POWER DISTRIBUTION & UTILIZATION (3+1)DR TAHIR MAHMOOD28/01/2013

Lecture #01 Course Contents 28-01-2013 Power Distribution and Utilization (3+1) 06th Semester Course 2K10-EEMarks Distribution: End Semester Exam=40%: Mid Semester=20%:Lab Work=20%: Assignments/Quiz/Seminar=20%

Lecture #01 Course Contents 28-01-2013 Course Objectives:Students are introduced to the basics of power distribution systems and effective utilization of power in heating and illumination applications.

Lecture #01 Course Contents 28-01-2013 Course Contents:Introduction to distribution system. Urban, suburban and rural distribution systems. Primary, secondary and tertiary voltages.

Radial and ring main systems, application of distribution transformers, estimation of load, load characteristics, substation switchgears and bus bar arrangements, calculation of voltage drop and regulation in distribution feeders.

Lecture #01 Course Contents 28-01-2013 Course Contents:Grounding and earthing, distribution transformer neutral, earthing resistance, earthing practice in L.V. networks.

Power Factor: Disadvantages and causes of low power factor, methods for improvement, application of shunt capacitors in distribution network.

Lecture #01 Course Contents 28-01-2013 Course Contents:Batteries & Electrochemical Processes: Main types of batteries and their working, battery charging, electroplating, electrolysis and electrometallurgical process. Cathodic protection of poles, gas pipes, oil pipes and water structures.

Lecture #01 Course Contents 28-01-2013 Course Contents:Heating and Welding: Electric heating, resistance, induction and dielectric heating, electric furnaces, microwave heating, electric welding, resistance welding and its types.

Fundamentals of Illumination Engineering: Laws, units and terms used, requirements for good lighting, illumination schemes for various situations (street lighting, commercial/industrial lighting, stadium/flood/stage/spot lighting etc.), types of lamps, their working and relative merit.

Lecture #01 Course Contents 28-01-2013Books:1. Principles of Power Systems, V.K.Mehta and Rohit Mehta.2. Electric Power Distribution System Engineering, Turan Gonen.3. Electric distribution systems, ABDELHAY A. SALLAM, OM P. MALIK.

Figure 1. One-line diagram showing basic power system structure

Figure 2. Radial distribution system

Figure 6.5 Loop system.

Figure 6.6 Network (Spot-network).

Table 1-1 shows typical transmission and distribution system voltagesin use at the present time.

Table 1-1. Typical Voltages in Use

Usually steel poles and towers are used for transmissionlines and wood and concrete poles for distribution circuits.However, this distinction doesnt always hold true.Pole SelectionTwo factors must be considered in choosing poles: length andstrength required. The length of poles depends on the required clearance above the surface of the ground, the number of crossarms to be attached, and other equipment which may be installed (Figure 2-4). Provision should also be made for future additions of crossarms, transformers, or other devices. Poles come in standard lengths ranging from 25 to 90 feet in 5-foot differences; that is, 25 feet, 30 feet, 35 feet, and so on. Special poles above 90 feet and below 25 feet are also available.

POLE STRENGTHRequired pole strength is determined by the weight of crossarms, insulators, wires, transformers, and other equipment it must carry, as well as by ice and wind loadings. All these forces tend to break a pole at the ground line.

POLE DEPTHSoil conditions, the height of the pole, weight and pull factors must be considered in deciding how deep a pole must be planted in the ground (Figure 2-9). Table 2-3 gives approximate setting depths for poles in particular given conditions.

CROSSARMSCrossarms are most commonly used are of Steel or wood. 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.

POLE PINSPole pins shown in Figure 2-12 are attached to the crossarms. They are used to hold pin-type insulators. Note that they are threaded so that the insulator can be securely screwed on.

Figure 2-12. Pole pins for attaching pin insulators to crossarms.

Connectors and SplicesMost primary connectors use some sort of compression to join conductors (see Figure 2.15 for common connectors). Compression splices join two conductors together two conductors are inserted in each end of the sleeve, and a compression tool is used to tighten the sleeve around the conductors.

Connectors and SplicesGood cleaning is essential to making a good contact between connector surfaces. Both copper and aluminum develop a hard oxide layer on the surface when exposed to air. While very beneficial in preventing corrosion, the oxide layer has high electrical resistance.

