10 kV cross-linked polyethylene(XLPE) cables are an essential part of urban distribution networks

and the reliability of power supply is directly affected by their insulation performance. Based on the voltage current ration method

this paper designs a low-frequency high-voltage impedance testing circuit suitable for the rated phase voltage of 10 kV cables and the frequency range from 0.1 Hz to 100 Hz. A protective resistor with a resistance of the same order as the cable capacitive reactance is connected in series to magnify small changes of capacitance and insulation resistance caused by slight insulation degradation. At the same time

by combining the microscopic inspection of XLPE insulation slices

a comprehensive assessment of cable insulation condition is achieved. The results show that the Fourier transform infrared spectroscopy and differential scanning calorimetry analysis of the 0.5 mm thick XLPE insulation slice samples indicates that the materials are in a slightly deteriorated state at each aging stage. The cable capacitance decreases with the increasing aging time at different temperatures. The insulation resistance remained nearly unchanged at 30 ℃ and decreases monotonically at 90 ℃. The simulation calculation and experimental results indicates that

after the series protective resistor is inserted

there is a significant phase difference between terminal voltage and current

and both the phase angle and the impedance amplitude decrease as the frequency increased. The equivalent capacitance obtained at 6 kV is significantly higher than the value measured at low voltage by a traditional LCR meter. However

in both cases the capacitance change little from 0.1 Hz to 100 Hz and increases notably at 0.1 Hz due to enhanced polarization. By integrating the macroscopic high-voltage impedance tests with microscopic characterization

the low-frequency high-voltage impedance testing method based on the voltage-current ratio method has good consistency with conventional impedance testing and microscopic detection test results and provided higher detection sensitivity for slightly degraded insulation in cables at low frequencies.