INDUSTRIAL TRAINING REPORT UNDERTAKEN AT “
220 KV GSS, IG NAGAR, JAIPUR
”
SUBMITTED TO DEPARTMENT OF ELECTRICAL ENGINEERING MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY
PARTIAL FULFILMENT OF B.TECH IN ELECTRICAL ENGINEERING SUBMITTED BY MOHIT BHAVSAR 2009UEE268
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Acknowledgement “An engineer with only theoretical knowledge is not a complete engineer.
Practical training is very important to develop and apply engineer skills.”It is a technical report of practical training at Rajasthan Rajya Vidhyut Prasaran Nigam LTD. It was of 45 days days from 17/05/2012 17/05/2012 to 30/06/2012 and taken at 220KV G.S.S. IG Nagar, Jaipur. I feel immense pleasure in conveying my heartiest thanks and deep sense of gratitude to Prof. K. R. Niazi, Head of the Electrical Engineering Department of Malaviya National Insti Institute tute of Technology for his efforts and for technical as well as moral support. I feel indebted to express my heartiest thanks and gratitude to Mr. D.C. Sharma(XEn) and Mr.Jitendra Khanna(AEn), for their valuable time, learned guidance, kind, candid, wise and illuminating advice during tr aining period. I am also thankful to our instructors and other technical and non technical staff, for helping in understanding the various aspects and constructional details of work and site in 220KV G.S.S. IG Nagar, Jaipur. It may not be possible for me to acknowledge the contribution of all my friends, but I am thankful to all those who came forward to help me. I express my sincere thanks to my colleagues and other trainees tr ainees for their valuable ideas and support during practical training.
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CONTENT:-
S. No.
TOPIC
Page No.
1
INTRODUCTION
4
2
LIGHTNING ARRESTOR
8
3
BUS BARS
9
4
INSULATOR
11
5
ISOLATORS
12
6
CIRCUIT BREAKER
14
7
PROTECTIVE RELAY
18
8
POWER TRANSFORMER
20
9
CURRENT TRANSFORMER
25
10
POTENTIAL TRANSFOMER
26
11
CVT
28
12
CONTROL ROOM
29
13
CAPACITOR BANK
33
14
PLCC
34
15
EARTHING SYSTEM
36
16
BATTERY ROOM
38
17
GIS
39
18
RATINGS
45
19
CONCLUSION
48
20
REFERENCE
49
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CHAPTER 1 INTRODUCTION Electrical power is generated, transmitted in the form of alternating current. The electric power produced at the power stations is delivered to the consumers through a large network of transmission & distribution. The transmission network is inevitable long and high power lines are necessary to maintain a huge block of power source of generation to the load centers to inter connected. Power house for increased i ncreased reliability of supply greater. The assembly of apparatus used to change some characteristics (e.g. voltage, ac to dc, frequency, power factor etc.) of electric supply keeping the power constant is called a substation. An electrical substation is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps.
Fig.1 - 220 KV GSS IGN Substations have switching, protection and control equipment and one or more transformers. In a large substation, circuit breaker are used to interrupt any short-circuits or overload currents that may occur on the network. 4
Depending on the constructional feature, the high voltage substations may be further subdivided:
(a) Outdoor substation (b) Indoor substation (c) Base or Underground substation
1.1) 220KV Grid Substation, Indira Gandhi Nagar: Its part of RRVPNL. It is situated about 8km away from Jaipur. The power mainly comes from two incoming feeders of 220KV (Heerapura) & 220KV (Bassi). The substation is equipped with various equipments and there are various arrangements for the protection purpose. The equipments in the GSS are listed previously. At this substation following feeders are established. 1. TIE FEEDERS 2. RADIAL FEEDERS 220KV GSS INDIRA GANDHI NAGAR is an outdoor type primary substation and distribution as well it has not only step down but t he distribution work The electrical work in a substation comprises to : 1.
Choice of bus bar arrangement layout.
2.
Selection of rating of isolator.
3.
Selection of rating of instrument transformer.
4.
Selection of rating of C.B.
5.
Selection of lighting arrester [LA]
6.
Selection of rating of power transformer
7.
Selection of protective relaying scheme, control and relay boards.
8.
Selection of voltage regulator equipment.
9.
Design a layout of earthing grids and protection against lightening stockes.
