Abstract
Online assessment of transient stability of power systems is critical for avoiding blackout. The increasing installation of phasor measurement units in power systems and the advancement of the wide-area measurement systems make it possible to develop methods for online assessment of power systems by using a large amount of real-time synchronous data. In this paper, we propose an approach based on the largest Lyapunov exponent (LLE) for online transient rotor angle stability assessment, using only wide-area measurement systems data. Through establishing a mathematical model that accounts for the LLE value and the rotor speed, as well as analyzing the post-fault phase-plane trajectory, we present a fast stability criterion to determine whether transient instability occurs. The proposed approach is model-free and does not need long-time LLE data to identify the final sign of the LLE. Furthermore, to reduce computational cost and realize online assessment for large-scale power systems, the critical generator pair (CGP) is recognized as the observation for the rotor angle stability assessment, and an effective algorithm for identifying the CGP is presented. Several case studies on the IEEE-39 bus test system and East China power grid are reported to demonstrate the accuracy and effectiveness of the proposed approach.
Highlights
Transient rotor angle stability is defined as the ability of synchronous generators of a power system to remain in synchronism after being subjected to a disturbance [1]
The power systems were monitored with different areas, and the phasor measurement unit (PMU) measurements from different substations in different areas were collected, time aligned by the phasor data concentrator, and submitted to the monitoring center
Since the proposed approach performs online stability assessment only using the rotor angle and rotor speed data of generators, the rotor angle and rotor speed of the unobserved generators can be estimated by the dynamic state estimation algorithms, which can provide accurate and real-time estimation with respect to PMU measurements [30,31]
Summary
Transient rotor angle stability is defined as the ability of synchronous generators of a power system to remain in synchronism after being subjected to a disturbance [1]. Several LLE-based methods for analyzing rotor angle stability of the post-fault power systems were proposed in [20,21,22]. Reference [20] proposed an online monitoring algorithm based on PMU for rotor angle stability of power systems, where LLE is used to identify the out-of-step behavior of the power system after a fault. A novel approach is proposed for assessing transient rotor angle stability by combining the LLE–time curve obtained by the model-free algorithm with the dynamic features of the post-fault phase-plane trajectory. Taking a GP of generators i and j as an example to analyze the transient rotor angle stability of a GP, the following is a discussion of the dynamic features of the post-fault phase-plane trajectories. Corresponding to Curve 4 in Figure 1, δij keeps increasing and ∆ω ij accelerates
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