Power capacitors and their application technologies have contributed greatly to the effective use of electric power and to the power quality improvement. Then, they have evolved into such static var compensators (SVC) and voltage dip compensators with the development of power electronics technology⁽¹⁾.

However, the fluctuation of voltage and the increase of harmonics, due to the increase of distributed power sources, and additionally the over-lead power factor or the Ferranti effect due to the promotion of “inverter-ization” and “energy saving” have occurred in recent years. The countermeasure to these problems by the changes of sources and loads in power systems has been requested not only to power capacitors but also to their applications cooperated with power electronics technology.

Considering these circumstances, this paper outlines that the voltage and reactive power control technologies of power capacitors and power electronics application, by which the countermeasures against the increase of over-lead power factor, steep voltage fluctuation and harmonics, and the trends of capacitors for power electronics.

Recently, online stability monitoring systems have become more important in response to the increasing complexity of power systems. Moreover, there has been a concern about multi-swing step-out due to the Japanese longitudinal power system. In this paper, a fast screening method is proposed considering multi-swing step-out using PCA (principal component analysis). In the proposed method, computers learn patterns of PCA in transient stability data as a form of library. In order to reduce the number of data in the library, k-means method, one of the partitioning-optimization clustering methods, is applied to extract features in the data. In addition, Gaussian mixture model is also applied to extract the feature from a different perspective. Simulations for the proposed method are performed using the IEEJ 10 machine 47 bus system to confirm the validity of the screening method.

A possibility of application of fast automated demand response (FastADR) aggregation of a cluster of office building air-conditioning facilities to the load frequency control (LFC) of the future smart grid is studied. An aggregation feedback control system design for the LFC is carried out comparing between the conventional 1st order delay and our asymmetric constant rate transfer functions for the response characteristics of air-conditioners' power consumption. Due to the non-linear and rate-limited power consumption changes of building multi-type air-conditioners, there were significant differences between the effects to the LFC responses. Although a recovery disturbance in the LFC result in the case of the conventional 1st order transfer function, the phenomenon disappeared in the case of our proposed transfer function.

Computational simulation is essential to evaluate the impact wind turbine penetration on the demand and supply power control. The observed time-series of wind turbine output in entire power system is required as input data for computational simulation, but it is difficult to obtain. In this study, we propose the method to generate simulated time-series of wind turbine output with conversion of wind speed by location and height based on Weibull distribution. In particular, wind speed data published by Japan Meteorological Agency and Weibull parameter by NEDO are utilized.

This paper proposes a new control system for Adjustable-Speed Pumped-Storage Generator (ASG) to decrease frequency fluctuations of power system with a large amount of wind farm introduced. When a large amount of wind power generation is connected to the power system, it can decrease power quality, e. g., frequency variations. There are some methods to suppress the frequency fluctuation in the power system, among which ASG can be an effective countermeasure. However, there has not been sufficient report on the frequency control by using ASG. This paper proposes a new output control system with dead band for ASG to smooth frequency fluctuations of the power system arisen from fluctuating output of the wind farm.

The aerial insulated wire is supported by the insulator and binding wire at the reinforced concrete pole. A compound insulation system consisting of the conductive wire core, wire insulation layer, insulator and binding wire exists on the wire supporting point. When the overvoltage due to the inductive lightning surge invades to the conductive wire core, the creeping discharge can develop along the wire surface from the free end of the binding wire just after a flashover at the post insulator. This creeping discharge may give rise to the accidents such as a melting or snapping of the wire. Generally, it has a lot of rain with the generation of a thundercloud that causes lightning strike, and then the insulated wire surface is the wet condition with waterdrops. In the previous paper, we have reported the characteristics of negative creeping discharge along the wire surface at the wet condition under the inductive lightning surge with the peak value V_m ≤ 80kV for the space restriction of the laboratory. In the experiment, the wire height is 75cm on the ground. Therefore, V_m = 80kV in the experiment is equivalent to V_m = 120kV in the real system. This paper presents the characteristics of negative creeping discharge at V_m ≥ 80kV (V_m ≥ 120kV in the real system) for the wet condition. It is reported that the propagation of negative creeping discharge is influenced greatly by the positive corona discharges occurring from the waterdrops surface under the wet condition.

This letter addresses reduction of the energy capacity of energy storage systems (ESSs) using H_∞ control theory. The ESSs have been widely used for smoothing fluctuations of wind generator outputs. We propose a direct and efficient method to design controllers that achieve the minimization considering the trade-off between the energy capacity of the ESSs and frequency variation in power systems.