1.2 INCOMING FEEDERS:
1. 220KV Heerapura 2. 220KV Bassi 3. 220 KV Puranaghat (Dead)
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1.3 OUTGOING FEEDERS:
The outgoing feeders of 132KV are: 91. PURANAGHAT 2. SITAPURA 3. MNIT (Future Line- under construction) The outgoing feeders of 33KV are: 1. JAGATPURA 2. MAHEL 3. INDIRA GANDHI NAGAR 4. BISALPUR 5. PRADHAN MARG 6. S/S SUPPLY 7. DEAD Rajasthan Rajya Vidyut Prasaran Nigam Limited (RRVPNL) a company under the Companies Act, 1956 and registered with Registrar of Companies as "RAJASTHAN RAJYA VIDYUT PRASARAN NIGAM LIMITED" vide No. 17-016485 of 2000-2001 with its Registered Office at VIDYUT BHAWAN, JYOTI NAGAR, JAIPUR-302005 has been established on 19 July, 2000 by Govt. of Rajasthan under the provisions of the Rajasthan Power Sector Reform act 1999 as the successor company of RSEB. The RERC has granted RRVPNL a license for transmission and bulk supply vide RERC/Transmission and Bulk Supply License 4/2001 dated 30. Our aim is to provide reliable electric transmission service to these customers. As a public utility whose infrastructure serves as the link in transporting electricity to millions of electricity users, RRVPNL has following duties and responsibilities: • Intra state transmission of electricity through Intra-State Transmission System. • Ensuring development of an efficient, coordinated and economical system of intra-state transmission of electricity from generating stations to Load Centers. • Non-discriminatory Open Access to its transmission system on pa yment of transmission charges • Complying with the directions of RLDC and SLDC, operating SLDC until any other authority is established by the State Govt. • Now RRVPNL is "An ISO 9001:2000 Certified Company". 6
CHAPTER 2 LIGHTNING ARRESTER
Fig. 3- Lightning arrester A lightning arrester (also known as surge diverter) is a device connected between line and earth i.e. in parallel with the over headline, HV equipments and substation to be protected. It is a safety valve which limits the magnitude of lightning and switching over voltages at the substations, over headlines and HV equipments and provides a low resistance path for the surge current to flow to the ground. The practice is also to install lightning arresters at the incoming terminals of the line. All the electrical equipments must be protected from the severe damages of lightning strokes. The techniques can be studied under:
Protection of transmission line from direct stroke.
Protection of power station and sub-station from direct stroke.
Protection of electrical equipments from travelling waves. 7
2.1) Types of Arrestors:2.1.1) Rod/sphere gap:- It is a very simple protective device i.e. gap is
provided across the stack of Insulators to permit flash-over when undesirable voltages are impressed of the system. 2.1.2) Expulsion type LA:- It have two electrodes at each end and consists
of a fiber tube capable of producing a gas when is produced. The gas so evolved blows the arc through the bottom electrode.
2.1.3) Valve type LA:- It consists of a divided spark-gap in series will a non linear resistor. The divided spark gap consists of a no. of similar elements, each of it two electrode across which are connected high resistor.
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CHAPTER 3 BUS BARS Bus Bars are the common electrical component through which a large no of feeders operating at same voltage have to be connected. If the bus bars are of rigid type (Aluminum types) the structure height are low and minimum clearance is required. While in case of strain type of bus bars suitable ACSR conductor are strung/tensioned by tension insulators discs according to system voltages. In the widely used strain type bus bars stringing tension is about 500-900 Kg depending upon the size of conductor used. Here proper clearance would be achieved only if require tension is achieved. Loose bus bars would effect the clearances when it swings while over tensioning may damage insulators. Clamps or even effect the supporting structures in low temperature conditions. The clamping should be proper, as loose clamp would spark under in full load condition damaging the bus bars itself.
3.1) BUS BAR ARRENGEMENT MAY BE OF FOLLOWING TYPE WHICH IS BEING ADOPTED BY R.R.V.P.N.L.:3.1.1) Single bus bar arrangement 3.1.2) Double bus bar arrangement a) Main bus with transformer bus b) Main bus-I with main bus-II 3.1.3) Double bus bar arrangement with auxiliary bus.
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3.1.1) SINGLE BUS BAR ARRANGEMENT : This arrangement is simplest and cheapest. It suffers, however, from major defects. 1. Maintenance without interruption is not possible. 2. Extension of the sub-station without a shutdown is not possible.
3.1.2) DOUBLE BUS BAR ARRANGEMENT : 1. Each load may be fed from either bus. 2. The load circuit may be divided in to two separate groups if needed from operational consideration. Two supplies from different sources can be put on each bus separately. 3. Either bus bar may be taken out from maintenance of insulators. The normal bus selection insulators cannot be used for breaking load currents. The arrangement does not permit breaker maintenance without causing stoppage of supply.
3.1.3) DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN BUS WITH AUXILARY BUS : The double bus bar arrangement provides facility to change over to either bus to carry out maintenance on the other but provide no facility to carry over breaker maintenance. The main and transfer bus works the other way round. It provides facility for carrying out breaker maintenance but does not permit bus maintenance. Whenever maintenance is required on any breaker the circuit is changed over to the transfer bus and is controlled through bus coupler breaker.
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CHAPTER 4 INSULATOR The insulator for the overhead lines provides insulation to the power conductors from the ground so that currents from conductors do not flow to earth through supports. The insulators are connected to the cross arm of supporting structure and the power conductor passes through the clamp of the insulator. The insulators provide necessary insulation between line conductors and supports and thus prevent any leakage current from conductors to earth. In general, the insulator should have the following desirable properties:
High mechanical strength in order to withstand conductor load, wind load etc.
High electrical resistance of insulator material in order to avoid leakage currents to earth.
High relative permittivity of insulator material in order t hat dielectric strength is high.
High ratio of puncture strength to flash over.
These insulators are generally made of glazed porcelain or toughened glass. Poly come type insulator [solid core] are also being supplied in place of hast insulators if available indigenously. The design of the insulator is such that the stress due to contraction and expansion in any part of the insulator does not lead to any defect. It is desirable not to allow porcelain to come in direct contact with a hard metal screw thread.
4.1) TYPE OF INSULATORS: 4.1.1:
Pin type
4.1.2:
Suspension type
4.1.3:
Strain insulator
Fig. 5-Suspension type insulator
Insulators, generally used in GSS, is suspension type insulator. SUSPENSION TYPE: Suspension type insulators consist of a number of porcelain
disc connected in series by metal links in the form of a string. Its working voltage is 66KV. Each disc is designed for low voltage for 11KV.
