High Voltage Underground Cables Research Articles

A Practicable Guideline for Predicting the Thermal Conductivity of Unconsolidated Soils

For large infrastructure projects, such as high-voltage underground cables or for evaluating the very shallow geothermal potential (vSGP) of small-scale horizontal geothermal systems, large-scale geothermal collector systems (LSCs), and fifth generation low temperature district heating and cooling networks (5GDHC), the thermal conductivity (λ) of the subsurface is a decisive soil parameter in terms of dimensioning and design. In the planning phase, when direct measurements of the thermal conductivity are not yet available or possible, λ must therefore often be estimated. Various empirical literature models can be used for this purpose, based on the knowledge of bulk density, moisture content, and grain size distribution. In this study, selected models were validated using 59 series of thermal conductivity measurements performed on soil samples taken from different sites in Germany. By considering different soil texture and moisture categories, a practicable guideline in the form of a decision tree, employed by empirical models to calculate the thermal conductivity of unconsolidated soils, was developed. The Hu et al. (2001) model showed the smallest deviations from the measured values for clayey and silty soils, with an RMSE value of 0.20 W/(m∙K). The Markert et al. (2017) model was determined to be the best-fitting model for sandy soils, with an RMSE value of 0.29 W/(m∙K).

Optimization of Ampacity in High-Voltage Underground Cables with Thermal Backfill Using Dynamic PSO and Adaptive Strategies

This article addresses challenges in the design of underground high-voltage transmission lines, focusing on thermal management and cable ampacity determination. It introduces an innovative proposal that adjusts the dimensions of the backfill to enhance ampacity, contrasting with the conventional approach of increasing the core cable’s cross-sectional area. The methodology employs a particle swarm optimization (PSO) technique with adaptive penalization and restart strategies, implemented in MATLAB for parameter autoadaptation. The article emphasizes more efficient solutions than traditional PSO, showcasing improved convergence and precise results (success probability of 66.1%). While traditional PSO is 81% faster, the proposed PSO stands out for its accuracy. The inclusion of thermal backfill results in an 18.45% increase in cable ampacity, considering variations in soil thermal resistivity, backfill properties, and ambient temperature. Additionally, a sensitivity analysis was conducted, revealing conservative values that support the proposal’s robustness. This approach emerges as a crucial tool for underground installation, contributing to continuous ampacity improvement and highlighting its impact on decision making in energy systems.

An EXPERIMENTAL STUDY ON DIELECTRIC PARAMETERS OF XLPE INSULATED HIGH VOLTAGE CABLES UNDER DIFFERENT OPERATING CONDITIONS

High voltage underground cables used in distribution systems provide benefits including aesthetics, reliability, low maintenance costs, and resistance to environmental factors. However, their initial installation expenses are considerably higher than overhead lines, and fault detection is quite challenging. Thus, a deep analysis of dielectric parameters is crucial. Typically, electrical specifications of high voltage underground cables provided by the manufacturer are used for nominal operating conditions. However, it is essential to acknowledge that variations in operational conditions have a discernible impact on the dielectric characteristics of cable insulation. This phenomenon results in an accelerated aging process of the insulation material and contributes to unexpected failures. Hence, it is imperative to determine dielectric parameters of cable insulation under varying operational conditions and elucidate the impact of these operational states on insulation properties. This study involved experimental determination of the dielectric parameters, including capacitance, relative dielectric constant, dielectric loss, and tanδ, for a XLPE insulated high voltage underground cable, designed for a nominal voltage of 12/20 kV. These assessments were performed under varying operating conditions, specifically for distinct voltage, temperature, and frequency. Based on the acquired findings, it is evident that the dielectric characteristics of the cable insulation exhibit substantial variations in response to alterations in voltage, temperature, and frequency, even when operating within the defined nominal limits.

