Transmission & distribution of electrical power

Transmission & Distribution of Electrical Power

1. Transmission & Distribution of Electrical Power Presented by : Priyanka Solanki Assistant professor

2. Brief Introduction of course Module I: Basics Of Transmission Module II: Transmission Line Components Module III: Transmission Line Parameters Module IV: Performance Of Transmission Line. Module V: Extra High Voltage Transmission. Module VI: Components Of Distribution System. Module VII: Underground Cables. Module VIII: Substations.

3. Module I: Basics Of Transmission Introduction to transmission. Necessity of transmission of electricity. Classification & comparison of different transmission

4. Introduction to transmission. The process by which large amounts of electricity produced are transported over long distances for eventual use by consumers. Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. These generating stations are not necessarily situated at the load center. Load center is the place which consumes maximum power. Hence there must be some means by which we can transmit the generated power to the load center..

5. NECESSITY OF TRANSMISSION Electricity is supplied to consumers through the National Grid at a very high voltage to reduce energy losses during transmission. Transformers are used to increase or decrease the voltage of the supply. Electricity is charged in units. Increasing the voltage decreases the current, which decreases the power loss. The advantage of transmitting electricity at high voltage is that is minimizes the power loss due to resistance in conductors. Power is dissipated as heat. . The power loss in the transmission line is be proportional to I^2.

6. CLASSIFICATION & COMPARISON OF DIFFERENT TRANSMISSION: 1.High voltage DC electrical transmission system. 2. High AC electrical transmission system.

7. Module II Transmission Line Components Introduction to line components. Types of conductors-Copper, Aluminum & state their trade names. Line insulators – requirements, types, and field of applications. Distribution of potential over a string of suspension insulators. Concept of string efficiency. Corona – corona formation, advantages & disadvantages, factors affecting corona, important terms related to corona. Spacing between Conductors. Calculation of Span length & sag Calculation  

8. Introduction to line components. A transmission line has resistance, inductance and capacitance uniformly distributed along the whole length of the line. Resistance . It is the opposition of line conductors to current flow. The resistance is distributed uniformly along the whole length of the line Inductance . When an alternating current flows through a conductor, a changing flux is set up which links the conductor. Due to these flux linkages, the conductor possesses inductance. Capacitance . We know that any two conductors separated by an insulating material constitute a capacitor. As any two conductors of an overhead transmission line are separated by air which acts as an insulation, therefore, capacitance exists between any two overhead line conductors.

9. Types of conductors An ideal conductor has following features. · It has maximum electrical conductivity. · It has high tensile strength so that it can withstand mechanical stresses. · It has least specific gravity i.e. weight / unit volume. · It has least cost without sacrificing other fact

10. 1. AAC (All Aluminum Conductor)

11. ACAR (Aluminium Conductor, Aluminium Reinforce) It is cheaper than AAAC but pro to corrosion. · It is most expansive.

12. AAAC (All Aluminium Alloy Conductor) It has same construction as AAC except the alloy. · Its strength is equal to ACSR but due to absence of steel it is light in weight. · The presence of formation of alloy makes it expensive. · Due to stronger tensile strength than AAC, it is used for longer spans. · It can be used in distribution level i.e. river crossing. · It has lesser sag than AAC.

13. ACSR ( Aluminium Conductor Steel Reinforced) It is used for longer spans keeping sag minimum. · It may consist of 7 or 19 strands of steel surrounding by aluminum strands concentrically. The number of strands are shown by x/y/z, where ‘x’ is number of aluminum strands, ‘y’ is number of steel strands and ‘z’ is diameter of each strand. Strands provide flexibility, prevent breakage and minimize skin effect.. If the Al and St strands are separated by a filler such as paper then this kind of ACSR is used in EHV lines and called expanded ACSR. · Expanded ACSR has larger diameter and hence lower corona losses.

14. T ypes of insulator There are mainly three types of insulator used as overhead insulator likewise 1. Pin Insulator 2. Suspension Insulator 3. Strain Insulator

15. Pin Insulator The pin insulator is used in power distribution for the voltage up to 33kV. It is placed on the cross arm of the supporting tower. The pin insulator has grooves on the upper end for keeping the conductor. The conductor is tied to the insulator on the top groove on straight line positions and side groove in angle positions by annealed binding wire of the same material as that of the conductor. A lead thimble is cemented into the insulator body to receive the pin.

16. Pin Insulator

17. Advantages of Pin Insulator It has high mechanical strength. The pin type insulator has good creepage distance. It is used on the high voltage distribution line. The construction of the pin type insulator is simple and requires less maintenance. It can be used vertically as well as horizontally.

