Flashover electrical

PCTFE exhibits very good electrical properties ia terms of high iasulation resistance, minimal trackiag, corona formation, and surface flashover due to the polymer s nonwettable surface and ultralow moisture absorption (Table 3). 

Dirt, soot, moisture, and other contaminants can provide paths for electrical flashover or short-circuiting in switchgear and other electrical equipment. 

Operational problems can arise with platelet type materials, which have a fairly large surface area but virtually no thickness. These are very light in terms of mass and tend to attach themselves on to the collectors and each other, thereby reducing electrical clearance, which leads to flashover. 

Knowledge of the flashover voltage of the necessary insulators in helium at low temperatures in addition to the breakdown voltage will be important. Flashovers can occur wherever surfaces of solid insulators are parallel to the electric field lines or their components. 

By increasing the electrode distance to 8 mm and, with this, decreasing the electric field strength, higher flashover voltages could be attained, however, not to the same degree as the electric field strength decreased (see Fig, 1),... 

Those spots where three media meet, namely, the electrode, the insulation material, and the helium, are indicated in Fig. 1 by a circle in dashed lines. Those spots appeared to be particularly critical. Special consideration was given to improvements to relieve those spots of the electric stress as far as possible. Because of a simpler test arrangement, these experiments were performed at first in liquid nitrogen. The particularly proper insulators were tested in helium. It was found that a conductive layer on the inner surface of the insulator contacting the inner electrode resulted in significant improvement of the flashover behavior. The reason for this is probably that the insulator and... 

Flashover. A discharge of electricity across the surface of an insulator. Damage may result. 

Bum injuries may be associated with shock and can be seen as bum marks on the body at the points of current entry and exit or may also occur in the burning of internal tissue. However, severe burn injuries are more likely to arise as a consequence of short circuit flashover. In fact the number of fatalities arising from this latter cause is similar to that resulting directly from electric shock. 

Short circuit flashovers caused during the course of live work are likely to result in serious injury for the simple reason that the worker is in close proximity to and probably directly facing the equipment that has been inadvertently short circuited. The extent of the flashover will depend on the amount of electrical energy available to flow into the fault. This will be determined by the fault level (the amount of current that the incoming electrical supply is capable of feeding into the fault) and the speed of operation of the electrical protection, e.g. a fuse or circuit breaker, to interrupt the flow of fault current. 

An electrical flashover is an electric arc between two components or a component and ground. 

When lighming strikes a tower (or a GW) as illustrated in Figure 2.36, the lighming current flows into the tower and causes a sudden increase in tower voltage. When the voltage difference between the tower and a phase wire (PW) reaches its electrical withstand voltage, a flashover from the tower to the PW occurs. This is called back flashover (BFO), because... 

Spurious effects can also occur due to space charge, as when insulating materials are treated by charged-particle beams, and may include electric-field-enhanced diffusion, sample degradation by surface flashover, and peak shifting and broadening during XPS analysis [34, 35]. 

Electrical machines and traction motors may suffer from commutator roughness and general contamination with dirt leading to the possibility of low resistance values and flashover. 

Flashover voltage can be increased by raising the gas pressure, by utilizing electronegative gases like SFe with a high electric strength, and by immersion in... 

Geometry affects the flashover voltag. For example, a copper rod placed inside a plastic tube distorts the electric field (9) and thereby reduces the flashover voltage. 

Under voltage stress, scintillation (tiny arcs) may occur on surfaces covered with a wet conducting contaminant. Under such conditions progressive electrical surface failure may take place by tracking. With serious contamination, a phenolic resin-paper laminate fails over a 12.5-mm spacing at only 115 V (162-V peak), a much lower voltage than for the Paschen flashover voltage (Fig. 9). 

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