High Voltage Cable Joints Research Articles

Study on the Configuration and Fire-Resistant Property of Cable Tunnel Fireproof Clapboard Based on Equivalent Fire Condition Testing

At present, the selection criteria and configuration methods for fireproof clapboards in cable tunnels are not yet perfect, making it difficult to achieve effective fire protection. Therefore, an equivalent fire condition testing method is proposed to analyze the fire-resistant property of fireproof clapboards of different materials. Firstly, a tunnel fire experiment platform was built to carry out the combustion experiment of the high-voltage cable intermediate joint. The cable combustion equivalent fire source device is developed based on the temperature rise characteristics under different combustion conditions. However, the temperature rise characteristics of the equivalent fire source and the actual cable combustion error are within 10%. Then, four typical fireproof clapboards were tested under equivalent fire sources. The results indicate that the organic molded board has the best performance. In addition, factors such as the thickness, side panel height, and installation method of the fireproof clapboards were tested and analyzed. The results indicate that a minimum thickness of 5 mm for the fireproof clapboard and a height of 200 mm for the side panel of the clapboard are necessary to ensure effective protection. The installation method of hoisting fireproof clapboards can effectively extend the protection time by about 30% compared to the flat method.

XLPE cable joint defects measurement method based on point cloud remapping

For the problems of low detection accuracy caused by weak texture and strong reflection on the surface of Cross-linked polyethylene (XLPE) high-voltage cable joint, this paper proposed a joint point cloud remapping and image segmentation method for the cable joint defects measurement, which improved the defects measurement accuracy from the correlation of the disordered point cloud and the salience of defects. Firstly, the discrete noise in the joint point cloud is removed using a modified radius filtering algorithm. Secondly, for the problems of disorderliness and weak association of the cable joint point cloud, we utilized Rodrigues' rotation formula (RRF) to correct the position of the XLPE cable joint point cloud. Then, for the demand of improving feature expression of non-significant defects, a point cloud remapping method is proposed, which remapping insignificant defects point cloud into saliency image for more effective detection. Lastly, an image segmentation method based on 8-neighborhood growth is applied for explicit defects detection, and the detected defects are quantified by the proposed measurement approach. Extensive experiments are conducted on the collected cable joints' point cloud and simulated cable joints' point cloud. With the help of the proposed method, we can achieve the best effects in DE, FR quantitative comparison, and the measurement inaccuracies are less than 4.5%. Experimental results demonstrate that the proposed method enjoys state-of-the-art performance in cable joint defects measurement.

Dimensional measurement of anti-stress cone of HV cable joints based on 3D point cloud

To solve the problem of automatic measurement of anti-stress cone of high voltage cable joints, a measurement algorithm based on 3D point cloud is proposed. Firstly, denoising and coordinate adjustment of point cloud of a cable joint are realized. Then the characteristic curve model of fitting circle radius indicating structure characteristic of cable joints is constructed by fitting circles with random sample consensus algorithm. After that, the discrete points on the characteristic curve are extracted according to the characteristics such as the fluctuation range of the characteristic curve for straight line fitting and the intersection of the fitted lines is calculated to complete the segmentation of the anti-stress cone area of the cable joint. Finally, the parameter measurement of the anti-stress cone was completed according to the structure of the anti-stress cone, and the error correction post-processing was performed. Two types of cable joint point clouds with standard dimensions and surface defects were used for measurement experiments, the absolute errors of the measurement results are less than 0.2 mm and 1.0 mm respectively, and the relative errors are less than 0.25% and 2% respectively, indicating that the proposed method has high robustness and measurement accuracy, which meet the measurement requirements in engineering practice.

Research on Defects of High Voltage Cable Fusion Joint Using XLPE Insulation Material

High-voltage cable fusion joints are made on site. Affected by environmental conditions, fusion joints are prone to small defects that are not easy to find, resulting in frequent accidents after the joints are put into operation. There is currently no effective method to detect small defects inside the joint. Therefore, this paper proposes to use digital radiography nondestructive test technology to detect the main insulation and conductor recovery process of high-voltage cable fusion joints. The results show that the digital radiography nondestructive test method can effectively find defects such as microporous bubbles, conductor bending, and eccentricity in the main insulation of XLPE fusion joints. The on-site anatomy demonstrates the accuracy of the test results, and the digital radiography nondestructive test can effectively detect the defects of high-voltage cable fusion joints. Experiments have verified that the decrease of cross-linked pipe temperature and nitrogen pressure can lead to the generation of microporous bubbles in the XLPE main insulation. For conductor bending and eccentricity defects, the limit value of the welding conductor bending gap is 11mm through simulation calculation.

