Leaky insulators

Many sources of noise can be overcome by careful design, such as the use of shielding to prevent pickup of random voltages, smoothing of power supplies to obviate the effect of main voltage variations, and the use of shock absorbers to reduce mechanical vibration. Other sources of noise can be avoided by simple precautions, such as avoiding defective components, poor contacts, leaky insulations, and temperature fluctuations which adversely affect the noise of ampliflers and photomultipliers (W8). 

Dielectric fluids such as liquid crystals are leaky insulators, i.e., they have low electrical conductivity and polarize in the presence of an electric field E. This means that the electric field induces internal charge reorganization, or distortion such as a net electric dipole moment per unit volume P appears. This is the polarization with units C/m. The sign of the polarization is defined as P > 0 if the direction is pointing from negative to positive charges. 

If a gauge is outgassed at too high a pressure, a layer of metal (from the electrodes) may be deposited outside the gauge envelope (some controllers prevent degassing at too high a pressure). This condition can cause the insulation to become leaky. A temporary solution can be achieved by grounding the electrical... 

Orazem et al. (1993, 1997) and Kennel-ley et al. (1993) took up this subject from the theoretical as well as the practical point of view, considering the cathodic protection of pipelines covered with insulation, characterized by leakiness (holidays and discrete holidays). Mathematical models have been created for different placements of anodes and their distance from the pipeline. In several papers, results are presented of theoretical calculations of the current and potential distribution and their comparison with experimental results. The finite element technique was used to solve the Laplace equation for potentials under boundary conditions, which describe the state of the insulation and the metal surface. Carson and Orazem (1998) also investigated the polarization characteristics of a pipeline as a function of time based on the formation of calcium precipitates. The results of these investigations were utilized in the construction of cathodic protection for the Trans-Alaska pipeline. More information on the CP of insulated pipelines is given in Sec. 8.4.4, while... 

The oldest Pearson method uses alternate currents for checking the insulation. In Fig. 8-19, a schematic diagram is shown of the detection of insulation leakiness by the Pearson method. 

Figure -20. Schematic diagram of testing insulation leakiness by the CIPS method. (From Global Cathodic protection Ltd.)...

Sometimes joint methods (e.g., CIPS and DCVG) are used. A worker walking along the pipeline records the distance as well as the on/off potential changes at small intervals of, e.g., 0.5 m, vs. a close CSE reference electrode. Measurements are supplemented with potential ON/OFF gradients in one or two directions perpendicular to the pipeline. The method requires synchronous switching off of all DC current sources polarizing the tested pipeline section. These types of measurements allow determination of the effectiveness of CP and detection of insulation leakiness (places of increased potential). Polaketal. (1997) point out that the applied methods of detection of insulation... 

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