A pre-breakdown phenomenon in the liquid dielectric hexane

Chadband, W.G.; Wright, G.T.

doi:10.1088/0508-3443/16/3/303

Cited by 78 publications

(25 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The background current can be viewed in two different ways: the 'electrotechnical' capacitance view where the streamer front is considered to be a capacitance surface moving towards the plane electrode, which constitutes the opposite capacitance surface [28,29], or the more physical view that the current comes from ionization events at the head of the streamer.…”

Section: Background Currentmentioning

confidence: 99%

Pre-breakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 2: behaviour under negative polarity and comparison with positive polarity

et al. 2020

View full text Add to dashboard Cite

This study addresses the dielectric performance of nonpolar hydrocarbon liquids and mineral oils under negative polarity stress. Stopping length for non-breakdown streamers, breakdown voltages and velocities for various pre-breakdown streamer modes have been studied for a selection of model liquids (cyclohexane and white oils), for a gas to liquid oil, and a refined naphthenic transformer oil. Studies of propagation modes were done using an 80 mm point to plane gap and a step voltage with 0.5 μs rise time. Light emission and pre-breakdown currents have been recorded and instantaneous velocities have been derived from images of propagating streamers. Compared to positive polarity, there are less differences in streamer behaviour in the oils examined under negative polarity. Breakdown voltages and acceleration voltages are higher for negative streamers than for positive ones, while their propagation velocities are lower. While propagation modes for positive voltages are quite distinct, the mode changes for negative ones are more gradual. The behaviour of both positive and negative streamers is in line with the hypothesis that the propagation is governed by electron avalanches and quantum chemical properties of liquid components.

show abstract

Section: Background Currentmentioning

confidence: 99%

Pre-breakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 2: behaviour under negative polarity and comparison with positive polarity

et al. 2020

View full text Add to dashboard Cite

show abstract

“…If the subsequent bubbles are supposed to be of radius 25 pm, an average velocity v,, of 106 m/s can be obtained applying to the recordings the equations given by Beroual [25] to evaluate the streamer velocities. However, if it is supposed that the subsequent bubbles have a radius of 5 p m as was estimated (for filamentary streamers) by Chadband and Wright [13], an average velocity of 197 m/s is obtained. According to the measurements of v,, carried out in cyclohexane by other authors [13,17,23], for experimental conditions similar to ours, the U,, value (for the subsonic regime) is nearer 106 than 200 m/s (X 30 m/s).…”

Section: Resultsmentioning

confidence: 96%

“…However, if it is supposed that the subsequent bubbles have a radius of 5 p m as was estimated (for filamentary streamers) by Chadband and Wright [13], an average velocity of 197 m/s is obtained. According to the measurements of v,, carried out in cyclohexane by other authors [13,17,23], for experimental conditions similar to ours, the U,, value (for the subsonic regime) is nearer 106 than 200 m/s (X 30 m/s). Consequently, even if one must be very careful, it appears that the most probable shape of that streamer is the bushlike one.…”

Section: Resultsmentioning

confidence: 96%

See 1 more Smart Citation

The dynamics of DC predisruption in liquid insulating media

Briggs

Béroual

Buret

1994

IEEE Trans. Dielect. Electr. Insul.

View full text Add to dashboard Cite

Results of predisruptive current, light and electrical charge measurements are presented for the liquids tetraester, transformer oil and cyclohexane, under point-plane electrode arrangements with negative and positive high dc voltages. Observed current and light pulses existed both in the kHz and the MHz frequency ranges for both polarities of the point electrode. The electrical charge for the current pulses either increased or decreased sharply whenever these pulses occurred. In general, three pulse regimes were evident: (1) current pulses with no associated light pulses, (2) current pulses correlated with light pulses and (3) light pulses with no associated current pulses. Analysis of the results obtained suggests the occurrence of charge injection followed by processes of bubble formation and electronic avalanche multiplication in the liquid phase, and partial discharges in localized expanding bubbles. The steplike propagation of streamers is explained and streamer velocities were estimated. Involvement of both electronic and gaseous phenomena in predisruptive processes is also suggested.

show abstract

“…Experimental work of this type began almost 40 years ago with the pioneering studies of Hakim and Higham [l] and of Farazmand [2], who were the first to publish flash-illuminated, schlieren photographs that optically resolve prebreakdown events. These studies were then continued by Chadband and Wright [3], and it is a measure of the success of the technique that many groups have taken up the method, and a considerable amount of photographic data of this type is now available [4]. From such high-speed schlieren and shadowgraph observations, electrical breakdown can be seen as a sequence of hydrodynamic processes involving the growth and distortion of a vapor cavity in the electric field, leading to streamers that cross the gap and cause the actual breakdown.…”

Section: Introductionmentioning

confidence: 99%

The growth of prebreakdown cavities in silicone fluids and the frequency of the accompanying discharge pulses

Watson

Qureshi

Chadband

1998

IEEE Trans. Dielect. Electr. Insul.

View full text Add to dashboard Cite

Measurements have been made of prebreakdown cavities in silicone fluids, and of the current pulses that accompany cavity growth. These experiments were carried out in silicone fluids of 0.65,10,100 and 1000 cS viscosity. Cavity growth, driven by the electrostatic field, is limited at low viscosities by inertia, and at high viscosities by viscous drag. The electrostatic force on the cavity wall is related to the local field and to the space charge density in the liquid adjacent to the cavity. We are concerned with the relationship between the electrostatic force and the cavity growth, and with the discharges that accompany cavity growth. Discharges occur in welldefined pulse trains: the first pulse in a train generates the cavity, and subsequent pulses are due to discharges within the cavity. Knowing the scaling laws for cavity growth we can use the time between the first and second pulses to estimate the cavity size when the first cavity discharge occurs; this gives a cavity diameter of -5 to 7 pm. The next pulse cannot occur until the charge from the previous discharge has dispersed. We find that the time between pulses is strongly viscosity dependent; at high viscosities the average time between pulses At is proportional to fluid-viscosity, but in the low viscosity limit the dependence approaches Q~/~, To explain this viscosity dependence we consider three mechanisms: (1) a decrease in charge density due to increase in cavity size; (2) ion detrapping from the cavity wall and drift in the applied field; and (3) diffusion of an impurity species to the cavity surface, charge exchange to create amobile ion, and its subsequent drift in the field. Our experimental results are consistent with the cavity expansion model, but there is evidence of diffusion effects in low viscosity liquids, and with ion-drift at high viscosities.

show abstract

A pre-breakdown phenomenon in the liquid dielectric hexane

Cited by 78 publications

References 6 publications

Pre-breakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 2: behaviour under negative polarity and comparison with positive polarity

Pre-breakdown phenomena in hydrocarbon liquids in a point-plane gap under step voltage. Part 2: behaviour under negative polarity and comparison with positive polarity

The dynamics of DC predisruption in liquid insulating media

The growth of prebreakdown cavities in silicone fluids and the frequency of the accompanying discharge pulses

Contact Info

Product

Resources

About