A system damping resistor (SDR), which is one of stabilizing equipments, is especially effective to decelerate the first synchronous generators' acceleration. An adjustable speed flywheel generator (FWG) is effective not only to decelerate the first acceleration but also to improve the dynamic stability.
We have studied combination effect of the SDR and FWG for a model network with a large-capacity and long-distance transmission system. It has two types of instability mode. One is immediate step-out type by unbalanced fault such as same-phase 1LG-OC (1φ2LG-OC). The other is dynamic unstable type by balanced fault such as 3LG-O. We concluded that SDR-FWG combination using proper control method has an effect of decreasing total capacity, which gives economical advantages.

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It is well known that the cost performance of PAM SVG (Pulse Amplitude Modulation Static Var Generator) is better than that of PWM SVG (Pulse Width Modulation Static Var Generator) because of its low loss in operation and more compact size of equipment. Despite the advantage, the PAM SVG has been deprived of opportunities to show its effectiveness in power systems, having reputation for inferior of continuous operating performance under unbalanced-voltages and for slow response. In this paper, analogue simulation results show that decoupling control and proper amount of capacitor furnish the PAM SVG with great continuous operation ability and quick response, which suffice to improve power system stability.

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This paper deals with dispersed installation of voltage-etection based shunt active filters for harmonic damping throughout a power distribution system. A main objective of the active filters is to achieve damping of harmonic propagation coming from series/parallel resonance between capacitors for power factor correction and line inductors in the distribution system. Either a harmonic current source or a harmonic voltage source is connected to a distribution system simulator consisting of two distribution feeders, each of which is rated at 200 V and 20 kW. A couple of active filters are installed to the simulator. As a result, it is clarified by experiment that dispersed installation on the end bus of each feeder is effective in attenuating the harmonic propagation.

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An improved robust H_∞-optimization techniques is used to design a robust supplementary controller for the Static Var Compensator (SVC) to increase the power system damping. The existing H_∞-approach for designing supplementary controller has limitation for the cancellation of the plant's poorly damped poles by the controller's zeros. In this case, supplementary controller designed with the standard H_∞-approach is unable to increase the damping of the lightly damped modes and thereby affect the performance and robustness of the system. Therefore, the bilinear transform has been used in the design to prevent the pole-zero cancellation of the poorly damped poles and to improve the control system performance. The model variations, because of the system operating condition variations, are treated as model uncertainties and are taken into consideration at the controller design stage. The magnitude of the current in the transmission line, I_m', is chosen as feedback signal. The performance of the controller has been evaluated extensively by non-linear simulation. The result have indicated that the designed controller can provide sufficient damping to the system under a wide range of operating conditions.

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FACTS devices such as high-speed phase shifter and variable series capacitor enable us to control active power flow in order to avoid thermal constraints on transmission lines, resulting in an increase of the network loadability and a reduction of production cost. However where to place these devices is an essential matter because their effects considerably depend on the locations. From an economic point of view, the investment cost must be taken into account as well as the reduction of the production cost. Therefore we propose to maximize return on investment (ROI) by searching not only the best location of FACTS devices but also the rating of each device. This problem is expressed as combinatorial optimization problem nested by nonlinear optimization problem. To solve this problem, tabu search incorporated with nonlinear programming method is used. And we discuss the remedial control of FACTS devices and simultaneous consideration of multiple load conditions. By considering remedial control, we can make better use of FACTS devices. Multiple load conditions bring us more appropriate solutions. Because the consideration makes our problem more difficult to solve, some efforts are necessary to be made. Numerical results are shown for a 3-generater 41-line model system and a 5-generator 42-line model sysytem.

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In this paper we describe STATCOM simulation of stabilizing low frequency oscillation of power system. We have chosen a STATCOM because it is a typical and basic FACTS device including voltage source converters (VSC), which is one of the kernel devices of FACTS. In the case of dynamic stability analysis, an effective value analysis is useful enough. But we have to be careful of transient phenomena such as overvoltage or overcurrent as well. So in order to estimate both of the dynamic stability and the transient phenomenon, the simulation has been carried out using real time digital simulator (RTDS). It performs instantaneous value analysis based on the algorithm similar to electromagnetic transients program (EMTP) in time step of about 70 microseconds for a long time such as minutes or hours.
As power system examples, 1 machine-infinite bus system is assumed. According to the simulation results, it is found out that the STATCOM is well controlled in the various conditions such as stable state, starting and stopping, fault near the equipment and stabilizing the power system.

