Discharge breakdown

Electrical stress can lead to partial discharge breakdown, thermal effects, electrochemical... 

High-voltage PE insulation thicker than 4 mm (0.16 in.) tends to form voids due to heat accumulation, the evolution of hydrogen gas, and discharge breakdown due to accumulation of excess charges when irradiated. To eliminate this problem, the addition of prorads (such as multifunctional... 

In the industrial situation thermal breakdown is the most significant mode of failure and is avoided through experience rather than by application of theory. Nevertheless it is important to appreciate the mechanisms leading to thermal breakdown. A third mode of failure, referred to as discharge breakdown, is of importance in ceramics because it has its origins in porosity. 

Finally, discharge breakdown may occur when gas discharges occur in the pores of a dielectric material. The electric strength of the ceramics depends upon the specimen and pore sizes in other words, larger pores will increase the probabUily of failure as the electric field in a pore, Ep, is greater than that in the surrounding... 

Static charge generation causes an ignition hazard only if the accumulated charges create an electric field sufficient to produce an electrical discharge in a flammable atmosphere. In most processes, this means that the electric field intensity at some location must reach the breakdown strength of air (nominally 3 X lO " V/m). The objective of static-control measures is to ensure that electric field intensities cannot reach this value. 

Electrostatic Discharges An electrostatic discharge takes place when a gas or vapor-air mixture is stressed, electrically, to its breakdown value. Depending upon the specific circumstances, the breakdown appears as one of four types of discharges, which vary greatly in origin, appearance, duration, and incendivity. 

Test results Any disruptive discharge or electrical breakdown during the application of high voltage should be considered as a dielectric failure. 

The procedure will be the same as that discussed for switchgear assemblies (Section 14.3.3). The test voltage may be applied for one minute as shown in Tables 32.1 (A) or (B) for series I and Table 32.2 for series II voltage systems. Any disruptive discharge or insulation breakdown during the application of high voltage will be considered to be dielectric failure. 

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