A
Seminar Report
On
“Practical Training”
Taken at
220 kV G.S.S. Dausa
And
Submitted in the partial fulfillment for award t...
2
3
ACKNOWLEDGEMENT
I feel immense pleasure in conveying my heartiest thanks and deep sense of
gratitude to Head of the Electr...
PREFACE
A rapid rise in the use of electricity is placing a very heavy responsibility on
electrical undertaking to maintai...
CONTENTS
1. Introduction……………………………………………………………..02-04
• 220 kV G.S.S. Dausa………………………………………………..03
• Incoming feeders……………...
8. Current transformer………………………………………………………...30
9. Potential transformer……………………………………………………….31
10.Capacitive voltage tr...
INTRODUCTION
Electrical power is generated, transmitted in the form of alternating
current. The electric power produced at...
Incoming feeders
Outgoing feeders
220 kV G.S.S. DAUSA
1. It is an outdoor type substation.
2. It is primary as well as dis...
220 kV:-
1. ANTA-1 & ANTA-2
2. PGCIL BASSI-1 & BASSI-2.
Out going feeders:
220 kV 132 kV 32 kV 11 kV
1) Alwar 1) Lalsot 1)...
BUS BARS
Bus Bars are the common electrical component through which a large no of feeders
operating at same voltage have t...
3.1.1) DOUBLE BUS BAR ARRANGEMENT :
1. Each load may be fed from either bus.
2. The load circuit may be divided in to two ...
Fig.:- Bus Bars
ISOLATORS
“Isolator" is one, which can break and make an electric circuit in no load
condition. These are ...
INSULATOR
The insulator for the overhead lines provides insulation to the power conductors
from the ground so that current...
4.1.2: Suspension type
4.1.3: Strain insulator
4.1.1) PIN TYPE: Pin type insulator consist of a single or multiple shells
...
Fig.:- Suspension type insulators
4.1.3) STRAIN TYPE INSULATOR: The strain insulators are exactly
identical in shape with ...
PROTECTIVE RELAYS
Relays must be able to evaluate a wide variety of parameters to establish that
corrective action is requ...
Fig.: -Relays
7.1) Distance Relays:
Distance relays respond to the voltage and current, i.e., the impedance, at the
relay ...
The admittance relay is the most commonly used distance relay. It is the
tripping relay in pilot schemes and as the backup...
Fig.:-Buchholz Relay
CIRCUIT BREAKER
The function of relays and circuit breakers in the operation of a power system is to
...
Each having its protective relays for determining the existence of a fault in that
zone and having circuit breakers for di...
opened, a small amount of gas is compressed and forced through the arc to
extinguish it.
Fig. 8-SF6 Circuit Breaker
6.1.2)...
Fig. 9-Air Blast Circuit Breaker
Advantages:
An air blast circuit breaker has the following advantages over an oil circuit...
• Due to lesser arc energy, air blast circuit breakers are very suitable for
conditions where frequent operation is requir...
1. It absorbs the arc energy to decompose the oil into gases, which have
excellent cooling properties.
2. It acts as an in...
this type of breakers the interrupter chamber is separated from the other parts and
arcing is confined to a small volume o...
At 50 c ambient: 1120 Amp
At 40 c Ambient: 1250 Amp
Short time current rating: 20 kV for 1 sec.
Rated operating duty: 0 to...
3. The SF6 circuit breaker gives noiseless operation due to its closed gas
circuit and no exhaust to the atmosphere unlike...
 120/240 volts single phase for residential customers,
 480Y/277 or 208Y/120 for commercial or light industry customers....
Fig. 11-Power Transformer
8.2) Tanks and fittings:
Tank shall be of welded construction & fabricated from tested quality l...
(b.) Cooling fans shall not be directly mounted on radiator bank which may cause
undue vibration. These shall be located s...
Both transformer oil and cellulosic paper are highly hygroscopic. Paper
being more hygroscopic than the mineral oil The mo...
As you all know this is the device which provides the pre-decoded fraction of the
primary current passing through the line...
