
Electric Distribution Systems
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Persons
ABDELHAY A. SALLAM, PhD, is a life senior member of the IEEE and Professor Emeritus of Electrical Engineering at the Port Said University, Egypt. Sallam and Malik coauthored the Wiley-IEEE Press book entitled Electric Distribution Systems.
OM P.??MALIK, PhD, is a Life Fellow of IEEE, and a Fellow of IET, the Engineering Institute of Canada, Canadian Academy of Engineering, Engineers Canada and World Innovation Foundation. He is a registered Professional Engineer in the Provinces of Alberta and Ontario, Canada.
Content
Preface xi
Acknowledgments xiii
Part I Fundamental Concepts
Chapter 1 Introduction 3
1.1 Introduction and Background 3
1.2 Power System Structure 3
1.3 Distribution Level 5
1.4 General 7
Chapter 2 Distribution System Structure 9
2.1 Distribution Voltage Levels 9
2.2 Distribution System Configuration 9
2.3 General Comments 22
Chapter 3 Distribution System Planning 23
3.1 Duties of Distribution System Planners 23
3.2 Factors Affecting the Planning Process 25
3.3 Planning Objectives 31
3.4 Solutions for Meeting Load Forecasts 37
Chapter 4 Load Forecasting 41
4.1 Introduction 41
4.2 Important Factors for Forecasts 42
4.3 Forecasting Methodology 43
4.4 Spatial Load Forecasting (SLF) 56
4.5 End-Use Modeling 64
4.6 Spatial Load Forecast Methods 65
Part II Protection And Switchgear
Chapter 5 Earthing Of Electric Distribution Systems 75
5.1 Basic Objectives 75
5.2 Earthing Electrical Equipment 76
5.3 System Earthing 93
5.4 MV Earthing Systems 99
5.5 Earthing Systems in LV Distribution Networks 104
Chapter 6 Short-Circuit Studies 111
6.1 Introduction 111
6.2 Short-Circuit Analysis 113
Chapter 7 Protection: Current-Based Schemes 163
7.1 Introduction 163
7.2 Types of Relay Construction 166
7.3 Overcurrent Protection 171
7.4 Directional Protection 187
7.5 Differential Protection 193
Chapter 8 Protection: Other Schemes 207
8.1 Overvoltage Protection 207
8.2 Thermal Protection 220
8.3 Reclosers, Sectionalizers, Fuses 223
Chapter 9 Switchgear Devices 235
9.1 Need for Switchgear 235
9.2 MV Switchgear Devices 237
9.3 LV Switchgear Devices 244
9.4 Protection Classes 250
9.5 Specifications and Implementation of Earthing 251
9.6 Assessment of Switchgear 253
9.7 Safety and Security of Installations 255
9.8 Application Trends in MV Switchgear 256
Chapter 10 Switchgear Installation 261
10.1 Steps for Installing Switchgear 261
10.2 Switchgear Layout 262
10.3 Dimensioning of Switchgear Installations 264
10.4 Civil Construction Requirements 275
10.5 ARC-Flash Hazards 282
Part III Power Quality
Chapter 11 Electric Power Quality 297
11.1 Overview 297
11.2 Power Quality Problems 298
11.3 Cost of Power Quality 304
11.4 Solutions of Power Quality Problems 310
11.5 Solution Cycle for Power Quality Problems 317
Chapter 12 Voltage Variations 321
12.1 Voltage Quality 321
12.2 Methods of Voltage Drop Reduction 329
12.3 Voltage Sag Calculations 345
12.4 Estimation of Distribution Losses 356
Chapter 13 Power Factor Improvement 361
13.1 Background 361
13.2 Shunt Compensation 365
13.3 Need for Shunt Compensation 366
13.4 An Example 368
13.5 How to Determine Compensation 370
Chapter 14 Harmonics in Electric Distribution Systems 379
14.1 What Are Harmonics? 379
14.2 Sources of Harmonics 384
14.3 Disturbances Caused by Harmonics 391
14.4 Principles of Harmonic Distortion Indications and Measurement 396
14.5 Frequency Spectrum and Harmonic Content 398
14.6 Standards and Recommendations 400
Chapter 15 Harmonics Effect Mitigation 403
15.1 Introduction 403
15.2 First Class of Solutions 403
15.3 Second Class of Solutions 404
15.4 Third Class of Solutions 406
15.5 Selection Criteria 409
15.6 Case Studies 409
Part IV Management And Automation
Chapter 16 Demand-Side Management And Energy Efficiency 431
16.1 Overview 431
16.2 DSM 432
16.3 Needs to Apply DSM 433
16.4 Means of DSM Programs 434
16.5 International Experience with DSM 437
16.6 Potential for DSM Application 438
16.7 The DSM Planning Process 439
16.8 Expected Benefits of Managing Demand 444
16.9 Energy Efficiency 444
16.10 Scenarios Used for Energy-Efficiency Application 445
16.11 Economic Benefits of Energy Efficiency 445
