Electrical power distribution and utilization

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1. Electric al Power Distribution and Utilization.

2. Power System  The generation, transmission and distribution of electric power is called P ower S ystem . 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

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

4. 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 6.6, 11, 13.2 .or 33 kV. Due to economic consideration , the generation voltage is 11kV. 6

5. 2. Primary Transmission  In this step 11kV is step up to 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 . 7

6. 3. Secondary Transmission  In this Step, after step down the primary transmission voltage to 132kV or 66kV the power is transmitted at Receiving Station and then sent to step down Transformer. 8

7. 4. Primary Distribution Step Down Transformer further step down the voltage up to 11kV and sent to next sub station and then to Distribution Sub Station (Distribution Transformer).This is called Primary Distribution. 9

8. 5.Secondary Distribution By converting 11 kV to 400V or 220V and sent to this power to consumer this step is known as Secondary Distribution 10

9. DISTRIBUTION SYSTEM

10. 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 400/2 2 volts (in three phase 4 wires system)

11. Important terms of distribution system Feeder Distributor Service mains 1. Feeder - A Feeder is conductor which connects the substation to the area where power is to be distributed .   Feeder are used to feed the electrical power from the generating station to the substation   No tapings are taken from the feeder   So the current in it remains the same throughout   Main consideration in the design of feeder is the Current carrying capacity.

12. 2.Distributer A distributer is a conductor from which tapings are taken from pole mounted transformer to the consumer  The current through a distributer is not constant because tapings are taken at various places along its length Voltage drop is main consideration   Limit of variation is 6% of rated at consumer

13. 3. Service mains A service mains is a generally a small cable which connects the distributer to the consumer ‘s meter.   The connecting links between the distributor and the consumer terminals. .

14. 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. 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.

16. Advantages of ac over dc: we got this supply by transmitting ac over long distances. AC can be transmitted using step up transformers but direct current or dc can not be transmitted by this method. The ac is easy to generate than dc. It is cheaper to generate ac than dc. The ac generators have higher efficiency than dc. The ac can be easily converted into dc. The variation of ac can easily be done using transformers either step up or step down.

17. Advantages of dc over ac : DC needs only two wires of transmission, while a 3 phase AC may need up to 4 wires. The Corona loss associated with DC is negligible, while for AC, it increases with its frequency. The skin effect is also observed in AC, leading to problems in transmission conductor designs. No inductive and capacitive losses. No proximity effect. In fact, High Voltage transmission over 650 km long is often done with DC.

18. 3 . According to number of wires : 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

19. 4. According to the system of connection: Radial system Ring main system 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.

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

21. Ring main system: In this system the only one Power Substation and there may be two or three feeders which are connected to the ring of distributors. Which further connected to controller switches A,B,C and D. Advantages of ring main system: it offers a great reliability of supply. In the event of fault on any system (Transformer) of feeder, the continuity of supply can be maintained. There may be two or three feeders but Power Substation is only one.

22. 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.

23. 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 .

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25. Types of Substations 1. Transmission substation A substation where two or more transmission lines which are come from Generation Station are connected is called Transmission substation. 22

26. 2. Distribution substation A S ubstation that receive power from Transmission Substation or Power Station and after step down the voltage, finally sent to the user is called Distribution substation. I t 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 . I 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

27. 3 . Switching substation A  switching  station is a  substation  without transformers and operating only at a single voltage level Sometimes they are used for switching or for parallelizing circuits in case of failure. 24

28. Components of Substations Various components are used at grid transmission substations. These are as follows: Conductors Current transformers Potential Transformers Lighting Arresters The isolator Bus Bar Circuit Breaker 26

29. Conductors Metals which do not allow the free movement of electrons or electric charge. They resist electricity with their high resisting property. Insulators It allows the flow of electric charge. It permits the free movement of the flow of electrons through them.

30. Conductor Insulator

31. A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary Current transformers

32. Potential transformer Transformer used for the transformation of voltage from a higher value to the lower value.

33. Lightning Arrester A lightning arrester (lightning diverter) is a device used on electric power systems and  telecommunication systems to protect the insulation and conductors of the system from the damaging effects of lightning.

34. The isolator The isolator is a mechanical switch which isolates a part of the circuit from the system as when required. Its main purpose is to isolate one portion of the circuit from the other and is not intended to be opened while current is flowing in the line

35. Bus Bar Bus Bar  is a metallic strips of copper , conductor or group of conductor which is used for electrical power distribution as junction or node. The  Bus bars  that makes the electrical power distribution much easier , less expensive and more flexible.  Bus Bar   manufactured by aluminum and copper.

36. Circuit Breakers  Circuit breakers  are used to open and close  circuits . They can be operated manually to perform maintenance or will automatically trip if a short  circuit  occurs.

37. Relays It is a set of many identical capacitors connected in series or parallel within an enclosure and is used for power factor correction and basic protection of the substation. Capacitor bank These are used for disconnection of the circuits by manual or automatic operation. It consists of coil which is excited or energized to break or make a circuit connection.

38. Relays Capacitor Bank