Abstract
The space charge accumulation is an important factor to design the oil-pressboard composite insulation of convertor transformer, which is greatly affected by the temperature. In this paper, the space charge accumulation and attenuation in the two layers and single layer under DC voltage were studied by the Pulsed Electro-Acoustic Method from 20°C to 60°C, and the electric field distribution was calculated by the space charge distribution. The studied results have indicated that the distributions of space charge and electric field in the test results do not follow the Maxwell-Wagner polarization. The space charge distribution is affected by the surface trap, bulk trap, charge migration and electric field. The temperature affected the polarity and amount of the charge at oil-pressboard interface. The space charge accumulation of the two layers is more complex than that of the single layer, and the space charge accumulation and attenuation of two layers need longer time to reach the stable stage. The space charge accumulation in the single layer is largest at 40°C, whereas the space charge accumulation in the two layers is largest at 20°C. Moreover, the increase in the temperature increases the attenuation amplitude and speed of space charge.
Highlights
The oil-paper insulation is the main insulation of the converter transformer, which is the core equipment for AC-DC conversion in the HVDC system
The interface charge will accumulate at the interface between the oil gap and the impregnated pressboard, which is affected by many factors, such as conductivity, interface barrier, space charge distribution and so on [4]
SPACE CHARGE DISTRIBUTION OF SINGLE LAYER PRESSBOARD UNDER DC VOLTAGE In order to study the effect of oil gap on the space charge distribution in the two layers of oil and pressboard, the space charge distribution of single layer pressboard at different temperature under +10kV and +20kV are shown in Fig. 3(a) and Fig. 3(b) respectively
Summary
The oil-paper insulation is the main insulation of the converter transformer, which is the core equipment for AC-DC conversion in the HVDC system. The valve side winding of the converter transformer works under AC-DC combined electric field during the operation [1], [2]. The space charge is easy to accumulate in the solid insulators under DC electric field [3]. The interface charge will accumulate at the interface between the oil gap and the impregnated pressboard, which is affected by many factors, such as conductivity, interface barrier, space charge distribution and so on [4]. The interface charge and the space charge will distort the electric field distribution. Most of the research focus on the single layer of oil-impregnated Kraft paper or pressboard.
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