Power Cable System Research Articles

A Novel Multi-Terminal Based Evaluation Method for an HTS DC Power Cable

High current capacity is one of the advantages of a superconducting power cable system. However, it creates difficulties when experimenting to analyze its characteristics. Short-length superconducting cables for a laboratory-scale experiment system present problems: large operating current and current distribution by terminal resistance. Experimental conditions, such as transient states, are limited by power supply capacity. In this paper, the authors suggest a new experimental method for the high-temperature superconducting (HTS) power cable to reduce the capacity of a power supply and solve current distribution problems. For the suggested method of this paper, each HTS wire has separated terminal and each HTS wire was connected in series through the separated terminal. All of HTS wires in the HTS power cable are insulated and connected in series. The cross-sectional area of the HTS power cable is the same, but the terminal structure is different. Thus, all HTS wires have the same current and cross-sectional area of HTS power cable. It is possible to test a large capacity HTS power cable under the transient state or fault conditions using a small-size power source. The design concept, configuration of the experiment system, and the experimental results were discussed in detail in this paper.

Advanced signal processing and modeling for partial discharge diagnosis on mixed power cable systems

Power cable grids have been growing enormously over the years; due to their aging, there is a strong need for Partial Discharge (PD) measurement techniques in order to identify incorrectly installed or damaged cable joints or cavities in cross-linked polyethylene (XLPE) insulated and paper-insulated lead-covered (PILC) cables. Mixed power cable systems consist of a mixture of interconnected cables of various types. The Time Domain Reflectometry (TDR) is a standard technique for the location of PD in power cables. However, the localization process on-the-field is impeded by various interferences and noise. Additionally, propagation velocities of PD pulses traveling on the line differ depending on the cable type (XLPE or PILC cables), which leads to significant location errors. This paper provides automatable signal processing tools for increasing the detection ratio as well as location accuracy in the field of mixed cable systems. A mixed cable system model provides the possibility of analyzing PD data of even complex cable interconnections.

Modeling of Second Generation HTS Cables for Grid Fault Analysis Applied to Power System Simulation

HTS power cable systems are an emerging technology aimed at competing with XLPE cable systems. Knowledge on the thermal operating conditions of HTS power devices is needed to estimate their availability when connected to a power system, because the HTS material must remain below its critical temperature to transport current. In this work, a simple finite difference method is used to assess the temperature distribution at certain cross-section of a second-generation coaxial HTS cable. This method has been implemented in MATLAB and its proper functioning has been verified with the software package FLUX. This method is a tool to establish temperature distributions among HTS cable layers under normal operating conditions. Additionally, the aim of this work is to serve as basis for future simulations including heat generation changes within the cable layers typically caused by grid fault events.

Transient analysis of an HTS DC power cable with an HVDC system

The operational characteristics of a superconducting DC power cable connected to a highvoltage direct current (HVDC) system are mainly concerned with the HVDC control and protection system. To confirm how the cable operates with the HVDC system, verifications using simulation tools are needed. This paper presents a transient analysis of a high temperature superconducting (HTS) DC power cable in connection with an HVDC system. The study was conducted via the simulation of the HVDC system and a developed model of the HTS DC power cable using a real time digital simulator (RTDS). The simulation was performed with some cases of short circuits that may have caused system damage. The simulation results show that during the faults, the quench did not happen with the HTS DC power cable because the HVDC controller reduced some degree of the fault current. These results could provide useful data for the protection design of a practical HVDC and HTS DC power cable system.

Generated heat within power cable sheaths per unit time and volume

An assessment of the generated heat per unit time and volume within cable sheaths is required to determine the corresponding temperature distribution through the domains with underground power cable systems. If the sheaths of a cable line, laid in a flat formation, are bonded and earthed at both ends of an electrical section, and if conductor currents form a balanced three-phase system, the generated heat per unit time and volume within solid sheaths can be accurately evaluated using: i) the filament method in the case of the cables laid in either touching or close arrangements, ii) both the filament method and the simple analytical IEC (International Electrotechnical Commission) relations associated with sheath losses in the case of spaced formations. By using the filament method, the modeling of the ground return path for sheath currents is not a mandatory task, regardless of the cable spacing.