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CHAPTER 5 ISOLATORS “Isolator" is one, which can break and make an electric circuit in no load condition. These are normally used in various circuits for the purposes of Isolation of a certain portion when required for maintenance etc. Isolation of a certain portion when required for maintenance etc. "Switching Isolators" are capable of
Interrupting transformer magnetized currents
Interrupting line charging current
Load transfer switching
Fig. 7- Isolators
Its main application is in connection with transformer feeder as this unit makes it possible to switch out one transformer, while the other is still on load. The most common type of isolators is the rotating centre pots type in which each phase has three insulator post, with the
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outer posts carrying fixed contacts and connections while the centre post having contact arm which is arranged to move through 90` on its axis. The following interlocks are provided with isolator: a) Bus 1 and2 isolators cannot be closed simultaneously. b) Isolator cannot operate unless the breaker is open. c) Only one bay can be taken on bypass bus. d) No isolator can operate when corresponding earth switch is on breaker.
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CHAPTER 6 CIRCUIT BREAKER The function of relays and circuit breakers in the operation of a power system is to prevent or limit damage during faults or overloads, and to minimize their effect on the remainder of the system. This is accomplished by dividing the system into protective
zones separated by
circuit breakers. During a fault, the zone which includes the faulted apparatus is de-energized and disconnected from the system. In addition to its protective function, a circuit breaker is also used for circuit switching under normal conditions. Each having its protective relays for determining the existence of a fault in that zone and having circuit breakers for disconnecting that zone from the system. It is desirable to restrict the amount of system disconnected by a given fault; as for example to a single transformer, line section, machine, or bus section. However, economic considerations frequently limit the number of circuit breakers to those required for normal operation and some compromises result in the relay protection. Some of the manufacturers are ABB, AREVA, Cutler-Hammer (Eaton), Mitsubishi Electric, Pennsylvania Breaker, Schneider Electric, Siemens, Toshiba, Končar HVS and others. Circuit breaker can be classified as "live tank", where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. Highvoltage AC circuit breakers are routinely available with ratings up to 765,000 volts.
6.1) Various types of circuit breakers:6.1.1) SF6 Circuit Breaker 6.1.2) Air Blast Circuit Breaker 6.1.3) Oil Circuit Breaker 6.1.4) Bulk Oil Circuit Breaker (BOCB) 6.1.5) Minimum Oil Circuit Breaker
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Circuit Breakers, generally used in GSS, are SF6 and Air blast circuit breaker . 1) SF6 CIRCUIT BREAKER:Sulphur hexafluoride has proved its-self as an excellent insulating and arc quenching medium. It has been extensively used during the last 30 years in circuit breakers, gas-insulated switchgear (GIS), high voltage capacitors, bushings, and gas insulated transmission lines. In SF6 breakers the contacts are surrounded by low pressure SF6 gas. At the moment the contacts are opened, a small amount of gas is compressed and forced through the arc to extinguish it.
Fig. 8-SF6 Circuit Breaker 2) AIR BLAST CIRCUIT BREAKER:
The principle of arc interruption in air blast circuit breakers is to direct a blast of air, at high pressure and velocity, to the arc. Fresh and dry air of the air blast will replace the ionized hot gases within the arc zone and the arc length is considerably increased. Consequently the arc may be interrupted at the first natural current zero. In this type of breaker, the contacts are surrounded by compressed air. When the contacts are opened the compressed air is released in forced blast through the arc to the atmosphere extinguishing the arc in the process.
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Fig. 9-Air Blast Circuit Breaker
Advantages:
An air blast circuit breaker has the following advantages over an oil circuit breaker:
The risk of fire is eliminated
The arcing products are completely removed by the blast whereas the oil deteriorates with successive operations; the expense of regular oil is replacement is avoided
The growth of dielectric strength is so rapid that final contact gap needed for arc extinction is very small. this reduces the size of device
The arcing time is very small due to the rapid build up of dielectric strength between contacts. Therefore, the arc energy is only a fraction that in oil circuit breakers, thus resulting in less burning of contacts
Due to lesser arc energy, air blast circuit breakers are very suitable for conditions where frequent operation is required
The energy supplied for arc extinction is obtained from high pressure air and is independent of the current to be interrupted. 16
Disadvantages:
Air has relatively inferior arc extinguishing properties.
Air blast circuit breakers are very sensitive to the variations in the rate of restriking voltage.
Considerable maintenance is required for the compressor plant which supplies the air blast
Air blast circuit breakers are finding wide applications in high voltage installations. Majority of circuit breakers for voltages beyond 110 kV are of this type.
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CHAPTER 7 PROTECTIVE RELAYS Relays must be able to evaluate a wide variety of parameters to establish that corrective action is required. Obviously, a relay cannot prevent the fault. Its primary purpose is to detect the fault and take the necessary action to minimize the damage to the equipment or to the system. The most common parameters which reflect the presence of a fault are the voltages and currents at the terminals of the protected apparatus or at the appropriate zone boundaries. The fundamental problem in power system protection is to define the quantities that can differentiate between normal and abnormal conditions. This problem is compounded by the fact that “normal” in the present sense means outside the zone of protection. This aspect, which is of the greatest significance in designing a secure relaying system, dominates the design of all protection systems .
