A TRAINING REPORT ON 220 KV G.S.S. HEERAPURA,JAIPUR
Submitted in partial fulfillment for the award of the degree of
BACHELOR OF TECHNOLOGY In ELECTRICAL ENGINEERING
2013-2014 Submitted To:
Submitted By:
Department of Electrical Engineering
VISHAL SHARMA B.TECH 4 th YEAR
DEPARTMENT OF ELECTRICAL ENGINEERING JAIPUR ENGINEERING COLLEGE & RESEARCH CENTER
JAIPUR(RAJ.)
ACKNOWLEDGEMENT
I am thankful to Mr. S.N. JHAWAR SIR(Head , EE Dept.) under whose guidance I have timely completed the report. Thanks for his valuable guidance. I am thankful to Mr.P.S. CHOUHAN SIR (EXECUTIVE ENGINEER, GSS , JAIPUR) for their inspiration, guidance during my training . Inspite
of their busy schedule, they fully cooperated me in my whole training period. I am thankful to the entire family of GSS HEERAPURA for arranging the training for me. It is because of their dedication and sincerity that the students find them with plenty of professional pr ofessional confidence. I would like to thank my family members, colleagues, friends and the training in charge of JAIPUR ENGINEERING COLLEGE
&
RESEARCH CENTER, JAIPUR and the entire faculty member for their
effort of constant co-operation which have been significant factor in the accomplishment of my summer training. VISHAL SHARMA B.TECH IV YEAR ROLL NO.-10EJCEE065 ELECTRICAL ENGINEERING JECRC JAIPUR
ACKNOWLEDGEMENT
I am thankful to Mr. S.N. JHAWAR SIR(Head , EE Dept.) under whose guidance I have timely completed the report. Thanks for his valuable guidance. I am thankful to Mr.P.S. CHOUHAN SIR (EXECUTIVE ENGINEER, GSS , JAIPUR) for their inspiration, guidance during my training . Inspite
of their busy schedule, they fully cooperated me in my whole training period. I am thankful to the entire family of GSS HEERAPURA for arranging the training for me. It is because of their dedication and sincerity that the students find them with plenty of professional pr ofessional confidence. I would like to thank my family members, colleagues, friends and the training in charge of JAIPUR ENGINEERING COLLEGE
&
RESEARCH CENTER, JAIPUR and the entire faculty member for their
effort of constant co-operation which have been significant factor in the accomplishment of my summer training. VISHAL SHARMA B.TECH IV YEAR ROLL NO.-10EJCEE065 ELECTRICAL ENGINEERING JECRC JAIPUR
CERTIFICATE
To whom so ever it may concern
This is to certify that VISHAL SHARMA of IV year VII sem. (EE) has submitted
his
practical
training
seminar
report
on
GSS
HEERAPURA,JAIPUR for practical fulfillment of degree of Bachelor of
Technology
in
Electrical
Engineering
branch
of
RAJASTHAN
TECHNICAL UNIVERSITY,KOTA(RAJ.)
Date :
MR. S.N.JHAWAR
Place:
(HOD, EE Department)
PREFACE Practical knowledge means the visualization of the knowledge, which we read in books. For this we perform experiments and get observations. Practical knowledge is very important in every field. One must be familiar with the problems related to that field so that he may solve them and became successful person. After achieving the proper goal of life an Engineer has to enter in professional life. According to this life he has to serve an industry, may be public or private sector or self-own. For the efficient work in the field he must be well aware of practical knowledge as well as theoretical knowledge. To be a good Engineer, one must be aware of the industrial environment & must know about management, working in industry, labour problems etc., so he can tackle them successfully. Due to all the above reasons & to bridge the gap between theory and practical, our engineering curriculum provides a practical training course of 30 days. During this period a student in industry and gets all type of experience and knowledge about the working and maintenance of various types of machinery. I have undergone by 30 days of training ( after III yr.) at GSS HEERAPURA,JAIPUR This report has been prepared on the basis of
the knowledge which I acquired during my 30 days (01-06-2013 to 030-062013) training at GSS.
CONTENTS Page No. i.
Certificate Acknowledgement Abstract
ii. iii. .
CHAPTER 1: INTRODUCTION TO 220 KV GSS,HEERAPURA
1
CHAPTER 2: TRANSMISSION LINES
4
CHAPTER 3: SINGLE LINE DIAGRAM
7
CHAPTER 4:-TRANSFORMERS
9
CHAPTER 5: ISOLATOR
20
CHAPTER 6: CIRCUIT BREAKER
23
CHAPTER 7: LIGHTNING ARRESTORS
29
CHAPTER 8: INSULATORS AND RELAYS CHAPTER 9: CONTROL ROOM & BATTERY ROOM
34 39
CHAPTER 10: BUS BAR SYSTEM
42
CHAPTER 11: WAVE TRAP
43
CHAPTER 12: POWER LINE CARRIER COMMUNICATION
44
CHAPTER 13: EARTHING
47
CHAPTER 14: CONCLUSION
50
CHAPTER 1
INTRODUCTION TO 220 KV GSS, HEERAPURA, JAIPUR 1.1 Introduction When
India
became
independent
its
overall
installed
capacity
was
hardly
1900MW.During first five year plan (1951-1956) the capacity was 2300MW.The contribution of Rajasthan state was negligible. Rajasthan state electricity board came into existence in July1957. In India electrical power is generated at a voltage of 11 KV to 33 KV. This is taken stepped up to the transmission level in the range of 66 KV to 400 KV. Member of transmission and switching have to be created. These are known as “SUB STATION”. A Sub Station is an assembly of apparatus, which transform the characteristics of electrical energy from one form to another say from one voltage level to another level. Hence a substation is an intermediate link between the generating station and consumer. Electricity boards are set up in all states of India which are responsible for 1. Generation 2. Transmission