PIN SPACINGThe spacing of the pins (see Figure 2-13) on the crossarms must be such as to provide enough air space between the conductors to prevent the electric current from jumping or flashing over from one conductor to another. Also, sufficient spacing is necessary to prevent contact between the wires at locations between poles when the wires sway in the wind.

PIN SPACINGIn addition, enough space must be provided to enable workers climbing through the wires to work safely. The spacing on a standard sixpin arm is 14-1/2 inches, with 30 inches between the first pins on either side of the pole for climbing space. A special six-pin arm with spacing wider than 30 inches is frequently used for junction poles to provide greater safety for the workers.

INSULATORSTwo practical insulator materials are porcelain and glass.

INSULATORS

Pin-Type InsulatorsInsulators, in compression, supporting conductors may be classified as pin type and post type.The pin-type insulator is designed to be mounted on a pin which in turn is installed on the crossarm of the pole. The insulator is screwed on the pin and the electrical conductor is mounted on the insulator (Figure 3-3).

INSULATORSPin-Type InsulatorsThis type of insulator is applicable for rural and urban distribution circuits, and it is usually constructed as one solid piece of porcelain or glass. In Figure 3-4, note the grooves for the conductor and for the tie wires.Larger, stronger pin-type insulators are used for high-voltage transmission lines. These differ in construction in that they consist of two or three pieces of porcelain cemented together. These pieces form what are called petticoats.

INSULATORSPost-Type InsulatorsPost-type insulators are somewhat similar to pin-type insulators.They are generally used for higher voltage applications with the height and number of petticoats being greater for the higher voltages. They may be mounted horizontally as well as vertically, although their strength is diminished when mounted horizontally.Advantage of Pin or Post over Suspension Insulators? Self-reading

Figure 1.5. The left substation is a typical design with two subtransmission lines and two transformers.The right substation is a very reliable design with a primary ring bus, motor operatedswitches, an energized spare power transformer, and a secondary transfer bus.

CONDUCTORSLine ConductorsLine conductors may vary in size according to the rated voltage.

