Gas insulated switchgears (GIS) have been increasingly introduced as main substation equipment since the late 1960s thanks to their high reliability, safety, and compactness. The UHF method to diagnose partial discharge (PD) is broadly employed in the field as an advanced insulation diagnostic technology. There are three primary factors related to the PD signal detection characteristics using this UHF method; namely the frequency spectrum of the PD signal itself inside GIS, the propagation characteristics of the PD signal inside the GIS tank, and the detection characteristics of the sensor measuring the PD signal. Accordingly, to further improvement of the diagnostic technique based on the UHF method, the PD phenomenon itself and its propagation characteristics should be clarified and the measurement system refined. From these perspectives, the present study reviewed the recent and latest findings concerning the PD phenomenon and its propagation characteristics inside GIS as well as the PD measurement system verification methods and diagnostic technologies, and summarized typical examples. Firstly, with regard to the PD phenomenon, measurement up to the high frequency band exceeding 10 GHz (even 30 GHz) clarified that the rise time of the PD current waveform is several tens of picoseconds, shorter than previously known. In the case of PD in micro-defects inside the epoxy insulator, however, the rise time is relatively long, in the order of nanoseconds, and a crack is the most critical defect. Subsequently, with regard to UHF PD diagnostics/monitoring technology, a novel technique using PD current waveform characteristics has been developed, and a more advanced PD diagnostic algorithm has been established by clarifying the influence of the shape and GIS internal structures on the electromagnetic wave propagation characteristics. Less uncertain and simplified calibration and verification technologies are also proposed both for a single UHF sensor and the entire UHF measurement system. These new technologies and further advanced studies in future are expected to make the UHF method more convenient and sophisticated.

Cameras used in outdoor scenes require high visibility performance under various environmental conditions. We present a visibility improvement technique which can improve the visibility of images captured in bad weather such as fog and haze, and also applicable to real-time processing in surveillance cameras and vehicle cameras. Our algorithm enhances contrast pixel by pixel according to the brightness and sharpness of neighboring pixels. In order to reduce computational costs, we preliminarily specify the adaptive functions which determine contrast gain from brightness and sharpness of neighboring pixels. We optimize these functions using the sets of fog images and examine how well they can predict the fog-degraded area using both qualitative and quantitative assessment. We demonstrate that our method can prevent excessive correction to the area without fog to suppress noise amplification in sky or shadow region, while applying powerful correction to the fog-degraded area. In comparison with other real-time oriented methods, our method can reproduce clear-day visibility while preserving gradation in shadows and highlights and also preserving naturalness of the original image. Our algorithm with low computational costs can be compactly implemented on hardware and thus applicable to wide-range of video equipments for the purpose of visibility improvement in surveillance cameras, vehicle cameras, and displays.

In the paper, several proposals to improve the sensitivity verification method for the application of UHF partial discharge monitoring systems in GIS, as described in CIGRE Electra No. 183, are presented. Verification results, which depend on the rise time of the test pulse signal, have previously been proposed to compensate for the various rise time pulses with their voltage magnitudes. As a complementary test method to the CIGRE Electra method, a network analyzer measurement is proposed. The influence of the rise time was experimentally investigated using a test GIS setup that had two internal type PD couplers. The scattering parameters of the test GIS were measured, and the computer simulation results corresponded well with the measurement results. The CIGRE method was applied to a 400 kV GIS and the test results of two different rise time conditions were analyzed. An increase of the magnitude due to a longer coaxial cable was demonstrated. The network analyzer method enables compensation of the test pulse specifications, and the scattering parameter data can be used to obtain a GIS trade certificate with the PD coupler. Pulse generators with a rise time shorter than 500 ps are subject to export control regulations when implementing the CIGRE method internationally, which makes the network analyzer advantageous in that it is free from this regulation in terms of using it for UHF measurements.