18. Disadvantages of Pin Insulator It should be used with the spindle. It is only used in the distribution line. The voltage rating is limited, i.e., up to 36kV. The pin of the insulator damaged the insulator thread.

19. Post Insulator Post insulators are similar to Pin insulators, but post insulators are more suitable for higher voltage applications. Post insulators have a higher number of petticoats and a greater height compared to pin insulators. We can mount this type of insulator on supporting structure horizontally as well as vertically The insulator is made of one piece of porcelain and it has clamp arrangement are in both top and bottom end for fixing.

20. S.No . Pin Insulator Post Insulator 1 It is generally used up to 33KV system It is suitable for lower voltage and also for higher voltage 2 It is single stag It can be single stag as well as multiple stags 3 Conductor is fixed on the top of the insulator by binding Conductor is fixed on the top of the insulator with help of connector clamp 4 Two insulators cannot be fixed together for higher voltage application Two or more insulators can be fixed together one above other for higher voltage application 5 Metallic fixing arrangement provided only on bottom end of the insulator Metallic fixing arrangement provided on both top and bottom ends of the insulator

21. Suspension Insulator

22. Suspension Insulator

23. Advantages of Suspension Type Insulator . Each unit operates the voltage of about 11kV and hence depending upon the voltage the appropriate number of discs are connected in series with the string. If one of the units is damaged, then it is replaced by the new one and hence no need of replacing the whole string. The string is free to swing in any direction and, therefore, great flexibility is provided to the transmission line. The conductors are placed below the suspension insulators and hence it partly protects the conductor from lightning.

24. Strain Insulator

25. Advantages of Strain Insulator The advantages of strain insulators include the following. These are used for low voltages upto 11kv These are insulated from the ground for low-voltage lines. These are designed with porcelain If the insulator is damaged, the stay or guy wires will not drop to the ground.

26. Distribution of potential over a string of suspension insulators.

27. Concept of string efficiency. The string efficiency is defined as the ratio of voltage across the string to the product of the number of strings and the voltage across the unit adjacent string.

28. Methods of improving string efficiency: Use of Long Cross Arm Capacitance Gradings or Grading of the unit Uses of Grading Rings or Static Shielding

29. Corona Effect The phenomenon of ionisation of surrounding air around the conductor due to which luminous glow with hissing noise is rise is known as the corona effect. Air acts as a dielectric medium between the transmission lines. The electric field intensity also increases because of the charging current.

30. Factors affecting Corona Effect Effect of supply voltage : Directly proportional with corona effect The condition of conductor surface : rough surface decrease corona Air Density Factor: inversely proportional to corona loss Effect of system voltage : Directly proportional The spacing between conductors : Directly proportional

31. Disadvantages of corona discharge: The glow appear across the conductor which shows the power loss occur on it. The audio noise occurs because of the corona effect which causes the power loss on the conductor. The vibration of conductor occurs because of corona effect. The corona effect generates the ozone because of which the conductor becomes corrosive. The corona effect produces the non-sinusoidal signal thus the non-sinusoidal voltage drops occur in the line. The corona power loss reduces the efficiency of the line. The radio and TV interference occurs on the line because of corona effect.

32. Minimizing corona : Conductor diameter The voltage of the line Spacing between conductors

33. Spacing between the conductors T he minimum distance between bottom conductor and ground of a 400KV transmission line is 8.84 meter. The minimum ground clearance of 33KV uninsulated electrical conductor is 5.2 meter .

34. Calculation of Span length & sag Calculation The sag in overhead line is a length in between support point of conductor and the lowest point on the conductor of transmission and distribution overhead line . Calculation of Sag:

35. Sag calculation when support are at unequal level:

36. Module III: Transmission Line Parameters R,L & C of 1-ph & 3-ph transmission line. Skin effect, proximity effect & Ferranti effect. Concept of transposition of conductors & necessity.

37. Classification of T ransmission line Short transmission line – The line length is up to 60 km and the line voltage is comparatively low less than 20KV. Medium transmission l ine – The line length is between 60 km to 160 km and the line voltage is between 20kV to 100kV. Long transmission lin e – The line length is more than 160 km and the line voltage is high greater than 100KV.

38. Skin Effect in transmission lines The phenomena arising due to unequal distribution of current over the entire cross section of the conductor being used for long distance power transmission is referred as the skin effect in transmission lines.

39. Factors affecting skin effect Frequency  Diameter  The shape of the conductor  Type of material 

40. Proximity Effect When the conductors carry the high alternating voltage then the currents are non-uniformly distributed on the cross-section area of the conductor. This effect is called proximity effect. The proximity effect results in the increment of the apparent resistance of the conductor due to the presence of the other conductors carrying current in its vicinity.

