When a line voltage notch at commutation flows into a distribution system, the commutation overshooting oscillations of various frequencies may be produced by the natural oscillation. The paper proposes a new analysis method for 6n-pulse convertor (n=1, 2, …). The features of this method are as follows: (1) By using the ϒδ transformation, a three-phase circuit model is modified into two singlephase circuits, and the influence of the line voltage notch appeare only in the δ-phase circuit. Therefore, this reduces calculation labor, and makes the physical evalution easier and clearer. (2) Since the 6n-pulse convertor is consisted with the n-sets of the 6-pulse convertor, the analysis model becomes large and the labor of the calculation is troublesome. Therefore, the method of symmetrical coordinates is applied to the ϒ/δ model and the analysis model is reduced to only the zero-phase. Then, some considerations are executed about the influence of the pulse number, and show that the effect of the oscillation reduction is depending on the construction of the distribution system.
This paper presents an on-line stabilization control method developed aiming at maintaining transient stability in the local power system which includes large capacity generation plants. The most outstanding features of this method are that the power/angle curve is estimated using the on-line data of the active and reactive power measured at the generator terminal and the most optimum amount of generation shedding for stabilization is determined by applying the equal area method to this curve. After realizing simulation tests by using detailed models of power system, the authors have confirmed that the most optimum amount of generation shedding for stabilization could be computed to best suit various fault conditions, regardless whether symmetrical or asymmetrical. Furthermore, it was also clarified that the sampling period of the on-line data to be used could be for several tens of milli-seconds after clearing the fault. Thus, this method is expected to serve as an effective control logic for the practical stabilizing system.
In high voltage measurement digital measuring system is widely used for its attractive features, for example automatic data acquisition. However, the accuracy in the measurement of both the amplitude and time parameters by digital measuring system is not known in detail, especially in the measurement of single-shot waveforms. In this paper, the accuracy of the peak value and the virtual front time of the standard lightning impulse without any signal processing of raw data is shown. From these results, the required characteristics for digital measuring system to satisfy the IEC Draft on digital recorders for measurement in high voltage impulse test techniques are shown. In addition, the accuracy of the peak voltage and the rise time of the Gaussian pulse is shown.
Snow accretion on transmission lines in heavy snowfall areas may cause critical accidents such as tower collapses, sleet jumps, etc.. In order to assist power system operators to prevent these accidents, a prototype expert system had been developed. The system has basic functions of forecasting snow accretion on transmission lines and making a list of all feasible and effective deicing countermeasures. The knowledge of the effect of weather conditions on the snow accretion process consistutes main rule base. To develop a more practical system on the base of the prototype, the authors constructed a new system using Knowledge System Language OPS83. This new forward-chaining production system with a engineering work station achieved high inference speed. The rules were improved and classified to have a hierarchical structure, and new rules were also added. A man-machine interface was attached to make the system easy to use. FUZZY concept was introduced to cope with inexact informations about weather and the state of the power system. Simulation results show that the proposed system is very promising.
In our country, a lot of high voltage cut-outs are commonly installed in front of the distribution pole transformers. The load-switch in the arc extinguish chamber and the expulsion-fuse are assembled into the h. v. cut-out. The switch and the expulsion-fuse have share the operation in such a way that the switch afford load operation, and the expulsion-fuse give over-current and short circuit operation. It is reported that the breaking-process of the large current in the expulsion-fuse is associated with the considerably high arc voltage and the post-arc current. In order to have the fundamental understanding of the physical phenomena of the breakingprocess in the expulsion-fuse, the experiments were made with the model of the cut-out and the expulsion-fuse. The discharge tube is installed at the one end of a fibre tube and the chamber is installed at the other end. A part of decomposed gas ejected from a fibre tube heated by the arc is discharged into the discharge tube and the remain flows into the chamber. The pressure of the discharge tube and the chamber was measured with the pressure sensor of diaphragmsemiconductor type. A series of tests were made on many different dimensions of fibre tubes and various values of arc-ignition current and arc energy. The paper gives the measuring results for cut-off current versus the maximum pressure of the region of shock wave and foward running wave characteristics, arc energy versus the maximum pressure of the region of the ejected gas flow characteristics in the discharge tube, the characteristics of the arc energy versus the maximum pressure in the chamber, consumed mass of the tube versus arc energy characteristics, and so on. The paper also gives the estimation of the pressure for the ends of the tube, pressure distribution and gas flow in the tube related to the pressure in the chamber.
Problems have been often caused in low-voltage distribution lines such as single phase 100/200V and three-phase 200 V systems. For instance, the burning of low-voltage devices and the unnecessary operation of ground fault interrupters have occured, which are possibly caused by lightning overvoltages. Experimental analysis was performed on the generation modes of lightning overvoltages on low-voltage distribution lines. A scale model line, 1/4 the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO) was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low-voltage distribution lines due to nearby lightning stroke. A baloon was flown at a location 30 m apart from the scale model line in a normal direction to it. A wire of 200m long is suspended from the baloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured. This paper analyzes those overvoltages by means of the experimental and the theoretical methods.