Cable Terminations Research Articles

Analysis of the Power Cable Fire Case in Busan-JungKwan Energy

In this paper, the fire cause of blackout occurred in the Busan-JungKwan Energy as a Community Energy System (CES) was analyzed. Through analysis of the data such as burn patterns at the site, melted shape of cable head by the fire, overcurrent relay (OCR) of the control system, and event log, it was confirmed that first ground fault occurred at the termination connection of secondary cable of transformer. It was concluded because the void space of insulation and electrical melting trace conductor were investigated in the cable stress cone by detailed investigation and X-ray inspection for cable termination. In addition, as the damage by the tool on the vertical direction to the conductor was identified, it was presumed that the accident occurred by deterioration progress of insulation which was accelerated than that of the other parts.

Antarctic subglacial drilling rig: Part II. Ice and Bedrock Electromechanical Drill (IBED)

AbstractA new, modified version of the cable-suspended Ice and Bedrock Electromechanical Drill (IBED) was designed for drilling in firn, ice, debris-rich ice and rock. The upper part of the drill is almost the same for all drill variants and comprises four sections: cable termination, a slip-ring section, an antitorque system and an electronic pressure chamber. The lower part of the IBED comprises an auger core barrel, reamers, a core barrel for ice/debris-ice drilling and a conventional geological single-tube core barrel or custom-made double-tube core barrel. First, the short and full-scale field versions of the IBED were tested at an outdoor testing stand and a testing facility with a 12.5 m-deep ice well. Then, in the 2018–2019 summer season, the IBED was tested in the field at a site ~12 km south of Zhongshan Station, East Antarctica, and a ~6 cm bedrock core was recovered from a 198 m-deep borehole. A total of 18 d was required to penetrate the ice sheet. The retrieved core samples of blue ice, basal ice and bedrock provided valuable information regarding the Earth's paleo-environment.

Electric Field and Thermal Analysis of 132 kV Ceramic Oil-Filled Cable Sealing Ends

This paper reports on a method combining the use of finite element simulations and external measurements to provide preliminary condition diagnosis of oil-filled cable sealing ends (CSEs) without requiring downtime. Good agreement has been obtained between the predictions from the electric field and thermal simulations and the measurements on a 132 kV oil-filled CSE. The electrostatic computation combined with electric field measurements can provide information regarding the electric field distribution inside the CSE and help in identifying potential issues with the CSE design, the materials or the cable termination process. The thermal computation combined with thermal imaging can reveal potential problems, such as high resistance connection to the busbar, and provide information regarding the cooling efficiency of the liquid dielectric. The method presented can provide the starting point for prioritizing maintenance operations on CSEs.

Study on Insulation Characteristics of Scratch Defects in 35kV XLPE Cable Terminals

In order to study the influence of different ring-shaped scratches on the insulation characteristics of 35kV Crosslinked polyethylene(XLPE) cable terminations, the model of air-gap defects caused by ring-shaped scratches was introduced at the end of the outer semi-conductor shielding layer, and the finite element simulation calculation was used to calculate the model. The electric field distribution characteristics inside the cable terminal were simultaneously made into cable end samples of different types of scratch defects, and the discharge characteristics were tested by a partial discharge test circuit. The results show that the air gap defect caused by the annular scratch defect increases the degree of electric field distortion. The maximum electric field strength is much larger than the breakdown field strength of the air, and it is prone to partial discharge activity. The Phase Resolved Partial Discharge(PRPD) of the cable terminal with ring scratch defects The spectrum shows a typical “rabbit ear” shape. As the scratch defects deepen, the PRPD spectrum begins to gradually transition to a short-feeling “cat ear” shape.

