Theoreticl study and phenomenal examination have been done for a long time, but some electric power company even today has instataneou power failure due to the galloping. Our study differs from other ones on the point that non-linear three dimentional simultaneous equations of conductor movement can be solved directly using numerical calculation. Foundamental characteristcs of galloping can be made clear by that calculation changing parameters variously. This time, we used the method that bundle conductor are changed equivalently to single conductor. We could also make it clear that instable domain becomes wider when rotational movement of conductor occurs.

抄録全体を表示

This paper deals with descriptive methods of differential equations as models of actual power system loads. Two classes of descriptive methods are discussed: description using power and voltage as descriptive variables (input/output description); description using state variables as descriptive variables (state variable description). Input/output description is frequently used for description of the general types of load actually measured at the load buses of power systems, while state variable description is ordinarily employed for descriptions of individual load devices. The following topics are specifically described. (1) Two descriptive methods are compared principally from the viewpoint of practicality, and state variable description is shown to be advantageous for many types of analysis. (2) The concept of transformation from input/output description to state variable description is described using block diagrams. (3)The transformation is applied to a first order nonlinear load model. (4) The instantaneous load characteristic is introduced as the concept related to the transformation.

抄録全体を表示

A Multi-layered-type neural network is an attractive technique for daily electric load forecasting because the neural network can acquire nonlinear relationship among the electric load data and their factors(weather, temperature, etc.) automatically. In this paper, we first discuss some essential issues to be considered in neural network applications. One is difficulty of getting sufficient effective training data, and one is influence of abnormal learning data, and the other is inevitable outerpolation. For these issues, we developed following three methods in order to forecast more accurately (1) a structure of the neural networks for insufficient training data, (2) detection and diminishing the influence of abnormal data, (3) employment of interpolation network and outerpolation network with additional data for outerpolation. Furthermore, to raise sensitivity between electric loads and factors, we developed (4) removal of base load. Those methods effectively work to decrease the average absolute errors of peak-load forecasting and 24-hour load forecasting to 1.78% and 2.73% respectively.

抄録全体を表示

We have studied the multivariable optimal control system, which coordinates excitation and governing systems of a generator, and to this control system a self-tuning adaptive control scheme is applied.
This paper describes the verification of applicapability of TAGEC to the long-distance longitudinal power system using in the AC/DC power system simulator owned by CRIEPI and the large scale analogue simulator of APSA (Advanced Power System Analyzer) owned by the Kansai Electric Power Co., Inc.
The test results verify the applicability of TAGEC to the long-distance longitudinal power system and the effectiveness of TAGEC to the low-frequency oscillations of various faults in power system. And also the TAGEC improves power system stability of the long-distance longitudinal system compared with conventional control.

抄録全体を表示

It is desireble for the power system planner to understand the voltage characteristics of power system without computational burden or with a munimum number of load flow calculations and dynamic simulations. The authors have been studying the voltage stability problem by means of voltage sensitivity, which can be easily obtained in the load flow calculation.
First, this paper proposes a voltage sensitivity map which can visualize the characteristics of the power system from the viewpoint of voltage stability. The planner can easily identify the weak busses from the viewpoint of voltage stability by the map.
Second, the paper clarifies the mechanism of the improvement of voltage stability by various apparatus such as shunt capacitor and Static Var Compensator (SVC) using the voltage sensitivity. The paper demonstrates that the effective location of such apparatus to improve the voltage stability can be found by the help of the voltage sensitivity.

抄録全体を表示

In order to understand some characteristics on superconducting generators (SCG's) in power systems, experimental studies by using the 20kVA SCG have been performed. It is necessary to inverstigate the characteristics for parallel operations of an SCG and a conventional generator(CG) when an SCG is installed to a present power station. In this paper, we describe some results of our studies on parallel running of the 20kVA SCG and the 20kVA CG. In the experimental system, the SCG is connected to regional power system (infinit bus) through reactors (artifical transmission lines) and the CG is connected to the terminal of the SCG. By the experiments and computer simulation, we investigate the transient characteristics at three-phase short-circuit faults 1) when CG is not isolated and 2) when CG is isolated after reclosing. We obtain two kinds of stable limit curves for output power at three-phase short-circuit fault for above two cases.

