Innovative Diagnostic Methods for On-Site Fault Analysis on Power Transformers

摘要

With the ageing of Power Transformers, it is very important to perform regular checks of the operating conditions. Dissolved Gas Analysis (DGA) is a proven and meaningful method, such that, if increased proportions of certain gases like H_2 and hydrocarbon gases are found in the oil sample, the fault must be located as soon as possible. However, to find out the reason for increase in these gases, further analysis shall be performed. Common conventional methods are winding resistance measurement (static), turns ratio and excitation current measurement, measurement of the leakage reactance and the measurement of capacitances and dielectric losses. Certain advanced diagnostic tools like On-Load Tap Changer (OLTC) test (dynamic resistance test), Frequency Response of Stray Losses (FRSL), the measurement of the transfer function with the Frequency Response Analysis (FRA), capacitance and dissipation factor measurement at different frequencies, the dielectric response analysis with Polarisation / Depolarisation Current (PDC) and Frequency Response Spectroscopy (FDS) and the Partial Discharge (PD) measurement with modern synchronous multi-channel and multi-frequency PD systems, enable more detailed diagnostic measurements on Transformers. This paper describes some of these new advanced methods and illustrates them with practical case studies for diagnosis and fault finding.