Voltage Impact on Oil Pipelines from High Voltage Underground Cables: Relocation of Overhead Lines at Kelanitissa

When a large-scale urban construction project requires the relocation of an electrical overhead transmission line, going underground becomes the only feasible solution. However, due consideration must be given to the interaction with underground steel pipelines already laid as the life of metallic pipelines is highly susceptible to corrosion when buried underground. Corrosion occurs because of an electrochemical reaction, with Impressed Current Cathodic protection, with an impressed negative dc voltage of the order of 850 mV, usually employed in many metal pipelines to mitigate the deterioration of the surface. This paper scrutinizes the impact of high voltage underground cables on the cathodic protection of buried metal pipelines. The induced voltage due to the addition of high voltage underground cables crossing the pipelines perpendicularly has been analysed using Ansys Maxwell’s electromagnetic software using actual dimensions and parameters. The introduction of two 220 kV underground cables from Biyagama - Kelanitissa line and two 132 kV underground cable circuits from Kelanitissa - Kolonnawa running perpendicular to six underground petroleum carrying steel pipelines has been investigated to study its influence on existing impressed current cathodic protection. The study has shown that the maximum induced voltage is less than 1.5 mV which has no adverse effect on any existing impressed current cathodic protection. The high voltage cables have been in fact installed and no adverse effects have been detected.

Investigation of effect of laying and bonding parameters of high-voltage underground cables on thermal and electrical performances by multiphysics FEM analysis

High-voltage underground cable systems are one of the critical systems used in the distribution of energy. During the design phase of these systems, important issues are to be considered, such as screen voltages, screen currents, thermal calculations, and power losses. If these issues are not considered properly, the system’s reliability and efficiency can be seriously reduced. In high-voltage underground cable systems, current carrying capacity and power losses vary according to the screen bonding type, the phase sequence, the distance between the cables, and the number of parallel systems. A detailed analysis is required during the system design phase in this context. In this study, electrical and thermal analyses of a cable system consisting of two parallel group were carried out according to different design parameters, and the performances of different system designs were evaluated. Trefoil and flat layouts were used in the analyzed systems. In addition, the structure of the single-side and solidly bonded systems was also examined. While carrying out the investigations, the variation of the distance between the cables according to three different parameters was also discussed. In total, 56 different scenarios were created, and the systems’ performances were examined. Screen currents, screen voltages, cable temperatures, and power losses were considered while conducting the investigations. In this context, coupled electrical and thermal calculations were performed in the Ansys Electronics Suite finite element software. Additionally, the study utilized the CymCap program to verify the finite element model created, with analytical analyses conducted in accordance with IEC 60287 standards. The significance of these calculations cannot be overstated, as the analysis results demonstrate the direct impact of various design parameters on the system’s overall performance.

An Investigation of Magnetic Field Influence in Underground High Voltage Cable Shields

Magnetic fields and the shielding efficiency of the shields of underground high voltage cables are studied in this paper regarding several shielding configurations and materials. Shielding efficiency and magnetic fields are computed for shields with the same mesh but from different shielding materials, such as aluminum, ferrite, metal, and steel. In order to get the best shield configuration depending on the source characteristics and the material, a conducting ferromagnetic region with various thickness values is considered as shielding. A finite element model is introduced to investigate the influence of the parameters of magnetic fields and the shielding efficiency of underground high voltage cables. Furthermore, the reduction of the magnetic fields with or without shieldings is also presented. The developed method is performed with the magnetic vector potential formulations and validated on a practical problem.