25

T-30

T-1

T-31

T-32

T-33

T-2

T-34

T-36

T-35

T-3

T-37

T-39

25

T-4

T-5

T-6

T-7

T-8

T-9

T-10

D

T-11

T-12

T-13

T-14

T-15

T-16

T-17

T-18

T-19

6

T-20

200

T-21

200

72

5

R

T-39b

D

D

T-38a

200

T-38

T-41

T-40

71

R

D

100

T-42

R

49

50

51

0.09

18

R

R

D

R

Osp

R

50

50

28

27

24

23

1

500MCM

2

22

3

4

7

21

8

D

9

D

D

R

20

50

25

132/11 KV, H-11,Substation

D

D

50

Osp

25

Osp

D

D

D

100

100

100

R

25

19

25

R

D

31

30

29

D

D

D

25

100

25

26

68

25

R

R

50

100

25

T-43

D

25

630

10

100

T-44

11

0.072

T-45

T-46

T-47

T-48

T-49

T-50

T-51

T-52

33

32

34

0.06

0.09

0.036

0.05

0.04

0.08

0.095

0.03

0.03

0.015

0.02

0.08

0.075

0.09

D

D

50

D

25

25

69

25

35

37

36

D

D

50

D

25

D

R

25

63

38

39

D

D

25

25

73

40

42

41

D

D

R

D

100

64

65

66

58

57

D

D

D

56

100

25

47

R

630

46

R

45

44

630

D

55

43

D

D

60

61

62

D

D

D

25

50

50

R

70

R

630

100

R

R

200

100

59

R

48

R

400

400

52

53

54

R

200

25

100

0.242

0.075

0.06

0.036

0.054

0.121

0.075

0.062

0.025

0.045

R

0.048

0.045

0.09

0.04

0.05

0.036

0.05

0.042

0.08

0.09

0.05

0.04

T-53

T-54

T-55

T-56

T-57

T-58

50

100

T-59

T-60

T-61

T-62

T-63

T-64

T-65

100

T-66

67

25

25

100

50

25

100

25

2.1

0.06

2.06

0.09

0.092

0.01

0.668

0.045

0.075

0.084

0.166

0.06

0.242

0.26

0.045

0.019

0.045

0.045

0.009

0.036

0.045

0.009

0.045

0.09

0.045

0.09

0.075

0.045

0.09

T-24

T-25

T-26

T-27

T-28

T-29

0.06

T-22

T-23

12

13

14

15

D

D

D

D

16

25

25

25

25

100

D

17

200

D

0.075

0.036

0.036

0.06

0.075

Node

ACSR Conductor

D

Dog conductor

Osp

Osprey conductor

R

Rabbit conductor

Transformer with rating

T-66

Transformer number

99.99

Distance (kM) between two nodes

ConductorStrandingAl/StGopher6/1Rabbit6/1Dog6/7Panther30/7Osprey18/1

ConnectorsConductors are sometimes spliced by overlapping the ends and twisting the ends together, taking three or four turns.

But to insure a good electrical connection as well as uniformity in workmanship, it is wise to connect conductors with mechanical connectors. (Different such connectors are shown in Figure 3-18.)

SWITCHESSwitches shown in Figure 4-25 are used to interrupt the continuity of a circuit. They fall into two broad classifications: air switches and oil vacuum or gas (SF6) switches. As their names imply, air switches are those whose contacts are opened in air, while the other type switches arethose whose contacts are opened in oil, vacuum, or gas. Oil switches are usually necessary only in very high-voltage, high-current circuits.Air switches are further classified as air-break switches and disconnect switches.

SWITCHESAir-break SwitchesThe air-break switch shown in Figure 4-26 has both the blade and the contact equipped with arcing horns. These are pieces of metal between which the arc resulting from opening a circuit carrying current is allowed to form.

As the switch opens, these horns are spread farther andfarther apart and the are is lengthened until it finally breaks.

Figure 4-25. Switches interrupt the continuity of a circuit. (a) Typicalswitch, (b) air switch, and (c) oil switches.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSThe ability of subtransmission lines and power transformers to be electrically connected is determined by bus connections, disconnect switches, circuit breakers, circuit switchers, and fuses. Together, these components determine the bus configuration of distribution substations. Bus configurations are an important aspect of substation reliability, operational flexibility, and cost.An infinite number of possible substation configurations exist.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSThe six most commonly encountered are shown in Figure 1.10.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSSingle Bus, Single Breaker all connections terminate on a common bus.They are low in cost, but must be completely de-energized for bus maintenance of bus faults. To improve reliability, the bus is often split and connected by a switch or breaker.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSMain and Transfer Bus a transfer bus is connected to a main bus through a tie breaker. Circuits are normally connected to the main bus, but can be switched to the transfer bus using sectionalizing switches. Since circuits on the transfer bus are not protected by circuit breakers, faults on one transferred circuit result in outages for all transferred circuits.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSDouble Bus, Single Breaker utilizes a single breaker per circuit that can be connected to either bus. A tie breaker between buses allows circuits to be transferred without being de-energized. Since this configuration requires four switches per circuit, space, maintenance, and reliability are concerns for AIS applications. Double bus, single breaker configurations are well suited for GIS applications where space, maintenance, and reliability of switches are significantly less of a concern.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSDouble Bus, Double Breaker each circuit is connected to two buses through dedicated circuit breakers. The use of two breakers per circuit makes this configuration reliable, flexible, and expensive.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSBreaker and a Half utilizes legs consisting of three series breakers connected between two buses. Since two circuits are connected on each leg, 1.5 breakers are required for every circuit. This configuration is more expensive than other options (except double bus, double breaker), but provides high reliability, maintainability, and flexibility. Protective relaying is more complex than for previously mentioned schemes.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSRing Bus arranges breakers in a closed loop with circuits placed between breakers. Since one breaker per circuit is required, ring buses are economical while providing a high level of reliability. For AIS applications, ring buses are practical up to five circuits. It is common to initially build a substation as a ring bus and convert it to breaker and a half when it requires more than this amount.

Chapter 1 : DISTRIBUTION SYSTEMS1.2.2 SUBSTATIONS BUS CONFIGURATIONSRing BusRing buses are a natural configuration for GIS applications with any number of circuits. Like the breaker and a half configuration, ring bus relaying is relatively complex.

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