Abstract: Insulation temperature is the critical parameter for dynamic rating of underground power cables. Power cables on medium voltage (MV) level are too numerous and widespread to economically justify solutions like optical fibers as temperature sensors, often employed for high voltage power cables. This paper proposes to utilize the propagation velocity of high frequency signals as indicator for MV cable dynamic rating. Laboratory scale tests are performed for both PILC and XLPE cables. Test results show that the high frequency signal propagation velocity for XLPE insulation increases with the temperature rise while PILC cable shows opposite behavior. The variation of propagation velocity with temperature is consistent with the variation of permittivity measured on test samples of both materials. The variation of propagation velocity of XLPE is confirmed by data of a power cable in service subjected to strong load cycling monitored over a week. Field data on propagation velocity also matches load variation observed for a PILC cable for load cycling recorded over one week. From laboratory tests and field measurements, it seems feasible to extract thermal information from MV cables for dynamic rating by means of high frequency propagation velocity.

Abstract: Insulation coordination is essential for designing and testing HV cable systems properly. In transient conditions, i.e., in the presence of transient voltage surges, insulation coordination is based on the individuation of a certain maximum acceptable risk of failure under the switching and lightning overvoltages that the insulation may encounter in service, and translates into a maximum number of expected failures per year per length of line that the cable line has to match. Given the design of the cable in steady-state conditions, the number of expected failures per year and per length of cable line can be reduced by a proper design of the shield wires of overhead lines, of the grounding systems of line towers and so on [1], and by selecting and installing properly voltage-surge arresters when needed.

Abstract: Xiamen ±320 k V Flexible DC Transmission Project is designed to work at the highest voltage among similar power transmission lines presently and it faces a lot of challenges. We discussed the selection of crosslink cable and cable accessory, cable operating temperature, length of cable segments, and cables' current-carrying capacity, as well as laying AC and DC cables in common tunnels. As a result, reasonable solutions for technology difficulties in the project are presented: setting the operating temperature of 70 ℃ for DC cables ensures good performance of the cables' insulation; cable conductors with sectional area of 1 800 mm2 have current carrying capacity of 1 617 A, satisfying the requirements of engineering; 962 m is a reasonable length of segment cables that reduces the number of joints as well as the project cost; the cable accessories should be injection in-site type; for the project under either transient state or steady state, common-cable-tunnel laying of AC and DC power cables satisfies the requirements of both security and stability.

Abstract: This paper has presented the current distribution analysis associated with parallel single-core cables. As the current distribution in a multi-phase cable distribution system is determined by the cable impedance, the FEM algorithm of the cable impedance matrix is introduced. Further, by using Maxwell-15, a 2-D model of single-core cables was established. The impedance matrix and current distribution under horizontal, double-row and triangle laying arrangement were then calculated. It is concluded that cables under triangle arrangement have the most balanced mutual inductance parameters, and the slightest electromagnetic coupling effects. Meanwhile, the current unbalanced degree of the triangle laying cables is also the least. The triangle laying arrangement is recommended in parallel single-core cable installations.

Abstract: This paper investigates on dielectric and partial discharge (PD) condition of aged XLPE insulated, medium voltage underground cables rated 20 kV, acquired on-site. The extracted samples have suffered PD and failed at different instants. First, the cable samples are grouped as per their timeline of failure. Following this, the dielectric integrity of the cable samples are assessed through modern diagnostic test methods over wide frequency. This implies involving dielectric response analysis and PD measurements respectively. The dielectric integrity of chosen samples are ascertained through frequency dependent dielectric properties. The PD measurements include recording the PD level or apparent charge level (QIEC) of chosen samples and analyzing their respective phase resolved PD pattern. Following this, the information of real time PD signals are transformed to frequency domain and analyzed. Altogether, the findings from all these measurements collectively describe the characteristics of chosen cable samples. In conclusion, it is believed that such an attempt might provide a deep insight in improving the present interpretation strategies.

