This paper reports current status of research activities in the field of high voltage engineering and its application in Indonesia. In general, the activities were driven by the application of high voltage (HV) and extra high voltage (EHV) transmission systems in the country. The operation and maintenance of HV and EHV equipments are greatly affected by the tropical climate of the country. This attracts researchers to investigate the effects of tropical climate on HV and EHV equipments. Other researches concentrated on the investigation of physics of tropical lightning and lightning protection. In this paper, applications and problems of high voltage engineering, research activities in universities, as well as in research institutes and utilities are briefly introduced.
For about a century, studies concerning summer thunderstorms in the middle latitude zone have elucidated data on both their meteorological and electrical features. By contrast, winter thunderstorms have been studied only for the last few decades. For both reasons of scientific interest and the practical purpose of preventing serious damage by winter thunderbolts to aircrafts and electric power systems, studies of winter thunderstorms have currently become one of the focuses of lightning research. Besides winter sprite was discovered about 10 years ago. This is the newest interesting phenomena in this field. The meteorological subjects about winter thunderstorms will be reviewed.
Current and leader development characteristics of winter lightning occurring in the coastal area of the Sea of Japan are reviewed. The characteristics of winter lightning are different from those of usual lightning that occurs mainly in summer. The occurrence of upward flashes, the percentage of current polarities, and the median values of current peaks in winter lightning are summarized. Typical current waveforms and the corresponding leader developments of winter lightning observed at the chimney of the Fukui thermal plant are shown. We examined the parameters (peak, duration, charge transfer, action integral) of the current waveforms of winter lightning.
Observation of electric and magnetic fields associated with lightning discharges has contributed much to reveal odd characteristics of winter lightning and to clarify part of its substance. The characteristics include high proportion of positive cloud-to-ground flashes among all the ground flashes, frequent occurrence of upward discharges even from structures of less than 50 m in height, and larger average charge amounts neutralized by ground flashes than in summer. Knowledge obtained so far from observations of quasi-static field, wideband electromagnetic field waveforms in VLF to LF frequency range, and VHF radiation associated with lightning discharges in winter is reviewed.
Winter lightning, which occurs along the Sea of Japan coast, often damages transmission lines and distribution lines with the conventional lightning protection. These lines in mountainous areas suffer extensive damage from winter lightning. It is very important to investigate the features of lightning outages in detail to improve the lightning protection measures against winter lightning, therefore observations of lightning strokes to transmission lines and distribution lines as well as measurements of lightning surges on these lines have been carried out. And then the lightning performance of various protection methods has studied by experiments and analyses. Taking into account these studies, the effective methods have been adopted. This paper presents the lightning protection of transmission lines and distribution lines against winter lightning.
It has already past 20 years since the first Adjustable Speed Hydro Generator Narude Unit No. 1 22MVA was put into commercial operation as an experimental unit for Ookawachi Adjustable Speed Generator/Motor 395MVA/388MW in June 1987. The adjustable speed generator (generator/motor) has a cylindrical rotor with 3phase winding like winding type induction motors. Its 11kV class winding must endure against 1,000G class centrifugal force which is much higher than that of pony motors for pumping storage generator/motors. Technologies for the rotor winding were developed as a combination of well experienced technologies on large rotating machines and specially developed material and manufacturing technologies on Nuclear Fusion Experimental Reactors such as Heliotron E and JT-60.
Micro discharge is investigated which is occurred with a pair of electrodes covered with dielectric barrier. The discharge gap is set at an order of micro meters by changing a spacer from 0 to 100μm. Paschen's law states the minimum sparking voltage of various gases for respective discharge gaps in atmospheric pressure. In this paper, characteristics of micro discharges, such as discharge voltages, discharge currents, discharge power, which is obtained with the help of Lissajous figures, and the relationships between these characteristics are presented. Characteristics of ozone generation and treatment of high concentration NOx, which is contained in exhaust gas of automobiles, are investigated. Byproducts are confirmed by FT-IR and GC-MS.
The authors measured lightning overvoltages in railway level crossing systems representing typical examples of wayside electronic signalling equipment at the field. This measurement was carried out to analyze quantitatively the frequency of lightning overvoltage occurrence and to collect basic data for countermeasures against lightning. As a result, an experimental equation to estimate the occurrence frequency of lightning overvoltages in the level crossing system was derived. This equation can estimate the occurrence probability of lightning damages caused by exceeding the withstand voltage of the level crossing system. Moreover, this equation is useful to evaluate the rate of reduction in lightning damages against the level of lightning protection. For example, if the level of lightning protection can be improved from 10kV to 30kV, it is calculated that the occurrence probability of lightning damages will be reduced to 1/10 or less according to the equation.
Regarding to a high-temperature CO2 added with CF3I, the present paper reports equilibrium compositions as one of fundamental properties. Firstly, 61 particles were taken into account and the equilibrium compositions were derived in a temperature range from 300 to 30,000 K. Secondly, the particles present after an arc interruption in the CO2-CF3I mixture are obtained as a function of CF3I concentration. Thirdly, the electron density of the CO2-CF3I mixture at high temperatures is discussed in comparison with that of pure CO2.