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This paper proposes a novel transmission concept of Low Frequency AC (LFAC) transmission system, which is suitable for a long distance and high power cable transmission. An HVdc system is conventionally adopted for a long distance power cable transmission by Oil Filled or Solid cables. An XLPE cable shows preferable performance as a power cable in the conventional AC system for relatively short distance transmission. But it has difficulty of operation in an HVdc system, for space charges accumulate in the insulating dielectrics under high dc electric field stress, and which may cause breakdown. A low frequency ac system can avoid this difficulty as a conventional utility frequency ac system does. In the proposed LFAC system, frequency converters are installed at the sending and receiving terminals. Then, the presened system is expected to control the power flow of the interconnection as an HVdc does. This paper shows the advantages and disadvantages of the presented LFAC system and its basic control strategy. They are confirmed through digital computer simulations using a simplified model.

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The feeding transformer for electric railway converts three phase electric power to a pair of single phase electric power for driving electric cars. In some cases, however, not a pair of single phase power feeding but only a single phase power feeding is required. For example, a single phase power feeding is suitable for a car depot from the viewpoint of preventing voltage fluctuation at three phase voltage.
For this reason, authors have developed a small mode of single phase feeding power conditioner (SFC).
SFC is made of a pair of self-commutated inverters, which connect the two phases of secondary side of feeding transformer, coupled with a DC side capacitor.
Two inverters operate independently at Main-phase and Teaser in order to control reactive power. On the other hand, the power control circuit of SFC controls active power of Main-phase load and Teaser load. This means that the power control circuit delivers active power from the larger load circuit to the smaller one via the DC capacitor. Then SFC can keep balance of active power between Main-phase load and Teaser load.
This paper describes the principle of unbalanced voltage compensation using SFC and test results using a SFC model.

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In recent years, many dispersed generators such as solar cells, fuel cells and micro-gas-turbines etc. have a tendency to be installed in demand side. These generators are connected to distribution systems through power electronics facilities. It is well known that protection and control of distribution systems will become difficult if many dispersed generators are installed in demand side. Therefore, several ideas or concepts have been proposed in world wide to cope with the situation. The authors also have proposed a new concept of power delivery system named FRIENDS (F_-lexible, R_-eliable and _-ntelligent E_-lectrical EN_-ergy D_-elivery S_-ystem) where power electronic facilities and dispersed generators are effectively utilized. In this paper, the optimal network configuration method of FRIENDS is proposed. The problem is formulated as a mixed integer programming problem and solved by using tabu search algorithm and sensitivity analysis. Several numerical results are shown to demonstrate the validity of the method.

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This paper proposes a transient simulation model of pole-type distribution transformers for electromagnetic transient studies. The proposed model takes into account the following effects: (1) capacitance between windings and an enclosure and also between primary and secondary windings, (2) skin effects of winding conductors and an iron core, and (3) multiple resonance due to the combination of winding inductance and turn-to-turn capacitance. Thus, the model accurately reproduces the frequency characteristics of a pole-type distribution transformer in a wide range of frequency. The parameters of the model can easily be determined by frequency-characteristic measurements using an impedance analyzer. Because of the above capability, the proposed model enables the accurate evaluation of overvoltages on distribution lines including consumer-side overvoltages. In this paper, a 10-kVA pole-type distribution transformer is modeled, and the proposed model is validated by comparisons between simulated and laboratory-test results.

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Recently gas insulated switchgears (GIS) have been applied to many substations because the large capacity, the high reliability and the small size of power equipments are required. If a. break-down happens in GIS, it needs a lot of man's power and a long time to restore. So, the diagnosis of GIS to find partial discharge on the early stage before a break-down is necessary. In this paper, for realizing it, an identification for sources of partial discharge using the time domain wave shapes by the ultra high frequency method is studied. Our experiments are carried out using four kinds of artificial sources such as (1) needle on central conductor, (2) floating needle, (3) needle on insulating spacer and (4) free metal particles in a model GIS (300 kV). It is pointed out that an important relation between the peak value of rectified waves and the half-width depends on the source. As a result, the sources of partial discharge can be identified more clearly by the combination of both the relation and the conventional phase characteristics.

