The Formation Characteristics of Bubble in Oil-Paper Insulation and its Effect on the Breakdown

Zhao, Tao; Cheng, Xiangrui; Liu, Yunpeng; Wang, Fochi; Lv, Fangcheng

doi:10.1109/icd.2018.8468505

Cited by 3 publications

(2 citation statements)

References 9 publications

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“…

p_{int} - p_{ext} = normalΔ p = \frac{2 σ}{r}

Equations (1) and (2) provide another key clue as to how bubbles form. Noting that the denominator in the equation is r, it becomes clear that a bubble cannot be formed from nothing, (the pressure gradient would need to be infinite when r = 0) resultantly bubbles tend not to form in the bulk oil instead they typically form at surface impurities or interfaces [11, 16, 17]. For bubbles in transformers, the solid insulation acts as a trap for released vapour phase molecules which then accumulate and are able to form a bubble [18].…”

Section: Introductionmentioning

confidence: 99%

Analysing the power transformer temperature limitation for avoidance of bubble formation

et al. 2019

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Failure of a transformer is a costly incident which can impact power system operation and result in loss of supply to customers. Transformers can fail through a number of mechanisms, one of which is from the formation of bubbles within the insulation. Currently, the loading guidance is set to avoid certain overload temperatures as high temperature is the main cause of bubbles forming. This paper analyses the limit set within the loading guides, comparing the most commonly cited temperature limit of 140°C with values taken from across the full spectra of available studies in literature. It is concluded that there is sufficient evidence for further investigation into formation of bubbles from transformer insulation as employing a single temperature limit may be inadequate. Use of a single temperature value is unsuitable, given the wide range of potential scenarios that the transformer fleet can present. It has become the go-to rationale that the moisture content of the solid insulation is the key driver for transformer bubbling temperature. This is true, however, it is shown that other factors such as solid insulation aged condition (determined through degree of polymerisation value) and the insulation type are also important considerations.

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“…

p_{int} - p_{ext} = normalΔ p = \frac{2 σ}{r}

Section: Introductionmentioning

confidence: 99%

Analysing the power transformer temperature limitation for avoidance of bubble formation

et al. 2019

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“…Insulation failures due to overheating are mostly encountered in oil type transformers (Ding et al, 2009; IEEE-C57.92:1981, 1981; Zhao et al, 2018). Therefore, the creep characteristics of the spacer used in oil type transformers should be determined for different temperature conditions (Widyanugraha et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation on creep characteristic of the spacer between winding turns of power transformers

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Arabul

et al. 2019

Transactions of the Institute of Measurement and Control

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The lifetime of insulation in a power transformer deteriorate in time by reason of high electrical/thermal stresses and contaminations from environmental factors. In particular, faults in oil type power transformers due to thermal stress ruin energy continuity and cause serious economic losses. Most of the faults due to thermal stress generally occur at the hot-spot location of transformer windings. Particularly, creeping of the spacer between windings and the resulting thermal stress constitutes a significant part of the transformer failures. Therefore, the determination of creep characteristics under different conditions is important in terms of fault estimation, aging calculations and product development. In this study, it is aimed to acquire creep characteristics and failure time of spacer for different test temperatures. For this reason, a test system is designed to determine the creep characteristics of the spacer between the windings. In order to specify temperature ranges of the tests to be done, thermal analysis is performed for different creep rates of the spacer. The test setup is designed according to the results of thermal analysis, and creep test results are presented. The results indicate that creep characteristics of spacers will provide to make the aging calculations and failure prediction algorithms more accurate.

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AC Flashover Characteristic at the Triple Junction of the Oil-Pressboard Insulation

et al. 2020

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Oil-pressboard insulation in transformers is prone to surface tracking or creeping discharge during operation. The oil-pressboard interface is believed to be one of the weakest points in the insulation system. In this paper, AC flashover characteristic at the triple junction of the oil-pressboard interface under a slightly inhomogeneous electric field has been studied. The results showed that the creeping discharge always started at the triple junction, then developed along the pressboard (PB) surface, and finally reached the opposite electrode. The reason was that the triple junction was subjected to the maximum electric field strength. The field strength corresponding to the breakdown of the pure oil gap (POG) was decreased with the increment in the gap distance between electrodes due to the volume effect. As a comparison, the field strength corresponding to the breakdown for PB only changed slightly with the gap distance. Besides, the breakdown electric field of both POG and PB hardly changed when the electrode diameter increased. The above results could be applied to the inverse calculation and estimation of the flashover voltage levels under longer gap distances with any electrode diameter. Moreover, the relative position of the oil gap and PB could influence the flashover voltage levels. The breakdown voltage with PB directly contacting the ground electrode was 10% higher than that with PB directly contacting the high voltage electrode. This could be explained by the different charge behavior. The obtained results could provide a reference for the insulation margin design in ultra-high-voltage transformers.

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The Formation Characteristics of Bubble in Oil-Paper Insulation and its Effect on the Breakdown

Cited by 3 publications

References 9 publications

Analysing the power transformer temperature limitation for avoidance of bubble formation

Analysing the power transformer temperature limitation for avoidance of bubble formation

Experimental investigation on creep characteristic of the spacer between winding turns of power transformers

AC Flashover Characteristic at the Triple Junction of the Oil-Pressboard Insulation

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