3. Distribution They also construct, install and maintain all the station made for these purpose. In Rajasthan R.R.V.P.N.L is responsible for transmission and distribution of electrical power all over Rajasthan. It has it’s on generating station and it’s also get’s power from various other stations also. It get’s power from following station:1. Badarpur Thermal Power Station Delhi
2. Bhakara Nangal Project (at Satlaj in Punjab) 3. Gandhi Sagar Dam Kota 4. Jawahar Dam Kota 5. Rana Pratap Sagar Dam Kota 6. Rajasthan Atomic Power Plant (RAPP) Kota 7. Kota Super Thermal Power Station (KSTPS) Kota 8. Anta Gas Power Plant (NTPC) Anta 9. Rajasthan Share in Bhankra Beas Management Board (BBMB)
Any substation has many types of civil and electrical works. Main components are :1. Bus bar 2. Power Transformers 3. Isolators 4. Circuit Breaker 5. Lightening Arrester6. Insulators
INCOMING FEEDERS :
HEERAPURA (400 KV)
OUTGOING FEEDERS :
SANGANER (220 KV)
HEERAPURA ITSELF (11KV)
SODALA (132 KV)
DUDU (132 KV)
BAGAD (132KV)
VIDAYADHAR NAGAR(11 KV)
1.2 Introduction Of R.S.E.B. Electrical energy occupies the top grade in energy hierarchy. It find innumerable used in home, industry, Agriculture etc and even in the transport. Rajasthan state electric board started functioning from 1st July 1957. But it has been divided into 5 companies namely. 1. RAJASTHAN RAJYA VIDYUT PRASARAN NIGAM LTD (RRVPNL) 2. RAJASTHAN VIDYUT PRASARAN NIGAM LTD (RVPNL) 3. JAIPUR VIDYUT VITRAN NIGAM LTD (JVVNL) 4. AJMER VIDYUT VITRAN NIGAM LTD (AVVNL) 5. JODHPUR VIDYUT VITRAN NIGAM LTD (JVVNL) R.S.E.B. is the big public organization, which is responsible for the supply of electricity to whole of the state. It is a organization of public having a business of unique quality the electricity must be use at the instant of its generation because electricity cannot be stored at large amount.
CHAPTER 2 TRANSMISSION LINES 2.1 Transmission Lines In this category the EHV lines viz. Extra high voltage lines of 400 kV, 220 kV, 132 kV and 66 kV are considered/are used voltage from one grid sub-station to other sub-station through six various types conductors. 2.1.1 The Conductors Used For:-
i. For 400 KV line: Taran Tulla and Marculla conductor. ii. For 220 KV line: Zebra conductor is used composite of aluminums strands
and
steel wires. iii. For 132 KV line: Panther conductor is used composite of aluminum strands
and
steel wires. The material used in these conductors is generally aluminum conductor steel reinforced (ACSR). The conductors run over the tower cross arms of sufficient height with the consideration to keep safe clearance of sagged conductor from ground level and from the objects (trees, buildings etc.) either side also.
2.2 Substation:A sub-station is a intermediate link between the generating station and consumer. It may be defined as the assemblies of apparatus which transfer the characteristic of electrical energy from one form to another for example one voltage to another. The electrical energy is generated at low voltage link 6.6 or 11 KV, through higher voltage to 33 KV are also possible due to economic considerations, low voltage is converted to high voltage like 66 KV, 132 KV, 220 KV, 400 KV, 765 KV for transmission purpose. This can be done with the help of the transformer. The consumers’ apparatus are made for low voltage so this voltage is again to be stepped down to the required voltage at the sub-station.
Figure 2.1- View of Transmission Line 2.2.1 Grid:-
Grid is a technical word use for the term for interconnection of power received from more than one place. It is network of main power lines f or distribution of electricity. Now Grid sub-station (G.S.S.) means a sub-station where power from more than one place is interconnected through equipment. 2.2.2 Aspects Of A Grid Sub-Station :-
The sub-station may compared of the following. a. A switch yard for locating various equipment and instruments protective CT & PT and Lighting arrester etc. if the substation is near to load center it will have L.T. distribution & sub transmission equipment and if the load is far from switch yard, will have transformers breakers and other H.T. control equipment. b. Transmission lines, towers, poles etc. c. Sub- Station (distribution) from where the feeders are run for consumers.
d. Workshop for the repairs and maintains every sub-station is designed keeping in of the following aspects. 1. Reliability 2. Minimum capital cost and operating cost. 3. Maximum demand of consumers groups.
Total No. Of the Towers are:a. Transmission Towers b. Dead end towers c. Tangent towers d. Angle towers e. Extension towers f. Spiral towers g. Section towers h. Narrow base towers (used in 33 KV lines)
CHAPTER-3
SINGLE LINE DIAGRAM
A Single Line Diagram (SLD) of an Electrical System is the Line Diagram of the concerned
Electrical
System
which
includes
all
the
required
ELECTRICAL
EQUIPMENT connection sequence wise from the point of entrance of Power up to the end of the scope of the mentioned Work. As in the case of 220 KV Substation, the SLD shall show Lightening Arrestor, State Electricity Board's C.T/P.T Unit, Isolators, Protection and Metering P.T & C.T. Circuit Breakers, again Isolators and circuit Breakers, Main Power Transformer, all protective devices/relays and other special equipment like NGR, CVT, GUARD RINGS, SDR etc as per design criteria. As these feeders enter the station they are to pass through various instruments. The instruments have their usual functioning. They are as follows in the single line diagram1. Lightening arrestors, 2. C V T 3. Wave trap 4. Current transformer 5. Isolators with earth switch 6. Circuit breaker 7. Line isolator 8. Bus Bar 9. Potential transformer in the bus with a bus isolator 10. Isolator 11. Lightening arrestors with earth switch 12. A capacitor bank attached to the bus.
