electrical power distributions

electrical power distributions - Dr. M. Safiuddin CHAPTER 4...

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Unformatted text preview: Dr. M. Safiuddin CHAPTER 4 REACTIVE COMPENSATION & HARMONIC SUPPRESSION 4.1 Power System Pollution 4.2 Static Motor Controllers 4.2.1 Classification of Motor Controllers 4.2.2 Controllers With AC-DC Rectifier Interface 4.2.3 Controllers With AC-DC Converter/Inverter Interface 4.2.4 Adjustable Voltage AC Motor Controllers 4.3 Power Factor Of Motor Controllers 4.3.1 Power Factor of Rectifier Interface 4.3.2 Power Factor of Converter/Inverter Interface 4.3.3 Power Factor of Soft-Starter Interface 4.4 Harmonics Produced By Static Power Converters 4.4.1 Harmonics Produced by Rectifiers 4.4.2 Harmonics Produced by Converters 4.4.3 Harmonics Produced by Soft-Starters 4.5 Power Factor Correction & Harmonic Control 4.5.1 Passive Filters 4.5.2 Active Power Line Conditioners 4.5.3 Adaptive Power Factor Controllers References Dr. M. Safiuddin CHAPTER 4 REACTIVE COMPENSATION & HARMONIC SUPPRESSION 4.1 Power System pollution The advances in the solid-state power electronics technologies over the last three decades have contributed to the development of compact, efficient and economical power supplies and motor controllers. However, those same technologies have also been responsible for pollution of the AC power sources, they are connected to, by demanding non-sinusoidal current flows. These distortions in the current waveforms are expressed in terms of a spectrum of sinusoidal currents of higher frequencies, which are multiples of the fundamental system frequency, referred to as the "Harmonics". Exhibit 4.11a shows two such examples from real installations. The first one is for a small capacity 400 Hz power system of a test facility. The second one is for the main drive of a large rolling mill system. When reactive power compensation with capacitors is implemented in such installations, resonance conditions can cause high harmonic voltages and currents when they occur at a frequency associated with one of these harmonics. Ideally, an infinite source of electric power (with zero source impedance) would be totally insensitive to the load characteristics. It would not only hold the terminal voltage constant at its rated RMS value but would also maintain its sinusoidal waveform under all load conditions. However, as the source capacity decreases from this ideal level, the source impedance increases resulting in an inherent voltage drop due to the load currents. Fundamental current components produce voltage drops of the fundamental frequency and the harmonic current components produce voltage drops of the harmonic frequencies. All other pieces of equipment connected to such sources then experience: * Variations in the RMS value of the terminal voltage * Distortions in the voltage waveform Higher the source impedance, worse the variations in the terminal voltage and waveform distortions; that is, worse the pollution gets. In this way, the pollution caused by one piece of equipment is transmitted throughout the AC system. As the magnitude of these distorted currents increases relative to the system capacity, the pollution they AC system....
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electrical power distributions - Dr. M. Safiuddin CHAPTER 4...

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