Analysis and Diagnosis of Typical Transformer DC Resistance

Abstract: To detect the defects of transformer winding and confirm the causes, the data of two transformers of Beijing Electrical Power Company are analyzed. The cause is that there is quality problem in coil welding. Measures are put forward. The method of determining the defect is summarized. 

Key words: Transformer, DC resistance, defect, welding, detection, advice      

Introduction

According to the Code for Commissioning Test and Preventive Test of Electrical Equipment, the commissioning test should be carried out prior to the running of power transformer. The power transformer is put into operation followed by  preventive test. The DC resistance of power transformer is one of important aspects, which reflect physical property of transformer winding. The abnormality of DC resistance always indicates that the coils are broken or poor partial contact exist. The DC resistance tests of one set of 250000kVA /220kV transformer and one set of 50000kVA/110kV transformer are analyzed in this paper. An preventive test is conducted on Beijing Electric company’s #3 transformer. It is found that the line difference of low voltage coil exceeds the limit and other electrical indicators are normal. After one year the DC resistance test is conducted again and the line difference further increases. The detailed data is listed in Tab.1.