Effects of Cascaded Voltage Collapse and Protection of Many Induction Machine Loads upon Load Characteristics Viewed from Bulk Transmission System

As is well known, two of the fundamental processes which give rise to voltage collapse in power systems are the on-load tap changers of transformers and the dynamic characteristics of loads such as induction machines. It is well established that, of these two, the former makes for a slower collapse while the latter makes for a faster collapse. However, in realistic simulations, the load levels of the induction machines are not uniform and it may be expected that some of the loads will collapse first, followed by the collapse of the loads which did not go into instability during the preceding collapses. In such situations, the overall equivalent collapse behavior viewed from the bulk transmission level becomes somewhat different from the simple collapse driven by one aggregated induction machine. This paper studies the process of cascaded voltage collapse among many induction machines by time simulation, in which the load distribution on a feeder line is modeled by several hundred induction machines and static impedance loads. It is shown that in some cases voltage collapse actually cascades among induction machines, with the macroscopic load dynamics viewed from the upper level resulting in a slower collapse than expected from the aggregated load model. We also show the effects of machine protection of induction machines, which results in slower collapse. (C) 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 19-27, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20894