Design of a Flexible UHF Antenna for PD Detection in Inverter-Fed Motors

When performing partial discharge inception voltage (PDIV) measurements by using the ultra-high frequency method on insulation systems of inverter-fed motors under repetitive impulsive voltages, the antenna charactaristics and sensor placement should be carefully considered to get high sensitivity. Different antennas have been reported for PDIV tests under impulsive voltages, but the antenna with fixed size would be difficult to install near the test object limited by both the size of the object and the antenna itself. To solve this problem, we present a design of a flexible, narrow-band antenna that can be attached to the surface of a motor stator. The designed antenna has a thickness of 0.16 mm and dimensions of 90*100 mm. Simulation and measurement reveal that as the bending curvature diameter of the antenna varies from 3.1831 mm to 22 cm, the resonance frequency point shifts towards a higher frequency, and its working frequency range is at least from 0.7 to 1.2 GHz. Subsequently, a platform for motor stator insulation PD detection is developed to assess the performance of the antenna. Experimental results indicate that, compared to an Archimedean spiral antenna (ASA), the flexible antenna exhibits hypersensitive, enabling a higher electromagnetic conversion efficiency for the near-field coupled PD under impulsive voltages with 200 ns rise times. The amplitude of the received PD signal distributed in the frequency range from 0.2 to 1.1 GHz is at least 100 times higher than the PD obtained by ASA. Therefore, the signal to noise ratio is increased significantly when performing PD tests at impulses with short rise times resorting to the designed antenna.