Search

Concurrent flashover characteristics with three gaps in parallel are analyzed theoretically considering the statistical characteristics of time to flashover of a gap. The analysis shows that the concurrent flashover phenomena are likely to occur if the overvoltage ratio is large even if there are three gaps. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

The features of lightning shielding of transmission lines have been calculated using the electrogeometric model (EGM) proposed by Armstrong and Whitehead. Discrepancies, however, have been found in the case of ultra-high voltage (UHV)-designed transmission lines. UHV-designed transmission lines often pass through high-altitude mountain areas, where foggy or rainy conditions are common when there is lightning. While the electrogeometric model determines the striking distance based on the lightning stroke current, environmental conditions, and how they might affect lightning discharge paths, they are not considered. It is possible, therefore, that foggy conditions may cause differences in the performance of transmission-line lightning shielding. This study used scale models of transmission lines for discharge tests with a 1-m air gap and analyzed differences in discharge paths and locations in dry and foggy conditions. The results showed that the polarity of the discharge had a significant influence, but differences in dry and foggy tests were negligible.

After reorganization of power industry in 1951, power system of Japan was remarkably expanded. To cope with this, R&D in vast area was conducted in the academy, MITI, electric power companies, manufactures, and research institutes. This paper generally describes the technical contents that the three research institutes, namely Electrotechnical Laboratory (ETL), High Voltage Power Laboratory (HVPL), and Central Research Institute of Electric Power Industry (CRIEPI), have contributed to the development of power transmission technology after the war.

Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower. Electromagnetic field waveforms are also observed by capacitive antennas at several tens of kilometers from the tower. Lightning current and electric field waveforms simultaneously observed in May 2012 are reproduced by using an electromagnetic model of a return stroke with the help of NEC-4. Observed lightning current waveforms are well reproduced by modeling the tower with small number of thin wires. Electromagnetic field waveforms also are reproduced by an inclined lightning channel model reconstructed from still photographs.

The effect of lightning channel inclination on the attachment of lightning flashes to UHV transmission lines is investigated using a lightning strike model that takes into account the competing connecting leaders issued from different conductors. The results show that the probability of screening failures increases with increasing inclination of the lightning channel.

Experiments to guide electric discharges with a chain of air breakdown plasmas (plasma channel) produced by a laser were carried out for use in power system protection applications. Electric discharges were guided up to 4.5m with a high power CO/sub 2/ laser focused by a 10m focal length mirror. Unusual 50% flashover voltage characteristics were obtained and the mechanism on the laser-guided discharge is shown. Experiments of laser-guided discharge in fog or rain were also carried out to clarify the effects of precipitation on the guiding characteristics, and the results are analysed quantitatively. >

Experiments to guide electric discharges with a chain of apparently discrete air breakdown plasmas (plasma channel) produced by a laser are reported. The electric discharge was guided up to 2 m with a high-power CO/sub 2/ laser focused by a 10 m focal length mirror. Voltage was applied at selected delay times tau following laser radiation. The relationships between 50% flashover voltage of a gap filled with laser-produced plasmas and delay times, and between guided length and the peak of the applied voltage, were obtained experimentally. The effects of the polarity of the applied voltage and the position of the plasma channel on flashover voltage are described. The development of the guided discharge is discussed. >

Lightning strikes not only metallic objects such as transmission towers and lightning rods but also insulated material such as blades of wind turbines. The discharge characteristics of insulated material are, however, not clarified till now. In this paper, discharge characterisitics of insulated material have been investigated experimentally using a 12-MV impulse generator. The effects of polarities of the applied voltages and surface conditions of the insulation material are also studied and it is found that pollution on the surface decreases the sparkover voltage drastically. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

For rational insulation design of a UHV substation, full-scale switching impulse tests of phase-to-ground (shielding ring-to-tower) and phase-to-phase (shielding ring-to-shielding ring) insulating clearance have been carried out in dry and wet conditions. In the tests, shielding rings that will be installed on bushings at actual UHV substations were used. The sparkover voltages depend on not only gap configurations but also the waveform of applied switching impulses; in other words, they show what we refer to as U-characteristics. Critical sparkover voltages are higher than those of rod-rod gaps by 20%-25% in dry conditions and by 7%-10% in wet conditions.

A current waveform at flashover of an arcing horn affects a peak value of a calculated transient overvoltage in lightning surge analysis of a power transmission system.

A new calculation method of leader development which considers predischarge currents is proposed. Calculated leader delopment characteristics with this model are compared with photographs of a image converter camera and close agreement is shown. Further, breakdown voltage-time characteristics of rod-plane and rod-rod gaps with standard and non-standard lightning impulses of both positive and negative polarities are calculated and these values agree with experimental results. This new calculation method is applicable to long gaps of several meters.