Excitation type and results of simulated electric field distribution in MV cable termination

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Observation of Exposure Test for Polymer Outdoor Cable Termination

Observation of Exposure Test for Polymer Outdoor Cable Termination

Study on insulation performance of EPR cable terminal containing metal particles

The 35kV EPR cable terminal is widely used in the distribution network. During the production process, metal particles are easily introduced due to environmental and technological reasons, resulting in frequent breakdown of the terminal breakdown accident. In order to study the influence of metal particles on the insulation performance of EPR cable terminals, a model of metal particles defect in cable terminals on the extension line of the main insulation and the control tube is built. The electric field distribution of cable terminals under power frequency voltage is calculated by COMSOL simulation software. At the same time, a sample of cable terminals containing metal particles is made, and local discharge is used. The partial discharge information of the cable terminal sample is tested by the electric test platform. The results show that the introduction of metal particles will increase the electric field distortion inside the cable terminal, strengthen the discharge activity of the cable terminal, and increase the discharge amount significantly, which seriously affects the insulation performance of the EPDM cable terminal.

Temperature gradient dependence on electrical tree in epoxy resin with harmonic superimposed DC voltage

Transient superimposed voltage, which is accompanied by a temperature gradient caused by Joule heat, can threaten the insulation safety of high-voltage direct current (HVDC) cable terminations. In this study, an electrical treeing experiment was conducted on epoxy resin with temperature gradient under harmonic superimposed DC voltage. The temperatures in the high voltage side and ground side were controlled by heaters within that maintained the range of 30 to 120 °C, while the DC voltage was ±12 kV. An isothermal surface potential decay (ISPD) experiment was used to obtain the trap level distribution. The effects of the temperature gradient and voltage polarity on the tree growth were depicted by the tree morphology, tree length and accumulated damage. The results show that the temperature gradient affects the tree structure and accelerates its growth. The tree growth rate has a nonlinear trend under an increased temperature in the high voltage side, and shows a steady increase under an increased temperature in the ground side. The positive voltage has a more obvious acceleration effect on the tree growth than the negative voltage does. A charge transport model is proposed to describe the tree behavior under a temperature gradient. The nature of the charge carrier accounts for the trap distribution and polarity effect. The local temperature rise and superimposed voltage pose a threat to the insulation safety, and more attention should be given to the operation of the electrical apparatus.

Design of an online monitoring system forthree-phasebelted HTS cables

Three-phase belted High Temperature Superconductor (HTS) cables have compact dimensions and small inter-phase magnetic interference, and have been applied in the Demonstration Project of Domestic km-Level HTS Cable System of State Grid Corporation of China. The three cores of three-phasebelted HTS cablesare bundled together in the same low-temperature bellows, so a single-phase fault may cause the quench of other two phases, and even lead to an overall failure of the three-phase belted cable. Based on the cable body characteristics, cable termination characteristics and cooling system characteristics of the three-phase belted HTS cables, the related online monitoring parameters and monitoring methods are proposed. The design of an online monitoring system for the three-phase belted HTS cables is introduced.

Failure of MV Cable Terminations Due to Supraharmonic Voltages: A Risk Indicator

This paper addresses the accelerated aging of medium-voltage (MV) cable terminations with resistive stress-grading due to supraharmonics. The paper introduces a simple and quick way to relate the risk of cable termination failure to the characteristics of supraharmonic distortion in the system. The motivation is to give practical recommendations and guidelines to evaluate the risk of failure of cable terminations under the presence of supraharmonics in MV networks. The underlying model relates the heating in the cable termination linearly with the frequency of the voltage applied and proportionally with the square of the magnitude of the voltage. The indicator can be used to decide whether given levels and frequencies of supraharmonics in the MV network represent a risk to cable terminations. The parameters of the cable termination design are not needed for that decision. However, the decision criterion is based on one sample data (Eagle Pass) and more field information is crucial to improve the approach.

