Power System Transient Stability Analysis

Abstract

The mechanical–electrical transient of a power system that has experienced a large disturbance can evolve into two different situations. In the first situation, the relative rotor angles among generators exhibit swing (or oscillatory) behavior, but the magnitude of oscillation decays asymptotically; the relative motions among generators eventually disappear, thus the system migrates into a new stable state, and generators remain in synchronous operation. The power system is said to be transiently stable. In another situation, the relative motions of some generator rotors continue to grow during the mechanical–electrical transient, and the relative rotor angles increase, resulting in the loss of synchronism of these generators. The system is said to be transiently unstable. When a generator loses synchronization with the remaining generators in the system, its rotor speed will be above or below what is required to produce a voltage at system frequency, and the slip motion between the rotating stator magnetic field (relative to system frequency) and rotor magnetic field causes generator power output, current and voltage to oscillate with very high magnitudes, making some generators and loads trip and, in the worst case, causing the system to split or collapse.