Discharge characteristics and arcing law of oil-paper insulation defect model under impulse voltage

作者： GOZ Electric 时间：2024-09-03 09:38:30 阅读：12

With the continuous development of UHV projects in my country, higher requirements are put forward for the insulation performance of key equipment such as transformers and shunt reactors. In particular, insulation accidents caused by operating impulse voltage and its superimposed power frequency electrical stress frequently occur during the switching transient process. The most typical case is that acetylene exceeds the standard when the million-volt shunt reactor is put into operation, resulting in discharge inside the equipment, affecting the performance of oil-paper insulation, and leaving safety hazards for the steady-state operation of the equipment. Therefore, it is of great significance to study the discharge characteristics of oil-paper insulation under operating impulse voltage and its superimposed power frequency electrical stress. At present, domestic and foreign scholars have done a lot of research on the breakdown characteristics of oil-paper insulation under lightning impulse voltage, including the comparison of breakdown characteristics under standard lightning impulse voltage and oscillating lightning impulse voltage, the influence of electrode type on breakdown characteristics, and the influence of oscillation frequency on breakdown characteristics. The oil-paper insulation volt-second characteristics and breakdown probability distribution under different lightning impulse voltage forms are obtained, and the insulation breakdown mechanism under lightning impulse voltage is preliminarily revealed. Compared with lightning impulse voltage, there are few reports on the discharge characteristics of oil-paper insulation under switching impulse voltage, and the research results under short-term lightning impulse voltage are difficult to apply. In particular, special discharge phenomena such as continuous partial discharge (PD) and breakdown restrike caused by switching impulse voltage deserve in-depth study. In addition, although domestic and foreign scholars have conducted research on the discharge characteristics and mechanisms of oil-paper insulation under complex steady-state electrical stress (AC/DC composite electrical stress, high-frequency AC electrical stress, high-frequency square wave electrical stress, etc.), the research on the discharge characteristics of oil-paper insulation under operating impulse voltage superimposed on power frequency electrical stress is still blank. This paper builds an experimental platform for the discharge characteristics of oil-paper insulation under impulse superimposed on power frequency electrical stress, studies the discharge characteristics and arcing laws of five common tip defects in oil-paper insulation systems under operating impulse voltage and superimposed on power frequency electrical stress, divides the breakdown process into stages and analyzes the discharge characteristics of each stage, and explores the influence of the phase of impulse voltage on the discharge characteristics under the environment of superimposed power frequency electrical stress, in order to provide a reference for the insulation design and status assessment of oil-immersed power equipment under transient operating environment.

This paper explores the discharge characteristics and arcing laws of five typical oil-paper insulation defect models under operating impulse electrical stress and superimposed on power frequency electrical stress in extremely non-uniform electric fields, and obtains the following main conclusions:

(1) After the pure oil gap tip defect is broken down under the operating impulse voltage, The arcing stage will still stimulate high-frequency discharge pulse signals, and there is a certain probability that the arc will reignite no more than twice; the arcing process of the defect model containing cardboard after breakdown can be divided into high-frequency reignition arcing stage, stable arcing stage, and reignition stage before voltage recovery.

(2) In the arcing process of the cardboard defect, repeated reignition arcing dominates, while the other models are dominated by stable arcing; compared with the reignition stage before voltage recovery, the recovery voltage amplitude of the high-frequency reignition arcing stage is lower but the reignition frequency is higher; the surface discharge reignition arcing phenomenon is weak, and the residual voltage of the arcing is Lower.

(3) Oil gap defects, paperboard insulation defects, and oil-paper composite defects are prone to high-amplitude short-interval discharge phenomena. Among them, defects containing oil gaps are prone to discharge at the wave head; surface defects are prone to low-amplitude long-interval discharge phenomena. Under the action of strong vertical components, they are prone to discharge at the wave head, and under the action of weak vertical components, they are prone to discharge at the wave tail.

(4) Different superimposed phases lead to different electric stress amplitudes. The lower electric stress amplitude weakens the reignition arc phenomenon in the reignition stage before voltage recovery, and also weakens the degree of local discharge in the absence of breakdown.