Simulasi Pengaman Pada Saluran Kabel Tegangan Tinggi Berupa Line Current Differential (LCD) Berbasis Arduino Mega 2560 Dengan Tampilan Human Machine Interface dan Notifikasi Blynk

Power transmission protection is a system that serves as a safety in the electrical equipment of a transmission network so that the process of channeling electrical energy to the consumer can run well. The power transmission system of the generating system can be through Extra High Voltage Overhead Line, High Voltage Overhead Line, and High Voltage Underground Cable. In each transmission line is required protection system that can protect the electricity distribution process to the consumer. High voltage underground cable is a transmission system that delivers electrical energy through a cable that is buried in the ground. Although it is in the ground and protected by an excellent insulation system, but does not escape also from the occurrence of interference. In the land cable channel protection system is known as the Line Current Differential (LCD) which is a protection system that works under Kirchoff Law 1 by comparing incoming flows and exiting flows, with uptime instantaneously. This research made a simulation of such system, using Arduino Mega 2560 and be equipped with Internet of Things (IoT) monitoring using Blynk. The test result indicated that the system can work properly

Evaluation of the effect of structural defects in the heat-shrink cable terminal on electric field distribution

Cable terminals are used for the connection of high voltage underground cables to busbars and transmission lines. Various defects may occur in cable terminals used as Heat-Shrink or Cold-Shrink. As a result of these defects, fires and long-term power outages may occur due to the breakdown of the cable terminal depending on partial discharge. Consequently, human life losses and economic losses are inevitable. In this study, a heat-shrink cable terminal with 36 kV phase-to-phase operating voltage randomly failed while measuring power quality parameters in the field is examined. In this context, it is aimed to examine the root causes of the failure in the field with the finite element method according to different design and structural defect situations. For this purpose, the cable terminal was modeled in real scale in Ansys Electronics Suite finite element software in line with the data received from the manufacturer. According to the analysis results, especially in case of peeling the entire outer semiconductor layer on the XLPE and partial peeling of the outer semiconductor layer on XLPE increases electric field significantly compared to the reference design. In addition, the thickness and relative permittivity changes of the critical elements used in the cable terminal affect the electric field distribution. According to the results of the analysis performed, the defect situations that could be the root cause of the failure was determined. Also, the effect of other defective situations was understood and reliability analysis was made.

Fault Location for Underground Cables in Ungrounded MV Distribution Networks Based on ZSC Signal Injection

A distributed zero-sequence-current (ZSC) carrier signal injection via current transformer (CT) is proposed for underground cable single-phase-to-ground fault location in neutral isolated medium voltage (MV) distribution networks. High-frequency ZSC carrier signal is directly injected to a high-voltage underground cable of an energized distribution network via CT. The injected carrier signal travels along the cable to the receiving center in the substation, and is processed for quick fault line selection and fault location. No external power supplies or signal generators are needed due to the self-contained nature of the injector. The device can be constructed as a sleeve to be mounted around the underground power cable. This permits economical retrofitting to existing installations of power line communication (PLC) devices. In this paper, the operational principle and the application considerations for such an injection device and fault location tricks are explained, followed by the theory behind the proposed technique. Finally, MATLAB based numerical simulations are performed and a low-voltage prototype is tested to verify the validity of the proposed approach.

Compressive strength and thermal properties of sand–bentonite mixture

Abstract Sand–bentonite mixtures are used in road embankments as a protective material for protecting underground high-voltage cables and utility pipelines supplying water and gas etc. The sand–bentonite mixtures provide benefits while laying high-voltage cables. The purpose of this study is to determine the proportions as well as mechanical and thermal properties of a dry-mixed sand–bentonite mixture and to investigate the suitability of such mixtures for installation around high-voltage underground power lines in road embankments. When selecting a sand–bentonite mixture, the following requirements must be ensured: the compressive strength must be greater than 0.5 MPa after 24 h; the thermal resistivity must be greater than 1.2 K m/W (thermal conductivity 0,833 W/(K m)); and the moisture content of the sand–bentonite mixture must be less than 13%. The following materials were used when selecting the bentonite mixture: bentonite, 0–4.0 mm fraction sand, cement (CEM I 42.5R), and water. In this study, six groups of samples were formed, in which the parts of concrete, sand, cement, and water were added in different proportions. The strength and thermal conductivity of the samples were analyzed. Studies about the use of bentonite around high-voltage cables have revealed the need for wet mixing of bentonite suspensions. The required thermal conductivity properties of the soil were not achieved by dry mixing. This method of mixing can be useful only in cases when the thermal conductivity of the mixed soil is not relevant, because the work can be continued after a day.

