Recently, a utilization scheme of distributed energy resources (DERs) is discussed as a countermeasure for mitigation of congestion in distribution networks. This paper describes the technological trends in Japan and overseas based on pilot projects. Additionally, the topics about DERs utilization verified in research papers are surveyed and summarized.

The paper proposes a method to select a power factor for an inverter of distributed power generation systems to keep appropriate voltage of a power system with the high penetration of inverter-interfaced generation. The increase of inverter-interfaced power sources, such as wind and photovoltaic power generation, arouses concerns on the voltage fluctuations in a power system. While constant power factor control of an inverter has been studied as a means to stabilize the voltage of a power system, there still remains room to improve the control. The proposed method in the paper selects the power factor based on the R/X ratio of the looking-back impedance into the interconnected power system. By normalizing the related variables, a general formula is derived for the power factor; and the resultant relationship between the apparent power and voltage of an inverter becomes identical irrespective of the R/X ratio with the control. Sample studies show that, by operating an inverter with the power factor, voltage fluctuations are effectively suppressed even for a power system with the high penetration of inverter-interfaced generation.

The frequency response analysis (FRA) of transformer has been expected to be a good method for diagnosing the transformer condition. The special measuring instrument is usually used for the FRA measurement. So, in this paper, a new method of FRA measurement using a general-purpose square wave source and the oscilloscope is proposed. FRA of this method is evaluated with the frequency response characteristic of the transformer input impedance. The procedures of this method are as follows. First, the square wave voltage is applied to a transformer and the input voltage and the input current at that time are measured with the oscilloscope. Next, the high order frequency components of voltage and current are calculated by Fourier series expansion. At last, high order transformer input impedance is calculated by doing division of the high order frequency component of the input voltage and the input current. Frequency response characteristics of the input impedance of the transformer are provided in the above-mentioned procedure. As the experiment that applied this method to a pole transformer was a good result, we report it.

Bus bar of substations are important equipment where multiple facilities are centrally connected, and the impact of a fault is significant. Therefore, bus bar protection relays have unique functions to correctly detect the point of fault, which allows high speed fault elimination and minimization of outage area. This paper describes functions and roles of bus bar protection relays applied in distribution substation of Kansai Transmission and Distribution. After describing the concept of installation of bus bar protection relays, recent trends in device development tailored to the bus bar configurations of substations and the unique functions of bus bar protection relays are introduced. The retrofit methods that are being increasingly applied as a renewal solution for bus bar protection relays are then described, as well as prospects for bus bar protection functions in the future IEC 61850 full-digital substations.

The isolated power system (off-grid) using only renewable energy resources (PCS supplies) is studied. On the other hand, the off-grid of the Japanese general transmission and distribution company using only PCS supplies has not been realized. To realize and clarify the safety operation of off-grid, in this paper, the fault detective sequencer is proposed using the simple simulation which was proposed in previous report.