Showing papers on "VLF cable testing published in 2016"
TL;DR: In this article, the authors consider the problem of estimating the maximum lengths of high voltage (HV) and medium voltage (MV) cables that can be scanned with sufficient sensitivity for partial discharge (PD) activity by present day PD detectors.
Abstract: Partial discharge (PD) measurement is becoming a common procedure in the commissioning and off-line diagnostic testing of cable systems. On-line PD cable monitoring is beginning to show growing interest as well. Arising from this is an important question being asked by testing companies, maintenance personnel, and asset managers: "What are the maximum lengths of high voltage (HV) and medium voltage (MV) cables that can be scanned with sufficient sensitivity for PD activity by present day PD detectors?" In other words, what is the maximum distance a PD measurement point can be from the PD source and still detect the PD. The answer can be complex, or not satisfactorily understood, being related to the measurement sensitivity, voltage level, type of insulation, and cable construction. Detection also depends on the bandwidth of the measurement circuit. The signal-to-noise ratio must be large enough to enable PD detection at a level compatible with the reliability of the cable, that is, terminating maintenance or commissioning diagnostic tests before cable breakdown. Indeed, the capability of detecting pulses with an apparent charge below 5 pC is a common requirement for HV polymeric cable systems [1], whereas a much lower sensitivity, i.e., 5 nC, for mass-impregnated cables is generally accepted. The meaning of such limits in cable systems is doubtful as PD measurements are most often done from the cable termination because localized sensors are often unavailable, and since not in close proximity to the source, a lumped-parameter network representing the cable network for picocoulomb calibration is invalid. In a cable system PD pulses travel on the conductor and metal sheath, and the cable is viewed as a distributed parameter network; thus, the PD quantity measured is typically volts or millivolts. As the PD pulses travel along the cable, they lose frequency content as a consequence of skin effect or ohmic loss at high frequencies, and semicon and insulation dielectric losses [2], [3].
56 citations
TL;DR: In this paper, two terminal synchronous tanδ measurement as a new method of on-line insulation monitoring had been put forward in order to solve the problem, and the working principle and theoretical basis of calculation were given.
Abstract: There are cross-linked metal sheath and voltage drop in the long distance power cable which make difference between the short and the long distance power cables on on-line insulation monitoring technology. In order to solve the problem, two terminal synchronous tanδ measurement as a new method of on-line insulation monitoring had been put forward in the paper. The working principle and theoretical basis of calculation were given. The feasibility of the method was demonstrated when there was synchronization error in the system. The Matlab software was used to simulate the circuit of three-phase cable and to calculate tanδ of cable insulation. The results show that the load current will not influence on tanδ measurement if choose the average of vector sum of voltage at the two ends of the cable. And the harmonic and frequency fluctuation had little influence on the methods. The methods were proved to be validity and feasibility in the paper. It can be obtained that the methods were suitable for all kinds of cable insulation monitoring whether the metal sheath of three-phase cable was cross-linked or not.
42 citations
19 Jun 2016
TL;DR: In this paper, a statistical approach to estimate the life of a cable insulation system when repetitive transients, of know probability distribution, are expected to affect insulation during operation is presented, and it is shown that life at a given reliability percentage can be shortened even significantly, depending on transient overvoltage and repetition rate.
Abstract: Transients and repetitive transients affect cable insulation life in a way, which is not easily predictable at the design stage. Therefore, cable system life can be shorter than that expected especially when loads controlled by power electronics are fed, or when HVDC systems are integrated in AC networks. This paper has the purpose to provide a statistical approach to estimate the life of a cable insulation system when repetitive transients, of know probability distribution, are expected to affect insulation during operation. It is shown, using the Miner law and a stochastic approach, that life at a given reliability percentage can be shortened even significantly, depending on transient overvoltage and repetition rate. Condition monitoring, however, remains the main tool to keep track of cable heath condition during operation life
12 citations
18 Apr 2016
TL;DR: In this paper, a 2D finite-element analysis for a 3-core cross-linked polyethylene (XLPE) underground cable (UGC) straight joint of the heat shrink type is presented.
