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Similar a Transmission_and_Distribution_System.pptx(20)



  1. T&D System • The demand for energy increases over time as populations grow and create a need for more homes, factories, office buildings, consumer products, and public infrastructure. To meet this demand, electricity must not only be produced, but also transmitted to areas where people live. Like any other industry, the electric power system may be thought of as consisting of three main divisions: • 1. Manufacture, production or generation, cogeneration, • 2. Delivery or transmission and distribution, • 3. Consumption.
  3. The grid of today • Transmission network • To transport the electric power from the point of generation to the load centers • All above a certain voltage • (Sub transmission) • Distribution network • To distribute the electric power among the consumers • Below a certain voltage
  4. Planning and Design • New transmission and distribution systems are planned and designed by a variety of professionals. Transmission planning engineers use information collected by utility forecasters to identify when and where more power lines are needed for the system to operate reliably. Siting, land rights, and permitting agents work with government agencies and landowners to acquire land and the rights to use land. CAD designers design the layouts for new transmission and distribution lines and facilities.
  5. Construction and Maintenance • Crews of line workers and utility workers build and fix transmission and distribution lines. Substation mechanics build and maintain the substations that step power down from power lines to be distributed for residential and commercial use. Millwrights help install and secure large equipment. Machinists fabricate special tools that are needed to construct and operate facilities.
  6. Operation and Control • The transmission of electricity across the grid from generation plants to distribution facilities is done in control rooms by system control operators. Reliability coordinators ensure that enough energy is available from generating facilities and elsewhere in the grid to meet demand. They also respond to and help resolve emergency conditions. When power outages occur, outage coordination dispatchers coordinate the response and send workers out to fix the problems.
  7. Safety and Regulations • Electricity is an essential component to modern life, but is also very dangerous. There are many regulations that govern the safety and reliability of power. Safety and occupational health coordinators coordinate safety programs. Training and development specialists lead classes that teach employees how to do their jobs safely and responsibly.
  8. The distribution system is particularly important to an electrical utility for two reasons • it’s close proximity to the customers • it’s high cost of investment
  9. Mainly distribution systems are two types • Primary Distribution (33KV/11KV) • Secondary Distribution (11KV/440V) Household electricity is alternating current (AC) Household voltages are typically 120V or 240V
  10. Distribution System Considerations design of distribution systems, three broad classifications of choices need to be considered: • The type of electric system: dc or ac, and if ac, single- phase or poly phase. • The type of delivery system: radial, loop, or network. Radial systems include duplicate and throw over systems. • The type of construction: overhead or underground.
  11. • The type of electric system: dc or ac, and if ac, single- phase or poly phase. • The type of delivery system: radial, loop, or network. Radial systems include duplicate and throw over systems. • The type of construction: overhead or underground.
  12. Types of Delivery Systems: • Primary distribution • Secondary distribution
  13. Primary distribution • which carries the load at higher than utilization voltages from the substation (or other source)to the point where the voltage is stepped down to the value at which the energy is utilized by the consumer.
  14. Primary distribution systems include three basic types: • Radial systems, including duplicate and throwover systems • Loop systems, including both open and closed loops • Primary network systems
  15. Secondary distribution • which includes that part of the system operating at utilization voltages, up to the meter at the consumer’s premises.
  16. • The maximum generation voltage in advanced countries is 33 kV while that in India is 11 kV. The amount of power that has to be transmitted through transmission lines is very large and if this power is transmitted at 11kV the line current and power loss will be large. There fore the voltage is stepped to a higher level by using step-up transformers located in sub-stations.
  17. Distribution system is consist of: • Substation • Utility or Distribution Pole • Primary wires • Cross arm • Insulators • Lighting Arrestor • Cut out • Transformer • Neutral wire • Secondary wire • Grounding • Guy wire
  18. Substation
  19. Substation • A substation is a part of an electrical generation, transmission, and distribution system. • Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer.
  20. Utility pole
  21. Utility pole • A utility pole is a column or post used to support overhead power lines and various other public utilities, such as cable, fibre optic cable, and related equipment such as transformers and street lights.