Abstract: This paper investigates the influence of XLPE-covered cables on the impulse withstand voltage of a typical structure used in single-phase compact distribution lines in Brazil. For comparison purposes, two different procedures are adopted for estimating the impulse withstand voltage of this structure under standard positive lightning impulses. One considers a bare cable and the other assumes a XPLE-covered cable. For the impulse withstand analysis considering the bare cable, the up-and-down method is used for determining the critical flashover overvoltage (CFO) of the structure. The corresponding Vxt curve is also determined using the standard procedures. For the impulse withstand analysis considering the XPLE-covered cable, the breakdown voltage was determined in two different laboratory tests, the first one considering a brand new cable and the second one considering a punctured cable. Both tests were performed for two different cable manufacturers.

Abstract: A new 525 kV DC cable system with a power rating range up to powers above 2 GW has been developed for both subsea and underground applications. The 525 kV extruded DC cable system can transmit at least 50% more power over extreme distances than previous solutions (i.e. the 320 kV extruded DC system). The technology enables the lowest cable weight per installed megawatt (MW) of transmission capacity and the higher voltages provide reliable transmission and low energy losses. This system utilizes a new cross-linked polyethylene (XLPE) DC insulation material, an oil- and porcelain-free termination based on wall bushing technology as well as a land joint and a flexible sea joint. The paper describes the product development of the cable as well as the accessories, the extensive testing procedures and the capability of the new cable system.

Abstract: For cable testing and partial discharge (PD) diagnostics many different test voltage wave shapes and frequencies have been established over the past years. Their application is well proven and is guided by IEC and IEEE standards/ recommendations. All off the allowed test voltage wave shapes have got their advantages and disadvantages for testing or for PD diagnosis. For testing purposes the voltage needs to produce enough stress to lead failures to breakdown. The very low frequency (VLF) waveforms turned out to be very effective and economical for that purpose on MV cables, for HV cables this method is not allowed yet, currently there are working groups available investigating the application on HV cables. For a reliable PD diagnosis voltages are needed, with waveforms close to power frequency and in its application non-destructive for the test object. A continuous increased voltage application, e.g. a VLF voltage, could cause in case of a long excitation time during PD diagnosis, unwanted breakdowns at defects even if the applied voltage is not that high like it is used for withstand testing. Damped AC voltage (DAC), which is close to power frequency (20–300Hz), is well proven to be very effective for partial discharge diagnosis and causes nearly no risk for breakdown due to the short excitation time even for critically aged cables. A new test and diagnostic system combining both, providing an effective test voltage for withstand testing and being non-destructive for diagnostic measurements, is introduced recently. This paper describes the application and comparison of the new test and diagnostic system for partial discharge diagnosis by using DAC. Furthermore true VLF cosine rectangular withstand testing with accompanying PD monitoring is discussed. It is demonstrated that cosine rectangular VLF waveform delivers comparable results of PD parameter to judge the severity and to locate PD defects in MV cable systems.

Abstract: Concentric neutral cables are commonly used in medium voltage power distribution systems. At present, the cable ampacity calculation methods can take into account only the fundamental frequency current and the harmonic currents in the phase conductors. In reality, the cable neutral can carry both fundamental frequency and harmonic currents (induced and unbalanced), leading to a further increase of cable temperature. In view of the increased harmonics and load imbalance in power distribution systems and the need to determine their impact on concentric neutral cables, this paper presents a method to estimate the ampacity of concentric neutral cables, especially for multi-grounded neutral systems. The proposed cable derating factor can be used to determine the increase in cable loading caused by both unbalanced load and harmonics. A chart is also presented as a simplified method for cable ampacity and cable loading estimation, for which only the total harmonic distortion (THD) and zero sequence current ratio of the phase current are needed.

Abstract: The goal of this work is to study the transient behavior of the cable against the application of standard and non-standard lightning impulse voltage waveforms. A 66 kV cable model has been developed in MATLAB Simulink and standard and non-standard impulse voltages are applied to it. A preliminary comparative study on the obtained voltages indicated that non-standard impulse voltage waveform developed higher voltage stress in the cable. Simulation results helped to investigate which impulses (standard or non-standard) represent the worst possible voltage stresses on the cables. This study provides the basis for further study of effects of non-standard impulse voltage waveforms and make necessary correction in the existing impulse testing standards.

