Effect of liquid flow velocity on the breakdown voltage of mineral oil under highly nonuniform fields

Zaky, A. A.; Megahed, I.Y.; El-Awa, M.

doi:10.1109/icdl.1990.202966

Cited by 8 publications

(5 citation statements)

References 6 publications

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“…Of the various factors that are known to affect the breakdown strength of insulating liquids, the influence of organic additives seems to have received least attention. A small number of workers (Zaky and Hawley 1973) have reported that weak concentrations of aromatic additives improve the electric strength of insulating oils and that there is an optimum additive concentration that results in a maximum increase in the breakdown strength. Recent work by the present authors (Evangelou et al1973) has shown that the breakdown voltage varies with additive concentration in a complex manner.…”

Section: Introductionmentioning

confidence: 99%

“…As far as the mechanism of electric breakdown of dielectric liquids is concerned, there is substantial experimental evidence in support of the theory that the breakdown process, particularly in the later stages, is governed by the presence of a gaseous phase (Tropper 1961, Krasucki 1966, Singh et a1 1972. Some investigators have held the view that there is a correlation between the breakdown strength and the gassing properties of insulating liquids (Zaky and Hawley 1973). If such a correlation exists, then one should expect some parallelism between the breakdown voltage and the gassing properties of an oil as a function of additive concentration.…”

Section: Introductionmentioning

confidence: 99%

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The effect of organic additives on the breakdown and gassing properties of mineral oils

Zaky

Megahed

Evangelou

1976

J. Phys. D: Appl. Phys.

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The effect of organic additive content on the direct voltage breakdown strength of degassed transformer oil and liquid paraffin is reported for a wide range of concentration of additives known to be effective gassing inhibitors. Their effect on the breakdown strength of oils saturated with hydrogen, nitrogen and oxygen is also reported. Measurements of the gassing properties of the oils were carried out for the same extended range of additive concentrations. The observed breakdown and gassing versus concentration characteristics indicate the presence of maximum and minimum points at concentrations which are independent of the matrix liquid and of dissolved gas and gas phase. There is a remarkable degree of correlation between the breakdown and the gassing properties of the liquids tested. This and other relevant observations indicate that gas generation is an intrinsic part of the breakdown process and strongly support the bubble theory of breakdown. This forms the basis for the discussion of the results.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of organic additives on the breakdown and gassing properties of mineral oils

Zaky

Megahed

Evangelou

1976

J. Phys. D: Appl. Phys.

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“…Some workers have found that the breakdown voltage is higher for a positive point polarity whereas others found that a negative point gave higher breakdown voltages. This apparent contradiction in the results has been explained by the actual existence of a crossover point in the breakdown voltage against gap length characteristics (Zaky and Hawley 1973). This crossover point corresponds to a critical gap length at which the breakdown voltage is the same for both polarities.…”

Section: Introductionmentioning

confidence: 87%

“…When the point is negative the results show that anodization of the sphere anode resulted in a marked reduction in the breakdown voltage at small gap spacings. The presence of an insulating film on the anode lowers the breakdown strength of liquid insulants (Zaky and Hawley 1973) for uniform field geometries. In the present case it is suggested that unneutralized positive ions enhance the local field at the anode thereby facilitating the initiation of a back streamer which will propagate towards the point cathode.…”

Section: Degassed Liquidmentioning

confidence: 99%

Electrical breakdown of mineral oil under non-uniform fields

Zaky

Nosseir

Megahed

et al. 1976

J. Phys. D: Appl. Phys.

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The dependence of the direct electrical breakdown voltage of degassed transformer oil and of gas-saturated oil on gap length for a point-sphere electrode system has been studied for the two polarities of the point. The effects of anodization of the sphere electrode on the breakdown voltage against gap characteristics have also been examined. The critical gap length at which the breakdown voltage is the same for both polarities of the point has been found to depend on the nature of the insulating film on the sphere electrode and on the type of gas dissolved in the oil. The discussion of the results is based on the propagation of a corona discharge from the point electrode and the possibility of formation of a back streamer from the sphere electrode.

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“…[121,122]. The authors attributed the higher resistance could be due to one or more of the fol- is determined from a three-dimensional topography of the crater obtained using a surface scanning laser as discussed in Sec.…”

Section: Comparison Of Spray-edm Wet-edm and Dry-edm Processesmentioning

confidence: 99%

Atomized Dielectric Spray-Based Electric Discharge Machining (Spray-EDM) for Sustainable Manufacturing

Pattabhiraman

Marla

Kapoor

2015

Volume 1: Processing

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Electrical Discharge Machining is a non-traditional machining process that is widely used in the tool and die-making industry, automotive, and aerospace industries due to its ability to produce complex three-dimensional geometries with good accuracy and surface finish. Despite the aforementioned advantages, the consumption of a large quantity of dielectric (especially hydrocarbon oils) poses a significant health and environmental hazard including respiratory and skin irritation issues. Further, the disposal of waste dielectric that contains a significant amount of metal particulates poses safety concerns. In order to comply with environmental safety standards, extensive filtration and treatment systems capable of handling huge amounts of dielectric waste need to be set up for their safe disposal.This leads to an increased energy consumption and hence higher operating cost for the machining process. Thus, there is a need to reduce the consumption of oil-based dielectrics without compromising their superior machining performance.Several techniques including dry and near-dry EDM have been developed to reduce the consumption of dielectrics. However, they have poor debris flushing capability. This research seeks to develop a technique that minimizes the consumption of dielectrics and also improves the flushing of debris from the inter-electrode gap.A novel method of using atomized dielectric spray in EDM (Spray-EDM) to reduce the consumption of dielectric is developed in this study. The atomized dielectric droplets form a moving dielectric film up on impinging the work surface that penetrates the inter-electrode gap and acts as a single-phase dielectric medium between the electrodes. It also effectively removes the debris particles from the discharge zone. Single-discharge EDM experiments are performed using ii three different dielectric supply methods, viz., conventional Wet-EDM (electrodes submerged in dielectric medium), Dry-EDM and Spray-EDM in order to compare the processes based on material removal, tool electrode wear and flushing of debris from the inter-electrode gap across a range of discharge energies. It is observed that Spray-EDM produces higher material removal compared to the other two methods for all combinations of discharge parameters used in the study.The tool electrode wear using atomized dielectric is significantly better than Dry-EDM and comparable to that observed in Wet-EDM. The percentage of debris particles deposited within a distance of 100 µm from the center of EDM crater is also significantly reduced using the Spray-EDM technique. iv

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Effect of liquid flow velocity on the breakdown voltage of mineral oil under highly nonuniform fields

Cited by 8 publications

References 6 publications

The effect of organic additives on the breakdown and gassing properties of mineral oils

The effect of organic additives on the breakdown and gassing properties of mineral oils

Electrical breakdown of mineral oil under non-uniform fields

Atomized Dielectric Spray-Based Electric Discharge Machining (Spray-EDM) for Sustainable Manufacturing

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