Dielectric withstand voltage

The commonly used D-subminiature connectors are available in 9,15, 25 and 37 way versions with each pin typically having a 1 A current carrying capability and a dielectric withstand voltage of... 

The dielectric breakdown voltage or dielectric strength of polymers may be determined by ASTM-D149. The dielectric breakdown voltage is the maximum applied voltage that a polymer can withstand for 1 min divided by the thickness of the polymer. 

Levels of protechon that are considered essenhally equivalent are a) earthing of any exposed metal surface, b) physical separahon (typically 4 mm) between any exposed metal and parts of the circuit containing high voltage, and c) a layer of approved insulator between any exposed metal and the high voltage. Note that the insulator must have a minimum dielectric withstand capability of 1500 V ac or 2121 V dc. 

The separation to be filled is between two planes generating a large voltage bias and additional dielectric separation is reqnired to minimize the potential of dielectric withstanding breakdown. 

The dielectric strength of a polymer is a measure of its ability to withstand voltage without breakdown or the passage of considerable amounts of current. It is defined as the minimum voltage at or below which no breakdown occurs. Rather similarly, the breakdown voltage is the voltage above which actual failure occurs and the two items are often used interchangeably. 

Verification of dielectric properties, limited to power frequency voltage withstand or HV test on power as well as control and protective circuits. 

Since a very small gap in vacuum can withstand a very high voltage, a larger gap than required w ill not increase its dielectric strength. This is the limiting factor for a VCB to exceed a certain voltage system, presently 36 kV. 

By the immediate first current zero it is assumed that the contacts have travelled sufficiently apart to achieve the required deionization and have built up adequate dielectric strength to withstand at least 0.95 V, . If the circuit does not interrupt at the immediate current zero at a which is so near to the point of chopping Vt , the interruption will take place only by the next current zero at point h and result in another 260 strikes by then. To study more accurate behaviour of an intenupter, with the number of restrikes and the formation of the actual transient voltage waveforms on current chopping, oscillograms similar to those during a short-circuit test may be obtained (Section 14.3.6). 

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