Abstract: This paper presents a 2d finite-element analysis for a 33-kV, three-phase, three-core cross-linked polyethylene (XLPE) underground cable (UGC) straight joint of the heat shrink type. The aim of this work is to show how the joint design parameters and different defects affect the electric field distribution, and find optimum material properties to enhance the lifetime of cable joints. This is investigated by calculating the electric field distributions and showing how the optimized selection of joint material properties can reduce the localized high electric field to avoid partial discharge activities. Several design parameters are investigated such as insulation layer's thickness and relative permittivity, and termination angles of ferrule and its insulation. In addition, size and location of different defects such as air voids, water droplets, sharp tips and delamination are examined. The paper concludes important points for proper design of medium-voltage (MV) cable joints to enhance their lifetime and hence increase the reliability of such cable systems.
10 citations
1 Sep 2016
TL;DR: In this article, diagnostic on a Medium Voltage (MV) underground cables using tan δ measurement that measures dissipation factor with 0.1Hz VLF (Very Low Frequency) high voltage source has emerged as an efficient way to assess water tree aging of MV cables.
Abstract: Transition from TBM(Time-Based Maintenance) to CBM(Condition-Based Maintenance) is required on aging estimation of power cable. To maximize the cable estimation efficiency, sequential reinforcement standards must be established in accordance with aging factor. In this paper, diagnostic on a Medium Voltage(MV) underground cables using tan δ measurement that measures dissipation factor with 0.1Hz VLF (Very Low Frequency) high voltage source has emerged as an efficient way to assess water tree aging of MV cables. Also it suggests that new method analysis on power cable by mean of the Used Cable Diagnosis-matrix.
9 citations
1 Aug 2016
TL;DR: In this article, the authors focus on the practical experience using combined very low frequency (VLF) testing with Tan Delta (TD) and Partial Discharge (PD) measurements to assess health condition and localize defects in medium voltage cables.
Abstract: Condition assessment of power cables is one of the most important tasks in maintenance and management of power networks. Significant investment has been made to ensure the reliability of cable systems. Very Low Frequency (VLF) test is an alternative method for 50 Hz AC voltage test. Using VLF voltage source, Tan Delta (TD) and Partial Discharge (PD) measurement can be carried out simultaneously. TD measurement is a nondestructive integral test to assess the overall cable condition, while PD measurement can be used to localize defects that generate electric discharge activities. This paper focuses on the practical experience using combined VLF testing with TD and PD to assess health condition and localize defects in medium voltage cables. Field experience with VLF TD and PD will be shared. Detailed testing and evaluation technique will be described.
9 citations
1 Sep 2016
TL;DR: In this article, the authors focus on the practical experience using combined very low frequency (VLF) testing with Tan Delta (TD) and Partial Discharge (PD) measurements to assess health condition and localize defects in medium voltage cables.
Abstract: Condition assessment of power cables is one of the most important tasks in maintenance and management of power networks. Significant investment has been made to ensure the reliability of cable systems. Very Low Frequency (VLF) test is an alternative method for 50 Hz AC voltage test. Using VLF voltage source, Tan Delta (TD) and Partial Discharge (PD) measurement can be carried out simultaneously. TD measurement is a nondestructive integral test to assess the overall cable condition, while PD measurement can be used to localize defects that generate electric discharge activities. This paper focuses on the practical experience using combined VLF testing with TD and PD to assess health condition and localize defects in medium voltage cables. Field experience with VLF TD and PD will be shared. Detailed testing and evaluation technique will be described.
8 citations
23 May 2016
TL;DR: In this article, the authors describe the progress of work towards an Open Source software toolset suitable for developing Spice-based multi-conductor cable models, and present the issues related to creating a transmission line model for implementation in Spice which include the frequency dependent properties of real cables.
