Breakdown Test

Bnich-kupfer, n. scrap copper, -last, /. breaking load, -metall, n. broken metal, scrap metal, -modul, m. modulus of rupture, -probe, /. breaking test, breakdown test, -punkt, m. breaking point, -riss, m. (Meial.) failure crack, -silber, n. broken silver, scrap silver, -spaonung,/. breaking stress tensile strength, -stein, m. quarry stone broken stone, -stelle,/. broken place, place of fracture. -strich, m. (Math.) fraction stroke (between numerator and denominator), -stiick, n. fragment shred, -stiicke, pi. debris scrap, -teil, m. fraction, -zahl, /. fractional number. 

In the first method a series of electrical breakdown tests is carried out at the maximum design service temperature and these data are fitted to a 3 parameter Weibull distribution... 

Equipment for breakdown tests is often constructed by the user from bought-in components. Some information is given in the test method... 

Electrodes attached to the surface of a specimen during a dielectric breakdown test will exert a compressive force on the specimen by mutual Coulombic attraction of the electrodes as the voltage V is imposed. If this is sufficient to... 

The DC breakdown strength was determined under conditions applied in the rapid rise AC breakdown test, but with direct current. In the absence of trees, both PE and XLPE exhibited DC breakdown strengths in excess of 50 kV, and flashovers at this stress prevented the determination of exact values. About wall penetration lowered this value to 15 kV for XLPE and it remained approximately constant at higher penetration. 

The electric strength or dielectric breakdown test method (ASTM D-877) indicates the absence, or presence, of free or suspended water and other contaminant matter that will conduct electricity. A high electric strength gives no indication of the purity of an oil in the sense of degree of refinement or the absence of most types of oil-soluble contaminants. This test method is of some assistance, when applied to an otherwise satisfactory oil, to indicate that the oil is free of contaminants of the type indicated above in practice, this ensures that the oil is dry. 

Atmospheric Breakdown) Test exposed outdoors are periodically sprayed with a... 

The effects of irradiation on both the electrical and the mechanical properties of the specimens were measured. Electrical tests comprised breakdown and in situ resistivity and postirradiation resistivity. Breakdown tests were performed after irradiation at room temperature. The need for tests in situ is recognized and being studied. Equipment originally designed for ASTM D 877-67 (breakdown testing of transformer coils) was modified to use solid... 

The preceding standards also contain specifications for conducting the various tests required in paragraph (a) of this section. For example, the ac and dc proof tests, the breakdown test, the water-soak procedure, and the ozone test mentioned in this paragraph are described in detail in these ASTM standards. 

Hi-Pot Faults. Hi-pot or high-potential voltage breakdown testing is often confused with isolation testing. The tests are very similar, and, to the extent that high voltage is... 

The electric breakdown of a dielectric liquid under high electric stress is a complex phenomenon where many elementary processes contribute to the change of the electrical current through the test gap from values of pico- to nano-amperes to values of kilo-amperes on a time scale of nanoseconds. Electronic processes are always involved in the initiation of the electric breakdown of nonpolar dielectric liquids. Unambiguous experimental evidence is scarce in the literature since a multitude of other effects obscures the electronic contribution of the breakdown process. In addition, many breakdown tests were performed on industrial-grade liquids, such as transformer oil etc., which are not pure liquids but rather mixtures of several components. More unambiguous information on electronic processes can be obtained from breakdown measurements with impulse voltages of nanosecond to microsecond duration. Complementary are studies of the laser-induced breakdown. 

We shall take transformer oil as an example since it is a liquid of major technological importance in high voltage insulation. Moreover, there is a multitude of data on breakdown tests in the literature than we can tentatively unify in the light of our own results. 

A comparison of a cyclic test newly developed by Hoogovens for automotive panels with the salt spray test, the SCAB (simulated corrosive atmospheric breakdown) test, and the VDA (Verein der Deutschen Automobilindustrie) test showed that some differences can be observed in the test results for the ranking as far as undermining is concerned. A negative relation exists between the results of the new cyclic test and the salt spray test. The new cyclic test shows reasonable agreement in Copyright 2002 Marcel Dekker, Inc. 

In the chapter Selection of an adhesive , we provide charts indicating which types of adhesives should be used to bond a material Ml to a material M2. The only way to measure adhesion to a given substrate is to prepare samples of actual bonded parts and test it by various mechanical breakdown tests. Basically, bonded joints may be stressed and eventually broken in 4 different modes tensile shear, tensile force, peel and cleavage. These modes are shown in Fig. 29. 

A similar test, known as the cathodic breakdown test, involves cathodic polarization to —1.6 V (versus saturated calomel electrode, SCE) for a period of 3 min in acidified NaCl. Again, the test was designed for anodized aluminum alloys because the alkali created at the large appUed currents will promote the formation of corroded spots at defects in the anodized film. 

Thermal Breakdown. After electric breakdown, many plastics are noticeably warm or even very hot. When breakdown tests are made at high frequencies (above 1 MHz), failure occurs at relatively low voltages and is usually accompanied by high heat emission. Pol3rmers with absorbed moisture and high dielectric loss may also fail at a low voltage with too much heat. 

Fig. 18. Configurations of plastic and electrodes for voltage-breakdown tests parallel to laminations, (a) Tapered pin electrodes in insulating oil (b) embedded point-to-plane test (c) opposed pins in opposite blind holes and (d) specimen placed at center of and in contact with wide electrodes inunersed in oU.

Typical electrodes for electric breakdown tests are described in ASTM D 149, lEC Publ. 243, and material specifications. Different procedures are used in the United States and Europe. It should be emphasized that electric breakdown values are influenced greatly by electrode geometry. For research and development, electrodes may be recessed in the material to be tested. Although tests are most often made in air, it is common to immerse the test specimens in oil or to use a pressurized gas, such as SFe to prevent flashover. 

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