41. Factors Affecting the Proximity Effect Frequency  – The proximity increases with the increases in the frequency. Diameter –  The proximity effect increases with the increase in the conductor. Structure –  This effect is more on the solid conductor as compared to the stranded conductor  (i.e., ASCR) because the surface area of the stranded conductor is smaller than the solid conductor. Material –  If the material is made up of high ferromagnetic material then the proximity effect is more on their surface.

42. Ferranti Effect The Ferranti effect is a phenomenon that describes the increase in voltage that occurs at the receiving end of a long transmission line relative to the voltage at the sending end

43. How to reduce Ferranti effect: Shunt reactor is an inductive current element connected between line and neutral to compensate the capacitive current from transmission line Electrical devices are designed to work at some particular voltage

44. Transposition of Conductors

45. Transposition of Conductors The transposition is a physical rotation of the conductors so that the conductor is moved to take up the next physical position in the regular sequence. The transposition of the conductor equalizes the mutual inductance and capacitance between the lines. The transposition is mainly done in the switching station and the substations.

46. Needs of Transposition The inductance of unsymmetrical line causes voltage drops even if the voltage is in a balanced condition. Because of the inducing voltages, the magnetic field exists in the conductor which causes the interference in the line. This can be reduced by continually exchanging the position of the conductor, which can be done by transposition the conductors.

47. Disadvantage of Transposition Frequently changing the position of conductors weakens the supportive structure which increases the cost of the system.

48. Module IV Performance Of Transmission Line. Classification of transmission lines. Losses, Efficiency & Regulation of line. Performance of single phase short transmission line(Numerical based on it ) Effect of load power factor on performance. General circuit & Generalized Circuit Constants( A, B, C, D )

49. Classification of transmission lines

50. Losses, Efficiency & Regulation of line

51. What are ABCD Parameters?

52. Parameter Specification Unit A = VS / VR Voltage ratio Unit less B = VS / IR Short circuit resistance Ω C = IS / VR Open circuit conductance mho D = IS / IR Current ratio Unit less

53. Module V: Extra High Voltage Transmission . Introduction & Requirement. EHVAC Transmission, Reasons for adoption &limitations. HVDC Transmission – Advantages, Limitations.

54. INTRODUCTION The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements. High voltage is used in electrical power distribution, in cathode ray tubes, to generate X-rays and particle beams, to demonstrate arcing, for ignition, in photomultiplier tubes, and high power amplifier vacuum tubes and other industrial and scientific applications. WHAT IS EHV TRANSMISSION ? Two factors considered in the classification of a "high voltage" are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. In electric power transmission engineering, high voltage is usually considered any voltage over approximately 35,000 volts.

55. NECESSITY OF EHVAC TRANSMISSION With the increase in transmission voltage, for same amount of power to be transmitted current in the line decreases which reduces I2R losses. This will lead to increase in transmission efficiency. With decrease in transmission current, size of conductor required reduces which decreases the volume of conductor. The transmission capacity is proportional to square of operating voltages. Thus the transmission capacity of line increases with increase in voltage. With increase in level of transmission voltage, the installation cost of the transmission line per km decreases. It is economical with EHV transmission to interconnect the power systems on a large scale. The no. of circuits and the land requirement for transmission decreases withthe use of higher transmission voltages.

56. ADVANTAGES Reduction in the current. Reduction in the losses. Reduction in volume of conductor material required. Decrease in voltage drop & improvement of voltage regulation. Increase in Transmission Efficiency. Increased power handling capacity. The no. of circuits & the land requirement reduces as transmission voltage increases. The total line cost per MW per km decreases considerably with the increase in line voltage.

57. DISADVANTAGES Corona Loss & radio interference Line Supports Erection Difficulties Need of Insulation Generates Electrostatic effects

58. HVDC Transmission

59. Components of HVDC transmission system

60. Comparison of HVAC &HVDC HVDC Transmission System HVAC Transmission System Low losses. Losses are high due to the  skin effect  and  corona discharge Better Voltage regulation and Control ability. Voltage regulation and Control ability is low. Transmit more power over a longer distance. Transmit less power compared to a HVDC system. Less insulation is needed. More insulation is required. Reliability is high. Low Reliability. Asynchronous interconnection is possible. Asynchronous interconnection is not possible. Reduced line cost due to fewer conductors. Line cost is high. Towers are cheaper, simple and narrow. Towers are bigger compared to HVDC.

