Condition Assessment of Power Transformer on-Load Tap-Changers Using Wavelet Analysis

The operation of a power transformer on-load tapchanger (OLTC) produces a well-defined series of vibration bursts as its signature. Due to the harmonic and nonstationary nature of the transient vibration signal traditional frequency and time-frequency techniques are on longer effective for characterization of this type of vibration signals as the localized time domain features-such as delays between bursts, the number of bursts, and the strengths of bursts-are essential for the condition assessment of OLTC. A wavelet transform-based technique is developed in this paper to characterize the OLTC vibration signals. This technique gives a simplified format for displaying and representing the essential features of the OLTC vibration signatures. Application results from a selector type OLTC demonstrate that the features extracted in the wavelet domain can be utilized to provide reliable indications of the actual heath of an OLTC.