This paper proposes an application of Genetic Algorithm (GA) to contingency screening in power systems. The contingency selected by the GA bused screening method is the double line outage which has the risk of causing transient instability. Generally, the contingency screening problem including multiple outage can be interpreted as the combinatorial optimization one for searching the combination of single outages which makes the system insecure. Therefore, GA which is one of the probabilistic search for combinatorial problems, is applicable for such contingency screening problem. In the GA based contingency screening method, a double line outage is represented as a chromosome. The fitness of chromosome for environment is defined by using transient energy function of power systems. The new procedure for avoiding the loss of important outage during contingency screening is developed and embedded in the proposed method by using the theorem of schema for GA. The validity of the proposed method is confirmed by applying to 6-machine 30-bus 40-line system. The result shows that the GA based contingency screening has the potential for practical use.

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Considering the fact that most problems in distribution lines are ground faults, we think that the technology to distinguish the causes in the distribution lines will be very useful in preventing faults beforehand or, at least finding any problems at an early stage. We analysed the waveforms of ground faults which were collected from data concerning problems in the districution lines and ground fault experiment. We then studied the possibility of technology which could predict classified groups drawn from the scale of Io (the waveform of ground fault's current) and Vo (the waveform of ground fault's voltage), and both of them in the ground faults. The results demonstrated that Io could be classified into three groups, that is, leaking ground faults are sine curve shaped, gap discharge ground faults are triangular and intermittent discharge ground faults are needle shaped. Also we calculated simulated equivalent impedance of the causes of ground faults by EMTP. Furthermore, we investigated the influence coused by the condition of the distribution lines. With these results, we proposed a technique which could predict the cause of problems in ground faults.

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Ablation arcs in a cylindrical tube which has a pressure chamber at one end of it are investigated experimen-tally and theoretically. The experimental data are interpreted by an arc model consisting of four processes which describes the relationship among the pressure distribution in the tube and gas flow in the tube and the pressure in the pressure chamber.
This paper presents theoretical analyses of the gas flow in the tube with symmetrical pressure distribution and of the compressed gas in the pressure chamber. Quasi-steady-state, one-dimensional theoretical solutions are shown, which describe the distribution of temperature, pressure, velocity, density, Mach number and specific enthalpy of the gas in the tube. Theoretical equations are shown also, which describe the time dependence of temperature, pressure and density of the gas in the pressure chamber.
Validity of the solutions describing the states of gas in the tube are shown by the comparison of studies of several authors. Validity of the equations describing the states of gas in the pressure chamber are shown by the comparison of calculated and measured pressure in the pressure chamber. This study revealed the essential features of gas flow within ablation arcs in the cylindrical tube.

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With decrease of the ratio of lightning impulse withstand voltage (LIWV) to rated power frequency voltage (AC) of power system, concerns are directed to the long term deterioration of the insulating spacer composing GIS by higher power frequency stress. An aging test of epoxy insulating spacer is carried out under rated power frequency voltage and 2, 300 Hz voltage which is evaluated to have the equivalency of frequency acceleration to investigate the long term deterioration characteristics of the insulating spacer. The test samples of the insulating spacer are divided into several groups and the samples of the same group are stressed at the same electric stress up to 22 kV_rms, /mm.
As the result, it is found that the reduction of lightning impulse breakdown voltage after aging is more considerable than the reduction of AC breakdown voltage. From these results, it is estimated that power frequency stress level which deteriorate scarcely the insulating spacer is about 12 kV_rms/mm.

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A series of studies about an ablation arc burning in an ablative capillary tube which has a pressure chamber at one end of it, has been reported recently. The processes of the gas flow have been described by a model, and the process that the flow stagnation point moves from the center of the tube to the tube end of the pressure chamber side and the gas flow becomes asymmetrical, is called second process. In this paper, the ther-modynamical properties of the gas flow in the tube corresponding to the second process are investigated theoretically and experimentally. The formulas describing the thermodynamical properties in the tube and in the pressure chamber are derived. The relation between the movement of stagnation point and the pressure in the pressure chamber is presented also. The experimental information including the arc voltage, current, ablated mass and the tube structure are used to obtain the simplifying formulas. A comparison between the measured pressure and the calculated pressure by the simplifying formulas in the pressure chamber indicates that the theoretical model can adequately describe the pressure raising in the pressure chamber. Illustrative analytical and numerical solutions of the equations are also presented. The experimental results support the theoretical model.

