuit three single pole arresters are required for 3-phase installation. The arresters are single pole design and they are suitable for indoor and out-door service. Each arrester unit consists essentially of permanently sealed Porcelain housing equipped with pressure relief and containing a number of thyrite value-element discs and exclusive locate gaps shunted by Thyrite resistors metal fitting cemented of the housing provide means for bolting arrester units into a stack. Each arrester unit is shipped assembled. No charging or testing operation is required before placing them in service. Installation Location Install arrester electrically as close as possible to the apparatus being protected Line and ground connections should be short and direct Grounding The arrester ground should be connected to the apparatus grounds and the main station ground utilizing a reliable common ground network of low resistance. The efficient operation of the Lightning arrester requires permanent low resistance grounds Station class arresters should be provided with a ground of a value not exceeding five ohms.
  9. 9. 9 Clearances These are given on the drawings. These are the maximum recommended. The term ‘clearance’ means the actual distance between any part of the arrester or disconnecting device at line potential, and any object at ground potential or other phase potential. Arrester voltage The thyrite station-class arrester is designed to limit the surge voltages to a safe value by discharging the surge current to ground; and to interrupt the small power frequency follow current before the first current zero. The arrester rating is a define limit of its ability to interrupt power follow current. It is important, therefore, to assure that the system power frequency voltage from line to ground under any condition switching, fault, overvoltage never exceeds the arrester’s rating. LIGHTENING ARRESTER 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 4.1: L.A. IN SITAPURA G.S.S.
  10. 10. 10 WORKING Lightning, is a form of visible discharge of electricity between rain clouds or between a rain cloud and the earth The electric discharge is seen in the form of a brilliant arc, sometimes several kilometers long, stretching between the discharge points How thunderclouds become charged is not fully understood, but most thunderclouds are negatively charged at the base and positively charged at the top However formed, the negative charge at the base of the cloud induces a positive charge on the earth beneath it, which acts as the second plate of a huge capacitor. When the electrical potential between two clouds or between a cloud and the earth reaches a sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes ionized along a narrow path and a Lightning flash results. Many meteorologists believe that this is how a negative charge is carried to the ground and the total negative charge of the surface of the Earth is maintained. The possibility of discharge is high on tall trees and buildings rather than to ground Buildings are protected from Lightning by metallic Lightning rods extending to the ground from a point above the highest part of the roof The conductor has a pointed edge on one side and the other side is connected to a long thick copper strip which runs down the building The lower end of the strip is properly earthed When Lightning strikes it hits the rod and current flows down through the copper strip These rods form a low-resistance path for the Lightning discharge and prevent it from travelling through the structure itself.
  11. 11. 11 Chapter-5 CAPACITIVE VOLTAGE TRANSFORMER (C.V.T.) CVTs are special king of PTs using capacitors to step down the voltage. A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of voltage transformers would be uneconomical In practice, capacitor C1 is often constructed as a stack of smaller capacitors connected in series This provides a large voltage drop across C1 and a relatively small voltage drop across C2. The CVT is also useful in communication systems CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency This forms a carrier communication network throughout the transmission network . Fig.5.1: capacitor voltage transformer
  12. 12. 12 Application: 1) Capacitive voltage transformer can be effectively as potential sources for measuring, metering protection, carrier communication and other vital functions of an electrical network. 2) Capacitive voltage transformers are constructed in single or multi-unit porcelain housing with their associated magnetic units. For EHV system. 3) In the case of EHV CVTs the multi-unit construction offers a number of advantages easy of transport and storing, Convenience in handling and erection etc. Description: 1) The capacitive voltage transformer comprises of a capacitor divider with its associated Electro-magnetic unit. The divider provides an accurate proportioned voltage, while the magnetic unit transformers this voltage, both in magnitude and to convenient levels suitable for measuring phase metering, protection etc. all W.S.I.capacitor units has metallic bellows to compensate the volumetric expansion of oil inside the porcelain. In the multiunit stack, all the potential point are electrically tied and suitably shielded to overcome the effects of corona, RIV etc. 2) Capacitive voltage transformers are available for system voltage of 33KV to 420KV. 3) Packing and transportation: 3.1) all the capacitor units of capacitive voltage X-mer are securely packed in woolen crates. The electro-magnetic unit form an integral part with the capacitor unit is hermetically associated with the electromagnetic unit; the wooden crate for this is exclusive and is sized heavier taller than for the capacitor unit alone. 3.2) each woolen crate is identified with the corresponding serial number of the unit. 3.3) each capacitor unit has one nameplate designing the rating of the unit Position of the unit in the complete assembly is also indicated in the nameplate by a suffix T or M RATINGS OF CVT:- Insulation Level : 460KV Rated Voltage factor : 1.2/cont. Time : 1.5/30 sec Highest system Voltage : 145KV Primary Voltage : 132/1.732KV Secondary Voltage : 33/1.732KV Weight : 850Kg.