Abstract: Firstly,cable voltage charging by rotating and rubbing on floor was measured referred to standard of IEC 61340-4-5,and category 6ethernet cable voltage was measured.Secondly,based on measurement of the cable voltage waveform,the cable voltage equivalent RC circuit model was deduced,and exponential function can be obtained to describe the cable voltage,the time constantτis determined by the cable resistance R and capacity C to the ground.Thirdly,the current,transient electric field and magnetic field was measured while the charged cable discharging on the metal target.At last,the current waveform was compared with MIL-STD-461FCS115 conducted susceptibility,bulk cable injection and impulse excitation.The results show that the CDE current waveform is similar,but current is higher.Therefore,the CDE protection method is required and the EMC testing standard needed to be improved to cover CDE measurement.

Abstract: The Medium Voltage (MV) cable network forms a large part of the distribution company’s physical capital. The MV network has a huge influence on interruption which customers suffer, due to the defects in MV network. Defects are not only harm to customers, but also to the distribution network company workers. In the last four years in South Cairo Electricity Distribution Company (SCEDC) increasing in the rate of the failures in MV power cables numbers is observed. It is noticed that 47 % to 49 % of the recorded faults are caused by breakdown of joints and terminations of medium voltage cables. This paper describes the latest developments and the off-line PD measurements by using Very Low Frequency (VLF) as an energizing method according to IEEE. It is interesting in this paper to investigate the conventional method by 50 Hz AC voltages, VLF 0.1 Hz (Sinusoidal), VLF 0.1 Hz (rectangular) and DC waveform and compare the PD magnitudes of each source to others. Addition to use VLF-PD as diagnostic technique with the two previous detection methods simultaneously for MV XLPE single core cables and compare the measurement results of each other on-site.

Abstract: It has been more than 20 years since the newer cable field-testing methods of very low frequency (VLF), tan delta, and field partial discharge testing were introduced to the field-testing arena. Over time, these technologies have matured, spawned a new testing industry, IEEE standards, technical committees, and a plethora of technical papers. How has this affected the cable manufacturer and what is its perspective on this area of field testing both as an acceptance and maintenance test method? This paper intends to discuss the guidelines established and some of the shortcomings that have been found. Although this paper may review the various standards and testing methods, its focus will be with the VLF test.

Abstract: The effects of increasing renewable energy production in grids including power cables has not previously been sufficiently investigated. Employing power cables originally designed for use in distribution networks for connecting renewable energy units into the energy system may cause problems, which have been observed in previous investigations. In order to study these effects, a number of cable testing methods must be applied. The purpose of this paper is to describe the possible effects of unconventional energy production on cable systems and list the various methods applicable in identifying and preventing cable failures. A long-term goal of this research is to gain a better understanding of cable system behavior in the presence of renewable power generation and how the reliability of cable systems could be increased.

Abstract: with the rapid growth of the using of power cables in distribution network, a large demand for mobile high-voltage cable test systems is expected in the near future. VLF test system has a great equivalence of AC test, so it is wildly used in power cable test. In this paper, a novel VLF high voltage generator, based on LCC resonant converter, is introduced detailed. The Extended Describing Function (EDF) is used to select parameter of LCC resonant converter. In order to generate a true sinusoidal test voltage, the control strategy, concluding changing duty cycles of LCC resonant converter and load resistors, is proposed. The generator can generate a sinusoidal test voltage of 20 kV at 0.1 Hz and the result shows that the total harmonic distortion can meet the requirement of IEEE 400.2 standard. Keywords-VLF test system; power cables; extended describing function (EDF)

Abstract: Very low frequency (VLF) method may be used for analysis of changes in the power cables' dielectric and electrical parameters during the service lifetime. This paper focuses on a more detailed description of this method and VLF method usage in the laboratory measurement conditions of the power cables. In the second part of the paper we specifically focus on this method applied for measuring the dielectric properties of the cable type 6-AYKCY 3×240. The aim was to analyze changes in dissipation factor values of power cables exposed to thermal aging during 135 days period.

