Cable Joints Research Articles

A precise inversion method of cable joint core temperature with non-embedded detection based on UMAP and ISSA-BPNN

Obtaining the core temperature of the cable joint is vital to ensure the safe operation of the modern power system with integration. To improve the speed and accuracy of core temperature inversion, this study proposed a non-embedded cable joint temperature inversion method named uniform manifold approximation and projection (UMAP) and the improved sparrow search algorithm (ISSA) optimized the back propagation neural network (BPNN). Firstly, UMAP is used to reduce the feature dimension of sample data input and enhance the data visualization effect. After dimension reduction, the model input features are consistent with the international ampacity calculation standard, and the calculation speed and accuracy of the model are improved. To improve the optimization ability of SSA, the Tent chaotic operator is introduced, and then the ISSA is used to optimize BPNN to address the issue of unstable output and easy falling into a local minimum. At last, the optimization ability and temperature inversion effect of the improved model were compared with other competing algorithms based on the 10 kV cable joint temperature-rise test and CEC2017 benchmark function. The experimental results show that the proposed method shortens the calculation time of the model, and the mean absolute error of temperature inversion is about 0.1°C. The overall performance is the most outstanding, the training data set is unbiased, and the interpretability of the model improves, which can provide a reliable reference for line operation and maintenance personnel.

Research of an intelligent fire extinguishing device for dense cable passage

In recent years, there have been many cable (accessory) burning events in the cable channel of the company, indicating that the fire isolation measures of dense cable channel and cable intermediate joint are still not perfect, and there are still fire risks. In view of the characteristics of dense cable passage, this paper puts forward a design idea of intelligent fire extinguishing device suitable for dense cable passage. It introduces the structure of each module in detail, puts forward the function of the device and fire extinguishing principle, and expects to provide a new technology for the fire prevention and control of cable passage.

Effect of Nano-MgO Doping in XLPE on Charge Transport and Electric Field Distribution in Composite Insulation of HVDC Cable Joint

The space charge characteristics of cross-linked polyethylene (XLPE) can be improved to some extent by doping the appropriate amount of nano-MgO. In this study, in order to explore the influence of nano-MgO on the space charge and electric field distributions of the composite insulation of high voltage direct current (HVDC) cable joints, the effect of nano-MgO concentration on the depth and density of the deep traps in MgO/XLPE was first analyzed. On this basis, the charge transport simulation model of a 320 kV HVDC cable joint was established with MgO/XLPE as the cable insulation, and the space charge and electric field distributions of the cable joint under different temperature conditions were simulated. It was found that the radial charge distribution in the joint shows different trends with the change of nano-MgO concentration. There is a significant difference in the charge density on both sides of the (MgO/XLPE)/EPDM interface, and the difference first decreased and then increased with the increase of concentration. When the nano-MgO concentration was 0.5 wt%, the number of charges in the radial direction is the fewest, and the maximum value is only 0.42 C/m−3. The radial electric field changed abruptly at the (MgO/XLPE)/EPDM interface, and it was homogenized to a certain extent with time. It was found that the highest electric field of the interface is at the root of the stress cone, which is the weakest point of the joint insulation. When the nano-MgO concentration was 0.5 wt%, the electric field at the root of the stress cone was found to be the lowest, with a value of 13.38 kV/mm. A comprehensive comparison shows that the joint can maintain better insulation when the concentration is 0.5 wt% compared to other concentrations. The results can provide a basis for further improving the insulation properties of HVDC cable joints through nano doping technology.

Analysis of yellowing phenomenon caused by electrical and thermal degradation in the interface of cross‐linked polyethylene cable joints

Analysis of yellowing phenomenon caused by electrical and thermal degradation in the interface of cross‐linked polyethylene cable joints

Feasibility of Space Charge Measurements on HVDC Cable Joints: Study Group—IEEE DEIS Technical Committee “HVDC Cable and Systems:”

This is the first time that the feasibility of space charge measurements on full-sized HVDC cable joints has been explicitly considered. In this article we also consider whether the PEA and TSM techniques could be used.

