A reference measuring system for lightning impulse high voltage maintained by Japan High Voltage Impulse Testing Laboratory Liaison (JHILL) is introduced. JHILL participated in the international comparison test of lightning-impulse-voltage measuring systems organized by the European Association of National Metrology Institutes (EURAMET). From the comparison-test results, it is confirmed that the reference measuring system of JHILL is compatible to those of national metrology institutes (NMIs) of developed countries.

According to rapid increase of photovoltaic (PV) and wind generations in recent power system of Japan, the cases arise that power generation exceeds demand, so PV generations must be curtailed in some area. Hereafter, part of PV and wind generations may be curtailed in other areas too. In Europe and America too, similar surplus electricity are genetated and capacity of battery to withdraw surplus electricity are researched. This paper analyzes basic supplying characteristics of PV and wind generations in the simplified model system based on the actual power system in north-east area in Japan. As a result, when penetration ratio of PV or wind generation exceed 10～20%, surplus energy arise. It needs much capacity of battery to withdraw surplus energy, so supplying cost including battery is several ten times of cost of generation alone. If minimum output of stable generations except PV and wind generations could be lowered, surplus energy, capacity of battery and supplying cost will lower remarkably. But unit supplying cost of stable generations increases. According to introduction of much PV and wind generations, more coordination of power system and PV, wind generations is necessary, i.e. scaling up and cost down of energy storage, extension of power control range of stable generations, demand side management, etc.

When a disconnection occurs in the high-voltage distribution line, the conductor of the wire contacts the ground belt, resulting in a ground fault accident. In the case where the conductor of the electric wire is covered with a coating, a ground fault accident does not occur even if it contacts the ground belt. Under such a situation, it is not possible to grasp the disconnection of the distribution line. Studies using a smart meter have been conducted to specify the disconnection point of the distribution line. In order to specify the disconnection point using the smart meter, it is necessary to install a large number of smart meters on the distribution line. The authors propose a method which can inexpensively locate disconnection points of power equipment to areas where it is difficult to install many smart meters or to emerging countries where power facilities are to be constructed in the future. In this method, only the ground wire at the end of the two distribution lines is connected, and the disconnection point is specified from the time difference of the zero crossing point of the current flowing at the rising of the common ground line of the two distribution lines at the time of disconnection. In this method, disconnection points can be specified by installing a current measuring device on the common ground line of the rising edge of the distribution line, resulting in an inexpensive system.

This paper investigates an efficient iron loss calculation method for soft magnetic materials of power transformers. To accurately estimate iron losses in the materials such as structural steels and magnetic shielding, the magnetic field analysis taking account of the nonlinear magnetic properties is considered to be effective. In this paper, quasi-DC magnetic properties of the soft magnetic materials are measured and the iron losses are calculated by using a 3D finite element method. Furthermore, the effect of considering hysteretic properties on the accuracy of the iron loss calculation is discussed based on a theoretical representation of eddy current loss in a conductive rectangular plate.