Cable Life Research Articles

Ageing Analysis of Power Cable used in Nuclear Power Plant

The aim of nuclear power plant ageing management and assessment is to maintain an adequate safety level throughout the life time of the plant and helps in determining the useful operation. Various factors involved in the insulation of polymeric cables such as continuous heat, radiation and atmosphere result in the alteration of chemical and physical properties as well as lowers the service life of material. PVC (Poly Vinyl Chloride) is the most commonly used insulation material in NPP (Nuclear Power Plant). Purpose of this work is to predict the service life of PVC insulation cable for which extrapolation ageing has been performed. Ageing mechanism proceeds in laboratory scale rig to provide temperature and radiation sources. The variation in temperature is regulated and monitored through thermocouple. At higher temperature, semi crystalline free radical may escape out resulting in the degradation of polymer. Different tests have been carried out like shore hardness testing, tensile testing, Differential Scanning Calorimeter and Thermo gravimetric Analysis before and after ageing to analyze the Ageing effect. The impact of ageing days upon yield strength of single stress ageing has been carried out in this research work and it is found that aging has significant effect on service life of cables used in power plants.

The Effects of Seasonal Factors on Life and Reliability of High Voltage AC Cables Subjected to Load Cycles

In previous articles by this author, a procedure was set up and validated for life and reliability evaluation of HV cables subjected to the time-varying electro-thermal stress associated with the typical daily cycles of conductor current. In this paper, the procedure is improved to account for the effects of seasonal factors, by taking for every season different daily cycles of cable current, as well as different values of thermal resistivity and temperature of the soil. The procedure is applied to a case-study HVAC XLPE-insulated cable. The results show that the fraction of life and reliability lost by cable insulation is strongly dependent on seasonal factors, in particular on soil resistivity and temperature, and the vast majority of cable life and reliability is lost within the hot (summer) season.

Main Approaches to Cable Aging Management at Nuclear Power Plants in Ukraine

The mechanisms of cable ageing at nuclear power plants (NPPs) mainly depending on the insulation material, as well as the damaging factors affecting cables that are determined by the operating conditions are considered in the paper. The main and additional mechanisms of aging resulting from the effects of damaging factors are provided. The paper presents the main methods of cable aging management: determining the actual service life and testing using field methods and other means. The basic principles for the arrangement of cable aging management at Ukrainian NPPs, as well as the methods used to investigate the technical condition of cables, are presented. A list of mandatory lists has been defined when performing activities on cable aging management. A methodology is described for lifetime extension of cables, and conditions for extending the service life of cables that are in service are provided. A number of methods of testing cables for aging management are considered: visual inspection of insulation and measurement of crack size, discoloration, etc.; insulation hardness test; insulation chemical analysis; electrical insulation tests; tensile strength measurement; measurement of elongation at break; measurements of dielectric loss at low frequency or sweep frequency; testing by dynamic reflectometry method; AC and DC current impedance measurements. The paper presents results of separate laboratory studies for selected 1 kV representative power cables with PVC insulation of SUNPP-1, ZNPP-1 and KhNPP-2 conducted within Ukrainian NPP long-term operation, which included a stage of laboratory examination and examination of cable samples in operating conditions. The following results were obtained: dependence of VVGng 4x6 cable lifetime on operating temperature; dependence of AVVG cable lifetime on operating temperature; dependence of AVVG (a) cable lifetime on operating temperature. There are possibilities and conditions under which the use of cables within long-term operation is permissible.

Determination of parameters of cable drums of capstanshunting winches

The article considers the problem of determining the rational geometric parameters of friction cable drums of capstan shunting winches. The basic technical means for performing shunting works within the cargo yards of railway stations and industrial enterprises are given. Today, shunting locomotives are the most common means of shunting works at railway stations and cargo yards of industrial enterprises. However, using them is not economically feasible for small amounts of shunting. Both sheave-type and capstan shunting winches are often used to move individual cars or groups of cars along the freight front. In the capstan shunting winches, a frictional drum of infinite coiling length is used, which rotates around a horizontal axis. It is established that the known sources give only the theoretical principles of the operation of drums of infinite coiling length and do not contain any practical recommendations for the design and operation of capstan shunting winches. The article provides a theoretical study of the forces of friction that occur between the drum and the cable, as well as between the cable lines when drums with different profiles of working surfaces are used. It was found that in shunting winches, the coefficient of friction of the rope along the drum can increase by 2.5 times, as a result of which it is necessary to increase the curvature of the profile of the drum. Also, friction forces between adjacent branches of a cable wound on a winch drum are considered. On the basis of the conducted study, recommendations on the type and geometrical parameters of cable drums of capstan shunting winches are proposed, which are aimed at extending the service life of traction cables of these mechanisms.