Fractal features-based pattern recognition of partial discharge in XLPE power cables using extension method

Partial discharge (PD) may cause insulation deteriorations in power facilities and may demonstrate impact on the reliability. Therefore PD detection with pattern recognition is seen as an effective approach in the high-voltage (HV) insulation diagnostics of power systems. Based on an extension method, a PD recognition system for HV power cables is proposed in this study. A PD detector is used to measure raw three-dimension PD patterns of cross-linked polyethylene (XLPE) power cables using an L sensor, according to which two fractal features (the fractal dimension and the lacunarity) and the mean discharge are extracted as critical PD features that form the cluster domains of defect types. The matter-element models of the PD defect types are then built according to the PD features derived from practical experimental results. The PD defect type can be directly identified by the correlation degrees between a tested pattern and the matter-element models. The recognition ability is investigated on 160 sets of PD patterns of XLPE power cables and compared with a multilayer neural network and K-means method. The results show that a high accuracy together with a high tolerance in the presence of noise interference is reached by use of the extension method.

극저온 헬륨가스의 절연파괴 및 연면방전 특성

Fixtures such as bushings in terminations of high temperature superconducting(HTS) power cable systems are subjected to high voltages, which have to transition from ambient to cryogenic temperatures. As such it is imperative to ensure the integrity of the dielectrics under all operating conditions, including thermal aspects brought about by the passage of current. Gaseous helium(GHe) at high pressure is regarded as a potential coolant for superconducting cables. The dielectric aspects of cryogenic helium gas are both complex and demanding. In this experimental study we looked at the interface between a smooth epoxy surface and high pressure helium gas in a homogeneous electric field. The alternating current(AC) flashover voltages of epoxy samples are presented. The results have been analyzed by using Weibull statistics. In addition to the behavior of the epoxy in gaseous helium as a function of pressure and temperature we also present data of the characteristics of the epoxy in mineral oil and in liquid nitrogen(<TEX>$LN_2$</TEX>). The breakdown characteristics of a uniform field gap in gaseous helium as a function of pressure and temperature under AC, direct current(DC) and lightning impulse voltages are also given. Electric field calculations have been made for one of the experimental geometries in an attempt to explain some of the anomalies in the experimental results.

The application of the cryogenic system on the HTS power cable circuit in actual grid

The 22.9kV/50MVA AC HTS power cable system consisted of power cable with 410m length and cryogenic system has been manufactured by LS Cable & System and installed in Icheon substation of KEPCO grid in the end of 2010. High temperature superconductor only appears the superconductivity at the constant temperate range. So in order to maintain the superconductivity, the cryogenic system is needed. The cryogenic system, the open-loop type, is consisted of the Pressure Control System (PCS), Gas/liquid separator, Circulation Pump, Decompression unit, Filter and so on. Decompression unit is a device that keeps the sub-cooled nitrogen by way of the latent heat of evaporation and includes the heat exchanger. The effectiveness-NTU method is used for the design of the heat exchanger. After installation of the cryogenic system on the site, the test of the cooling capacity of the cryogenic system and commissioning tests were performed. During the grid operation of the HTS power cable system, no major problems have been encountered to this point. The cryogenic system has been operated sufficiently to maintain a stable of the HTS power cable system. This paper will summarize the design of the cryogenic system and the results of the grid operation.

지중 배전계통 적용을 위한 광복합 케이블 실시간 감시시스템 개선

Since power system is switching to smart grid, on-line monitoring technology has become necessary for underground distribution power cable. Therefore, the application of DTS(Distributed Temperature Sensing) technology using OFCPC(Optical Fiber Composite Power Cable) capable of monitoring underground distribution power cables has been developed. These can bring about reductions in faults and increases in operating capacity of underground distribution system. To date, the test-bed of optical fiber composite power cable on-line monitoring system has been constructed. Then, matters to be improved have been drawn through verification experiments. This paper presents the improvement and experiment results of the optical fiber composite power cable on-line monitoring system to apply to underground distribution lines in the field.