  13. 13. 13 Chapter-6 POTENTIAL TRANSFORMER Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications. The primary terminals can be connected either in line-to-line or in line-to-neutral configuration. Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two fuses. A Potential Transformer is a special type of transformer that allows meters to take readings from electrical service connections with higher voltage (potential) than the meter is normally capable of handling without at potential transformer. 6.1 Potential Transformer Potential transformers are instrument transformers. They have a large number of primary turns and a few number of secondary turns. It is used to control the large value of voltage. Potential Transformer is designed for monitoring single-phase and three-phase power line voltages in power metering applications. The primary terminals can be connected either in line-to-line or in line-to-neutral configuration Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two fuses.
  14. 14. 14 Chapter-7 ISOLATOR Fig.7.1 Isolator An isolator switch is part of an electrical circuit and is most often found in industrial applications. They are commonly fitted to domestic extractor fans when used in bathrooms in the UK. The switch electrically isolates the circuit or circuits that are connected to it. Such a switch is not used normally as an instrument to turn on/off the circuit in the way that a light switch does. Either the switch isolates circuits that are continually powered or is a key element which enables an electrical engineer to safely work on the protected circuit.
  15. 15. Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent operation is not possible (see: Lock).In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated. The major difference between an isolator and a circuit breaker is that an isolator is an off-load device, whereas a circuit breaker is an on-load device. 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: - 15 1. Bus isolator 2. Line isolator cum earthling switch 3. Transformer isolating switch. 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 Construction of Isolator: Isolator for three-phase we provided in such a manner that for each phase one frame of isolator. These three isolator must be operated all together. In each frame, line is connected to terminal stud. Terminal stud is coupled with contact. Contact arm are supported by isolators. Contacts are made or broken by motor operated mechanism. When contact is to be open then both arms are rotated in opposite direction, so that contact is broken. Same time earthing pole moves upward to make contact with a female contact situated adjoined to terminal stud. Hence, that terminal gets earthen. On these criteria isolator can be carried out manually but for quick operation motor is used.
  16. 16. 16 Chapter-8 WAVE TRAP To communicate between two G.S.S. we use power line itself. Power line carrying 50Hz power supply also carries communication signals at high frequency. Wave Trap is a device used for this purpose. It traps the frequency of desired level for communication and sends it to P.L.C.C. department. It is used to trap the communication signals & send PLCC room through CVT. Rejection filters are known as the line traps consisting of a parallel resonant circuit ( L and C in parallel) tuned to the carrier frequency are connected in series at each and of the protected line such a circuit offer high impedance to the flow of carrier frequency current thus preventing the dissipation. The carrier current used for PLC Communication have to be prevented from entering the power equipments such as attenuation or even complete loss of communication signals. For this purpose wave trap or line trap are used between transmission line and power station equipment to avoid carrier power dissipation in the power plant reduce cross talks with other PLC Circuits connected to the same power station. Ensure proper operating conditions and signal levels at the PLC transmit receive equipment irrespective of switching conditions of the power circuit and equipments in the stations. Line Matching Filter & Protective Equipments For matching the transmitter and receiver unit to coupling capacitor and power line matching filters are provided. These flitters normally have air corral transformers with capacitor assumed. The matching transformer is insulated for 7-10 KV between the two windings and perform two functions. Firstly, it isolates the communication equipment from the power line. Secondly, it serves to match. Transmitter:- The transmitter consists of an oscillator and an amplifier. The oscillator generates a frequency signal within 50 to 500 HZ frequency bands the transmitter is provided so that it modulates the carrier with protective signal. The modulation process usually involves taking one half cycle of 50 HZ signal and using this to create block to carrier. Receivers:- The receivers usually consist of and alternate matching transformer band pass filter and amplifier detector. The amplifier detector converts a small incoming signal in to a signal capable of operating a relatively intensive carrier receiver relay. The transmitter and receiver at the two ends of protected each corresponds to local as far as transmitting.