Electrical treeing behavior in XLPE insulation due to content AL2O3 nanoparticles

XLPE is currently commonly used in high voltage underground cables. Several researchers recently chose several nanofillers to improve the electric tree’s strength in the polymer matrix. Alumina AL2O3 nanofiller have been utilized to investigate the effects on the electrical treeing in XLPE. The percentage concentration were used as follows with different amounts “0.3wt.” % and “1wt.”% from weight of base material. The needle-plane electrodes were used in this investigation and gap selected between needle and plane earth is 3 mm. The growth and morphology of treeing in XLPE insulation have been observed by using charge coupled device camera CCDc and microscope system. Scanning of electron microscopes SEM has been investigated the nanoparticles spread in base material. The outcomes show the tree inception voltage TIV values 12.5, and 14.8 KV “0.3wt.” % and “1wt.”%, respectively in XLPE composites that is mean the TIV increase with increase concentration nanofiller, while the tree propagation time at 2mm length increase about 40 min and 2 hours in “0.3wt.” % and “1wt.”% AL2O3/XLPE, respectively compared with unfilled XLPE, as well as the breakdown time BDT enhancement by4.347% and 13.043% for 0.3wt% and 1 wt% nano AL2O3 composites compared with unfilled XLPE insulation. And showed pictures taken with a SEM Diffusion and accumulation of nanoparticles in the XLPE material.

Mediate relation between electrical and thermal conductivity of soil

Thermal conductivity is a key parameter for many soil applications, especially for dimensioning shallow and very shallow geothermal systems based on the possible heat extraction rate and for modelling heat transfer processes around high voltage underground cables. Due to the limited purview of direct thermal conductivity measurements, for an investigation of extensive areas, usually other geophysical methods like electrical resistivity tomography measurements are applied. To derive thermal conductivity of soil from geoelectrical measurements a relation between electrical and thermal conductivity is needed. Until now only few approaches worked on a direct correlation between both conductivities. Due to the difficulties of a direct relation, within this study a modular approach of a mediate correlation between electrical and thermal conductivity was investigated. Therefore, a direct relationship between a corrected electrical conductivity and water content as well as the standard and simple thermal conductivity model of Kersten (Bull of the Univ Minnesota 28:1–227, 1949) was used. To develop this concept soil types of sand, silt loam and clay were investigated where different saturation steps and pressure loads were applied. For each configuration electrical and thermal conductivity as well as water content and bulk density was determined. To refine the results of the calculated water content a corrective factor was applied. Furthermore, bulk density as an inlet parameter of the Kersten equation was also derived based on electrical conductivity. The suggested proceeding enables the determination of thermal conductivity solely based on electrical conductivity without prior soil property information.

STUDI SISTEM PROTEKSI LINE CURRENT DIFFERENTIAL RELAY PADA SALURAN TRANSMISI 150 KV

Increasing electricity demand in South Bali requires a reliable electrical system. Reliableelectrical systems can be achieved in various ways, one of which is the replacement of highvoltage overhead line to high voltage underground cable. The replacement high voltageoverhead line to high voltage underground cable requires adjustment of the protection system.The previous main protection system used in high voltage overhead line is distance relay, whilethe protection system for the new transmission network is line current differential relay. Thepurpose of this study is to analyze GIS Pesanggaran to GI Nusa Dua transmission line’sprotection system. The covered in this analysis is to power flow analysis simulation, 3 phaseshort circuit simulation, relays setting calculation and testing the relays setting.The power flowsimulation showed that the current at peak load from GIS Pesanggaran to GI Nusa Dua is 337A. The 3 phase short circuit simulation showed that the largest short circuit, if a fault occurs onthe GI Nusa Dua of 9.54 kA. The relays setting calcullation showed that of 0,2 A with 20 %slope for Is1 and 2 A with 150% slope for Is2. The results showed that the relays setting hasworked properly.

