Abstract
With the increasing use of sensitive loads in frequency converters and in relays in distribution networks, voltage sag has become a major power quality issue that urgently needs to be solved. For the purpose of improving the understanding of voltage sag severity in distribution networks, a comprehensive weight-based severity evaluation method of voltage sag is presented in this paper. First, a multi-side index system that takes into account the combined influence of the source, network, and the load is established. A comprehensive weight method, which combines the improved analytic hierarchy process (IAHP) and the entropy method, is then adopted to determine the index weight. The weight of each index and the degree of superiority are linearly weighted to obtain the severity of voltage sag at different observation points. Finally, the effectiveness of the proposed method is verified using a distribution network model established in DIgSILENT PowerFactory (15.1.7, Gomaringen, Germany).
Highlights
Voltage sag, which can last from half the grid frequency cycle to 1 minute, is one of the most pervasive power quality problems at present [1,2]
Voltage sag can be caused by motors starting up, high-capacity load switching, transformer energization, or a short circuit in a power system, which may result in equipment malfunctioning and can lead to significant economic losses [3,4,5,6]
The index superiority degree and index weight of each observation point are linearly weighted in order to obtain the voltage sag severity, yj, at each observation point, and the severity, yj, is found
Summary
Voltage sag, which can last from half the grid frequency cycle to 1 minute, is one of the most pervasive power quality problems at present [1,2]. Factors considered in existing studies pertaining to severity assessment methods for voltage sag issues in distribution networks are not objective and comprehensive. It is necessary to find a more appropriate method to evaluate the severity of voltage sags, which facilitates a more useful perspective on the problem of voltage sags in distribution networks. Research on the severity of voltage sag and relevant evaluation indexes has attracted many scholars’ attention. The IEEE P1564 standard provides a framework for voltage sag evaluation [7]. For a single voltage sag event, the common indexes can include the voltage sag magnitude severity index (MSI ), the duration severity index (DSI ), the energy index, the system average RMS frequency index as well as the (SARFI) index, etc. [8]
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