The voltage stability problem, which is caused by the heavy loading of long-distance transmission lines and the insufficient local reactive power supply, has become one of the most important problems to be solved urgently in a modern bulk power system.
Earlier, it was made clear that the voltage instability phenomena of the bulk power system under heavily loaded conditions are closely related to multiple load flow solutions which are caused by the nonlinearity of load flow equations. In addition, the dynamic characteristics of loads of constant power type play an important role for this unstable phenomenon. Since the dynamic load characteristics are not known correctly, it is desired to develop an effective voltage stability index and remedial measures to prevent the voltage collapse taking into account a static structure of multiple load flow solutions.
A new static voltage stability index proposed in this paper indicates the extent to which the current operating point is close to the static voltage stability limit, or the limit of total load demand (active power) of the whole power system from a static viewpoint. The proposed index is defined on the basis of multiple load flow solutions and it physically means the first order approximation of a stability margin of total load demand. It is possible to calculate it on the on-line basis by using operating conditions which are always changing with time.

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Recently, several phenomena of voltage collapse at the load end of electric power systems have been reported at home and abroad, and there have been various papers explainning this phenomena and method of avoiding this voltage collapse.
Chubu Electric Power Co., and Hitachi Ltd. developed real system of 1 MJ Superconductive Magnetic Energy Storage System (SMES) in 1989, and confirmed several its power system stabilizing effects connecting this system to the simulated power system model.
In this paper, we present the results of the P-V characteristics measured at the point of load end using resistance and induction motor and present the results of the effects of SMES control when the voltage becoming low level or voltage collapse occurred.

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The previous generator excitation control system is based on AVR control of generator terminal voltage. This system can't accommodate reactive power up to the facility limit even when the power system voltage decreases to the limit for stable operation. We attempted to develop advanced excitation control system (PSVR) to achieve higher constant sending end voltage of power station. We intended to apply the system to the generator connected to a 500kV system which contributes most effectively to the voltage stability of a bulk power transmission system. This PSVR produces higher control gains than the AVR, the following functions were adopted: (1) AVR gain reduction circuit, (2) phase compensation circuit, and (3) damping improvement by enlarging the limiter of the PSS. In addition, various functions were provided. These include voltage slope characteristics to balance the reactive power of adjacent generators and PSVR output and terminal voltage limiter to stabilize the generator operation. Previously to an application to a real system, a transient response test was performed by combining PSVR and generator simulator to verify the damping improvement and stability of the voltage control.

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On-line Monitoring of voltage stability conditions is a new requirement for the energy management systems of the electric power industry. Preferred by the utility engineers and dispatchers is an index which represents explicitly the margins to a voltage stability limit (collapse point) expressed in a physical unit ordinarily used. For example, such indices are the system load and voltage voltage-stability-margins (SVVSM) between the present operating point and a voltage collapse point. However, it takes long computer time to accurately calculate the voltage collapse point by the conventional method, because many mutltiple load flow solutions are required.
This paper presents a new algorithm to directly, exactly, and fast calculate the voltage stability limit. The algorithm uses the load flow equations and the explicit expressions of the voltage collapse conditions which are derived from the equal root conditions of the load flow equations. The equal root conditions are expressed as dR/dV=0, where R is active or reactive power node injection, and V is node voltage magnitude. A solution program by the proposed method is developed by simply modifying the conventional N-R load flow program, and is not numerically bothered by singular Jacobians. The proposed algorithm is verified through calculating the voltage stability limit of a 176 node power system.

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The transmission length and capacity of recent power systems grow longer and larger day by day. At their receiving end, constant power loads with low power factor and large condenser capacity are installed. This thesis shows new equations which physically specify system and load conditions that cause voltage instability. On the basis of the equations, voltage stability limit curves can be drawn easily, taking account of system and load coditions such as transmission distance, transmission power, phase angle difference, percentage voltage drop, condenser capacity at receiving end, load factor and load voltage characteristics. From the limit curves, voltage stability indexes including voltage stability power angle limit and margin ratio of voltage ragulation, are obtained. In addition, the generation area of voltage instability is clarified by using the equations. These considerations have been verified with the experiments we conducted. Thus, the theory discussed in this thesis is believed to make it easy to detect voltage instability and prevent unstable voltage situations.

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The voltage stability problems are becoming increasingly important in contemporary power systems. In the preventive control stage, the behaviour of a power system can be successfully represented by static P-V curves and the voltage instability is expected to take place at the critical load flow point of the power system. This paper defines several concepts such as Critical Load-Flow Manifold (CLM). A fact is found that the unit vector computed from the singularity of the load flow Jacobian matrix is nothing but the unit normal vector of the correspnding CLM. Utilizing the geometrical property of the CLM, the closest critical load flow point is computed, and moreover, a suboptimal preventive control method is proposed. The proposed suboptimal preventive control enables us to know the most effective countermeasures for prevention of anticipated voltage collapse under the assumption that the future load demand increase is known. The proposed method determines an appropriate control action taking into account the operating constraints and equality constraints about the direction of the demand increase by using SUMT. A numerical study is carried out in order to confirm validity of the proposed method.

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In order to prevent the voltage collapse on bulk power system considered to be originated by long distance and heavily loaded transmission line between generating site and load center accompanied with the increase of voltage-independent type of load, it is needed to clarify the dynamic behavioures of collapse and recovery process of system voltage, and to establish a suitable guide for system operation against the voltage collapse possibility.
This report describes the newly developed calculation method to clarify the phenomena which gives not only the simulation of dynamic behavioures of system voltage but also the evaluation of load margin for any given condition of power system as to the basic index to keep the system voltage stable.

