The aging characteristics of the Nomex paper for the flameproof dry-type transformer

The insulation system of a flameproof dry-type transformer under the combined thermal, electrical, mechanical, and environmental stresses undergoes gradual deterioration, which ultimately leads to transformer failure. It is hence important to test the aging characteristics of the Nomex insulation paper (aramid paper) which is the main insulation material of the flameproof dry-type transformer. In the paper, thermal and electrical aging of aramid paper specimens was performed, and during which the DP (degree of polymerization) of aramid paper specimens were measured, periodically. The experiment result indicate that DP of aramid paper specimens dramatically declines with the thermal and electrical aging time. And the microstate observation result indicate that the mechanism of the thermal aging and electrical aging for the aramid paper is different.

I. Introduction

Transformers play an important role in the electrical power transmission and distribution networks. The first transformer in the world invented in the 1880s was of dry type [1]. The lifetime of a dry-type transformer mainly depends on the condition of insulation material. The insulation system under combined thermal, electrical, mechanical, and environmental stresses undergoes gradual deterioration, which may lead to serious accidents and great losses for utilities and customers. The insulation system of a dry-type transformer mainly refers to the winding insulation, and whose main material is aramid paper. Therefore, it is important to study the aging characteristics of the aramid paper. The aging characteristics of oil-paper insulation used in oil-immersed transformers has been studied systematically and the aging mechanism theoretical system of the oil-paper insulation was researched by many scholars [2]–[5]. And some research has been done on aging evaluation of the insulation of dry-type transformers [6]–[7]. However, few research has been done in the aging of aramid paper.