A potential transformer (PT) is used to transform the high voltage of a power line
to a lower value, which is in the range...
least one set of secondary terminals for connection to the instrumentation or
protective relay. CVTs are typically single-...
voltage of 132KV and above where it becomes increasingly more economical. It
enables measurement of the line to earth volt...
The insulation oil of voltage- and current-transformers fulfills the purpose of
insulating as well as cooling. Thus, the d...
 An instant after ignition of the arc, the test voltage is switched off
automatically by the testing device. Ultra fast s...
A lightning arrester (in Europe: surge arrester) is a device used on power
systems and telecommunications systems to prote...
electrons go through the lightning arrester rather than traveling on to the television
set and destroying it.
A lightning ...
No. of phase: One
Rated voltage: 360 kV
Nominal discharge current: (8×20µs) 10 kA
High current impulse: (4× 100µs) 100 kA
...
Control panel contain meters, control switches and recorders located in the control
building, also called the dog house. T...
12.1.1) ENERGY METER: To measure the energy transmitted energy meters
are fitted to the panel to different feeders the ene...
Unlike the active power, reactive power can be produced, transmitted and absorbed
of course with in the certain limit, whi...
EARTHING OF THE SYSTEM
The provision of an earthing system for an electric system is necessary by the
following reason.
• ...
Neutral earthing of power transformer all power system operates with grounded
neutral. Grounding of neutral offers several...
17.2) CIRCUIT BREAKER:
No. of 220KV breaker - 6
No. of 132KV breaker - 13
No. of 33KV breaker - 12
No. of Capacitor Bank (...
440AH VDC HBL NIFE LTD.
Capacitor BankNo.-1 BHEL 38KV 6.6MVAR
Capacitor BankNo.-2 BHEL 38KV 7.2MVAR
Capacitor BankNo.-1 AB...
CONCLUSION
A technician needs to have not just theoretical but practical as well and so
every student is supposed to under...
REFERENCE:-
Principles of Power System-by V.K. MEHTA
Electrical Power System-by C.L. WADHWA
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  1. 1. A Seminar Report On “Practical Training” Taken at 220 kV G.S.S. Dausa And Submitted in the partial fulfillment for award the degree of Bachelor of Technology In Electrical Engineering From Rajasthan Technical University, Kota Session 2012-2013 Submitted To Submitted by Mr. Arun Sharma Rinku Kumar Meena Head Of Department B.Tech. 4th year (7th Sem.) Electrical Engineering Roll no. 10EDSEE099 S.D.I.T. Dausa Enroll. no. Submitted to Department of Electrical Engineering SHREE DIGAMBER INSTITUTE OF TECHNOLOGY, BHANDAREJ MODE, DAUSA 1
  2. 2. 2
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  4. 4. ACKNOWLEDGEMENT I feel immense pleasure in conveying my heartiest thanks and deep sense of gratitude to Head of the Electrical Engineering Department of SHREE DIGAMBAR INSTITUTE OF TECHNOLOGY, Dausa for his efforts and for technical as well as moral support. Engineers and other technical and non technical staff, for helping in understanding the various aspects and constructional detail of work and site in 220kV Grid-Sub Station, Dausa. It may not be possible for me to acknowledge the support of all my friends, but I am thankful to all my colleagues and other trainees for their valuable ideas and support during training period. 4
  5. 5. PREFACE A rapid rise in the use of electricity is placing a very heavy responsibility on electrical undertaking to maintain their electrical network in perfect condition, young engineers is called upon to do design, system planning and construction and maintenance of electric system before he had much experience and practice soon may be responsible for specialize operation in an ever expending industry. Theoretical knowledge gained in their college courses need to be supplemented with practical know-how to face this professional challenge, so…….. As a part of our practical training we have to attempt the rule of Rajasthan Technical University, Kota. I look my practical training at 220 kV G.S.S. Dausa. Since my training centre was of Grid Sub-station hence I have included all updated information, to the extent possible, including general introduction and brief description of starting sub-station of 220 kV G.S.S. in this study report. During my 30 Working days practical training, I had undertaken my training at 220 kV G.S.S. at DAUSA. I had taken my first practical training at 220 kV G.S.S. Dausa. The period of training was from 17/05/2012 TO 15/06/2012. This report dealt with the practical knowledge of general theory and technical data/detail of equipments, which I have gained during the training period at 220 kV GSS, Dausa. 5
