Wire-Plane Electrode System for Electrical Tree Initiation Exposed to AC and DC Voltage Stress
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2011
Electrical treeing in XLPE exposed to DC (of both polarities) and 50 Hz AC voltages has been analysed in a wire-plane electrode geometry using real-time optical detection and microscopic observations. It has been found that treeing mechanisms differ between AC and DC stresses. For AC voltage, the tree initiation and growth is easily observable in real time during the testing. In the case of DC stress a complete breakdown of the XLPE occurs before electrical trees can be discerned with the use of CCD camera. However, in the microscopic observations of the specimens, very fine tree structures can be distinguished. The effect of voltage ramping rate was also analysed. For AC stress, the faster ramping results in a higher tree inception voltage. The opposite trend is true for DC stress, where the faster ramp results in a lower breakdown voltage level. When comparing the effect on polarity of the DC breakdown voltage, negative polarity results in higher voltage levels than positive polarity.