Study on the Effect of Cable Group Laying Mode on Temperature Field Distribution and Cable Ampacity

The reliability and service life of power cables is closely related to the cable ampacity and temperature rise. Therefore, studying the temperature field distribution and the cable ampacity is helpful to improve the construction guidelines of cable manufacturers. Taking a 8.7/15 kV YJV 1 × 400 XLPE three-loop power cable as the research object, cable temperature is calculated by IEC-60287 thermal circuit method and numerical simulation method, respectively. The results show that the numerical simulation method is more in line with the actual measured temperature, and the relative error is only 0.32% compared with the actual measured temperature. The temperature field and air velocity field of cluster cables with different laying methods are analyzed by finite element method. The corresponding cable ampacity are calculated by secant method. The results show that when the cable is laid at the bottom of the cable trench, the cable current is 420 A, which is 87.5% of the regular laying. Under irregular laying mode, the temperature of cable is higher than that of regular laying mode and the cable ampacity is lower than that of regular laying mode. At the same time, a multiparameter online monitoring system is developed to online monitor the temperature, water level and smoke concentration of the cable.

A reliability assessment model for an outdoor 88 kV XLPE cable termination

A metropolitan power utility has been experiencing systematic and premature failures of a particular type of XLPE cable terminations operating at 88kV (rms). The utility therefore desired to understand the modes of failure in order to evaluate the risk with the terminations still in service. Failed terminations were forensically analysed. The dominant modes of degradation were identified as electro-thermal, galvanic corrosion and thermomechanic fatigue. Based on the weakest link principle, a reliability model was developed using the life factor models corresponding to the identified modes of degradation. Galvanic corrosion and thermomechanic fatigue life factors were found to have the predominant influence on the overall reliability of the termination as they reduced the cable termination life by more than 10 years. The model can be used to track the probability of the remaining life of the terminations as well as evaluating the effectiveness of alternative designs and/or in-situ repairs.

Analysis of Temperature Conditions Influence on Cables Insulation Operation Life

Electrical equipment fault current interruptions reduce is one of the most important problems of electrical power engineering and diagnostics. Power cables operation life is one of the parameters mostly affecting fault current interruptions on cables. The paper describes the research on thermal degradation of low voltage cables insulating materials and its influence on insulation operation life. The known mathematical models of the insulation aging depending on its temperature are considered. Low voltage cables have an insignificant electrical aging influence, so it is assumed that such cables aging mostly caused by their thermal operating conditions. Experimental research of cables insulation temperature monitoring is performed. Seven weeks of the experiment showed a temperature change between 17˚C and 27˚C. The mean temperature was 21.9˚C. Assuming that cable has normal operation life with an average temperature of 20˚C and accounting thermal conditions cable insulation operation life is reduced for about 20%. Such operation life reduce is significant and shows a considerable influence of insulating material thermal deterioration.

A Holistic Approach to Risk-Based Maintenance Scheduling for HV Cables

Regular maintenance inspection and testing is essential in extending cable life and reducing failure probability. This can be achieved by improving the conduit conditions and taking corrective actions on faulty cable components and accessories. Regulators and corporate governance among power utilities require the implementation of risk-based approaches to asset management. However, practitioners lack sufficient historical event data and knowledge that allow them to determine the failure probability of individual cable components, which is an essential component for risk assessment, due to that the high voltage (HV) cable population are relatively young, and many have not yet reached the end of their design life. This paper presents a novel holistic approach to allow the risk based maintenance strategy to be conveniently implemented for the cable conduit, cable terminations, joints, main bodies and the earthing systems separately for each cable circuit. Contributions include: (i) a failure frequency model which accounts for every past failure record of individual cable circuit components to approximate the probability of failure. This, when multiplying with the cable importance or failure consequence, yields the risk level of an individual cable component or a cable circuit; and (ii) a method of optimally scheduling the maintenance activities by setting the objective functions as the minimal cable system risk. The benefit of the simple failure frequency model has the advantage of not having to depend on human intervention and it does not need a large sample to generate valid results, as is the case with other statistical methods. Results of applying the proposed maintenance scheduling model to 21 selected High Voltage (HV) cable circuits show that the average risk can be significantly reduced while continuing with the same number of inspections and test operations.