CHAPTER 4 TRANSFORMERS 4.1 Introduction:A transformer is a static (or stationary) piece of apparatus by means of which electric power of one circuit is transformed into electric power of same frequency in another circuit. In brief, a transformer is a device that: 1. Transfer electric power from one circuit to another 2. It does so without change of frequency 3. It accomplishes this by electromagnetic induction 4. Where the two electric circuits are in mutual inductive influence of each other A high voltage is desirable for transmitting large powers in order to decrease the IR losses and reduce the amount of conductor material. A very much lower voltage, on the other hand, is required for distribution, for various reasons connected with safety and convenience. The transformers make this easily and economically possible. There are single phase and three phase transformers which are used as requirement. The main advantage of a 3-phase X-former is that 3-phase load tap changing mechanism could be used further the installation of a single 3-phase transformer is simple than 3 phase transformers.
In 220kv GSS HEERAPURA, there are four power transformers. There are two
220/132/11kv,50/70/100MVA
220/132/11kv,
rating
transformers
and
two
100 MVA Transformer no.1& no.2
Company –Crompton Greaves Ltd.,Bombay Type – SAFLOCK Auto transformer with ON LOAD tap changer. Type of cooling :-
ONAN/aN/ODAF
CAPACITY
-
50/70/100 MVA
VOLT
HV
220kv
LV
132kv
RATIO
-
220/132/11kv
AMP
HV(A)
131.3/184/263
LV(A)
219/307/438
(at no load)
(line value)
Percentage Impedance - 6.34 (100 MVA base HV-LV) Connect on symbol
YNod 1
No. of phases
3
Frequency
50Hz
Mass of core & winding
67000 Kg
Mass of oil
45000 Kg
Total mass
144000 Kg
Volume of oil
5000 Kg
Mass of heaviest PKg.
83300 Kg
Oil circulation
3400 L/mm
Air circulation
4x 200m3/mm
Guaranteed max. temp. rise of oil 400 C Wdg.500C
ON LOAD TAP CHANGER DETAILS
Tripping range
+10% to -15%
Step voltage
2000V
Rated current
800A
Breaking capacity(max)
1400KVA
Diverter switch resistance
9.3 ohm
Max. short ckt withstand
3sec.
time capability
160 MVA Transformer no.1& no.2
Company –Crompton Greaves Ltd.,Bombay Type – SAFLOCK Auto transformer with ON LOAD tap changer. Type of cooling :-
ONAN/ONAF/ODAF
CAPACITY
-
96/128/160 MVA
VOLT
HV
220kv
LV
132kv
RATIO
-
220/132/11kv
AMP
HV(A)
251.94/335.92/419.90
LV(A)
419.90/559.87/699.80
(at no load)
(line value)
Connect on symbol
YNa0d 1
No. of phases
3
Frequency
50Hz
Mass of core & winding
69800Kg
Mass of oil
48700Kg
TANK & FITTING MASS
36100Kg
Total mass
154600 Kg
Volume of oil
54700 Kg
Oil circulation
3400 L/mm
Air circulation
4x 200m3/mm
4.2 Power Transformer:The transformer is oil immersed with triple rating of 100 MVA auto under ON (natural cooling) (oil immersed with natural air-cooling) or (oil immersed with forced oil cooling). The tertiary is suitable for 11MVA continuous synchronous condenser loading.
When
the tertiary is load the secondary load should be limited, such that no industrial individual winding is over loaded and are also that total loss es are not exceeds. It is ensured that the tertiary winding will also operate satisfactory with each other. The transformer is provided with separate tank of radiators, fans, pumps and associated control equipment. The control equipment is housed in a tank mounted marshalling commercial. It is provided with on load tap charge.
Figure- 4.1- A 100MVA Power Transformer A transformer double wound or auto wound has minimum of two voltage, one corresponding to the supply and second to the load side. Many time a third winding is
introduced in primary and secondary, winding requires it because another voltage may be required at the place of supply to load. In either core the third winding is connected to delta formation and is generally known as "tertiary" winding in the case of star/star methods of connection three phase shell type transformer is used which causes a serious problem of the third harmonic components of the magnetic currents. The tertiary delta provides a short circuit for flow of the third harmonic currents therefore eliminating third harmonic multiple connection are provided on primary and secondary winding. The neutral point of such winding is therefore stable and can earthen without any effect to the X-mer on the system The territory winding helps1. To reduce the unbalancing in the phase of the primary side due to unbalanced three phase loads; 2. To redistribute the flow of faults currents; 3. To supply an auxiliary load in addition to the main load. This could be consists of the power factor improvement synchronous condensers or shunt capacitors. In such a case the purchaser of a power X mer should always specify the voltage and power ratings of the tertiary winding; 4. As compared with star/delta connection of fault current in the event of secondary form line to neutral tertiary delta consists in the laminations. This of course further depends upon the impedance between tertiary and main winding.
PARTS & FITTINGS OF THE TRANSFORMER:1 CORE:-
It is used to provide closed magnetic coupling b/w L.V. & H.V. coils &to reduce leakage flux & to provide low reluctance path. Core is made of laminated magnetic material. The material is generally in the form of laminated Silicon alloy steel. Silicon risks the permeability at low flux density, reduces hysteresis loss & eddy current loss. Each lamination is coated with thin layer of insulation varnish.
2 WINDING:-
Winding of a t/f that is L.V. & H.V. winding are attached on the limbs. They are made up of copper. Cylindrical, concentric winding are used for core type t/f for L.V. & H.V. 3 TANK & TANK COVER:-
Inside the tank oil is filled & the core is placed. The tank cover is used to prevent the entry of dust particles & external impurities.
4 L.V. & H.V. BUSHINGS:-
Bushings comprises of a central conductor surrounded by graded insulation. A bushing is necessary when a conductor is taken out through a metallic tank.