Estimation of Underground MV Network Failure Types by Applying Machine Learning Methods to Indirect Observations

Electrical utilities performance is measured by various indicators, of which the most important are very dependent on the interruption time after a failure in the network has occurred, such as SAIDI. Therefore, they are constantly looking for new techniques to decrease the fault location and repair times. A possibility to innovate in this field is to estimate the failed network component when a fault occurs. This paper presents the conclusion of an analysis carried out by the authors with the aim to estimate failure types of underground MV networks based on observable indirect variables. The variables needed to carry out the analysis must be available shortly after the failure occurrence, which is facilitated by a smart-grid infrastructure, to allow for a quick estimation. This paper uses the groundwork already carried out by the authors on ambient variables, historical variables, and disturbance recordings to design an estimator to predict between four MV cable network failure types. The paper presents relevant analyses on the design and performance of various machine learning classification algorithms for estimation of the types of MV cable network failures using real-world data. Optimization of performance was carried out, resulting in an estimator with an overall 68% accuracy rate. Accuracy rates of 94% for cable failure, 63% for excavations, and 79% secondary busbar failures were achieved; as for cable joints, the accuracy was poor due to the difficulty to identify a feature that can be used to separate this failure type from cable failures. Future work to improve that accuracy is discussed.

Real-time reconstruction of temperature field for cable joints based on inverse analysis

Temperature monitoring is important for the operation management of cable joints. However, owing to the problems associated with calculation cost and parameter determination, existing research can only calculate the local temperature with limited accuracy in the operation stage. This does not enable temperature management and condition assessment. Therefore, combined with the analytical, numerical, and inverse analysis methods, a real-time reconstruction method of the 3-D temperature field for cable joints is proposed. In this study, the temperature distribution of the cable joint is analysed by the combination of the Ohm's law and heat transfer rules. The transient heat transfer process is transformed into a stable state heat transfer process under discrete-time conditions using the equivalent analysis method. The inverse problems aimed at identifying the surface heat transfer coefficient and the equivalent current are constructed, which can be solved by iterative calculation. The temperature experiment platform is then built to verify the proposed method. The reconstruction results are consistent with the experimental ones and meet the accuracy requirements of the operation analysis. Finally, the influence of current fluctuation, heat dissipation condition, and measurement accuracy on reconstruction results are analysed. The results show that the proposed method realizes the real-time reconstruction of the temperature field, which is reliable, robust, and anti-interference. It promotes the practical applications of temperature monitoring.

Heat transfer enhancement method for high-voltage cable joints in tunnels

A cable joint is regarded as a hot spot in the cable line. Especially for the case of high loads, a cable joint is prone to overheating, which can eventually cause electrical accidents such as explosions. There is still a lack of heat transfer enhancement methods to address this overheating. In this study, a forced convection method of applying cooling fan for cable joints in tunnels was proposed. Combined with the heat transfer characteristics and structural characteristics of cable joints, a forced convection thermal rating (FCTR) model was established. The effects of cooling fan positions and air velocity on cable joint heat transfer enhancement performance were determined using the FCTR model. The results show that the optimal position for a cooling fan is segment C1/C2 of a cable joint. At this position, the recommended air velocity is 4 m/s. This is because the heat transfer enhancement performance of cable joints at a higher air velocity is almost the same as that when the air velocity is 4 m/s. Based on the experimental measurements, the maximum error of the FCTR model is 2.2%. Compared with the previously reported model, the FCTR model is conducive to obtaining a more accurate conductor temperature with the accuracy improved by 4.8%. The results of this study can provide more accurate theoretical guidance for evaluating the heat transfer performance of cable joints in engineering.

Study on a 110 kV combined prefabricated joint fault caused by premature failure of grounding grid

The grounding grid on the outside of the epoxy insulator breaks under the long-term oxidative corrosion of moisture, fails prematurely, and may eventually develop into a breakdown failure. However, the impact of this process has not yet been discovered.In this paper, a 110 kV combined prefabricated cable joint breakdown fault is discussed. Through the inspection and comparative analysis of the faulty joint, it is speculated that the premature failure of the grounding grid causes the breakdown of the epoxy insulator. The fault process can be divided into the grounding failure stage and the insulation damage stage. In this paper, the corresponding two-dimensional electric field simulation calculation model is established, the fault development process is restored, and the possible effects of different stages is analyzed.The results show that due to the corrosive effect of moisture, when the grounding grid is broken, a floating potential will be generated on the surface of the epoxy insulator. With the expansion of the grounding failure range, the local field strength on the surface of the epoxy insulator is distorted, which will cause partial discharge. When the failure range is 220 mm, the electric field distortion of the joint reaches the maximum value of 23.3MV/m, which will destroy the insulation strength of the epoxy insulator and cause insulation breakdown, eventually leading to an accident.The research results point out the importance of the continuity of the grounding grid, and the improvement measure is proposed to reduce the occurrence of such accidents. The analysis method for cable joint failure case can provide a reference for dealing with similar accidents.

