Antenna factor computation of UHF dipole antennas used for partial discharge detection in power equipments

The ultra-high frequency (UHF: 300MHz–3GHz) detection has been presented as a promising and effect way to diagnose the partial discharge (PD) activities in power equipments in recent years. The characteristics of UHF detection in the near field when the receiving antennas arranged and worked in the near electromagnetic (EM) field radiated from PD source are different from the far field detection. In this paper, the receiving characteristics of UHF dipole antennas both in the near and far field detection are investigated by using finite difference time domain (FDTD) method. The near and far field antenna factor (AF) of three UHF dipole antennas are computed and compared by coupling the FDTD method and total-field/scattered field (TF/SF) technology together. The spherical and plane waves are employed as near and far field incident EM waves, respectively. It is revealed that, the PD detection can be considered as the far field detection when the received antenna arranged about 0.1-1m from PD source corresponding to the UHF band. The simulation results show that, the multiple odd resonances of dipole antennas can be observed in both near and far field AFs. The lowest AF values in the far field appear near their designed frequencies and the AF values at the resonant frequency are in good agreement with the factory designed data. However, the frequency with the lowest AF values in the near field and their AF values are higher and lower than that of designed data, respectively, indicating the sensitivity of dipole antennas working in the near field is lower than that working in the far field PD detection. The AF values difference of dipole antennas between the near field and designed data decreases gradually with the increment of resonant frequency. This research is helpful for people to select and design the antennas and analyze detection data in UHF PD diagnosis.