  6. 6. CONTENTS 1. Introduction……………………………………………………………..02-04 • 220 kV G.S.S. Dausa………………………………………………..03 • Incoming feeders…………………………………………………….03 • Outgoing feeders…………………………………………………….04 • Radial feeders………………………………………………………..04 2. Bus bars…………………………………………………………………05-07 • Bus bar arrangement………………………………………………...05 3. Isolators…………………………………………………………………….08 4. Insulators………………………………………………………………..08-11 • Type of insulators……………………………………………………09 o Pin type……………………………………………………….10 o Suspension type………………………………………………10 o Strain type…………………………………………………….11 5. Protective relays………………………………………………………...12-16 • Differential relays…………………………………………………...14 • Buchholz relay………………………………………………………14 o Construction…………………………………………………..14 o Operation……………………………………………………..15 o Advantages…………………………………………………...15 o Disadvantages………………………………………………...16 6. Circuit breakers………………………………………………………....16-24 • Operating principle………………………………………………….16 • Arc phenomenon…………………………………………………….17 • Classification of circuit breakers…………………………………….18 • SF6 C.B……………………………………………………………...18 o Construction…………………………………………………..19 o Working………………………………………………………20 o 220 kV SF6 C.B. ratings……………………………………...21 o Advantages of SF6 C.B………………………………………22 o Demerits of SF6 C.B………………………………………….23 o Applications…………………………………………………..24 7. Power Transformers…………………………………………………….24-29 • Basic parts of transformer…………………………………………...25 • Transformer ratings………………………………………………….26 6
  7. 7. 8. Current transformer………………………………………………………...30 9. Potential transformer……………………………………………………….31 10.Capacitive voltage transformer (CVT)…………………………………31-33 • Description…………………………………………………………..31 • Applications…………………………………………………………32 • Ratings of cvt………………………………………………………..33 11.Transformer oil & its testing……………………………………………34-35 • Breakdown voltage………………………………………………….34 • Flash point…………………………………………………………...34 12.Lightening arrestor……………………………………………………...36-38 • Thyrite type………………………………………………………….36 • 220 kV lightening arrestor…………………………………………..38 13.Control panel……………………………………………………………39-41 • Reactor………………………………………………………………39 • C.B…………………………………………………………………..39 • Bus couplers…………………………………………………………40 • Disturbance reactor………………………………………………….40 • Event logger…………………………………………………………40 • On load tap changer (OLTC)………………………………………..40 • No load tap changer (NLTC)………………………………………..41 • Synchronoscope……………………………………………………..41 14.Earthing of the system………………………………………………….42-43 • Procedure of earthing………………………………………………..42 • Neutral earthing……………………………………………………...42 15.Power line carrier communication…………………………………………44 • PLCC system in Rajasthan…………………………………………..44 16.Corona effect……………………………………………………………45-47 • Factors affecting corona……………………………………………..46 • Advantages and disadvantages of corona…………………………...47 17.Conclusion………………………………………………………………….48 18.Reference…………………………………………………………………...49 7
  8. 8. 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 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. Depending on the constructional feature, the high voltage substations may be further subdivided: (a) Outdoor substation (b) Indoor substation (c) Base or Underground substation 8
  9. 9. Incoming feeders Outgoing feeders 220 kV G.S.S. DAUSA 1. It is an outdoor type substation. 2. It is primary as well as distribution substation. 3. One and half breaker scheme is applied. Incoming feeders: The power mainly comes from: 220 kV G.S.S. Dausa 9
  10. 10. 220 kV:- 1. ANTA-1 & ANTA-2 2. PGCIL BASSI-1 & BASSI-2. Out going feeders: 220 kV 132 kV 32 kV 11 kV 1) Alwar 1) Lalsot 1) Paprada 1) Hodaily 2) Bharatpur 2) Bassi 2) Bhandarej 2) Nangal 3) Hindaun 3) Toonga 3) Bapi 3) Dausa-1 4) Padasoli 4) Dausa-2 5) Dausa-3 6) Dausa-4 As this substation following feeders are established: 1. Radial Feeders. 2. Tie Feeders RADIAL FEEDERS: 1. 220 kV DAUSA - ALWAR. 2. 220 kV DAUSA – HINDAUN. 3. 220 kV DAUSA – BHARATPUR 10
  11. 11. 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 affect 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. 11
  12. 12. 3.1.1) 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 can not be used for breaking load currents. The arrangement does not permit breaker maintenance without causing stoppage of supply. 3.1.2) 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. 12
  13. 13. Fig.:- Bus Bars 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 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 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. 13