  17. 17. Figure-8.1 Wave Trap 17
  18. 18. 18 Chapter-9 CIRCUIT BREAKER A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city. In any circuit, carrying a large amount of current, if a contact is opened then normally a spark is produced due to fact that current traverses its path through air gap Arcing is harmful as it can damage precious equipment media are provided between contacts. This 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 There are different arc quenching media:- 1) Air blast 2) Oil 3) SF6 gas 4) Vacuum In 132 KV GSS, SF6 gas circuit breaker are used, as for greater capacity GSS SF6 type breakers are very efficient. 9.1 AIR BLAST CIRCUIT BREAKER Air blast circuit breakers are normally only used at low voltage levels but are available with high current ratings up to 6000 A and short circuit ratings up to 100 kA at 500V.The air blast circuit breakers according to type of flow of blast of compressed air around the contacts are three namely (i) Axial (ii) Radial (iii) cross flow of blast air type.
  19. 19. 19 Construction & working: The physical size of such units, which contain large arc chutes, quickly makes them uneconomic as voltages increase above 3.6KV. Their simplicity stems from the fact that they use ambient air as the arc quenching medium. As the circuit breaker contacts open the arc is formed and encouraged by strong thermal convection effects and electromagnetic forces to stretch across splitter plates. The elongation assists cooling and deionization of the air/contact metallic vapor mixture. The long arc resistance also improves the arc power factor and therefore aids arc extinction at current zero as current and circuit breaker voltage are more in phase. Transient recovery voltage oscillations are also damped thus reducing over voltages. Arc products must be carefully vented away from the main contact area and out of the switchgear enclosure. As we know many MCB and MCCB low-voltage current limiting devices are only designed to have a limited ability to repeatedly interrupt short circuit currents. Care must therefore be taken when specifying such devices. Air circuit breaker with fully repeatable high short circuit capability as typically found in a primary substation auxiliary supply switchboard. 9.2 OIL CIRCUIT BREAKER Mineral oil has good dielectric strength and thermal conductive properties. Its insulation level is, however, dependent upon the level of impurities. Therefore regular checks on oil quality are necessary in order to ensure satisfactory circuit breaker or oil-immersed switch performance. Carbon deposits form in the oil (especially after heavy short circuit interrupting duties) as a result of decomposition under the arcing process. Oil oxygen instability, characterized by the formation of acids and sludge, must be minimized if cooling properties are to be maintained. Insulation strength is particularly dependent upon oil moisture content. The oil should be carefully dried and filtered before use. Oil has a coefficient of expansion of about 0.0008per°C and care must be taken to ensure correct equipment oil levels. The oil can be moved into arc zone after the current reaches zero by the following actions. (i)By the pressure caused by the natural head of the oil, (ii) By the pressure generated by the action of the arc itself (iii) by the pressure caused by external means. Thus the oil circuit breakers may be classified as: (i)Plain break oil circuit breakers. (ii) Self blast or self-generated or arc control oil circuit oil circuit breakers. (iii) Externally generated pressure oil circuit breakers of forced blast oil circuit breakers or impulse oil circuit breakers. Oil, as an arc quenching medium, has the following advantages and dis-advantages. Advantage:- (i)arc energy is absorbed in decomposing of oil (ii)The gas formed, which is mainly hydrogen have a high diffusion rate and high head absorption in changing from the diatomic to monotonic state and thus provides good cooling properties. (iii)Surrounding oil presents the
  20. 20. cooling surface in close proximity to the arc.(iv)The oil used such as transformer oil is a very good insulator and allows smaller cleaner between live conductors and earth components.(v)The oil has ability to flow into the arc space after current is zero. Disadvantage:- (i)There is a risk of formation of explosive mixture with air(ii)Oil is easily in flammable and may causes fire hazards(iii)Owing to formation of carbon particles in the oil due to heat, the oil is to be kept clean and thus requires periodical replacement. 20 9.3 SF6 BREAKER The outstanding physical and chemical properties of SF6 gas makes it an ideal dielectric media for use in power switchgear. These properties of SF6 gas makes it an ideal dielectric media for use in power switchgear, these properties are included: 1) High dielectric strength 2) Unique arc quenching ability 3) Excellent thermal stability 4) Good thermal conductivity In addition, at normal temperature SF6 is chemically inert, inflammable, noncorrosive and non-condensable at low temperatures. Working of circuit breaker: Interrupter unit fixed contacts that are connected through a moving contact. Fixed contacts are of rod shape. There contacts are known as male contacts. In closed position, fixed contacts are joined by a moving contact known as female contact. This female contact is of hollow cylindrical shape. Main parts of female contacts are blast cylinder, contact tube and guide tube. In closed position female contact overlaps male contacts. Contact tube shorts two made contacts and current completes its path from one male contact to another through contact. Counteracting piston moves towards contact compressing the SF6 present in blast cylinder. When it is required to open the contacts then piston is forced to move vertically download by hydraulic or pneumatic pressure. This piston pulls operating rod pulls blast cylinder using bell and crank mechanism. Contact tube moves away from contact. Counteracting piston moves towards contact compressing the SF6 present in blast cylinder. When contact between male and female contacts is just going to break. Then counteracting piston reaches its extreme position performing maximum compression of SF6 gas .when arc is produced, SF6 at very high pressure quenches the arc.
