Simultaneous Measurement of Space Charge Distribution and Leakage Current in 6.6 kV CV Cable Under Polarity-Reversed Voltage

This paper presents an experimental study on temporal changes in space charge distribution in a 6.6 kV CV cable and associated dc leakage current under high temperature. A test sample is clamped between two half-split aluminum cylinders with a PVDF sensor and with a current detection terminal. A dc 20 kV voltage application for 1
$h$
is repeated with changing in its polarity. Many space charges (
$Q_{\text{sc}}$
) are accumulated in the cable at every polarity reversal, though total charges (
$Q_{\text{tot}}$
) calculated from the integration of the current for 1 h decreases with increasing the repetition number.
$Q_{\text{tot}}$
per unit area at 10th and 11th repetitions were decreased about half of those at 5th and 6th. On the other hand,
$Q_{\text{sc}}$
per unit area at 10th and 11th were almost same as those at 5th and 6th. These results suggest that the current reduction phenomena caused by the repetitive voltage application with the polarity reversal is not due to the decrease in the absorption current component but due to the decrease in the conduction current component. Temporal changes in
$Q_{\text{sc}}$
can be roughly expressed with an exponential function. In a few cases, however,
$Q_{\text{sc}}$
does not saturate within 1 h because the field concentration due to the hetero charge accumulation induces successive charge injection from a heated inner electrode into the XLPE.