Design of a Small Antenna for Detecting UHF Partial Discharges in Power Transformers

Detection of partial discharge using the UHF methods on transformers by inserting a small antenna into the transformer tank through a valve has some advantages including better sensitivity than e.g., external sensors. Therefore, the use of a modern, small low-cost antenna is investigated in this paper. This paper aims to design and test a small microstrip antenna that dimensionally can be inserted into the oil-immersed transformer tank. It should perform partial discharge (PD) measurements within a wide bandwidth. The antenna was designed using several references from previous studies, then the antenna dimensions were scaled to a smaller size and return loss simulations were carried out. Then some optimizations were done to get the return loss with a low resonance frequency and wide bandwidth, especially at frequencies below 1 GHz. Optimizations carried out include the use of resistive loading. The antenna design was printed on a double-layer Printed Circuit Board (PCB), then several experiments were carried out including frequency analysis as well as PD detection experiments inside a tank. The results of the PD detection measurements using a small antenna were compared with conventional measurements based on IEC 60270 standard. This small antenna design has proven to detect PD properly. With small dimensions and low cost, this antenna has the potential to be used for online monitoring systems.