This paper describes a general prediction method of audible noise and radio noise generated from HVDC transmission lines with 4×3.84cm conductor bundles. This method is based on the longterm test results of audible noise and radio noise arranged by the maximum conductor surface gradient in the presence of space charge. The feature of the method is as follows: (i) It is applicable to 4×3.84cm DC transmission lines with any line configuration and any polarity arrangement. (ii) It has a high prediction accuracy because it is confirmed by a large quantity of measured data.
For improvement of detection techniques on the partial discharges in gas-insulated substations, it is important to make clear the physical process of micro-gap discharge in air and in SF6 gas. The discharge current wave shapes and temporal variations of the emitted light were observed using a streak camera, and a simulation of spark-type discharge process in micro-gap was also performed. The measured results show that as the gap size increases from 0.5 to 3.5mm, front time Tf and tail time Tt of the discharge current wave shapes in air increase from 1 and 20 ns to 2 and 51 ns, while the current peak value Ip decreases from 2.6 to 0.2 A. On the other hand, in SF6 gas, Tf and Tt are shorter and Ip is greater than those in air. The measured results on temporal variation of the discharge light show that there is some difference in the wave shapes between the current and the emitted light. The calculated results on the wave shapes of discharge current and emitted photons indicated clearly these characteristics.
A new transient memory, which has 1 Mbytes buffer memories and can record the electric field changes due to lightning discharges for at most 524 mill seconds, is designed to study the whole process of the lightning discharge. To realize the system, a commercially avallable personal computer and a memory board are used and the special software is also developed. As the sensor, a new type slow antenna, which maintains the features of both so called slow antenna and fast antenna, is also manufactured. The system itself is controlled by the personal computer, and then without any manual operation the obsrevation can be carried out. With this system the obsrevations during both summer and winter thunderstorm seasons were performed. During summer the system recorded the eletric field changes with multi strokes and continuous current. During winter it recorded the whole process of lightning discharges from the preliminaly breakdown through the return stroke, and continuous current. The utility of the system can be approved and some remarkable features of lightning discharges are obtained.
A simple arcing horn flashover model for a lightning surge analysis is developed based on a theory of leader development. Conventionally, an arcing horn impedance is modeled by linear inductors and switches. However, the inductances and the timing of the switching operation depend on circuit conditions, and the voltage across the arcing horn. In this paper, the characteristic of an equivalent inductance to an arcing horn flashover is investigated and is approximated by a simple equation which is a function of arcing horn current. The proposed model consists of nonlinear and linear inductances and two switches. The switches are controlled by the arcing horn voltage and current. The switching operation is easily realized by TACS subprogram of the EMTP. The proposed model is more general than conventional models and its accuracy is satisfactory enough. Furthermore, experimental results are compared with the results using proposed model, and confirmed the accuracy of the model.
Cloud-to-ground lightning flashes in Niigata area have been observed for a few years by a magnetic direction-finder network, Data obtained so far are carefully analyzed taking into account the operating characteristics of the system. As a result, frequency distributions of return-stroke current for each polarity are produced, and their seasonal variations and the occurrence probabilities of high current exceeding 200kA are clarified. Based on the estimated current distributions, back-flashover rates of 500kV 2cct transmission lines are calculated. It is known that the back-flashover caused by downward flashes can account for most of the line outages in summer for both single and multiple line faults, however, this mechanism cannot explain the high outage rate in winter experienced in winter thunderstorm area in late 1970s. In spite of the low lightning flash density in winter, the multiple-line fault rate in winter caused by back-flashovers is predicted to be comparable to that in summer, because of the seasonal variation of the frequency distributions of return-stroke current.
This paper proposes a new approach to the restorative problem of electric power system, and shows the characteristics and the effectiveness of the method. The method develops the restorative plans using shortest tree algorithm and searching mechanism according to over-load information, and doesn't require the knowledge that is usually required in the expert system approach. The method also has the merit of the easiness to get alternative restorative plans and to reflect the operator's will to the restorative plans.
Numerical simulations are performed to theoretically make clear the detailed performance characteristics of nonequilibrium disk MHD generator of demonstration-scale. Cesium seeded helium plasma is used with about 100 MW thermal input. A new two-dimensional time-dependent simulation code is developed for this purpose, which code can treat not only the shock wave but also the two-dimensional interactions between electrical and gas dynamical quantities due to the ionization instability of the plasma. The following results are obtained by the calculations. The designed MHD generator can be stably operated in the designed conditions. The load voltage is nearly constant in the high load resistance region while the load current becomes nearly constant in the low load resistance region. The two-dimensional distributions of electrical quantities affect the flow field and then the distributions of gas dynamical quantities become fairly inhomogeneous and two-dimensional in the low load resistance region. The change of seed fraction does not change the qualitative characteristics of the voltage-current curve.
The gas insulated switchgears are widely adopted in recent electric power substations. The SF6 gas is decomposed by arc discharges and the white powder is produced due to chemical reactions with the contact metal. This kind of undesirable materials are usually absorbed by associated filters. However, if the contacts are contaminated by the resolved gases or the produced powder, they possibly bring about unexpected troubles in the GIS due to abnormal contact resistance. The alternating current carrying features of copper spot-contacts contaminated by the decomposed gas as well as by the accumulated powder between them are experimentally investigated in this paper. When thickness of the powder is about a few layers of particles with diameter of some tens of micro-meter, several hundreds micro-ohm of the contact resistance is obtained with contact load of 9.8 N at around 100 A. This magnitude decreases to a level of less than 200 μΩ, when the carrying current is forced to increase to a few thousands amperes. The associated voltage across the contaminated spot-contacts takes always somewhat triangle wave forms low current level and they change into usual sinusoidal ones in a long period current carrying. This aspect is artificially realized in the spot-contacts with other kinds of contaminated powder between them.