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In Japan, large and small power systems were interconnected over time and thus ultimately grew into large-scale national power system. A highly important stability problems arising from large-scale power system. interconnections is low-frequency oscillation (about 0.3Hz to 0.5Hz) of interconnected systems. The ΔP-type PSS has been applied to all generators in trunk power systems as a measure to improve the damping of local mode oscillation (about 1Hz) . However, it is difficult for this PSS to improve the damping of low-frequency oscillation because of the hardware and the design of PSS control constants. It has therefore become necessary to develop a new two-input PSS. This paper explains the development of this two-input PSS and the study of a low-frequency oscillation model. The abstract of the paper can be summerised as followes:
(1) The effect of control over low-freqency oscillation is affected by the kinds of PSS detecting signals. The Δω-type or Δf-type detecting signals used for lead phase compensation are suitable for this purpose.
(2) It is possible to cause low-frequency oscillation studies in a one-machine infinte-bus power system model with medium loads.
(3) According to the simulation of a three-machine and an actual large power system models, dynamic stability was largely increased by this two-input PSS used for generators.

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To scale up the capacity of a SMES for a practical application, it should be necessary to adopt a high voltage system, a large current system or a module type system. The first system is difficult because of the very low withstanding voltage of a supercon-ducting coil and second one also leads difficulties such as multiple connections of many units of convertors at dc side and large current conductors of superconducting coil. The third system which is composed of some numbers of modules with small scale convertor units and element coils might be a solution of above difficulties.
In this paper, based on conceptual designs of the SMES system with 350kWh and 550MVA, features of the module type SMES are discussed by comparison between systems with different numbers of modules. Discussions are made on technical points as well as on economical points. The result elucidates features of this type SMES. Then to confirm operations of the module type SMES, the experimental system of two module units with a GTO convertor and two superconducting coils is constructed. Experimental results show that the module type system can be operated without any troubles in case of normal operation and also in case of energy transfer between two modules.

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The size and complexity of power systems increases greatly and the operating points of power system are liable to be close to the limitation of capacity of equipments in power systems. Small signal instability may occur under these situations. The eigen values obtained from a set of the state equations representing dynamics of power systems are useful for stability check.
The authors developed two programs computing eigen values: one is based on the S-method ^[1] and the other Iterative-inverse approach^{[2, 3]} (IIA method). In order to reduce computation time, elements are stored in Linked-list form in which the structure of the list is formed so that the fill-in data can be stored with less computation time and the selection of elements used for computation can be performed efficiently. In order to check stability when the operating condition is changed gradually, the computations of eigen values under these changed conditions will be required. Several number of eigen values near the instable states can be calculated by using the program based on S-method. Then these values are used for initial values and new eigen values under the changed operating condition are obtained by using the program based on IIA method.

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Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analy-sis and (2) time-dependent l-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u-a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u-a are unstable in the diagonal channel with fixed loading current and the u+a wave becomes unstable in the diagonal channel with fixed electrode current.
Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growing of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u+a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of channel, being consistent with the linearized analysis which indicates that the u-a and u waves are unstable.

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A new Transient Stability Controller system (TSC) based on on-line transient stability calculation has been developed. The TSC system prevents the power system from wide-area blackout by shedding generators optimally when a serious fault occurs. This system consists of a central processing unit(TSC-P), and four local units for fault detection(TSC-C), and seventeen units for generator shedding(TSC-T). The TSC-P selects optimal generators to be shed for stabilization based on on-line transient stability calculation for contingencies at 500kV lines and buses every five minutes. The results are transmitted to the TSC-Cs periodically. Should any fault occur, only one TSC-C will detect the fault occurrence and send control signals to the TSC-Ts which actually generate shedding signals. To realize the TSC system, essential are fast stability evaluation method for a large number of contingencies and effective selection method of optimal generators to be shed for stabilization.
This paper presents total algorithms applied in the TSC-P, the results of algorithm verification tests using a prototype system combined with a large-scale analog simulator, and the characteristics of the actual system.

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In recent power systems in Japan, in some special districts, extremely high parallel capacitances have been connected, such as high capacity shunt capacitor banks for the purpose of voltage stability enhancement and EHV cables transmitting powers to large cities. As for short-circuit breaking currents for circuit-breakers, till now a days, only power frequency and dc components, both of which are supplied from the power sources, have been considered. Regarding the transient components due to the discharges of the parallel capacitances, because of relatively high frequencies and high damping rates, little attention has been paid. But due to the increase of the parallel capacitance values resulting higher amplitude and lower frequencies of the transient components, and also introducing facilities with low loss rates, the effect of the transient compo-nents on circuit-breakers' performances may not be possible to be disregarded
Introducing a model power system covering the conditions of today and near future, and applying EMTP, with reviewing the simulation accuracy comparing with field measuring data, some calculations have been performed. The results show the possibilities of cer-tain effect on circuit-breaker performances in the, especially, thermal mode of quench-ing phenomena such as breakings of short-line fault currents.

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