Ryoji Oshiro

Proposal of EMTP analysis model for a surge phenomenon arising on a power cable assembled in a iransmission lower

EMTP (Electro-Magnetic Transient Program) is one of the best programs for surge analysis. However, the surge simulation model that corresponds to the power cable used in the transmission tower is not included in EMTP. In order to adequately treat the surge issue that arises on the electrical system, a more detailed simulation has been requested. Therefore, our research has focused on a new approach to the EMTP model. The best way to achieve this is to compare the analysis results between the proposed model and an experiment. The experiment was conducted with actual devices such as transformers, transmission towers, power cables, etc. Because executing such an experiment is very difficult, VSTL rev (Virtual Surge Test Lab rev), which is a surge analysis program based on the finite-difference time domain (FDTD) method, was utilized to confirm the accuracy of the proposed EMTP model. In this paper, the VSTL rev model, the EMTP models, and their comparison results are discussed.

Investigation on surge phenomena arising on vertical power cable

AbstractIn electrical systems, power cables are often arranged vertically. Some past researches mentioned that treating conductors arranged vertically to a ground (e.g. transmission tower, wind turbine and so on) by EMTP was difficult. Recently, FDTD (Finite Different Time Domain) method has been applied to the surge simulation regarding the vertical conductor, and the method has high accuracy for the surge simulation. VSTL rev. (Virtual Surge Test Lab. rev.) is a surge analysis program based on FDTD method. However, in FDTD method, the more complex the analysis model becomes, the longer the calculation time is needed. Therefore, we believe that it is necessary to propose an appropriate modelling of EMTP to the power cable analysis. In our research, the proposal of the EMTP model of a vertical co-axial cable is aimed. In this paper, VSTL rev. and EMTP models regarding the simulation of the co-axial cable, and the comparison of these simulation results are discussed.

Study on high frequency current interruption characteristics of vacuum circuit breaker

It is well known that vacuum circuit breakers (VCB) have such superior characteristics as small size, light weight, small noise, frequent interruption, easy maintenance, and no decomposition products emission. On the other hand, some kind of surge generation may be their only one drawback. Just after the small current interruption with a very short arcing time, a repetitive re-ignition or three phase simultaneous interruption sometimes occurs. Surges related to these phenomena are considered the serious causes of insulation damage of the equipment in distribution power systems. In order to clarify these surge generation mechanisms, we did the experiment on the high frequency (HF) current interruption and the recovery characteristics of VCB with very short arcing time. We investigated the effect of a high frequency current on the dielectric recovery characteristics after the high frequency current interruption by means of synthetic test circuit in short electrode gap. For experiment parameters, we changed HF current frequency, amplitude of HF current values (about 350A and 750A) and impulse voltage (less than 8kV), arcing time(several hundred micro seconds) and delay time of impulse voltage application after HF current interrupted(several micro seconds). In this paper, the result of experiment will be reported.

FDTD analysis about surge phenomena arising on co-axial cable

In electrical systems, co-axial cables have come to be widely used (for example, transmission systems, building inner wirings and so on). A surge current entering into the cables might cause severe damage to them. Therefore it is necessary to investigate surge phenomena of the cable from the surge propagation point of view. An FDTD method (Finite Difference Time Domain) has recently been applied to analyze this kind of surge phenomena. Accordingly, we have adopted a VSTL rev. (Virtual Surge Test Lab. rev.) which is a surge analysis program developed by CRIEPI (Central Research Institute of Electric Power Industry) in Japan to carry out surge simulation. In this paper, we first discuss the comparison results of surge experiment results by means of a co-axial cable (Type RG58 A/U) and of simulations by means of VSTL rev. Secondly, we illustrate surge phenomena that have arisen on a co-axial cable which is connected with a transmission line through a cable junction. Finally, we discuss these results.

Investigation about influence on breakdown voltage by arc condition befor quenching

When the contacts of a circuit breaker are opened just before the current zero, the gap between the contacts after the current interruption will still be very short. Therefore, it cannot withstand the recovery voltage across the contacts after the interruption. In such a case, the multiple re-ignitions likely take place. Many investigators had tried to clarify this phenomenon, and many reports have been published. Generally, the high frequency current interruption and the dielectric recovery characteristics after the current interruption are relates to many parameters (value of the current, the arc time, and so on). In addition, the arc phenomena are very complicated. Hence, it looks difficult to understand these phenomena accurately. Therefore, we conducted the dielectric recovery test after the high frequency current interruption, and the observation experiment using the vacuum chamber in order to investigate the effect on recovery characteristic by the DC current before injecting with the high frequency current. At the end, we calculated the plasma density in the space between the electrodes after the high frequency current interruption by considering the result of the observation experiment and the dielectric recovery test. In this paper, the result about the experiments and the calculations are reported.