  14. 14. 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 that 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 14
  15. 15. 4.1.2: Suspension type 4.1.3: Strain insulator 4.1.1) PIN TYPE: Pin type insulator consist of a single or multiple shells adapted to be mounted on a spindle to be fixed to the cross arm of the supporting structure. When the upper most shell is wet due to rain the lower shells are dry and provide sufficient leakage resistance these are used for transmission and distribution of electric power at voltage up to voltage 33 KV. Beyond operating voltage of 33 KV the pin type insulators thus become too bulky and hence uneconomical. Fig.:- Pin Type Insulator 4.1.2) 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. 15
  16. 16. Fig.:- Suspension type insulators 4.1.3) STRAIN TYPE INSULATOR: The strain insulators are exactly identical in shape with the suspension insulators. These strings are placed in the horizontal plane rather than the vertical plane. These insulators are used where line is subjected to greater tension. For low voltage lines (< 11KV) shackle insulator are used as strain insulator. Fig.:- Strain Insulators 16
  17. 17. 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. 17
  18. 18. Fig.: -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 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: 18
  19. 19. The admittance relay is the most commonly used distance relay. It is the tripping 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. 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. 19
  20. 20. Fig.:-Buchholz Relay 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. 20
  21. 21. 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. High-voltage 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 (MOCB) 6.1.5) Minimum Oil Circuit Breaker 6.1.1) 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 21
  22. 22. opened, a small amount of gas is compressed and forced through the arc to extinguish it. Fig. 8-SF6 Circuit Breaker 6.1.2) 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. 22
  23. 23. 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 23
  24. 24. • 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. Disadvantages: Air has relatively inferior arc extinguishing properties. • Air blast circuit breakers are very sensitive to the variations in the rate of restricting 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. 6.1.3) OIL CIRCUIT BREAKER: Circuit breaking in oil has been adopted since the early stages of circuit breakers manufacture. The oil in oil-filled breakers serves the purpose of insulating the live parts from the earthed ones and provides an excellent medium for arc interruption. Oil circuit breakers of the various types are used in almost all voltage ranges and ratings. However, they are commonly used at voltages below 115KV leaving the higher voltages for air blast and SF6 breakers. The contacts of an oil breaker are submerged in insulating oil, which helps to cool and extinguish the arc that forms when the contacts are opened. Oil circuit breakers are classified into two main types namely: bulk oil circuit breakers and minimum oil circuit breakers. The advantages of using oil as an arc quenching medium are: 24
  25. 25. 1. It absorbs the arc energy to decompose the oil into gases, which have excellent cooling properties. 2. It acts as an insulator and permits smaller clearance between live conductors and earthed components. The disadvantages of oil as an arc quenching medium are: 1. Its inflammable and there is risk of fire 2. It may form an explosive mixture with air. 3. The arcing products remain in the oil and it reduces the quality of oil after several operations. 4. This necessitates periodic checking and replacement of oil. 6.1.4) BULK OIL CIRCUIT BREAKER: Bulk oil circuit breakers are widely used in power systems from the lowest voltages up to 115KV. However, they are still used in the systems having voltages up to 230KV. The contacts of bulk oil breakers may be of the plain-break type, where the arc is freely interrupted in the oil, or enclose within the arc controllers. Plain-break circuit breakers consist mainly of a large volume of oil contained in a metallic tank. Arc interruption depends on the head of oil above the contacts and the speed of contact separation. The head of oil above the arc should be sufficient to cool the gases, mainly hydrogen, produced by oil decomposition. A small air cushion at the top of the oil together with the produced gases will increase the pressure with a subsequent decrease of the arcing time. 6.1.5) MINIMUM OIL CIRCUIT BREAKER: Bulk oil circuit breakers have the disadvantage of using large quantity of oil. With frequent breaking and making heavy currents the oil will deteriorate and may lead to circuit breaker failure. This has led to the design of minimum oil circuit breakers working on the same principles of arc control as those used in bulk oil breakers. In 25
