In this article, from the viewpoint of mathematical science, we clarify a class of mathematical models with grid-forming function by considering the principle of frequency synchronization. In particular, it is shown that the two-axis model and classical model of the synchronous generator, and the frequency-droop-control model are all equivalent in terms of frequency synchronization. It is also explained that systematic stability analysis with a generalized synchronizing power coefficient matrix, derived as the Hessian of a strain energy function, is possible for all those models.

We are planning to develop the new Advanced Distribution Automation System (ADAS) equipped with optical communication network and sectionalizer with sensor for more grid reliability and efficiency on maintenance operation. The new system is featured with the function of fault cause or damaged part estimation. The new sectionalizer captures the waveform of electrical line surge originated by fault and the system analyzes the waveform for this function. This paper mainly introduces the system configuration of ADAS and an early stage examination of fault cause estimation technology.

Liquid insulators such as mineral oil and silicone oil have excellent cooling and insulation performance, but impurities, dissolved gases and/or moisture in the liquid are known to have a significant influence on insulation performance. So far, the authors have shown that partial discharge (PD) current waveforms in mineral oil differ significantly depending on degassing treatment condition and on positive and negative polarity by super high frequency-wideband measurement. In this paper, using aged mineral oil which was used in a distribution transformer over 48 years, difference in PD current waveforms between new and aged mineral oil and between mineral and silicone oils as difference in insulation oil type were investigated by the super high frequency-wideband measurement system, so-called “SHF_PDPW system” with a 33GHz oscilloscope. In addition, PD-emitted electromagnetic (EM) waves in those oils were measured with an antenna with sensitivity in the UHF band, and differences in the polarity and relationship between PD current and PD-emitted EM waves were investigated from the viewpoint of applicability of the UHF method.

The daytime sky at Toyohashi city was observed every five seconds from April 2021 to December 2021 by using two all-sky cameras. Based on the images, the number of the cloud layer was statistically analyzed for every hour. The results indicate that two-layer clouds occupy a large temporal fraction as well as one-layer clouds. Therefore, the motion of the two-layer clouds was examined by the optical flow analysis with Lucas-Kanade method. Two directions were clearly obtained from the polar histogram of the angle of the optical flow vectors.