Technical Review on Parallel Ground Continuity Conductor of Underground Cable systems

The Induced sheath voltage is significantly increased at single point bonding section when the ground fault occurs on power cable system because there is no return path of fault current. For solving this problem, therefore, many researchers recommend the PGCC (Parallel Ground Continuity Conductor). In this paper, the characteristics of PGCC are extensively analyzed for reducing the level of induced sheath voltage at the single point bonded section for Korea underground power cable system

Prediction of Incipient Faults in Underground Power Cables Utilizing S-Transform and Support Vector Regression

Incipient faults usually emerge from partial discharges which eventually cause insulation degradation between two insulated cable cores. Early detection of incipient faults is of particular importance because insulation defects caused by incipient faults may lead to permanent faults in underground distribution networks. This paper presents a novel approach using S-transform and support vector regression to predict the occurrence of incipient faults in underground cable networks. The results of this study proved that the new approach is capable to predict the existence of partial discharges in underground power cable systems in Malaysia.

Design research on the conductor of 10 kA class HTS DC power cable

High temperature superconducting (HTS) DC power cable shows a wide application prospect in the field of power transmission for its nearly lossless and rather high capacity. A 360m/10kA HTS DC power cable system, which connects the rectifier output of a substation with the bus bar of an electrolytic aluminium cell, will be put into operation at Henan Zhongfu Industrial Co., Ltd. As one of the items in this project, a 5m/10kA HTS DC power cable was developed, which is used to investigate the conductor design, fabrication, current-carrying capacity and stability of the 360m/10kA HTS power cable.The HTS DC power cable core consists of five conductor layers wound with spliced Bi-2223 wires with the length of 600m. The cable core has five layers and 23 conductors in each layer with the outer diameter of 45.42mm. The superconducting power cable is fabricated and tested. The critical current is about 14.3kA at 77K. The superconducting power cable is charged to 10kA with rate of 10A/s and operates at steady-state for 30min.In this paper, the 10kA HTS DC power cable design, fabrication and test are presented. The experimental research of the performance of spliced superconducting wire and charging, steady-state operating performance of the cable was carried out.

First Russian long length HTS power cable

The Russian R&D Program for superconducting power devices is underway, supported both by government and electric power companies. In this program R&D on HTS power cables is considered as most advanced and close to commercialization. In the framework of the program, several, heavily instrumented, 5m cables have been tested following by the 30m – 3 phase experimental power cable development and testing in 2008–2009. The latest achievement is development and testing of the first long length 3×200m power cable with rating 1.5/2kA–20kV. In parallel with just the cable development the innovative cryogenic system has been developed as well for the cable cooling. The system is using neon as working substance and radial turbo-machines in refrigerator. Cooling power is up to ∼8kW at 65K, inter-maintenance time ∼30,000h. The cryogenic pump with superconducting motor can be used to provide subcooled liquid nitrogen flow ∼0.1–1.5kg/s at 0.1–2.5MPa pressure. After extensive tests at special test facility, HTS power cable and cryogenic system are planning to be installed at some substation in Moscow utility grid. In this review some details about Russian HTS power application program, 200m cable and cryogenic system designs and tests results are presented.

A nonlinear frequency analysis based approach for power cable insulation fault detection

PurposeThe present study is concerned with the application of a nonlinear frequency analysis approach to the detection and location of water tree degradation of power cable XLPE insulation without turning off electric power.Design/methodology/approachThe use of power cable system responses to power line carrier signals are proposed to conduct the required signal analysis for damage location purpose. This technique is based on the fact that the water tree degradation in power cables can make the system behave nonlinearly. Consequently, the location of water tree degradation can be determined by detecting the position of nonlinear components in power cable systems.FindingsA novel method has been proposed for locating water tree degradation in power cable systems; numerical simulation studies have demonstrated the effectiveness of the new technique.Originality/valueThe proposed technique has the potential to be applied in practice to more effectively resolve the power cable damage location problem.