  26. 26. this type of breakers the interrupter chamber is separated from the other parts and arcing is confined to a small volume of oil. The lower chamber contains the operating mechanism and the upper one contains the moving and fixed contacts together with the control device. Both chambers are made of an insulating material such as porcelain. The oil in both chambers is completely separated from each other. By this arrangement the amount of oil needed for arc interruption and the clearances to earth are roused. However, conditioning or changing the oil in the interrupter chamber is more frequent than in the bulk oil breakers. This is due to carbonization and slugging from arcs interrupted chamber is equipped with a discharge vent and silica gel breather to permit a small gas cushion on top of the oil. Single break minimum oil breakers are available in the voltage range 13.8 to 34.5 KV. 220 kV SF6 C.B. RATINGS:- Manufacture: BHEL Hyderabad. Type: DCVF (220-245 kV) Rated voltage: 245 kV Rated Frequency: 50 Hz Rated power Frequency voltage: 460 kV Rated Impulse withstands voltage: Lightning: 1450 kV Switching: 1050 kV Normal current Rating: 26
  27. 27. At 50 c ambient: 1120 Amp At 40 c Ambient: 1250 Amp Short time current rating: 20 kV for 1 sec. Rated operating duty: 0 to o.3 sec. c-0-3min-mb Rated short circuit duration: 1 sec. BREAKING CAPACITY [BASED ON SPECIFIED DUTY CYCLE]: a. Capacity at rated voltage: 14400 MVA [220 kV] b. Symmetry current: 20 kV c. Asymmetry current: 25 kV Making capacity: 100kV Rated pressure of hydraulic operating (gauge): 250-350 bars. Rated pressure of SF6 gas at degree: 7.5 bars. Weight of circuit breaker: 1500 Kg. Weight of SF6 gas: 76.5 Kg. Rated trip coil voltage: 220 V AC Rated closing voltage: 220 V DC ADVANTAGES OF SF6 CIRCUIT BREAKER: 1. Due to the superior arc quenching property of SF6, such circuit breakers have very short arching time. 2. Since the dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt much larger currents. 27
  28. 28. 3. The SF6 circuit breaker gives noiseless operation due to its closed gas circuit and no exhaust to the atmosphere unlike the air blast circuit breaker. POWER TRANSFORMER Distribution transformers reduce the voltage of the primary circuit to the voltage required by customers. This voltage varies and is usually: 28
  29. 29.  120/240 volts single phase for residential customers,  480Y/277 or 208Y/120 for commercial or light industry customers. Three-phase pad mounted transformers are used with an underground primary circuit and three single-phase pole type transformers for overhead service. Network service can be provided for areas with large concentrations of businesses. These are usually transformers installed in an underground vault. Power is then sent via underground cables to the separate customers. Parts of Transformer:- 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. 29
  30. 30. Fig. 11-Power Transformer 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: 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. 30
  31. 31. (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. 12-Radiator with fan 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. Fig. 14-Winding and oil temperature indicator 8.4.3) Silica Gel Breather: 31
  32. 32. 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.:-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 transformer 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. CURRENT TRANSFORMER 32
  33. 33. 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. 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. Fig.:-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. POTENTIAL TRANSFORMER 33
  34. 34. 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. 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. CAPACITIVE VOLTAGE TRANSFORMERS (CVT) 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 34
  35. 35. 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, C2, and hence the secondary terminals. Fig.:- CVT connection 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. 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. Capacitive voltage transformer is being used more and more for voltage measurement in high voltage transmission network, particularly for systems 35
