الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The design engineers in the field of OHTL face a lot of difficulties in selecting the optimized insulating materials. Egypt is going to connect the Egyptian electrical grid with the Saudia electrical grid. Because of the difference in frequencies and the very long distance between the two grids, we have to connect them through DC OHTL. The problem is the rare of the research regarding DC voltages because of the rare of its applications. So we have to dig deeper to understand and evaluate the insulators under DC voltages and especially the polymeric insulators.
There are a lot of methods for evaluating the insulators. It can be classified into field experience evaluation and lab experiments. The field experience considers all the environmental stresses that will face the insulators, but it is very risky, expensive, and dangerous, and take several years for an evaluation. It has been founded that lab experiments are less dangerous and take a few hours to evaluate the insulators although it doesn’t cover all the environmental stresses.
The inclined plane test (IPT) is the most common lab test for evaluating the surface of the insulating material to face environmental stresses. The main advantage of this test is that it evaluates the insulating material even before the manufacturing of the insulator itself by preparing a small dimension sample. This will save time and cost of evaluation of the insulators after manufacturing them.
IEC60587 and ASTMD2303 are the standards for IPT under AC voltages. The main problem is that there is no similar standard for evaluating the materials under DC voltages. Our target in this thesis is to try to standardize the DC IPT. So we have to understand the performance of the insulators subjected to DC voltages and
also we have to understand the difference between the AC and DC voltages behavior on the insulators.
In the practical field, the insulators` manufacturers are using AC-designed insulators in DC applications but at lower rating voltage. The short lifetime of the insulators has been noticed. This occurs because the DC voltages form electrostatic forces on the insulator’s surface, these forces attract the pollution on the insulators surface.
In this thesis, we made a comparative study of the effect of different voltage modes (AC, +DC, -DC). It has been found that the +DC is the most severe voltage and causes the highest erosion. Also, we have correlated the leakage current with the variation of the voltage levels and modes. Also, we have correlated the leakage current with the contamination flow rate. These correlations have been modeled by using COMSOL and ELECNET software. We have also correlated the rank of the insulators with the practical application, where insulator samples that pass at 6 kV are used in the HV applications. On the other hand, the samples that pass at 4.5 kV are used in the MV and LV applications. A comparative study has been done between the performance of the SIR, porcelain, and RTV-coated porcelain. It has been founded that porcelain is the most robust material, RTV-coated insulators form pods thatcollect pollution and may cause the failure of the insulators. The reason for the superior performance of the porcelain insulator has been justified by using the COMSOL and ELECNET software. One of the gaps that have been resolved in this thesis is the contradiction between the role of the residue formed after the passage of the leakage current on the surface of the insulators. We have found that cleaning the SIR by removing the residue reduces the resistance of the SIR surface for erosion and tracking.