High-voltage equipment like gas-insulated switchgear (GIS) has been widely applied since the late 1960's thanks to its compactness and high reliability. However, the equipment over 40-year-old will be increasing from now on, and lower reliability of the equipment due to the in-service ageing and retirement of engineers/technicians with the equipment know-how are now in great concern. This brochure reports mainly the following three study items. Firstly, the number of the equipment (GIS) installed up to now was surveyed, and the average major/minor failure rates were evaluated from the viewpoints of ageing of GIS. Secondly, the transition of GIS components/construction and their actual operation/maintenance were reviewed. Lastly, the latest techniques were summarized in terms of monitoring/diagnostics for appropriate GIS renovation, GIS lifetime assessment, and lifetime extension of aged GIS.
This paper presents simplified models to represent a grid connected wind farm composed of variable speed wind turbines with Doubly Feed Induction Generator (DFIG) and Permanent Magnet Synchronous Generator (PMSG) for dynamic simulation study. Aim of the simplified models is to diminish the complexity and simulation time of the analysis of grid connected wind farm. The proposed simplified models can be used as an aggregated and individual wind generator model representations. Simulation analyses in time domain have been performed for steady state and transient scenarios to demonstrate the accuracy of the proposed model. Comparative analysis between the proposed simplified and detailed models is also performed and presented. The simulation results show that the simplified models have sufficient accuracy in both steady state and transient conditions.
This paper proposes a dynamic updating method of the optimal control parameters of multiple advanced step voltage regulators (SVRs) in a single feeder considering a massive introduction of photovoltaic (PV) systems. Each advanced SVR can adjust their tap position according to the updated control parameters in a certain period. The main feature of the proposed method is that the optimal parameters which minimize the voltage violation amount from the proper range and the tap operation count of SVR are determined quickly based on greedy algorithm. A numerical simulation is carried out on an actual distribution system model with the measured PV and load data so that the effectiveness of the proposed method can be evaluated.
Recently, concept of the lightning risk management has been proposed for the minimization of damages caused by lightning. In distribution systems (power distribution lines, low voltage distribution lines, telecommunication lines and customer appliances), lightning protection measures based on the lightning risk management are effective since the number of facilities is enormous. In this paper, for the establishment of lightning risk management method of distribution systems, we expressed the lightning risk assessment method of distribution systems and examined the influence of arrangement of customer house on the lightning risk values of power distribution lines and customer appliances.
When the contacts of circuit breaker are opened just before current zero, the gap between contacts will still be very short. Therefore, it cannot withstand recovery voltage between the contacts. In such a case, multiple re-ignition is likely to take place. Many investigators had tried clarify this phenomenon, and many reports have been published. However, high frequency current interruption and dielectric recovery characteristics are relates to some parameters (value of current, arc time etc). In addition, arc phenomenon also has been implicated. Hence, it is difficult to understand this phenomenon accurately. In this paper, we conducted dielectric recovery test and high frequency current interruption test. Further, we conducted observation experiment using vacuum chamber in order to investigate the effect of small DC current. At the end, we calculated plasma density in the electrodes after high frequency current interruption by considering the result of observation experiment and dielectric recovery test.
We have made an attempt to use an acoustic emission (AE) sensor as a failure forecast diagnosis for a wind turbine in Japan. The obtained AE signals has analyzed with the Mahalanobis distance method on the damaged blade. Mahalanobis distance method has established the fault level in the 40 mm cut scale.