Comparison of acoustic emission signals generated by high voltage current transformer insulation system

Exemplary measurement results of acoustics emission (AE) signals generated by partial discharges (PD) occurring in high voltage current transformer (HVCT) internal insulation system are presented in the paper. High voltage current transformers are commonly used apparatus in electrical power distribution systems. HVCT insulation system design is quite complex. High voltage and grounded parts are separated by porcelain insulation. Inside of the porcelain there are windings covered with an oil paper insulation, furthermore a proper electric field distribution is provided by some additionally mounted electrodes. Due to insulation system ageing process some degradation of dielectrics may occur which usually leads to local partial discharge generation. Various combustible gasses production is accompanied by PD generation as well as a significant pressure increase may also be noticed inside of a HVCT. In some exceptional circumstances an internal pressure may exceed a critical value and a porcelain insulator may explode thus a fire of the entire insulation system is also possible Presented measurements are proceeded on the J110-4a type HVCT with nominal voltage of 110 kV, wherein an internal insulation system fault is detected. Indication of AE signals occurring inside of a HVCT potential application possibilities for insulation fault detection and localization are the main purpose of the presented research. Three different piezoelectric joint AE sensors, with different response characteristics are applied for the research. Various voltage supply levels are investigated in order to every sensor sensitivity threshold to be assigned. Exemplary representative AE signals generated inside of the HVCT are registered for selected supply voltage levels. Fundamental time, frequency and time-frequency domain descriptors are applied for AE signals further analysis. According to conducted comparative analysis results an optimal AE sensor for on-site measurements on apparatus under normal operation conditions is pointed.