Development of the Packer and its Application for Fixing Production Casing Leaks of Oil and Gas Wells

A large number of oil and gas wells at the late stage of operation are characterized by high and constantly increasing water cut of the extracted product. One of the reasons for the high water cut is the presence of production casing leaks. The occurrence of production casing leaks is connected both with the quality of primary cementing and various operating conditions of wells. To solve this problem, different technologies are applied with the use of plug-back mixtures and technical means, each of which has its own advantages and disadvantages as well as its own application area. In particular, the packers of various structures are widely used. Among the many options, the retrievable packers benefit in the market even in the case of their relatively high costs due to their easy removal and reuse. The article presents the results of the work on the development of a new structure of the retrievable packer with cable termination glands and hydraulic opening system in the well. The structure of the retrievable packer was tested in the laboratory conditions with the use of a purpose-designed test rig and in the field environment. The designed stand for testing individual structural units and the packer as a whole is a casing string simulator in which the test packer is placed. The stand is equipped with a hydraulic cylinder to simulate the movement of the packer, hydrostations to simulate hydraulic loads on the packer and breakthrough fluid from the leakage of the production string, circulation pumps to simulate circulation pumping through the packer. Field tests were carried out at one of the fields in Eastern Siberia, Russian Federation, at wells with very high water cuts. Full compliance with the claimed requirements concerning the reliability of operation of mechanisms and well plugging of the leak interval was shown. Besides that, the advantage of the packer is the possibility of communication between spaces above and below the packer. At the same time, the possibility of technological washing, acid treatment, killing and other technological operations is preserved. The use of packer during repair and insulation works in wells has made it possible to reduce the duration of works on the average by 2.5 times.

Investigation of tail pipe breakdown incident for 110 kV cable termination and proposal of fault prevention

For cable termination, which is regarded as a key segment of power grid connecting cable lines with other electrical equipments, its insulation parts withstand much higher electric field strength than the average electric field strength of overall cable line. The excessive local electric field strength may result in the appearance of cable termination breakdown fault which can cause serious harm to the power supply reliability of whole transmission line. Historical statistics show that the breakdown location of cable termination is not confined to the vicinity of stress cone. However, the existing researches have not attached enough importance to the breakdown faults at the tail pipe of cable termination. Thus, it is of considerable significance to study the mechanism of breakdown fault at the tail pipe of cable termination. In this paper, a breakdown fault case of cable termination tail pipe on a 110 kV transmission line is investigated. Firstly, the disassembly inspection is applied to cable terminations of this fault line, and the possible breakdown reasons are preliminarily inferred. Then, a three-dimensional electric field simulation model of intact cable termination is established, and the mechanism of creeping discharge and air discharge inside the tail pipe occurred at the initial stage of breakdown fault is explained by this model. Subsequently, by setting defects on cable insulation surface in the simulation model of intact cable termination and varying the size of defects, the process of cable insulation damage inside the tail pipe formed in the initial stage developing into a penetrating cable insulation damage is simulated. Finally, the mechanism of breakdown fault case of cable termination tail pipe is concluded, and some improvement measures for the installation of cable terminations are proposed to reduce the incidence probability of such breakdown fault at the tail pipe of cable termination. The method for analyzing the breakdown fault case of cable termination tail pipe presented in this paper, which combines the disassembly inspection and simulation analysis, can provide reference and suggestions for the investigation and solution in similar cases.

Design of Partial Discharge Test Environment for Oil-Filled Submarine Cable Terminals and Ultrasonic Monitoring

Based on the principle of operating an oil-filled-cable operation and the explanation of the oil-filling process provided in the cable operation and maintenance manual of submarine cables, this study investigated oil-pressure variation caused by gas generated as a result of cable faults. First, a set of oil-filled cables and their terminal oil-filled simulation system were designed in the laboratory, and a typical oil-filled-cable fault model was established according to the common faults of oil-filled cables observed in practice. Thereafter, ultrasonic signals of partial discharge (PD) under different fault models were obtained via validation experiments, which were performed by using oil-filled-cable simulation equipment. Subsequently, the ultrasonic signal mechanism was analyzed; these signals were generated via electric, thermal, and acoustic expansion and contraction, along with electric, mechanical, and acoustic electrostriction. Finally, upon processing the 400 experimental data groups, four practical parameters—maximum amplitude of the ultrasonic signal spectrum, Dmax, maximum frequency of the ultrasonic signals, fmax, average ultrasonic signal energy, Dav, and the ultrasonic signal amplitude coefficient, M—were designed to characterize the ultrasonic signals. These parameters can be used for subsequent pattern recognition. Thus, in this study, the terminal PD of an oil-filled marine cable was monitored.

