Introduction to electric power transmission and distribution

introduction to transmission and distribution of electrical power

1. Introduction to Electric Power Transmission and Distribution

2. Introduction Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network. The combined transmission and distribution network is known as the "National Grid". 2

3. Power System The generation, transmission and distribution of electric power is called power system. A power system has the following stages: - Generation of electric power - Transmission of electric power. - Distribution of electric power. Most transmission lines are high-voltage three-phase alternating current (AC). High-voltage direct-current (HVDC) technology is used for greater efficiency over very long distances (typically hundreds of miles). Electricity is transmitted at high voltages (115 kV or above) to reduce the energy loss which occurs in long-distance transmission. 3

4. Layout of Power System A power system is consist of the following stages: Power Station Primary Transmission Secondary Transmission Primary Distribution Secondary Distribution 4

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6. 1. Power Station The bulk power is generated at the power station by 3-phase, 3 wire system employing several alternators in parallel. The usual generation voltage is 11kV. Due to economic consideration , the generation voltage( ie ; 11kV ) is step up to 220kV or 132kV at the power station with the help of step up transformers. 6

7. 2. Primary Transmission High voltages of the order of 66 kV 132 kV 220 kV and 400 kV are used for transmitting power by 3 phase 3 wire overhead system. This is supplied to substations usually at the out skirts of major distribution centre or city. 7

8. 3. Secondary Transmission On the outskirt of the city, there are sub-station which step down the primary transmission voltage to 66kV or 33kV and power is transmitted at this voltage. This forms the secondary transmission system. 3 phase wire system is used. 8

9. 4. Primary Distribution The transmission lines or inner connectors terminate at large main substations from which the power is distributed to small secondary substations scattered throughout the load area. The voltage may range from 11 kV to 132 kV. 9

10. 5. Secondary Distribution This consists of the low-voltage network laid along the streets, localities and over the rural areas. From these sources connections to individual customers are provided. The circuit used for this purpose is 3 phase 4 wire, 440 V/220 V from which either 3 phase 440 V or single phase 220 V supply to the consumers may be provided. 10

11. INTRODUCTION OF DISTRIBUTION SYSTEM Distribution of electric power is an important part of power system. The important requirement of a distribution system is that the power should be distributed to various consumers economically and efficiently . The electric energy is made available for use in a factory or a residential building by distribution system which can be subdivided into three distinct parts. Feeders Distributors Service mains

12. DISTRIBUTION SYSTEM The arrangement of conveying electric power from bulk power sources (generating stations or major substations) to the various consumers is called distribution system. Distribution is of two types. – High voltage or primary distribution Low voltage or secondary distribution   High voltage distribution is carried out at voltages of the order of 33kv,66kv or,11kv. Low voltage distribution which is carried out at 400/230 volts (in three phase 4 wires system)

13. Important terms of distribution system Feeder Distributor Service mains Feeder- A feeder is a conductor which connects sub-station or generating station to the are where the power is to be distributed. These are the conductors which carry large currents to the feeding points. In Fig. 3.1, s is the sub-station and SA and SC are the feeders. A and C are the feeding points.

14. 2. Distributor : A distributor is a conductor from which tapings are taken for supply to the consumers or it is the conductor t which carries current to the service main form the feeding points. The current loading of a distributor varies along its length. 3. Service mains : A services main is generally a small cable which connects the distributor to the consumer terminals .   CLASSIFICATION OF DISTRIBUTION SYSTEMS 1. According to Nature of Construction : Overhead distribution system Underground distribution system overhead system is cheaper than underground system. However, underground system is used in thickly populated areas where overhead system may not be practicable.

15. 2 . According to nature of current : D.C distribution system A.C distribution system A.C distribution is universally adopted due to many advantage of a.c . power over d.c. power. According to number of wires : a. 2-wire d.c. system 3-wire d.c. system Single phase, 2-wire a.c . system 3-phase, 3-wire a.c . system 3-phase, 4—wire a.c . system

16. 4. According to the system of connection: (a) Radial system (b) Ring main system (c) Interconnected system Radial System: when the distributor is fed at one end only, it is called radial distribution system. A single line diagram of radial system is shown in fig.

17. Advantages of radial system: 1. its initial cost is minimum. 2. this system is employed when electrical energy is generated at low voltage and power station is situated at the center of load. Disadvantages: 1. the end of the distributor nearest to the supply end would be heavily loaded. 2. the consumers at the distant end of the distributor would be subjected to serious voltage variations. When the load on the distributor changes.

18. Ring main system: when the distributor is supplied by two feeders, it is called a ring main distribution system. In this system the feeder closes on itself, i.e. it forms a complete ring and hence the name ring mains. Advantages of ring main system: 1. it offers a great reliability of supply. In the event of fault on any system of feeder, the continuity of supply can be maintained. 2. each distributor is supplied via two feeders, for example,- the distributor connected at a point “D” is fed via feeder ABC and ADC

19. Inetrconnected system: In an “interconnected system” the feeder ring is energised by two or more than two generating stations or substations fig. shows the single line diagram of an interconnected system. The closed feeder ring ABCDA is supplied by four stations S1, S2, S3 & S4 at points D,A, B & C.

20. Introduction of Substations A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. Generally substations are unattended, relying on SCADA for remote supervision and control. 20

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22. Types of Substations 1. Transmission substation A transmission substation connects two or more transmission lines. The simplest case is where all transmission lines have the same voltage. In such cases, substation contains huh-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. A transmission station may have transformers to convert between two transmission voltages, voltage control/power factor correction devices such as capacitors, reactors or static VAR compensators and equipment such as phase shifting transformers to control power flow between two adjacent power systems. 22

23. Types of Substations 2. Distribution substation A distribution substation transfers power from the transmission system to the distribution system of an area. It is uneconomical to directly connect electricity consumers to the main transmission network, unless they use large amounts of power, so the distribution station reduces voltage to a level suitable for local distribution. The input for a distribution substation is typically at least two transmission or sub transmission lines. Input voltage may be, for example, 115 W, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2.4 kV and 33 kV depending on the size of the area served and the practices of the local utility. 23

24. Types of Substations 3. Collector substation In distributed generation projects such as a wind farm, a collector substation may be required. It resembles a distribution substation although power flow is in the opposite direction, from many wind turbines up into the transmission grid. Usually for economy of construction the collector system operates around 35 kV and the collector substation steps up voltage to a transmission voltage for the grid. The collector substation can also provide power factor correction if it is needed, metering and control of the wind farm. In some special cases a collector substation can also contain an HVDC converter station. 24

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26. Components of Substations Various components are used at grid transmission substations. These are as follows: Conductors Current transformers Potential Transformers Power transformers(Auto Transformer) Capacitive voltage Transformers Line Isolators Bus Isolators Lighting Arresters Capacitor Bank Circuit Breaker 26

27. Thank You 27 Prepared by: Abdul Rahman Al Ghanim (1621091102 ) Submitted to Professor: Shivani Balyan