With the development of electric power industry, power cable will play a more and more important role not only widely used in distribution network, but also in the field of AC/DC and high voltage transimission system. Power cable is generally underground or underwater, the problem that fault concealment and long time troubleshooting make serious impact on the power supply reliability of power system. Evaluate real-time operation state of power cable by using multi-parameters from variety of monitoring and detection information, and strengthen early defect equipment monitoring on the basis of evaluation result, it can reduce equipment failure rate and prevent accident expanding and it has very important significance for improving power supply reliability, From the perspective of information fusion, the method of evaluation algorithm based on RBF (Radial basis function) neural network is proposed. Multi-parameter including online detection data, environmental factors, testing and equipment information is used to conduct a comprehensive evaluation on cable status. The method using data fusion in decision-making level by RBF neural network for results of different algorithms including catastrophe theory and ANP fuzzy theory can make up applicability problem of different evaluation algorithm, and achieve complementary functions between the algorithms. To further adapt to the actual conditions of parameters, the integrity of input parameters was associated to credibility of evaluation results, it will make evaluation results more complete. The affectivity of the algorithm was verified by practical data.

State evaluation of power cable based on RBF information fusion algorithm using multi-parameters

The contact of Gas insulated switchgear (GIS) will become loose in its long-term operation, which directly leads to partial discharge and overheating. This paper described an online temperature monitoring technology based on fiber Bragg grating (FBG) for GIS bus contact. Temperature distribution of GIS bus was established by coupled method of electromagnetic and thermal field. To monitor the bus temperature accurately, a novel FBG sensor that combined plating and welding technology together was designed. Comparing with other FBG sensors, it was proved to have a high sensitivity up to 30 pm/° and a pretty well linearity. Finally, wavelength interrogation system was utilized to realize wavelength and temperature modulation. The paper for the first time applied FBG sensors to GIS temperature monitoring and could detect fault in advance, which was quite beneficial to the operation of GIS and power transmission.

Fiber bragg grating technology used in temperature online monitoring for GIS bus contact

With the continuous development of power grids, power cables are widely used in urban power grids. But cables are generally laid underground, and the fault is not easy to be found and the recovery time is long, the reliability of power supply was seriously threatened. The traditional planned maintenance has not been able to solve the existing problems accurately. Therefore, it is of great significance to improve the reliability of power distribution and reduce the failure rate by assessing the operational status of power cables through the relevance analysis of massive monitoring and testing data. This paper proposes a power cable state assessment algorithm based on association rule data mining technology from the perspective of big data and information relevance. Firstly, by analyzing the online monitoring data, detection data, experimental data, and the interrelation of the state parameters of the cable and transformer fault types, the set of cable synthetic status parameters can be set up. Then, use the association rule method to calculate the weight coefficient of each state parameters; In order to effectively avoid the influence of subjective factors on the evaluation results, weighted theory of equilibrium function was used to calculate the weight coefficient of the synthetic status parameters; Finally, combined with the existing assessment process, an accurate and objective evaluation system power cable was established. The results of the example verify the validity and accuracy of the assessment method, which provides a new novel idea for cable status assessment.

A State Assessment Algorithm of Power Cable Based on Association Rules Data Mining Technology

3D real-time display system of cable temperature monitoring is introduced in this paper. With the technology of distributed optical fiber measurement, real-time temperature getting from the full range monitoring of the power cable is used to build the 3D model of monitoring object, so that 3D real-time display could be realized for power cable temperature monitoring.

3D real-time display system for cable temperature monitoring

The operating condition of cross-linked polyethylene (XLPE) cables is related to the safe and stable operation of the power system. This paper proposes a data-driven comprehensive evaluation model based on the radar chart for the operating state of XLPE cables. Aiming at the multi-dimensional characteristics of XLPE power cables, a comprehensive evaluation method based on radar chart features is established. Then this artificial studied the feature sorting of the radar chart, and an optimal ranking method of XLPE power cable graph features combining genetic algorithm and historical data is proposed. The experimental results show that the method proposed in this paper can effectively improve the accuracy of the comprehensive evaluation of the operating status of the XLPE cables.