  36. 36. 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 TRANSFORMER OIL & ITS TESTING 36
  37. 37. The insulation oil of voltage- and current-transformers fulfills the purpose of insulating as well as cooling. Thus, the dielectric quality of transformer is a matter of secure operation of a transformer. Since transformer oil deteriorates in its isolation and cooling behavior due to ageing and pollution by dust particles or humidity, and due to its vital role, transformer oil must be subject to oil tests on a regular basis. In most countries such tests are even mandatory. Transformer oil testing sequences and procedures are defined by various international standards. Periodic execution of transformer oil testing is as well in the very interest of energy supplying companies, as potential damage to the transformer insulation can be avoided by well timed substitution of the transformer oil. Lifetime of plant can be substantially increased and the requirement for new investment may be delayed. Transformer oil testing procedure To assess the insulating property of dielectric transformer oil, a sample of the transformer oil is taken and its breakdown voltage is measured.  The transformer oil is filled in the vessel of the testing device. Two standard-compliant test electrodes with a typical clearance of 2.5 mm are surrounded by the dielectric oil.  A test voltage is applied to the electrodes and is continuously increased up to the breakdown voltage with a constant, standard-compliant slew rate of e.g. 2 kV/s.  At a certain voltage level breakdown occurs in an electric arc, leading to a collapse of the test voltage. 37
  38. 38.  An instant after ignition of the arc, the test voltage is switched off automatically by the testing device. Ultra fast switch off is highly desirable, as the carbonization due to the electric arc must be limited to keep the additional pollution as low as possible.  The transformer oil testing device measures and reports the root mean square value of the breakdown voltage.  After the transformer oil test is completed, the insultaion oil is stirred automatically and the test sequence is performed repeatedly. (Typically 5 Repetitions, depending on the standard)  As a result the breakdown voltage is calculated as mean value of the individual measurements. LIGHTNING ARRESTOR 38
  39. 39. A lightning arrester (in Europe: surge arrester) is a device used on power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high-voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth. In telegraphy and telephony, a lightning arrestor is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them. Smaller versions of lightning arresters, also called surge protectors, are devices that are connected between each electrical conductor in power and communications systems and the Earth. These prevent the flow of the normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the connected equipment. Their purpose is to limit the rise in voltage when a communications or power line is struck by lightning or is near to a lightning strike. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices. Lightning-produced extreme voltage spikes in incoming power lines can damage electrical home appliances. Potential target for a lightning strike, such as a television antenna, is attached to the terminal labeled A in the photograph. Terminal E is attached to a long rod buried in the ground. Ordinarily no current will flow between the antenna and the ground because there is extremely high resistance between B and C, and also between C and D. The voltage of a lightning strike, however, is many times higher than that needed to move electrons through the two air gaps. The result is that 39
  40. 40. electrons go through the lightning arrester rather than traveling on to the television set and destroying it. A lightning arrester may be a spark gap or may have a block of a semi conducting material such as silicon carbide or zinc oxide. Some spark gaps are open to the air, but most modern varieties are filled with a precision gas mixture, and have a small amount of radioactive material to encourage the gas to ionize when the voltage across the gap reaches a specified level. Other designs of lightning arresters use a glow-discharge tube (essentially like a neon glow lamp) connected between the protected conductor and ground, or voltage-activated solid- state switches called varistors or MOVs. Lightning arresters built for power substation use are impressive devices, consisting of a porcelain tube several feet long and several inches in diameter, typically filled with disks of zinc oxide. A safety port on the side of the device vents the occasional internal explosion without shattering the porcelain cylinder. Lightning arresters are rated by the peak current they can withstand, the amount of energy they can absorb, and the break over voltage that they require to begin conduction. They are applied as part of a lightning protection system, in combination with air terminals and bonding. 220 kV LIGHTNENING ARRESTOR: Manufacture: English electric company 40
