Concept of energy transmission & distribution

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Purpose of Electrical Transmission System
Main Parts of Power System
One-Line Diagram of Generating Station
Main Parts of Generating Station
Components of a Transmission Line

Prepared by:
Zunaib ALi
Muqadsa
Madiha

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  • Different types of towers
  • Fig. Typical 400 KV tower structure
  • Height of tower is determine by-
  • Where-
  • asf
  • I1=current rating for temp rise
  • Concept of energy transmission & distribution

    1. 1. Concept of Energy Transmission 1
    2. 2. Group Members Madiha Naeem Muqadsa Iftikhar Zunaib Ali COMSATS INSTITUTE OF INFORMATION & TECHNOLOGY, ABBOTTABAD 2
    3. 3. Purpose of Electrical Transmission System The purpose of the electric transmission system is the efficient interconnection of the electric energy producing power plants or generating stations with the loads. 3
    4. 4. Main Parts of Power System Four Main Parts: Generation System Transmission System Distribution System Consumer (LOAD) 4
    5. 5. Simplified Diagram of Power System 5
    6. 6. Generating Station The commonly used power plants are: Thermal Power Plant Nuclear Power Plant Hydro Power Plant Gas Turbine Power Plant Combined Cycle Power Plant 6
    7. 7. One-Line Diagram of Generating Station Fig.1: Simplified Connection Diagram 7
    8. 8. Main Parts of Generating Station Circuit Breaker (CB) A circuit breaker is an automatically operated electrical switch, designed to protect an electrical circuit from damage caused by faultcurrent or short circuit Types based on Insulators Oil Circuit Breaker Air Circuit Breaker SF6 Circuit Breaker Vacuum Circuit Breaker Fig.2: CB Diagram 8
    9. 9. Table.1: Circuit Breaker Description Type Medium Air break Circuit Breaker Air at atmospheric pressure Miniature CB. Air at atmospheric pressure (430-600 ) V Tank Type oil CB. Dielectric oil (3.6 – 12) KV Minimum Oil CB. Dielectric oil (3.6 - 145 )KV Compressed Air 245 KV, 35000 MVA (20 – 40 ) bar up to 1100 KV, 50000 MVA Air Blast CB. Voltage, Breaking Capacity (430 – 600) V– (5-15)MVA (3.6-12) KV - 500 MVA 12 KV, 1000 MVA SF6 CB. SF6 Gas 36 KV , 2000 MVA 145 KV, 7500 MVA 245 KV , 10000 MVA Vacuum CB. Vacuum 36 KV, 750 MVA H.V.DC CB. Vacuum , SF6 Gas 500 KV DC 9
    10. 10. Main Parts of Generation Station… Disconnect Switch Provides visible circuit separation and permits CB maintenance. It can be operated only when the CB is open i.e. in no-load condition. Surge Arrester Used for protection against lightning and switching over-voltages. They are voltage dependent, nonlinear resistors (Varistors). The arrester provides a low-impedance path to ground for the current from a lightning strike or transient voltage and then restores to a normal operating condition. 10
    11. 11. Main Parts of Generation Station… Current Transformers (CT) and Potential Transformers (PT) Used to lower the magnitude of the current and voltage to be measured. In case of normal meters, to measure current and voltage in a high voltage circuit at 220kV, properly insulated meters are needed to withstand that voltage. The meters will be very big for that purpose. The CT and PT is used to solve this problem. The CT and PT works on the principle of transformer and lowers the current and/or voltage at a lower value which can be safely and easily measured. 11
    12. 12. 12
    13. 13. Components of a Transmission Line Conductor Earth wire Insulator Transmission Tower Wave trap and other hardware(Clamp, Spacer, Vibration dampers, connectors etc. 13
    14. 14. Design Methodology • Gather preliminary line design data and available climatic data • Select reliability level in terms of return period of design • Calculate climatic loading on components • Calculate loads related to safety during construction and maintenance • Select appropriate correction factors, if applicable, to the design components such as use factor, strength factors related to numbers of components, quality control, and the characteristic strength. • Design the components for the above loads and strength. 14
    15. 15. Selection of Transmission Voltage Standard Voltage: 66,110,132, 220, 400 KV Tolerances - ±10% up to 220 KV & ±5% for 400 KV Selection Criterion of Economic Voltage • Quantum of power to be evacuated • Length of line • Voltage regulation • Power loss in Transmission • Initial and operating cost 15
    16. 16. Economic Voltage of Transmission of Power E = Transmission voltage (KV) (L-L). 5 .5 KVA 1 .6 *E L 150 L = Distance of transmission line in KM KVA=Power to be transferred * 16