Data-Driven Comprehensive Evaluation Model Based on the Radar Chart for the Operating State of XLPE Cables

The loading current quantity and overload ability of power cable line is able to be adjusted accurately if the temperature of cable conductor was detected in real time. Specially, the bottleneck effect of loading current quantity of long power cable line may be formed because the partial over-hot spot caused by the differences of soil thermal resistance, heating resources and laying conditions, etc. along this cable line. On the other hand, partial defect in dielectric of cable accessories and breakdown foreboding as well as fire accidents are relation with the temperature of power cable to a certain extent. Therefore, it is a basic method to ascertain the bottleneck location, dielectric operating state and calculating the loading current quantity in real time by continuously detecting operation temperature of power cable line on-line. But it is well known that conductor temperature of power cable being detected is more difficult than detection of outer sheath temperature . That is, it is very easy to realize outer sheath temperature detection on-line with the help of distribution optic fiber or thermoelectric couple. According to detecting results of outer sheath temperature of power cable in real time, the temperature of power cable conductor may be calculated by mathematic principles, i.e. Node Voltage Method at the same time. In this paper, we prefer to choose distribution optic fiber for temperature detection on-line due to its reliability, accuracy and temperature detected continuously in real time. The temperature detection technique of distribution optic fiber applied to power cable line on-line based on optic frequency domain reflection (OFDR) theory and TCP/IP communication criterion were researched in this paper. Comparing with optic time domain reflection (OTDF), OFDR solves many problems such as prolonging the life of laser generator and optic switch, decreasing the power of laser generator, and increasing space distinguish ratio as well as data network transmission and background processing easily, etc. The research results proved that the temperature detection technique based on OFDR may meet the requirements of outer sheath temperature detection of power cable line rated voltage from 110kV up to 500kV in real time on-line and its temperature detection accuracy and space distinguish ratio are 1.5 °C and ±1.0 m.

Application of Operation Temperature Detection Technique for On-line Power Cable Lines

VLF(0.1Hz) voltage test as one of the quality evaluation methods has been applied to medium voltage capacitive equipments,i.e.electrical generators,electrical motors and power cable lines for more than 20 years.Until today,it has been disputed that how to validate the test time and test voltage when taking VLF voltage test on power cable line because the different probability of identifying faults hidden in dielectric in advance by the test effectively.The validity and equivalence of these test results have been researched and discussed since 1980's.Unfortunately,the test results are not obvious evidence.In fact,the technical standards of VLF voltage test including test voltage range from 2U_0 up to 3.5 U_0 and test time range from 15 min up to 60 min are confirmed by different countries in the word.Practice experience in field and many results of theoretical research as well as parallel tests in laboratory in China have proved that extending test time and increasing high voltage are not necessary and very harmful to dielectric of power cable due to the power cable using high resistive solid dielectric.Even the damage of power cable dielectric is not rehabilitated and lead power cable line early or unexpected broken.Therefore,it is important to optimize the combination of test time and test voltage of VLF(0.1Hz) voltage test today.For optimizing validation of test voltage and test time,the validity and equivalence as well as relation of test voltage and test time of VLF(0.1Hz) voltage test is discussed and analyzed in detailed by mathematic statistics based on a mass of test experience in field and in laboratory in this paper.The results of research and optimization in the paper prove and verify that the test method of 3U_0 test voltage and 40min test time is much better fit for power cable lines in field test,and may meet the estimation of dielectric quality of power cable lines on-site testing.

Luo Junhua

Papers

Application of Operation Temperature Detection Technique for On-line Power Cable Lines

Optimizing Validation of Voltage and Time for VLF(0.1Hz) Voltage Testing