Abstract: This paper describes the progress of work towards an Open Source software toolset suitable for developing Spice based multi-conductor cable models. The issues related to creating a transmission line model for implementation in Spice which include the frequency dependent properties of real cables are presented and the viability of spice cable models is demonstrated through application to a three conductor crosstalk model. Development of the techniques to include models of shielded cables and incident field excitation has been demonstrated.
7 citations
19 Jun 2016
TL;DR: In this paper, a test setup was established in Aalto University to study the changes of temperature across different power cable layers in various cable operating modes, including three different types of joints to identify differences in behavior during temperature change.
Abstract: Thermal aspects of power cable performance are an important field of research as power grids depend increasingly on the reliability of underground cable systems. Overheating is a possible cause of cable faults and it should be ensured that no part of the cable exceeds its rated operating temperature. A test setup was established in Aalto University to study the changes of temperature across different power cable layers in various cable operating modes. The setup also includes three different types of joints to identify differences in behavior during temperature change. Temperature measurement was achieved using thermocouples inserted into the cable and each of the joints: heat shrink joint, cold shrink joint and hybrid shrink joint. This paper discusses the structure of the test setup and the capacity of different tests available with the given setup.
5 citations
23 Aug 2016
TL;DR: In this article, a transient analysis software for high voltage cables has been developed as an aid to partial discharge measurements carried out to assess the insulation condition of installed cables, which can be used to know if a specific measuring PD system is sensitive enough to detect partial discharge pulses that can occur along a high voltage cable.
Abstract: A transient analysis software for high voltage cables has been developed as an aid to partial discharge measurements carried out to assess the insulation condition of installed cables. Knowledge of the transient behavior of cable systems allow to know if a specific measuring PD system is sensitive enough to detect partial discharge pulses that can occur along a high voltage cable. Series impedances of a high voltage cable are analyzed considering its semiconducting layers using Bessel functions. The influence of semiconducting layers is also taken into account to determine the parallel impedance of a high voltage cable. A Gaussian pulse is considered as a PD pulse traveling along the cable and the inverse Laplace transform is used to determine the resulting pulse at the end of a cable length. The results presented in this paper show that attenuation and distortion of PD pulses traveling along any cable system depend largely on the resistivity and the permittivity relativity of semiconducting layers of the high voltage cables.
5 citations
Patent•
6 Feb 2016
TL;DR: In this paper, a voltage source having a first voltage multiplier for a positive voltage and a second voltage multipliers for a negative voltage current source that are connected to one another in combination with the multipliers to generate a test voltage over the load impedance of the cable to charge and discharge the cable and a control device that is interconnected with the voltage source and the current sources and other devices with a circuit arrangement of that type.
Abstract: The invention relates to circuit arrangements for cable checking, cable testing, cable diagnosis and/or cable fault localization with
a voltage source having a first voltage multiplier for a positive voltage and a second voltage multiplier for a negative voltage current sources that are connected to one another in combination with the voltage multipliers to generate a test voltage over the load impedance of the cable to charge and discharge the load capacitance of the cable and a control device that is interconnected with the voltage source and the current sources and
devices with a circuit arrangement of that type.
The circuit arrangements distinguish themselves, in particular, by the fact that arbitrary voltage curves of different amplitudes can be generated through the cable as the impedance acting as the test specimen.
1 Jan 2016
TL;DR: In this article, the dielectric properties of 12/20/24 kV XLPE power cables including cable joints were investigated by using polarization and depolarization current (PDC) measurement, conventional partial discharge measurement according to IEC 60270, and high frequency current measurement measured by high-frequency current transformer (HFCT).
