Voltage Sag Severity Research Articles

Modelling of Dynamic Voltage Restorer against Balanced and Unbalanced Voltage Sags in Distribution systems

The Dynamic Voltage Restorer (DVR) is used to regulate the voltage at the load terminals from various power quality problems like sag, swell, harmonics, unbalance etc. in supply voltage. This paper presents modelling aspects of several types of Dynamic Voltage Restorer (DVR) working against various voltage sags by simulation. Dynamic voltage restorers (DVRs) are used to protect sensitive loads from the effects of voltage sags on the distribution feeder. Significant simulation results show that these several types of the modelled device can work very well against balanced and/or unbalanced voltages caused by faults in a distribution system. Detailed analyses illustrate that with suitable parameter setting these devices can deal with different levels of voltage sag severity. In addition, appropriate ways to obtain a good quality output voltage by a DVR during voltage sag is also presented. It then provides analyses of working performance of the device, including capability and quality of compensation. Index Terms- Dynamic Voltage Restorer (DVR), Balanced and unbalanced faults, Compensation capability, Power quality sag severity, voltage sag.

The influence of transformers, induction motors and fault resistance regarding propagation voltage sags

This article presents an analysis of voltage sag propagation. The ATPDraw tool was selected for simulating the IEEE 34 node test feeder. It takes into account both voltage sags caused by electrical fault network, as well as voltage sag propagation characteristics caused by induction motor starting and transformer energising. The analysis was aimed at assessing the influence of transformer winding connections, the impedance of these transformers, lines and cables, summarising the effects on disturbance magnitude and phase. The study shows that the influence of an induction motor on voltage sag propagation results in increased voltage sag severity. Voltage sags caused by induction motor starting and transformer energising have no zero-sequence component, so they are only affected by type 3 transformers. The influence of fault resistance on voltage sag magnitude and phase characteristics is examined and some aspects of interest in characterising these electromagnetic disturbances is identified.

Generic Failure-Risk Assessment of Industrial Processes due to Voltage Sags

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper proposes methodologies for modeling and assessment of equipment and industrial processes susceptibility to voltage sags and short interruptions. Voltage sag severity indices are proposed that translate physical disturbance events into expected equipment behavior, allowing fast identification of possible process failure. Based on these indices, probabilistic and fuzzy-based methodologies are developed to provide realistic equipment representation and to incorporate flexibility for customized process modeling. Extensive simulations showed that the proposed models and methodologies yield greater accuracy in assessments compared to conventional approaches. </para>

Estimation of Sensitive Equipment Disruptions Due to Voltage Sags

This paper presents a method for predicting the number of equipment disruptions due to voltage sags in a unit of time based on a concept described in IEC 61000-3-7. The proposed method uses the probabilistic distributions of system disturbance and equipment immunity indices obtained from a unified fuzzy inference engine to represent the disturbance severity and equipment susceptibility of voltage sags. It takes stochastic behavior of service performance into account in the estimation of equipment disruption. The proposed framework is also applicable if other power-quality indices, such as the voltage sag energy index and voltage sag severity index, are adopted. It can be used as an alternative for performing voltage sag coordination and financial analysis

System Voltage Sag Performance Estimation

This paper describes an analytical method for evaluating the voltage sag performance of a power-supply distribution network. The severity of voltage sag, as a result of system fault, is quantified by its magnitude and duration, and illustrated using a voltage sag density table. Since different loads have a different tolerance level to voltage sags, different evaluation algorithms are proposed in this paper to account for each type of sensitivity. It is illustrated that once the failure rates of the power components making up a system are known, the number and severity of the ensuing voltage sag events can be readily estimated. These estimates would be useful for predicting potential impacts on the operation of sensitive loads and for planning mitigating solutions to improve or maintain the power quality of the supply system. The possibility of incorporating other influencing factors from the behavior of the load and the fault events is also discussed.