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To realize the commercial Molten Carbonate Fuel Cell (MCFC) plant, it is necessary to estimate the performance of MCFC during 40, 000 hours and improve the voltage decay rate to final target level (0.25%/1000 hours). We analyzed the factor of performance decay through operating bench-scale cells for 3, 000_??_10, 000 hours and obtained following results. The main factors of cell performance decay are identified to increase internal resistance and cathode reaction resistance. Suppose these resistances are expressed by Arrhenius type equation, the increase of resistances to operating time is caused by that of frequency factor in respective resistances, while the activation energy in respective resistances is appeared constant to operating time. The time dependence on increasing resistances is seemed to be linear (αt^1.0) since 3, 000 hours operation, and the increase rate of resistances would be rearranged by Arrhenius plot about operating temperature. As the above results, we propose a model for estimating MCFC performance with operating time.

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There are reports that lightning strikes to bulk transmission lines have caused serious accidents involving electrical apparatus, such as failures of electrical transmission. It is important to analyze the transient characteristics of grounding systems of electrical apparatus in order to understand all phases of such accidents and to apply the results to accident prevention. However, the transient characteristics have so far been difficult to evaluate. Therefore, a method that can easily be used in grounding systems under various conditions for computational analysis of transient grounding resistance (TGR) is highly desirable.
We have applied the first such method, which is based on the Finite Difference Time Domain method (FD-TD), to analysis of TGR. The characteristic features of this method are as follows:
(i) It can be used to simulate propagation phases of a transient electromagnetic field and enable their visualization.
(ii) Because the FD-TD method is a type of computational analysis method in the time domain, the calculated results can be more intuitively and easily understood than those of analysis method in frequency domain.
(iii) It can be used to precisely model grounding systems, although there are limitations depending on the computer resources available.
Using this method, the TGR at the foot of towers for 500 kV - 1, 000 kV transmission lines was calculated and compared with the measured results. The relationship between calculated TGR and conductivity of the ground agreed with the measured results.
This calculation method for TGR based on the FD-TD method is expected to provide a practical understanding of all phases of accidents and facilitate the rational design of grounding systems. It is also expected to contribute to the prevention of serious accidents involving electrical apparatus.

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The purpose of this study was to investigate the effect of ELF (Extremely Low Frequency) electric and magnetic fields (EMF) exposure on the EEG (Electroencephalograph) of human. In this study 4 healthy-male-volunteers were exposed for 30min to 60-Hz EMF at 30 V/cm emitted from the high voltage transformer. The electric field strength emitted from the aerial power line was defined to be below 30V/cm at 1 meter above the ground and the magnetic field strength was not defined, according to the provision of the 27 th article of “the Japanese technology-standard of the electric installation” established by the Ministry of International Trade and Industry. Prior to participation in the EMF exposure, each volunteer was given a complete description of the purpose and character of the investigation. The EEG of the volunteers were recorded based on the international 10-20 system before and after the EMF exposures and analyzed by the Fourier Transform and the Wavelet Transform. The result of this paper indicated that no direct effects on the frequency- spectra by the Fourier Transform and the dynamic-spectra by the Wavelet Transform of the EEG were seen before and after EMF exposures.

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This paper proposes a new control scheme for a decentralized generator excitation and governor control system in multi-machine power systems. The authors have developed the adaptive, multivariable optimal generator control systems which coordinates the excitation and governor control systems. They are based on Linear Quadratic Integral (LQI) control theory. They are confirmed to be effective for the improvement of power system stability compared with conventional excitation and governor control systems. However, it is impossible to design the system considering overall power system stability because it is usually designed using one machine infinite bus system model. The proposed scheme is designed using a model of each generator considering relation among other generators. Interactions among generators are modeled as equivalent disturbance from other generators. The order of the model is reduced using model reduction methods. Therefore, the decentralized control is realized by applying a disturbance rejection control based on H_∞ control theory. The performance of the proposed scheme is evaluated by simulations using two different multi-machine power system models. Simulation results indicate that the proposed scheme improves overall power system stability and can outperform the conventional controls including LQI control.

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It is reported that the gas turbines chain tripped out due to the big decline of the system frequency brought about a large-scale blackout in the foreign country. There is a need of the analysis of gas turbine dynamic behaviors during the large frequency disturbances from such a background. For this purpose a combined cycle plant model for power system dynamic simulation studies has been developed.
In this paper, the process physical relationships and model block diagrams are shown and the modeling method of multi shaft combined cycle plant is proposed. The dynamic behaviors of the plant in the system frequency change in addition to the static characteristic are considered. A comparative evaluations between field test results and simulation results by the model are described.

