Laser-guided discharge is promising for protection of power transmission systems against lightning. Several experiments concerning the laser induced electrical discharge have been performed up to now. However, it is necessary to understand the mechanism of the laser induced electrical discharge to achieve the laser-triggered lightning. When a high power laser beam is focused in air, a high degree of ionization is produced as brilliant beams nearby the focus. In this paper, the electrical discharge induced up to 2-meter with a high power CO2 laser focused by a 10-meter focal length mirror is described. Experiments of the laser-guided discharge were carried out by application of an impulse voltage to a rod-rod gap after laser radiation. This paper deals with the effects of delay times and polarity of the impulse voltage on 50% flashover voltage characteristics and the observation results of discharge phenomena taken by a still camera, a special camera named ALPS (Automatic Lightning Discharge Progressing Feature Observation System) and an image converter camera.
Voltage instability is now under intensive study in Japan. Some dynamic methods for analyzing voltage collapse have been already presented. However, propriety of load models used in the methods and generality of the results have not been verified. In this paper, precious data of voltage collapse acquired in real power system are presented. The measured data are compared with the result of dynamic digital simulation to verify propriety of an induction motor load model. In the latter half of this paper, the dynamic simulations of voltage collapse taking into account dynamics of generators are carried out. An interconnected power model system with 10 nodes is analyzed. The generality of basic characteristics concerning voltage collapse which have been already obtained by ignoring dynamics of generators is verified by such simulations.
The voltage control calculation is the combinational optimization problem, and it has been difficult to solve this type of problem quickly with the conventional digital computer. However according to the modelling of excellent parallel processing ability of neurons, it has become possible to carry out the optimization with the Hopfield neural network model. In this paper, in order to solve the voltage control problem we propose an improved Hopfield model which has an individual input-output function for an individual neuron to achieve a drastic improvement in the calculation time.
This paper presents fast load flow caluculation methods using a preconditioned technique. The load flow calculation may be expressed by solving a set of linear equations. A lot of studies on load flows have been made since Ward and Hale. The Newton-Raphson method is widely-spread due to the good convergence characteristics. The N-R method updates the Jacobian matrix and solves a set of linear equations at each iteration. On the other hand, the exact second-order load flow is attractive in terms of computational effort since it utilizes a constant Jacobian matrix. In this paper, the preconditioned conjugate residual and conjugate gradient squared methods are proposed to solve a set of linear equations in the load flow calculation. The precondition technique has an advantage that it can improve the convergence characteristics of the conjugate gradient type algolithms. Also, the algorithms are effective for solving a set of linear equations with large sparse coefficient matrices. The proposed methods are applied to the Newton-Raphson and the exact second-order load flow calculation. A comparison is made of the proposed and conventional methods in terms of computational effort. The effeciveness of the proposed methods are demonstrated in the IEEE 14, 30, 57 and 118 node systems.
This paper presents a state representation method for diagnostic problems of power system based on many-sorted logic. A state has three terms which are an object term, a status term and a temporal term. By using relations among same type terms, relations between states, Generalization and Instantiation, are derived. Diagnostic inferences to search more detail states and more whole states are explained by using these derived relations. As a reuslt, a state which explains observed states can be derived from observed states and relations among same type terms which are used in the states. Finally, inference system were developed, and outputs for some examples are shown. This method unifies object, status and temporal representation in a state representation. Also, the inference system based on this method can compose solution states which are not explicitly represented in initial data.
Lightning voltage induced by nearby strokes is one of the causes of major overvoltages which threaten insulation of power distribution lines. Surge arresters as well as an overhead ground wire are usually used for the protection of equipments and line insulation on overhead power distribution lines. The fundamental mechanism of suppressing effects of overvoltages induced by nearby strokes has been demonstrated by one of the authors independently for surge arresters and for an overhead ground wire. In this paper, the protective effect of the combination of surge arresters and overhead ground wire is analyzed. As a result, it is found that the effect of surge arresters used together with an overhead ground wire is almost the same as that of surge arresters alone.
It is proposed that the gas permeabilities should be adopted as the indices for evaluating the characteristics of power generation and reliability of solid oxide fuel cells in this paper. The gas flow properties in the ceramic membranes could be expressed as viscous flow and the theoretical gas permeability coefficients can be expressed as the function of the square of porosity and are proportional to the inverse of the viscosity or kinematic viscosity. The gas permeation in porous alumina tube wall was measured in the tempereture range room temperature to 600°C with use of various gases such as H2, He, CH4, N2 and Ar. The flow velocity of gas is expressed in the order H2>He>CH4>N2>Ar, and these tendency coincides with the order of gas viscosity. The gas permeability coefficients are preferable to analize the data and are expressed as the function of viscosity or kinematic viscosity of gases at high tempereture range.
Insulation deterioration of power cable can be measured by the method of partial discharge. If a large partial discharge is detected in a cable, the cable is concluded to be defective and a partial discharge is located to find the position of the defect. However partial discharge location methods have generally disadvantages that they require much skill for operation and are inferior sensitivity and accuracy. To solve these problems, we have developed a locating method using two-phase cable and an automatic partial discharge locator which automatically localizes the generating site of discharge immediately after making partial discharge measurement by simple operations. We have made field measurements on SL (separately lead-coverd) cables and other cables with the locator in order to test its accuracy and reliability, and it was found that the device is effective and useful.
To clarify the contact failure phenomena and their development in the Gas-Insulated Switchgear (GIS), tests were conducted by simulating abnormal current-carrying conditions using an actual 300kV-2, 000A GIS. This paper describes the process observed in the range from contact failures to ground faults, deteriorative phenomena and some detection methods for initial contact failure conditions. A summary of this study is as follows; (1) The contact resistances are greatly dependent on the materials and construction of contacts. (2) The relation between the initial contact resisitance and the carried current resulting in an arcing is derived with approximately constant Joule-heat generation. (3) Ground faults result from a sagging of a shield molten by arcing or a combination of two causes; (i) scattering of molten metal caused by arcing and (ii) sagging of a conductor caused by melting down of bolts. (4) For detection of initial contact failures, it is recommended to observe the contact resistance, the temperature rise on the tank surface or the electrical partial discharges.
In Mitsubishi Electric, two types of internal reforming molten carbonate fuel cell (IR-MCFC) are being developed in parallel, e. g…, Direct Internal Reforming (DIR) and Indirect Internal Reforming (IIR). Recently, a 3kW DIR and a 10kW IIR stacks have been built and tested. The main objectives of the stacks are to investigate the thermal balance in the stacks as well as full scale size cell and stack technologies. The 3kW DIR stack have attained a good performance as high as 0.799V of average cell voltage at 150mA/cm2 of current density and more than 0.7V even at 200mA/cm2. After the achievement of initial tests on various operating conditions, the stack has operated as long as 5, 070 hours. The 10kW IIR stack has also showed a good performance. Especially, the degradation rate of cell voltage was as low as 5mV/1, 000h.