  21. 21. Fig.9.1 SF6 Circuit Breaker Rating of SF6 breaker: Type: pneumatic operated Make: ABB Rated Voltage 145KV 21
  22. 22. Rated normal current 2000A Rated Lightning withstand impulse voltage: 650KV Rated short circuit breaking current: 31.5KA Rated short time withstand current and duration: 31.5KA, 3 sec. Rated line charging, breaking current: 50A Rated SF6 gas pressure at 200c (abs.): 7.0bar Closing and opening device supply voltage: 110Vdc Auxiliary circuit supply voltage: 240Vac Rated air pressure: 22bar Rated frequency: 50Hz Maximum weight: 1750Kg. 22 9.4 Vacuum Circuit Breaker Vacuum interrupter tubes or ‘bottles’ with ceramic and metal casings are evacuated to pressures of some 10-6 to 10-9 bar to achieve high dielectric strength. The contact separation required at such low pressures is only some 0 to 20mm and low energy mechanisms may be used to operate the contacts through expandable bellows. Below figure shows a cut away view of such a device. The engineering technology required to make a reliable vacuum interrupter revolves around the contact design. Interruption of a short circuit current. Figure 9.2 vacuum circuit breaker
  23. 23. 23 Chapter-10 CURRENT TRANSFORMER When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high. Current transformer is an instrument transformer which is mainly used for measuring currents where very high currents are flowing. According to the construction of the current transformer the primary winding of transformer is in series with high current carrying line & measuring instrument is connected to the secondary. Figure 10.1 CURRENT TRANSFORMER
  24. 24. The current transformer is mounted one of the power transformer leads; it can be associated with an Lv or Hv lead; depending on voltage and current consideration. A section of the lead is demountable locally to enable the current transformer to removed, should the necessity arise, without disturbing the main connection. The secondary of CT is connected to the heating coil directly located under the main cover in the oil. On the larger transformers the various connections may be brought up to terminals in the main the cover for external linkage. 24 RATINGS OF CT:- Frequency : 50 Hz Highest System Voltage : 145 KV Short Time Current : 40KA Rated Current : 600A Current ratio : 600-300-150/1 Min. Knee Potential Voltage : 850 V at 150/1 Max. Exciting Current : 100MA at 150/1 Max. Sec. Winding Resistance: 2.5 ohm at 150/1
  25. 25. 25 Chapter-11 BUS BAR SYSTEM The conductors used (i) For 400KV line : Taran Tulla and Marculla conductor. (ii) For 132KV 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. Figure 11.1 Bus bar This bus bar arrangement is very useful for working purpose as every GSS. It is a conductor to which a number of cut .Are connected in 132 KV GSS there are two bus running parallel to the each other, one is main and another is auxiliary bus is only for standby, in case of failure of one we can keep the supply continues. If more loads are coming at the GSS then we can disconnect any feeder through circuit breaker which is connected to the bus bar. This remaining all the feeders will be in running position .if we want to work with any human damage. In this case all the feeders will be on conditions. According to bus voltage the material is used .Al is used because of the property & features and it is cheap.