5 TAP CHANGER:-
Adjustment of voltage is done by changing the effective turns ratio of the system transformer by proper selections of tapings on the winding. There are 2 types of tap changing:
OFF LOAD TAP CHANGING
ON LOAD TAP CHANGING In the first form as none implies it is essential to switch off the t/f before
changing the tap. On load tap changers are employed to regulate voltage while t/f is delivering normal load. Tap changers are provided on the outer winding or moreover the H.V. side has number of turns. During transition two adjacent taps are momentarily connected & the short circuit is limited by the automatic insertion of impedance b/w the corresponding tapping. 6CARRIAGE:-
It is used to move the t/f when it is to be installed or is to be taken to repair.
7 JACKING OR LIFTING LUGS:-
They are used to lift the t/f.
8.5 FITTINGS:-
1 RADIATOR:-
It is used for cooling purpose of the insulating oil.
2 PRESSURE RELIEF PIPE OR VENT PIPES:-
It is a cylindrical steel pipe whose one end is connected to the main tank through the bolts & the other is connected to diaphragm (thin glass plate). It prevents the tank from bursting when excessive gas gets collected in the tank.
3 BREATHER:
If the moisture enters the t/f then the dielectric strength of the oil reduces. The breather absorbs the moisture from the conservator. It is connected to the conservator. It consists of crystals of silica gel. Dry cell gel is of blue color. Moist silica gel becomes pink.
4 ARCHING HORN:-
To prevent the t/f from lightening & excessive voltage & to send the current obtained from this to earth, two rods of horn shape are fitted on the voltage bushing.
5 OIL GAUGE:-
It is used to note the oil level in the conservator tank.
6 PRESSURE GAUGE:-
It is used to note the pressure inside the tank.
7 OIL TEMPERATURE INDICATOR:-
It indicates the temperature of the oil inside the main tank of the t/f.
8 WINDING TEMPERATURE INDICATOR:-
It indicates the temperature of the windings of the t/f.
9 OIL LEVEL INDICATOR:-
It indicates level of oil in the conservator tank & also show the level of oil according to temperature.
4.3 Auto Transformers:Basically auto-transformer comprises of only one winding per phase, part of which is used by both primary and secondary winding. This arrangement results into an appreciable saving in cost as well as higher operating efficiency is achieved, but their extensive use is not being favored by power utilities due to certain inherent disadvantages which are as follows: 1. It has got low inherent reactance as such is subjected to severe short circuit conditions. 2. Since primary and secondary side uses same windings, there is always possibility of imposition of higher voltage on secondary in case of fault. 3. Both the windings make use of common neutral, as such neutral is required to be earthed or isolated on both sides.
4.4 Instrument – Transformer:The transformer are used in A.C. system for the measurement of current , voltage, power and energy, the actual measurements being done by measuring instruments. Transformer used in conjunction with measuring instrument for measurement purposes are called as "instrument transformer". The transformer used for the measurement of current is called "current transformer". Transformer used for voltage measurement are called as "voltage transformer" or" potential transformer". 4.4.1 Current Transformer :-
In electrical engineering , a current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently
connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current
transformers
are
commonly
used
in
metering
and protective relays in
the electrical power industry. RATINGSREF. Standard
-
IS : 2705/1992
C.T. RATIO
-
400-800/5 A
System Voltage
-
245kv
Frequency
-
50Hz
Current/Time
-
40 KA for 1 SEC
Current
-
100 KAP
Insulation Level
-
460/1050 KV
Figure- 4.4- Current Transformer
4.4.2 Voltage Transformers:-
Voltage transformers (VT) or potential transformers (PT) are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed
to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that met ering and protective relay equipment can be operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 V or 120 V at rated primary voltage, to match the input ratings of protection relays. The transformer winding high-voltage connection points are typically labeled as H 1, H2 (sometimes H0 if it is internally grounded) and X 1, X2 and sometimes an X 3 tap may be present. Sometimes a second isolated winding (Y1, Y2, Y3) may also be available on the same voltage transformer. The high side (primary) may be connected phase to ground or phase to phase. The low side (secondary) is usually phase to ground. The terminal identifications (H1, X1, Y1, etc.) are often referred to as polarity. This applies to current transformers as well. At any instant terminals with the same suffix numeral have the same polarity and phase. Correct identification of terminals and wiring is essential for proper operation of metering and protection relays. Some meters operate directly on the secondary service voltages at or below 600 V. VTs are typically used for higher voltages (for example, 765 kV for power transmission), or where isolation is desired between the meter and the measured circuit.
Figure- 4.5- Voltage Transformer Voltage transformers which step-down systems voltages to sufficiently low values are necessary on every system for: a. Induction of the voltage conditions b. Metering of the supply (or exchange of energy)
c. Relaying and d. Synchronizing On account of cost and voltage the indicating instruments meters and relays are designed for the voltage as obtainable from the secondary sides of the voltage transformer. The calibration of the indicating instruction and meters is however done accordingly to the primary voltage of the V.Ts. The voltage transformers are classified as under: a Capacitive voltage transformer or Capacitive type b. Magnetic type
CHAPTER-5 ISOLATOR 5.1 Introduction:When carrying out inspection to disconnect reliably the unit or section on which the work to be done from all other live parts on the in-station in order to ensure completely safety of the working staff. To afford against minute mistakes it is desirable that it should be done by an apparatus which makes a visible break in the circuit such an apparatus is the isolating switch (for insulator). It may be defined as a device used to open (or use) a circuit either when negligible current is interrupted (or established) or when no significant charge the voltage across the terminals of each pole of the isolator will result from the operation. Isolator may be classified as single pole and 3-pole isolator i.e. according to number of poles. According to the service type these are: i. Indoor type and ii Outdoor type
5.2 Operation:The operation of an isolator may be manual i.e. by hand without using any other supply or storage of energy meter power operated isolates during the cause of operation utilize energy which is not supplied by the operator. The energy may be electrical pneumatic or the energy previously stored in spring or counter weight.
