Space charge behavior in thick oil-impregnated pressboard under HVDC stresses

Abstract

The space charge accumulation can affect the dielectric performance of oilimpregnated pressboard in convertor transformers. In this paper, the space charge behaviour in 1mm thick impregnated pressboards is investigated by the means of pulsed electroacoustic method. The dried pressboards are separately impregnated in fresh oil and service aged oil as comparison. The space charge distributions are investigated under ±15 kV/mm and ±25 kV/mm at room temperature. The homocharge injection can be observed for all the samples, which is much more significant in the aged oil impregnated samples. The amount of injected charges and the depth of the injected charges accumulation in the pressboard bulk are closely related to the oil properties, amplitude and polarity of the applied voltages. The service aged oil shows the dominant effects on the local electric field distortion, about 48% enhanced in the aged oil impregnated samples while about 15% enhanced in the fresh oil impregnated samples. The estimations of the apparent charge mobility and trap depth also indicate the great impacts caused by the service aged oil.

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

“…However, these differences are usually very small as mentioned in Ref. 5. When the second polarity reversal operation is finished, the applied electric field reverses to +20 kV/mm again, as shown in Fig.…”

“…(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. Similarly to polymeric materials, researchers also found that the accumulated homocharges in a single layer of impregnated paper/pressboard with oil can lead to electric field enhancement in the surface region after polarity reversal.…”

Influence of Endurance tests on Space Charge Distribution of 160kV HVDC XLPE Cable

“…Supposing that the released electron will not be trapped again in the decay process [23,24]. As can be seen in Fig.…”

Space charge dynamics in oil-impregnated pressboard under AC electric field

“…It has been demonstrated that the presence of the space charge in the oil pressboard insulation under DC stresses can result in significant electric field distortion [1][2][3]. However, the space charge behaviour under AC stresses, especially with the power frequency, has been rarely investigated, due to the much smaller quantity of AC charge amount compared with DC one; and the requirement of the much faster data acquisition system in order to measure the phase related charge dynamics [4].…”

“…The impacts of the degradation of the mineral oil are also involved in this work as comparison. Based on the previous works [3,11], the aged oil pressboard, and the presence of the oil gap can be regarded as the enhancement of charge mobility. Therefore, the impacts of charge mobility on the AC space charge behaviour are discussed.…”