Diagnosis and Remedial Procedure of Transformer Insulation Resistance Decline Induced by Deteriorated Oil

摘要

As core equipment to the power grid network, transformers' safety operation is essential to the reliable power supply. Insulating mineral oil is widely used in power transformers as a dielectric and cooling medium. And the quality of insulating oil is critical to ensure the stable operation of power transformers. Recently, many exceptional examples of the transformer's insulation resistance decline of the high and low winding are reported, which are probably induced by deteriorated oil. Firstly, hot oil circulation and vacuum oil filtering methods were employed to deal with the insulation resistance decline of the transformer, as the problem may derive from humidity. However, the magnitude of insulation resistance was still lower than that of the standard. It is interesting to note that the insulation resistance was improved after oil draining, which suggested that the insulating oil was deteriorated and caused harmful effects to the oil-paper insulating system. Subsequently, the quantitative determination method of copper content was developed according to the ASTM D 7151 standard - standard test method for determination of elements in insulating oils by inductively coupled plasma atomic emission spectrometry (ICP-AES). We performed a general survey of 495 transformers all around Guangdong Province in southern China that may suffer from insulating resistance decline problem. The results show that higher concentration of copper content is highly correlated to this problem. And the influence of copper content on the dielectric loss factor of transformer oil was also studied, coming up similar results. Then, the chemisorption method using modified activated clay was developed to efficiently remove the copper complex aging product from transformer oil, delivering restoration of insulation resistance. Transformers' surveillance was also conducted to ensure effective following treatment with chemisorption procedure for 2 years.