A Life Loss Tool for an Optimal Management in the Operation of Insulated LV Power Cables

An optimized system management of a power system must take care of the actual operational and energetic duty of the power system distribution, promoting a high efficiency of power cables and avoiding their excessive gap on load and gap on lifetime. A procedure based on the Arrhenius model of the Thermal Aging of Insulating Materials allows implementing a tool to calculate the life loss and the residual useful life for insulated power cables. The paper deals with simplified models to evaluate the power cable temperature behavior considering the load current variable in the time. The life loss analysis can be performed both “off-line”, based on the available circuit parameters and measurements, or “on-line” by appropriate control systems. Furthermore, the paper proposes a specific device to count the “life loss hours”. The employment of such tools supports the system operators to monitor the cables life loss in the effective installation conditions, to optimize their operation and maintenance and, possibly, to upgrade the efficiency of the distribution system.

Examination of State of the Cable Insulation by the Return Voltage

Abstract The relevance of the study is conditioned by the need to determine the state and residual life duration of high-voltage cable lines to identify faulty and maintainable cables. The aim of the article is to determine a reliable scientifically grounded criterion for assessment of insulation characteristics of the cables in use and to perform a comparative analysis of the results obtained by the traditional method of diagnosing insulation with the results of a new method of assessment by the return voltage. In this regard, the article deals with the issues related to the testing of cables having oil-impregnated paper insulation, as well as with the issue of switching from planned replacement of cables to assessment of their actual state and period of residual life. The authors propose to use the method of examining the cables by the return voltage using the device for testing electrical insulation “UDEI-1” developed at the department of Electrification and Automation of the Nizhny Novgorod State University of Engineering and Economics. The article presents the results of measuring the return voltage of three cables that operated under different conditions. The cables had different technical state. The analysis of the estimation of the residual life of cables by the return voltage was carried out using such criteria as the PIRV polarization index, the LIRV electrical conductivity index, and the P-factor. The P-factor is the physical criterion demonstrating the aging of paper-oil insulation by the shape of the return voltage curve. It represents such characteristics of insulation aging as moistening. To compare the results of testing the cables by the return voltage with the conventional methods of diagnostics and to determine the actual technical condition of power cables, the authors applied the method of spatiotemporal reflectometry and the method of measuring insulation resistance with the determination of such indicators of state as insulation resistance normalized per one kilometer, absorption coefficient, and polarization index. The results of this article confirm that the return voltage gives a qualitative assessment of the state and degree of aging of cables with impregnated paper insulation. The authors proposed a new system for evaluation of cable condition by weighting coefficients. In this approach, the determination of residual life of cables with impregnated paper insulation is based on the values of the return voltage. Application of the new system gives opportunity to improve reliability of the power lines. Recommendations for the further operation of the studied cables are given. The materials of the article are of practical value for carrying out complex assessment of the technical condition of power cables by the return voltage and can be useful for drawing up a schedule for replacement or repair of cable lines depending on their actual state.

Fatigue life assessment of FRP cable for long-span cable-stayed bridge

This study evaluates fatigue life of carbon fiber reinforced polymer (CFRP), basalt fiber reinforced polymer (BFRP) and steel cables considering the sag effect for cable-stayed bridges with various safety factors. The fatigue cycles of the cables during designed service period were first studied by an analysis of vehicle load statistics. The least favorable cables and their stress amplitudes were determined by finite element (FE) analysis. Fatigue life assessment based on the design stress and service life of the cable was conducted by developing the combined algorithm of equivalent transformation. The results indicate that the cables in the bridge undergo approximately up to 1.14 × 109 fatigue cycles during 100 service years. The most unfavorable cable is the one in the mid-span position, and its equivalent stress amplitude is almost 12 times the actual stress amplitude. The fatigue life of CFRP cables increases much faster than that of BFRP and steel cables with increasing of safety factor. The fatigue lives of CFRP and BFRP cables are 3 and 1.4 times, respectively, compared to that of a steel cable with the safety factor of 2.55. To satisfy 100 years of design life, safety factor of CFRP, BFRP and steel cables should be no less than 2.55, 3.27 and 3.64, respectively.