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The problem of distribution system expansion planning is ordinarily formulated as a mixed integer programming (MIP) problem. So, it is difficult to solve a large scale problem accurately. So as to solve the problem approximately, an algorithm which incorporates the merit of the MIP model as well as those of the branch exchange model, has been proposed. However, this method calculates the pivot operation of the simplex tableau in every branch exchange operation, and its computation time is huge.
In this paper, the authors propose a new fast approximate solution algorithm which is based on the above method. The algorithm is improved by applying the fact that every changed element of the simplex tableau caused by the pivot operation can be calculated quickly through electrical circuit calculation instead of through the pivot operation ; that is, the branch exchange sensitivity for determining which branch should be deleted or added, can be easily calculated by the current injection to appropriate nodes. The calculation speed of the proposed algorithm has been improved by the order of 10³ compared to the existing method. The validity and effectiveness of the proposed algorithm are demonstrated by a 59 nodes 69 branches numerical example system.

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In a molded-case circuit breaker (MCCB), an arc column is not always kept to burn inside deion plates but several times is shorten in the narrow area between electrodes. This unstable arc behavior brings several sudden drops in the arc voltage and stops for a time the current limiting process. In this paper, three different methods are proposed to control the unstable arc motion in the MCCB and their effects on the current limiting performance of the MCCB is experimentally discussed.
An arc-runner is mounted on the moving contact to keep the arc column inside all deion plates. A pertition wall is inserted between arc chamber and mechanical operation section to control high temperature air flow. The moving contact is coated with epoxy resin to prevent the shortcut of the arc column. It is found out from experiments that they are useful to repress the unstable arc motion and to improve the current limiting performance of the MCCB. For example, the arcing time is reduced to 80% of that in the normal MCCB by each method.

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This paper reports the observational result on characteristics of lightning stroke current at the coastal area of the Sea of Japan in winter season from December 1978 to March 1987. It was revealed that it had a lot of different features from results reported by others.
Main results are as follows.
(1) The frequency distribution for the peak value of lightning stroke current are similar to those of previous reports.
(2) The ratio of the lightning strokes of positive polarity to the negative polarity is 1:2.
(3) The duration of wave-front of lightning stroke current for positive polarity spreads in the range from several microseconds to several milliseconds.
(4) Electrical charge of lightning strokes varies from 0.1 coulomb to several thousand coulombs

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Large number of researches are done about damping and synchronizing torque of synchronous generator. However, these researches require accurate model and data of the power system. Therefore when unexpected changes occur in the power system, damping and synchronizing torque derived from these researches become inaccurate. Loss of data will also rises same problems. Online monitoring of damping and synchronizing torque is worth to do to avoid situation mentioned above especially in the large scale power system. Online monitoring technique is also useful for autonomous controls of the power system apparatuses.
In this paper, discrete type algorithms to identify synchronizing and damping power of generator in the power system using least mean square error method are presented. Easily observable data, rotor frequency and active power output of generator, are used as input data for identification to avoid difficulty to adapt the algorithms to the generator in use.
Experiments using microcomputer and micromachine power system is taken to show the validity of algorithm. Result of simulation and experiments using one generator and finite bus power system show validity of algorithm and feasibility to install actual system.

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The MHD generator must be integrated into the combined MHD and steam-turbin generation system which consists as topping cycle and steam-turbine system as bottoming cycle. The dc power generated with MHD generator must be transferred into ac power grid through inverter. The present paper treats the electrodynamical aspect of the combined MHD-synchronous generators system.
Some experimental tests and numerical analyses are reported, which studied behavior of MHD generator linked to power transmission line through inverters. Overall electrical behavior of the total binary combined system, however, has not been studied. In the present study, the MHD generator is supersonic or subsonic diagonal type of about 10MW output and is linked to the transmission line by the line-commutated inverter. The synchronous generator is two-poles sylindrical type of 30MW output, while the thermal input is 110MW.
Numerical results show that the present combined system can be stably operated with the rated conditions. When various faults occur in inverter or transmission line, the subsonic and supersonic MHD generators behave differently each other, whereas the transmission line behaves much the same. Some interaction between MHD and Synchronous generators is found. The shoutdowns of the MHD generator and/or faulted line is effective as protective counterplan of faults.

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Energy Problems in the future are full of uncertainties, especially with regard to fuel prices, environmental problems and energy demand. In this paper two types of novel energy plants and a novel energy system are proposed to deal with these uncertainties. The first type can utilize multiple kinds of fossil fuels and economically remove CO₂. The second can produce multiple kinds of final energy so as to respond to fluctuations in energy demand. Specifically, the fuel costs of the first type have been shown to be more economical when the prices of different fuels are closer, less correlated and uncertainties are larger. Characteristics of a novel energy system (A Flexibly Integrated Energy System ; FIES), which includes novel energy plants as described above, has been investigated with a linear programming model. A reference system has also been represented which behaves similarly to the present energy system for comparison. In model analysis we have focused on the greenhouse problem and compared the performances of these two models assuming restrictions on CO₂ emissions. Computational results have shown that CO₂ emissions can be suppressed more economically and efficiently in FIES than in the reference system if it is combined with CO₂ removal systems.

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Electric power is in great demand, and it is transmitted to distant places for consumers with high efficiency, where insulators are used to transmission and distribution line for insulation.
Insulators which had been contaminated by salt particles caused flashovers on this surface under high voltage in humid climate and light rain.
Exposure tests of insulators in Okinawa Island have been carried out with exposure period ranging over 1 month, 3 months, a half year and as often as necessary since about 1979. This report concerns on salt contamination of insulator surfaces by typhoons in Okinawa Island. A summary of the results obtained from the exposure tests are:
(1) Maximum salt contamination is caused almost all by typhoons.
(2) Mountains form shelters against salt contamination in wind direction.
(3) Precipitation during a typhoon has a great influence on salt contamination of insulator surfaces.

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