On the other hand, for the purpose of not affecting the safe operation of transformers and the convenience of installation, an antenna as small as possible is needed. Publication presented the fundamental frequencies of Hilbert fractal antenna, while the calculated formula was presented in publication. The lower first resonant frequency is important for the fractal antenna used in detecting UHF PD signals. On the one hand, the resonant frequencies of UHF PD antennas are required to fall into a lower range between 300 MHz and 1000 MHz with a wide bandwidth. Two criteria have to be considered for design of UHF antennas detecting PD in transformer.
The horn antenna, biconical log-periodic antenna, loop antenna, and dipole antenna were used for PD detection for gas insulated switchgear (GIS).
In addition to transformers, UHF antennas have been used for PD detection for other high voltage apparatuses. A dipole antenna model and its waveform characteristics were introduced in, and a small loop antenna was given in to detect PD signals in transformer insulation oil. Literatures presented a two-wire Archimedean planar spiral antenna and its application in PD detection. Currently, there are many types of UHF antennas used in PD detection for electrical plants. The performance of antenna will affect the extraction and postprocessing of PD signals. Īntenna is the core component of an UHF PD online monitoring system. By receiving the UHF electromagnetic waves of PD occurred in a power transformer, the UHF detection technology can measure the PD magnitudes and locate the PD source. Compared with traditional detection methods, the ultra-high-frequency (UHF) technology has advantages such as high sensitivity and strong anti-interference, which make it more suitable for PD online monitoring. Hence, it is important for monitoring PD signals online for power transformer.
Partial discharge (PD) online monitoring is an effective approach to inspect insulation defects and identify potential faults in power transformer. The experimental results show that Peano fractal antenna is qualified for PD online UHF monitoring and a little more suitable than the Hilbert fractal antenna for pattern recognition by analyzing the waveforms of detected UHF PD signals. Actual PD experiments had been carried out for two typically artificial insulation defect models, while the proposed antenna and the existing Hilbert antenna were both used for the PD measurement. The optimal geometric parameters of the antenna were obtained through simulation. The results show that the first resonant frequency of the Peano fractal antenna is smaller than the Hilbert fractal antenna when the outer dimensions are equivalent approximately. The approximate formula for calculating the first resonant frequency of the Peano fractal antenna is presented. This paper presents a Peano fractal antenna for UHF PD online monitoring of transformer with small size and multiband. Ultra-high-frequency (UHF) approaches have caught increasing attention recently and have been considered as a promising technology for online monitoring partial discharge (PD) signals.