1Department of Electrical & Electronics Engineering, Ghousia College of Engineering, Ramanagaram - 571511, Karnataka, India. Phone: +919900650035
2Department of Electrical & Electronics Engineering, BNM Institute of Technology, Banashankari, Bangalore - 560070, Karnataka, India. Phone: +919845038229
3Department of Electrical & Electronics Engg., JNTU, Hyderabad - 500085, Andhra Pradesh, India Phone: +919347277771
Behavior of high voltage power transformer winding insulation to fast front time surge voltages such as lightning overvoltages for initial stress distribution is dependent upon the square root of the ratio of total ground capacitance to total series capacitance of the winding which is termed α. Voltage distribution across power transformer winding sections can be controlled by providing suitably designed metal oxide surge absorber (MOA) blocks across these sections. Computer simulations have been carried out to analyze effect of providing MOA blocks on different sections of power transformer winding. High voltage windings having α values 6, 12 and 18 have been analyzed. Initially, several variations were carried out in the computer simulations to investigate whether MOA blocks could be provided across first few sections of windings only. All these investigations indicated that such an arrangement transfers high electrical stresses to sections across which the surge absorber blocks are not provided. In addition these investigations have shown that by providing MOA blocks on each of the sections of the entire winding can only result in considerable reduction of stresses for appearance of fast transient voltages at line terminal. The results have also shown that, for α values 6, 12 and 18, the maximum voltage stress across a section of winding without MOA blocks can be 35%, 51% and 68% respectively and these values with MOA blocks across sections is limited to between 23% to 24%.
Lightning overvoltage, transformer windings, MOA blocks, voltage distribution, stress reduction