61. Disadvantages of HVDC Transmission Converters with small overload capacity are used. Circuit Breakers, Converters and AC filters are expensive especially for small distance transmission. No transformers for altering the voltage level. HVDC link is extremely complicated. Uncontrollable power flow.

62. Application of HVDC Transmission Undersea and underground cables AC network interconnections Interconnecting Asynchronous system

63. Module VI: Components Of Distribution System. Introduction. Classification of distribution system. Connection schemes of distribution system. A.C. distribution calculations

64. INTRODUCTION Electric Power Distribution System states that part of power system which distributes elec­tric power for local use is known as distribution system.

65. Classification of Distribution Systems: Nature of current : (a) d.c. distribution system (b) a.c . distribution system. Type of construction : (a) overhead sys­tem (b) underground system. The overhead system is generally employed for distribution as it is 5 to 10 times cheaper than the equivalent underground system. In general, the underground system is used at places where overhead construction is impracticable or prohibited by the local laws. Scheme of connection : (a) radial system (b) ring main system (c) inter-connected system.

66. CONNECTION SCHEMES OF DISTRIBUTION SYSTEM ( i ) Radial System

67. ( ii) Ring main system.

68. The ring main system has the following advantages : ( a)  There are less voltage fluctuations at consumer’s terminals. ( b)  The system is very reliable as each distributor is fed via *two feeders. In the event of   fault on any section of the feeder, the continuity of supply is maintained. For example, suppose that fault occurs at any point F of section SLM of the feeder. Then section SLM of the feeder can be isolated for repairs and at the same time continuity of supply is maintained to all the consumers via the feeder SRQPONM.

69. ( iii) Interconnected system.

70. The interconnected system has the following advantages : ( a) It increases the service reliability. ( b) Any area fed from one generating station during peak load hours can be fed from the other generating station. This reduces reserve power capacity and increases efficiency of the system.

71. Module VII: Underground Cables. • Introduction & requirements. • Classification of cables. • Cable conductors. • Cable insulation, Metallic sheathing & mechanical protection

72. Requirements of Underground Cable The conductor used in underground cable shall be tinned copper or aluminum conductor of high conductivity. Stranding is very important to provide flexibility and increase current carrying capacity. The size of conductor shall be sufficient enough to carry load current without heating and appreciable voltage drop. The voltage drop shall be within the permissible range. The cable must have proper thickness of insulation to provide high degree of safety and reliability at operating voltage. It must have been provided with suitable mechanical protection to withstand rough handling during lying of cable. The material used in the manufacture of cable should be such that there is complete chemical and physical stability throughout.

73. Module VIII: Substations. • Introduction. • Classification of indoor & outdoor sub-stations. • Selection & location of site. • Main connection schemes. • Equipment’s circuit element of substations.

74. INTRODUCTION Substations serve as sources of energy supply for the local areas of distribution in which these are located. Their main functions are to receive energy transmitted at high voltage from the generating stations, reduce the voltage to a value appropriate for local distribution and provide facilities for switching

75. Classification of Substations: Classification of Substations on the Basis of Nature of Duties: 1. Step-Up or Primary Substations: Associated with generation 2. Primary Grid Substations: Associated with Transmission 3. Step-Down or Distribution Substations: Associated with Distribution

76. Classification of Substations on the Basis of Service Rendered: 1. Transformer Substations: 2. Switching Substations: 3. Converting Substations:

77. Classification of Substations on the Basis of Operating Voltage: 1. High Voltage Substations (HV Substations) involving voltages between 11 kV and 66 kV. 2. Extra High Voltage Substations (EHV Substations) involving voltages between 132 kV and 400 kV. 3. Ultra High Voltage Substations (UHV Substations) operating on voltage above 400 kV.

78. Classification of Substations on the Basis of Importance: 1. Grid Substations: 2. Town Substations:

79. Classification of Substations on the Basis of Design: 1. Indoor Type Substations  2. Outdoor Substations: (a) Pole Mounted Substations (b) Foundation Mounted Substations

80. Selection and Location of Site for a Substation: 1. Type of Substation 2. Availability of Suitable and Sufficient Land 3. Communication Facility 4. Atmospheric Pollution 5. Availability of Essential Amenities to the Staff 6. Drainage Facility

81. Main Electrical Connections: The main connection scheme is drawn keeping in view the following factors: ( i ) General bus-bar arrangement, (ii) Operating voltage, (iii) Number of incoming and outgoing lines, (iv) Number of transformers, (v) Safety to equipment, (vi) Safety to operating personnel, and (vii) Future extension requirement.

82. Equipment’s circuit element of substations