It is shown in this paper that voltage sags experienced by three-phase loads, such as adjustable-speed drives, can be classified into four types. Each sag can further be characterized by a magnitude and a phase-angle jump. Relations between fault type, sag type and load connection are presented. The transfer of sags through transformers is discussed. The magnitude and phase-angle jump of sags are directly related to the voltage in the faulted phase, or between the faulted phases, at the point-of-common coupling between the load and the fault.

Characterisation of voltage sags experienced by three-phase adjustable-speed drives

This paper analyzes the characteristic of voltage dips in power systems with special emphasis on unbalanced dips and electrical components analysis. A generalized dip model is built for all unbalanced dips, taking into account the fault types, transformer types and load connections. It shows the transformation for different types of unbalanced dips. The characterization results in a so-called remaining complex voltage (a generalized magnitude phase angle shift) for balanced and unbalanced dips as well as a factor, related to the rotating machine contribution to the source impedance for unbalanced dips. It is shown that the factor is close to unity, so that both balanced and unbalanced dips can be characterized with one phaser.

Characteristic of voltage dips (sags) in power systems

In this paper we discuss two stochastic assessment methods for voltage sags and apply them to a 98-bus model of the 400 kV National Grid of England and Wales. The method of fault positions is most suitable for implementation in a software tool. It has been used to get exposed areas and sag frequencies for each bus. The results are resented in different ways, including a so-called voltage sag map showing the variation of the sag frequency through the network. The method of critical distances is more suitable for hand calculations, as both the amount of data and the complexity of the calculations are very limited. It has been used to obtain sag frequencies for a number of buses. A comparison with the results obtained by using the method of fault positions, shows that the method of critical distances is an acceptable alternative were software or system data are not available for a more accurate analysis.

Stochastic prediction of voltage sags in a large transmission system

This paper analyses the characteristic of voltage dips in power systems with special emphasis on unbalanced dips and symmetrical components analysis. A generalized dip model is built for all unbalanced dips taking into account the fault types, transformer types and load connections, which shows the transformation for different types of unbalanced dips. The characterization results in a so-called "remaining complex voltage" (a generalized magnitude and phase angle shift) for balanced and unbalanced dips and a factor, related to the rotating machine contribution to the source impedance for unbalanced dips. It is shown that the factor is close to unity, so that both balanced and unbalanced dips can be characterized through one phasor.

Based on a simple voltage divider model, a relation is derived between the load sensitivity to voltage sags (expressed as a critical voltage) and the exposed area (expressed as a critical distance). The critical distance increases about linearly with voltage level. The relation found is remarkably similar to relations found in power quality surveys. An equivalent expression is found for the critical distance as a function of the critical phase-angle jump. Realizing that faults downstream of a transformer do not significantly influence the expected number of sags, it is possible to estimate the number of sags at a specific load location. The method is extended to some nonradial systems: simple subtransmission loops, local generation, feeding from two substations, and operating with a normally open breaker.

Fast assessment methods for voltage sags in distribution systems

Voltage sags, also known as dips, are increasingly important to industrial reliability. Modern process controls are often sensitive to voltage sags. The combination of a voltage sag and sensitive equipment may cause significant production outages. Less sensitive equipment may be available at a premium price, but the designer must know the sag characteristics of the electric system to make the best choices between reliability and cost. This proposed chapter offers a way to predict voltage sag performance without long term monitoring and before plants are constructed. The analysis technique proposed for a new chapter 9 in the next revision of IEEE std 493 is shown. >

Proposed chapter 9 for predicting voltage sags (dips) in revision to IEEE Std 493, the Gold Book

Voltage sags, also known as dips, are important to industrial reliability. Modern process controls are often sensitive to voltage sags. The combination of voltage sags and sensitive equipment may cause significant production outages. Less sensitive equipment may be available, but the designer must know sag characteristics of the electric system to make the best choices between reliability and equipment cost. This paper shows how to predict voltage sag performance of electric supply systems by combining a new analysis method with reliability data. The analysis method is proposed for a new chapter in the next revision of IEEE Std 493. >

Proposed chapter 9 for predicting voltage sags (dips) in revision to IEEE Std 493, the gold book

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Proposed chapter 9 for predicting voltage sags (dips) in revision to IEEE Std 493, the Gold Book

Proposed chapter 9 for predicting voltage sags (dips) in revision to IEEE Std 493, the gold book