We have proposed the double rod type jumper horns in strain assemblles with pipe-jumpers for 500kV transmission lines, the structure of which are very simple. It can be estimated that no corona discharge appears on the horns under the line voltage of 525kV. The arc behavior on the double rod type jumper horns is similar to that on the single rod type horns. The arc can be held stably for 60ms against strong wind (10m/s). The stable duration increases more than 300ms under the windless condition. Therefore the horns have been adopted in practical use.

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Recently, research and inverstigation of multi-lightning strokes have been advanced. Making good use of their information, we have studied the interruption performance of SF₆ gas circuit breaker (GCB) on multi-lightning strokes.
In the case of GCB interruption on the trouble by multi-lightning strokes, we illustrate the phenomena occurring in GCB against time, and show the countermove, test method, test equipment and test result on model GCB in the case of most severe phenomenon of them, which is that lightning voltage is imposed on GCB just after interruption.

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SF₆ Gas Insulated Switchgear (GIS) so constructed that the main Conductive Parts are totally enclosed in metal enclosures which are filled with compressed SF₆ gas. Present study examines a method for detection of the abnormal overheating caused by poor conductivity under the power supply conditions and for prevention previously of the internal faults leading to arcing which may be occured on such conductive parts.
In this paper, we propose the gas monitoring method which can permit the detection of not only the overheating conditions but also the events of gas leakage and the internal faults.

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In order to investigate a fault locating method for cable lines, we measured temperature rise at the shield near each fault point by artifical fault tests. We also examined the methods of how to attach the optical fiber type temperature sensors. The results can be summarized as follows:
(1) When the fault curent is 400A, the shield temperature rise at the fault point can be appraised by the mean value during 30 seconds after the fault initiation. The temperature rise value are several tens degrees. Therefore, we considered that there was a good possibility of locating the fault point at a moment by optical fiber type temperature sensors.
(2) Methods of attaching optical fiber type temperature sensors to a cable can be proposed as follows.
•In case that the shields are soft-copper wires, optical fiber type temperature sensors are necessary in axisymmetrically located two lines, and are inserted in the gap between soft-copper wires at a winding pitch of 27cm.
•In case that the shields are soft-copper tapes, optical fiber type temperature sensors are necessary also in axisymmetrically located two lines, and are wound around the soft-copper tapes at a winding pitch of 40cm.

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For the preventive maintenance of overhead power transmission lines, it is important to predict the possibility of disasters due to snow accretion. The authors propose a new method to estimate the possibility of these disasters for the localized areas covering over Kanto Plain. This method uses neural networks with the input data of ambient temperature, precipitation, wind velocity, and the product of precipitation and wind velocity as time series for 6 hours for each local area meshed by 6km squares. Within Tokyo Electric Power Co., 155 records of the disaster experiences and their meteorological conditions in the recent 13 years are first investigated in detail. Then the relationship between the disasters and the meteorological conditions is analyzed by neural networks. As a result, it was clarified that the neural networks can accurately classify the meteorological conditions by learning the disaster experiences. The simulation results show that the performance of this method exceeds that of conventional method using multiple regression, and that the method can estimate the possibility and the severity of snow disasters with the accuracy of 87% and 76%, respectively.

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Recently large capacity power stations have been built far from load center with long distance transmission lines. Therefore, if a fault occurs at the line, generators in the large capacity power station may lose synchronism from the remaining generators ⁽¹⁾⁽³⁾. To prevent an extension of loss of synchronism to other generators, fast shedding of some generators is effective measures.
Following methods were proposed so far. One⁽³⁾ is based on energy function approach. The other⁽²⁾ estimates and predicts the relative swing among generators using data measured on-line at each generator and sheds some generators for stabilization. Therefore this method requires a large communication network for an exchange of data between power stations. This paper presents new stabilizing method and newly developed stabilizing control system which does not require a large communication network because it utilizes generator output, voltage and current measured on-line in the vicinity of the large capacity power station. Using these measured data, the system estimates and predicts relative swing between generators in the large capacity power station and the remaining generators. Finally the number of generators to be shed for stabilization is decided and shedding is performed. Configuration and characteristics of the developed stabilizing control system are shown. Validity of this method is confirmed by simulation and testing using an artificial power system.

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This paper discusses the preventive controls of the generator outputs to improve security in the decentralized power system. Preventive controls of the power system can improve security level. However the preventive control requires too many computation time because of too many considerable faults in the power system. We can consider multiarea decentralization to reduce computation time of the power flow calculation. We assume that the effects of disturbances in the external systems are relatively smaller than the effects of disturbances in the study area. Linearized sensitivity analysis is used to evaluate the effects of the external systems to reduce computation time. Linear programming is used to determine the control signals of generators considering the incremental cost of generators. The NewEngland 38 buses system is used as an example system to check the validity of algorithm in this paper. The calculations of the example system show the satisfactory results.

