Diagnosis of the Non-Concurrent Operation of the On-Load Tap Changer Contacts by the Acoustic Emission Method

On-load tap changers (OLTC) are some of the main transformer elements that
make voltage adjustment in a power network possible. Their failures often cause
shutdowns of distribution transformers. The paper presents research work aimed
at the assessment of the technical condition of OLTCs by the acoustic emission
method (EA). This method makes the OLTC diagnosis possible without the need
of disconnecting the transformer from the system. The measurements were taken
in laboratory conditions. The influence on the operation non-concurrence of the
power tap changer contacts on the AE registered signals has been investigated. The
signals registered were subjected to analyses in the time and time-frequency do-
mains. The result analysis in the time domain was carried out using the Hilbert
transform and calculating characteristic times for the particular runs. A short-time
Fourier transform was used for the assessment of results in the time-frequency do-
main.