Abstract: Medium voltage power cables are an important element of electric power distribution. Most of cable failures occurring in XLPE insulation and cable accessories are due to insulation failure. This research work represents the dielectric investigation of 12/20(24) kV XLPE power cables including cable joints by using polarization and depolarization current (PDC) measurement, conventional partial discharge measurement according to IEC 60270, and high frequency current measurement measured by high frequency current transformer (HFCT). In this research work, six case studies, case 1: PE sheath damaged, case 2: semi-conducting layer damaged, case 3: void defect in extruded cable, case 4: void defect in extruded cable at cable joint, case 5: semiconductive contaminant at cable joint, and case 6: conductive contaminant at cable joint, were investigated. The test results showed that two basic properties, polarization and depolarization current, of cable insulation can be utilized for classification of cables with joint problems. The defects in extruded cable and cable joint can be identified by the PDC shapes. However, to clarify the problems occurring at the cables by conventional PD measurement and HFCT measurement was performed. Moreover, it was found that the sensitivity of HFCT was clearly lower than conventional tool.
19 Jun 2016
TL;DR: In this article, a diagnostic measurement method for power cables is presented, which uses travelling waves and their interference characteristics to generate local energy losses inside the test object, which can be measured and give a qualitative indication of the local physical condition of the cable insulation.
Abstract: In this paper, experimental results of a diagnostic measurement method for power cables will be presented. This new method uses travelling waves and their interference characteristics to generate local energy losses inside the test object. This losses can be measured and give a qualitative indication of the local physical condition of the cable insulation. The method has been tested in several simulations, which are based on discretized cable models, which were sectionally degraded. Also different lengths and different types of cables have been tested. From this set of experiments, the most significant results will be presented in this paper. In the described experiments, the proposed approach of a diagnostic method shows local degradations of power cables and coaxial signal cables both in simulation and laboratory measurements, which cannot be detected by established reflectometry methods.
1 Sep 2016
TL;DR: In this paper, a diagnostic system for off-line diagnosis of medium voltage cables has been developed by conduction of an artificial aging experiment on paper insulated lead covered cables, the aging behavior of this cable type could be pointed out.
Abstract: Actual condition and the remaining lifetime of medium voltage cables are of high interest for a condition based asset management. By the conduction of an artificial aging experiment on paper insulated lead covered cables, the aging behavior of this cable type could be pointed out. With this knowledge, a new project with the focus on application in field has been started. Within the project, a diagnostic system for off-line diagnosis of medium voltage cables has been developed. After a short description of the aging experiment and its results, the measurement system and some results from the field measurements will be presented.
10 May 2016
TL;DR: In this article, the authors used three common materials in each situation and compared them to find the best group of material to use in this sample high voltage cable, to have a good insight and a trustworthy comparison between these groups of materials.
Abstract: In todays life using of high voltage cables increase day by day. One of the key factors in insulating is the stress distribution that is the determining factor of the age of these cables. In this paper, we work on capacitance grading method and show how the choice of material could change the stress distribution. We use three different common materials in each situation and compare them to find the best group of material to use in this sample high voltage cable. To have a good insight and a trustworthy comparison between these groups of materials we use finite element method that widely used nowadays for analyzing the electric stress in the cable insulation.
Dissertation•
11 Oct 2016
TL;DR: In this article, a research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in South Africa, describes the requirements for the degree of Master of Science in Engineering.
Abstract: A research report submitted to the Faculty of Engineering and the
Built Environment, University of the Witwatersrand, in ful lment
of the requirements for the degree of Master of Science in
Engineering.
June 2016
1 Sep 2016
TL;DR: In this paper, a finite element method (FEM) model of simulating the cable temperature is built and verified by temperature-rise experiment to optimize the position of six-loop cable group and additional cable in ducts.