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Commutation of a semiconductor power converter connected to distribution network triggers a notching oscillation current in the high frequency region due to system resonance. While the high frequency oscillation causes the power-factor improvement capacitor to produce noise, it is difficult to locate the oscillation source by conventional measurement. We have developed methods for locating the oscillation source and evaluating the extent of the problem by simulating an LC equivalence circuit for the distribution network. This is achieved by utilizing a transfer function and impulse response calculation techniques based on the state-space method.

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In recent years, information technology has been developed and applied to various manufactural fields. In this paper, we present information technology application to the protection relay system in the electric power system.
We restructured the protection relay system as the decentralized network system by using Ethernet. we proposed the method of synchronization control and real time communication on Ethernet in order to achieve high accuracy of data sampling synchronization and high response speed. In performance test, it was confirmed that the proposed system could meet the requirement of the protection relay system.

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This paper presents an active power control by a dual-excited synchronous rotary condenser. A dualexcited synchronous machine has two field windings (d-and q-axis) which intersect perpendicularly each other. It is possible to adjust an active power by regulating each field voltages individually. The conventional stabilizing facilities such as static condensers and synchronous rotary condensers improve the stability of main network systems by adjusting a reactive power. On the other hand, an application of the dual-excited synchronous machine to a rotary condenser can improve the stability more effectively. In this paper, to begin with, experimental results show that the dual-excited synchronous rotary condenser is effective in improving the transient stability subjected to a large disturbance in a single machine infinite bus power system. Next, some case of a single transmission line fault in a double transmission system is demonstrated by computer simulations. Simulation results show that the proposed facility yields good dynamic performance.

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This paper presents a new methodology that can evaluate transfer capability of composite power systems from the adequacy point of view in power system planning stages. To evaluate practical load supplying capability, nonlinear optimization problems of maximum load supplying capability (MLSC) and economic load supplying capability (ELSC) are formulated and solved by nonlinear primal-dual interior point method. Physical constraints are considered in the optimization problems concerning the limits of bus voltage, line overloading, and real & reactive power generation. Also, an evaluation method of transfer capability is proposed based on the margins calculated by the MLSC and ELSC. Especially, to evaluate transfer capability effectively, simple indices such as expected MLSC, transfer capability margin, and power not supplied are respectively proposed by considering (N-1) line outage probability. Numerical results on IEEE RTS 24, IEEE 118, and IEEE 300 bus systems show that the proposed algorithm is effective and useful for power system planning stages.

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Number of photovoltaic power generators interconnected to the power network through inverter is rapidly increasing. Detection of the islanding condition taking place in these power generating systems through inverter is relatively simple as the inverter's function to maintain the frequency is low. When the synchronous generator is interconnected to the power network, the islanding condition is hardly detected since the system is highly capable of maintaining the frequency.
We have recently developed an islanding protection system based on the method named as “Q Control Mode Frequency Shift”, by which an active effect of positive feedback of frequency change is provided with based upon the changing rate of the power frequency (df/dt). It is also applicable to such a case where more than one generators are installed within the same power distribution network.
The protection system is combined with synchronous generator and tested. A good result was gained from the test, which has proved that the islanding condition was successfully detected within 3 sec. even when induction motor is contained in the load.

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In this paper, a parallel algorithm of tabu search (TS) is developed to handle capacitor placement in distribution systems. As a metaheuristic approach, TS is effective for solving combinatorial optimization problems. The advantage of meta-heuristics resides that they focus on solutions near a global minimum rather than a local one. The idea is important in saving cost in power system operation and planning. Capacitor placement in distribution systems means the problem that minimizes both network transmission losses and capacitor installation cost while satisfying the voltage and capacitor constraints. It is necessary to determine the location of capacitor installation and the number of capacitor banks. Namely, the problem results in a complicated combinatorial problem. To solve it, this paper proposes parallel tabu search (PTS) that considers the decomposition of the neighborhood and the multiplicity of tabu lengths. To demonstrate the effectiveness, the proposed method is tested in 9-node, 69-node and 345-node distribution systems in comparison with SA, GA and TS.

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A method of variable structure control (VSC) using the frequency criteria of H∞ control theory for sliding surface design is proposed in windmill power systems. Using quasi-linearization transform technique to the windmill power systems, we develop a type of equation which is suitable for H∞ control full information problem. By solving the Riccati equations arising in H∞ control a stable sliding surface is decided. Then we design the control law which consists of a linear control law and a nonlinear control law to drive the state variable into the sliding surface and thereafter maintain within this subspace. The capability of the proposed controller to damp out the oscillations of the power and angular velocity, and the robustness with respect to the system parameter variations and model errors are evaluated in the simulation study.

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