ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...
ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ... ÇUKUROVA UNIVERSITY INSTITUTE OF NATURAL AND APPLIED ...
2. POWER QUALITY Mustafa İNCİ of all PQ disturbances are of the voltage quality type, where the interest is the study of any deviation of the voltage waveform from its ideal form. The best well-known disturbances are voltage sags and swells, harmonic and interharmonic voltages, and, for three-phase systems, voltage imbalances (Roncero-Sanchez et al., 2009). A number of national and local surveys helped to quantify the statistical aspects of this problem. The most common disturbances and the most commonly affected equipments are illustrated in Figure 2.1 (Emanuel et al., 1997). Figure 2.1. Basic disturbances: (a) Causes at customer side, (b) Causes at utility side and (c) Affected equipment (Köroğlu,2012) Another survey result is given in Figure 2.2 which shows the percentage occurrences of PQ disturbances in equipment interruptions (Köroğlu , 2012). Figure 2.2. Percentage occurrences of PQ disturbances in equipment interruptions (Köroğlu,2012) 7
2. POWER QUALITY Mustafa İNCİ 2.2.1. Voltage Sag Voltage sags are now one of the most important power quality problems in the distribution system. A voltage sag is a momentary decrease in the RMS ac voltage (10%–90% of the nominal voltage), at the power frequency, of duration from 0.5 cycles to a few seconds. Voltage sags are normally caused by short-circuit faults such as a single-line-to-ground fault in the power system or by the starting up of induction motors of large rating. Voltage sags may cause the malfunction of voltagesensitive loads in factories, buildings, and hospitals (Kangarlu et al., 2010). Voltage sags can cause tripping of contactors, motor starters, relays, restarting expense of computers and shutdown of an entire production line. The sources of voltage sags are basically faults on adjacent feeders, lighting, short circuit event, start up of heavy loads, transformer energizing and motor starting (Bollen, 2001). 2.2.2. Voltage Swell Voltage swell is defined as a short duration increasing in RMS supply with increase in voltage ranging from 1.1 pu to 1.8 pu of nominal supply. The main causes for voltage swell are switching of large capacitors or removal of heavy loads (Kangarlu et al., 2010). Voltage swells might not be as common as voltage sags, however are much more harmful and disruptive to static power converters. In fact, they may severely damage or trip them, causing shutdowns of entire processes. This overall situation has become even more critical given the recent industrial trend to increase operating voltages of power converters (a practice that has pushed semiconductor devices up to their limit. A closer look to this phenomenon is, hence, required (Burgos et al., 2005). 2.2.3. Voltage Fluctuations 8
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- Page 5 and 6: ACKNOWLEDGEMENTS First and foremost
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2. POWER QUALITY Mustafa İNCİ<br />
of all PQ disturbances are of the voltage quality type, where the interest is the study<br />
of any deviation of the voltage waveform from its ideal form. The best well-known<br />
disturbances are voltage sags and swells, harmonic and interharmonic voltages, and,<br />
for three-phase systems, voltage imbalances (Roncero-Sanchez et al., 2009).<br />
A number of national and local surveys helped to quantify the statistical<br />
aspects of this problem. The most common disturbances and the most commonly<br />
affected equipments are illustrated in Figure 2.1 (Emanuel et al., 1997).<br />
Figure 2.1. Basic disturbances: (a) Causes at customer side, (b) Causes at<br />
utility side and (c) Affected equipment (Köroğlu,2012)<br />
Another survey result is given in Figure 2.2 which shows the percentage<br />
occurrences of PQ disturbances in equipment interruptions (Köroğlu , 2012).<br />
Figure 2.2. Percentage occurrences of PQ disturbances in equipment interruptions<br />
(Köroğlu,2012)<br />
7
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