Search

Orta Gerilim şebekelerin büyümesi ile enerji kablolarının kullanımı gün geçtikçe yaygınlaşmaktadır. Kullanılan kablolar hem dış etkilere karşı mukavemeti arttırmak hem de topraklama amacıyla zırh ve ekran katmanlarına sahiplerdir. Bu katmanların kablonun her iki ucunda topraklaması için literatürde farklı yöntemler bulunmaktadır. Kablo topraklaması için seçilen yönteme göre zırh ve ekran katmanlarında gerilim veya akım endüklenir. Endüklenen bu gerilim veya akım da kabloların hem güvenli işletilmesini hem de akım taşıma kapasitesini doğrudan etkilemektedir. Bu makalede konuyla ilgili teori incelenerek, güç kabloları analiz yazılımında gerçekleştirilen benzetim çalışmasıyla XLPE 240 mm2 bakır iletken için oluşan değerler teyit edilmiştir., The use of energy cables is getting widespread day by day. These cables have armor and screen layers for grounding purposes. There are different methods in the literature for earthing of these layers. Voltage or current is induced in the armor and screen layers according to the method used. This induced voltage or current directly affects both the safe operation and current carrying capacity of the cables. In this article, the theory on the subject has been examined and confirmed by the simulation study performed in power cables analysis software.

This work presents a multi-parameter optical fiber monitoring solution applied to an underground power distribution network. The monitoring system demonstrated herein uses Fiber Bragg Grating (FBG) sensors to measure multiple parameters, such as the distributed temperature of the power cable, external temperature and current of the transformers, liquid level, and intrusion in the underground manholes. To monitor partial discharges of cable connections, we used sensors that detect radio frequency signals. The system was characterized in the laboratory and tested in underground distribution networks. We present here the technical details of the laboratory characterization, system installation, and the results of 6 months of network monitoring. The data obtained for temperature sensors in the field tests show a thermal behavior depending on the day/night cycle and the season. The temperature levels measured on the conductors indicated that in high-temperature periods, the maximum current specified for the conductor must be reduced, according to the applied Brazilian standards. The other sensors detected other important events in the distribution network. All the sensors demonstrated their functionality and robustness in the distribution network, and the monitored data will allow the electric power system to have a safe operation, with optimized capacity and operating within tolerated electrical and thermal limits.

In many countries, the proportion of high-voltage cables is increasing to address the issue of public resistance to transmission system extensions. A major technical challenge in this is the propagation and amplification of existing background harmonics caused by system resonances at lower frequencies.This paper presents a method to explain harmonic propagation in transmission systems using theory of standing waves. By analyzing the characteristics of standing waves, one can find useful information on the nature and extent of harmonic propagation. It is shown that the presented method describes the standing harmonic voltage on power system lines with different topology and therefore, how a simple change in grid configuration affects the harmonic propagation. The results are verified with good agreement against simulations with commercial power system software. Guides to advance this study to meshed systems is given.

The paper deals with the important challenges in terms of electricity transmission by means of underground cable lines. The power cable’s performance is characterized by an ampacity that represents its maximum electric current-carrying capacity. The ampacity of power cables depends on their ability to diffuse the heat generated by the current flow into the environment. In the performed research, the analysis of the efficiency of heat dissipation from the cable is based on the measurement of temperatures at selected points in individual sections of the cable. As a consequence, the proposed test stand and applied research methodology are vital for the experimental evaluation of the analyzed thermal phenomena in the investigated underground cable lines. The research program covers an in-depth analysis based on the results related to the vital parameters of the investigated cable. The experimental methodology was used to analyze the influence of the properties of the medium surrounding the cable on its temperature, and thus on the ampacity of the cable. A novelty of this paper concerns the carrying out of the experimental laboratory research with actual measurements of the temperature distribution in specific points of the casing pipe based on the original test stand. The paper presents the novel concept of the developed stand for testing heat dissipation from the cable in a casing pipe with pipe sections filled with various media, equipped with a power supply system ensuring easy control of the power dissipated in the cable. The preliminary results of the comparative tests, in which the temperature distribution in the sections of the casing pipes was recorded, indicate that the findings are satisfactorily consistent with the assumptions related to the purpose of the research. The use of appropriate materials surrounding the cable contributes to more effective heat dissipation, and as it has been shown for the examined case in originally planned and conducted tests, it can lower the cable temperature by more than 20 °C, contributing to a significant increase in the ampacity of the cable. For example, it was recorded that for different media filling the pipes, the cable reached 30 °C with different currents flowing through cable of 60 A and 120 A, respectively.