Fig. 10-Relays
7.1 ) Distance Relays: Distance relays respond to the voltage and current, i.e., the impedance, at the relay location. The impedance per mile is fairly constant so these relays respond to the distance between the relay location and the fault location. As the power systems become more complex and the 18
fault current varies with changes in generation and system configuration, directional over current relays become difficult to apply and to set for all contingencies, whereas the distance relay setting is constant for a wide variety of changes external to the protected line.
7.2) Types of Distance relay:7.2.1) Impedance Relay:
The impedance relay has a circular characteristic centred. It is non directional and is used primarily as a fault detector. 7.2.2) Admittance Relay:
The admittance relay is the most commonly used distance relay. It is the tri pping relay in pilot schemes and as the backup relay in step distance schemes. In the electromechanical design it is circular, and in the solid state design, it can be shaped to correspond to the transmission line impedance. 7.2.3) Reactance Relay:
The reactance relay is a straight-line characteristic that responds only to the reactance of the protected line. It is non directional and is used to supplement the admittance relay as a tripping relay to make the overall protection independent of resistance. It is particularly useful on short lines where the fault arc resistance is the same order of magnitude as the line length.
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CHAPTER 8 POWER TRANSFORMER For stepping up or down the system voltage, power transformers are used in the substations. At generating end, the voltage is only stepped up for transmission of power while at all the subsequent substations the voltage is gradually stepped down to reach finally to working voltage level. General natural cooled, oil immersed, two winding, three phase transformers upto the rating of 10 MVA are installed upon length of rails fixed on concrete slabs having foundations 1 to 15m deep . For more than 10 MVA ratings, forced oil, water cooling and air blast cooling type may be used. The tap changers are used for regulating the voltage of transformers. 8.1) Windings:
Winding shall be of electrolytic grade copper free from scales & burrs. Windings shall be made in dust proof and conditioned atmosphere. Coils shall be insulated that impulse and power frequency voltage stresses are minimum. Coils assembly shall be suitably supported between adjacent sections by insulating spacers and barriers. Bracing and other insulation used in assembly of the winding shall be arranged to ensure a free circulation of the oil and to reduce the hot spot of the winding. All windings of the transformers having voltage less than 66 kV shall be fully insulated. Tapping shall be so arranged as to preserve the magnetic balance of the transformer at all voltage ratio. All leads from the windings to the terminal board and bushing shall be rigidly supported to prevent injury from vibration short circuit stresses.
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8.2) Tanks and fittings: Tank shall be of welded construction & fabricated from tested quality low carbon steel of adequate thickness. After completion of welding, all joints shall be subjected to dye penetration testing. At least two adequately sized inspection openings one at each end of the tank shall be provided for easy access to bushing & earth connections. Turrets & other parts surrounding the conductor of individual phase shall be non-magnetic. The main tank body including tap changing compartment, radiators shall be capable of withstanding full vacuum.
8.3) Cooling Equipments: FACTS AND IMPORTANCE OF TRANSFORMER COOLING
Needed to maintain and regulate the proper cooling for the core and coil assembly of the transformer.
Heat is directly related to moisture
Paper insulation is destroyed by heat and moisture
The life expectancy of a transformer is largely based on moisture and heat management.
Cooling equipment shall conform to the requirement stipulated below: (a.) Each radiator bank shall have its own cooling fans, shut off valves at the top and bottom (80mm size) lifting lugs, top and bottom oil filling valves, air release plug at the top, a drain and sampling valve and thermometer pocket fitted with captive screw cap on the inlet and outlet. (b.) Cooling fans shall not be directly mounted on radiator bank which may cause undue vibration. These shall be located so as to prevent ingress of rain water. Each fan shall be suitably protected by galvanized wire guard.
Fig-Radiator with fan
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8.4) Transformer Accessories: 8.4.1) Buchholz Relay:
This has two Floats, one of them with surge catching baffle and gas collecting space at top. This is mounted in the connecting pipe line between conservator and main tank. This is the most dependable protection for a given transformer. Gas evolution at a slow rate that is associated with minor faults inside the transformers gives rise to the operation or top float whose contacts are wired for alarm. There is a glass window with marking to read the volume of gas collected in the relay. Any major fault in transformer creates a surge and the surge element in the relay trips the transformer. Size of the relay varies with oil volume in the transformer and the mounting angle also is specified for proper operation of the relay.
Fig. 13-Buchholz Relay
8.4.2) Temperature Indicators:
Most of the transformer (small transformers have only OTI) are provided with indicators that displace oil temperature and winding temperature. There are thermometers pockets provided in the tank top cover which hold the sensing bulls in them. Oil temperature measured is that of the top oil, where as the winding temperature measurement is indirect.
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This is done by adding the temperature rise due to the heat produced in a heater coil (known as image coil) when a current proportional to that flowing in windings is passed in it to that or top oil. For proper functioning or OTI & WTI it is essential to keep the thermometers pocket clean and filled with oil.
Fig. 14-Winding and oil temperature indicator 8.4.3) Silica Gel Breather:
Both transformer oil and cellulosic paper are highly hygroscopic. Paper being more hygroscopic than the mineral oil The moisture, if not excluded from the oil surface in conservator, thus will find its way finally into the paper insulation and causes reduction insulation strength of transformer. To minimize this conservator is allowed to breathe only through the silica gel column, which absorbs the moisture in air before it enters the conservator air surface.
