Space charge formation and its modified electric field under applied voltage reversal and temperature gradient in XLPE cable

Abstract

The results of space charge evolution in cross-linked polyethylene power cables under dc electrical field at a uniform temperature and during external voltage polarity reversal are presented in the paper. A mirror image charge distribution was observed in the steady state, but the pre-existing field altered the way in which the steady state charge distribution was formed from that obtaining when the cable was first polarized. Polarity reversing charge was generated in the middle of the insulation and moved towards the appropriate electrodes under the influence of a field in excess of the maximum applied field. Our results show that the mirror effect is a steady state effect that is due to crossinterface currents that depend only on the interface field and not its polarity. Measurements on cable sections with an elevated mean temperature and temperature gradient show that the interface currents are temperature dependent, and that differences between the activation energies of the interface and bulk currents can eliminate and possibly even invert the polarity of the space charge distribution.Index Terms -Space charge, PEA, XLPE insulated power cables, voltage polarity reversal, temperature gradient, "mirror image effect".

Review of high voltage direct current cables

“…Particularly, after polarity reversal, the presence of space charge can lead to considerable electric field enhancement that is usually not acceptable and can easily cause failure in the insulation [71]- [74]. Many studies suggest that the accumulation of space charge could lead to severe impacts on the solid dielectrics, especially polymeric insulation [63], [75]- [87].…”

“…Today, the PEA method is one of most popular measurements for evaluating dielectric materials on space charge behavior; this method can also be modified and improved for different purposes. In [71], [73], [99]- [103], the space charge behavior in real extruded cables is investigated using the modified cable PEA system, as shown in Fig. 16.…”

“…16. The temperature gradient effects in cables have also been successfully studied [71], [73], as shown in Fig. 17.…”

Study of Space Charge Dynamics in Oil and Pressboard Composite System under Different Polarity Reversal Voltages

“…An almost symmetric space charge profile can be observed, similarly to that for the first polarity reversal, which is also known as the "mirror image effect". (4) Again, the interfacial charges in the oil gap can rapidly change to negative charges following the polarity of the ground electrode. The positive charges within the pressboard induce more negative charges at the ground electrode, leading to a slightly larger negative peak (about 1.1 C/m 3 ) than the peak after the first polarity reversal.…”

“…(2)(3)(4) On the other hand, the dielectric properties of oil/paper and oil-paper composite systems, which are widely used in converter transformers, can be significantly influenced by space charge characteristics. (5)(6)(7)(8)(9)(10)(11) The accumulation of space charge at the interfaces and in the bulk solid parts of an oil-paper composite insulation system can greatly enhance the electric field distributed in the central region of the paper.…”