Electrical insulation breakdown

ASTM D149, Test Methodsfor Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commercial Power Frequencies, Vol. 8.01, ASTM, Philadelphia, Pa., 1987. 

ASTM D149, 97 (2004). Standard test method for dielectric breakdown voltage and dielectric strength of electrical insulating materials at commercial power frequencies. 

Polymeric materials usually have low dielectric breakdown voltages. Fortunately, the electrical insulation property of PDMS is sufficient (R > 1015 O/cm) [159]. Moreover, the use of a lower electric field ( 1100 V/cm) helps alleviate this... 

Lubricant film between the moving parts generally provides an electrical insulation, and breakdown voltage ranges between 30 and 50 V. Electrical bridges may form due to soiling, metal particles, or insufficient lubricant. 

In addition to high breakdown strength, the electrical insulators for superconducting magnets must have excellent dielectric properties at cryogenic temperatures. Chant reported the results of measurements on dielectric constant and loss tangent (tan 5) for several polymers over the temperature range from 4.2 to 300 K [83], The variation of dielectric constant of samples as a function of temperature is shown in Fig. 15. The dielectric constants of nonpolar polymers, such as polyethylene, polypropylene and polytetrafluoroethylene, are substantially independent of temperature, whereas those of polar polymers except polyimide decrease by a maximum of 20% as the temperature is reduced. The values of tan 8 at the frequency of 75 cps for nonpolar polymers decreased by... 

Jarosz, G., Signerski, R., and Godlewski, J., in Proceedings- IEEE Fifth International Conference on Conduction and Breakdown in Solid Dielectrics, IEEE Dielectrics and Electrical Insulation Society, Leicester, England, 1995, p. 134. 

In reality, however, salts dissolved in water find or create paths into a hydrophobic polymer matrix and cause the breakdown of an insulating layer or the corrosion of the substrate metal. In contrast to the diffusion process described above, the process of salt going into polymer matrix could be termed salt intrusion because the breakdown of the surface state does not occur with water that does not contain salts. The salt intrusion starts with the breakdown of the surface state. In a study of the electric insulation characteristics of LDPE film, it was found that salt ions intrude into the polymer matrix by different mechanisms [3,4]. The exact mechanisms for salt intrusion are not known, but the phenomenological salt intrusion found can be summarized as follows, in an effort to explain the nature of salt intrusion that causes the breakdown of the surface state. 

The insulation breakdown under electrical stress occurs in a fatigue mode, i.e., not a gradual deterioration but an abrupt failure, and is correlated to the salt intrusion characteristics of the film, as shown in Figures 24.12 and 24.13. The hydrophobic surface state created by plasma polymerization of (HFE + H2) significantly prolongs the time when the breakdown of surface state by salt intrusion occurs. 

The electrical properties of interest for ceramics include conductivity, resistivity, dielectric breakdown strength, dielectric constant, loss factor, and electromechanical coupling. Most ceramics do not have high electrical conductivity, and thus ceramics have found application as electrical insulators for many years. The electrical insulating capability of some ceramics is also retained under high electric field this is referred to as high dielectric breakdown strength... 

Because of the high breakdown voltage, wide band-gap material can and have been used as electrical insulators. There has been a great deal of interest in pressed nanophase SiC and diamond powders as an electrical insulator for capacitors. 

The third problem associated with water based varnishes is poor electrical insulation properties of the laminate after moisture conditioning. This problem is probably the most critical problem because insulation failures of the laminate can lead to electrical failure of the finished printed circuit board. This property is measured by conditioning the finished laminate in a high moisture environment and then testing the dielectric breakdown strength. ED24574 has excellent insulation resistance. This was achieved by a proprietary resin composition. 

Long-term behavior of insulation systems can be estimated after the temperature index has been determined by the impregnated twisted pair test (IEC 172, criterion breakdown voltage) or helical coil test (IEC 1033, Method B, criterion bond strength). The two tests lead to differing results that do not correlate and the end user of the system enameled wire/impregnating resin has to decide which test is applicable for his electrical appliance. It is important to choose a suitable combination of materials and to ensure close cooperation between manufacturers of electrical insulating materials and those who later process them. 

If the fluid film separating two metallic bounding surfaces is an electrical insulator, then loss of insulating behavior and appearance of conductance can be interpreted as contact between these surfaces. This is the premise behind the electrical conductance method of detecting lubricant film failure. A practical limit on the applicability of this premise is electrical breakdown of the fluid as thinning of the film concentrates the field intensity. Another complication arises from the fact that for the structured surfaces of every day experience first contact is at the highest asperities rough surfaces may therefore come into initial contact sooner than indicated by the overall trend of the resistance measurements. 

Most gases arc good electrical insulators at normal conditions. When an electric field applied to a certain set of electrodes exceed a critical field, breakdown occurs in the gas. This breakdown phenomenon is affected by various parameters of electrode gap distance, pressure, type of gas, temperature, type of voltage, amplitude of applied voltage and frequency etc. 

Retention of a required level of electrical Insulation to protect against electrical breakdown, arcing, etc., with the associated dangers and hazards of electrical fires, and human safety. 

In addition, a wide field of application of polymeric materials is in sheet or tubular material for electrical insulation, where the area exposed to electric stress is very large. A small failure frequency on proof test" may be commercially significant. Here, the individual values of voltage at which breakdown occurs are by definition much lower than the average breakdown voltage of a. small test area. At the same time, the failures cau.sing concern are obviously located within the actual area of the electrodes. 

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