In addition to grasping the actual conditions of maintenance and maintenance work of hydroelectric power plants and the actual conditions of the technologies adopted so far, a new technological development trend was investigated for further rationalization. In this paper, the outline of the survey result about these is shown.

This paper presents a fast computation algorithm for a multi-area optimal power flow (OPF) with discrete variables. The multi-area OPF with discrete variables is formulated as a Mixed Integer Non-Linear optimization Problem (MINLP) that includes both continuous and discrete variables as decision variables. In this paper, in order to solve the multi-area OPF with discrete variables efficiently, we propose a resource allocation-type decomposition algorithm considering continuous relaxation of discrete variables. By using the resource allocation type decomposition, it is possible to guarantee the feasibility in the optimizing process, and it is possible to suppress the amount of error by absorbing and buffering the relaxation error by the resource allocation variables. In addition, since the variables that interfere between adjacent Areas is utilized as resource allocation variables, the sub-problems obtained by the decomposition become independent problems, and the original MINLP can be solved in completely distributed approach. Numerical examples against several multi-area test systems show that the computational costs can be significantly reduced with less computational errors compared to a centralized approach.

This paper proposes a configuration of multi-circuit HVDC system and its protection scheme for DC line faults for improving reliability. The system consists of multiple DC lines connected in parallel to a DC bus through diodes. These diodes can instantaneously disconnect a faulted line, with the result that no fault current flow from the other non-faulted lines. It can immediately clear the DC fault current by shorting the submodules of the modular multilevel converter (MMC) in the supply side. Simulation results confirm the validity of the proposed protection scheme under a pole-to-ground fault (DC1LG) and a pole-to-pole fault (DC2LG).

The idea of dynamic rating system to maximize the use of existing facilities is effective for solving the lack of transmission line vacant capacity that prevents a large amount of dispersed generations from connecting power grids. Such system requires a new arithmetic device for implementing the complicated formula to calculate the current capacity together with the overload protection device for transmission line. This paper considers the implementation of a dynamic rating system and a transmission line overload protection using one Intelligent Electronic Device (IED) and contrives a formula for calculating the current capacity that can be implemented in IED. It also shows the result of implementation of the proposed capacity calculation formula and transmission line protection.

In this paper, a method of estimating the zero-sequence circulating current ZC in the steady state and the grounded faulted state of the power system is proposed, when three-phase constant data is given in part of transmission line data of the power system. The proposed method can efficiently estimate the ZC of each grid point for any grid configuration. The methods of estimating ZC for pre-determined specific systems configurations have been used in Japan for many years, but lack generality to complex system configuration. On the other hand, three-phase calculation, which is a direct means of calculating ZC, has advantages in accuracy and the applicability to any system configuration, but is difficult to apply to large-scale systems. In this paper, a new ZC estimation method is proposed by taking the transformation of the a-b-c variable in the phase coordinate system into the 1-2-0 coordinate variable in the symmetric coordinate system. (1) Arbitrary system configuration and system scale are allowed to estimate. (2) Based on symmetric coordinate method single-phase data, only three-phase data is needed for a target of ZC estimation. (3) ZC of each part of the system can be efficiently estimated, not only in steady state but also in any grounded fault condition. The usefulness of the proposed method was verified by demonstrative application for the test system.

This paper examines the performance of two representative schemes—i.e., proportional-dispatching and target-period-sharing schemes—for load frequency control (LFC) of a power system, in which battery energy storage systems (BESSs) and thermal power plants are used for LFC. The target-period-sharing scheme has been recently proposed for LFC with BESS while the proportional-dispatching scheme has been widely used in LFC with thermals. However, few researches compare the performance of the two schemes. The paper examines their performance with spectral analysis techniques through simulation studies on the AGC model published by IEEJ—i.e., AGC30. The results show that the target-period-sharing scheme is preferable to the proportional-dispatching scheme when an appropriate time constant is chosen for a filter in the target-period-sharing scheme. The approximate time constant depends on the response characteristics of the LFC-regulated plants. On the other hand, regulation capacity should be carefully examined for the slow-response LFC-regulated plants in the target-period-sharing scheme because limiters in the control circuits tend to become active for the plants in the scheme.