A new Phased Array Radar (PAR) system for meteorological application has been developed by Toshiba Corporation and Osaka University under a grant of NICT, and installed in Osaka University, Japan in 2012. The phased array radar system developed has the unique capability of scanning the whole sky with 100m and 10 to 30 second resolution up to 60km. The system adopts the digital beam forming technique for elevation scanning and mechanically rotates the array antenna in azimuth direction within 10 to 30 seconds. The radar transmits a broad beam of several degrees with 24 antenna elements and receives the back scattered signal with 128 elements digitizing at each elements. Then by digitally forming the beam in the signal processor, the fast scanning is realized. After the installation of the PAR, SIP project has started to develop a new PAR with polarimetric capabilities.
A capacitive-coupled magnetohydrodynamic (MHD) generator was demonstrated in a dense working fluid which was generated by a microwave discharge. In this study, the induction voltage from the capacitive-coupled MHD generator was observed in a sinusoidal magnetic field. The observed output voltage of capacitive-coupled MHD generator was not sinusoidal shape waveform in the condition of high Hall parameter conditions. On the other hand, the output voltage of capacitive-coupled MHD generator became the ideal output waveform as lower Hall parameter condition. It suggests that the capacitive-coupled MHD generator also consider the electrode structure for avoiding Hall effect.
In recent years introduction of renewable energy (RE), such as photovoltaic (PV) power generation and wind power generation, has rapidly increased. Since output of the RE is affected by weather conditions, it will be difficult to keep supply and demand balance of power. As a method of verifying the output fluctuation suppression effect of renewable energy in the frequency domain, a method of comparing the power spectra before and after suppression has been proposed. However, this method has not quantitatively obtained the contribution ratio of each system to the stability of the power system. Therefore, we used the method proposed to clarify the contribution ratio of electrolysis cell and storage battery when suppressing PV output fluctuations. And we analyzed how much each system contributes to the stabilization of the power system.
Downsizing of distribution lines while maintaining feasibility of network reconfigurations would save monetary costs in a distribution system planning. In this study, we propose a method to find distribution lines with reducible capacities based on a set of non-dominated solutions for network reconfiguration problem under the condition that appropriate reconfigurations can be performed even after the downsizing. To alleviate the computational burden, the proposed method consists of three steps. First, (i) the current flowing on distribution lines when performing the network reconfigurations are found by a developed evolutionary algorithm for solving many-objective network reconfiguration problems. Second, (ii) the distribution system operator specifies his or her preferred solutions among them to perform reliable network reconfiguration for all maintenance areas. The maximum current flowing on lines are computed based on the specified preferred solutions. Finally, (iii) distribution lines with possibilities of the downsizing are chosen based on the maximum current flowing on the lines before/during/after the reconfiguration and then feasibility of reconfigurations after the downsizing are validated. The computational experiment using a large-scale distribution system model demonstrates that the proposed method identifies the distribution lines with reducible capacities and their line types after the possible downsizing.
As the installed capacity of renewable energy sources is increasing, the role of inverters is becoming more important in the maintenance of power system stability. Therefore, in this study, we propose the use of a wide area control system (WACS) to control the inverters of photovoltaic (PV) systems in a coordinated manner to improve transient stability. In this method, we select PV systems whose reactive power injections are deemed to suppress the acceleration of the critical generator, based on a time-domain simulation for each possible fault before the fault occurs. When a fault occurs, we trigger the reactive current injections with the selected PV systems that is, the WACS operates as an event-based emergency control system. Numerical simulation results demonstrate that this method can further improve transient stability compared with an autonomous reactive current support function that is applied to existing PV inverters. The proposed WACS could be a promising approach to address the transient instability phenomena under unscheduled power flow conditions by periodically updating the control table based on real-time information.