  22. • Most utility poles are made of wood, pressure-treated with some type of preservative for protection against rot, fungi and insects. Southern yellow pine is the most widely used species in the United States; however, many species of long straight trees are used to make utility poles, including Douglas-fir, Jack pine, lodge pole pine, western red cedar, and Pacific silver fir.
  23. Cross arm • The woods most commonly used for crossarms are Douglas Fir or Longleaf Southern Pine because of their straight grain and durability. The top surface of the arm is rounded so that rain or melting snow and ice will run off easily. The usual cross- sectional dimensions for distribution crossarms are 3-1/2 inches by 4-1/2 inches; their length depending on the number and spacing of the pins.
  24. Cross arm
  25. Insulator
  26. Insulator • An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it very hard to conduct an electric current under the influence of an electric field. A perfect insulator does not exist, but some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical insulators.
  27. Types of Insulators • Pin type insulator • Suspension insulator • Strain insulator • Shackle insulator • Line post insulator • Station post insulator • Cut-out
  28. Pin type insulator • As the name suggests, the pin type insulator is mounted on a pin on the cross-arm on the pole. There is a groove on the upper end of the insulator. The conductor passes through this groove and is tied to the insulator with annealed wire of the same material as the conductor. Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators become too bulky and hence uneconomical.
  29. Pin type insulator
  30. Suspension insulator • For voltages greater than 33 kV, it is a usual practice to use suspension type insulators shown in Figure. Consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. The number of disc units used depends on the voltage.
  31. Suspension insulator
  32. Strain insulator • A dead end or anchor pole or tower is used where a straight section of line ends, or angles off in another direction. These poles must withstand the lateral (horizontal) tension of the long straight section of wire. In order to support this lateral load, strain insulators are used. For low voltage lines (less than 11 kV), shackle insulators are used as strain insulators. However, for high voltage transmission lines, strings of cap- and-pin (disc) insulators are used, attached to the crossarm in a horizontal direction.
  33. Strain Insulator
  34. Shackle insulator • In early days, the shackle insulators were used as strain insulators. But now a day, they are frequently used for low voltage distribution lines. Such insulators can be used either in a horizontal position or in a vertical position. They can be directly fixed to the pole with a bolt or to the cross arm.
  35. Shackle insulator
  36. Conductor • a conductor is an object or type of material that permits the flow of electrical current in one or more directions. For example, a wire is an electrical conductor that can carry electricity along its length.
  37. Conductor
  38. Lightning Arresters • A lightning arrester is a device used on electrical 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.
  39. Lightning Arresters
  40. Wire Sizes • In the United States, it is common practice to indicate wire sizes by gage numbers. The source of these numbers for electrical wire is the American Wire Gage (AWG) (otherwise known as the Brown & Sharpe Gage). A small wire is designated by a large number and a large wire by a small number
  41. American Standard Wire Gage (AWG)
  42. American Standard Wire Gage (AWG)
  43. Cut out • a fuse cutout or cut-out fuse is a combination of a fuse and a switch, used in primary overhead feeder lines and taps to protect distribution transformers from current surges and overloads. An overcurrent caused by a fault in the transformer or customer circuit will cause the fuse to melt, disconnecting the transformer from the line. It can also be opened manually by utility linemen standing on the ground and using a long insulating stick called a "hot stick".
  44. Cut out
  45. Transformers • transfers energy between two or more circuits through electromagnetic induction.
  46. transformers
  47. Phone/Cables Wires • These wires were typically copper, although aluminium has also been used, and were carried in balanced pairs separated by about 25 cm (10") on poles above the ground, and later as twisted pair cables. Modern lines may run underground, and may carry analog or digital signals to the exchange, or may have a device that converts the analog signal to digital for transmission on a carrier system.
  48. Grounding • Electrical circuits may be connected to ground (earth) for several reasons. In mains powered equipment, exposed metal parts are connected to ground to prevent user contact with dangerous voltage if electrical insulation fails. Connections to ground limit the build-up of static electricity when handling flammable products or electrostatic-sensitive devices.
  49. Guy wire • A guy-wire or guy-rope, also known as simply a guy, is a tensioned cable designed to add stability to a free-standing structure. They are used commonly in ship masts, radio masts, wind turbines, utility poles, fire service extension ladders used in church raises and tents.