  26. 26. 26 Chapter-12 POWER TRANSFORMER A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductor -the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electro-motive force, or voltage in the secondary winding this effect is called mutual induction If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. By appropriate selection of the ratio of turns, a transformer thus allows an alternating current voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np Fig.12.1: POWER TRANSFORMER Very high cost of transformers is due to three parts:- 1) CORE 2) WINDING 3) OIL Now we describe the three major parts of transformer
  27. 27. 27 CORE Core is the main part of the transformer It is subjected to magnetic flux For efficient operation, it is essential that the core of transformer must be constructed from laminated magnetic material of low hysteresis loss and high permeability Transformers for use at power or audio frequencies typically have cores made of high permeability silicon The steel has permeability many times that of space and the core thus serves to greatly reduce the magnetizing current, and confine the flux to a path which closely couples the windings Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude Thinner laminations reduce losses, but are more laborious and expensive to construct Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz. A steel core's remanence means that it retains a static magnetic field when power is removed When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied alternating current Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to passion transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. WINDING:- Core type transformers use concentric type of winding Each limb is wound with a group of coil consisting of both primary and secondary winding, which are concentric to each other Low voltage winding is placed near to the core (which is at earth potential) and high voltage winding is placed outside, however L T and H T windings are inter-leaved to reduce the leakage reactance. It is found that the magnetic properties of transformer sheet steel vary in accordance with the direction of the grain oriented by rolling, sheet are cut as far as possible along the grain which is the direction in which the material has a higher permeability It must be made In building the core, considerable pressure is used to minimize air gaps between the plates, which would constitute avoiding loosed of area and might contribute to noisy operation The reduction of core sectional area due to presence of insulating material is of the order of 10%. The winding is layered type and used either rectangular or round conductors. In a cylindrical winding. Using rectangular conductor, the conductors are wound on the flat side with three-
  28. 28. layer side parallel to the core axis. The winding using rectangular conductors may be simultaneously wound from or more parallel conductors. The layered winding may have conductors wound in one, two or more layers and is therefore accordingly called one, two or multi- layer winding. The windings using rectangular conductors are usually two layered because this case it is easier to secure the lead out ends. The windings designed for heavy currents are wound with a number of conductors connected in parallel located side by side in one layer. The parallel conductors have the same length and are located in the magnetic field or almost the same flux density and hence it is not necessary to make any transposition of conductors. A wedged shaped packing is used at each of two entrance ends of winding in order to level it, the packing is made of press bar strips. Cylindrical winding using circular conductors are multi layered. They are wound on a solid paper Bakelite cylinder. 28 TRANSFOMER OIL: Oil in transformers construction, serves the double purpose of cooling and insulating. For use in transformer tank, oil has to fulfil certain specifications and must be carefully selected. All type of oils are good insulators. Animal oil are good insulator but they are too viscous that they tend to form fatty acids, which attack fibrous materials (e.g. Cotton) and therefore are undesirable for transformers. Vegetable oils are opt to be inconsistent in quality and like animal oils, tend to form to form destructive fatty acids. Mineral oils are suitable for electric purpose; some have a bituminous and other have a paraffin base. The crude oil as tapped, is distilling producing a range of volatile spirits and oils ranging from the very light to the heavy paraffin wax or bitumen.  Viscosity:  Insulating properties:  Flash point:  Fire point:  Slugging TRANSFORMER- ACCESSORIES  WINDING TEMPERATURE INDICATOR Winding temperature indicator consists essentially of a current transformer and a thermal unit comprising a heating coil and a thermometric device. The thermal unit, which is designed to have a thermal performance similar to that of the win windings of the power X-mer, is influenced by two factors: (1) The temperature of the surrounding oil, and (2) The current flowing through the heater coil, which will raise the temperature of the unit above that of the surrounding oil.