We examined the connection method of the high-voltage cable to the structure for adopting the separate type down-conductor for reducing the internal magnetic field of building. In construction of high-voltage cable type down-conductor, it is necessary to minimize safety separation distance considering side lightning flash. For this purpose, it is necessary to reduce the overvoltage generated between the sheath conductor of the cable and the structure of building as small as possible. Therefore, in order to achieve both reductions of the internal magnetic field of the building and of the overvoltage between the cable and the structure, the matching resistances for reducing the reflection inside the cable and for reducing the reflection between the cable and the structure are calculated, and introduced into the analytical model of the building. We confirmed that the internal magnetic field of the building and the overvoltage between the cable and structure reduced effectively by connecting the matching resistance between the sheath conductor and the building pillars. On the other hand, the matching resistance between the core and the sheath conductor in the cable can suppress the reflection inside the cable does not effect for reducing both the internal magnetic field and the overvoltage.
Most indoor polymeric insulators are used for a long term over 30 years. Those insulators rarely fail due to partial discharge depending on the used material and installation environment. Therefore, we have been developed a new risk analysis method of partial discharge occurrence on indoor polymeric insulators. We conducted experiments simulated dry-band discharge and uncontaminated-band discharge, and defined the decision making criteria for occurring partial discharge. The criteria for dry-band discharge are insulation resistance under maximum humidity and surface resistance ratio before and after drying. The criteria for uncontaminated-band discharge is surface resistance ratio of before and after cleaning. In order to on-site measuring the surface resistance in the on-site switchgear, we developed portable measuring device. This device which consists of high humidity generator, insulation resistance tester and surface contact sensor can measure the surface resistance between pin electrodes under local high-humidity space. We analyzed the partial discharge risk on different switchgears used for over 25 years using this device. As a result, the risk due to partial discharge of long-term used insulators are kept extremely low by periodically maintenance and environmental control.
Surface charge accumulation on insulating epoxy spacer in DC-GIS under high DC electric field decreases breakdown voltage on the spacer, but charge accumulation phenomena of insulators are not clear in detail. In this paper, the numerical simulation of electrical conduction in epoxy is conducted to discuss proposed charge transport model. The charge transport model which had developed to explain electrical conduction in polyethylene is modified to simulate the prior profiles of space charge distribution in epoxy. With this model, space charge accumulation is simulated and compared with the experimental results. As a result, the simulated and experimental space charge distributions are consistent under multiple conditions with different electric fields, temperatures and measurement times. In particular, the hetero-charge in the bulk could be reproduced by extraction barrier, and the homo-charge near the electrode could be reproduced by locally increased trap density. It can be explained that changes in space charge density with conditions are determined by the electric field and temperature dependence of charge injection and de-trap rate. From these results, the usefulness of the charge transport model in epoxy is verified.
Degradation rate of electrical insulation performance of oil-filled (OF) cables has been considered small since void-less conditions are realized due to their oil-impregnated insulation systems under insulation oil pressure that exceeds atmospheric pressure. However, recently, insulation breakdowns have occurred in OF cable joints at extra-high voltage, and they were not predicted by dissolved gas analysis (DGA) of insulation oil. Therefore, it is necessary to improve the prediction accuracy of DGA for detection of partial discharges (PDs), which are known as a pre-breakdown phenomenon. Recently, it has been reported that traces of black color in oil-impregnated insulation papers are sometimes compounds of oxide sludge or copper sulfide, which were all regarded as carbonization due to PDs. Moreover, it has been reported that PD inception fields decrease with an increase in the rate of the total thickness of insulation papers with discoloration to the insulation thickness. To improve the prediction accuracy of DGA, such new findings should be taken into account when ranking abnormal conditions of insulation systems of cable joints and terminations, which gives the basic data for the prediction by DGA. In this study, abnormal conditions of oil-impregnated insulation papers were redefined and classified into trace of occurrences of PDs and two types of discoloration, and those of 264 aged OF cable joints and terminations removed after service were investigated. In addition, the above-mentioned rate was quantitatively evaluated for cable insulation systems, and locations of the abnormal conditions were investigated in detail for reinforced insulation systems. Taking these results into account, a new classification method for the ranking of abnormal conditions of oil-impregnated insulation systems was proposed.
Equal area criterion is frequently used as a means to assess transient stability. The method can be hardly applied to observed data because the method is based on rotor angles which need to be measured with specially deployed sensors. This paper presents the equal area criterion using generator terminal voltages instead of the rotor angles. It is easy to measure the voltages, thus the novel method would be more acceptable to industry.