Sparkover Characteristics Research Articles

がいしの塩汚損が配電線直撃雷によるスパークオーバ発生率に与える影響

To improve the lightning-outage-rate calculation method of medium-voltage distribution lines, it is important to accurately assess sparkover rates of insulators. In salt polluted areas, lightning outage rates may increase due to the deterioration of insulation performance of insulators. Although the sparkover characteristics of salt-polluted insulators against the standard lightning impulse voltage have been reported in previous works, the sparkover characteristics against short-wave-tail lightning impulse voltages, which occur across insulators on distribution lines by direct lightning strikes, still remain not clarified.

Influence of Medium Voltage Distribution Line Configuration on Phase to Phase Sparkover Rate due to Direct Lightning Strike

In recent years, to reduce maintenance and management cost of distribution facilities, overhead ground wires are sometimes removed in a certain area. In such distribution lines, wire breaking at mid-span due to direct lightning is of concern. Although phase to phase sparkover is considered to be one of the factors of wire breaking at mid-span, its quantitative study has not yet been carried out. In this paper, at first, we experimentally examined detailed sparkover characteristics between phase conductors against short tail lightning impulse voltage, which is assumed to be phase to phase voltage. Next, based on experimental results, we estimate the phase to phase sparkover rate by means of lightning outage calculation program developed by CRIEPI. Estimated results suggest the phase to phase sparkover rate depends on the configuration of distribution lines, such as span length, arrangement of conductors, and so forth.

Corona Charge Injection Prior to Sparkover in an Inversed Rod-Plane Gap Under Composite Voltages

Research on the sparkover characteristics of long air gaps under composite voltages has important significance on the design and operation of transmission lines and equipment. In this paper, corona charge injection prior to sparkover in an inversed rod-plane gap under composite voltages was studied. The variation of charge injection to the initiation of leader and breakdown was measured by a capacitor divider. Two photomultipliers were positioned to study corona development at two positions between the tip of the rod and the plane, from which the light output could be compared with the charge injected into the gap. When a positive prestress voltage is employed at the plane, charge injection is enhanced and leader inception and breakdown occur at lower voltages than with prestress voltage of opposite polarity. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50%</sub> sparkover voltages are in inverse proportion to the charge and power inputs up to the time of the leader initiation. The results of corona charge injection to sparkover are helpful for understanding the physical process of the gap breakdown in depth.

Sparkover Characteristics in CF3I Gas and CF3I/N2 Gas Mixture under Non-uniform Field Gaps

A steep-front square pulse voltage generator, which has a rise time of 16ns, a dumping factor less than 2.5% after 10μs duration and a peak value of 200kV, is successfully used to survey the V-t characteristics in nanosecond range. The V-t characteristics of CF3I, SF6, CF3I/N2 and SF6/N2 gas mixtures under non-uniform field gaps by using the steep-front square pulse voltage. When the field utilization factor are measured less than 0.38, the sparkover voltage of CF3I is lower than that of SF6. On the contrary, when the field utilization factor is more than 0.38, the sparkover voltage of CF3I is higher than that of SF6. The corona inception voltage calculated by using Schumann's criteria and compared with measured one. The V-t characteristics for a uniform field gap in CF3I/N2 gas mixture containing N2 gas of 40% are equivalent to those in pure SF6 gas. The synergism for appears when CF3I gas is mixed with N2 gas.

Effects of a Charged Metallic Particle of Milli-size on DC Sparkover Voltages

Effects of a charged metallic particle of milli-size on sparkover characteristics under dc quasi-uniform gap of 2 cm long in atmospheric air. The results show that the sparkover voltage depends on the position and charging of the sphere particle of 0.1 or 0.2 cm in diameter along the gap axis. Ions generated by natural radiation in the gap lead to charge the metallic particle and contribute significantly to the sparkover voltage depending on the humidity in air. With the high humidity, the particle is quickly charged and the sparkover voltage falls in lower than half of the voltage without the metallic particle.

Short Time Region Sparkover Characteristics of Compressed N2 and CO2 using Square Impulse and their Quantitative Estimation Method

SF6 is used as a main insulation gas for gas-insulated switchgears (GIS), but it has recently become a gas to be restricted because of its greenhouse effect. Up to now, we have studied the insulation characteristics of compressed N2 and CO2 as a possible SF6-alternative gas. As GIS are subjected to very fast transient voltage due to incoming lightning surges or at disconnector switching operation, it is necessary to clarify the sparkover voltage-time (V-t) characteristics in the short time region. In this report, we describe the V-t curves ranging from 30ns to 10μs for high pressure (0.6 and 1.0MPa) N2 and CO2 obtained by applying square impulse voltage. We next studied the V-t curves for standard lightning and oscillating impulses for the same experimental conditions. Based on these results, we investigated the possibility of quantitatively estimating of the V-t curves for these waveforms by applying the “equal-area criterion”. The minimum sparkover voltage estimated by the criterion very well agreed with the measured characteristic in all conditions studied, and thus it has become clear that the quantitative estimation of the sparkover characteristics is possible for high pressure N2 and CO2.

Impulse sparkover characteristics of sphere-rod gaps

The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined.

Phase-to-ground and phase-to-phase sparkover characteristics of external insulation at the entrance of a UHV substation

Phase-to-ground and phase-to-phase sparkover characteristics of external insulation at the entrance of a UHV substation

Phase-to-Ground and Phase-to-Phase Sparkover Characteristics of External Insulation at the Entrance of an UHV Substation

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.

