Development Of On-line Assessment System Of Insulation Characteristics For High Voltage Cables In Coal Mine

The project in this thesis is one important part of the major project "Study on the system of Condition Monitoring and Fault Diagnosis & Early-warning for Ventilation and Security of the Power Supply System in Coal Mines", which is the sub-project of "Safety Status Monitoring and Fault Diagnosis Forecast of Mine Ventilation Power Supply System"(No:2007BAK29B05), sponsored by the National Key Technology R&D Program of China during the Eleventh Five-year Plan Period. The task is mainly proposed for the lacke of online monitoring and evaluation system for the insulation characteristics of mining high voltage EPR cable.With the development of fully mechanized working face and the increase of power in shearers and scraper-conveyors, in more and more coal mine the power is directly supplied using a voltage of lOkV. It has brought stringent test for the power supply system. Under the coal mine all of the power is supplied with cables. Due to the harsh environment, the humidity air, unstable working conditions and load changing, the cable insulation will deteriorate and the leakage current will increase in the long run. If the damage is not discovered earlier, coal dust combustion and gas explosion will be caused easily. Mine safety production will face serious threat. Therefore, it is important and significant for the safety in production and the reliability in power supply to explore the mechanism of insulation deterioration, study the detecting methods for insulation characteristics, develop an on-line system to detecting the insulating condition in real-time, find out potential insulation defects timely, and realize pre-failure warning.After literature reviewing and site investigation, considering the feasibility, safety and economy, the insulation parameters was determined and an on-line evaluation system for mine high voltage cables was develoged, based on depth analysis of existing insulation assessment methods. The main contents of this thesis are as follows:1. the establishment of corresponding relationship between insulation characteristic parameters and fault typesBased on the research of the basic structure of the mining EPR cables and underground lOkV supply line connection, after analysising common failure causes and failure types, The relationship between the insulation characteristic parameters and the type of fault is established, which laid the foundation for the fault diagnosis.2. the establishment of circuit model of the dielectric polarization based on insulation aging mechanismThe polarization circuit model of cable insulation dielectric is established, by deeply analysising the aging mechanisms and the insulation degradation trend of insulation medium. It provides theoretical reference for the analysis of cable insulation on-line assessment methods.3. the design of cable insulation performance evaluation scheme based on a plurality of insulation characteristic parametersOn consideration of the coal mine power supply line connection and installation environment, the scheme of on-line evaluating mine high voltage cable insulation characteristics is designed. The insulation resistance, conductor temperature and partial discharge are selected as the insulation characteristics of online detection. The results of tests show that the scheme is feasible.4. the development of mine high voltage cable insulation properties on-line assessment systemBased on the characteristics of the detection signal, the signal condition circuit, sampling circuit, communication circuit, power supply circuit and FPGA data processing system are designed. Combining with the host machine fault diagnosis procedures, the functions of on-line detecting and evaluating insulation state are implemented. It accumulates valuable experience and provides a solid foundation for the future development of mine high voltage cable life evaluation system.The results of commissioning tests in the laboratory and underground coal mine show that:The system is simple in structure and reliable in operation, and the insulation characterization parameters of mine high voltage cable are accurately captured and processed in real-time, the on-line assessment of insulation characteristics is achieved. The successful development of the system lays the foundation, accumulates experience for the further study and fills the blank of mine high voltage cable insulation on-line assessment, both at home and abroad.