Case Study of Load Shedding Caused by Voltage Sag: Mechanism Analysis and Optimization Measures

Based on an actual fault case in the power grid, this article firstly summarizes and analyzes the network transmission of voltage sag event from high voltage level power grid to low voltage level power grid and the corresponding load reduction. Two categories for the causes for load reduction are summarized, i.e., sensitive equipment shutdown and distribution transformer tripping out. By comparing the operating data with the tolerance curves of computer equipment as well as semiconductor equipment, the reason for shutdown of sensitive equipment is revealed; by analyzing the protective action types of the distribution transformer, the reason for tripping out of distribution transformer is revealed. Then, the impact of under-voltage relay and tripping device is further analyzed. On the basis of the above analysis, the measures to reduce the impact of voltage sag and correspondingly load reduction are put forward from two aspects, i.e., protection configuration and parameter optimization setting, as well as cooperative management between power supply enterprises and important power users.