    17. 17. Typical Transmission Voltage Levels Voltages Level Range (KV) Maximum Length (Miles) High Voltage 100 to 230 200 Extra High Voltage 230 to 800 400 to 500 Ultra High Voltage Above 800 1300
    18. 18. Types of Towers Type A Tower (Tangent Tower with suspension string) Type B Tower (Small Angle Tower with tension string) • Used on straight runs and up to 2° line diversion • Used for line deviation from 2° to 15° Type C Tower (Medium Angle Tower with tension string ). • Used for line deviation from 15° to 30°. Type D Tower (Large angle tower with tension string) • Used for line deviation from 30° to 60° Type E Tower (Dead End Tower with tension string) • Used for line termination & starting Suspension Tower (Span ≈ 1000 m) Transposition Tower • Used for River crossing, Mountain crossing etc. • Used for transposition of tower 18
    19. 19. Suspension Tower Transposition Tower Tension Tower
    20. 20. Different Types of Towers 20
    21. 21. Selection of Tower Structure Single circuit Tower/ double circuit Tower Length of the insulator assembly Minimum clearances to be maintained between conductors, and between conductors and tower Location of earth wire/wires with respect to the outermost conductor Mid-span clearance required from considerations of the dynamic behavior of conductors and lightning protection of the line Minimum clearance of the lowest conductor above ground level 21
    22. 22. EHV- Tower Tower: • The figure shows a lattice, steel tower. Insulator: • V strings hold four bundled conductors in each phase Conductor: Foundation and grounding: • Each conductor is stranded, steel reinforced aluminum cable. • Steel-reinforced concrete foundation and grounding electrodes placed in the ground Shield conductors: • Two grounded shield conductors protect the phase conductors from lightning. 22
    23. 23. Tower Design Tower height Base width Top damper width Cross arms length Fig. Typical 765 KV Tower Structure 23
    24. 24. Height of Tower Structure Height of tower is determine by- H h1 h2 h3 h4 h1=Minimum permissible ground clearance h2=Maximum sag h3=Vertical spacing between conductors h4=Vertical clearance between earth-wire and top conductor 24
    25. 25. Determination of Base Width The base width(at the concrete level) is the distance between the centre of gravity at one corner leg and the centre of gravity of the adjacent corner leg. A particular base width which gives the minimum total cost of the tower and foundations Ryle Formula An applied force that causes a structure to turn over The ratio of base width to total tower height for most towers is generally about one-fifth to one-tenth. 25 25
    26. 26. Spacing and Clearances Ground Clearances CL 5.182 Where- K 0.305 * K V 33 33 S.No. Voltage level Ground clearance(m) 1. ≤33 KV 5.20 2. 66 KV 5.49 3. 132KV 6.10 4. 220 KV 7.01 5. 400 KV 8.84 26
    27. 27. Clearance for Power Line Crossings Crossing over rivers: Crossing over telecommunication lines • 3.05m above maximum flood level. • Minimum clearances between the conductors of a power line and telecommunication wires are Voltage Level Minimum Clearance(mm) ≤33 KV 2440 66KV 2440 132 KV 2740 220 KV 3050 400 KV 4880 27
    28. 28. Power line Crossing another Power line System Voltage Level Clearance(m) ≤ 66 KV 2.40 132 KV 2.75 220KV 4.55 400 KV 6.00 28
    29. 29. Spacing Between Conductor(Phases) Mecomb's formula WhereSpacing ( cm ) 0 . 3048 * V 4 . 010 D W S V= Voltage of system in KV D= Diameter of Conductor in cm S= Sag in cm W= weight of conductor in Kg/m VDE formula Spacing ( cm ) 7 .5 S V 2 2000 Where- V= Voltage of system in KV S= Sag in cm 29
    30. 30. Still's formula 2 Spacing ( cm ) 5 . 08 l 1 . 814 * V Wherel = Average span length(m) 27 . 8 NESC formula Spacing ( cm ) 0 . 762 * V 3 . 681 S L 2 WhereV= Voltage of system in KV S= Sag in cm L= Length of insulator string in cm 30
    31. 31. Swedish formula Where- Spacing ( cm ) 6 .5 S 0 .7 * E E= Line Voltage in KV S= Sag in cm French formula Where- Spacing ( cm ) 8 .0 S L E 1 .5 E= Line Voltage in KV S= Sag in cm L= length of insulating string(cm) 31
    32. 32. Clearances b/w Conductors SYSTEM VOLTAGE TYPE OF TOWER Vertical spacing b/w conductors(mm) Horizontal spacing b/w conductors(mm) SINGLE CIRCUIT 132 KV 4500 DOUBLE CIRCUIT 2060 5550 SINGLE CIRCUIT 66 kV 1080 4200 7140 DOUBLE CIRCUIT 3965 7320 32
    33. 33. Types of Conductors • AAC(All Aluminium Conductor) • AAAC(All Alloy Aluminium Conductor) • ACSR Conductor(Aluminium Conductor Steel Reinforced) Fig. AAC Conductors Fig. AAAC Conductors 33
