J. V. Milanović

Sensitivity of AC adjustable speed drives to voltage sags and short interruptions

This paper discusses the sensitivity of adjustable speed drives (ASDs) to voltage sags and short interruptions on the basis of extensive test results. Existing standards and previously published work are critically reviewed, and a description of test procedures needed for appropriate assessment of ASD sensitivity is presented. The following tests were performed: sensitivity to rectangular three-phase, two-phase, and single-phase voltage sags with ideal and nonideal supply characteristics, as well as sensitivity to nonrectangular-balanced three-phase voltage sags similar to those caused by the starting of large motors. The results show that although the behavior of this equipment has a rather complex pattern, a simple representation of ASD sensitivity to various types of voltage sags and short interruption can be established.

Locating dynamic loads which significantly influence damping

The paper proposes a techniques for locating loads where dynamics have a significant influence on the damping of power system inter-area oscillations. A feedback interpretation of load dynamics underlies this technique. It is shown that eigenvalue sensitivity and residues can be used to provide the desired information. This approach is applicable for the analysis of large systems. Use of these ideas allows limited resources to be devoted to obtaining good models of important loads, rather than trying to obtain adequate models of many extra loads.