Inertia Assessment From Transient Measurements: Recent Perspective From Japanese WAMS

Currently, the substantial renewable penetration brings a low inertia issue to the Japanese power system, threatening stability and resiliency than ever. The inertia estimation based on transient events provides a reliable basis for system control and operation. However, the poor rate of change of frequency extraction from different types and locations of phasor measurement units (PMUs) could significantly lead to inertia estimation errors. As a remedy with a lesson learned, this paper analyzes effective inertia estimations based on transient measurements of the Japanese wide-area monitoring in both distribution and transmission levels. Due to the longitudinally interconnected configuration of the 60 Hz Japanese power system, the polynomial approximation technique is proposed to restrain the strong effect of oscillatory components. To enhance the estimation performance considering an existing center of inertia, the comprehensive mode-shape analysis is performed via geographical measurement locations, indicating sufficient PMUs with precise estimation. The effectiveness of inertia estimation techniques is verified through actual system events corresponding to various transient sites. The numerical results demonstrate that recent inertia of the 60 Hz Japanese system with existing renewables ranges around 7.12 - 8.13 s in its system load base.