Search

Electrical tree initiation in LDPE under positive DC stresses with controlled AC ripple is investigated. Needle-plane geometries were used and partial discharge (PD) signals recorded. Tree initiation occurred around +45 kV, and the initial growth within the first second was long compared to the more gradual processes seen with AC excitation. In each case, when the first tree image was captured, they were of the branch type and at least one order of magnitude longer than those seen under pure AC stresses. 5 kV peak AC superimposed onto +45 kV led to rapid sample failure. Unlike in pure AC cases, PD detection did not correlate well with the progress of electrical treeing (initiation, growth or breakdown) under pure DC stresses. Phase resolved PD analysis did however provide useful information in the presence of an AC ripple.

Measurement systems for determining the space charge distribution within the insulation of full-size extruded HVDC cables gained significantly more importance over the last years. This is induced by an increasing number of HVDC cable projects and increasing voltage levels and hence insulation thicknesses of these cables available on the market. Driven by this evolution, this contribution focuses on the development of a space charge measurement system based on the pulsed-electro-acoustic (PEA) method. The system is designed in order to realize space charge measurements on 30 mm thick cable insulations in principle. Besides tackling critical issues of the hardware and software development, deconvolution and acoustic recovery, some example measurements, which were conducted on a 80kV XLPEinsulated DC-cable with 8 mm insulation thickness, are shown to validate the performance.