干式变压器用Nomex绝缘纸老化规律及其可靠性分析

Aging Law and Reliability Analysis of Nomex Paper Used for Dry-type Transformer Insulation

Nomex绝缘纸的可靠性是保证干式变压器安全运行的主要因素,为此设计了干式变压器匝绝缘模型,并模拟绝缘运行环境,对Nomex绝缘纸进行电–热联合老化试验,试验期间定期测试Nomex/浓硫酸溶液的粘度特性,并分析其特性粘度与Nomex聚合度的关系。建立了基于聚合度的退化可靠性评估模型,通过热重分析试验(TGA)确定Nomex热动力学参数,进而确定退化模型参数。最后对10组不同老化程度的试样进行了可靠性分析。研究结果表明:Nomex/浓硫酸特性粘度随着Nomex绝缘纸试样老化时间呈下降趋势;Nomex/浓硫酸的特性粘度与Nomex绝缘纸聚合度两者的对数具有线性关系,因此特性粘度可以用来反映Nomex绝缘纸的老化状态;10组试样剩余寿命与可靠性分析结果一致,因而退化模型可以用来评估Nomex绝缘纸的可靠性。

Reliability of the Nomex paper is a main influential factor for safe operation of dry-type transformers, thus we designed an interturn insulation model of dry type transformer and simulated its service environment to carry out electrical and thermal combined aging test on the Nomex paper. Then, the viscosity properties of the Nomex/sulfuric solution were measured periodically during the aging test while the relationship between the intrinsic viscosity of the Nomex/sulfuric solution and the degree of polymerization（DP） for Nomex was analyzed. We proposed a degradation model based on DP to analyze the reliability of the Nomex paper, and obtained the thermodynamic parameters of the Nomex through the thermogravimetric analysis（TGA）, with which the parameters of the degradation model were calculated. Finally, we estimated the reliability of ten groups of specimens with the established model. Results show that the intrinsic viscosity of the Nomex/sulfuric solution drops with the aging time of the specimens, and the logarithm of intrinsic viscosity is linearly related with the DP, indicating that intrinsic viscosity can reflect the aging degree of the Nomex paper. In addition, the remaining life of the ten groups of specimens corresponds with their reliability analysis results obtained from the degradation model, so that the proposed reliability model can be used for reliability estimation of the Nomex paper.