Location of PD sources in power transformers by UHF and acoustic measurements

Diagnostic Measurements for Power Transformers

“…The high noise level in field strongly disturbed the electrical PD measurements made according to [2] at frequencies lower than 1 MHz. Source of noise was in that case the 400 kV bus bar above the transformer producing audible corona discharge [15].…”

“…It must be assumed that the Figure 10. Positions of UHF and acoustic PD sensors and the localized PD source in a 333 MVA/400 kV single phase autotransformer [15].…”

“…Furthermore, the acoustical PD localization process also has to deal with acoustic waves travelling faster through the steel tank wall than through transformer oil. The time of flights of the acoustic signals can be computed accurately with the help of the Hinkley criterion [9], which is based on the signal energy of the measured signal [15].…”

“…The visual inspection of the active parts at the tap changer confirmed the localization results. After repair procedure, the transformer passed the acceptance test without any indication of PD activity and was put back into service [15].…”

“…40 cm on all space axes. The time of flight differences were measured with six sensors, which are the three UHF sensors (UHF 1-UHF 3) and the three acoustic sensors (A2, A5, A6) placed near to the PD source [15].…”