There is a possibility that a low-frequency oscillation gets unstable due to autoparametric resonance in a longitudinal power system. This paper clarifies that the physical cause of the resonance is load. First, we superimpose two oscillation modes, and examine changes in voltage and consumed power at load buses. The changes in comsumed power almost directly lead to changes in generator output, and change the force applied to the low-frequency oscillation. Next, we show through simulations and the Mathieu diagram that the strength of the resonance conspicuously changes with quantity of load. Furthermore, the quantity of allowable load is inversely proportional to the length of system, and does not depends on the number of generators. Namely, the length of system automatically determines the quantity of allowable load. The length of system is essentially an electrical distance related with reactance of transmission line. Lastly, we show that construction of a new system with same capacity as existing one is equivalent to electrically halving its length. On the other hand, if we divide a system into two short subsystems, then each subsystem can carry double load, and the system can carry quadruple load in all.

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This paper relates to the forecasting method of the electric power demands (kWh & kW) of a region, approached by not only time series analysis but economic and social indexes. Those indexes, based on historical statistics such as census and establishment statistics, are rearranged from an administrative division to a managerial division of the electric power company, and applied as fundamental information for forecast-ing the area's kWh and also sales promotion.
This method of forecasting the area's kWh is based on the concept that area's kWh is strongly connected with the population ; their lifestyle and their activity within the region.
In the paper, the framework of the computational model system and forecast result are discussed. The population, number of households and their members, and number of employed persons, are all evaluated.
The forecasting method of the area's population proposed here is based on the concept that the transition of population consists of both natural growth and immigration. By estimating both factors, the future area's population can be easily forecasted.
The information of whether the population is increasing or decreasing is useful for forecasting the region's kWh and required sales promotion.

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As the method to reduce the induced voltage, the shielded cable with aluminum sheath and iron tape has been mainly used. In order to increase screening effect of the shielded cable, the grounding resistance at the terminal of the cable must be low. To obtain the low grounding resistance, the method using the buried straight horizontal wire with vertical ground rod at the terminal of the shielded cable is considered. Then, we carried out the theoretical analysis of screening effect for the shielded cable by buried straight horizontal wire laid parallel to the power line.
Now then, because of restriction of the site to lay the buried straight horizontal wire, it is often laid obliquely for the power line. Then, in this paper, the analysis method of screening effect by the wire laid obliquely for the power line and knowledges obtained from calculated results are clarified. Further, we propose the approximate calculation method of the shielding factor, which is useful in the practical design for grounding resistance.

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A new method which produces electric energy by utilizing the density difference of water, by means of a “chimney effect”, is proposed. Density difference of water occurs in two ways, namely differences of water temperature and consistency of suitable materials such as salt. For instance hot water made by solar energy is pointed out as an example of the former, while fresh water of river versus sea water and sea water versus concentrated salt water may account for the latter.
This paper deals with the above three cases in the practical scale. The analysis estimates that the proposed method generates energy of several hundreds or more, ten thousands and millions kW in the respective cases. The amount of extracted energy in the third case is ompared with those of usual electric power stations by nuclear energy. The method is considered as a kind of the so-called renewable energy conversion systems which is free of CU₂, high energy density and controllable.

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This paper shows a method, in the Weibull-power model, of estimating the parameters and the residual lifetime of insulation which had been under the specified service voltage stress for a long period. The deterioration model is assumed to include a threshold stress below which a breakdown will not occur. When a presumptive threshold is higher than the service voltage stress, the insulation will not deteriorate at all. In such a case, a hypothesis test which determines whether the threshold is higher than the service stress is shown ; the test can also support the existence of a strictly positive threshold. These methods will be applicable to the residual lifetime analysis for cross-linked polyethylene insulated cables which had been used for decades. Some simulated examples are demonstrated.

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This paper presents a new algorithm of the interior point quadratic programming which can solve power system optimization problems with profoundly less computational efforts. The proposed algorithm has the following two special features. First, it is based on the path-following interior point algorithm, the search direction of which is taken as Newton direction, thus having quadratic convergence. In the second place, it solves directly a symmetric indefinite system instead of reducing it to the usual system with a positive-definite matrix. Under this artifice, the algorithm avoids the formation of [ADA^T] and generates fewer fill-ins than the case of factorizing the positive definite system matrix for large scale systems, realizing its impressive speed-up. Since the formula of the interior point method have been deduced more generally, the proposed algorithm can start from either a feasible (interior point) or an infeasible point (non-interior point).
Numerical results on the IEEE test systems and a Japanese 344 bus system (2100 variables, 2088 equality constraints and 1400 inequality constraints) have verified that the proposed algorithm possesses enough robustness and needs significantly less solution time compared with already reported applications of the interior point method.