抄録全体を表示

As the capacity of the generator increases, a cross-compound turbine-generator consisting of two axes is generally adopted at thermal power stations in our country that are connected to a 50 Hz power system. If oscillation occurs to this cross-compound turbine-generator because of a power system disturbance, a local mode is formed between a primary machine and a secondary machine. This mode coex-ists with the intertie mode that is formed between the cross-compound turbine-generator and the power system to which it is connected. When the PSS is applied to the design of the cross-compound turbine-generator, a full understanding of these two oscillation modes is therefore required to optimize the design and to improve the effect of damping. The abstract of this paper can be summarized as follows:
(1) With a power system using cross-compound turbine-generators, a local mode of 2 Hz to 3.5 Hz is formed across operating machines along with the intertie mode that has an oscillation of about 1 Hz.
(2) We could build a two-machine infinite-bus power system model consisting of primary and secondary machine, which can tune the PSS design for the cross-compound turbine-generator with a high level of accuracy.
(3) To improve efficiency of the PSS design, we proposed that the equivalent one-machine infinite-bus power system model be established for the intertie mode and the local mode. In conclusion, we presented the PSS design procedures that can be used in actual power systems.

抄録全体を表示

There is a possibility that satisfactory protective effects for a three-phase power distribution line are attained even if it has surge arresters on only two phases. In order to evaluate the lightning protection effects, experiments of direct lightning strokes and analysis using the EMTP were done.
Lightning protection effects were quantitatively clarified by experiments of direct lightning strokes on simulated full-scale power distribution line with surge arresters on two phases.
Analytical results, which were got by taking the reducing effect of grounding resistance into account, agree well with experimental results. If the value of grounding resistance is less than 30 ohm, the power distribution line with surge arresters on two phases did not suffer from any flashover against the direct lightning stroke with a peak current of-40kA.

抄録全体を表示

Exploiting GPS systems, we synchronized three wideband (0.1Hz-2MHz) slow antennas with the time accuracy of lμs. With this slow antenna system, we recorded many lightning flashes at Hokuriku district area from December 2, 1993 to January 28, 1994. Almost all lightning flashes show consecutive pulses superimposing on their slow field changes with the time intervals of tens microseconds. We analyzed the arrival time difference of the pulses to different stations and succeeded in locating the sources of the pulses which are from PB(Pleliminary Breakdown), L(Leader), R(Return stroke), and C(Continuing current) stage for a positive cloud to ground discharge, and from recoil streamers for a cloud discharge. Since we combine the functions of traditional slow antennas with lightning location method, this paper would provide a significant tool to study lightning physics, especially the physics of the initiation of lightning.

抄録全体を表示

Arc interruption in a high voltage circuit breaker is usually performed in gas blast to an arc column through a nozzle throat. The authors have pointed out in various types of the flat air blast quenching chamber that better interruption performance was found when a sharp minimum of electron density was brought about at the nozzle throat around current zero and it was realized in an orifice type of nozzle.
This paper describes effect of air flow passage on current interruption ability in the flat type of arc chamber with the orifice nozzle. The following three kinds of air blast are tested by modifying the flow passage: (a) oblique blast in which air flow passes through the arc column at an angle with it, (b) both-side blast in which air flow passes along both sides of the column, this corresponding to a usual gas blast method, (c) single-side blast in which air flow passes along only one side of the arc column. The flat type of quenching chamber makes easy for measurements of the pressure rise distribution and of the electron density by microwave at 70 GHz in the nozzle throat space.
The obtained results are summarized as follows.
(1) The oblique blast type has more excellent interruption capability than the both-side and single-side blast type.
(2) The pressure rise in the upstream region of the nozzle throat as well as the electron density decay at the nozzle throat are both remarkable in the oblique blast type. These are brought about by a nozzle clogging-like action and by effective arc energy dissipation due to direct cross of air flow with the arc column.

抄録全体を表示