Electrical power transmission Distribution System and Tariff

Electrical power distribution and transmission System

1. UNIT-01 Distribution System and Tariff

2. D efinition:  load curve or chronological curve is the graphical representation of load (in kw or mw) in proper time sequence and the time in hours. it shows the variation of load on the power station. when the load curve is plotted for 24 hours a day, then it is called daily load curve. if the one year is considered then, it is called annual load curve. the load curve of the power system is not same all the day. it differs from day to day and season to season. Load Curve Prof. Tathe S. G. ICEEM

3. Prof. Tathe S G ICEEM The load curve is mainly classified into two types, i.e., the summer load curve and the winter load curve . The following are the information obtained from load curves . 1. Load duration curve determines the load variation during different hours of the day. 2. It indicates the peak load which determines the maximum demand on the power station.

4. Prof. Tathe S G ICEEM 3.The area under the load curve gives the total energy generated in the period under consideration. 4.The area under the curve divided by the total numbers of hours gives the load. 5.The ratio of the area under the load curve of the total area of the rectangle in which it is contained gives the load factor . The ideal load curve is flat, but practically it is far from flat. For a flat load curve, the load factor will be higher. Higher load factor means the more uniform load pattern with fewer variations in load.

5. Prof. Tathe S G ICEEM Load Duration Curve Definition : The load duration curve is defined as the curve between the load and time in which the ordinates representing the load, plotted in the order of decreasing magnitude, i.e., with the greatest load at the left, lesser loads towards the rights and the lowest loads at the time extreme right.  The load duration curve is shown in the figure below.

6. This curve represents the same data as that of the load curve. The load duration curve is constructed by selecting the maximum peak points and connecting them by a curve. The load duration curve plotting for 24 hours of a day is called the daily load duration curve. Similarly , the load duration curve plotted for a year is called the annual load curve. Prof. Tathe S. G. ICEEM

7. That part of power system which distributes electric power for local use is known as distribution system. It generally consists of feeders, distributors and the service mains. Feeders: A feeder is a conductor which connects the sub-station (or localized generating station) to the area where power is to be distributed. Generally , no tappings are taken from the feeder so that current in it remains the same throughout. The main consideration in the design of a feeder is the current carrying capacity. D istribution System

8. Distributor . A distributor is a conductor from which tappings are taken for supply to the consumers. In Fig. AB, BC, CD and DA are the distributors. The current through a distributor is not constant because tappings are taken at various places along its length. While designing a distributor, voltage drop along its length is the main consideration since the statutory limit of voltage variations is ± 6% of rated value at the consumers’ terminals.

9. An   electric power distribution  system can be classified according to its feeder connection schemes or topologies as follows 1. Radial distribution system 2. Ring main distribution system 1.Radial distribution system : This system is used only when substation or  generating station  is located at the center of the consumers. In this system, different feeders radiate from a substation or a generating station and feed the distributors at one end. Prof. Tathe S. G. ICEEM Types of Electric distribution

10. Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction . Single line diagram of a typical radial distribution system is as shown in the figure below. It is the simplest system and has the lowest initial cost. Prof. Tathe S. G. ICEEM

11. Although this system is simplest and least expensive, it is not highly reliable. A major drawback of a radial distribution system is, a fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors . 2. Ring main distribution system A similar level of system reliability to that of the parallel feeders can be achieved by using ring distribution system. Here , each distribution  transformer  is fed with two feeders but in different paths. Prof. Tathe S. G. ICEEM

12. The feeders in this system form a loop which starts from the substation bus-bars, runs through the load area feeding distribution transformers and returns to the substation bus-bars. The following figure shows a typical single line diagram of a ring main distribution system. Prof. Tathe S. G. ICEEM

13. Advantages Of Ring Main Distribution System There are fewer voltage fluctuations at consumer's terminal. The system is very reliable as each distribution transformer is fed with two feeders. That means, in the event of a fault in any section of the feeder, the continuity of the supply is ensured from the alternative path. Prof. Tathe S. G. ICEEM