5.3 Control:In case power operated isolators are purchased for any installation it may be worthwhile to examine further weather control should be local in switchyard or remote in the control room.
The extra cost enrolled in the isolated is quite substantial particularly at voltage 132 kV and below. It should therefore considered in detail whether any installation really instifies the procurement of remote operated isolators keeping in view the past that the frequency of operation of isolators is rather low.
5.4 Auxiliary Switch:This is an operating and important accessory and is designed as a switching device working in conjunction with an isolator for controlling a circuit for auxiliary device such as trip coils indicators or indicating lamps. The number of normally closed and normally open contacts should be specially worked out particularly if electrical interlocking between breakers and isolators is chosen. 5.4.1 Make Before And Break After Contacts:-
These are provided in series with the main contacts so that in case of load isolators, the arcing is taken and whenever necessary only the arcing contacts are replaced.
5.5 Arcing Horns:These are provided on each stack of post Insulator for the purpose of insulation coordination some time confusion is created in the function of these arcing horns vis a vis (make before and break after contacts. These ma y be fixed or adjustable types). The use of arcing horns is avoided where insulation strength between poles or phases and between higher than that of earth. This is necessary for safety and security. Any travelling wave meeting an isolator is the closed position should causes of it must a flash over to earth rather than between phase or between terminal of the same pole where the design of the isolator itself provides for this. It is necessary to use arcing hours on the insulator stacks.
Figure:-5.2- View of Arcing Horn
5.6 Interlocking:In correct operation of an isolating switch may be accidentally harmful effects and may cause distribution of part of the plant as well as costly service interruption for preventing such incorrect operation inter locks are used i.e. isolating switches. The mechanical interlocking between isolating switches and it is earthing switch consists of a rod linkage between isolating switch and its earthing switch shafts of the respective switches. The mechanical interlocking between isolation switches and circuit breaker and different isolating switches is generally in the form of lock and key arrangement. There is usually a common key for a number of locks mechanical interlocking is generally provided on hand operated are isolating switch only. Electrical interlocking is achieved with blocking magnets; these magnets are arranged on the isolating switch on the hand drive or in the value controlled. The pneumatic drive and are controlled by pilot switch contents.
CHAPTER-6 CIRCUIT BREAKER 6.1 Introduction:A circuit breaker is equipment, which can open or close circuit under all condition viz. No load, full loads an fault conditions. It is so designed that it can be operated manually under normal conditions and automatically under fault conditions, for the later operation, relay circuit is used. Circuit breaker can be defined as an electrical device, which protects the system from short circuits or overloads with the help of relays. In case, circuit breaker is not of adequate capacity, its failure may result into interruption of power, shut downs, injury to personals and damage to property. Installation of over rated circuit breakers or extra sensitive and costly protective devices will mean un-warranted expenditure. It is therefore necessary that calculations in respect of short circuit currents for the concerned system be made before correctly rated circuit breakers are selected or steps are taken to improve the existing system.
IN heerapura,there are SF6 Circuit Breakers.
TYPE
-
QFCI-200
RATED VOLTAGE
-
245 KV
NORMAL CURRENT
-
2000 A
FREQUENCY
-
50 Hz
RATED SHORT CIRCUIT
-
40KA
BREAKING CURRENT
6.2 Operating Principle:A circuit breaker consists of fixed and moving contacts under normal operating conditions, these contacts remain closed. In this condition, the emf in the secondary winding of current transformer (CT) in sufficient to operate the trip coil of the breakers but the contacts can be opened by manual or automatic control. When a fault occurs on any part of the system the resulting over current in the C.T. primary winding increases the secondary winding EMF and hence the current through the relay operating coils. The relay contacts are closed and the trip coil (tripping coil) of the breaker is energized. The moving contacts are pulled apart by some mechanism thus operating the circuit breaker. When the contacts of the circuit breaker are separated under fault conditions, arc is produced between them (male and female contact). The current is thus able to continue until the arc ceases. This arc generates enormous heat, which may cause damage to the system or to the breaker itself. Therefore, the main problem in a circuit breaker is to extinguish the arc within the shortest time so that heat generates by it may not reach a dangerous value.
6.3 Classification Of Circuit Breakers For Various Voltages:1. Bulk oil circuit breaker.
2. Air blast circuit breaker.
3. SF-6 circuit breaker. 4. Minimum oil circuit breaker. 5. Vacuums circuit breaker . 6.3.1 Bulk Oil Circuit Breaker :-
In such circuit breaker transformer oil is used for arc extinction. The contacts are opened under oil, which absorbs the heat of arc, and decomposed into gases as hydrogen, which have excellent cooling properties due to high heat conductivity. Circuit breaker compresses of three-pole contact assembly housed in a circular welded steel tank. Circuit breaker is mounted on an angle iron frame grounded in cement concrete base the breaker is provided with spring or solenoid operating mechanism. The contacts are of but type the stationary portion comprises of two contacts pivoted at the base of the explosion pot. The cross jet assembly is made of blocks of insulating materials, which together form a chamber of irregular shape. The throat block and single block have circular holes located centrally through which moving contact passes. The barrier plates are shaped to form nozzle outlets through which the oil and arc glasses are projected from the explosion pot. When the breaker is tripped on load or on fault, the moving contact breaks circuit with the stationary contacts and the resulting arc is drawn downward through the throat hole. The gas produced from the oil by the arc accumulated in the expulsion a pot at high pressure. This pressure acts downward on the end of the moving contact and so accelerates its movement. As the moving contacts descends, the flush of oil and gas sweeps through the arc an passes out through nozzle outlets thereby producing powerful quenching effect and causing disruption of the arc before the contact leaves the cross jet assembly.
The disadvantages of oil as an arc excitation medium for an arc: -
1. It is inflammable and there is a risk of fire. 2. The quality of oil deteriorates, due to increase of carbon in oil with the excessive use of breaker. This needs periodic checking and replacement of oil.