Fig. 15-Silica gel Breather 8.4.4) Conservator:
With the variation of temperature there is corresponding variation in the oil volume. To account for this, an expansion vessel called conservator is added to the t ransformer 23
with a connecting pipe to the main tank. In smaller transformers this vessel is open to atmosphere through dehydrating breathers (to keep the air dry). In larger transformers, an air bag is mounted inside the conservator with the inside of bag open to atmosphere through the breathers and the outside surface of the bag in contact with the oil surface.
Fig. 16-Conservator with Buchholz relay and tank [ref.-6]
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CHAPTER 9 CURRENT TRANSFORMER As you all know this is the device which provides the pre-decoded fraction of the primary current passing through the line/bus main circuit. Such as primary current 60A, 75A, 150A, 240A, 300A, 400A, to the secondary output of 1A to 5A. Now a day mostly separate current transformer units are used instead of bushing mounting CT’s on leveled structure they should be for oil level indication and base should be earthed properly. Care should be taken so that there should be no strain as the terminals. When connecting the jumpers, mostly secondary connections is taken to three unction boxes where star delta formation is connected for three phase and final leads taken to protection /metering scheme. There should be no chance of secondary circuit remaining opens as it leads to extremely high voltage which ultimately damages the CT itself
Fig. 17-Current Transformers
It can be used to supply information for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and distribution circuit or for power transformer. These current transformers have the primary winding connected in series with the conductor carrying the current to be measured or controlled. The secondary winding is thus insulated from the high voltage and can then be connected to low voltage metering circuits. 25
CHAPTER 10 POTENTIAL TRANSFORMER A potential transformer (PT) is used to transform the high voltage of a power line to a lower value, which is in the range of an ac voltmeter or the potential coil of an ac voltmeter.
Fig.18-Potential Transformer
The voltage transformers are classified as under:
Capacitive voltage transformer or capacitive type
Electromagnetic type.
Capacitive voltage transformer is being used more and more for voltage measurement in high voltage transmission network, particularly for systems voltage of 132KV and above where it becomes increasingly more economical. It enables measurement of the line to earth voltage to be made with simultaneous provision for carrier frequency coupling, which has reached wide application in modern high voltage network for tele-metering remote control and telephone communication purpose. The capacitance type voltage transformers are of twp type:
Coupling Capacitor type
Pushing Type 26
The performance of CVT is affected by the supply frequency switching transient and magnitude of connected Burdon. The CVT is more economical than an electromagnetic voltage transformer when the nominal supply voltage increases above 66KV. The carrier current equipment can be connected via the capacitor of the CVT. There by there is no need of separate coupling capacitor. The capacitor connected in series act like potential dividers, provided, the current taken by burden is negligible compared with current passing through the series connected capacitor.
CVT as coupling capacitor for carrier current application: The carrier current equipments is connected to the power line via coupling capacitor. The coupling CVT combines the function of coupling and voltage transformer.
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CHAPTER 11 CAPACITIVE VOLTAGE TRANSFORMER A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an inductive element used to tune the device to the supply frequency and a transformer used to isolate and further step-down the voltage for the instrumentation or protective relay. The device has at least four terminals, a high-voltage terminal for connection to the high voltage signal, a ground terminal and at least one set of secondary terminals for connection 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 the first capacitor, C1, is often replaced by a stack of capacitors connected in series. This results in a large voltage drop across the stack of capacitors that replaced the first capacitor and a comparatively small voltage drop across the second capacitor, C 2, and hence the secondary terminals.
The porcelain in multi unit stack, all the potentials points are electrically tied and suitably shielded to overcome the effect of corona RIV etc. Capacitive voltage transformers are available for system voltage.
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CHAPTER 12 CONTROL ROOM In IGN GSS not only remote control carry the appropriate mean by which circuit breaker may be open or close but also indicating device, indicating lamps ,isolating switches, 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 panel are located at different stages and on each control panel switch is provided on the board .Colors of signals are synchronized as follows: 1 Red - For circuit breaker or isolator switch is in closed position. 2 Green - For circuit breaker is in open condition. 3 Amber - Indicates abnormal condition. There are different relays located. ANNOUNCING SECTION This section is always checked by shift incharge. If any faults or any relays moves from L.T. alarms swings and type of fault is indicated on the announcing box. The most important section is indicated by announcing box. The most important section is transformer controller section, winding temperature indicator, tap position selector is situated on control panel. A control engineer controls loading of various lines, outgoing feeders, synchronizing the indicating lines with bus bar. CONTROL & RELAY PANEL The arrangement of control and relay power is such that the indicating apparatus is clearly visible from control panel. These respective panels are provided for control and indicating equipment. Relay and recording equipment, the synchronizing switch is put to auto position when condition of synchronism is satisfied. The white lamp on the top indicating ”synchronizing relay operated” glow and C.B. is auto automatically closed when bus bar is dead there is no need of synchronizing in that case line is directly connected to bus bar by pulling a switch marked 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 required.