The higher contamination flashover voltage performance of a transmission line polymer insulator has been shown to be attributable not only to its surface hydrophobicity but also to its configuration. A larger ratio in the shed to core diameter of the transmission line polymer insulator brings about higher surface resistances in its individual trunks, and therefore the voltage applied to the entire insulator can be divided and allotted to these trunks, resulting in a higher flashover voltage. We expected a similar effect by applying a silicone rubber coating having hydrophobicity only to all the trunk surfaces of a porcelain long-rod insulator. We tested by the clean fog method and confirmed only about a 10% improvement. In this paper, the same such effect was evaluated by the salt fog test method, which confirmed a significant improvement. The detailed investigation results are presented.
Nearby trees and buildings affect frequency of direct lightning strokes to distribution lines because the lines can be located lower than nearby structures. It is necessary to grasp lightning performance in distribution lines based on observation data. Lightning phenomena on actual distribution lines have been continuously observed for the last 10 years to rationalize lightning protection designs. The observation has been carried out with still cameras and monitoring sensors of lightning surges. The observation has clarified the frequency of direct lightning strokes to distribution lines, and the ratio of flashover probability. Those results can be useful to calculate the lightning faults rate of distribution lines.
The power frequency withstand voltage tests are specified on electric power equipment in JEC-0102 by evaluating the lifetime reliability with a Weibull distribution function. It may be applied on 66-154kV transformer for non-effectively grounded voltage class. The present paper describes the results that measured AC insulation characteristics (Voltage-time characteristics) and Weibull parameters for oil-filled transformer of 66-154kV class. These measurement parameters were compared with the conventional Weibull parameters, which were applied for oil-filled transformer of voltage class above 154kV. Furthermore the non-partial discharge test voltage was evaluated by trial calculations, using the parameters obtained this time or typical parameters.
This paper has investigated the basic characteristics of switching surges in a gas-insulated substation and induced surges to a control cable based on EMTP simulations. It has been found that a switching surge voltage on the core conductor of a gas-insulated bus (GIB) tends to increase and the oscillating frequency becomes lower as the number of spacers increases. The maximum switching overvoltages become greater at the nodes nearby an operating disconnector (DS)/circuit breaker (CB) and become smaller at the source side. An induced surge to a control cable tends to increase as the parallel length of the GIB and the control cable increases. However, in the case of an open-circuited GIB, there exists a length which gives the highest voltage. A transient current becomes very large if a voltage transformer (VT) or a spacer is installed right next to an operating CB or DS, although this current does not affect the induced and VT transferred surge to the control cable. Also it is observed that a ramp wave voltage causes polarity reversing of a transient voltage on the GIB tank and the control cable.
This paper has investigated surge propagation and overvoltages on a coaxial cable when a lightning current flows into the metallic sheath based on experiments, EMTP simulations and analytical calculations. At the instance of the current flowing into the sheath, the core voltage becomes the same as the sheath voltage, which is given as a product of the sheath surge impedance and a half the current, following the theory of electrostatic shield. Thus no voltage difference appears between the core and the sheath across the insulator. When a traveling wave arrives at a transition point, i.e. cable termination, an insulating or crossbonding joint, the voltages change suddenly and a significant voltage appears across the insulator. An EMTP simulation shows that the overvoltage across the insulator exceeds 1200kV at a crossbonded node on a 400kV underground cable when an ac source voltage is in the opposite polarity of the lightning surge voltage on the sheath and the inductance of a crossbonding lead wire is taken into account. The high overvoltage appears in a narrow region of the cable between the current injected node and the crossbonded node due to traveling wave reflection between the nodes. The phenomenon investigated may occur if there exists a pinhole or a watertree on an underground cable.
The electro-geometrical method (EGM) has been adopted for lightning protection design of transmission lines. In this paper, probability calculations of direct lightning strokes to wind turbines are carried out by using the EGM. The distributions of the peak values of lightning current mentioned in various documents are based on observational results of lightning strokes onto structures. These distributions are different from those corresponding to lightning strokes from a thundercloud to the surface of the ground. Therefore, we have estimated the peak value of the lightning current and the probability of shielding failure by using the EGM. In addition, the equivalent collection areas of structures were calculated on the basis of an assumed lightning striking angle in three-dimensional space.
The electric field waveforms associated with lightning discharges that were observed simultaneously with faults of power transmission lines in winter are analyzed. Also, electric field waveforms associated with high current lightning discharges in winter around the coastline of the Sea of Japan are analyzed for comparison. All of the negative lightning discharges simultaneously observed with transmission line faults produced different field waveforms from those produced by normal cloud-to-ground strokes. Positive high-current lightning discharges, however, produce field waveforms which look more like those produced by normal cloud-to-ground strokes. These high-current lightning discharges distribute differently around the coastline depending on their polarities.