Voltage variations, electrical properties

One of the main reasons why plastics have become so widely used in electronics and electrical applications is that they are good dielectric materials with readily controllable electrical properties. However, the fact that plastics are good insulators does not mean that they are inert in an electrical field and the intrinsic properties of a material can usually be related to performance under specific test conditions. The electrical properties that have to be considered when selecting a material are the dielectric constant, the volume resistivity, surface resistivity, dissipation, power and loss factors, arc resistance and dielectric strength. When selecting a plastic for a specific application the variation of these properties with changes in the likely service environment has to be taken into account since many of them are temperature, frequency, voltage and environmentally variable. 

Some important dielectric behavior properties are dielectric loss, loss factor, dielectric constant, direct current (DC) conductivity, alternating current (AC) conductivity, and electric breakdown strength. The term dielectric behavior usually refers to the variation of these properties as a function of frequency, composition, voltage, pressure, and temperature. 

The heat flux was varied for every fixed mass flow rate in order to obtain a series of outlet vapour qualities between 0.2 and 1 with a step of 0.05. Steady state values were monitored using a Hewlett Packard 3421A with a 30 minutes time lapse between each mass flow rate or heat flux change. Averaging was carried out after every 20 values and uncertainties were calculated according to the Kline and McClintock (1953) method. The total electrical power dissipated in the test section was calculated as the product of voltage and current. The variations of R134a thermophysical properties with temperature were calculated with the REFPROP 6.01 software. 

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