Transfer matrix method for analyzing dynamic response of multi-span elastically supported SFT under moving load

This paper proposed a new theoretical model for analyzing the submerged floating tunnel(SFT) under moving load, whose boundary at two ends was regarded as elastic constraint, and the anchor cable was simplified as the discrete spring support. Besides, the tunnel joint was simulated as a flexural spring to connect two adjacent tube segments. The modes and natural frequencies of the model were solved by transfer matrix method, and the dynamic response of the SFT under moving load was investigated by the modal superposition method, which was verified by comparing with the results obtained by the general FEM software. The influence of boundary conditions, dissimilarity of cable stiffness and joint flexural stiffness on the dynamic response of the SFT was analyzed. The difference of the response between the beam on elastic supports (BOES) and the beam on elastic foundation (BOEF) was compared. The results showed that the boundary conditions had little influence on the vibration response of SFT's intermediate spans, but had great influence on the displacement and bending moment of the side span. Besides, even in the case when the frequency differentials of the BOES and the BOEF were small (1.84%), the displacements of the two models also had significant difference. The disparity of the cable stiffness and joint flexural stiffness had great influence on the distribution of displacement and bending moment of SFT.

Offshore Wind Farm Layout Optimization Considering the Power Collection System Cost

The paper proposes a method for optimizing the layout of offshore wind farms to increase their efficiency by reducing the effect of aerodynamic shading, minimizing electrical losses in cable lines of the system for receiving and transmitting electrical energy generated by wind turbines to the electrical grid of the power system. The task is reduced to determining several parameters that define the geometric dimensions and shape of the layout grid with pre-installed tur-bine locations. This approach, in contrast to the coordinate-wise search method, makes it possible to build symmetrical grid layouts of wind power plants, which in practice are more convenient in terms of maintenance and operation. Together with the optimization of the layout, the search for the optimal location of the offshore transformer substation and the synthesis of the scheme of cable joints between wind power plants has been carried out. To solve this problem, a heuristic algorithm was used to search for a minimum spanning tree with a restriction on the conductivity of connections, which made it possible to build realistic schemes and more adequately assess their technical and economic characteristics. As the results of testing the proposed methodology on the example of optimizing the layout of the Horns Rev 1 wind farm have shown, the use of this approach has reduced the cost of the electrical system by 10–12 %. This is 7–11 % higher than the result obtained by using the MST algorithm, which performs the construction of a circuit of cable joints of a simplified topology. The change in the size and shape of the boundaries of the wind farm site resulted in an increase in the estimated electricity generation by 2.3 % and a decrease in its cost by 4 %. When optimizing the layout of wind turbines within the fixed boundaries of the site, these indicators are improved by only 1 and 2 % as compared to the original scheme.

Selective PD Measurements on DC Cable Joints Using a HFCT-Balanced Circuit Arrangement

Due to the many advantages of medium-voltage (MV) and high-voltage (HV) DC cable transmission lines and the possibility of converting AC transmission to DC transmission, this technology is becoming increasingly relevant. One of the most important diagnosis tools used to investigate the condition of the insulation of highvoltage cables is to apply partial discharge (PD) measurements. Cable joints and terminations are of particular importance, as these represent weak spots due to human interaction. Especially under DC voltage, it is of crucial importance to determine whether the detected PD pulses occur inside or outside the cable accessories.For this purpose, a PD test method for cable joints using two high-frequency current transformers (HFCT) was optimized with modern electronic devices, including an instrumentation amplifier and a modern PD measuring instrument. Two HFCT with opposite winding directions were placed on the outer semi-conductive layer on both sides of a cable joint. The signals were fed into an instrumentation amplifier to separate the PD pulses originating from inside and outside the cable joint. This method automatically suppresses PD pulses occurring outside the cable joint and was tested on a 12/20 kV AC cable joint under DC voltage and with thermal and electrical stress.