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Power system analysis is the basis of operation and planning. Since power system is very large and complex, however, it takes long computation time for the analysis. It is desired to develop a fast method especially for transient stability analysis. In this paper, a parallel algorithm for sparse matrix factorization, forward substitution, and backward substitution are discussed. The algorithm is made operational on the actual transputer network. The computation time using the algorithm is measured and compared with that of the ordinary (single processor) algorithm. Finally, the parallel transient stability program is developed and evaluated.

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Voltage instability is now under intensive study in Japan. It is very important to make clear the mechanisms of voltage collapse for the purpose of establishing the countermeasures.
Voltage instability depends greatly on the dynamic characteristics of load and dynamic digital simulations are mainly adopted to analyze the dynamic phenomena of voltage collapse. In order to analyze the dynamic voltage stability, however, eigenvalue method has been already proposed by the authors, which requires a long computing time. In this paper, a simple method using “short-term P-Vcurves” is presented. It make it possible to show the power supply capability at any load nodes.
A radial power system with 3 induction motors is analyzed and stability transition during voltage collapse is made clear. This phenomenon is useful for explaining the cascaded voltage collapse well.

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On the methanol fuel cell which uses methanol as fuel directly, the important problem to keep high efficient and stable operation is to exhaust water generated in air electrode appropriately and to keep the best water balance without over wetting or drying in air electrode. Therefore, the theoretical equations were introduced to consider the relation between generated water by electrochemical reaction and exhausted water by the flowing air along the air flow direction.
By using these equations, simulation on various conditions of operation and structure were made. As a result, the countermeasure to keep best water balance was found as follows.
(1) The increasing of water reservation in air electrode with thicker electrode and the increasing of hydrophilic ability by addition of electrolyte were effective and applicable methods for practical use.
(2) The reduction of water permeability in electorolyte layer is effective, which was attained by the system with solid polymer electrolyte and without sulfuric acid.
(3) Larger air chamber depth and appropriate humidity control of inlet air are effective. However, these methods are limited to use because of the increasing of size and flow-rate.

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When a single-phase load is applied to a three phase power system, negative-phase-sequence current flows in the circuit. The negative-phase-sequence current brings about local heating on the surface of generator rotor, which connected to the circuit. In the single-phase AC railroad system, Scott-connected transformers are used in order to reduce the power unbalance among three phases and also negative-phase-sequence current.
Recently, regenerative braking system has come to be applied to electric rolling-stocks. But in this system, when one phase in the Scott-connected transformer feeds power, and another phase in the Scott-connected transformer receives power from regenerative braking system, power unbalance among three phases increases and negative-phase-sequence current also increases.
This paper describes a newly developed static negative-phase-sequence current compensator which is applied to rotary frequency converters (50/60Hz) feeding 60Hz electric power to the Tokaido Shinkansen in 50Hz power system area.
Basic principle of compensation of negative-phase-sequence current is generating negative-phase-sequence current in reverse phase to the negative-phase-sequence current to be compensated using a fixed capacitor and a thyristor controlled reactor.
In this paper, the principle of negative-phase-sequence current compensation, characteristics of the compensation circuit and digital simulation study are described.

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The objective of the present paper is to examine effects of external circuits including the Master/Slave current controller and the side-by-side power suffling circuit on the coal-fired diagonal channel, which was designed for a pilot-plant. Numerical analysis are carried out, where time-dependent 1-D gas dynamic equations are solved together with 2-D electrical equivalent circuit method. It is shown that simple current controller can be operated with much smaller electrical stress than power shuffler although the power shuffler gives better performance to a small extent. The external circuit can extend workable range of channel.

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This paper presents experimental studies and analytic considerations on water transport and accumulation phenomena in an electrode during air electrode performance testing for phosphoric acid fuel cells.
Humidity of exhausted air and its response time are measured with varying air flow rate, current density, temperature and concentration of phosphoric acid. Quantity of water vapour exhausted from the electrode at a no load condition depends on concentration of phosphoric acid and test temperature. When current flows, a large amount of water generated by the electrochemical reaction is added to the exhausted water at the no load condition, while a small amount of water seems to diffuse to the oposite side and dilute the phosphoric acid. Accumulated water in the electrode is estimated by integrating exhausted water after current shutdown. It increases with current density and decreases with air flow rate.
These phenomena can be explained by analyzing an equivalent circuit model in which water transport and accumulation in the electrode is proportional to water vapour pressure.

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