The protection relay changed from electromechanical or analog static type to digital type using the progress of microprocessor against the growth of power network. The digital relay improved protective performance and reliability based on establishment of various protection schemes and the embedded automatic supervising function using the development of the digital technique. Additionally, the recent protection system technique enable to make the configration and operation of power system efficient. Multi-terminal transmission lines can be realized by use of PCM current differential relay. The out-of-step protection, the voltage stability control and the over load failure extension protection can increase transmission capacity.
In future, it will need to develop the protection system for the distributed power generation and decrease the cost of protection systems against the progress of deregulation.

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Due to the explosion in use of the Internet, it is expected that a variety of services will be provided through the communication network in the near future. Protection and control systems using the latest communication and information technology also allow for innovative solution to a wide range of power system problems. This paper describes a network centric approach to protection, control and monitoring systems. When the proposed “Network” devices, server and browser can communicate with each other, they can share information which can enhance the overall protection and control of the power systems. The paper includes: overview of network devices, key technologies, protection and control applications, issues, conclusion.

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This paper describes the advance of the ground relay of the line protection.
First of all, we examined the ground fault in a resistively grounded power system. The protective relay detects the ground fault by the zero phase current in the system. There are two methods for the current input to the relay. One uses the residual circuit of CT secondary winding, and the other uses the CT tertiary winding. When the ground current is insufficient in the residual circuit, the CT tertiary winding is used. In order to omit the CT tertiary winding and to get more reliability, we reviewed the full-scale of relay and evaluating the error of CT. As result, almost all transmission lines could omit the CT tertiary winding.
Next, we examined the ground fault with high fault resistance in a solidly grounded power system. When that fault occurs in the system, the PCM current differential relay acts by fault current. So, this relay possibly mal-operates when the CT secondary circuit is disconnected. Therefore, it uses a special CT to raise the reliability. Nowadays GIS has become small and the CT installation space has been decreased, it is needed to reduce these CT cores. In order to omit the special CT, we utilized the combination of the power relay and the rate of change of relay current. As a result, there is a prospect that the relay would not need the special CT.
These improvements are effective to reduce cost too.

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Stability of a power system has been investigated in the view of chaos and bifurcation. In this paper, the OGY (Ott-Grebogi-Yorke) method for controlling chaos of three machines operating onto an infinite-bus system is investigated by computer simulations. The swing equation with the controlling input u is used. The OGY method is extended to the form in the six-dimensional space. The 8 equilibrium points are obtained. The swing equation is normalized and transformed into a discrete-time state equation from which the control input is calculated. The time series of the phase angles of generators without the control input show the chaotic irregular motion and the step-out. The time series of the phase angle of generators with the control inputs by OGY method show the stable motion. The phase angles are successfully controlled onto the unstable equilibrium points with the three unstable manifolds and the three stable manifolds.

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In near future, many Independent Power Producers (IPPs) will participate in power generations according to their own strategic contracts by the deregulation. Loop or mesh systems can be designed to balance the power flow and to regulate the voltage resulting to the flexibility of power system operation, improvement of reliability and economical efficiency. Nevertheless, they bring to the problem of increased fault levels which may raise beyond the withstand capability of existing circuit breakers in the power systems. Short-circuit current is strongly related to the cost of apparatus and the effective use of power transmissions. Therefore, the introduction of Superconducting Fault Current Limiters (SFCLs) becomes an effective way for suppressing such a large short-circuit current. In this paper, first the authors evaluate the behavior of the S/N transition-type SFCL by considering the sub-transient and transient effects of generators in order to obtain smaller SFCL circuit parameters, i.e.\ the resistance of the superconducting coil and the reactance of the current-limiting inductor. Then the authors propose a method by using a hierarchical genetic algorithm (HGA) combined with a micro-genetic algorithm (micro-GA) to search for the optimal locations and the smallest SFCL circuit parameters simultaneously. The flexibility in defining the required objective function by using the proposed method makes it possible to evaluate the requirement of SFCLs in large power systems. Analysis by computer simulation has been carried out in an example loop power system.