    34. 34. Table: Technical Data of ASCR Conductors Commonly used in EHV Transmission By Wapda. Code Words Stranding Aluminum Steel Conductor Core Weight Per Km Aluminum Steel No/mm kg/km No/mm kg/km Weight Complete Conductor kg/km Diameter Complete Steel Conductor Core mm mm Cross Area of Aluminum Area of Complete Conductor Rated Ultimate Strength D.C Resistance at 200 mm2 mm2 kg ohm/km Gopher 6/2.36 1/2.36 72 34.1 106 7.08 2.36 26.25 30.62 980 1.093 Rabbit 6/3.35 1/3.35 145.1 68.8 214 10.05 3.35 52.88 61.69 1875 0.543 Dog 6/4.72 7/1.57 288.1 106.2 394 14.15 4.71 104.98 118.53 3225 0.273 Hare 6/4.72 1/4.72 288.1 136.5 425 14.16 4.72 105 122.5 3225 0.273 Osprey 16/4.465 ¼.465 777 121.8 898.8 22.23 4.465 281.9 297.56 6220 0.123 Cuckoo 24/4.62 7/3.08 1116 407.6 15424 27.72 9.24 402.33 454.48 12385 0.072 Zebra 54/3.18 7/3.18 1182 439 1621 28.62 3.18 428.9 484.59 13000 0.0686 Moose 54/3.53 7/3.53 1463 535 1998 31.77 3.53 528.5 597.0 16224 0.0559 Panther 30/3 7/3 588 387 976 21 3 212.1 261.5 9150 0.07311 400kv - 'Moose' ACSR 220kv - 'Zebra' ACSR 132kv - 'Panther' ACSR Fig. ASCR Conductors 34
    35. 35. Selection of Conductor Size • Mechanical Requirement • Electrical Requirement • Tensile Strength(For Tension) Mechanical Requirement • Strain Strength(For Vibration) Use vibration damper for vibration control. 35
    36. 36. Electrical Requirement • Continuous current rating. • Short time current carrying rating. • Voltage drop • Power loss • Minimum dia to avoid corona • Length of line • Charging current 36
    37. 37. Continuous Current Rating. The designated RMS alternating current in amperes which a conductor will carry continuously in free air without tripping or exceeding temperature limits. The normal continuous current rating of line traps is per manufacturer’s nameplate and based at 40°C ambient temperature. This current rating can be adjusted for specific ambient temperature without exceeding the normal allowable maximum temperature a line trap can withstand. 37
    38. 38. Short Time Rating According to short time rating conductor size is given by- A 7 . 58 * I F * t Where A=area of conductor(mm2) IF= fault current(KA) t= fault duration(1 sec.) 38
    39. 39. Corona A corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor that is electrically energized. Visual corona voltage in fair weather condition is given by- V 0 21 . 1 m r (1 0 .3) r • • • • log n D r V0= corona starting voltage, KV(rms) r= radius of conductor in cm D= GMD equivalent spacing b/w conductors in cm m= roughness factor = 1.0 for clean smooth conductor =0.85 for stranded conductor 39
    40. 40. INSULATOR Insulator are required to support the line conductor and provide clearance from ground and structure. Insulator material• High grade Electrical Porcelain • Toughened Glass • Fiber Glass Choice of insulator material is govern by availability, price and ease of maintenance. Porcelain insulator are largely used in Pakistan.
    41. 41. Earth Wire Earth wire provided above the phase conductor across the line and grounded at every tower. • It shield the line conductor from direct strokes • Reduces voltage stress across the insulating strings during lightning strokes Design criterion: • Shield angle • 25°-30° up to 220 KV • 20° for 400 KV and above • Earth wire should be adequate to carry very short duration lightning surge current of 100 KA without excessive over heating • Duration should be consider as 200 µ-sec A 5 I t A= Area(in mm2) of cu conductor I =current in KA t = Time insecond • Safe temp rise limited to 300°C 41
    42. 42. Mid span clearance: • Direct distance b/w earth wire and top power conductor. Following value of mid span clearance should be considered System voltage Mid span clearance(m) ≤ 66 KV 3.0 110 KV 4.5 132 KV 6.1 220 KV 8.5 400 KV 9.0 42
    43. 43. Tower Grounding Used to reduce earth wire potential and stress on insulators at the time of stroke and also for safety • Tower footing resistance will be 10Ω and should not be more than 20 Ω under any condition throughout the year • Earth resistance depend upon soil resistivity(general 100 Ω-m) 43
    44. 44. Method of Tower Grounding Buried Conductor • One or more conductor are connected to tower lags and buried in back filled of tower foundation. • Used where soil resistivity is low Counterpoise Wire • A length of wire/ Strip of 50 m is buried horizontally at depth of 0.5 m bellow ground. This wire is connected to tower lags. • Used when earth resistance is very high and soil conductivity is mostly confined to upper layer) Rod Pipe • Pipe/Rod of 3 to 4 m is driven into ground near the tower and top of rod is connected to tower by suitable wire/strip • Used where ground conductivity increase with depth Treated Earth Pits • Pipe/Rod of 3 to 4 m are buried in treated earth pits and top of rod is connected to tower by suitable wire/strip. • Used in very high resistivity near tower 44
    45. 45. 45

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