Study on factors of repetitive impulse influencing online IFRA test

Online impulse frequency response analysis (IFRA) is an advanced method for detecting winding faults in transformers. In this method, square wave impulse is commonly used as the excitation signal. In theory, the frequency response curve of a transformer is not related to the excitation signal. However, it is discovered that the test results can be influenced by the input impulse. The influence may cause misinterpretation of the frequency response curve. This study has concentrated on three factors - the pulse width, repetition frequency, and in particular, injection moment. Analyses on these factors are presented. Then, simulation and experimental studies are carried out to verify the influence of these factors.