Three-dimensional defects detection of high-voltage cable joint based on iterative residual fitting

Aiming at the three-dimensional (3D) defects detection of high-voltage cables joint, a method based on iterative residual fitting is proposed. The 3D point cloud data was obtained by reconstructing the laser line projected onto the surface of the high-voltage cable joint. In order to remove noise generated by reconstruction which is located above or below the curve, a simple and effective strategy that the noise can be filtered by the gradient change in the neighborhood is adopted. Then a continuous iterative residual fitting method is proposed to effectively reduce the interference of the defect area on the curve fitting accuracy, thereby obtaining the accurate equation expression of the cable surface curve. By comparing the residual value of the high-voltage cable surface points relative to the fitting curve, the points of the defect area are marked. Finally 3D defect area is extracted through segmentation and clustering. Experiments have verified the effectiveness of the proposed method on artificial standard size defects and real manual ground defects. The absolute error of the depth (height) of artificial standard size defects is less than 0.05 mm. Compared with the traditional cylindrical fitting method, it can be seen that the recognition rate of the proposed method for manually ground defects of high-voltage cable joint is much higher than that of cylinder fitting method.

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.

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.

Research on main insulation defect of cable fusion joint based on IDIP-DR detection technology

The cable connector is the weak link of the electrical part of the cable. Most of the cable breakdown accidents occur at the connector, which will have a huge impact on the safe power supply of the city. In recent years, with the development and maturity of 10 kv cable fusion joint technology, high-voltage cable fusion joint technology is gradually applied in the field, but the key process problems in the production process lack of effective control means. In order to solve such problems, this paper use IDIP - DR digital radiographic testing technology. The key technology of high voltage cable melting joint detection, effectively detect the main insulation problems bubble construction technology. Through the anatomical, proved the accuracy of the test results, for the subsequent company to carry out the weld joint process control provides an effective means of. The causes of defects were analyzed and the corresponding process control suggestions were put forward.

Research on live detection technology of cable joint defects based on high-speed light sensing and pressure wave method

With the widespread application of stable high-voltage power cables, cable failures have gradually become the main source of major accidents in the process of power transmission. The most easily damaged part is the cable joint. Since the cable joints are made on site, it is easy to introduce high-voltage cable defects and cause insulation failures. Therefore, the defect detection of high-voltage voltage joints is particularly important. In order to promote the process of urbanization, ensure people’s life quality and personal safety, the popularization of high-voltage cables is an inevitable trend. However, difficulties will be encountered in the detection of cable joint faults. To improve the detection efficiency, relatively extensive research has been carried out on the detection of high-voltage cable joints at home and abroad. Based on the high-speed light sensing and pressure wave method, the online detection method of cable joint defects proposed in this paper has accurate, fast, convenient and non-contact online detection features.

Application of Fuzzy Entropy to Improve Feature Selection for Defect Recognition Using Support Vector Machine in High Voltage Cable Joints

This study presents a method for defect-recognition in high voltage cable joints based on partial discharge (PD). This recognition involves three major systematic procedures. In the first procedure, the PD patterns are produced by two different laboratory models representing two types of defects in a high voltage cable. The PD data are collected from a set of experiments in the PD tests with six high voltage cable joints, including prefabricated artificial defects. The second part involves feature selection by employing a fuzzy entropy algorithm by which the entropy value of each defect is computed. Using this fuzzy entropy algorithm, the features that have the most useful characteristics for distinguishing the defects in cable joints are found. In the third part, the selected features are used for testing and training the support vector machine (SVM) model, and the accuracy testing rates are calculated in order to obtain optimal results. The SVM model in this study achieves a higher accuracy rate of 96% for classification with the proposed feature-selection-based fuzzy entropy algorithm.

Defect simulation and state characteristic analysis of cable joints with tip defects

In recent years, the breakdown of the body and accessories of high voltage cables has increased gradually. Taking the tip defect of 110 kV high voltage cable joint as an example to carry out electric field simulation analysis, the distribution and change law of electric field under this defect are put forward. Based on full working condition detection platform of high voltage cable, the simulation test of the defect is carried out. The effectiveness of various charged detection methods and on-line monitoring methods has been studied, and the variation rules of cable state under different working conditions have been obtained. The results show that, when tip defect is between stress cone silicon rubber and main insulation of cable body, electric field distortion around the tip shows discharge, and the breakdown potential is 83 kV. The high frequency partial discharge detection method and ultrasonic partial discharge detection method can detect the defects effectively, among which anti-interference ability of high frequency partial discharge detection at the capacitive arm is the best, and detection sensitivity of the grounding current is higher in the on-line monitoring. The thermal efficiency of load current has little effect on development of tip defects. But with the increase of test voltage, the high frequency emission volume increases obviously and breakdown occurs easily at higher voltage.

