This paper reviews on the location techniques of VHF electromagnetic (EM) source associated with lightning discharges. Thousands of VHF EM pulses are radiated during all processes of lightning discharge, especially in leader developing phase. Impulsive EM source locations give us information not only on lightning channel, but also the charge distribution. Two major techniques of VHF lightning observations, time of arrival and interferometry, have been developed since the 1970s. They have been contributing to reveal the mechanisms and characteristics of lightning with the advanced technology in digital electronics.

Electric vehicle (EV) will prevail in the near future and many EV's are expected to be parked all day or almost all day according to a survey in Japan. They can contribute as vehicle-to-grid (V2G) to primary frequency regulation in power systems. However, as lithium-ion battery or EV battery is still expensive, it is economically important to evaluate V2G frequency regulation cost. This paper proposes the evaluation method of the frequency regulation cost. The proposed method is based on the EV battery cost and longevity which is shortened by performing the frequency regulation. The battery degradation consists of calendar aging and cycle aging, and an empirical model is used in this paper. Simulation results are shown using the proposed method under the various conditions such as state of charge (SoC) of the EV battery. Those results indicate a V2G control strategy to increase the cost-benefit of primary frequency regulation.

It is important to measure the operating voltage of a cell sealed in a photovoltaic module as well as well-known faults such as abnormal hot spots observed by thermography or a dark part in electro-luminescence distribution on the module for detecting a fault module. This paper proposes a method that radiating modulated light toward a cell and extracting the synchronized signal from the module output by phase detector can estimate the operating voltage quantitatively by using a standard line predicted by shading the module partially.

Recently, three phase and three leg transformers are many in use. Zero sequence flux of the three leg transformer flows outside of the iron core. Therefore, the zero sequence inductance will be small. The first pole clear factor of recovery voltage at current interruption is decided by positive and zero sequence impedances. At transformer limited fault (TLF) interruption for the three leg transformer, the first pole clear factor will be small. However, there was few quantitative investigation for the recovery voltage of the TLF with three leg transformer. ATP-EMTP used for calculation of the power system transients has the three leg transformer model. In this paper, the first pole clear factors at various TLF conditions are discussed by using the three leg transformer model.

In order to prevent blackouts initiated by instabilities, early prediction of the potentially dangerous conditions is essential. This paper presents a novel method to early predict the out-of-step condition after being subjected to a severe disturbance. The proposed technique is based on the product of the post-disturbance voltage magnitudes and their differentiations (VΔV) used as the transient stability index. The novel method is computationally simple and fast compared to the rotor angle based transient stability prediction methods. In addition, the algorithm is transparent and does not require machine learning methods, thus would be more acceptable to the industry.