  29. 29. The CT secondary current is chosen to the max ‘hot spot’ winding gradient occurring in either Hv or Lv windings of the power transformer. Thus the thermal unit’s capable of simulating the hottest-spot temperature of the transformer windings under al conditions. 29  THERMAL DEVICE The bulb of a capillary type dial thermometer is screwed into a blind pocket, which is fitted inside the heating coil. This type of pocket enables the dial thermometer to be removed from the transformer without having to lower the oil level. The heating coil with its blind type pocket fitted inside is supported independently under the cover of the transformer; hence it is always in the hottest oil. The dial thermometer is provided with one or more sets of contacts for alarm/ or trip circuit and at time for controlling cooking equipment when forced cooling is called for.  OIL TEMPERATURE INDICATOR An oil temperature indicator has been provided for measuring the transformer top oil temperature. The heat sensitive device of the thermometer is placed in an oil pocket mounted at the transformer cover, the thermometer has two adjustable mercury contacts and a maximum reading pointer. The contact may be used to close circuit for alarm and tripping device. The mercury switches are accessible by removing the top cover of the instrument and are adjustable for different temperature ratings by location of the mount a repeater dial is for remote indication of the oil temperature in the control room. The thermometer is housed in the marshalling box.  OIL SURGE REALY FOR OLTC GEAR An oil- operated relay having one set of contracts is designed to trip the transformer between the oil conservator. The relay is designed to trip the transformer on the occurrence of violent oil surges arising out of any malfunction in the OLTC operation. The conservator for the OLTC gear is separate from the main transformer conservator forms the conservator forms the conservator for the OLTC the terminals from the relay are wired to the terminal block located in the marshalling box.  MARSHALLING BOX The marshalling box is of sheet steel, weatherproof construction, mounted on the side of the transformer. It is provided with a hinged door and pad lock, and housed the following instrument and terminal block:- (a) Winding temperature indicator (b) Oil temperature indicator
  30. 30. (c) Terminal block for alarm and contacts of buchholz relay (d) Terminal block for oil level alarm and contacts of Magnetic oil level Gauge. 30 (f) Heater with switch (g) Magnetic oil gauge The oil level gauge is mounted on the flat end of the con servitor. The indicator reads the oil level inside the conservator and initiates an alarm by closing the mercury contacts switch when the oil level is below the predetermined minimum. The contacts from the oil level gauge are wired to the terminal block located in the marshaling box. (h) Cooling equipment The transformer having mixed cooling ONAF and ONAF is provided with detachable radiators foxed to the tank wall through valves. The ONAF cooling equipment comprises of four 457 mm dia fans, each blowing 3600 cu.ft. Of air per minute on the radiator element directed in such a way that the no longer effective they turn pink. At the bottom of the breather a cup containing the transformer oil is screwed this oil acts as a seal, preventing the crystals from absorbing moisture except when breathing is taking place.  COOLING PLANT Oil cooling is normally achieved by heat exchange to the surrounding air. Sometimes a water jacket acts as the secondary cooling medium. Fans may be mounted directly onto the radiators and it is customary to use a number of separate fans rather than one or two large fans. Oil pumps for OFAF cooling are mounted in the return pipe at the bottom of the radiators. The motors driving the pumps often use the transformer oil as their cooling medium. With ODAF cooling, the oil-to-air coolers tend to be compact and use relatively large fan blowers. With this arrangement the cooling effectiveness is very dependent on proper operation of the fans and oil pumps since the small amount of Cooling surface area gives relatively poor cooling by natural convection alone. Water cooling (ODWF) has similar characteristics to the ODAF cooling described above and is sometimes found in power station situations where ample and well-maintained supplies of cooling water are available. Cooling effectiveness is dependent upon the flow of cooling water and therefore on proper operation of the water pumps. Natural cooling with the out-of-service water pumps is very limited. Operational experience has not always been good, with corrosion and leakage problems, and the complexity of water pumps, pipes, valves and flow monitoring equipment. The ODAF arrangement is probably favorable as a replacement for the ODWF designs. Double wall cooler pipes give added protection against water leakage. The inner tube carries the water and any leakage into the outer tube is detected and causes an alarm. This more secure arrangement is at the expense of slightly reduced heat transfer for a given pipe size. Normal practice with cooling plant is to duplicate systems so that a failure of one need not directly affect operation of the transformer. Two separate radiators or radiator
  31. 31. banks and duplicate oil pumps may be specified. In the larger ODAF cooling designs there may be four independent unit coolers giving a degree of redundancy. The transformer may be rated for full output with three out of the four coolers in service. Dry type transformers will normally be naturally air-cooled (classification AN) or incorporate fans (classification AF). 31  TAPPINGS AND TAP CHANGER The transformer has an on load tap changer to cater for a variation of +5% to -15% in the HV voltage in 14 equal steps of 1.43% each for a constant power output. The tappings from the HV tapping winding are connected to a 15 position ‘66’KV Crompton greaves make high-speed resistor transition on load tap-changer. The tap-changer may be either manually operated or motor driven. The motor driving mechanism is also described in the leaflet and is arranged for the following types of control.  Local electrical independent  Remote electrical independent  Remote electrical group parallel control Tap changer is used to change the HV voltage. We use tap changer in HV side only because in HV side current is less hence it is easy to handle lower amount of current. Tap changers are of two types. 1) No Load Tap changer 2) On Load tap changer No Load Tap changer in this type tap changer, we have to cut off load before changing the taps. These kinds of tap changer are used in small transformers only. On Load tap changer In this type tap changer load remains connected to transformer while changing the taps. This kind of tap changer requires special construction. Tapping winding is placed over HV winding. Generally, tapping winding is divided in 6 parts by the combination of these 6 winding and HV winding 17 different tap positions are used.