  50. Guy wire
  51. Guy wire
  52. Overhead Power Line • An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors (commonly multiples of three) suspended by towers or utility poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of power transmission for large quantities of electric energy.
  53. Overhead Power Line
  54. Overhead power transmission lines are classified in the electrical power industry by the range of voltages: • Low voltage (LV) – less than 1000 volts, used for connection between a residential or small commercial customer and the utility. • Medium voltage (MV; distribution) – between 1000 volts (1 kV) and to about 33 kV, used for distribution in urban and rural areas.
  55. • High voltage (HV; subtransmission less than 100 kV; subtransmission or transmission at voltage such as 115 kV and 138 kV), used for sub-transmission and transmission of bulk quantities of electric power and connection to very large consumers. • Extra high voltage (EHV; transmission) – over 230 kV, up to about 800 kV, used for long distance, very high power transmission. • Ultra high voltage (UHV) – higher than 800 kV.
  56. Underground wires • Undergrounding refers to the replacement of overhead cables providing electrical power or telecommunications, with underground cables. • Underground cables take up less right-of-way than overhead lines, have lower visibility, and are less affected by bad weather. However, costs of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair.
  57. Underground wires
  58. ARELIABILITYTESTSYSTEMFOREDUCATIONAL PURPOSES -BASICDISTRIBUTIONSYSTEMDATAANDRESULTS • It describes an electrical distribution system for use in teaching power system reliability evaluation. It includes all the main elements found in practical systems. However, it is sufficiently small that students can analyze it using hand calculations and hence fully understand reliability models and evaluation techniques. The paper contains all the data needed to perform basic reliability analyses. It also contains the basic results for a range of case studies and alternative design/operating configurations.
  59. IEEE Application of Probability Methods (APM) • Subcommittee published a Reliability Test System (RTS) in 1979 .This has proved to be a valuable and consistent reference source for copying alternative techniques and computer programs. It has been used extensively in recent years in reliability assessment of generation systems and in composite systems by utilities, consultants and universities. Its major advantage is that it provides a consistent set of data, since extended in Refs [4,5], enabling a wide range of techniques and applications to be much more easily compared than previously possible. It is sufficiently large that practical factors can be realistically modeled and assessed but also sufficiently small that the effect of sensitivity studies can be easily identified. The major weakness of the RTS is that it requires the web of computer programs to perform the vast majority of the reliability analyses.
  60. DESCRIPTIONOF THE DISTRIBUTION NETWORKS • The RBTS has 5 load bus bars (BUS2-BUS6). Two of these bus bars (BUS2 and BUS4) were selected and distribution networks designed for each. BUS2 has generation associated with it and BUS4 does not. This permits the effects and differences caused by the generation and transmission system on the overall load point indices to be seen. The peak loads defined in the RBTS for different customer types are shown in Table 1.
  61. SYSTEM STUDIES • The studies performed include: 11kV feeders. These studies consider the 11kV feeders only and ignore any failures in the 33kV system, the 33/11kV substation and the 11kV breakers. They assume the 11kV source breaker operates successfully when required, disconnects are opened whenever possible to isolate a fault, and the supply restored to as many load points as possible using appropriate disconnects and the alternative supply if available.
  62. 33kV system. These studies evaluate the reliability indices at the 11k V supply point busbars. They ignore any failures on the incoming 33kV supply circuits. They include the effect of passive and active failures [8] on all components from the 33kV busbars down to the 11kV supply point busbars together with active failures on the outgoing 11kV feeder breakers.
  63. This paper has presented an extension to the EUBTS by providing all the basic data for teaching reliability assessment of distribution systems. All the networks, 33kV and 11kV, can be analyzed using hand calculations, permitting full understanding and use of the basic models and evaluation techniques. Students can then either use existing computer programs or develop their own in order to analyze more practical systems and to perform an increasing number of sensitivity studies. A selected number of results are included in this paper in order to give confidence to students in their endeavors. These should first be repeated at the initial stage of the teaching program. They can then be followed by a greater number and range of studies.