16.12 Application of Efficient Technology 445
Chapter 17 SCADA Systems 465
17.1 Introduction 465
17.2 Definitions 469
17.3 SCADA Components 470
17.4 SCADA Systems Architectures 473
17.5 SCADA Applications 480
17.6 SCADA and Grid Modernization 484
Part V Distributed Energy Resources And Microgrids
Chapter 18 Distributed Generation 489
18.1 Power Systems and Distributed Generation 489
18.2 Performance of Distributed Generators 493
18.3 Case Study 518
Chapter 19 Electrical Energy Storage 535
19.1 Introduction 535
19.2 Electrical Energy Storage 535
19.3 Role of Electrical Energy Storage 538
19.4 Types of EES Systems 540
19.5 Energy Storage Application 550
Chapter 20 Microgrids And Smart Grids 553
20.1 Background 553
20.2 MG Benefits 555
20.3 MG Operation 556
20.4 Challenges 556
20.5 Handling the Challenges 557
20.6 Control Methodology 558
20.7 Case Study 560
20.8 Protection for MGs 570
20.9 Concluding Remarks on MGs 572
20.10 Smart Grids 572
Appendix A Data Of Microgrid Components 581
Appendix B Matlab Simulink Models 583
References 589
Index 601
CHAPTER 2
DISTRIBUTION SYSTEM STRUCTURE
2.1 Distribution Voltage Levels
North American and European practices are the two systems of distribution voltage levels in most use around the world. The primary and secondary voltages (MV and LV, respectively) are given in Table 2.1 for both systems. The voltage choice depends on the type of load (residential, commercial, industrial), load size and the distance at which the load is located. This is illustrated by a typical block diagram shown in Figure 2.1.
Table 2.1 Distribution Voltages for North American and European Systems
Type of voltage North American system European systemPrimary distribution voltage (line-to-line)
From 4 to 35 kV From 6.6 to 33 kVThree-phase secondary voltage (line-to-line)
208, 480 or 600 V 380, 400 or 416 VSingle-phase secondary voltage (line-to-neutral)
120/240, 277 or 347 V 220, 230 or 240 VFigure 2.1 Distribution voltages for different loads (values written between parentheses describe the European practice; otherwise the values describe the North American practice).
It is seen that the distribution voltage in the European system is higher than that in the North American system. It has both advantages and disadvantages as listed in what follows.
- Advantages: The system can carry more power for a given ampacity and has less voltage drop and less line losses for a given power flow. Consequently, the system can cover a much wider area. Because of the longer reach, the system needs fewer substations.
- Disadvantages: more customer interruptions because the circuits are longer, that is, lower level of reliability. Therefore, a major concern is to keep reliability at the desired level depending on the load category (more details are given in Section 2.2.2). From the cost point of view, the system equipment (transformers, cables, insulators etc.) is more expensive.
2.2 Distribution System Configuration
Configuration of the distribution networks follows one or a combination of the following standard systems:
- radial system where the load is supplied through one radial feeder;
- open-ring system where the load is supplied through one of two available feeders, that is, one side of the ring;
- closed-ring system where the load is supplied through the two sides of the ring simultaneously;
- dual-ring system in which the load is connected with two rings at the same time, that is, it has four incoming feeders; and
- multiradial system, which means supplying the load by more than one radial feeder.
These systems can be applied to establish the distribution network at either the MV or the LV level.
2.2.1 MV Distribution Networks
The MV distribution networks are the intermediate networks between the sources and the DPs in different zones of the load area.
The DP can be connected to the source through two in-service parallel feeders. At the same time, one feeder can operate at full load if a fault occurs in the second feeder, as shown in Figure 2.2a. For more reliability, two DPs can be connected to each other as shown in Figure 2.2b. In this case, DP2 is connected to the source through two parallel feeders while DP3 is connected to the same source through one feeder.