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Optimal power flow (OPF) is to minimize a certain objective function such as generation cost or transmission loss while satisfying various constraints posed from system operations and hence can be a powerful tool for making up reasonable operation plans. Since the advent of DC transmissions in mid 1950's, it has been used as a useful substitute of an ac transmission in cases of long distance transmission, transmission through marine cables, frequency changers, ac-dc parallel transmission, etc. Therefore, it is highly needed to develop an efficient OPF algorithm into which dc transmission systems can be integrated without significant modifications of an OPF program for ac systems.
This paper presents an extension of the current Newton OPF program, which directly solves the Kuhn-Tucker conditions and is regarded as most efficient and robust at present, so that the OPF can incorporate dc transmission systems. The control schemes of a dcsystems have been satisfactorily integrated into the developed OPF algorithm. Numerical experiments on a test system have verified the effectiveness of the proposed algorithm.

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Recently, the operation of electric power systems has become more difficult because the peak demand load is increasing continuously and also the daily load factor is worsening. Furthermore, global environmental issues are required in electric power systems. One countermeasure to overcome these problems is a study on the operation methods of a new electric power system that includes Dispersed Energy Storage (DES) Systems.
This paper deals with the introduction evaluation methods of the DES systems, especially based on the Secondary Battery Energy Storage System. Because DES systems are costly, it is important that their introduction evaluation is performed in a synthetical and quantitative fashion. The direct and indirect benefits of DES systems are classified and analyzed on utility and customer sides for cases where DES systems are introduced to distribution systems. On the utility side, the multiple functions of DES systems such as load leveling, uninterruptible power supply and effective utilization of distribution facilities are evaluated by quantitative methods, which are the successive approximation solution considering both the optimal generation mix and the optimal operation of DES systems, the interruption cost and present worth analysis, respectively. In addition, on the customer side, the forward dynamic programming approach related to the hourly pricing policies is presented. From the simulation results of the methods presented, it is verified that Secondary Battery Energy Storage Systems can be commercialized and introduced to the utility and customer in the near future.

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Since an adjustable-speed generator/motor (ASGM) is excited by AC voltage fed by a quick-response cyclo-converter, a rotating speed of the rotor can be changed continuously. The ASGMs installed at some pumping-up power stations are now operated effectively for automatic frequency control under the lightly loaded condition at night by changing the pumping-up power due to the rotating speed change. It is expected, on the other hand, that under the generating condition in the daytime the ASGM will be used for enhancement of transient stability because it can generate or absorb active and reactive power independently of each other by AC excitation voltage control. This paper proposes a novel control method of excitation system of ASGM for improving the transient stability of a multi-machine power system including multiple ASGMs. The controller which is designed based on an energy function works well for the stability enhancement. In comparison with the conventional excitation control of synchronous generator and constant output control of ASGM, the effectiveness of the proposed method is shown by digital simulations.

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An identification of source is important for countermeasure of transient oscillation problem. The paper proposes a new identification method in primary distribution system. For example, a convertor, which is a source, makes a line voltage notch at commutation time and, then, the natural oscillation of distribution system is occurred. Because the natural oscillation frequency is determined by the location of convertor in distribution system, the frequency is a very important indicator of identification. The features of new method are as follows:
(1) Using the eigen values and eigen vectors of system state differential equation, the correlation matrix of each natural oscillation is introduced as the indicator of identification. Since the value of matrix element shows the correlation intensity between nodes, the matrix of measured natural frequency is useful for identification of commutation voltage notch oscillation source.
(2) Since the components of particular Fourier order are intensified with the influence of convertor operation mode, it is difficult to determine the natural frequency. To avoid this problem, an quasi-transient data are introduced with modification of measured data and the determination of natural frequency can be executed easily.
Then, the new method is eximined by field test, and shows that it is very effective for identification of commutation voltage notch oscillation source.

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This paper proposes a determination method of tuning parameters based on a High Speed Genetic Algorithm (HSGA) for a fuzzy type Load Frequency Control (LFC) in power systems. The proposed method avoids unnecessary computation of a conventional Genentic Algorithm (GA) to reduce the computing time and determinates tuning parameters of the fuzzy control used a phase plane. The principal features of the proposed method show the following:(1) It evaluates whether the individual is practiced the selection or not within the caluculation of the fitness. When the individual is practiced the selection, the computation of the fitness is closed at the point. (2) In case of the crossover, it evaluates whether the partial genes of crossover are identical or not. When the partial genes are jugeded the same it and the individual isn't done the mutation, the fitness is used it of the last generation.
To study the effectiveness of the proposed method, a 3-area longitudinal system is considered as a model system for the computer simulation.