14. T he Load Factor is defined as a ratio of the average load divided by the maximum (or peak) load in a given time of period . In other words, the Load Factor is the ratio of total energy (kWh) used over a specific period of time to the total possible energy available within that period (i.e. peak demand over that specific time period). Load Factor can be calculated on a daily, monthly, or yearly basis. The equation of Load Factor is; Load Factor Prof. Tathe S. G. ICEEM

15. Demand factor: It is defined as the ratio of maximum demand on the power station to its connected load. Demand factor = Maximum demand / Total connected load. The value of the demand factor is usually less than 1. It is because maximum demand is always less than the connected load Demand factor Prof. Tathe S. G. ICEEM

16. The diversity factor of the power station is defined as the ratio of sum of individual maximum demands to the maximum demand on the power station, i.e . The diversity factor of a power station is always greater than 1. The diversity factor plays a vital role in the determination of cost of generation of power. The greater is the diversity factor, the lesser is the cost of generation of power. Demand factor Prof. Tathe S. G. ICEEM

17. E lectric load forecasting   The electric load forecasting (ELF) is indispensable procedure for the planning of power system industry, which plays an essential role in the scheduling of electricity and the management of the power system (PSM ). Hence, ELF in advance stage has numerous great values for managing the generation capacity, scheduling, management, peak reduction, market evaluation, etc . Most of the electric load-forecasting methods are dedicated to short-term (a few minutes to 24 hours) forecasting, but not as many are dedicated to long-term (1 to 10 years) or intermediate-term (a few days to several months) load forecasting. Prof. Tathe S. G. ICEEM

18. Accurate long-term and mid term electric load forecasting plays an essential role for  electric power system planning . It corresponds to load forecasting with lead times long enough to plan for long-term and mid term maintenance, construction scheduling for developing new-generation facilities, purchasing of generating units, and developing of transmission and distribution systems. The accuracy of the long-term load forecast has a significant effect on developing future generation and distribution planning. An extensive overestimation of load demand will result in substantial investment for the construction of excess power facilities, whereas underestimation will result in customer discontentment. Prof. Tathe S. G. ICEEM

19. The time horizon for long-term and mid-term forecasting ranges between a few weeks to several years. Unfortunately, it is difficult to forecast load demand accurately over a planning period of this length . This fact is due to the uncertain nature of the forecasting process. A large number of influential factors characterize and directly or indirectly affect the underlying forecasting process; all of them are uncertain and uncontrollable . Therefore, any long-term forecast, by nature, is  inaccurate! Prof. Tathe S. G. ICEEM

20. The  electricity tariff  is defined as the rate at which the electrical energy is sold to a consumer. However, the tariff should include the total cost of producing and supplying electrical energy plus the profit to the power company. In practice, the tariff cannot be same for all types of consumers because the cost of production of electrical energy depends upon the magnitude of electrical energy consumed by the user and his load conditions. Therefore , the tariff is fixed by considering the different types of consumers such as domestic, industrial and commercial, etc. tariff   Prof. Tathe S. G. ICEEM

21. It should recover the cost of production of electrical energy at the power station. It should recover the cost on the investment in transmission and distribution of electrical energy. It should recover the cost of operation and maintenance of elements of power system such as meters, equipment, bills, etc. It should also generate a profit on the investment . Objective of Tariff   Prof. Tathe S. G. ICEEM

22. Proper Return  - The tariff should be such that the total receipts from the consumers must be equal to the cost of producing and supplying electrical energy plus reasonable profit. Therefore, the tariff should be such that it ensures the proper return from each consumer so that each power supply company can ensure the continuous and reliable service to the consumers. Simplicity  - The tariff should be simple so that it can easily be understood by an ordinary consumer. Desirable Characteristics of Tariff Prof. Tathe S. G. ICEEM

