Evaluation of Space Charge Accumulation Characteristics in XLPE under DC Electric Field Based on Laser Vibration Measurement

Space charge effect of polymer has always been the focus of attention in the field of high voltage cable insulation. However, with the wide application of polymer in extreme ambient temperatures such as aerospace and deep sea, it is difficult to realize the space charge measurement under the condition of extreme temperatures by traditional space charge measurement methods. In order to explore the application of laser vibration measurement in the field of space charge measurement, based on the electro-acoustic conversion principle of PEA method, this paper adopted laser Doppler vibration measurement instead of piezoelectric detection, and conducted space charge measurement and electrode surface vibration test under 5-50kV/mm DC field for degassed 48h cross-linked polyethylene, and the characteristics of charge accumulation threshold were evaluated based on the vibration velocity signal. The results of space charge response showed that the average bulk charge density characteristic
$\rho_{\text{absolute}},\rho_{+}$
and
$\rho$
- all showed a three-stage distribution with electric field, and the corresponding charge injection threshold field
$E_{1}$
and charge recombination field
$E_{2}$
were 15.77kV/mm and 30.44kV/mm, respectively. The results of electrode vibration test showed that
$\varphi_{1\text{MHz}}^{\prime}$
also presented a three-stage distribution with electric field, and the switching electric fields
$E_{\varphi 1},E_{\varphi 2}$
were in good agreement with
$E_{1}$
and
$E_{2}$
. In order to ensure the evaluation accuracy of
$\varphi_{1\text{MHz}}^{\prime}$
for the space charge threshold field,
$\varphi_{\max}$
was generally set at about 20°, and the appropriate AC excitation frequency can be selected according to the thickness of the sample. This paper can provide theoretical reference and experimental support for polymer space charge measurement and charge accumulation evaluation.