Significantly Improved Electrical Properties of Photo-Initiated Auxiliary Crosslinking EPDM Used for Cable Termination.

In order to achieve high quality electrical materials for cable terminations, the crosslinked ethylene-propylene-diene monomer (EPDM) materials, with adequate breakdown strength, appropriately increased conductivity and are developed by employing auxiliary crosslinker and ultraviolet (UV) photoinitiated crosslinking technique. The characteristic cyclic anhydrides with coupled carbonyl groups are utilized as auxiliary crosslinkers to promote crosslinking efficiency and provide polar-groups to EPDM molecules in UV-initiated crosslinking processes, which can be effectively fulfilled in industrial cable production. The results of infrared spectroscopy show that the auxiliary crosslinkers have been successfully grated to EPDM molecules through UV initiation process. The conductivity of EPDM increases after individually utilizing three auxiliary crosslinkers to EPDM at various temperatures of cable operations, by which the highest conductivity has been acquired by grafting N.N-m-phenylene dimaleimide. The first-principles calculations demonstrate that some occupied local electronic-states have been introduced in the band-gap of the EPDM crosslinked by N.N-m-phenylene dimaleimide (EPDM-HAV2), which can be thermally excited from valence band to conduction band at lower temperature or in higher density, leading to augmentation in electrical conductivity. Meanwhile, the breakdown strength achieves a significant improvement in consistency with the theoretical estimation that deeper hole-traps can be introduced by auxiliary-crosslinking modification, and will consequently increase breakdown strength through the trapping mechanism of space charge suppression. in relation to the appropriately increased conductivity, in combination with persistent breakdown strength, the finite element simulations of the electric field distribution in EPDM cable terminations suggest that the effectively homogenized electric field at the root of stress cone will be realized for EPDM-HAV2. The present study offers a fundamental strategy to ameliorate EPDM materials in the application of insulated cable accessories.

MSSB to Prevent Cable Termination Faults for Long High Voltage Underground Cable Lines

Cable termination fault is one of the most important problems for high voltage underground cable lines (HVUCL). Harmonic current (HC) and the sheath current (SC) are causes of cable termination faults of HVUCL. The sheath voltage (SV) of cable increases due to SC and HC also. So, the electroshock risk for human occurs. In this study, cable termination faults are examined for long HVUCL that is connected to electric network with high harmonic distortion rate. In literature, solid bonding (SB) and sectional solid bonding (SSB) methods are used to reduce harmonic distortion rate and SC effect in HVUCL. However, when SB and SSB methods are used for bonding of long HVUCL, harmonic distortion limit and touch voltage limit are exceeded. Therefore, the modified SSB (MSSB) method is developed for bonding of long HVUCL. SV of HVUCL should be known to use MSSB for bonding of long HVUCL. Then SV of HVUCL is forecasted by using artificial neural network and hybrid artificial neural networks (HANN) before the long HVUCL is installed. MSSB parameters should be optimized, so that optimization methods are used for optimization of MSSB and HANN. When MSSB method is used for bonding of long HVUCL, harmonic distortion limit and touch voltage limit are not exceeded under high harmonic distortion conditions.

High‐voltage cable bonding to prevent cable termination faults based on zero‐sequence current

High‐voltage cable bonding to prevent cable termination faults based on zero‐sequence current

Assessment of Overvoltage and Insulation Coordination in Mixed HVDC Transmission Lines Exposed to Lightning Strikes