Mechanical Behavior of Aged EPDM Insulation of High-Voltage Cable Joints in Thermal-Oxidative Environment

In this thesis, the thermal aging behaviour at 130°C, 145°C and 160°C for 220kV cable joint EPDM insulation was investigated. The tensile strength and elongation of EPDM insulation both before and after the thermal-oxidative aging were measured, and the microstructure of materials was observed by SEM. The microstructure observation showed that pores formed and expanded into pieces inside the EPDM insulation with thermal aging course, the cracks would appear at the end of aging process. Both tensile strength and elongation of EPDM insulation decreased with aging process lasting, and decreased more gradually with increasing aging temperature. The tensile strength was more sensitive than elongation for aging process. The results can provide theoretical support for the fabrication, operating and maintenance for EPDM cable joint.

A Study on the Propagation Characteristics of Partial Discharge in Cable Joints Based on the FDTD Method

Partial discharge (PD) is the main cause of cable insulation deterioration. It is of great theoretical significance and practical value to carry out PD research on high voltage (HV) cable joints for fault detection and operational status evaluation. In this paper, a three-dimensional finite-difference time-domain (FDTD) simulation model of cable joint is built. According to typical fault types of PD in 110kV XLPE cable, four types of insulation defect models, including electrical tree discharge, surface sliding discharge, air gap discharge, and floating discharge, are designed and manufactured. Based on the three-dimensional simulation model of cable joint, the propagation characteristics of PD signals caused by the aforementioned insulation defects are analyzed, the effects of different types of insulation defects and fault locations on the propagation characteristics are investigated. A PD experimental platform based on a cross-bonded three-phase 110 kV cross-linked polyethylene (XLPE) cable system is built for verifying the feasibility of the three-dimensional simulation model. Results show that the model can reasonably explain propagation characteristics of PD signals in cable joints, including polarity, peak values, attenuation characteristics and symmetry, which provided the theoretical basis for judging the fault locations and types of PD caused by insulation defects in cable joints.

Research on Control System of Installation Environment for 500kV Cable Tunnel Joint

The environment in the 500kV cross-linked cable tunnel is bad, which is not conducive to ensuring the joint manufacturing process, and it is easy to cause joint installation defects. A joint installation environmental control system stabilizing the temperature and humidity of the joint installation area and reducing dust particles in the air was designed and developed. A closed space in the joint area was formed by use of sliced inflatable membranes. The integration of refrigeration and air-conditioning technology, air dehumidification technology, air filtration technology and air volume adjustment technology realized temperature, humidity, and cleanliness control of the joint installation area. Stable temperature and humidity, as well as clean air atmosphere can greatly improve the installation quality of high-voltage cable joints in the complex cable tunnel environment, and help reduce the failure rate of joints.

Automatic partial discharge recognition using the cross wavelet transform in high voltage cable joint measuring systems using two opposite polarity sensors

This paper presents a new wavelet analysis approach in partial discharges cable joint measurements in noisy environments. The proposed technique uses the Cross Wavelet Transform (XWT) to separate PD signals from noise and external disturbances in partial discharges measurements in cable joints using two opposite polarity sensors. The partial discharge measurements were performed during impulse and superimposed voltages, leading to a huge amount of noise and pulse shaped external disturbances. The XWT foundations, the experimental setup and the XWT methodology proposed are presented together with the results of the recognition of PD originated in the cable joint. In the experiments, 51,898 signals were acquired, in which 733 were PD signals from the joint and 51,165 corresponded to noise or external disturbances. The XWT performance was studied, finding that 97% of the PD signals were correctly separated by the technique proposed. The results demonstrate the effectivity of the XWT in separating PD signals from noise and external disturbances in this particular measuring system configuration.

