Dynamics and Control of Electric Transmission and Microgrids

8Analysis of Voltage Stability and Control

8.1 Introduction

Power system stability has been primarily associated with rotor angle (synchronous) stability in the past. The transient (angle) stability relates to the stability under large disturbances such as line or bus faults followed by clearing of the fault. The advent of fast‐acting static exciters with high gain automatic voltage regulators (AVRs) in the 1960s introduced the new problem of small, low‐frequency oscillations (0.2–2.0 Hz) that can grow and lead to loss of synchronism. In the 1970s, the problem of torsional oscillations (10–50 Hz), which can be sustained or negatively damped, led to the investigation of subsynchronous resonance (SSR) and its various facets.

In the 1980s, the problem of voltage instability and collapse resulted in several major system blackouts [1–3]. For example, on July 23, 1987 in Tokyo, Japan, loads increased at 400 MW/minute after the noon hour. Despite connection of all available shunt capacitors, the voltage decayed, with voltages on the 500 kV system at 460 kV at 13.15 hours and at 370 kV at 13.19 hours. Collapse began at 13.19 hours; 8168 MW was interrupted. Similar events occurred in France on December 18, 1978 and 29 GW of load was interrupted with energy outage of 100 GWh. Similar incidents have also been experienced in other countries.

Voltage collapse incidents have also been observed in HVDC systems. In the Nelson River HVDC system, Winnipeg, Canada, partial voltage collapse occurred ...