CHAPTER 1&2-Example.docx - CHAPTER 1 INTRODUCTION TO...

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CHAPTER 1 INTRODUCTION TO HIGH VOLTAGE TECHNOLOGY Example 1: There are two type of field distribution, known as homogeneous and non-homogeneous field. What are differences of both field distributions? State the electrodes-gap configuration to simulate the homogeneous and non-homogeneous field. ANSWER: Homogeneous field:
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E is the same throughout the field region. Uniform or approximate uniform field distributions exist between 2 infinite parallel plates, or 2 spheres of equal diameters with gap spacing < sphere radius. “Profiled” parallel plates of finite sizes are also used to simulate homogeneous fields. Non-homogeneous field: E is different at different points in the field region. In the absence of space charges, E usually obtains the maximum value at the surface of the conductor which has the smallest radius of curvature non-homogeneous and asymmetrical. Most of the practical HV components have non-homogeneous and asymmetrical field distribution. In some gaps – will produce non-homogeneous fields and symmetrical, e.g. rod-rod or sphere- sphere (large distance between spheres) gaps. HV electrode has higher E than the grounded electrode. Example 2: Experimental analog is one of the methods for determining the potential distribution, Briefly describe any two of the experimental analogs used for space-charge-free fields. ANSWER : 1. Electrolytic Tank Widely used for decades. Equipotential boundaries are represented in the tank by specially formed sheets of metal. Example, a single dielectric problem such as a three-core cable may be represented by electrolytes of different conductivities separated by special partitions.
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Fig: Electrolytic tank model of a three-core cable represented at the instant when one core is at zero voltage, the same as the sheath 2. Semiconducting Paper Analog Less accurate but attractively simple alternative to the electrolyte. Errors in this method result from the nonhomogeneity of the paper resistivity. Errors also dependence on the ambient humidity and the contact resistance to the electrodes. Fig: Field plot between two spheres with skanks, as plotted by a semiconducting paper model 3. Resistive-Mesh Analog The continuous field is replaced by a discrete set of points as depicted by a mesh of resistors. The used of discrete resistors introduce an error arising from the finite mesh analysis. This error may be reduced by reducing the mesh size.
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Fig: Resistive mesh analog of the field pattern between two electrodes. The potential at node 0; V 0 = V1+ V2+ V3+ V4 4 Due to discretization, simulation of electrostatic fields in the vicinity of curved surfaces of the electrodes is bound to be of reduced accuracy.
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  • Spring '18
  • ZULKIFLI IBRAHIM
  • Volt, High Voltage, Permittivity, Dielectric

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