A predictive model for polyethylene cable insulation degradation in combined thermal and radiation environments

Reliable prediction of material service lifetime is important for ensuring safe operation in safety-critical systems such as nuclear facilities. Materials in these environments degrade due to several simultaneous effects, most important stressors are heat and radiation. In this work, samples of medium density polyethylene cable insulation were subjected to thermal (110 °C) and γ-radiation stress (500 Gy h−1); a combined thermal and radiation test (85 °C and 4.5 Gy h−1) was also performed. Stability of cable insulation was studied by differential scanning calorimetry and isoconversional kinetic analysis employing a non-Arrhenian temperature function was carried out. From the dependence of residual stability on the degradation dose a predictive model for the cable service life was developed based on the thermal and radiation stress tests; the model validity was verified using the combined stress test results. The model assumes a first-order exponential decay of the residual stability with degradation dose. It allows to predict the degree of insulation damage in wide range of environmental conditions as both temperature and radiation dose effects are considered and radiation dose rate effect is also taken into account.

Analysis of the Topologies of Power Filters Applied in Distributed Generation Units - Review

Considering the current scenario of the advance of the use of renewable energy sources, mainly wind and solar photovoltaic, in the Brazilian energy matrix. At the same time, there is concern about the stability of the power system and its respective power quality (PQ), due to this type of generation of non-linear loads, such as current converters, which in turn cause distortion Of the current and voltage waveform. The generation of energy by renewable sources does not participate in the control of the voltage and frequency of the electrical system, and in the occurrence of disturbances that exceed the pre-established limits and that affect the system's PQ, are disconnected until the PQ is restored, to be Reconnected after normal operation returns. In order to standardize and quantify the electromagnetic disturbances of the QEE, as well as ensure the quality of the product and services, standards and procedures were designed to instruct from generators to energy consumers. In Brazil, the Electric Power Distribution Procedure in the National Electric System (PRODIST) - module 8. The disturbances of the PQ in the generating units, mainly wind and solar photovoltaic are caused by the harmonics of current, generated by the converters, causing the distortion in the waveform, which in turn, increases the losses in transformers and transmission lines, reduction of cable and equipment life, flicker. Among the possible techniques to minimize the effects of harmonics, the use of passive, active and hybrid filters stands out. However the applicability of each type of filter depends on each system where it will be applied according to the characteristics of the electrical system. Thus, in order to contribute to the advancement of the topic, it can be observed that the use of power filters has a good functionality in harmonic attenuation as well as economical solution. Therefore, this work presents a mapping of the main technologies and methodologies for the design of power filters that can be customized for the mitigation of harmonic disturbances and improvement of the power factor. Finally, it presents a comparative analysis between the topologies of power filters, followed by an alternative proposal of an automated filter for microgeneration of energy connected in low voltage.

Research of Electro-Thermal Aging Process of Cross-Linked Polyethylene

Cable XLPE-insulation operation capability and reliability highly depends on its insulation condition. Statistical analysis showed that more than 70% of cable technological disturbances are insulation breakdowns, caused by insulation aging or poor quality of cable jointing. This paper is devoted to the cable XLPE-insulation aging under the influence of electro-thermal stress. The goal of the research is to develop the technique of cable insulation residual life calculation. Theoretical and experimental research was carried out for this goal. During theoretical research Kuchinsky insulation aging model was considered and statistical research of cable insulation breakdown was performed. Experimental research of cable insulation accelerated electro-thermal aging was carried out. XLPE-insulated cable samples were exposed to the influence of temperature and voltage above rated. The results of theoretical and experimental research showed that partial discharge dependence on electric field has variable coefficients and requires an additional research, taking all possible influencing factors into account.

Fatigue load estimation of a spar-type floating offshore wind turbine considering wave-current interactions

This paper considers the effects of current and wave-current interactions in fatigue analysis of floating offshore wind turbines (FOWTs). Surface water waves experience frequency shifts and wave shape modification when traveling on underlying currents. The wave-current interactions are known to be important for the responses of offshore structures, however, they have not been considered in FOWT fatigue analysis. To include such interactions, a nonlinear mooring hydrodynamics model is presented which is able to consider the cable geometric nonlinearity, seabed contact, and the current effect. The mooring model is then coupled with a spar-type FOWT model which simulates the structural dynamics of turbine blades and tower; aerodynamics of the wind-blade interaction and wave-current actions on the spar. Analytical wave-current interaction models based on Airy’s theory considering the current effect are applied for generating the flow field. Based on a spar-type FOWT and the wave-current interaction model, numerical simulations have been performed for three cases with only waves, wave and current without and with interactions. The comparison of the structural responses shows that the current and the wave-current interaction can have significant influences on FOWT tower and cable responses. Furthermore, cable fatigue life is estimated for two particular cases when the cable tension is decreased and increased respectively due to the presence of current. It is found that if the current tends to increase the cable tension, neglecting the current and wave-current interactions leads to overestimate of the cable fatigue life.