23. Fairness  - The tariff should be fair so that different types of consumers are satisfied with the rate of charge of electrical energy. Therefore , a big consumer should be charged at a lower rate than a small consumer because the increased energy consumption spreads the fixed charges over a greater number of units, which reduces the overall cost of production of Similarly, the consumers whose load conditions are non-variable should be charged at lower rate than the consumers whose load conditions change considerably from the ideal. Attractive  - The tariff should be attractive so that a large number of consumers are encouraged to utilise the electrical energy. Reasonable Profit  - The tariff should be such that it also earns a reasonable profit. Prof. Tathe S. G. ICEEM

24. Types of Tariff Simple Tariff - When there is a constant rate per unit of electrical energy consumed, then it is called the simple tariff or uniform rate tariff. Flat Rate Tariff - When different types of consumers are charged at different fixed rate per unit of electrical energy consumed, then it is called the flat rate tariff. Block Rate Tariff - When a given block of electrical energy is charged at a specified rate and the succeeding blocks of electrical energy are charged at progressively reduced rates, then it is called the block rate tariff. Prof. Tathe S. G. ICEEM

25. Two-Part Tariff - When the rate of electrical energy is charged on the basis of maximum demand and the units consumed, then it is called the two-part tariff. Maximum Demand Tariff - When the rate of electrical energy is charged on the basis of maximum demand, then it is called maximum demand tariff. The maximum demand tariff is similar to the two-part tariff with the only difference that the maximum demand of the consumer is measured by installing maximum demand meter in the consumer's premises. Power Factor Tariff - When the rate of electrical energy is charged on the basis of power factor of the consumer's load, it is called the power factor tariff. Prof. Tathe S. G. ICEEM

26. Three-Part Tariff  - When the total charges made from the consumers are split into three parts namely, fixed charges, semi-fixed charges and running charges, then it is called the  three-part tariff . Prof. Tathe S. G. ICEEM

27. Prof. Tathe S. G. ICEEM The various Types of Load in Power System are : Domestic load Commercial load Industrial load Municipal load Irrigation load Traction load 1. Domestic load: Domestic load consists of lights, fans, refrigerators, heaters, television, small motors for pumping water etc. Most of the residential load occurs only for some hours during the day (i.e., 24 hours) g.,  lighting load  occurs during night time and domestic appliance load occurs for only a few hours. For this reason, the load factor is low (10% to 12%). Types of Load in Power System:

28. Prof. Tathe S. G. ICEEM 2. Commercial load: Another Types of Load in Power System is Commercial load consists of lighting for shops, fans and electric appliances used in restaurants etc. This class of load occurs for more hours dining the day as compared to the domestic load. The commercial load has seasonal variations due to the extensive use of air-conditioners and space heaters. 3. Industrial load: Industrial load consists of load demand by industries. The magnitude of industrial load depends upon the type of industry. Thus small scale industry requires load upto 25 kW, medium scale industry between 25kW and 100 kW and large-scale industry requires load above 500 kW. Industrial loads are generally not weather dependent.

29. Prof. Tathe S. G. ICEEM 4. Municipal load: Municipal load consists of street lighting, power required for water supply and drainage purposes. Street lighting load is practically constant throughout the hours of the night. For water supply, water is pumped to overhead tanks by pumps driven by electric motors. Pumping is carried out during the off-peak period, usually occurring during the night. This helps to improve the load factor of the power system. 5. Irrigation load: This Types of Load in Power System is the electric power needed for pumps driven by motors to supply water to fields. Generally this type of load is supplied for 12 hours during night.

30. Prof. Tathe S. G. ICEEM 6. Traction load: This Types of Load in Power System includes train cars, trolley buses, railways etc. This class of load has wide variation. During the morning hour, it reaches  peak value  because people have to go to their work place. After morning hours, the load starts decreasing and again rises during evening since the people start coming to their homes.