Tests on the breakdown of air at elevated temperatures in non-uniform electric fields

Sparkover voltage characteristics have been obtained using a 20 cm rod–plane gap at temperatures between 294 and 770K. Lightning and slow-front impulse and alternating voltages have been applied; pre-breakdown corona has also been investigated under impulse voltages. The nature of the sparkover characteristics depends strongly on the type and polarity of the applied voltage. These are discussed in terms of the changes in relative air density with temperature and the relationship to the recommendations of IEC 60-1 for the adjustment of sparkover measurements to changes in atmospheric conditions.

Sparkover in the rod–plane gap under combined direct and impulse voltages

Experiments are described in which composite voltages, produced by superimposing positive and negative switching impulse voltages on pre-stressing positive or negative direct voltages, are applied to a rod–plane gap of lengths up to 1 m. Changes in 50% sparkover voltages are described over a range of positive and negative pre-stressing voltages; it is shown that negative pre-stressing always reduces the composite sparkover voltage, but that positive pre-stress increases the positive composite sparkover voltage and reduces the negative one. Recordings of photomultiplier observations and ‘still’ photography of pre-breakdown corona have been made at the 50% sparkover level and the results related to the sparkover characteristics. It is shown that the latter depend on the way in which leader initiation is affected by the preceding DC corona.

Application of portable protective gaps for live work on compact 550 kV transmission lines

This paper presents result of research on the application of a portable protective gap (PPG) to live work on a compact 550 kV steel lattice tower. The objective of the research was to provide experimental evidence which confirms the needed coordination of the PPG sparkover characteristics with the sparkover characteristics of the worksite on the compact tower during live work. Sparkover characteristics of the worksite are strongly affected by the presence of the worker, the live working tools, and damaged insulators.

Dielectric breakdown in nonuniform field air gaps

The sparkover characteristics of rod-rod and rod-plane gaps in air under DC voltages are reviewed. The linear characteristics of both configurations are associated with the prominence of streamer discharges during the prebreakdown phase. The limits of linearity are shown to be a function of humidity, gap spacing and electrode profile, all of which determine the predischarge mode. It is shown that the rod-plane gap offers a wider range of linearity than the rod-rod gap and that it can have a valid role as a DC voltage measurement tool.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis and comparison of rod—plane and rod—rod gaps as direct voltage measurement devices

The direct voltage sparkover characteristics of the rod—rod and the rod—plane electrode gaps systems are presented and compared. It is shown that for both arrangements the linearity is limited by the effects of atmospheric humidity for small ( 1 metre) electrode separations. The characteristics are discussed in terms of leader growth in the prebreakdown discharge; this is humidity dependent and is shown to be more prominent in the rod—rod gap. The precision and useful range of measurements in the two gaps are compared, particularly in relation to the recent approval of the rod—rod gap as a device for direct voltage measurement by the IEC.

Sparkover Characteristics of Long Fog-Contaminated Air Gaps

The paper constitutes a systematic experimental investigation into the effect of fog on the sparkover characteristics of rod-plane gaps with special reference to power frequency voltages. The tests covered gap spacings in the range of 15-400 cm. Special care was taken to separate the effects of the mode of voltage application from those due to physical changes in the gap under investigation. Tests were also performed under a variety of air humidity conditions and under artificial rain. Finally, tests with switching impulses and direct voltage of both polarities are reported.

Sparkover Characteristics of Long Fog-Contaminated Air Gaps

The paper constitutes a systematic experimental investigation into the effect of fog on the sparkover characteristics of rod-plane gaps with special reference to power frequency voltages. The tests covered gap spacings in the range of 15-400 cm. Special care was taken to separate the effects of the mode of voltage application from those due to physical changes in the gap under investigation. Tests were also performed under a variety of air humidity conditions and under artificial rain. Finally, tests with switching impulses and direct voltage of both polarities are reported.

Line Entrance Protection of 500 KV Gas Insulated Substations by SF6 Spark Gaps

The use of both station arresters and line entrance arresters provides absolute protection for all operating conditions of gas insulated substations (GIS). However, it represents a costly installation. Hence the adoption of line entrance rod gaps in air can be taken into consideration. But their protection ability is questionable because the slope of the V-t curves for air gaps is much steeper than that for GIS, while SF6 spark gaps with good sparkover characteristics would meet the requirements for the ability to protect the line entrance apparatus of GIS.

Effect of Large Electrodes on Sparkover Characteristics of Air Gaps and Station Insulators

The paper constitutes a laboratory investigation into the influence of large electrodes on the dry and wet sparkover characteristics of air gaps and high voltage insulator supports. Tests were carried out with power frequency and switching impulse voltages.

Influence of rain on switching impulse sparkover voltage of large-electrode air gaps

The paper deals with a laboratory investigation into the influence of rain on the switching impulse sparkover characteristics of large-sphere and toroid plane air gaps. Tests were also carried out on coneterminated rod-plane gaps for reference purposes. The factors investigated include the high voltage electrode geometry, nature of the surface, rain intensity as well as the impulse form and polarity. Attention is also paid to the influence of rain on the statistical dispersion of the sparkover voltage and on the nature of the cumulative probability curve. A general correlation, valid for a wide variety of electrodes, has been established between the mean spark-over voltage gradient for positive switching impulses under dry conditions, and the corresponding influence of rain on the breakdown voltage.

Sparkover Characteristics of High Voltage Protective Gaps

Published data on sparkover characteristics of high-voltage protective gaps with 50-200 cm spacings have been reviewed and statistically analyzed. The results are presented, including: volt-time curves for times to sparkover up to 8 Ms, average critical sparkover gradient for various types of gaps for lightning impulse and for switching impulse, and average sparkover gradient for power-frequency voltage. Wherever justifiable, 95 percent confidence intervals are also given.