Design of a compact ultra-high frequency antenna for partial discharge detection in oil immersed power transformers

Abstract

Oil-immersed Power transformers are considered to be one of the most essential parts of the electrical system and partial discharges (PD) are one of the dangerous problems that face transformer insulation. PD is localized dielectric breakdown of an insulation degradation or defect in an oil power transformer. Ultra-high frequency (UHF) detection technique can be utilized in PD detection inside oil-filled power transformers, by capturing the electromagnetic waves generated by PD using an antenna. This research presents a design for a compact double layer printed UHF antenna to detect and discriminate various types of PD activity in a power transformer. PD activity in the transformer has been proposed in this paper by using four different artificial insulation defects, metal protrusion defect in air medium, metal protrusion defect in an oil medium, surface discharge defect, and oil-paper void defect. The presented design guarantees a small-size wideband antenna for detection. The designed antenna has small/simple size and ultra-wide frequency passband from 1.4 to 1.85 GHz, 2.2 to 2.65 GHz, and 3.2 to 3.4 GHz. The normalized power frequency spectra of the captured UHF-PD signals of the four defective models showed that every PD type has its signature, and this could help in the discrimination among different types on site.

Keywords

• UHF
• Power transformer
• Hilbert fractal antenna
• Electrical discharge
• Condition monitoring