SUPERVISORY CONTROL AND DATA AQUISITION SYSTEM (SCADA) For power system operation and control includes Data collection system Data transmission telemetric equipment Data monitoring equipment Main machine interface 29
Data collection equipment as data logger collects the primary data from source and converts it into suitable form of information and then transmitting and processing data logger records and rating from different location in this plant. Data logger is designed for plant performance computation for logical analysis of alarm condition, thus minimizing possible confusion during emergency. The intervals of recording are selected by letters of a deal of a push button on the data logger, which is 1 hour. The input scanner is an automatic sequence switch, which select each signal in turn transducers are used to converts original signal into suitable electric form for the input of scanner. It is converted into high signals. SCANNING AND INDICATION The automatic control necessities a series and checks at regular intervals, which provided indications whether and when appropriate action is to be indicated. The scanning gives necessary data regarding the values of various input variables. The decision regarding follow up section is taken according to the program. CRT DISPLAY The operation in the control room needs information regarding parameters and configuration according to the feeders. It Is divided into many parts. 1. Indication system 2. Control switches 3. Relay section 4. Meter section 5. Announcing section 6. DC supply system 7. Transformer control unit INDICATING SYSTEM It is used to indicate total load, bus bar voltage, indication of C.B., isolator position lever type arrangement for opening and closing of C.B. and isolator. A relay indicates position of C.B. close or open. RELAY SECTION This section indicates the position of different relay at different feeders. Fault in any feeder is denoted by corresponding relay that gives alarm signals. MASTER RELAY This relay gives the signal to the trip coil of C.B. and thus faults feeder is disconnected from supply. METER SECTION This includes a different type of meter .One network CRT display provides operator with following information whenever he works. Two type of display includes Tabulated values of parameter 30
Measured values and computed characteristic symbolic representation of equipment states usually in the forms of diagram of substation.
MEASURING INSTRUMENT USED: 12.1.1) ENERGY METER: To measure the energy transmitted, energy meters are fitted to the panel to different feeders the energy transmitted is recorded after one hour regularly for it MWHr, meter is provided. 12.1.2) WATTMETERS: It is attached to each feeder to record the power exported from GSS. 12.1.3) FREQUENCY METER: To measure the frequency at each feeder there is the provision of analog or digital frequency meter. 12.1.4) VOLTMETER: It is provided to measure the phase to phase voltage .It is also available in both the analog and digital frequency meter. 12.1.5) AMETER: It is provided to measure the line current. It is also available in both the forms analog as well as digital. 12.1.6) MAXIMUM DEMAND INDICATOR: There are also mounted the control panel to record the average power over successive predetermined period. 12.1.7) MVAR METER: It measures the reactive power of the circuit.
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Fig: Control Panel
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CHAPTER 13 CAPACITOR BANK The capacitor bank provides reactive power at grid substation. The voltage regulation problem frequently reduces so of circulation of reactive power. Unlike the active power, reactive power can be produced, transmitted and absorbed of course with in the certain limit, which have always to be workout. At any point in the system shunt capacitor are commonly used in all voltage and in all size.
Fig. 20-Capacitor Bank
Benefits of using the capacitor bank are many and the reason is that capacitor reduces the reactive current flowing in the whole system from generator to the point of installation. 1 .Increased voltage level at the load 2. Reduced system losses 3. Increase power factor of loading current
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CHAPTER 14 POWER LINE CARRIER COMMUNICATION As electronics plays a vital role in the industrial growth, communication is also a backbone of any power stations. Communication between various generating and receiving station is very essential for proper operation of power system. This is more in case of large interconnected system where a control leads dispatch station has to co-ordinate the working of various unit to see that the system is maintained in the optimum working condition, power line communication is most economic and reliable method of communication for medium and long distance in power network.
14.1) Wave Trap: Line trap also is known as Wave trap. What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleprotection panel in the substation control room (through coupling capacitor and LMU).
Fig. 21-Wave Trap
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This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleprotection signals and in addition, voice and data communication signals.
The Line trap
OFFERS HIGH IMPEDANCE TO THE HIGH FREQUENCY COMMUNICATION SIGNALS
thus obstructs the flow of these signals in to the substation bus bars. If there were not to be there, then signal loss is more and communication will be ineffective/probably impossible.
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CHAPTER 15 EARTHING OF THE SYSTEM The provision of an earthing system for an electric system is necessary by the following reason.
In the event of over voltage on the system due to lightening discharge or other system fault. These parts of equipment, which are normally dead, as for as voltage, are concerned do not attain dangerously high potential.
In a three phase, circuit the neutral of the system is earthed in order to stabilize the potential of circuit with respect to earth.
The resistance of earthing system is depending on:
Shape and material of earth electrode used.
Depth in the soil.
Specific resistance of soil surrounding in the neighbourhood of system electrodes.
15.1) PROCEDURE OF EARTHING: Technical consideration the current carrying path should have enough capacity to deal with more faults current. The resistance of earth and current path should be low enough to prevent voltage rise between earth and neutral. The earth electrode must be driven in to the ground to a sufficient depth to as to obtain lower value of earth resistance. To sufficient lowered earth resistance a number of electrodes are inserted in the earth to a depth, they are connected together to form a mesh. The resistance of earth should be for the mesh in generally inserted in the earth at 0.5m depth the several point of mesh then connected to earth electrode or ground conduction. The earth electrode is metal plate copper is used for earth plate.
15.2) NEUTRAL EARTHING: Neutral earthing of power transformer all power system operates with grounded neutral. Grounding of neutral offers several advantages the neutral point of generator transformer is connected to earth directly or through a reactance in some cases the neutral point is earthed through an adjustable reactor of reactance matched with the line.
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The earth fault protection is based on the method of neutral earthing.
The neutral earthing is associated switchgear.