Abstract: In the original design of urban power distribution cables, the ducts are not full of cables. With the increase of electrical loads, additional cables are needed. For different position of original and additional cables, its temperature field and ampacity are different, so it is necessary to optimize the position of original cables and additional ones. The finite element method (FEM) model of simulating the cable temperature is built in this paper and verified by temperature-rise experiment. According to the principle that temperature of the hottest cable conductor is lowest, this paper optimizes the position of six-loop cable group and additional cable in ducts. The simulation shows that the more scattered the cables are, the better the distribution of temperature field can be. The optimal position of additional cable is related to the position of original cable group. Therefore, it is suggested that additional cable should be considered when optimizing the original position of cable group.
1 Oct 2016
TL;DR: In this article, experimental measurements of currents and voltages in the elements of cable power lines and communication lines at occurrence of single-phase short-circuit of power cable lines 110 and 220 kV are present.
Abstract: The results of experimental measurements of currents and voltages in the elements of cable power lines and communication lines at occurrence of single-phase short-circuit of power cable lines 110 and 220 kV are present. The effect of the short circuits on the operation of the communication cable lines that are laid in the same trench with power cables is evaluated. Explanations to the emerging effects and recommendations for practical use of the results obtained in design, operation and repair of cable lines are given.
19 Jun 2016
TL;DR: In this paper, a cable test van for field measurements of PILC-cables with a nominal voltage of 20 kV has been designed for off-line measurements of medium voltage cables.
Abstract: In the past years a long-lasting aging experiment on PILC-cables with a nominal voltage of 20 kV has been carried out. In order to verify the results and to make those data utilizable for the asset management, a new project with the focus on field measurements has been started. Thus, a diagnostic system appropriate for field measurements, a cable test van, has been designed comprising both a 50 Hz and 0.1 Hz voltage source. For the recording of the measurement values, a mobile measurement unit and a voltage divider have been developed. Starting with a short description of the aging experiment and an overview of the relevant results, the design of the diagnostic system for off-line measurements of medium voltage cables as will be described in the paper. As field measurements have been started in 2015, first results will be presented and discussed.
4 May 2016
TL;DR: In this article, the authors proposed a non-destructive platform to detect voltage-energized cables by measuring the distribution pattern of magnetic flux density around the cable surface, which can potentially prevent deadly consequences such as electrocution and explosion.
Abstract: Identification of voltage-energized cables can potentially prevent deadly consequences such as electrocution and explosion. We find that the voltage-energized status can be identified by measuring the distribution pattern of magnetic flux density around the cable surface. The weak magnetic fields emitted from the charging current of the voltage-energized cable are measured by sensitive magnetoresistive sensors in high spatial resolution. The feasibility of this non-destructive platform was verified on a 22 kV three-phase underground power cable. The platform can improve situational awareness of serviceman dramatically.
3 May 2016
TL;DR: In this paper, the authors present a detailed analysis and the optimization of a very low frequency high-voltage test system for cable tests with test voltages up to 200kVrms.
Abstract: This paper presents a detailed analysis and the optimization of a very low frequency high-voltage test system for cable tests with test voltages up to 200kVrms. In the analysis, the limitations of the test system due to the initial hardware setup are discussed. An advanced design is proposed based on a parameter optimization, which enlarges the possible operating range and improves the quality of the test voltage.
1 Sep 2016
TL;DR: In this article, the insulation breakdown characteristics of existing commercial semi-conductor and developed semiconductor composite materials, VLF(0.1Hz) withstand voltage destruction test was carried out, using the Weibull distribution and the results were analyzed statistically.
Abstract: In this study, we compare the insulation breakdown characteristics of existing commercial semi-conductor and developed semi-conductor composite materials, VLF(0.1Hz) withstand voltage destruction test was carried out, using the Weibull distribution and the results were analyzed statistically.
25 Aug 2016
TL;DR: In this paper, the authors compare the available techniques, mainly focusing on their ability to detect damages that are relevant to LOCA testing, and the possible role of partial discharge measurement is proposed.