Traditionally, extra high voltage (EHV) transmission systems consist exclusively of overhead lines (OHL) but in the recent years the utilization of high voltage AC (HVAC) power cables is increasing due to environmental, political and operational aspects. To study the impact of HVAC power cables on temporary overvoltages and slow front transients, a simulation model of the large-scale network is required. Guidelines concerning the modeling detail for the surrounding network need to be established to ensure sufficient accurate results. Existing guidelines for purely OHL transmission networks may not be adequate since the integration of HVAC power cables shift the harmonic impedance of the network to lower frequencies and that can affect the extent of the needed simulation model. Much effort can be saved from obtaining detailed data for an extensive but proper model, but a less detailed model might not describe the network behavior with sufficient accuracy. In this study, simplification options are considered, for which the time to construct and analyze a simulation model can be reduced. The simplification options are compared with the reference model (full detail), and judged based on three indicators for the level of accuracy: frequency and amplitude of the main resonance, and maximum over-voltage. As a result, guidelines on the extent of the simulated network and in which detail the model has to be built are proposed. The inverse approach, i.e. increasing level of detail until simulation results hardly change leads to similar results, but requires equivalent short-circuit networks for the rest of the grid. The method is tested for the Dutch 380 kV grid where an underground cable connection of 10.8 km length is introduced in 2013 and a second connection is planned for 2017.

Lafarge Gruntar™ material is proposed in this paper as a new thermal backfill component, and different mass fractions such as 5%, 10%, and 15% are examined. The thermal properties of the developed backfill are determined by experiments with respect to water content and time. Based on the experimental data it is found that the 15% mass fraction Lafarge Gruntar™ material provides the most favorable thermal conductivity i.e. over 1.00 W/(m K) in the dry state. This paper also presents a thermal performance optimization procedure for the high voltage underground power cable system. The new thermal backfill material is considered to be installed within the cable system to improve its thermal performance. The analyzed system consists of three underground power cables situated in a flat formation (in−line arrangement) in thermal backfill, buried in the native soil. To avoid extensive mechanical loads caused by vibrations, when locating beneath a paved ground (e.g. under road crossings), the cables are situated in High Density Polyethylene (HDPE) casing pipes filled with sand−bentonite mixture. The pipes are then placed into a thermal backfill and buried in the native soil. The Installation of thermal backfill material is relatively expensive since in many cases the buried line is installed over many kilometers. Therefore, it is important to determine the optimal dimensions of the cable bedding layer to minimize the material and installation costs while keeping efficient heat dissipation from the cables. The momentum-type Particle Swarm Optimization (PSO) solver, with a dynamic penalty function, is used to minimize the cable backfill cross-sectional area while not exceeding the allowable temperature of the cable operation. The performed optimization procedure obtains the converged solution. The temperature distribution in soil, cables, and the cable backfill layer is determined using the Finite Element Method. The Campbell − de Vries thermal conductivity model is employed for the soil surrounding the underground power cable system. An MATLAB code is written for solving the heat conduction equation and to determine the temperature distribution within the underground power cable system. By using the momentum-type Particle Swarm Optimization algorithm, it is possible to design the best-found dimensions of the cable bedding layer (width and height). Moreover, the dynamic penalty function employed in the optimization procedure has assured the determination of the maximum temperature of cable conductor close to its best-found value.

Mahasarakham International Journal of Engineering Technology, 4, 2, 41-49

For the study of switching transients in Extra High Voltage (EHV) networks it is common practice to model a relatively small part of the EHV network. The downstream network is either disregarded or modeled as a parallel RC or RL circuit, based on the powerflow, directly at the secondary side of the transmission transformer. In this paper an investigation for the extent and model type of the downstream network (below 380 kV) is performed. A detailed model for an example downstream network is developed. Different simplifications and equivalent models are compared in frequency domain and in time domain, during cable energization. The impact of the lower voltage network on both the maximum overvoltage and the harmonic content during energization is assessed. Moreover, components that are of major importance are identified and proper equivalent models for the downstream network are proposed. Simulation results show that in particular the type of the 150 kV network (underground cable or overhead line) affects greatly both the maximum overvoltage and the harmonic content during energization. On the other hand, the parameters of end customer loads have only minor effect.

Traditionally, Extra High Voltage (EHV) transmission systems consist exclusively of Overhead lines (OHL) but in the recent years the utilization of High Voltage AC (HVAC) underground power cables (UGC) is increasing due to environmental, political and operational aspects. The application of EHV cables will influence the operation of the transmission system in both steady and transient state. Therefore, formulation of accurate cable simulation models is of great importance in order to understand the new phenomena introduced. This paper presents a comparison between two cable models, a detailed and a more simplified one, as well as a sensitivity analysis on several cable parameters. In this way, guidelines can be extracted concerning the parameters that have larger impact on the cable response and must be modeled in detail and the ones where simplifications can be made for achieving better computational speed. The simulations are performed using software package PSCAD/EMTDC.

International Conference on Education Technology and Computer -- APR 17-20, 2009 -- Singapore, SINGAPORE Faruk ARAS, Dr./0000-0001-5513-9139; bicen, yunus/0000-0001-8712-2286 WOS: 000275740500005 This paper presents a novel computer simulation program designed to aid teaching process in course of underground power cables for engineering students. The calculation of power cable ratings uses several different formulas and long analytical processes based on JEC 60287 and IEC 60853 standards. Therefore it is difficult to examine different variations such as power cable properties, installations and operation conditions, during the restrictive lesson time. For these reasons, a program has been developed to use for teaching process of the power cable course. The program allows the users to effectively learn the rating of underground power cables under different operation conditions with illustrative figures. The program details are presented and explained in this paper. IACSIT, Singapore Inst Elect