Accelerated aging test and life expectancy of reduced-wall high-stress MV TRXLPE cables

Accelerated aging test based on the AEIC CS8 AWTT (Accelerated Water Treeing Test) protocol was carried out on both standard and reduced-wall high-stress MV TRXLPE cables with different insulation thicknesses. Results were compared with existing data for cables with different insulation types. Furthermore, a comprehensive statistical analysis based upon the maximum likelihood method was applied to reveal the life expectancy of reduced-wall high-stress TRXLPE cables as compared to the standard wall cable. This comparison was also made with previous ACLT (Accelerated Cable Life Test) results.

Research on Improving Electric Field Distribution of Cable Terminal Based on Non-linear Materials

The electric field distribution of the power cable terminal is very complicated, and there is a large concentrated electric field at the interface between the stress cone and the main insulation. Such a high electric field will accelerate the aging of the insulation and lead to the breakdown of the insulation. In addition, the cable terminal need to be produced in the field, once the production process is poor, leaving bubbles or impurities and other defects in cable terminal, the electric field distribution of the cable terminal will be very uneven, local high field strength lead partial discharge, shorten the cable terminal life. In this paper, based on the non-linear insulation material can play a uniform electric field role in the non-uniform electric field, to explore the effect of non-linear SiC/silicone rubber composites on homogenizing electric field, the electric stress distribution of cables termination were simulated by COMSOL Multiphysics software. The results show that the maximum electric field strength at cable terminal decreases extremely when the 45wt% nano-SiC/silicone rubber composites were used.

Residual Life Prediction of Mine Cable Based on RBF Neural Network

In this paper, the RBF (Radial basis Function) neural network forecasting model is constructed for the mine cable life prediction problem. As the mine cable is in line with the characteristics of accelerated life test, the temperature and the dielectric dissipation factor are chosen as the model input. In order to obtain the enough sample data and to construct the detecting sample possibly, using the linear interpolation generates a large amount of simulation data as the training target vector, RBF neural network is established accessibly for life prediction. Then life prediction value and design life was verified and the result confirms that the RBF neural network model can reflect the relationship between the dielectric dissipation factor and residual life under a certain humidity and different levels of temperature. The residual life prediction of cable insulation can protect the safety of underground power supply.

Determining Time Variation of Cable Tension Forces in Suspended Bridges Using Time‐Frequency Analysis

A feasibility study was conducted to develop a novel method to determine the temporal changes of tensile forces in bridge suspender cables using time‐frequency analysis of ambient vibration measurements. An analytical model of the suspender cables was developed to evaluate the power spectral density (PSD) function of a cable with consideration of cable flexural stiffness. Discrete‐time, short‐time Fourier transform (STFT) was utilized to analyze the recorded acceleration histories in both time and frequency domains. A mathematical convolution of the analytical PSD function and time‐frequency data was completed to evaluate changes in cable tension force over time. The method was implemented using acceleration measurements collected from an in‐service steel arch bridge with a suspended deck to calculate the temporal variation in cable forces from the vibration measurements. The observations served as proof of concept that the proposed method may be used for cable fatigue life calculations and bridge weigh‐in‐motion studies.

MODIFICATION OF COMPOSITE MIXTURES FOR MANUFACTURING SHIP CABLEWARE MATERIALS

The purpose of this work was to develop a modified polymeric composite mixture for the manufacture of the outer shell of a ship's cable operating under conditions of aggressive environment and increased fire hazard. The performed research resulted in the analysis of the basic polymeric composite mixtures. A complex of the most important technical and operational characteristics of the cable shell was formed. These characteristics are wear resistance, oil resistance and fire safety. On the basis of these assumptions a new polymer composition based on chloropolyethylene TYRIN CM 3630E with an increased oxygen index and improved physical and mechanical properties was developed. Modification of the mixture was carried out by increasing the mass fraction of flame-retardant additives and adding stabilizers to the mixture. Thanks to a balanced combination of technical and operational properties the use of the developed compound will increase the cable service life and operating time and will reduce the overall weight of the cable by using conductors of a smaller cross-section at a higher operating temperature.