Understanding slow voltage instability

Abstract

This paper will explain the dynamics of slow voltage instability on large power systems at a basic and intuitive level. This paper will outline the voltage instability phenomenon and leave the specific details for individual investigation. Slow Voltage Instability is a phenomenon which occurs over several minutes to an hour; where as Transient Voltage Collapse occurs over several seconds. Understanding what causes voltage instability and why this may cascade into a voltage collapse requires knowledge of how key components of the power system are affected by low voltage. Some of these components will respond at different time frames, contributing to faster transient voltage instability, and/or slower long term voltage instability. Simulations will show how the components of voltage instability contribute to cause low voltage. Popular power flow methods such as PV and QV curves are used to show how a system can be analyzed for voltage stability. Finally, there are several possible solutions that will be discussed that could help stabilize voltage for large power systems.