Abstract
The electric field distortion caused by space charge is an important factor affecting the operation reliability of oil–paper insulation in a converter transformer. To study the accumulation and decay characteristics of the space charge within oil-impregnated pressboard under DC and polarity reversal voltage, and consider the possible operating conditions of the converter transformer, the space charge behavior of oil-impregnated pressboard was measured by the pulsed electro-acoustic (PEA) method in the temperature range from −20 °C to 60 °C. The effect of temperature on the accumulation and decay characteristics of space charge is also analyzed. The space charge accumulated within the pressboard at low temperature is mainly homocharge injected by the electrode, while heterocharge formed by ion dissociation counteracts some of the homocharge at high temperature. Thus, the space charge of pressboard first increases, then decreases, with an increase in temperature. However, slow decay of the space charge causes severe distortion of the electric field distribution in the pressboard during voltage polarity reversal.
Highlights
A converter transformer is one of the core pieces of equipment for AC/DC conversion in HVDC transmission projects [1]
Tang et al studied the space charge characteristics of multi-layer oil-impregnated paper at high temperatures, and concluded that space charge distribution and charge mobility were affected by the temperature [9]
George Chen et al studied the effects of space charge on electric field distribution in oil-paper insulation under polarity reversal voltage by a numerical calculation method, and concluded that the space charge accumulated inside the pressboard increased the electric field in the oil after the voltage polarity is reversed [15]
Summary
A converter transformer is one of the core pieces of equipment for AC/DC conversion in HVDC transmission projects [1]. The HVDC transmission project has the function of bi-directional power flow, which is achieved through changing the polarity of the DC voltage In this case, the converter transformer will work under polarity reversal voltage. George Chen et al studied the effects of space charge on electric field distribution in oil-paper insulation under polarity reversal voltage by a numerical calculation method, and concluded that the space charge accumulated inside the pressboard increased the electric field in the oil after the voltage polarity is reversed [15]. Zhou et al used the pulsed electro-acoustic (PEA) method to study space charge distribution in oil-impregnated pressboard under polarity reversal voltage at room temperature, and concluded that the charge and the electric field at the interface were severely distorted after the voltage polarity was reversed [16,17]. The effects of temperature on the space charge and electric field of oil-impregnated pressboard under DC and polarity reversal voltage was studied
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