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Power Quality in Power Systems and Electrical Machines von Fuchs, Ewald (eBook)

  • Verlag: Elsevier Reference Monographs
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Power Quality in Power Systems and Electrical Machines

The second edition of this must-have reference covers power quality issues in four parts, including new discussions related to renewable energy systems. The first part of the book provides background on causes, effects, standards, and measurements of power quality and harmonics. Once the basics are established the authors move on to harmonic modeling of power systems, including components and apparatus (electric machines). The final part of the book is devoted to power quality mitigation approaches and devices, and the fourth part extends the analysis to power quality solutions for renewable energy systems. Throughout the book worked examples and exercises provide practical applications, and tables, charts, and graphs offer useful data for the modeling and analysis of power quality issues. Provides theoretical and practical insight into power quality problems of machines and systems, enabling the reader to solve the power quality problems that they encounter Worked examples and end of chapter exercises (with available solutions) show practical applications of the material discussed in the chapter New to this edition: identifies problems and solutions associated with renewable energy sources, provides more practical examples, and provides a website with downloadable examples using SPICE, Mathematica, and Matlab©


    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 1140
    Sprache: Englisch
    ISBN: 9780128009888
    Verlag: Elsevier Reference Monographs
    Größe: 47119 kBytes
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Power Quality in Power Systems and Electrical Machines

1.8 Power quality improvement techniques

Nonlinear loads produce harmonic currents that can propagate to other locations in the power system and eventually return back to the source. Therefore, harmonic current propagation produces harmonic voltages throughout the power systems. Many mitigation techniques have been proposed and implemented to maintain the harmonic voltages and currents within recommended levels:

- high power quality equipment design,

- harmonic cancellation,

- dedicated line or transformer,

- optimal placement and sizing of capacitor banks,

- derating of power system devices, and

- harmonic filters (passive, active, hybrid) and custom power devices such as active power line conditioners (APLCs) and unified or universal power quality conditioners (UPQCs).

The practice is that if at PCC harmonic currents are not within the permissible limits, the consumer with the nonlinear load must take some measures to comply with standards. However, if harmonic voltages are above recommended levels - and the harmonic currents injected comply with standards - the utility will have to take appropriate actions to improve the power quality.

Detailed analyses of improvement techniques for power quality are presented in Chapters 8 to 10 .
1.8.1 High Power Quality Equipment Design

The use of nonlinear and electronic-based devices is steadily increasing and it is estimated that they will constitute more than 70% of power system loading by year 2010 [ 10 ]. Therefore, demand is increasing for the designers and product manufacturers to produce devices that generate lower current distortion, and for end users to select and purchase high power quality devices. These actions have already been started in many countries, as reflected by improvements in fluorescent lamp ballasts, inclusion of filters with energy saving lamps, improved PWM adjustable-speed drive controls, high power quality battery chargers, switch-mode power supplies, and uninterruptible power sources.
1.8.2 Harmonic Cancellation

There are some relatively simple techniques that use transformer connections to employ phase-shifting for the purpose of harmonic cancellation, including [ 10 ]:

- delta-delta and delta-wye transformers (or multiple phase-shifting transformers) for supplying harmonic producing loads in parallel (resulting in twelve-pulse rectifiers) to eliminate the 5th and 7th harmonic components,

- transformers with delta connections to trap and prevent triplen (zero-sequence) harmonics from entering power systems,

- transformers with zigzag connections for cancellation of certain harmonics and to compensate load imbalances,

- other phase-shifting techniques to cancel higher harmonic orders, if required, and

- canceling effects due to diversity [ 57 - 59 ] have been discovered.
1.8.3 Dedicated Line or Transformer

Dedicated (isolated) lines or transformers are used to attenuate both low- and high-frequency electrical noise and transients as they attempt to pass from one bus to another. Therefore, disturbances are prevented from reaching sensitive loads and any load-generated noise and transients are kept from reaching the remainder of the power system. However, some common-mode and differential noise can still reach the load. Dedicated transformers with (single or multiple) electrostatic shields are effective in eliminating common-mode noise.

Interharmonics (e.g., caused by induction motor drives) and voltage notching (e

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