Design of Bowtie Antenna With Rounded Edge and Middle-Sliced Modifications for UHF Partial Discharge Sensor

Partial Discharge (PD) detection using ultra-high frequency (UHF) method has been proven as more noise-resistant in GIS condition monitoring, compared to the conventional PD detection methods, where the common noise frequency range such as in the power plants is below UHF frequency range. However, noise in UHF range may occur at certain conditions. Thus, UHF sensors with high sensitivity are necessary to detect PD-induced electromagnetic wave in UHF range. This paper discusses the modified design of a bowtie antenna as UHF sensor and its performance in detecting PD in the air. The modification method is conducted through simulation using antenna design software, resulting in rounded edge and middle-sliced bowtie antennas. The designed bowtie antenna has wider bandwidth of above 300 MHz, reflection coefficient lower than −10 dB, and the voltage standing wave ratio (VSWR) less than 2. During initial design, the antenna geometry including gap distance, wing radius, and flare angle are adjusted to obtain the optimum antenna characteristics. The final designed sensors are then fabricated on a printed circuit board (PCB) with FR4-epoxy substrate material and tested using Vector Network Analyzer (VNA). Furthermore, the modified antennas are also tested in the high voltage laboratory to detect PD in needle–plane electrode. The experiment results show that both modified bowtie antennas can successfully detect the PD signal with correct phase patterns, and that the middle-sliced modified bowtie antenna is more sensitive than the rounded-edge modified bowtie antenna.