Thermo-mechanical analysis of solid interfaces in HVAC cable joints

Mechanical stresses affect the electrical performance of solid-solid interfaces in high-voltage cable joints. This paper assesses the influence of insulation material mechanical properties and temperature on interface pressure. Based on a hyper-elastic model, the mechanical stresses inside silicone rubber joint tube were determined. Circumferential stresses can reach 50% of the silicone rubber tensile strength at normal pre-operation expansion ratios. An analytical method to determine the thermally induced mechanical stress during operation is presented and its accuracy is confirmed using finite element method. This method is modified to account for the variation of the mechanical properties with temperature. This paper shows that circumferential stresses at the interface increase as temperature drops, which may have a significant impact on the electrical performance of the interface during operation.

Measuring method for partial discharges in a high voltage cable system subjected to impulse and superimposed voltage under laboratory conditions

A partial discharge (PD) measuring system has been deployed in order to identify and measure PD in a high voltage (HV) cable joint under impulse and superimposed voltages under laboratory conditions. The challenge is to enable the detection of PD during the impulse conditions. The method of measurement has been investigated by introducing an artificial defect in the cable joint in a controlled way to create conditions for partial discharges to occur. Next the HV cable system is subjected to AC, impulse and superimposed voltage. Two high frequency current transformers (HFCT) installed at both ends of the cable joint were used to identify PD from the cable joint and to separate PD from disturbance. Transient voltage suppressors and spark gaps are applied to protect the measuring equipment. Band pass filters with selected characteristics are applied to suppress transient disturbances and increase the chance to detect PD during the impulse. PD signals are separated from transient disturbances during data post processing and by means of pulse polarity analysis. The developed system enables the detection of so-called main and reverse discharges respectively occurring during the rise and tail time of the superimposed impulse. The measurement results obtained show the effectiveness of the presented PD measuring system for investigating the effects of voltage transients on a HV cable system in laboratory conditions.

Modeling of a new type of reinforcing insulation of 110 kV cable joints

This article is devoted to the creation of a new reinforcing insulation of high-voltage cable joints at 110 kV. According to statistics for 2016, about 65% of accidents on the cable line occur at the junction of the two cable segments. The problem of leveling the electric field in the cutting is one of the important in the cable industry. To date, it has become possible to create new composite materials with special properties. With this help, a new type of 110 kV amplifying insulation will work on a new combined method of leveling the electric field. Using the finite element method, the model of amplifying insulation (tube-regulator) was modeled. It consists of several components that are responsible for a different principle of leveling the field.

On-line PD detection and localization in cross-bonded HV cable systems

This paper addresses the detection and localization of partial discharge (PD) in crossbonded (CB) high voltage (HV) cables. A great deal has been published in recent years on PD based cable insulation condition monitoring, diagnostics and localization in medium voltage (MV) and high voltage (HV) cables. The topic of pulse propagation and PD source localization in CB HV cable systems has yet to be significantly investigated. The main challenge to PD monitoring of CB HV cables is as a result of the interconnectedness of the sheaths of the three single phase cables. The cross-bonding of the sheaths makes it difficult to localize which of the three phases a PD signal has emanated from. Co-axial cables are used to connect cable sheaths to cable link boxes, for ease of installation and protection against moisture. A second challenge is, therefore, the coupling effect when a PD pulse propagates in HV cable joints and the co-axial cables, making PD detection and localization more complex. The paper presents experimental investigations into PD pulse coupling between the cable center conductor and the sheath and the behavior of PD pulse propagation in CB HV cables. It proposes a model to describe PD pulse propagation in a CB HV cable system to allow monitoring and localization, and also presents the knowledge rules required for PD localization in CB HV cable systems.

An improved optically based PD detection system for continuous on-line monitoring of HV cables

An optically-based remote sensing technique using a laser source, polarization scrambler, standard single mode fibers, fiber polarizer, electro-optic (EO) modulator and optical receiver, for continuous on-line monitoring of partial discharges (PD) in high voltage cable joints is proposed. Both the fiber polarizer and EO modulator, which are placed near cable joints, are passive without any power requirements. An EO modulator with no electrical bias, which operates close to the half-intensity point, was used and proved to have much better light transmission performance and higher measurement sensitivity than the bias modulator approach investigated earlier. Various multiplexing techniques including optical switches and a fused fiber coupler have been investigated in order to implement multi-channel monitoring so that one laser source can be used to provide light to several fibers. The revised PD optical remote sensing technique has been applied to practical PD measurements on both 132 kV cable joint at the University of Southampton in the UK and 400 kV cable joints at Sudkabel GmbH in Germany. Obtained results have verified the principle and demonstrated the effectiveness of the developed technique.