Experimental Study on Dual parameter WeiBull Failure Model of Oil-Paper Insulation in Converter Transformers Considering the Influence of Harmonic Voltage

The main causes of harmonic distortion in new power systems are high percentage renewable energy grid connections and high percentage power electronic equipment access. These factors pose a serious threat to the ultra-high voltage converter transformers’ ability to perform as oil-paper insulation, and little research has been done on the failure law of oil-paper insulation that takes the effects of harmonic voltage into account. This paper presents the design and construction of a typical oil-paper insulation structure breakdown test platform, as well as the oil-paper insulation breakdown voltage under various frequency and content of harmonic voltage superimposed on the fundamental voltage. The dual parameter WeiBull distribution model is used to investigate the oil-paper insulation failure law under the influence of various harmonic voltage components. The experimental results show that the breakdown voltage of oil-paper insulation significantly decreases relative to the breakdown voltage of power frequency under the action of harmonic voltages with different frequencies and contents, and all follow a dual parameter WeiBull probability distribution. Among them, the minimum $\boldsymbol{U}_{63.2 \%}$ is about 13.47 kV when the 7 th and 11th harmonic voltage are superimposed, and the minimum $U_{63.2 \%}$ is about 13 kV when the 5th and 13th harmonic voltage are superimposed, which is about $\mathbf{2 3 \%}$ lower than the power frequency. Secondly, the fitting distribution of test data under the action of harmonic voltage of different frequencies and contents is approximately parallel, indicating that the failure mechanism of oil-paper insulation is the same.

I. Introduction

China has a substantial demand for high voltage, long-distance, large capacity power transmission from the west to the east in the future due to the new power system [1]. The challenges of unpredictability and volatility in new energy production can be resolved by the blocky interconnected big DC power grid based on LCC-HVDC and MMC-HVDC, which can achieve complementary regulation between various distinctive power sources like wind, light, water, and fire in the west [2–3]. But as a result, the new power system displays a “dual high” characteristic of a high percentage of access to power electronic equipment and a high percentage of grid connection for renewable energy [4], increasing harmonic source pathways, content and raising the bar for large power equipment’s insulation performance in the power grid [5].