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access icon free Investigation on space charge properties of Nomex insulation paper in the mining dry type transformer during hygrothermal ageing

  • Author(s): Lu Li 1 ; Jiancheng Song 1 ; Zhengyu Wang 1, 2 ; Rui Zhang 1 ; Jinmei Cao 1 ; Yun Ma 3 ; Yongzhi Li 1
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  • Source: Volume 14, Issue 5, July 2020, p. 576 – 584
    DOI:  10.1049/iet-smt.2019.0215 , Print ISSN 1751-8822, Online ISSN 1751-8830
© The Institution of Engineering and Technology
Received 11/05/2019, Accepted 07/01/2020, Revised 12/11/2019, Published 09/01/2020

Nomex insulation paper has been widely used in mining dry type transformer insulation because of its excellent performance. However, the injection of space charge can affect the electrical properties of the Nomex paper and accelerate the ageing process of the insulation system, which causes the insulation system failure or even breakdown. Therefore, it is of great practical value to study the space charge characteristics of Nomex insulation paper in different hygrothermal ageing conditions. The accelerated hygrothermal ageing tests of Nomex insulation specimens with different initial moisture contents were conducted. The space charge distribution of specimens impregnated by varnish were measured by the pulsed electro-acoustic method at different ageing stages. Simultaneously, the space charge characteristics during polarising and depolarising phases were deeply analysed. Experimental results show that negative charges accumulate between the varnish-paper interface in specimens near the anode. The number of negative charges gradually decreases with the increase of ageing degree. Under the influence of humidity, Nomex paper can be hydrolysed, which increases the trap density and trap level. Finally, a large amount of positive and negative charges in aged specimens would result in the distortion of the local electric field, which could decrease the breakdown strength of Nomex insulation specimens and be a threat to transformer insulation.

Inspec keywords: electric breakdown; insulation testing; ageing; paper; power transformer insulation; space charge; pulsed electroacoustic methods

Other keywords: depolarising phases; mining dry type transformer insulation; hygrothermal ageing conditions; Nomex insulation paper; electrical properties; trap level; ageing stages; pulsed electroacoustic method; negative charges; breakdown strength; space charge distribution; accelerated hygrothermal ageing tests; moisture contents; ageing process; space charge properties; aged specimens; trap density; polarising phases; Nomex insulation specimens; anode; local electric field; insulation system failure; varnish-paper interface

Subjects: Organic insulation; Transformers and reactors; Dielectric breakdown and discharges

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