3. In B.O.C.B. the increase in carbonization weakness the dielectric strength of the oil of breaking strength of oil.
Figure 6.1- Bulk Oil Circuit Breaker 6.3.2 Air Blast Circuit Breaker:-
In such circuit breaker, high-pressure air blast is used for arc extinction. The contacts are opened in the flow of air blast. The air blast cools the arc and removes the arcing products (mainly composed of carbon) to the atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevents the arc restricting. Consequently the arc is extinguished a flow of current is interrupted. For the interruption of current on load, air blasts C.B. are used. In 220kv A.B.C.B. is used. This type of circuit breaker has four interrupter terminals while in 132kv there are three interrupter terminal of A.B.C.B. A pole chiefly consists of number of identical column each are standing on it compressed air rec eiver supporting interrupter. The C.B. can be operated both electrically either from relay station or with a separate master switch and a push button operate valve in the central controlling cabinet AB-5.
The controlling impulse are transmitted from the controlling cabinet AB-5 electrically or pneumatically to the control again in the panel box and from these to the intermediate value AB-5 which in turn determines the condition in air insulators and position of C.B.. The controlling cabinet has alarm type pressure gauge for the pressure in the receiver of the pole pressure switches and mechanically lode pressure blocking device.
Figure:-6.2 View of Air Blast Circuit Breakers 6.3.3 SF6 Circuit Breaker:-
The arc excitation process in SF6 gas removes the heat from the arc by axial convention and radial dissipation. As a result the arc diameter reduces during the decreasing made of the current zero and arc is extinguished due to its Electromagnetic and low arc time constant, the gas remains its dielectric strength rapidly after the final current zero. The rate of rise of dielectric strength is very high and time constant is very small. The arc extinguished properties of SF6 gas has pointed out in 1983.
Figure- 6.3- SF6 Circuit Breaker 6.3.4 Minimum Oil Circuit Breaker:-
Oil circuit breaker uses dielectric oil (transformer oil) for the purpose of arc extinction. In bulk oil circuit breaker the arc extinction takes place in the tank where as in M.O.C.B. the current interruption takes inside interruption. The enclosure of the interpreter is made of insulating material like porcelain. Hence clearance between the live part and the enclosure can reduce and layer quality requires of internal insulation.
Figure 6.4- Minimum Oil Circu
CHAPTER-7 LIGHTNING ARRESTER 7.1 Introduction:Lightning Arresters are installed in power houses and sub-stations to safeguard the major equipment like power-transformers, switch gear and to ensure the flow of power uninterruptedly. It is true that lightning arresters require minimum post-installation care, but their importance as a critical equipment can hardly be disputed.
7.2 Lightning Strokes And Over-Voltages:The overhead transmission lines and connected electrical apparatus i.e. Power Transformers, Switch gear etc. are subjected to over voltages on account of lightning discharges caused by atmospheric disturbances and or by switching operations. Abnormal voltages are caused by atmospheric disturbances as a result of:
Figure- 7.1- Lightning Arrester
7.3 Types Of Lightning Arresters:Lightning protective devices, which are in market, are of the following type: 7.3.1 Rod Gap or 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 on the system. It does not fulfill the function of ideal lightning arresters i.e. it does not cut off power voltage after it has flashed over by a surge, in other words a short circuit will be caused on the system every time a surge causes a flash-over. Flash over conditions are also affected by rain, pollution, humidity temperature and polarity of the incident waves. In view of these disadvantages it can be only used as "back up" protection in case main lightning arrester gets damaged.
Figure:-7.2 View of Rod Gap Type Lightening Arrest er
7.3.2 Expulsion type Lightning arresters:-
Expulsion type lightning arresters are also called "expulsion protector tubes", "de-ion tubes" and "line type expulsion arresters." Constructional details and salient features of expulsion type lightning arresters are shown in fig.
Figure:- 7.3 View of Expulsion Type Lightning Arrester
7.3.3 Valve Type Lightning Arresters:-
Valve type Lightning arrester consists of number of spark gaps in series with non-linear resistors, the whole assembly being rigidly housed inside a hermetically sealed bushing. Under normal conditions, power frequency system voltage does not cause break down of series spark gaps and thereby insulate the line from ground for the highest system voltage. When undesirable transient voltages due to lightning are super-imposed over the system, the series gap assemblies spark over at a pre-determined value. After the breakdown of the gaps, the non-linear resistors conduct the surge current to the ground offering very low resistance and limit the power frequency current, to a value, the gaps can interrupt at the first current zero. During the flow of the discharge current the nonlinear resistor limit the voltage drop across the arrester to a value far below the BIL of the equipment. The valve type lightning arresters are generally classified as station type and line type. Station type lightning arresters are very robust and efficient and are installed in substations and power houses. Line type lightning arresters are similar to station type lightning arresters but are smaller in cross-section and are less costly. Line type arresters allow higher surge voltages across their terminals and have low surge current capacity
Figure:-7.4 View of Valve Type L.A.
7.4 General Rating Recommendations Of Lightning Arresters:i. 10 KV rated lightning arresters: Arresters of this rating are used in case of power stations and E.H.V. sub-stations. ii. 5 kA rated lightning arrests: Arresters of this capacity normally are used in case of high voltage sub-stations having system voltage as 66 KV or less. These are also used in case of small power houses. iii. 2.5 kA rated lightning arresters: Arresters of these ratings are used in case of system up to 11 KV. iv. 1.5 KA rated lightning arresters: arresters of these ratings are normally used in case of distribution system.
7.5 Location of Lightning Arresters:In order to ensure effective protection of the equipment lightning arresters should be located:
a. Very close to the equipment to be protected and connected with shortest leads on both the line and ground side to reduce the inductive effects of the leads while discharging large surge currents. b. In order to ensure the protection of transformer windings it is desirable to inter-connect the ground lead of the arrester with the tank and also the neutral of secondary. This interconnection reduces the stress imposed on the transformer windings by the surge currents to the extent of the drop across the earth resistance and the inductive drop across the ground lead.
