This paper investigates the dissolved gases evolution in transformer oil under combined DC/AC electrical-thermal stress. Dissolved gases detected in transformer aged insulation oil reveal that oil under AC electric field combined with thermal stress can produce more dissolved gases than oil under DC electric field with thermal stress but less than the gases produced in oil under distorted AC or combined AC/DC voltage stress. This is attributed to the divergent migration properties of the charged components under different types of electric fields. To further understand this behavior, carrier recombination coefficient is proposed to explain the oil DGA results under various aging stresses. Results show that diagnostic parameters such as breakdown voltage, oil interfacial tension, and moisture content in pressboard should be used along with DGA results in order to accurately diagnose the insulation condition within converter transformers that impose a combined AC/DC voltage stress on the insulation system.

中文翻译：

---

高压直流换流变压器油纸绝缘老化特性综合分析

本文研究了在直流/交流电-热应力联合作用下变压器油中溶解气体的演化。变压器老化绝缘油中检测到的溶解气体表明，在交流电场和热应力作用下，油在直流电场和热应力作用下产生的溶解气体比油中产生的溶解气体多，但比在畸变交流或交直流电压下油中产生的气体少压力。这归因于带电成分在不同类型电场下的不同迁移特性。为了进一步理解这种行为，提出了载流子复合系数来解释各种老化应力下的油 DGA 结果。结果表明，诊断参数如击穿电压、油界面张力、