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This paper presents a new digital type protection relay based on matrix operations. The basic principle of the matrix operation type protection scheme has been already discussed and investigated. However, further studies have been required especially to confirm the real time capability of the proposed scheme, in addition to evaluate the accuracy of fault detection and the identification of fault location. The off-line pre-calculation has been proposed for solving the time-consuming problem. Furthermore, the interpolation technique based non-iterative solution has been developed, which replaces the traditionally iterative Newton-Raphson's method for saving required calculation time. Combining both of the off-line pre-calculation and the interpolation method enables to ensure the activation time of the proposed protection relay within two cycles after a fault occurrence. Moreover, a high accuracy of fault detection can be achieved. In order to demonstrate the reliability of the proposed scheme, numerical simulations have been performed through using the actual data measured on real power systems with different voltage levels. The compared results indicate the highly precise estimation of the fault locations compared with the inspected fault locations on transmission lines. The required computation time is also estimated with considering types of numerical calculations included in the proposed algorithm. The estimated computation time is short enough for the real time implementation of the proposed scheme.

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This paper proposes an algorithm for obtaining the periodic steady-state solution of a multiphase network, which includes nonlinear and switching elements, to be used for steady-state initialization in electromagnetic transient analysis. The algorithm takes rigorously into account the inter-harmonic couplings in the Jacobian matrix of the proposed Newton-Raphson iteration process and is capable of handling any circuit topology by use of Modified Nodal Equations. In this paper, the algorithm is first described and then applied to a test case to demonstrate its performance.

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Japan Western 60Hz System consists of six major electric power companies. Due to its longitudinal structure there are some significant oscillation modes represented by long term oscillation among whole system. Independent load frequency control based on Tie-Line Bias control (TBC) is adopted in each company. Also some independent power producers are participating in the power generation business. In the circumstances the system may show some interesting dynamics. So far, some oscillative characteristics have been measured in own area or in the interconnected tie lines. However, there was little observation as a whole power system. In this paper the authors present an global monitoring system of power system dynamics by using the synchronized phasor measurement technique, which are located in some universities in the 60Hz power system. Phasor measurements are synchronized based on the global positioning system (GPS) and measured data are transmitted via Internet. Some oscillative features and variation of phasor in a day, a week or a year are analyzed using the acquired data.

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Typical molded-case circuit breakers have deion plates to limit and interrupt the fault currents by increasing arc voltage. The rise in the arc voltage by deion plates is considered to result from the following two phenomena: (1) the elongation of an arc length and (2) the generation of an electrode fall voltage of the arc split up between deion plates. In order to clarify the contribution of deion plates in molded-case circuit breakers, an arc voltage was measured for different arrangement of deion plates. In this experiment, optical observation of the arc behavior was also made to find out the arc length and the number of the deion plates dividing the arc. By using the expression of the arc voltage derived in terms of the arc length, the number of deion plates dividing the arc and the arc current, the rise in the arc voltage was successfully decomposed into arc column voltage and electrode fall voltages near the electrodes and the deion plates.

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The authors recently proposed a solid oxide fuel cell (SOFC) and closed-cycle MHD combined carbon-dioxide-capturing high-performance power generation system using pure oxygen as the oxidant. This combined system can make the best use of the merit of pure oxygen combustion, while its demerit of efficiency deterioration by large required power for oxygen generation still remains. In the present study, the authors modify this already proposed system and newly propose an improved carbon-dioxide-capturing SOFC/MHD combined power generation system with higher total thermal efficiency. In the system, pure oxygen is only supplied to the afterburner to save the required power for oxygen generation, and pressurized air is selected as the oxidant gas of the SOFC. The saved power amounts to about 5% of the thermal input, resulting in the very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value as the total thermal efficiency of carbon-dioxide-capturing systems. The proposed system is worth carrying out further research and development.

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The novel thyristor voltage regulator (TVR) for power distribution lines is discussed. It has faster response time, lighter weight, and higher maintainability compared with the existing TVR's. The newly developed “jumping-tap method” demonstrated high-speed response of 0.1 second. Thanks to this method, a big voltage disturbance caused by motor starting, for example, could be compensated. Reverse power flow cause judgement is discussed.

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