The partial discharge (PD) method of evaluating insulation problems and finding possible faults in a power transformer is quite successful. Ultrahigh-frequency (UHF) sensors in the frequency spectrum higher than 300 MHz can detect electromagnetic waves emitted by PD. However, for practical placement inside a transformer, the size and frequency bandwidth of a UHF sensor for PD detection are a worry. To detect the PD signal early, sensors with high sensitivity and multiband frequency are required. Sensors with high sensitivity and multiband frequency are required to detect the PD signal early on. This paper presents a variety of side dimension sizes and thicknesses of a 4th order Hilbert fractal UHF sensor for PD detection inside a power transformer. This UHF sensor was designed to capture PD signals at frequencies ranging from 300 MHz to 3 GHz. The sensor is designed by using CST software where the setting the dimension of 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm and 150 mm for length and width with different thickness which is by fixed and by formula with an FR4 epoxy substrate of thickness 1.6 mm. Based on the simulation results, the suggested sensor can measure PD signals with a reflection coefficient of less than -10 dB and a VSWR of less than 5. This sensor's benefits include a wide bandwidth, excellent sensitivity, and an appropriate size for straightforward installation. As a result, this sensor has been approved for use in the power transformer as a UHF PD detection sensor.