CHAPTER-8 INSULATORS & RELAYS
In order to present the flow of current to the each earth from support the transmission line and distribution lines are secured to the supporting tiers or pole with the help of insulators. Thus the insulators play an important role in the successful operation of lines.
8.1 Requirements For Insulators :1. Mechanically Strong 2. High dielectric strength 3. High insulation resistance to the leakage current 4. Free from internal impurities 5. They should be porous 6. They should not be affected with change in temperature.
8.2 Types Of Insulators:8.2.1 Pin Type Insulators: - It is one of the earliest designs used for supporting lives
conductors. is used for low voltage up to 33 KV. The pin insulators are screwed on and firmly attached to galvanized steel bolts.
Figure- 8.1- Pin Type Insulator
8.2.2 Suspension Type Insulators :-
For higher voltage up to 132 KV suspension insulators are used, a number of them are connected in series by metallic links to form a chain and the line conductor is carried by the bottom most insulator.
Figure- 8.2- Suspension Type Insulator 8.2.3 Shackle insulators :-
It is mostly used for low voltage distribution lines such insulators can either be used in a horizontal position or in a vertical position. The conductor in the groove are fixed with the help of soft binding wires.
Figure 8.3- Shackle Type Insulator
8.2.4 Strain Insulators :-
When there is a corner or a sharp curve or the lines crosses river etc., the line is to withstand great strain.
Figure 8.4- Strain Type Insulator
8.3 Bus Bar It is a incoming 220kv feeder BUS from which the line is taken to the transformer for further step down. There are two bus systems.
8.3.1 Double Main Bus & Transfer Bus System Merits:-
1. Most flexible in operation. 2. Highly reliable. 3. Breaker failure on bus side breaker removes only one circuit. From servi ce. 4. All switching done with breakers. 5. Simple operation, no isolator switching required. 6. Either main bus can be taken out of service at any time for maintenance. 7. Bus fault does not remove any feeder from the service.
Demerits:-
1. High cost due to three buses.
8.3.2 Mesh (Ring) Bus Bar System Merits:-
1. Bus bars gave some operational flexibility. Demerits :-
1. If fault occurs during bus maintenance, ring gets separated into t wo sections. 2. Auto-reclosing and protection complex. 3. Requires VT’s on all circuits because there is no definite voltage reference point. These VT’s may be required in all cases for synchronizing live line or voltage indication. 4. Breaker failure during fault on one circuit causes loss of additional circuit because of breaker failure.
8.4 Synchronoscope:-
A synchronoscope is used to determine the current instance of closing the switch, which connects new supply to bus bar.
8.4.1 Basic Equipment Or Requirement Of Protective Relays:-
Basic requirements of protective relays are as follows
1. Speed
Protective relaying should do's connect a faulty element as quickly as possible. 2. Selectivity
The ability of the protective relay to determine the point of which have the fault occurs and select the nearest circuit breaker tripping of which will lead the clearing of fault with min-or so damage to the system. 3. Sensitivity
It is the capacity of the relaying to operate relay under the actual condition that produces the last operating condition tendency. Depending upon the method of element connected primary relay (series element connect directly on the circuit of protective element) and secondary relay (sensing element connected through a current and voltage transformer).
8.5 Relay There are many type of relays1. Over current relays 2. I.D.M.T. fault relay 3. Impedance relay 4. Earth fault relay 5. Buchholz relay 6. Differential relay 7.0 Auxiliary relays .
CHAPTER-9 CONTROL ROOM & BATTERY ROOM 9.1 CONTROL ROOM:There is a “Control Room” in the “HEERAPURA, JAIPUR ” in which “Control Panel” is present. All the connections of the transformer & feeder’s are done here from “Remote Operation”. These panels operate by DC supply. From this I/C & O/G supply are connected. The “Control Cables & Conduit System” is required for affecting automatic controls. The cable system generally operates at 110 V or 220 V. For laying these cables generally, ducts run from “Control Room” basement to centrally located ”Junction Box” from where the conduits are send to the required points. For providing D.C. voltage 55 dry cells connected in series. There is a s eparate room or ”Battery Room” for having these batteries.
Fig 9.1 CONTROL ROOM
9.2 Battery Room 9.2.1 Introduction:-
Storage battery is the most dependable source of supply of D.C. power required for closing and tripping of circuit breakers, operation of automatic protective devices; signaling equipment, remote control apparatus, telephone service and emergency lighting in case of power plants and sub-stations. Correctly selected and properly maintained battery will withstand heavy stresses and strains during service without causing much headaches to the maintenance Engineer. D.C. Auxiliary power supply is provided from storage batteries maintained continuously charged by some type of supply set or a charger. The voltage of the auxiliary supply is maintained at 110/220 .The battery room should be ready in all respects by fulfilling the following minimum requirements1. The walls and the ceiling of the battery room should be well black washed and should remain clean and dry. 2. The flooring of the battery room shall be acid resis tant tiles and material. 3. The battery room should be well lit. there should be no direct sun light on the cells. 4. Suitable exhaust fans shall be fixed to provide a minimum of six air charges per hour. 5. The exhaust fans shall be suitably distributed and placed on the wall, which open to atmosphere, equally sufficient air inlet should be provided to prevent any negative pressure developing in the room. 6. Necessary blowers are to be provided to maintain sufficient air inlet in to room 7.Never the entrance door should be kept closed which will lead to a negative pressure developing in the batter room due to the continuous operation of exhaust fans. 8. Inlet air should be free from effluents (such as chlorine, acetic acid). 8.6.2 Advantages of Storage Batteries:-
1. High Reliability 2. Independences of A.C. power circuit conditions of existence of the faults.
Figure:-9.2 View of Battery Room
CHAPTER-10 BUS BAR SYSTEM This bus bar arrangement is very useful for working purpose as every GSS. It is a conductor to which a number of cut .Are connected in 220 KV GSS there are two bus running parallel to the each other, one is main and another is auxiliary bus is only for stand by, in case of failure of one we can keep the supply continues.