  32. 32. 32 Chapter-13 RELAY A relay is an electrically operated switch Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches Relays allow one circuit to switch a second circuit which can be completely separate from the first For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification. Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. 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. Buchholz’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.  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
  33. 33. 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 flowing 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:- i. Electromagnetic Induction type ii. Permanent magnetic moving coil type 33 iii. 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 we can say that this relay works as circuit breaker .
  34. 34. 34 Chapter-14 INSULATORS In order to avoid current leakage to the Earth, through the supporting structure provide to the conductor of overhead transmission lines, insulators are used. The conductors are secured to the supporting structures by means of insulating feature, which do not allow current to flow through these support and hence finally to the earth . Bus support insulators are porcelain or fiberglass insulators that serve to the bus bar switches and other support structures and to prevent leakage current from flowing through the structure or to ground. These insulators are similar in function to other insulator used in substations and transmission poles and towers. An Insulator should have following characteristic:- High Insulation resistance. 1. High mechanical strength 2. No internal impurity or crack Disc Generally Porcelain or glass is used as material for insulators. Porcelain because of its low cost.is more common. Insulators can be classified in following ways:- 1. Pin Type: - These are designed to be mounted on a pin, which in turn is installed on the cross arm of a pole. As the name suggests, the pin type insulator is mounted on a pin on the cross-arm on the pole. There is a groove on the upper end of the insulator. The conductor passes through this groove and is tied to the insulator with annealed wire of the same material as the conductor. Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky and hence uneconomical. Figure-14.1 Pin Type Insulator
  35. 35. 2. Suspension Type:-These insulators hang from the cross arm, there by forming a string. For voltages greater than 33 kV, it is a usual practice to use suspension type insulators shown in Figure. Consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. The number of disc units used depends on the voltage. Figure-14.2 Suspension Type Insulator 3. Strain insulator - A dead end or anchor pole or tower is used where a straight section of line ends, or angles off in another direction. These poles must withstand the lateral (horizontal) tension of the long straight section of wire. In order to support this lateral load, strain insulators are used. For low voltage lines (less than 11 kV), shackle insulators are used as strain insulators. However, for high voltage transmission lines, strings of cap-and-pin (disc) insulators are used, attached to the cross arm in a horizontal direction. When the tension load in lines is exceedingly high, such as at long river spans, two or more strings are used in parallel. Figure-14.3 Strain Type Insulator 4. Shackle insulator - In early days, the shackle insulators were used as strain insulators. But now a day, they are frequently used for low voltage distribution lines. Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm. 35
  36. 36. Figure-14.4 Shackle Type Insulator 36
  37. 37. 37 Chapter-15 POWER LINE CARRIER COMMUNICATION 15.1 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. Power line 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. All power line communications systems operate by impressing a modulated carrier signal on the wiring system. Different types of power line 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. 15.2 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. 15.3 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.
  38. 38. 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. 38 15.4 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. 15.5 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. 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.
  39. 39. 39 15.6 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. 15.7 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.
  40. 40. 40 Chapter-16 CONTROL ROOM To remote control of power switch gear requires the provision of suitable control plates located at a suitable point remote from immediate vicinity of CB’s and other equipments. In GSS the separate control room provided for remote protection of 132KV switch yards transformer incoming feeder, outing feeders. Bus bar has their own control plant in their control rooms. The control panel carrier the appropriate relays. Necessary meters indicating lamp control switches and fuses. There are meters for reading purpose. A circuit concerning the panel is shown on the panel with standard colour. On each panel a control switch is provided for remote operation of circuit breaker. There are two indicators which show that weather circuit breaker is closed or open. A control switch for each insulator is also provided. The position indicator of isolator is also done with the help of single lamp and indicator. The colour of signal lamps are as follows:-  Red:- for circuit breaker or isolator is close option  Green - for circuit breaker is in open position.  Amber - indicates abnormal condition requiring action. In addition to used indication an alarm is also providing for indicating abnormal condition when any protective relay or tripping relay has operated. Its constants energies on auxiliary alarm. Relay which on operation completes the alarm belt circuit. Synchronizing:- There is a hinged Synchronizing panel mounted at the end of control panel. Before coupling any incoming feeders to the bus bar. It just be synchronized with switches. When the synchronous copy shows zero we close the circuit breaker. Synchronoscope is used to determine the correct instant of closing the switch which connect the new supply to bus bar. The correct instant of synchronizing when bus bar incoming voltage. 1. Are in phase 2. Are equal in magnitude 3. Are in some phase sequence 4. Having same frequency 5. The voltage can be checked by voltmeter the function of synchronoscope is to indicate the difference in phase and frequency.
