Major factors influencing static electrification in an aged transformer

Kobayashi, Takayuki; Yajima, Kouji; Tsukao, S.; Ebisawa, Y.; Hosokawa, N.

doi:10.1109/ceidp.2005.1560723

Cited by 8 publications

(3 citation statements)

References 1 publication

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“…Recently, static electrification was found more likely to occur in aged power transformers. Deteriorations of both mineral insulating oil and solid insulators such as pressboard were found to facilitate electrostatic charging of these insulating materials [2][3][4][5]. This static electrification has been paid more attention because many aged power transformers exceeding their design lifetime are still in service.…”

Section: Introductionmentioning

confidence: 97%

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Diagnosis on increase in electrostatic charging tendency of mineral insulating oil for power transformers due to aging

Okabe

Kohtoh

Amimoto³

2010

IEEE Trans. Dielect. Electr. Insul.

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Diagnosis on electrostatic charging tendency (ECT) of mineral insulating oil for power transformers has been performed. Increase in the ECT is derived from sulfonium ions, which are generated by sulfoxide compounds and hydrogen ions. Strong correlation between the ECT and the sulfoxide concentration is obtained in a series of thermal aging tests with oxygen and/or copper catalyst. The volume resistivity of oil is used as an alternative indicator for the concentration of hydrogen ion because hydrogen ions increase the electrical conductivity of oil and the sensitivity of conventional property such as total acid value is too low to evaluate the aging deterioration of closed-type transformers. Analysis of oils extracted from 98 actual transformers, whose operating years are between 3 and 46 years, are performed. High ECT values more than 200 pC/ml are detected in some oils and their volume resistivity values are less than 4 x 10 14 Ωcm. Degree of the correlation between the ECT and the sulfoxide concentration is low compared to the result of the thermal aging tests. A diagnostic map with four areas classified using a pair of indicators of volume resistivity and sulfoxide concentration is useful to predict prospective increases in the ECT. Appropriate transformer operation and maintenance including air exposure avoidance of their mineral insulating oils is one of the effective solutions to prevent the ECT from increasing.

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Section: Introductionmentioning

confidence: 97%

“…Deterioration due to aging also increases the ECT even under normal transformer operating conditions. Thus acceptable values (500 pC/ml) and periodical measurements of the ECT have been proposed for preventive maintenance of power transformers [4]. Measurement of the ECT was also contained in the latest IEC standard [6].…”

Section: Introductionmentioning

confidence: 99%

Diagnosis on increase in electrostatic charging tendency of mineral insulating oil for power transformers due to aging

Okabe

Kohtoh

Amimoto³

2010

IEEE Trans. Dielect. Electr. Insul.

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“…For maintenance management, the Electric Technology Research Association has proposed a control value (500 pC/ml) as well as measurement cycles and other parameters [1]. Recently, there have been reports of pronounced static (streaming) electrification in aged transformers caused by deterioration of both insulating oil and solid insulators [2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Influence of various compounds on electrostatic charging tendency in insulating oil

Okabe

Kotoh

Tsuchie

et al. 2011

Electrical Engineering Japan

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SUMMARYThe influence of various compounds on the increase of the electrostatic charging tendency (ECT) in insulating oil was investigated. Sulfide compounds, which are contained in new mineral oil, are identified for the first time as the original materials involved in the increase of the ECT. This is verified by heating tests of alkylbenzene with the addition of various compounds. Coexistence with copper and injection of oxygen enhance the increase of the ECT. Some sulfide and sulfoxide compounds increase the ECT markedly. On the other hand, the influence of sulfones, which are oxidation products of sulfoxides, is negligible. Although sulfonic acids, which are oxidation products of sulfones, markedly increase the ECT, the polarity is reverse. Thus, the ECT is influenced by the kinds and the molecular structures of additive sulfur compounds. The influence of nitrogen compounds and that of oxygen compounds are confirmed to be smaller than that of sulfur compounds. Since the amounts of nitrogen compounds and oxygen compounds are much smaller than those of sulfur compounds in mineral insulating oils, the influence of these compounds is considered negligible. Since the ECT of oils with the addition of sulfides or sulfoxides increases after heating, the other compounds should be created from these compounds that increase the ECT directly. Thus, the increase of the ECT is mostly caused by the oxidation of sulfides, which creates sulfoxides. Then certain compounds, which directly increase the ECT, are created from sulfoxides. If sulfones or sulfonic acids are created by the oxidation of sulfoxides, the ECT decreases because of the influence of these compounds on the ECT. It is most likely that some process other than oxidation occurs in the creation of the compounds that increase the ECT directly.

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Investigation of electrostatic charging mechanism in aged oil-immersed transformers

Okabe

Kohtoh

Amimoto

2010

IEEE Trans. Dielect. Electr. Insul.

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Major factors influencing static electrification in an aged transformer

Cited by 8 publications

References 1 publication

Diagnosis on increase in electrostatic charging tendency of mineral insulating oil for power transformers due to aging

Diagnosis on increase in electrostatic charging tendency of mineral insulating oil for power transformers due to aging

Influence of various compounds on electrostatic charging tendency in insulating oil

Investigation of electrostatic charging mechanism in aged oil-immersed transformers

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