Accurate Fault Current Phasor Estimation in Series‐Compensated Transmission Lines Using Improved Particle Swarm Optimisation

The fault locator is an important unit of a distance relay that determines the fault point based on the measured impedance. When a fault occurs, the fault current may contain a decaying DC offset due to the inductive‐resistive nature of transmission lines. In series‐compensated lines, interaction between the series capacitor and inductor causes current signals to contain subsynchronous frequency components (SSFC). Since conventional phasor estimation methods, such as the Fourier transform, can experience significant errors that may lead to maloperation of the fault locator, this study introduces a new evolutionary search algorithm based on a two‐stage improved particle swarm optimisation (PSO). The proposed algorithm can readily incorporate physical constraints without relying on model linearisation or any form of approximation. Moreover, it provides an effective balance between global exploration and local exploitation, leading to improved search efficiency. The proposed method performance is evaluated through extensive simulations considering transient components, harmonics, and frequency variations under both noiseless and noisy conditions. The obtained results show that the maximum phase displacement error and magnitude error of the fundamental component do not exceed 0.9452° and 0.8988%, respectively. Therefore, the effectiveness of the proposed method for fault location applications is demonstrated by its high estimation accuracy.