Abstract: Continuous, high-quality supply of electrical energy is the backbone of any modern economy. Any equipment operating at a power station must be reliable and safe. All major power supply components such as transformers, cables, generators, and switchgear need to be kept in perfect operating condition. The lifetime of power cables, used as the main means of transferring electric power, is understood to be about 30 years, from the time of manufacturing. The dielectrics between two conductors of a cable must be able to withstand electrical stresses from high-voltage input. This condition should be verified throughout the lifetime of the cable system. Several techniques, such as VLF-tan, partial discharge, and insulation resistance are used in order to determine the operating conditions of cables. In this paper, we present our work on insulation resistance to diagnose cables in operation at the Western Power station in Taean, Chungcheong Namdo Province, South Korea. As a result we have found cables the life time of which is 38 years.

Abstract: Impacts of temperature on the distribution of electric field in high voltage direct current (HVDC) cable joint have been investigated with COMSOL Multi-physics. The simulation of electric field under combined thermal-electrical conditions was carried out on a three-dimensional joint model, in which constant dc voltage and combined dc/impulse voltage were applied on the cable core while the temperatures of conductor were 298K, 333K and 363K respectively. The results show that the maximal field in the model and the tangential field on XLPE/SR interface increase a lot with the temperature increasing under dc voltage, and the position of maximal field changes from the head of high-voltage screen to the head of stress cone. When applied with combined dc/impulse voltage, the maximal field distribution appears at three different points in cable joints.

Abstract: The power cable has been widely used for decades. As an important accessory of power cable, the cable joint is the weak link because of site installation conditions. Partial discharge and insulation aging in it cause temperature rise, which may lead to explosion of the cable joint in serious conditions. There are many researches about temperature rise of the cable and cable joints. By measuring the surface temperature and conductor current, some scholars in Tokyo proposed a way to estimate conductor temperature in cable joint with a 2-D thermal circuit[1]. A method to estimate soil thermal parameters and assess cable ratings is introduced, in which the location of hot spots, cable installation data, load and DTS-recorded temperature should be the given information[2]. Considering the influence of moisture content on thermal resistivity and specific heat of the cable surroundings, an algorithm for the estimation of the time-dependent temperature evolution of power cables is presented[3]. Just as partial discharge is an feature of defect in the cable joint, temperature rise can also reflect defect in it. So, the estimation of transient temperature is of great meaning. In this paper, the authors propose a novel approach to estimate transient temperature of conductor in cable joint for buried cables.

Abstract: A 30-m-long 275-kV 3-kA high-temperature superconducting (HTS) cable had been developed in a national project of the Materials and Power Applications of Coated Conductors project in Japan. The design of the cable was based on the design values obtained from ac loss properties, thermal behavior under short-circuit tests, and electrical properties, such as partial discharge properties, impulse withstand properties, and dielectric properties. Through the development, the material of the cable insulation was determined and designed on the basis of its design stresses and test conditions based on the IEC, JEC (Japan electrical standards), and other HTS demonstrations. This cable was also designed to withstand a short-circuit test of 63 kA for 0.6 s and to have low losses of 0.8 W/m at 3 kA, 275 kV, including ac loss and dielectric loss. Based on these designs, a 50-m cable was manufactured and tested. The short samples obtained from 50 m were confirmed to have the designed characteristics. Furukawa Electric constructed a demonstration system of a 30-m cable with two terminations and a cable joint. The demonstration had started since November 2012 at Shenyang in China. In this demonstration, a 30-day long-term test was conducted and monitored at a current of 3 kA and at a test voltage selected to verify a 30-year operational lifetime. Removal tests revealed the superior reliability of the 275-kV HTS cable system.