The neutral earthing is provided for the purpose of protection arcing grounds unbalanced voltages with respect to protection from lightening and for improvement of the system.
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CHAPTER 16 BATTERY ROOM In a GSS, separate dc supply is maintained for signalling remote position control, alarm circuit etc. Direct current can be obtained from 440volt 3 phase ac supply via rectifier and in event of ac failure, from the fixed batteries, which are kept, charged in normal condition by rectifier supply.
Fig. 22-Battery Room
Battery System: The batteries used are lead acid type having a solution of sulphuric acid and distilled water as electrolytes. In charged state, it has a specific gravity of 1.2 at temperature of 30C.In the battery room batteries are mounted on wooden stand. The cells are installed stand by porcelain. Following precautions are taken in a battery room:
The conductor connecting the cells are greased and coated with electrolyte resisting varnish.
Proper care is taken so that acid vapours do not accumulate in the room to avoid risk of explosion, smoking, winding etc.
The windows of battery are of forested glass to avoid the batteries from direct action of sun light.
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CHAPTER17 GIS (Gas Insulated Substation) The increasing demand of electrical power in cities and industrial centers necessitates the installation of a compact and efficient distribution and transmission network. High voltage gas insulated switchgear (GIS) is ideal for such applications. The range of application of SF ₆ Gas Insulated Switchgear extends from voltage ratings of 72.5 kV up to 800 kV with breaking currents of up to 63 kA, and in special cases up to 80 kA. Both small transformer substations and large load-center substations can be designed with GIS technology. The distinctive advantages of SF ₆ Gas Insulated Switchgear are: compact, low weight, high reliability, safety against touch contact, low maintenance and long life. Extensive in-plant preassembly and testing of large units and complete bays reduces assembly and commissioning time on the construction site. GIS equipment is usually of modular construction. All components such as bus-bars, disconnectors, circuit-breakers, instrument transformers, cable terminations and joints are contained in earthed enclosures filled with sulphur hexafluoride gas (SF₆ ).
Sulfur hexaflouride (SF6) It is an inert, nontoxic, colorless, odorless, tasteless, and nonflammable gas consisting of a sulfur atom surrounded by and tightly bonded to six flourine atoms. It is about five times as dense as air. SF 6 is used in GIS at pressures from 400 to 600 kPa absolute. The pressure is chosen so that the SF 6 will not condense into a liquid at the lowest temperatures the equipment experiences. SF 6 has two to three times the insulating ability of air at the same pressure. SF 6 is about 100 times better than air for interrupting arcs. It is the universally used interrupting medium for high voltage circuit breakers, replacing the older mediums of oil and air. SF6 decomposes in the high temperature of an electric arc, but the decomposed gas recombines back into SF 6 so well that it is not necessary to replenish the SF6 in GIS.
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ADVANTAGES:
Gas Insulated Switchgear (GIS) that uses compresses sulfur hexafluoride (SF6) gas overcomes many of the limitations of the conventional open type AIS, as it offers the following advantages: (1) The space occupied by the switchgear is greatly reduced. (2) It is totally unaffected by atmospherically conditions such as polluted or saline air in industrial and coastal areas, or desert climates. (3) It possesses a high degree of operational reliability and safety to personal. (4) It is easier to install in difficult site conditions ( e.g. on unstable ground or in seismically active areas) (5) In addition to having a dielectric strength much greater than that of air, SF 6 has the advantages of being nontoxic and non flammable.
GIS COMPONENTS:
In GIS all live parts are enclosed in compressed gas system which is divided into a number of compartments. This division enables the isolation of one compartment for maintenance or 40
repair purpose while the other compartments remain pressurized. In figure below the singleline diagram of a double bus-bar arrangement is shown.
In figure below the diagram shows a typical gas GIS circuit breaker Bay. Basic components that make up any one GIS bay are as follow: 1. Circuit Breaker 2. Disconnectors 3. Earthing Switch 4. Current Transformer 5. Voltage Transformers 6. Cables Compartment 7. Control Cubical
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PASS (Plug and Switch System) The term “Hybrid” refers to the combination of both conventional air insulated switchgear (AIS) and the newer SF 6 metal-clad insulated switchgear (GIS), which takes advantage of the two different technologies. The Hybrid switchgear solution uses already existing, tried-andtested gas insulated switching components but also a conventional and very reliable AIS bus to connect the various hybrid modules. All the functions (except the ring type current transformers) are sealed in a single SF 6 gas insulated housing: Circuit Breaker
Disconnectors
Earth switches
Cable sealing ends
Fast earthing switches
SF6 VTs or voltage sensor
Control and protection cabinet
PASS could also be called “Performance and Save Space” as any subs tation layout can be obtained by making efficient use of the available space.
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ADVANTAGES PASS combines all the typical functions of a complete AIS bay for electrical substations with voltage ratings of up to 245 kV in a unit whose volume is comparable to that of a conventional circuit-breaker of equal class. It takes advantage and widens the scope of the operating philosophy of the PASS series whose dominating factors, those that have dictated the product s success with more than 2000 systems sold throughout the world, is briefly ‟
outlined below: 1. Relatively inexpensive AIS bus bar.
Yet traditionally highly reliable.
2. All live contacts in SF6.
Experience has shown that AIS disconnector switch contacts require relatively high
levels of maintenance whereas the experience with GIS has been exactly the opposite. SF6 technology means less ongoing maintenance.
