Testing breakdown voltage

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. 

The specimen is placed between heavy cylindrical brass electrodes, which carry electrical current during the test. There are two ways of running this test for dielectric strength. In the short-time test the voltage is increased from zero to breakdown at a uniform rate. The precise rate of voltage rise is specified in the governing material specifications. In the step-by-step test the initial... 

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

The AC rapid rise test was performed at 0.5 kV per second stress rate on similarly treated sanqples, and resulted in a decrease from 32 to 8 kV breakdown voltage for XLPE with tree penetration progressing from 0 to 100% of the insulation (Figure 22). Comparably shaped curves represent the performance of XLPE in... 

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. 

Several tests are essential for the evaluation of plastics in electrical applications. These tests include dielectric constant (permittivity ASTM-D150-74), which is the ratio of the capacitance of the polymer compared to air, dielectric strength, and dielectric breakdown voltage (ASTM-D149-75). Dielectric breakdown voltage is... 

The electric strength is generally highly dependent on the interelectrode distance, the surrounding medium and. to a lesser extent, the electrode area. For this reason it is preferable to report breakdown voltage, specimen dimensions, and test conditions rather than simply electric strength,... 

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. 

Two procedures are useful. The first makes no assumption about the actual statistical distribution of the observed breakdown voltage values, other than that the known data are similar to those that might be obtained in further tests. 

Test (he electrical properties (resistivity and or permittivity) of the immersion liquid to be used. Contamination of the liquid can often lead to erroneously high breakdown voltage values. 

The breakdown voltage increases proportionally less than thickness increases, and as a result the dielectric strength of a material decreases with the thickness of specimen (Figure 3.52b). For this reason, testing of insulation plastic should be done with approximately the thickness in which it is to be used in service. 

Any specimen thickness can be used the most common thickness is between 0.8 and 3.2 mm. ] The test specimen is placed between two electrodes in air or oil. To test for the breakdown voltage, voltage is applied across two electrodes and increased from zero until electrical bum-through punctures the sample, or decomposition occurs. ]... 

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