Space charge dynamics at the physical interface in oil-paper insulation under DC voltage

Abstract

Space charge has received much attention recently because an understanding of space charge in oil-paper insulation is useful for the design of converter transformers. This paper presents a study of space charge dynamics at the physical interface using the pulsed electroacoustic (PEA) method. After sample inversion, space charge in the vicinity of semiconductor electrode could be clearly observed when the sample is under depolarization. When an unexposed sample was placed next to a previously polarized one, negative charge appeared at the dielectric interface. These results indicated that there were other reasons in addition to acoustic loss that led to space charge distribution distortion. As regards the dielectric interface, it was found that an electrical double layer was formed at the interface, and the space charge sign was dependent upon the polarity of applied voltage. Space charge behavior at the interface depended on several aspects of the status of the interface, and during voltage polarity reversal, the interface was a weak point of the insulation.Index Terms -Space charge, interface, pulsed electroacoustic method, oil-paper insulation, polarity reversal voltage.

Progress of Space Charge Research on Oil-Paper Insulation Using Pulsed Electroacoustic Techniques

“…Under negative voltage, the negative charge accumulated at the interface. The positive charge could accumulate at the interface under the positive voltage, and the same phenomenon could be found in the literature [31][32][33]. Different from the oil-paper interfaces mentioned above, when homo-charge injection takes place, the polarity of charge accumulated in the paper-paper interface is usually opposite to the polarity of the nearest electrode in the vicinity of the PVDF sensor.…”

Physicochemical Characteristics and Dynamic Charge Mapping in Thermally Aged Two-Layered Polymer Considering Surface States: Experiment and Simulation

“…When the dissipation rates of holes and electrons at the interface were different, the superposition effect of bipolar charges led to the net negative interfacial charge density increasing first and then gradually decreasing with the increase in depolarization time. As for the charge decay phenomenon in the bulk, although only a single trap level E T was considered in this area, and it is usually treated similarly in most literature [4,6,15], not all charges in the bulk were trapped charges. Some free charges in the layer near anode dissipate quickly and then remain stable, which is very similar to the present experiment.…”

“…However, insulation performance degrades under combined thermal, electrical, and mechanical stresses during long-term operation. Under a high DC field, dielectric-dielectric and metal-polymer interfaces combine a potentially mechanically weak boundary with substantial interface (surface) charges and a corresponding large field gradient [1][2][3][4][5]. Therefore, electrical failure likely occurs at these particular positions.…”

“…The way in which space charge trapping/detrapping occurs at the interface must be investigated. In terms of experimentation, the majority of studies investigated the effects of thermalization [1], electrical aging [5], voltage polarity reversal [4], temperature [3], and moisture [2] on the charge dynamics in multidielectrics.…”

Effect of Temperature on Space Charge Distribution in Two Layers of Transformer Oil and Impregnated Pressboard Under DC Voltage

“…Moreover, the increase in electric field and aging period will increase the space charge amount [8]- [10]. However, the published works on the space charge characters in the two layers of oil gap and impregnated pressboard are very few, and most of them are studied under room temperature [11]. Many test results show that the electric field and charge distribution in the multi-layer may not followed the Maxwell-Wagner polarization theory [12], [13].…”