110-220kV XLPE Cable Insulation On-line Monitoring Technique

110～220kV XLPE power cable has been an important component of the power system. XLPE power cable has many advantages, such as excellent dielectric properties and heat resistance, large transmission capacity, light weight, simple structure of cable terminations, and facilitated installation. With the development of power grid and the needs of urban power network renovation, the proportion of XLPE cable lines is increasing in power system. But its failure would cause huge economic losses and serious social impact so the safe operation of power systems is important for 110～220kV XLPE cable.As the concept of condition-based maintenance has been accepted by people, on-line monitoring technology has been developing rapidly. However, XLPE cable insulation on-line detection technology is always a difficult problem of insulation monitoring technique. Particularly, the existing low-voltage XLPE cable insulation on-line detection method cannot always adapt to the 110～220kV high-voltage XLPE cables. Therefore, it is necessary for 110～220kV XLPE cable to carry out the specialized research.1,It is a summary of 110～220kV high voltage XLPE cable insulation online detection that whose importance, research significance and the history development have been made in this paper. And the author has made comments on various online insulation detection methods and research status, in which the key problem and development has been pointed out.2,It is a basic theory which has been made a deep research into the XLPE cable insulation. The research shows that the water tree length is increasing as voltage amplitude and frequency, and the smaller the tip radius of curvature, the longer the length of water tree. The cable insulation resistance, tan 8 and Grounding Current can respond to the degree of water tree aging. Secondly, the aging mechanism of electrical trees has been studied and the trap theory has been applied to explain the XLPE power cables in the formation of branches. Finally, partial discharge of XLPE cables to the theoretical study of aging has been studied.3,It is Single-ended earthing of metal shield layer XLPE cable insulation on-line detection which is made focus research on with Grounding Current. The study of simulation results shows that Grounding Current and tanδof cable can reflect the cable insulation defects. Then, the method on diagnosing of insulation characteristics has been proposed. Finally, an insulation on-line detection system is successfully developed by the application of the virtual instrument technology and Grounding Current method. This system can be real-time detection of the grounding line current, tanδ, insulation equivalent resistance and insulation equivalent capacitance. Through three years'site operating, the system is stable, reliable and accurate. The operating personnel can realize the situation of cable insulation with convenience.4,A new insulation on-line monitoring method on metal shielding layer of cross--bonding XLPE cable has been proposed in this paper. Because the metal shield layers of the cable is crossing, the leakage current and tanδof a single cable cannot be obtained through direct measuring. So it is impossible to judge accurately the situation of the cable insulation. It is calculating amplitude difference and phase angle difference between XLPE cable grounding line current and initial installation of the current grounding line that through which the result reflects the changes in each cable insulation condition. By analyzing the vector diagram, the author demonstrates the Physical Meaning of the new method. According to the theory of circuit, it has been deduced the relationship between the cable insulation fault location with variables of grounding--line current amplitude and phase. Based on ART2A-E neural network, Cross-Bonding XLPE cable insulation fault section diagnosis algorithm has been created. It is a new way for Cross-Bonding XLPE Power cable insulation diagnosis.5,It has been put forward to the new partial discharge signal extraction technology of XLPE cable which is based on broadband high-frequency sensors and blind source separation algorithm. Firstly, current signal of test object and coupling capacitor have been measured respectively with two high-frequency sensors. And then it improves blind source separation algorithm to realize partial discharge signals'separation from outside interference signals. Simulation tests and laboratory simulation experiments show that this method can extracting accurate partial discharge signal from mixed-signal of outside interference and partial discharge signal.6. It is the first time that the negative entropy as the measurement of Partial Discharge Pulse Shape of sparse or non-Gaussian according to their characteristics. A new vector graph is built, in which time domain Negentropy of PD pulse is the X-axis and frequency domain Negentropy of PD pulse is the Y-axis. Simulation tests and laboratory simulation experiments show that different types of partial discharge pulse can form clusters in the time-frequency spectrum. So classification of partial discharge pulse can be completed through the spectrum. And then the application of PCA algorithm can realize the extraction of partial discharge pulse characteristics. All of that have laid the foundation of the partial discharge pulse pattern recognition.