Test and Simulation of PT Saturation Characteristics During Single-Phase Grounding Fault Recovery of 10kV Distribution System

Abstract

In the 10kV distribution system, a large number of potential transformers (PT) are used as voltage measurement devices for control and protection. It is generally believed that when the system scale reaches a certain level, there will be no ferromagnetic resonance and PT damage. However, it is found that PT burnout or its fuse blows frequently in large-scale distribution systems during operation, causing frequent replacement of equipment and loss of monitoring signals of branch voltages. Through experiments and simulation, this article concludes that, PT and fuse failures may occur during the voltage recovery process after the system's single-phase discharge, which often caused by lightning and insulation defects. Through the laboratory test of the simulated 10kV distribution system, the PT voltage and current transient waveforms in the voltage recovery process are obtained firstly, and the simulation model of this process is established by using ATP / EMTP, the conclusion reached by the two is consistent, that is, the peak current of PT exceeds 1A, which exceeds the selected fuse's rated current 0.5A, reaching thousands of times the normal current (1mA), thereby confirming the cause of the PT failure in this system. Secondly the article analyzes the influencing factors of the PT saturation by Changing the system size in the simulation model, and gives the change law of the transient voltage and current of PT during the fault recovery process under different system equivalent capacitances. It is concluded that as the equivalent capacitance increases, the frequency of the oscillating attenuation component in the transient recovery voltage decreases, resulting in the continuous accumulation of PT magnetic flux and the increase in the duration and amplitude of transient overcurrent, which ultimately leads to equipment ablation.