Research On Detection And Location Methods Of Latent Faults In Medium Voltage Distribution Cable

In recent years,the proportion of cables in urban medium-voltage distribution network lines has gradually increased.Cable line faults caused by the decrease in the strength of the cable’s own insulation layer have become an important safety hazard in urban distribution networks.During the operation of the medium voltage distribution cable,its local insulation performance will be reduced due to its own defects,environmental factors and external force damage,and it may cause multiple short-term and self-healing arcs at the location where the insulation performance is reduced.And this type of arc fault will often eventually develop into a permanent ground fault.We call this type of fault a cable latent fault.Detecting and locating latent cable faults is of great significance for preventing permanent cable faults,reducing power loss caused by faults,and ensuring the safe operation of power systems.In this paper,based on the Kizilcay arc model,an equivalent model suitable for cable latent faults in low-resistance grounded power distribution systems is first established in this paper.Insulation defect channels such as water tree or electrical trees are equivalent to fixed grounding resistance to simulate the severity of latent faults.If the fixed ground resistance is large,it proves that the insulation still has good performance,and the latent fault is not serious;if the fixed ground resistance is small,it proves that the insulation performance is weak and the latent fault is more serious.By changing the value of the fixed grounding resistance and the arc duration in the equivalent model,it is possible to simulate cable latent faults of different severity,and build a typical 10k V low-resistance cable distribution network model in the PSCAD/EMTDC platform.The cable latent faults of different severity are simulated,and the influence of different fault parameters（characteristic voltage u₀ of arc,characteristic resistance r₀ of arc and time constantτ）on the characteristics of latent faults is analyzed.Secondly,based on the phase space reconstruction and fractal theory,the latent fault characteristics of medium voltage distribution cables are extracted.The phase space characteristic trajectory of the fault phase current is constructed,and the singular attractor of the empty phase space trajectory of the fault phase current is extracted based on the fractal dimension,and the 8-dimensional fault feature vector is extracted from the fractal dimension.Thirdly,based on the latent fault feature vector,combined with the KNN algorithm classifier,a new type of medium voltage distribution cable latent fault detection method is proposed.The 8-dimensional fault feature vector is used as the input parameter,combined with the KNN algorithm classifier to classify and detect the normal operating state,latent faults of different severity,and permanent ground faults.The PSCAD/EMTDC simulation verifies the effectiveness of the proposed latent fault detection method.It is effective,and the accuracy of the proposed latent fault detection method is verified by comparing the classification results of different algorithm classifiers.Finally,a method for locating latent faults of medium voltage distribution cables based on the principle of double-terminal traveling waves is proposed.Taking the proposed fault detection method as the starting condition,the wavelet packet transform is used to perform multi-dimensional time-frequency domain analysis on the latent fault phase current signal to determine the arrival time of the latent fault traveling wave,and combine the field simulation parameters to calculate the latent fault traveling wave velocity.Cable latent fault location,and the effectiveness of the proposed latent fault location method is verified by PSCAD/EMTDC simulation.Through the detection and location methods of medium voltage distribution cable latent faults mentioned in this article,it is possible to timely and effectively detect,identify and locate cable latent faults online,which is useful for preventing permanent cable ground faults,improving the safety of cable line operation,and improving cable The service life has far-reaching significance.