Dynamic simulation of induced voltages in high voltage cable sheaths: Steady state approach

This paper presents a novel approach to the modeling of high voltage underground cables. Its main contribution is that it considers induced effects. Indeed, it incorporates the estimate of induced voltages and currents in cable sheaths in steady state due to the nearby cables and sheaths, for different types of sheaths connections and for various single-phase short-circuit configurations and three-phase short-circuits. Furthermore, it allows multiple circuits to be coupled automatically in a simple way. An intuitive and friendly simulation tool has been implemented that allows the automatic generation of multiple coupling circuits and to calculate all these induced effects caused by the connection of the sheaths and the distance between cables. It has been validated by comparing it with the expected theoretical data and to other simulators with satisfactory results.

FAULT DETECTION IN UNDERGROUND CABLES BY USING WAVELET TECHNIQUE (WT)

This paper describes a novel fault-detection technique of high voltage underground cables. Electric power systems have rapidly grown for the past fifty years. Speedy and precise fault location plays an important role in accelerating system restoration, reducing outage time, reducing great financial loss and significantly improving system reliability. Therefore, this paper presents a fault detection, classification and fault location estimation method based on Discrete Wavelet Transform for medium voltage 11kV underground cable. Different faults (Lg, LLg, and LLLg) and at different locations 2km, 4km and 6km of 10km length are simulated by Mat Lab, and then certain selected features of the wavelet transformed signals are used as an input. From the results, it was found that the percentage error in wavelet Transform output is very less. Hence, it can be concluded that the proposed technique is able to offer high accuracy in both of the fault classification and fault location.

되메움재 특성을 고려한 전력구 열환경 변화 예측 수치해석모델 개발

최근 전력구 지중 송전선의 허용 전류용량에 대한 정부규제로 인해 전력구 공사에 현장 되메움재의 열적 거동에 대한 연구가 중요해졌다. 점차 증대되는 고용량 전력공급에 대한 수요와 더불어, 허용 전류용량을 산정하기 위해, 전력 케이블 주변 온도 증가를 유발하는 요인을 예측하고 분석하는 것이 시급하다. 전력구 내부의 과도한 열확산으로 인한 지중 송전선로 주변의 온도 증가는 지중 송전선 자체의 열저항을 증가시켜 절연 파괴 및 열 폭주 현상을 야기한다. 따라서 전력구 설계 및 시공시, 되메움재에 따른 전력구 현장 열거동 메커니즘을 규명하는 것이 매우 중요하다. 본 논문에서는 현장 시험시공을 기반으로, 전력구내부와 주변지반의 온도 변화 및 열저항을 산정하기 위한 수치해석 모델을 개발하였다. 전력구 열거동 파악을 위한 수치해석은 현장시험 시공시 획득한 4개의 다른 종류의 되메움재의 열적 그리고 물리적 물성치를 기반으로 수행되었다. 또한, 실내 시험을 통해 산정한 각 되메움재의 열저항을 수치해석 모델에 입력변수로 적용했다. 전력구 내부에 일정한 열량이 공급될 때, 되메움재의 단위중량, 함수비, 열적 특성 등 여러 변수를 고려한 열거동 메카니즘을 모사할 수 있도록 열거동 수치해석 모델을 구성하고 1년 동안의 수행된 현장계측값과 비교를 통하여 개발된 수치해석 모델을 검증하였다. The thermal analysis of an underground power conduit for electrical cables is essential to determine their current capacity with an increasing number of demands for high-voltage underground cables. The temperature rises around a buried cable, caused by excessive heat dissipation, may increase considerably the thermal resistance of the cables, leading to the danger of "thermal runaway" or damaging to insulators. It is a key design factor to develop the mechanism on thermal behavior of backfilling materials for underground power conduits. With a full-scale field test, a numerical model was developed to estimate the temperature change as well as the thermal resistance existing between an underground power conduit and backfill materials. In comparison with the field test, the numerical model for analyzing thermal behavior depending on density, moisture content and soil constituents is verified by the one-year-long field measurement.