If more loads are coming at the GSS then we can disconnect any feeder through circuit breaker which is connected to the bus bar. This remaining all the feeders will be in running position .if we want to work with any human damage. In this case all the feeders will be on conditions.
According to bus voltage the material is used .Al is used because of the property & features and it is cheap.
With the help of bus bar arrangement we can connect all the incoming supply which is coming from different higher order GSS.
CHAPTER-11 WAVE TRAP It is used to trap the communication signals & send PLCC room through CVT. Rejection filters are known as the line traps consisting of a parallel resonant circuit ( L and C in parallel) tuned to the carrier frequency are connected in series at each and of the protected line such a circuit offer high impedance to the flow of carrier frequency current thus preventing the dissipation. The carrier current used for PLC Communication have to be prevented from entering the power equipments such as attenuation or even complete loss of communication signals. For this purpose wave trap or line trap are used between transmission line and power station equipment to-
avoid carrier power dissipation in the power plant reduce cross talks with other PLC Circuits connected to the same power station.
Ensure proper operating conditions and signal levels at the PLC transmit receive equipment irrespective of switching conditions of the power circuit and equipments in the stations.
CHAPTER-12
Power Line Carrier Communication : Introduction
Power Line Carrier Communication (PLCC) provides for signal transmission down transmission line conductors or insulated ground wires. Protection signaling, speech and data transmission for system operation and control, management information systems etc. are the main needs which are met by PLCC.
PLCC is the most economical and reliable method of communication because of the higher mechanical strength and insulation level of high voltage power line which contribute to the increased reliability of communication and lower attenuation over the larger distances involves.
High frequency signals in the range of 50 KHZ to 400 KHZ commonly known as the carrier signal and to result it with the protected section of line suitable coupling apparatus and line traps are employed at both ends of the protected section. Here in Sanganer and also in other sub-station this system is used. The main application of power line carrier has been from the purpose of supervisory control telephone communication, telemetering and relaying.
Power line carrier communication
PLCC Equipment The essential units of power line carrier equipment consists of :-
Wave trap
Coupling Capacitor
LMU and protective equipments .
MERITS AND DEMRITS OF PLCC Merits I.
The severity that a power line can withstand is much more than that odd communication line due to higher mechanical strength of transmission line power lines generally provide the shortest route between the Power Station and the Receiving Stations.
II.
The carrier signals suffer less attenuation, owing to large cross sectional area of power line.
III.
Larger spacing between conductors reduces the capacitances which results in lesser attenuation of higher frequencies.
IV.
Large spacing also reduces the cross talk to a certain extent.
V.
The construction of a separate communication line is avoided.
Demerits i.
Utmost care is required to safeguard the carrier equipment and persons using them against high voltage and currents on the line.
ii.
Noise introduced by power line is far more than in the case of communication line. This is due to the discharge across insulators and corona etc.
iii.
Induced voltage surges in the power line may affect the connected carrier equipment.
CHAPTER-13
EARTHING Earthing is the provision of a surface under the sub station, which has a uniform potential as nearly as zero or equal to Absolute Earth potential. The provision of an earthing system for an electric system is necessary by the following reason. 1. In the event of over voltage on the system due to lighting 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. 2. 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 earthing is of two principal types :
Neutral Earthing.
Equipment Body Earthing.
Neutral Earthing:Neutral Earthing also known as System Neutral Earthing (or Grounding) means connecting the neutral point i.e. the star point of generator,transformer etc. to earth. In rotating machines, generator, transformer circuit etc., the neutral point is always connected to earth either directly or through a reactance. The neutral point is usually available at every voltage level from generator or transformer neutral. If neutral point is not available, then the most common method used is using a Zigzag transformer. Such a transformer has no secondary. Each phase of primary has two equal parts. There are 3 limbs and each limb has two winding, providing flux density under normal condition. Since the fluxes are opposite, the transformer takes very small magnetizing current under normal conditions. During fault, the circuit is primary side,which provides very less impedance to the current. The grounding transformers are short time rating. Their size is almost one tenth as compared to power transformer.
Electrical Earthing:Electrical Earthing is different from neutral earthing. During fault condition, the metallic parts of an electrical installation which do not carry current under normal conditions, may attain high potential with respect to ground. As human body can tolerate only
I=0.165A/T current for a given time t so to ensure safety we connect such metallic parts to earth by means of Earthing system ,which comprises of electrical conductor to send fault current to earth. The conductor used is generally in the form of rods, plates, pipes etc.
Earthing system ensures safety in following ways :-
The potential of earthen body does not reach dangerously high value about earth, since it is connected to earth.
Earth fault current flows through earthing and readily causes the operation of fuse or an earth relay.
Merits of neutral Earthing:1. Arcing grounding is reduced. 2. Voltage of heating with respect to earth remains at harmless value they don't increase to root 3 times of normal value. 3. Suitable neutral point. 4. The earth fault relaying is relatively simple useful amount of earth fault current is available to operate earth fault relay. 5. The over voltage due to lightening are discharged to earth. 6. Improved service reliability due to limitation of arcing ground and improved of unnecessary fringing of CB.
At GSS the neutral point of power transformer is connected solidly to earth generally the earth connection are provided which leads reliability.
EARTHING The resistance of earthing system is depending on shape and material of earth electrode used.
CHAPTER-14 CONCLUSION The training at grid substation was very helpful. It has improved my theoretical concepts of electrical power transmission and distribution. Protection of various apparatus was a great thing. Maintenance of transformer , circuit breaker, isolator, insulator, bus bar etc observable. I had a chance to see the remote control of the equipments from control room itself , which was very interesting. So the training was more than hope to me and helped me to understand about power system more.