Many geographical constraints and aesthetic concerns necessitate the partial use of cable sections in the High Voltage DC (HVDC) transmission line, resulting in a mixed transmission line. The overhead sections of mixed lines are exposed to lightning strikes. The lightning strikes can not only result in flashover of overhead line (OHL) insulators but can enter the cable and permanently damage its insulation if adequate insulation coordination measures are not taken. In this work, we have analyzed the factors that affect the level of overvoltage inside the cable by simulating a fast front model in PSCAD. It has been determined that surge arresters must be provided at cable terminals when the length of cable sections is less than 16 km to limit the core-ground overvoltage within the lightning impulse protective level (LIPL). The level of sheath-ground overvoltage is independent of the length of cable; however, it can be limited within LIPL by lowering the sheath grounding impedance to 1.2 Ω. Insulation coordination measures do not impact the likelihood of OHL insulators’ flashover. The flashover performance of OHL can be improved by lowering the footing impedance of the second tower closest to the cable terminals, which is otherwise most likely to flashover.

The optimized bonding method for long high voltage cable lines under the unbalanced cases

In the unbalanced loading (UL) and phase to ground fault (PGF) cases, zero sequence current (ZC) flows on neutral point of power transformer, and the sheath current (SC) and the sheath voltage (SV) increase due to ZC. Thus, overvoltage (OV) and high harmonic distortion (HD) occur in cable termination (CT). OV causes high and imbalanced electric field, and high HD causes increasing of insulation temperature in CT, so CT faults occur. In the literature, bonding methods are used to prevent SC and SV effects, but these methods are not sufficient to prevent ZC effects, so the modified sectional solid bonding (MSSB) is suggested to prevent ZC effects. The aims of this study are minimizations of SV and HD on CT to prevent CT faults, so MSSB parameters are optimized by optimization method. In optimization algorithms of MSSB, the forecasting methods (FM) and optimization methods (OM) are used to optimize MSSB parameters. The best FM is selected according to training and forecasting errors, and the selected FM is used as an objective function of OM. Training and forecasting errors of hybrid ANN are less than the other methods, so hybrid ANN methods are used as FM. When bonding methods that are in literature are simulated under UL and PGF cases, SV and HD values exceed the limits. When the optimized MSSB method is used, HD and SV do not exceed the limits. Therefore, the optimized MSSB is suggested to prevent CT faults for the unbalanced cases.

Doppler Shift in a Radiating Cable System in Tunnel Environments: A Theoretical Analysis

For many years, radiating cables have been used to provide coverage inside tunnels or underground venues. Due to the progress in transport technology and the increasing demand on mobile communications the necessity of having a clear understanding of the behaviour of the wireless channel in these environments is essential to successfully deploy radiating cable systems. In this context, the main objective of this paper is the study of the Doppler shift generated in a radiating cable system due to a mobile receiver changing positions along a defined path inside a tunnel. Doppler shift is an important effect in mobile communications as it degrades system performance. The study shows that a correct selection of the operating frequency used for the radiating cable can help reduce the Doppler shift and in turn the Doppler spread in the channel. At the same time the study reveals how the Doppler shift of a radiating cable generated by a fast-moving user is related to its radiation pattern, especially at the cable terminations. Finally, Doppler spread is accentuated when the cross section of the tunnel is reduced. These results can be used as a reference for improving the design of radiating cable systems applied in mobile communications with fast-moving vehicles, e.g. high-speed trains.

2D spatial optimisation of functionally graded materials used as insulators for field stress control

Functionally graded materials (FGMs) are expected to be useful in the electrical industry, especially for achieving an efficient electric field stress control. However, as these are relatively new materials, there are a number of unanswered research questions around them. A novel method to obtain an optimised spatial distribution of permittivity or electrical conductivity of FGMs used as insulators for electric stress control is presented in this study. The problem is envisaged as the realisation of two objectives viz., (i) to minimise maximum stress and (ii) to achieve a more uniform electric stress distribution. Permittivity or electrical conductivity of FGMs is considered as variables of optimisation and based on this a unique stochastically-controlled multi-objective particle swarm optimisation technique is developed. The spatial optimisation of the properties has been carried out in 2-dimensions, which, unlike previous studies is more realistic. After validation with results available in the literature, it has been found that the electric field distribution in a cable termination is greatly improved by using stress control tube (SCT) having optimised permittivity gradation, which further improves by using SCT of optimised conductivity gradation.