  41. 41. Fig.16.1: panel of control room  ENERGY METER: - These are fitted on different panel to record transmitted energy and recorded in energy hours. For this purpose MWH meter have been provided.  WATT METER: - This is mounted on each feeder panel to record import or export 41 power.  FREQUENCY METER: - Provided to each feeder to measure frequency which analog or digital.  VOLT METER: - Provided on each panel or the purpose of indication of voltage.  AMMETER: - These are used to indication the line current.  MVAR METER: - Provided for indicating power factor of import and export.  MAXIMUM INDICATOR DEMAND: - Chief requirement of these indicators to record the minimum power factor taken by feeder during a particular period. This record the average power successive predetermined period.
  42. 42. 42 Chapter-17 BATTERY ROOM In a GSS, Separate dc supply is maintained for signaling remote position control, alarm circuit etc. There is a battery room which has 55 batteries of 2 volt. Therefore D.C. power available is for functioning of the control panels. A battery charger to charge the battery. Various parts of lead acid batteries:- Fig.17.1: a view of battery room 1. Plates 2. Separators 3. Electrolyte 4. Container 5. Terminal port 6. Vent plugs
  43. 43. 43  CHARGING OF BATTERIES:- It is the first charging given to batteries by which the positive plates are converted to “lead peroxide”, whereas the –ve plates will converted to spongy lead. Also in a fully charged battery the electrolyte specific gravity will be at its highest venue of 1.2.  DISCHARGING:- When a fully charged battery delivers its energy out by meeting a load the lead peroxide of the +ve plates slowly gets converted to lead sulphate and the spongy lead of the –ve plates also gets converted into lead sulphate during this time the specific gravity of the electrolyte also decreases the value around 1.00 and the terminal voltage also decreases from its initial to a lower value which may be around 1.85 or 1.8.
  44. 44. 44 Chapter-18 CAPACITOR BANK Capacitor banks are used to improve the quality of the electrical supply and the efficient operation of the power system. Studies show that a flat voltage profile on the system can significantly reduce line losses. Capacitor banks are relatively inexpensive and can be easily installed anywhere on the network. Fig.18.1:- CAPACITOR BANK The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series connected groups, within a steel enclosure. The internal discharge device is a resistor that reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a variety of voltage ratings (240 V to 24940V) and sizes (2.5 KVAR to about 1000 KVAR).capacitor bank used for 33 KV at GSS has 2 units of 7.2 MVAR.
  45. 45. 45 Chapter-19 CONCLUSION It was a very good experience of taking vocational training at 132KV GSS Sitapura, Jaipur. All the Employees working there were very helpful and were always ready to guide us. They gave their best to make us understand. The Assistant Engineer, Junior Engineer & Technicians gave us the detailed theory. Training at 132KV GSS Sitapura, Jaipur gives the insight of the real instruments used. There are many instruments like transformer, CT, PT, CVT, LA, Relay, PLCC, Bus Bars, Capacitor bank, Insulator, Isolator, Control Room, and Battery Room etc. The training at grid substation was very helpful. It has improved my theoretical concepts of electrical power transmission and distribution. Protection of various apparatus was a great thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc. was observable. I had a chance to see the remote control of the equipments from control room itself, which was very interesting. All in all the training at 132KV GSS Sitapura, Jaipur was a memorable experience.
  46. 46. 46 Chapter-20 REFERENCES 1. Electrical Technology By B.L.Theraja & A.K.Theraja 2. Power System Protection And Switchgear By Badri Ram & D N Vishwakarma 3. Power System By J.B.Gupta 4. http://electricalpowerengineering.blogspot.in 5. http://www.electrical4u.com/ 6. http://en.wikipedia.org/wiki/Insulator_(electricity) 7. http://www.engineersgarage.com/articles/plcc-power-line-carrier-communication 8. Electrical Machine By P.S.bhimbra
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132kv Gss report of sitapura jaipur

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