Nonlinear Conductivity and Space Charge Characteristics of SiC/Silicone Rubber Nanocomposites.

To achieve a preferable compatibility between liquid silicone rubber (LSR) and cable main insulation in a cable accessory, we developed SiC/LSR nanocomposites with a significantly higher conductivity nonlinearity than pure LSR, whilst representing a notable improvement in space charge characteristics. Space charge distributions in polarization/depolarization processes and surface potentials of SiC/LSR composites are analyzed to elucidate the percolation conductance and charge trapping mechanisms accounting for nonlinear conductivity and space charge suppression. It is verified that SiC/LSR composites with SiC content higher than 10 wt% represent an evident nonlinearity of electric conductivity as a function of the electric field strength. Space charge accumulations can be inhibited by filling SiC nanoparticles into LSR, as illustrated in both dielectric polarization and depolarization processes. Energy level and density of shallow traps increase significantly with SiC content, which accounts for expediting carrier hopping transport and surface charge decay. Finite-element multiphysics simulations demonstrate that nonlinear conductivity acquired by 20 wt% SiC/LSR nanocomposite could efficiently homogenize an electric field distributed in high-voltage direct current (HVDC) cable joints. Nonlinear conductivities and space charge characteristics of SiC/LSR composites discussed in this paper suggest a feasible modification strategy to improve insulation performances of direct current (DC) cable accessories.

Numerical Analysis of Electric Field Characteristics and Interfacial Pressure of HVDC XLPE Cable Joint Considering Load Cycles

Recent innovations in HVDC extruded cable systems require the development of reliable and safe cable accessories. Cable accessories are made of several insulating materials and contain several interfaces. Interfaces made of different materials can cause electric field distortion and localized enhancement of the field. In addition, the internal temperature profiles of accessories differ depending on load conditions or installation environments, which may lead to an increase in or loss of interfacial pressure due to changes in the mechanical properties of materials. The loss of interfacial pressure degrades the contact state between materials. The micro voids formed due to pressure loss can cause partial discharge and tree, which in turn can lead to reduced lifespan and failure of the cable system. Therefore, it is necessary to study the electrical and mechanical characteristics of cable accessories considering various transient states. However, there is a limit to experimentally analyzing the actual structure. In this paper, electric field and mechanical stress for pre-molded cable joints were analyzed using an electrical model based on the conductivity of the material and a mechanical model based on elastic theory. Temperature fluctuations were simulated according to the sequence of the cable load cycle test, and time-varying electric fields and mechanical stresses were analyzed. From the simulation results, it was confirmed that the electric field and stress distribution in the joint continuously changed according to the heating and cooling periods. In addition, during the cooling cycle, the field strength at the interface near the conductor increased and the interface pressure decreased. In conclusion, it is important to ensure sufficient initial pressure so that the dielectric strength at the interface does not decrease even if there is a loss of interface pressure due to temperature fluctuations.

Spraying Core–Shell ZnO To Achieve High Insulation Performance for HVDC Cable Factory Joints

Spraying Core–Shell ZnO To Achieve High Insulation Performance for HVDC Cable Factory Joints

Kinematics and control of a cable-driven snake-like manipulator for underwater application

Abstract. In view of the large volume, complex structure, and poor performance of traditional underwater manipulators in some complicated underwater scenarios, a cable-driven snake-like manipulator (CDSLM) is proposed. In this paper, the kinematics model of the proposed CDSLM is firstly established, which can be decomposed into three parts: motor–cable kinematics, cable–joint kinematics, and joint–end kinematics. A tip-following algorithm is then presented to weave through the confined and hazardous spaces along a defined path with high efficiency. The main merit of the algorithm is that only the terminal section variables need to be calculated and recorded, which solves the problem of expensive computational cost for the inverse kinematics of snake-like manipulators. Finally, evaluation indexes of the path-following performance are proposed to evaluate the effect of the tip-following algorithm. Simulations of the path-tracking performance are carried out using MATLAB. The results demonstrate that the average computation time is about 1.6 ms, with a deviation of less than 0.8 mm from the desired path, and the stability and effectiveness of the tip-following algorithm are verified.