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A high voltage and large capacitor bank is commonly used as the pulsed power source because of the easy handling to store energy and to release as a high power pulse. A PFN (Pulse Forming Network) is often used as a pulsed power source for generating a square-wave pulse current. However the current` decay arising from the loss of bank system cannot be neglected for longer pulse in case of inductive load such as coils for generating a magnetic field. Therefore we studied the behavior of PFN bank for inductive loads, and obtained a guide for designing the PFN bank for inductive load. Afterthat, we traced to the origin of current decay and got that the decay was caused mainly by the resistance of PFN coils. Although some conventional methods to compensate decay are estimated, these cannot completely compensate for the decay. Therefore we researched a new idea of compensating for the decay through some auxiliary PFN banks connected to the trunk PFN bank (branched PFN system). The obtained current wave form of branched PFN shows that the pulse parameters are well agreed with the calculation and the current decay is effectively compensated. The new system also has a large freedom in controlling the pulse wave form by selecting the number and LC parameters of auxiliary PFNs without' restricting the pulse length.

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This paper presents new additional findings on a new power system transient stability simulation technique proposed in an authors' previous paper (Part 1). In standard simulations of short circuit faults in power systems, it is common 'to neglect transients of the transmission networks and stator circuits of synchronous machines. Therefore, it is not possible to obtain instantaneous responses of state variables of generators, by standard method. In addition, it is well known that the standard method can not evaluate backswing phenomena caused by stator transients. The new method can approximate DC offset currents that arise from stator transients, and thus, it can approximate also backswing phenomena. However, the method is based on a standard model with stator and network transients neglected.
In this paper, three problems left unsolved in the previous paper are investigated. They are: (1) an accurate estimation of a time constant for DC offset currents, (2) a treatment of unsymmetrical network during a clearing operation of circuit breakers, (3) large computation time needed in the new method. Solutions of these problems are presented in this paper. Finally, the validity of improved new method is confirmed on experimental results obtained from a Transient Network Simulator (TNS) and simulation results obtained from EMTP.

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This paper presents a calculation method for gaseous concentration distribution in the electrode of a phosphoric acid fuel cell with a reactant gas leakage through cell edge seals. Gas leakage phenomena at an edge of a cell electrode may result in the serious electrode corrosion quite similar to gas crossover phenomena. The method takes into account for gas diffusion based on a concentrtion gradient besides the usual Knudsen flow along gas channels, and, therefore, permits strict analysis.
The experiments using full size cells were conducted for two cases; one was for measuring gas flow rate distribution and another was for measuring gas concentration distribution. These experimental investigations clarfied the method could be applied to diagnosis of cell conditions with satisfactory accuracy.
The knowledge of the gas leakage phenpmena acquired in this study is expected to improve cell design and fabrication procedures.

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This paper proposes an approximate formula of lightning-induced voltages on distribution lines considering a wavefront dulation of a return stroke current. Rusck's approximate formula has been used because its expression is very simple. However, Rusck's formula has enough accuracy only for a steepfront return stroke current with a slow velocity. Wavefront durations of natural lightning strokes are more than a few microseconds. Therefore, Rusck's formula has an error for a lightning surge analysis. Calculated results by the proposed formula agree well with those by a numerical analysis for various wavefornt durations and return stroke velocities. It is convenient to roughly evaluate overvoltages on distribution lines caused by an indirect lightning stroke by the use of a pocket computer.

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This paper presents a new distance relaying algorithm for transmission line protection and the method of estimating integral coefficients in this algorithm. The presented algorithm is based on the differential equation that satisfies the relation between the voltage and the current of transmission line. This algorithm calculates impedance values by approximating the integral term of the integro-differential equation, which is obtained by taking integral to differential equation. Spectrums of voltage and current due to faults of transmission lines are obtained by Prony's analysis. To find optimal integral coefficients in a least-square-error sense in the frequency domain, each weighting function of voltage and current coefficients can be derived by considering these spectrums and analog filter together. These weighting functions give the optimal coefficients appropriate to transient voltage and current after faults. The simulation and the test result show that the proposed algorithm can be used successfully to protect transmission lines.

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