A validated accurate fault location approach by applying noise cancellation technique

Generally, fault location in underground transmission cable system is very difficult because of many noises. Therefore, a method to remove the noise in power cable systems is proposed by applying noise cancellation technique based on the correlation of multiple scales of the transients using wavelet analysis. After the noise cancellation, the transient signals reflected from fault point and other end of cable can be used to locate the fault using single-ended approach when the single line-to-ground fault occurs in underground transmission cables. This paper proposes a fault location algorithm using noise cancellation technique in noisy environment. This algorithm is simple and straightforward. The simulation results of 225 fault conditions including different fault resistance, fault location and fault inception angle and real test results prove it can accurately locate the fault in very noisy situations when the single line-to-ground fault occurs in the system.

Steady-state thermal analysis of power cable systems in ducts using streamline-upwind/petrov-galerkin finite element method

In this paper, numerical steady-state thermal analysis and ampacity evaluation of underground power cable systems placed in PVC ducts are presented. Between the outer surface of the cable and inner surface of the duct, there are three heat transfer modes, thermal conduction, thermal natural convection and thermal radiation. A Streamline-upwind/Petrov-Galerkin (SUPG) stabilized finite element method is proposed to solve the air governing formulas including the mass conservation equation, the momentum conservation equation and the energy conservation equation in the region between the cables and the containment ducts. During the numerical thermal field analysis, the Newton-Raphson iteration method is used to solve the weak electromagnetic-thermal coupling of underground power cable systems. The radiation heat exchange between the outer surface of the cable and inner surface of the duct is solved by the Newton-Raphson iteration method too. An experiment with several holes and three cables was conducted and the test results were compared with the results of analytical method and SUPG finite element method. The comparison reveals that the convection induced heat exchange is much stronger than the conduction induced heat exchange in the air between the outer cable surface and inner duct surface and calculation accuracy of SUPG finite element method is better than the analytical method. Finally, the Newton-Raphson iteration method is used to evaluate the ampacity of power cable systems placed in PVC ducts.

2개 센서를 이용한 부분방전 위치추정 기법 연구

This study deals with the location of partial discharges(PDs) for power cables and GIS using 2 PD sensors and long coaxial signal cables. Throughout the experiments by use of simulated PD pulses and corona discharges in the power cable system, it is found out that the impedance matching between the coaxial signal cable and the measuring equipment should be done for good S/N ratio and the on-site measurement using more than 100m-long coaxial signal cable is possible. In addition, new PD location algorithm with the polarities of PD pulses and the arrival time difference between two pulses was proposed and was proved through the partial discharge experiments for the cable joint defect and artificial void defect.

Calculation of the Magnetic Field in Air Produced by the Underground Conductor Using Pollaczek Integral

A fast approach for evaluating the magnetic field in air generated by an underground conductor is proposed in this paper. By means of the asymptotic extraction technique, the magnetic field can be decomposed into two parts. One is the contribution from the asymptotic integrand, which can be calculated analytically; and the other can be expressed by a sum of the definite integral and the exponential integrals. Due to the fact that there is no improper integral involved, the approach proposed here is highly efficient. Meanwhile, the impact of the eddy current to the magnetic field is quantitatively analyzed. The proposed approach could be used in the electromagnetic environment assessment for underground power cable systems.

Analysis 2.5-D Permutation Power Transmission Line to Decrease Electro-Magnetic Influence at High Technology Nano-Fab

We present optimal permutation with 2.5-D power transmission lines system to reduce electro-magnetic influence at high technology nano-Fab. In this study, the magnetic field was lessened by mirror array power cable system, and simulation of results predicted the best permutations to decrease electromagnetic influence (EMI) value below 0.28 mG at working space without any shielding. Furthermore, this innovative method will cost down at high technology nano-Fab especially for 28 nanometer process.

Cooling test of the 200 m superconducting DC transmission power cable system at Chubu University

A second cooling test of CASER2, the 200m class superconducting direct current power transmission system at Chubu University, was performed from August to October 2010. During this time, the system was cooled down and the liquid nitrogen which cooled the superconducting power cable was circulated in the cryogenic pipe of CASER2. The heat leak of the cryogenic pipe was measured and the values of about 300W was obtained. This result will be used further improvements of CASER2.