Study Of Safety Forecast Theory And Real-time Monitoring Technique For Switching Overvoltage Of Large Power Stations

With the constant development of the extra-high voltage electric power network, large generator units are continuously put into the electric power network for generating electric energy. Because the relationship between the large generator and the large electric power network is being reinforced increasingly, these large generators dominate a most important productive position for large power stations and they have become hearts for the electric power systems. However, with the increment of working voltage for the long-distance transmission line, the switching overvoltage in large power stations is threatening the insulation safety of large generators at any time, and not only the safety generating operation of generator units can be directly damaged, but also will the safety power supply of electric power systems to the national economy be finally affected. The stator insulation failure can be finally resulted in by the insulation damage of the generator stricken by switching overvoltage, for the problem about the insulation safety of large generator stricken by switching overvoltage, but some appropriate methods for diagnosing the stator insulation faults have not been even solved. Therefore, in order to protect large generating equipment against the switching overvoltage, the research on safety forecast theory and real-time monitoring technique for the surge overvoltage of large power stations has not only importance and benefit to safety operation of generators, but also has the great importance for the engineering of transferring electricity from the west to the east in China and the safety operation of large electric power network with great capacity and long-distance transmission line.Based on the investigation of analysis methods for the overvoltage striking on rotating electric machines and its research status at home and abroad, the safety forecast theory and the analysis method for the switching overvoltage of large power stations are firstly presented based on the field-circuit analysis, and the transient field distribution and the insulation condition in the stator winding insulator stricken by the switching overvoltage in large power stations are studied and analyzed on line. At the same time,some insulation fault point and domain in generators can be predicted and even detected successfully, and the insulation safety analysis method and assessment model for large generator units are studied seriously. Moreover, in order that large generators are protected to work safely, the useful technique of safety forecast and real-time monitoring for the switching overvolatge is also approached and studied so that the preventive protection and maintenance can be supplied to the large generators.Therefore, the main contents and the creative results of this paper are described as follows:(1)The on-line safety forecast theory for switching overvoltage of large power stations based on the field-circuit analysis is presented by analyzing the electromagnetic transient for electric network of large power stations.(2) A new method for on-line forecast and analysis of the insulation safety of large generators is found by combining the topology construct of the electric network in power stations with the electromagnetic relationship inside large generators and using the field-circuit analysis theory.(3) The law and characteristic of electromagnetic transient process for the switching overvoltage in the electric network of power stations have been studied by analyzing the electromagnetic transient process of switching overvoltage in power station and specially approaching the surge overvoltage transferred from the switchgear station through power transformers.(4) The transient field-circuit model of large generator and the network model of power station are all studied. Moreover, the coupling finite-element model with fast computational speed and high accuracy is found, which is very suitable for the on-line insulation safety forecast diagnosis of large generators.(5) The...