Analysis of Insulating Material of XLPE Cables considering Innovative Patterns of Partial Discharges

This paper aims to analyze the quality of insulation in high voltage underground cables XLPE using a prototype which classifies the following usual types of patterns of partial discharge (PD): (1) internal PD, (2) superficial PD, (3) corona discharge in air, and (4) corona discharge in oil, in addition to considering two new PD patterns: (1) false contact and (2) floating ground. The tests and measurements to obtain the patterns and study cases of partial discharges were performed at the Testing Laboratory Equipment and Materials (LEPEM) of the Federal Electricity Commission of Mexico (CFE) using a measuring equipment LDIC and norm IEC60270. To classify the six patterns of partial discharges mentioned above a Probabilistic Neural Network Bayesian Modified (PNNBM) method having the feature of using a large amount of data will be used and it is not saturated. In addition, PNN converges, always finding a solution in a short period of time with low computational cost. The insulation of two high voltage cables with different characteristics was analyzed. The test results allow us to conclude which wire has better insulation.

Bottlenecks reduction using superconductors in high voltage transmission lines

Energy flow bottlenecks in high voltage transmission lines known as congestions are one of the challenges facing power utilities in fast developing countries. Bottlenecks occur in selected power lines when transmission systems are operated at or beyond their transfer limits. In these cases, congestions result in preventing new power supply contracts, infeasibility in existing contracts, price spike and market power abuse. The “Superconductor Technology” in electric power transmission cables has been used as a solution to solve the problem of bottlenecks in energy transmission at high voltage underground cables and overhead lines. The increase in demand on power generation and transmission happening due to fast development and linked to the intensive usage of transmission network in certain points, which in turn, lead to often frequent congestion in getting the required power across to where it is needed. In this paper, a bottleneck in high voltage double overhead transmission line with Aluminum Conductor Steel Reinforced was modeled using conductor parameters and replaced by Gap-Type Superconductor to assess the benefit of upgrading to higher temperature superconductor and obtain higher current carrying capacity. This proved to reduce the high loading of traditional aluminum conductors and allow more power transfer over the line using superconductor within the same existing right-of-way, steel towers, insulators and fittings, thus reducing the upgrade cost of building new lines.

English

English

Magnetic fields and childhood cancer: an epidemiological investigation of the effects of high-voltage underground cables

Epidemiological evidence of increased risks for childhood leukaemia from magnetic fields has implicated, as one source of such fields, high-voltage overhead lines. Magnetic fields are not the only factor that varies in their vicinity, complicating interpretation of any associations. Underground cables (UGCs), however, produce magnetic fields but have no other discernible effects in their vicinity. We report here the largest ever epidemiological study of high voltage UGCs, based on 52 525 cases occurring from 1962–2008, with matched birth controls. We calculated the distance of the mother’s address at child’s birth to the closest 275 or 400 kV ac or high-voltage dc UGC in England and Wales and the resulting magnetic fields. Few people are exposed to magnetic fields from UGCs limiting the statistical power. We found no indications of an association of risk with distance or of trend in risk with increasing magnetic field for leukaemia, and no convincing pattern of risks for any other cancer. Trend estimates for leukaemia as shown by the odds ratio (and 95% confidence interval) per unit increase in exposure were: reciprocal of distance 0.99 (0.95–1.03), magnetic field 1.01 (0.76–1.33). The absence of risk detected in relation to UGCs tends to add to the argument that any risks from overhead lines may not be caused by magnetic fields.