ELECTRIC STRENGTHS

Grade G-9, glass fabric with moisture-resistant melamine resin binder, is similar to Grade G-5 but with better electric strength properties under wet conditions. Electrical appHcations should be limited to operating temperatures of 50°C (122°F) or less. 

Grade G-10, glass fabric with epoxy resin binder, has extremely high mechanical strength (flexural, impact, and bonding) at room temperature and good dielectric loss and electric strength properties under both dry and humid conditions. 

The insulating property of any insulator will break down in a sufficiently strong electric field. The dielectric strength is defined as the electric strength (V/m) which an insulating material can withstand. For plastics the dielectric strength can vary from 1 to 1000 MV/m. Materials may be compared on the basis of their relative permittivity (or dielectric constant). This is the ratio of the permittivity of the material to the permittivity of a vacuum. The ability of a... 

The efficiency of transformer oils as dielectrics is measured by electric strength tests. These give an indication of the voltage at which, under the test conditions, the oil will break down. Various national standards exist that all measure the same basic property of the oil. There is an international specification, lEC 296/1982, which may be quoted by equipment manufacturers in their oil recommendations. 

The negative resistance effect is observed when anodic oxides are subjected to so-called electroforming (i.e., annealing in vacuum).93 Such a treatment removes the special features of the anodic oxides (asymmetry of conduction and electric strength, electret effect, etc.), and the negative resistance effect may be explained using the general approach developed for amorphous dielectrics.5... 

A collective term for rubber and rubber-like substances. Tree rubber is a natural elastomer and man-made rubbers are synthetic elastomers. Electric Strength... 

Methods for measuring the resistivity of insulating materials are based on IEC 60093 [24] and insulation resistance is covered by IEC 60167 [25]. For conducting and antistatic materials the methods for rubbers, ISO 1853 [26] for resistivity and ISO 2878 [27] for resistance, could be adapted and there is a draft IEC standard. The general method for electric strength is IEC 60243 [28] and methods for power factor and permittivity are often based on IEC 60250 [29]. 

IEC 60243, Electrical strength of insulating materials - Test methods - Part 1 Tests at power frequencies, 1998. 

DS (ASTM D-149) is an indication of the electrical strength of an insulating material and it is dependent on the particular test conditions. 

CF2)4 mw 200,04 chemically inert dry gas, bp —6°(760mm) high,electric strength. Can be prepd by dimerization of tetrafluoroethylene at high temp. Used for electric equipment and as aerosol proplnt for foods and pharmaceuticals... 

Resistance or resistivity Surface charge Electric strength Tracking resistance Power factor and permittivity... 

Electric strength is usually taken as the nominal voltage gradient (applied voltage divided by test piece thickness) at which breakdown occurs under specified conditions of test. These specified conditions of test are important as the measured electric strength is not an intrinsic property of the material but depends on test piece thickness, time of electrification and the electrode geometry, as well as on conditioning of the material. 

Grade Electrical strength Insulation Tensile strength, MPa/ Lengthwise Crosswise Modulus of elasticity, GPa Lengthwise Crosswise Rockwell Density, g/mL... 

Testing of polyurethanes for their electrical properties due to the voltages required must be carried out using properly designed equipment. The electrical tests that are normally carried out are resistivity, insulation resistance, electric strength, tracking resistance, power factor, and permittivity. 

The temperature plays, of course, a role in both mechanisms the electric strength decreases with increasing T. Moreover, though expressed in volts per meter thickness, it depends on the thickness (again non-linearity). Thin films have a considerably higher strength than most values found in tables of properties, which are results of tests on thicker samples. 

Thermal elasticity of varnish film on copper at 200 °C, hours, not more than Electric strength of varnish film after baking at 200°C, KV/mm, at 40 20 20... 

Of considerable interest is the use of silicone rubbers for insulation in electrotechnical equipment. This is accounted for by superior heat resistance of elastomers and their good dielectric properties. E.g., the dielectric permeability of polyorganosiloxane elastomers at 500 V and 60 Hz is 3.5-5.5, their electric strength at 60 Hz is 15-20 KV/mm, and the dielectric loss tangent, which characterises the losses of electric energy in insulation, at 500 V and 60 Hz amounts only to 0.001. It is very important that these characteristics are preserved in a much wider temperature range than in the case of natural and synthetic organic elastomers. 

Electric strength data are meaningful only if the test conditions are adequately defined for example, if d.c. loading is employed the rate of voltage increase should be specified, if pulsed voltages are used the rise time should be specified and if a.c. loading is adopted the frequency and waveform should be specified. 

When testing electric strength there is the risk of flash-over across the specimen surface between the electrodes. This is avoided by making the measurement with the specimen immersed in an insulating liquid, such as transformer oil, which displaces air from the ceramic surface. 

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