Highly reliable equipment leading to a lower global life cycle cost.
3. Fewer switching elements.
Use of highly reliable GIS style switches allows the switching elements to be rationalized
4. Per-tested in Factory also for earthquake.
5. Competitive installation cost.
time on site minimized
less risk of delay due to adverse site conditions
less demand for skilled resources at site
6. High degree of factory assembly.
Higher quality finished bay than if it was assembled under site conditions
7. Facilitates monitoring / on-line diagnostics
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Integrated nature of the plant facilitates the introduction of electronic monitoring and on-
line remote diagnostic analysis
8. Modularization of the substations.
savings during the design and construction phases
minimal variations using standardized components
less risk of design errors
higher confidence in project estimation as costs are predictable
That means:
Very high reliability and availability of the substation
Drastic reductions in the time needed to install the equipment
Much less space required
Simplified substation layout
Less maintenance required (maintenance on demand)
Very good cost performance for purchasing, maintenance, operation, outage and
relocation Environmentally friendly: recycling / disposal at end of life
9. Gas Density Control
Each PASS pole has a single gas compartment. Since the dielectric strength of the switchgear and the breaking capacity of the SF 6 circuit-breaker depend on the density of the SF6 gas, a gas density relay is installed to control gas density and detect leakage.
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CHAPTER 18 RATINGS 17.1) TRANSFORMER: Total No. of transformers = 4
No. of transformers
220/132 KV------------------------------------ 100MVA
2
132/33 KV--------------------------------------50MVA
2
MAKE
Company
220/133 KV, 100MVA X-Mer 1----------------------------------- TELK 220/133KV, 100 MVA
X-Mer 2---------------------------------- ALSTOM
132/33 KV, 20/25 MVA X-Mer 1---------------------------------- TELK 132/33 KV, 40/50 MVA X-Mer 3-----------------------------------T&R
For 220KV/132KV, 100MVA ,3-PHASE,50HZ,AUTO-TRANSFORMER Type of cooling
ONAN
Rated power
MVA HV,IV&LV
Rated Voltage
ONAF
50
70
100
16.66
23.33
33.33
HV IV
200 KV
132
LV Rated line
11
HV
current IV
A
HV
Impedence Voltage (Normal Tap) At 100MVA
No. of phases
ODAF
131.37
183.92
262.74
218.95
306.53
437.90
875.45
1225.96
1751.44
HV-IV HV-LV IV-LV
%
12.17 37.04 22.70
3 45
Max. Temp. Ambient of 50’C
‘C Top oil avg. wdg
Load Loss
TAP Position 1Max 2 3 4 5 6 7 8 9NOR 10 11 11a 11b 11c 12 13 14 15 16 17 18 19 MIN
KW
OLTC Connect 3TO 15TO
HV side Line voltage(KV)
4
14 13 12 11 10 9 8 7 6 5 4 3
242.00 239.25 236.50 233.75 231.00 228.25 225.50 222.75 220.00 217.25 214.50 214.50
14 13 12 11 10 9 8 7 6 5 4
214.50 211.75 209.00 206.25 203.50 200.75 198.00 195.25 192.50 189.75 187
14
40 55
AT TAP 1
AT TAP 9
AT TAP 21
173.4
154.9
232.7
Line current (A) ONAN ONAF 50MVA 70MVA 119.43 167.20
ODAF 100MVA 238.86
IV side Line Voltage (KV)
Line Current (A) ONAN ONAF 50MVA 70MVA
ODAF 100MVA
132.00
218.95
407.90
306.53
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CURRENT TRANSFORMER RATING Ratio
Acc. Class
Burden (VA)
1VCT 1VCT1
Knee Point Voltage
Exciting Current ATVK(mA)
CORE1
600/1
PS
1000
CORE2
1VCT2
600/1
PS
309/2
3
1000 30
2VCT 2VCT1
-
600/1
PS
1000
-
CORE2
2VCT2
600/1
PS
438/2
3
1000 30
NVCT NVCT1
-
600/1
PS
1000
-
CORE2
600/1
PS
NCT
CORE1
600/1
PS
CORE2
600/1
PS
WTI
5
R.E.F. Protection
5
Differential Protection
-
WTI
5
R.E.F. Protection
5
Differential Protection R.E.F. Protection Differential Protection
60
NWCT
-
60
CORE1
Differential Protection
60
2WCT
5 60
CORE1
Purpose
60
1WCT
Max. Sec. Resistance 75’C(ohms) 5
1000
60
-
1000
60
5
-
1000
60
5
R.E.F. Protection
POTENTIAL TRANSFORMER Secondary Winding I II
V/R(KV)
VA
Class
11/0.110 11/0.110
50 50
0.5/3P 3P
Primary Terminals A2B2C2N -
Secondary Terminals a2b2c2 da2-dn
Purpose Measurement Protection
BATTERY CHARGER: Battery Charger – 220AH
440AH
VDC HBL NIFE LTD. VDC HBL NIFE LTD.
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CONCLUSION Training at 220KV GSS IG Nagar, 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, isolators, control room, Battery room etc. What is the various problem seen in substation while handling this i nstruments. There are various occasion when relay operate and circuit breaker open, load shedding, shut down, which has been heard previously.To get insight of the substation, how things operate, how things manage all is learned there. Practical training as a whole proved to be extremely informative and experience building and the things learnt at it would definitely help a lot in snapping the future ahead a better way.
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