Figure 2.2 MV supply network to DP with parallel feeders (CB = circuit breaker with overcurrent protection; F = feeder, DP = distribution point).
Of course, it is better and more reliable to use different sources feeding the DPs. In Figure 2.3a, DP1 has two incoming feeders; the first is connected to source #1 while the second is connected to source #2. In this case, one feeder only is in service. The other feeder is a standby and feeds DP1 through automatic reserve switching (ARS). Another way is to divide the bus bar of DP2, Figure 2.3b, into two sections connected to each other by a bus-coupler circuit breaker that is normally open. Each section has an incoming feeder connected to an independent source, as shown in Figure 2.3b. Different configurations can be applied such as given in Figures 2.4a and 2.4b, respectively. A ring bus scheme, shown in Figure 2.5, can also be applied (popular in the United States). In this scheme, a fault anywhere in the ring results in two circuit breakers opening to isolate the fault. For example, when a fault occurs in source #1 circuit breakers CB1 and CB4 would operate to isolate the fault, while source #2 would feed the loads. Circuit breakers are installed with two manual isolating switches on both sides to perform maintenance safely and without service interruption. Alternatively, radial and multiradial configurations can be used as shown in Figures 2.6 and 2.7, respectively. Two additional configurations, an integrated open-ring and a radial distribution network, are shown in Figures 2.8 and 2.9, respectively.
Figure 2.3 MV supply network to DP with independent feeders (ARS = automatic reserve switching, F = feeder, CB = circuit breaker, DP = distribution point).
Figure 2.4 Combined MV supply network to DP.
Figure 2.5 Ring bus scheme.
Figure 2.6 Radial nonreserved distribution network.
Figure 2.7 Multiradial distribution network with automatic reserve switching on MV side.
Figure 2.8 Open-loop distribution network.
Figure 2.9 Radial MV network with DP (ARS on LV bus-bar of TP). TP = transformer; DP = distribution point; ARS = automatic reserve switching; SWB = switchboard.
2.2.2 LV Distribution Networks
2.2.2.1 North American System
Radial structure is the most commonly used in North America. The secondary feeders transmit power to the loads through distribution transformers (MV/LV). Single-phase power at voltage level 120/240 V is usually supplied to residences, farms, small offices and small commercial buildings (Fig. 2.10a). Three-phase power is usually supplied to large farms, as well as commercial and industrial customers. Typical voltage levels for three-phase power are 208Y/120 V, 480Y/277 V or 600Y/347 V (Fig. 2.10b).
Figure 2.10 North American MV/LV distribution transformers. (a) 120/240 V single-phase service, (b) Typical 208 V, 3-phase Y-connected service.
To increase the reliability, in particular, for LV applications with a very high load density, two or more circuits operate in parallel to transmit power into a secondary (LV) bus at which the load is connected. Each circuit includes a separate primary (MV) feeder, distribution transformer, and secondary feeder that is connected to a secondary bus through a network protector. This scheme is known as a "secondary spot network" (Fig. 2.11). If a fault occurs on a primary feeder or distribution transformer of one of the circuits, its network protector receives a reverse power from the other circuits. This reverse power causes the network protector to open and disconnect the faulty circuit from the secondary bus. The load is only interrupted in case of simultaneous failure of all primary feeders or at fault occurrence on the secondary bus. Of course, this scheme is more expensive because of the extra cost of network protectors and duplication of transformer capacity. In addition, it requires a special construction of the secondary bus to reduce the potential of arcing fault escalation as well as a probable increase of secondary equipment rating since the short-circuit current capacity increases in case of transformer parallel operation.
Figure 2.11 Secondary spot network.
2.2.2.2 European System
For European distribution systems, the choice of any of the standard structures (Section 2.2) to establish the LV distribution networks depends on the type of the majority of loads and the reliability level required supplying these loads.
For reliability level 3, the distribution transformers are supplied by two incoming feeders (one is a standby to the other) on the medium voltage side. The outgoing feeders at the low voltage side are radial feeders (cables or overhead lines) as shown in Figure 2.12. If a fault occurs on one of these outgoing feeders, the concerned load is disconnected until the fault is repaired.
Figure 2.12 Supply system to a third-category customer.
For reliability level 2, the medium-voltage side of the distribution...
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