Application of Pulse Sequence Partial Discharge Based Convolutional Neural Network in Pattern Recognition for Underground Cable Joints

In this study, a pulse sequence analysis (PSA) method is presented, which does not measure the voltage signal for the defect-type recognition of power cable joints based on partial discharges (PDs) using convolutional neural networks (CNNs). The PSA showed effective results in comparison to a conventional phase-resolved PD (PRPD) pattern, which is a combination of a PD and voltage signals. The optimal drawing formats of the PSA patterns, including the size, type, color, and marker size of the images, which influence the recognition accuracy, were evaluated. In total, 12 sets of PD data, consisting of three types of cable joint defects, were trained and tested using CNN-based models. The results show that the performance of the PSA-based CNN model is as good as that of a PRPD even when the voltage signal is lost, whereas PRPD mostly fails under such cases. The total recognition accuracy obtained from a PSA-based CNN was 95.3%, whereas that of the PRPD-based CNN was 90.6%. In addition, an advanced and useful application of a PSA pattern is discussed herein.

Stress Cone Effect Analysis and Optimum Design of Extra High-Voltage Cable Joint Using Neural Networks

The major problem in high-voltage cable accessories is the electric field stress caused by the high-voltage level at the cable junction. In this paper, a neural network and simulation-based optimal design for extra high-voltage (EHV) cable accessory is proposed to ensure the optimum electrical design. The different kinds of geometries of the EHV underground cable accessory are realized in the Comsol Multiphysics software program, and the electric field analyses are conducted based on the finite element method. The design of high-voltage underground cable accessories is examined both within and without the optimal stress cone geometry. A neural network-based model is developed according to the analysis results obtained in the simulation. Thanks to this model, the geometry of the stress cone is determined. In the simulation-based analysis, the electric field stress caused by the high-voltage level at critical points is controlled with an optimum joint design using neural networks. The proposed model will contribute to EHV cable joint design at different stress levels.

Identification and assessment method of cable joint health status based on traveling wave reflection.

Due to the difficulty in accurately detecting the health status of cable joints, a new method of identifying and assessing the cable joints' health status based on traveling wave reflection is proposed. By transmitting nanosecond pulse signals at the head end of the cable, the health status characteristics of the cable joints can be obtained, and the noise reduction of the measurement signals is performed by the wavelet function to identify the reflected wave at the joint and the end of the cable. The equivalent circuits and simulation models of contact resistance and leakage resistance are established, and the contact resistance and leakage resistance of the cable joints are calculated according to the amplitude and phase of the reflected signals at the joint and the end of the cable. By comparing with the resistance when the joint is in healthy operation, any measured parameter exceeding the corresponding standard is considered a joint fault. Simulations and test results show that the method can accurately identify the reflected signals of the cable joints in different operating states, and with changes in joint health, clear regular features can be extracted from the reflected signals, and the quality and health of the joints can be determined. The traveling wave method can be used to detect cable joint faults and provide an early warning of defects, which provides a new idea for online monitoring and early warning of cable joints in both theory and engineering practice.

Research on the Matching of Unequal Diameter Cables to Improve the Carrying Capacity of High-voltage Submarine Cable Landing Section

The conventional method of increasing the current carrying capacity of the submarine cable landing section increases the manufacturing cost of the submarine cable and the long-term operational reliability. This paper introduces the unequal diameter cable joint technology, the actual current-carrying capacity of the 220kV submarine cable landing section and the submarine section was checked. A differentiated unequal diameter submarine cable landing section and submarine section conductor cross-section matching principle was put forward. The economic efficiency of the unequal diameter cable matching scheme was evaluated. The research results show that, the larger the conductor cross-section of the submarine cable, the greater the drop in current-carrying capacity during the landing section. In the unequal diameter matching method, the single-core or copper wire armored submarine section cable requires a smaller conductor cross-section. The maximum transmission capacity can be obtained when the submarine cable line is all single-core copper wire armored. When it is all single-core steel wire armor, it can take into account the larger transmission capacity of the submarine cable line and the optimal unit capacity cost. This article provides a reference for the design and selection of submarine cable lines.