Abstract: The originally long and further prolonged lifespan of nuclear power plants poses tremendous long-term reliability requirements towards low voltage measurement and control cables. Strict requirements towards their performance are prescribed until the end of the operation of the power plant, including the adverse environment of a loss of coolant accident (LOCA). These requirements cannot be met and verified without diagnostic measurements performed at selected intervals. Various methods have been developed or are investigated to fulfill this task. This article compares the available techniques, mainly focusing on their ability to detect damages that are relevant to LOCA testing. Furthermore, the possible role of partial discharge measurement is proposed.
1 Sep 2016
TL;DR: In this article, a case study is presented, which emphasizes the role of local degradation detection besides the general condition assessment of the high voltage cable line insulation, and emphasizes that from the point of view of reliability, the weakest points of the HV cable lines are the cable accessories.
Abstract: In this paper, a case-study is presented, which emphasizes the role of local degradation detection besides the general condition assessment of the high voltage cable line insulation. The applied damped AC method provides several diagnostic parameters e.g. PD inception and extinction voltages, PD map and loss factor therefore it is an effective tool in cable diagnosis. The partial discharge tests detected the weak points of the investigated cable line, which were mounted with porcelain terminations. After the replacement of the terminations the cable line has become PD free. This case study emphasizes that from the point of view of reliability, the weakest points of the HV cable lines are the cable accessories. The time of the failure of these components cannot be predicted exactly, the only way to prevent the failure is the regular diagnostic testing of critical cable lines.
TL;DR: The lower fault rate of high voltage DC (HVDC) cables matches the need of transmission and distribution system operators for high reliability in power delivery as discussed by the authors, and sometimes they are the only solution, e.g., submarine links.
Abstract: Nowadays, when compared with overhead lines, power cables are becoming increasingly attractive for the delivery of electrical power. Their reduced environmental impact complies with the public concern on the compatibility of electrical infrastructures in residential areas. The lower fault rate of high voltage DC (HVDC) cables matches the need of transmission and distribution system operators for high reliability in power delivery [1], [2], and sometimes they are the only solution, e.g., submarine links. In general, the growing demand and dependency on offshore produced renewable energy makes submarine cables essential, and they have become critical infrastructures for the reliable delivery of electrical power [1]-[3].
TL;DR: The Federal Grid Company of Unified Energy System (PJSC “FGC UES”) initiated an R&D program that includes the creation of high-temperature superconducting ac and dc cable lines, with obvious advantages for the transmission of large power flow through an electric network compared with conventional cables.
Abstract: Urgent problems of the power industry of the 21st century require the creation of smart energy systems, providing high efficiency in the generation, transportation, and consumption of electricity as well as increased requirements for the manageability of energy systems and environmental and resource-saving characteristics. One of the solutions to the many problems of the power industry is the creation of new high-efficiency electrical equipment for intelligent power systems based on superconducting technologies to ensure a qualitatively new level of functioning of the electric power industry. In most industrialized countries, superconducting power cables are one of the most advanced developments of superconducting devices. Taking into account the obvious advantages of superconducting cable lines for the transmission of large power flow through an electric network, compared with conventional cables, the Federal Grid Company of Unified Energy System (PJSC “FGC UES”) initiated an R&D program that includes the creation of high-temperature superconducting ac and dc cable lines. Two cable lines and accessories on the transmitted power of 50 MW at 20 kV were made. Tests of both types of cables were conducted in the R&D Center at FGC UES JSC in Moscow. The test results are presented in the report.
TL;DR: In this paper, a contributing problem is that power cable accessories are sometimes conveniently assembled manually on site by subcontractors rather than by the cable or accessory manufacturers, thereby increasing the risk on compromising quality.
Abstract: Most power cable faults begin as defects in the cable accessories: terminations, joints, and junctions. Poor workmanship is a common cause of the accessory faults [1], [2]. A contributing problem is that power cable accessories are sometimes conveniently assembled manually on site by subcontractors rather than by the cable or accessory manufacturers, thereby increasing the risk on compromising quality.