Paralleling Filter Capacitors

In an HT system, either the star is not grounded or it is a delta-connected system and hence the third harmonic is mostly absent, while the content of the. second harmonic nuiy be too small to be of any significance. For this purpose, where harmonic analysis is not possible, or for a new installation where the content of harmonies is not known, it is common practice to use a series reactor of 6% of the reactive value of the capacitors installed. This will suppress most of the harmonics by making the circuit inductive, up to almost the fourth harmonic, as derived subsequently. Where, however, second harmonics are significant, the circuit may be tuned for just below the second harmonic. To arrive at a more accurate choice of filters, it is better to conduct a harmonic analysis of the system through a harmonic analyser and ascertain the actual harmonic quantities and their magnitudes present in the system, and provide a correct series or parallel filter-circuits for each harmonic. 

A simplified schematic of the APLC power circuitry is given in Fig. 10.174. The DC bus (Vac) is the energy storage device that supplies the power required for voltage compensation and current injection. The parallel filter serves two purposes. First, the IGBTs in this portion of the APLC keep the DC link capacitor... 

A further step in this direction is to place a capacitor parallel to the resistor R2 (Fig. 3-36). If this differentiator is combined with a low-pass filter and an impedance converter, we have an effective network (Fig. 3-37) with which higher-order derivative devices can also be constructed. 

But w hen the third and/or second harmonics are also present in the system, at a certain fault level it is possible that there may occur a parallel resonanee between the capacitor circuit and the inductance of the system (source), resulting in very heavy third or second harmonic resonant currents, which may cause failure of the series reactor as well as the capacitors. In such cases, a 6% reactor will not be relevant and a harmonic analysis will be mandatory to provide more exacting filter circuits. 

These are meant to be used with a capacitor to tune a filter circuit, with resonances in the audio frequency range for reducing and filtering the harmonics or communication frequencies. They provide a near short-circuit for the required harmonics to filter them out of circuit. They may be single-phase or three-phase and connected in series or parallel of the capacitor circuit and may have a fixed or variable reactance, rated continuously with saturated magnetic characteristics. They may incur heavy losses. 

As one can see, there is the familiar choke input filter (T-C) on the output, which is characteristic of the buck and all forward-mode converters. The configuration shown in Figure 4—10 is called a parallel resonant topology because the load impedance (the T-C filter acting as a damping impedance) is placed in parallel to the resonant capacitor. The input to the T-C filter stage... 

Harmonic filters are broadly classified into passive and active filters. Passive filters, as the name implies, use passive components such as resistors, inductors, and capacitors. A combination of passive components is tuned to the harmonic frequency that is to be filtered. Figure 4.22 is a typical series-tuned filter. Here the values of the inductor and the capacitor are chosen to present a low impedance to the harmonic frequency that is to be filtered out. Due to the lower impedance of the filter in comparison to the impedance of the source, the harmonic frequency current will circulate between the load and the filter. This keeps the harmonic current of the desired frequency away from the source and other loads in the power system. If other harmonic frequencies are to be filtered out, additional tuned filters are applied in parallel. Applications such as arc furnaces require multiple harmonic filters, as they generate large quantities of harmonic currents at several frequencies. 

The photovoltaic measurements were carried out in the parallel plane capacitor arrangement. The capacitor consisted of the anodically oxidized Al+Si film on the silicon substrate, a 10 pm thick mica spacer and a semitransparent top electrode. The silicon substrate and the semitransparent electrode served as the reference and the probe electrodes, respectively. The photovoltage transients were excited with single pulses of N2 laser (wavelength 337 nm, pulse duration 10 ns, intensity 0.1 mJ/cm ) and recorded within the time range from 10 ns to about 1 ms. The excitation intensity was changed over four orders of magnitude with calibrated neutral density filters. 

Section 8.2.3 also considers the effect of an abrupt parametric fault in one phase of the inverter s load. In this case study, the load of the three-phase inverter is an RL-network in delta configuration often used in studies of three-phase PWM voltage source inverters. The study may be extended by replacing the RL-network by a sophisticated BG-model of an induction motor (see for instance [31, Chap. 8]). Studies of the three-phase diode bridge rectifier typically assume a resistive load in parallel to a filter capacitor. 

Series-Parallel RLC Resonant Filter The Pole Zero Pattern Description of Resonance Time-Domain Description of Resonance Resonance and Energy Storage in Inductors and Capacitors Physical Hazards with Resonant Circuits... 

Bleeder A high resistance connected in parallel with one or more filter capacitors in a high voltage dc system. If the power supply load is disconnected, the capacitors discharge through the bleeder. 

Figure 2-22 shows three types of rectifiers and their output-signal forms. Each uses semiconductor diodes (see Section 2C-2) to block current in one direction while permitting it in the opposite direction. To minimize the current fluctuations shown in Figure 2-22, the output of a rectifier is usually filtered by placing a capacitor with a large capacitance in parallel with the load Ri, as shown in Figure 2-23. The charge and discharge of the capacitor has the effect of decreasing the variations to a relatively small r/pp/c. In some applications, an inductor in series and a capacitor in parallel with the load serve as a filter this type of filter is known as an L section. By suitable choice of capaci-...

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