A New Explanation of Gas Evolution in Electrically Stressed Oil-Impregnated Paper Insulation

Abstract

In void-free oil-impregnated paper, gas evolution starts at a critical stress which is markedly dependent on the degree of dryness of the paper. The gas first formed arises from decomposition of water in the cellulose, the nature of the impregnant having little effect. Subsequent more rapid gassing resulting from decomposition of the oil is a secondary process depending on ionization within gas bubbles previously formed. Study of the fundamental primary process suggests that water absorbed by the cellulose is ionized by electron bombardment in regions of high stress and is then decomposed electrochemically.

Proton conduction and injection in solids

“…Electrolysis experi-ments432- 434•441 Indicate that the conduction is primarily electronic at low water contents (perhaps intrinsic but possibly via injected charge),253,435 but is predominantly protonic at higher water contents. Cellulose,436, 437,4546 gelatin,4236,438 collagen,434•493 and melanin434 behave in a similar fashion. The changeover from primarily electronic to primarily protonic conduction has been ex-plained439 for hemoglobin as arising when sufficient water is adsorbed to create a contiguous path of water molecules through which the protons may pass.…”

A Short Review of Some of the Factors Affecting the Breakdown Strength of Insulating Oil for Power Transformers

“…Non-uniform field configurations are also very useful since they supply information about the expected performance of practical devices as was pointed out in [55]. Non-uniform field configuration affects the breakdown mechanism [56], with the authors claiming that -regarding paper/oil insulation-gas evolution is of primary importance with decomposition starting from the decomposition of water in the paper. In [29], the authors using non-uniform field configurations suggested that the initiation of the breakdown can be divided into two parts: one including the formation of gas bubbles in the liquid at the cathode, and the other, being an adequate multiplication by a gaseous ionization in the bulk of the liquid.…”

Characteristic properties of oil-impregnated laminated synthetic insulation for extra-high-voltage cables

“…It has been demonstrated that one of the possible causes of gassing in oil-impregnated paper is connected with the electrolysis of residual moisture at local points of stress concentration, such as those formed by cellulose fibres or conducting inclusions. 20 The moisture absorption of the nonpolar plastic materials used in our experiments is about two orders of magnitude lower than that of paper, while this water is loosely bound and can be removed quite easily. Moreover, such local points of stress concentration exist to a far lesser extent.…”