| With the rapid development of power transmission and distribution grid scale year by year,high-voltage cables are increasingly used in power transmission systems due to their advantages of meeting the requirements for large-capacity power transmission and protecting the city from damage.Therefore,keeping abreast of the operating status of cables and ensuring the normal operation of high-voltage cables plays a vital role in the safety and stability of the power system.In order to discover the faults in the cross-connected grounding system of high-voltage cables in time,a new criterion is proposed to realize the fault diagnosis of cables,which reduces the workload of fault maintenance to a certain extent.The specific research contents are as follows:First of all,the research status of on-line monitoring technology of cable faults at home and abroad is analyzed,and the grounding current method is determined to be used to study the cross-connected grounding system of high-voltage cables.After that,the harm caused by excessively high induced voltage on the metal sheath of the cable and the four metal sheath grounding methods to limit the excessively high induced voltage of the sheath are briefly described.Then,the flow mechanism of sheath current in the case of normal cable operation and different faults under the cross-connected grounding mode is emphatically analyzed,and the calculation method of sheath current under different faults is obtained by combining the corresponding circuit wiring diagram and equivalent circuit diagram.Secondly,a new criterion for identifying faults in the cross-connected grounding system of high-voltage cables is proposed.For the current problems of insufficient feature quantity required for online monitoring of high-voltage cable cross-connected grounding system and the complex and variable currents at coaxial cables on the cross-connected grounding box that is difficult to reflect the state information of each cable metal sheath,etc.In this paper,a new criterion is proposed,the characteristic parameters of new criterion are constructed by using the amplitude ratio and phase ratio of grounding current at both ends of the same metal sheath circuit and the absolute value of phase difference of grounding current at both ends of different metal sheath circuits,and a characteristic quantity matrix corresponding to new criteria is established by multi-dimensional characteristic fusion.And the matrix contains not only the amplitude and phase information of a single sheath current,but also the phase relationship between different sheath currents,which can more accurately reflect the state information of each cable metal sheath.After that,a simulation model of high-voltage cable cross-interconnection grounding system was built in PSCAD/EMTDC software,six common cable faults were simulated,and the classification of cable faults was realized by comparing the differences between the characteristic quantity matrix corresponding to each fault type,and the feasibility of the new criterion was verified.Finally,taking the characteristic quantity matrix corresponding to the new criterion as the input of the random forest algorithm,a cable fault classification model based on the random forest algorithm is proposed,and the classification performance of the cable fault classification model based on the random forest algorithm and the decision tree algorithm is compared.In addition,the performance of the new criterion proposed in this paper and the traditional criterion in the classifier algorithm are simply compared,and from the results of the sample test,it is concluded that the new criterion proposed in this paper has certain advantages compared with the traditional criterion.And the feature quantity used in constructing the fault criterion in this paper is small and easy to collect,which is easy to realize in practical engineering applications,and provides a new idea for online monitoring of high-voltage cable line faults. |
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