  41. 41. No. of phase: One Rated voltage: 360 kV Nominal discharge current: (8×20µs) 10 kA High current impulse: (4× 100µs) 100 kA Long distribution rating: (200µs) 500 kA CONTROL PANEL 41
  42. 42. Control panel contain meters, control switches and recorders located in the control building, also called the dog house. These are used to control the substation equipment to send power from one circuit to another or to open or to shut down circuits when needed. Fig.:-Control Room in GSS Dausa 12.1) MEASURING INSTRUMENT USED: 42
  43. 43. 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 analogue 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 is to measure the reactive power of the circuit. Capacitor Bank:- The capacitor bank provides reactive power at grid substation. The voltage regulation problem frequently reduces so of circulation of reactive power. 43
  44. 44. 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 44
  45. 45. 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: 45
  46. 46. 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. • The earth fault protection is based on the method of neutral earthing. RATINGS 17.1) TRANSFORMER: Total No. of transformers = 6 No. of transformers 220/132 KV------------------------------------ 100MVA 2 132/33 KV--------------------------------------20/25MVA 2 132/33KV---------------------------------------40/50MVA 1 132/11 KV---------------------------------------10/12.5 MVA 1 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, 20/25 MVA X-Mer 2-----------------------------------BBL 132/33 KV, 40/50 MVA X-Mer 3-----------------------------------T&R 132/33 KV, 10/12.5 MVA X-Mer 1---------------------------------EMCO 46
  47. 47. 17.2) CIRCUIT BREAKER: No. of 220KV breaker - 6 No. of 132KV breaker - 13 No. of 33KV breaker - 12 No. of Capacitor Bank (33kv) - 4 No. of 11KV breaker - 7 SF6 CB BREAKER SERIAL NO. 030228 RATED VOLTAGE 145KV NORMAL CURRENT 1250A FREQUENCY 5OHz LIGHTNING IMPULSE WITHSTAND 650KV (Peak) FIRST POLE TO CLEAR TO CLEAR FACTOR 1-2 SHORT TIME WITHSTAND CURRENT 31.5KA DURATION OF SHORT CIRCUIT 3 Sec. (SHORT CIRCUIT SYM. 31.5KA BREAKING CURRENT) ASYM. 37.5KA SHORT TIME MAKING CURRENT 8.0KA OUT OF PHASE BREAKING CURRENT 7.9KA OPERATING SEQUENCE 0-0.3-CO-3min-CO SF6 GAS PRESSURE AT 20C 6.3 Bar TOTAL MASS OF CB 1300Kg MASS OF SF6 GAS 8.7Kg 17.3) BATTERY CHARGER: Battery Charger – 220AH VDC HBL NIFE LTD. 47
  48. 48. 440AH VDC HBL NIFE LTD. Capacitor BankNo.-1 BHEL 38KV 6.6MVAR Capacitor BankNo.-2 BHEL 38KV 7.2MVAR Capacitor BankNo.-1 ABB 38KV 7.2MVAR Capacitor BankNo.-1 WS 38KV 7.2MVAR 17.4) CURRENT TRANSFORMER: FREQUENCY 50Hz HIGHEST SYSTEM VOLTAGE 245KV SHORT TIME CURRENT 40KA/15 RATED CURRENT 600A CURRENT RATIO 600-300-150/1 MIN. KNEE POTENTIAL VOLTAGE 850V at 150/1 MAX. EXCITING CURRENT 100MA at 150/1 MAX. SEC. WINDING RESISTANCE 2.5OHM at 150/1 17.5) CAPACITIVE VOLTAGE TRANSFORMER: SERIAL NO. 0173537 INSULATION LEVEL 460KV RATED VOLTAGE FACTOR 1.2/cont TIME 1.5/30sec. HIGHEST SYSTEM VOLTAGE 245KV PRIMARY VOLTAGE 22OKV/1.732 TYPE OUTDOOR Wgt. 850Kg PHASE SINGLE TBONP.CAT 50C SECONDARY VOLTAGE 110/1.732 110/1.732 RATED BURDON 220Va 110Va FREQUENCY 49.5-50.5Hz 48
  49. 49. CONCLUSION A technician needs to have not just theoretical but practical as well and so every student is supposed to undergo practical training session after 2nd year where I have imbibed the knowledge about transmission, distribution, generation and maintenance with economical issues related to it. During our 30 days training session we were acquainted with the repairing of the transformers and also the testing of oil which is a major component of transformer. At last I would like to say that practical training taken at 220 kV GSS has broadened my knowledge and widened my thinking as a professional. 49
  50. 50. REFERENCE:- Principles of Power System-by V.K. MEHTA Electrical Power System-by C.L. WADHWA 50

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