Measurement of Space Charge Distribution Characteristics in the Actual HVDC Cable

The accumulation effect of space charge in high voltage direct current (HVDC) cable may lead to the distortion of internal electric field, accelerate insulation aging and even cause insulation breakdown, which seriously affected the reliability of operation of HVDC cable. With the operation of HVDC cable, the radial distribution of temperature gradient is developed within the insulation material among the temperature presented high on internal layer and low on external layer. However, as the existence of non-linear phase distortion of the measurement system, cylindrical geometric structure for HVDC cable and temperature gradient, the measured waveforms of space charge in HVDC cable based on pulsed electro-acoustic (PEA) method induces distortion. In this paper, the temperature at cable core is set at 30°C, 60°C and 90°C respectively in order to form different temperature gradients, the negative DC electric Field of 10 kV/mm is applied to HVDC cable, space charge distribution characteristics are researched based on the space charge measurement system using PEA method for HVDC cable, the measured waveforms developed by our laboratory can be corrected by modified recovery algorithms. It is concluded that with the increase of temperature at cable core, heterocharges gradually accumulate near the lower temperature side of HVDC cable. The higher temperature at cable core can also promote the injection of homocharges in HVDC cable. The temperature gradient in HVDC cable has importance impact on space charge accumulation, the research on space charge distribution characteristics can provide basis for further study on space charge behavior mechanism under temperature gradient.