The Study On Insulation Diagnosis Technique Of Electric Cable In Urban Areas

With the rapid development of China's economic, the electrical load is increasing in urban power network. As a transmission of the energy carrier, the reliability of power cable affects the safe operation of the entire power system. Due to the city planning and the requirements of network structure, a lot of cable lines were put into power grid construction in urban areas. At present, there are many 110 kV voltage grade XLPE power cables have come in service and in a trend of fast-growing. At the same time, the failure rate of power cables is greatly increased. Therefore, the study on insulation diagnosis technique of electric cable in urban areas is more and more important to make the entire power system more safe and stable.XLPE power cables are widely used in urban grid due to their superior advantages. In order to master the insulation operating conditions, it is necessary to carry out insulation monitoring and diagnosis online. In this thesis, first analyzed and compared the insulation preventive experiment with online monitoring for the current power cables, and pointed out their advantages and disadvantages. Then, summarized the research with XLPE cables insulation testing technology at home and abroad, and pointed out the develop direction in the future.For Crossing-linked high voltage grounding cable in urban areas,vector analysis method is proposed to judge the cables insulation status in this paper. A standard unit of cables cross connection grounding was analyzed, according to the feature of current flowing through the cable shielding layer of power frequency vector can be combined with the vector operation, getting flow through each section load current and voltage of the main insulation, the status for each sections of the cable insulation can be judged according to Ohm's law. For the 10 kV cable's transient faults to urban distribution, we propose a simple and economical way for their fault diagnosis. Through the establishment of the cable model, Both distances of fault and fault resistance can be estimated by a least square fitting algorithm, than compared and analyzed with history information, the final diagnosis decision was making by the control processing center to determine the point of failure location..Finally, the insulation on-line monitoring system was designed in urban areas. Through communication between GPRS and internet network, by analysis and processing the collected circulation signal which is sent to the remote integrated information management system to determine the cable insulation condition to achieve overrun warning function, which can effectively prevent the occurrence of cable insulation accidents, improve the safe operation of for power system stability.