Demonstration projects of high temperature superconducting (HTS) electric power apparatus and systems are undergoing in the world. In addition, their verification tests in real grids are also conducted toward the commercialization of HTS power applications in the near future. In consideration of these situations, this article reviews the recent R&D progress of HTS power applications and their technical problems to be solved, focusing on HTS cables and transformers as main apparatus of electric power transmission system, and fault current limiters (FCL) expected as control devices. Especially, HTS cables and HTS transformers with FCL function have been developed as one of recent R&D trends on HTS power applications. Such multifunctional HTS power apparatus can be realized only by HTS technology with zero resistance in the steady operating condition and will contribute to propose a novel application scheme of HTS power apparatus and systems. This article consists of the followings: (1) fundamental common technology (HTS wires, electrical insulation, cooling system), recent progress on (2) HTS FCL, (3) HTS cables, (4) HTS transformers and (5) toward high performance and multifunction of HTS power applications.

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FIT (Feed-In Tariff) has been enforced to promote utilization of renewable energy since 2012 in Japan. Considering FIT, we propose an integration plan of incinerator plants (IPs) with high efficiency power generation for the whole area of prefecture. The plan includes disposal of forest biomass by reserve capacity of IPs. The model prefecture's population is set to 1,200,000 and the rate of the forest area is set to 70% of the model area according to the data of the North-Eastern district. The present 16 IPs are integrated into new 3 IPs. The relay transportation (RT) facility of refuse is located at the abolished IP, and the refuse of the area is carried to new IP. For calculation of the RT cost, an approximation formula of the RT distance is estimated through the IPs integration study. The plan will realize about 37% cost reduction and 1.8 times CO₂ reduction including RT against the IPs renewal plan. Forest biomass of 56,500 tons per year, which is about 45% of available forest biomass volume in the model prefecture, will surely be able to dispose at new IPs. On the other hand, enough profit is not expected at the exclusive biomass power generation plant with chipping process fee etc. The plan will help developing local forestry.

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As many wind farms have been installed in power systems in the world, frequency fluctuations due to output power variations have become a serious problem. Various countermeasures for the problem such as battery systems have been investigated. It is very important to evaluate the magnitude of frequency fluctuation for designing compensating systems. This paper presents a new and simple method to evaluate expected value of the frequency deviation due to variations of wind farm output, which is based on the intensity of turbulence and annual probability distribution of wind speed.

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Large integration of intermittent renewable energy generation causes the system frequency fluctuation. To solve this problem, more frequency control services will be required. Air conditioners in the commercial sector are one of the potential resources for demand side controllable load. This study proposes a model of coordinated LFC system that considers transient power consumption characteristics of commercial air conditioner and simulates system frequency fluctuation to analyze the effect of frequency fluctuation suppression by air conditioners power consumption control. To demonstrate the usefulness of controllable load, the reduction of inverter capacity in a battery energy storage system is evaluated.

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This paper proposes a system reduction method to reduce a bulk power system. Recently, power system is affected tight demand-supply, and is operated in more severe power flow condition. So, it is desired an accuracy improvement of reduction model (interconnected system) dynamics. In this paper, we propose a method to create a reduction model and its parameters suitable for preservation of dynamics in bulk power system. The model is determined based on evaluation function using the Power Spectrum Density of oscillation waveforms obtained using original detailed model and reduced order model. The proposed method has features that it requires only a couple of necessary data (short circuit capacity, total demand, reference oscillation waveform), without the detailed power system data about the interconnected system. The proposed method is applied to the real-size system, and verifies the accuracy of the dynamics of that system.

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It is expected by applying switch with built-in sensor to distribution line that effective operation and voltage control method in distribution line improve to solve the voltage problem by reverse power flow from renewable energy resources. There is a possibility of the estimation of ground faults location from current and voltage of wave form in ground faults using switch with built-in sensor information. The study to estimate ground faults location is performed continuously, but this technology has not been implemented because sufficient observation information related to aspect of ground faults location and test condition cannot be obtained. The authors report that distribution line simulator changing length of distribution line in the laboratory is constructed in consideration of neutral point connecting method at high resistivity and effect from other distribution line in same substation and that validity is evaluated by voltage value in sound-phase and ground faults current of wave form.

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In order to improve S/N ratio for partial discharge (PD) detection using a resistance-temperature detector laid in stator windings of hydro-power generator, continuous wavelet transform (CWT) is applied as a kind of time-frequency analysis. Relying on the combination of frequency resolution and time resolution using an applied power voltage phase angle distribution, PDs occurring in voids of stator windings are thought to be found within mixed environment of large noises and confusable noises. Furthermore, we found that CWT may make it possible to calibrate PD charge quantity in a few tens of MHz band under favorable conditions where the calibration is usually difficult for generator stator windings.

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Partial discharge (PD) characteristics and degradation mechanism of an oil-impregnated insulation system with an oil gap at the electric field adopted in the design of OF cables at 275kV class were investigated. First, we investigated its time transition of PD characteristics under a continuous alternating current (AC) voltage application. As a result, PDs continued with the AC voltage that was lower than that of the PD inception voltage and the test sample broke down after approximately 16 days. These results suggest that a certain amount of lead time is expected even when oil gaps are overlapped on the inner conductor or under the outer shield due to core movement of OF cables after lengthy operation and PDs continuously occur. Also, phase angle characteristics of PD charge magnitude (ϕ-q pattern) showed typical patterns of PDs in a void until before breakdown that changed just before that point. Therefore, ϕ-q patterns are useful for removing outer noises and for determining the occurrences of PDs in OF cable systems under operation. Finally, we observed insulation papers subjected PDs for certain time. As a result, carbonization due to PDs was found especially around the edge of an oil gap and a pin hole was formed in the carbonized area of the oil gap edge after more than 8 days. Based on this result, degradation progress and mechanism was discussed.

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