Thermal analysis of power cables in multi-layered soil. II.Practical considerations

For Pt.I, see ibid., vol.8, no.3, p.761-771, 1993. A practical study is presented of the heat dissipated from the cable in the surrounding soil using the finite difference method as well as the energy conservation principle proposed by the authors. The trench dimensions, soil properties and environmental conditions are varied to simulate the actual field situation. The backfill thermal conductivity, the width of the trench, and the cable size are among the main parameters that influence heat dissipation from the cable     

Thermal modeling of portable power cables

The US Bureau of Mines investigated the performance of portable power cables under time-varying load conditions. This research had a twofold purpose: (1) to define the thermal characteristics of electrically overloaded trailing cables; and (2) to construct a thermal model for cables to predict cable temperature rises resulting from load currents. Several tasks were undertaken in support of these goals during the three-year research effort. Overload tests ranging from 2 to 12 times rated ampacity were conducted in the Pittsburgh Research Center's Mine Electrical Laboratory. A thermal model of energized type G-GC trailing cables was constructed based upon empirical data from the US Bureau of Mines load tests. This model was then incorporated into an interactive computer program that can assist designers and approvers of mining machines in selecting the appropriate size trailing cable. This program can be the basis for a cable protection system which ensures that cables are not the source of fires, ignitions, burns, or explosions underground     

Technological progress in high-voltage XLPE power cables in Japan.I

The author reviews technological progress in the design and production of cross-linked polyethylene cable and discusses the present status of the products taking advantage of this technology. A brief historical background is given. The methods for determining or choosing cable characteristics, such as insulation thickness, service life, and cable quality, are discussed. Progress in production technology is discussed, covering improvements in polyethylene, three-layer common extrusion, dry curing, and smoothing of the semiconductive shield layers     

不均匀土壤中电缆集群的优化运行

电力电缆集群在统一的栽流量下运行,未能充分挖掘电缆的输送能力.为提高地下电缆集群的总体输送能力,本文采用基于有限差分法的电缆温度场数值计算程序和人工鱼群优化算法,以电缆群电流之和最大为目标函数,以所有电缆温度低于其最高额定温度为约束条件,确定带回填土的电缆集群每一回路的优化运行电流.计算结果表明,回填土热阻系数较大时,...     

Theoretical investigation on skin effect factor of conductor in power cables

This paper describes a newly derived theoretical equation on the skin effect factor of power cables, and its application to large‐size OF and XLPE cables with segmental conductors, including insulated wires. The skin effect factors calculated with the new equation were fit very well to measurements in a wide range of conductor sizes. In the new equation, the important factor which characterizes the skin effect of segmental conductors is the “equivalent conductivity ratio” v defined by the ratio of longitudinal conductivity in axial direction of conductor to conductivity of conductor wires. Since the obtained ratio v in XLPE cable was three times greater than that in OF cable, the larger longitudinal eddy current passing from a wire to another increased the eddy current loss in conductor, which increased the conductor loss of XLPE cable. The new equation enables us to investigate quantitatively the dominant loss component affecting the skin effect factor. Then, the skin effect factors and coefficients for OF and XLPE cables were investigated with the new equation. It was revealed that the best number of separation, in which the skin effect reached a minimum, existed in OF and XLPE cables with segmental conductors. In addition, it was confirmed that the skin effect coefficients ks1 calculated with the new equation were very consistent with those used in JCS. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 18–34, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20576     

Accelerated aging of extruded dielectric power cables. I. Controland monitoring methodology

An improved accelerated cable life test is described. Through the use of programmable logic controllers (PLCs), very precise and consistent control of the accelerated aging process has been achieved. A computer has been utilized to make continuous real-time acquisition and storage of key operating parameters possible. This precise control and monitoring methodology has permitted the study of the synergistic effects of voltage and temperature on the accelerated aging of full-sized cables in the laboratory     

Thermal analysis of power cable systems in a trench inmulti-layered soil

A system of three underground cables in a trench is modelled using the finite difference method. The model accommodates most of the geometrical parameters and the working conditions. The heat dissipation from each individual cable is calculated for various parameters including the cables' diameters, the trench width and the spacing between cables. Some of the geometrical dimensions have great influence on improving the total ampacity of the system     

Statistical approach in power cables diagnostic data analysis

This paper describes the application of statistical analysis to the on-site diagnostic data of HV power cables to set-up knowledge rules and measuring criteria for particular cable insulations and accessory (joints, terminations). Such approaches can successfully be employed later in Asset Management decision processes. In this paper based on different cable data populations of two diagnostic parameters like: partial discharges and tan ?, statistical analysis has been applied. Besides this, several practical examples also have been presented.     

ESCA analysis of semiconducting layer materials in XLPE power cables

This paper describes an application of ESCA analysis to semiconducting materials in XLPE power cables in terms of the oxygen ratio (integrated intensity of oxygen spectrum/integrated intensity of carbon spectrum). Analyzed materials were carbon black, an additive mixed into semiconducting materials, and several semiconducting materials treated in various cross‐linking conditions. It was found that the additive increases the oxygen ratio of semiconducting materials as well as does the cross‐linking treatment. The higher the oxygen ratio of the semiconducting materials, the smaller is the average lamellar angle in the XLPE insulation at the semiconducting interface. The angle is thought to be a parameter which expresses the hyperstructure of polymer insulation and smaller angles correspond to a better state of the semiconducting interface in XLPE power cables. © 1998 Scripta Technica, Electr Eng Jpn, 126(2): 15–22, 1999     

电力电缆相序阻抗计算与分析

在城市电网建设中 ,2 2 0 k V和 1 1 0 k V线路愈来愈广泛采用电力电缆 ,因此必须正确认识和掌握电缆线路的相序阻抗参数特点。本文论述了电力电缆正、负和零序阻抗的理论计算和采用单相电源法进行参数实测的试验方法 ,阐述了金属护套不同的接地互联方式下电缆相序阻抗参数特点和各序阻抗之间的关系 ,有助于电缆参数的正确测量和继电保护装置的可靠运行     

Accelerated aging of extruded dielectric power cables. II. Lifetesting of 15 kV XLPE-insulated cables

For pt.I see ibid., vol.7, no.2, p.596-602 (1992). Preliminary results are described in which 15 kV XLPE cables were subjected to accelerated aging tests under a variety of controlled voltage stress and thermal load cycle conditions, with loss of life being calculated for each set of conditions in terms of the geometric mean time to failure (GMTF). The relative influence of voltage stress and load cycle temperature are discussed. Accelerated aging results show a reduction in GMTF for 15 kV XLPE-insulated cables as the voltage stress or conductor load cycle temperature is increased in a controlled manner. The relative influence of voltage stress versus load cycle temperature can be compared. The GMTF increases more in going from 90°C to 60°C at constant applied voltage stress than in going from 4X to 2X rated voltage at constant load cycle temperature conditions     

Theoretical model to calculate steady-state and transient ampacity and temperature in buried cables

The temperature distribution and ampacity in a multilayered soil surrounding a system of three cables are calculated in the steady state and in emergency situations. In this paper, we present the mathematical model, which solves the heat diffusion equation in cylindrical coordinates inside the cables and in Cartesian coordinates in the surrounding soil. The finite difference method is used to solve the equations. In order to reduce the number of points studied that are of no interest to the results, a variable step discretization is used. Here, we present the development of the model and the effect of some of the parameters which influence the convergence and accuracy of the method. The application of the model in different configurations and situations is given in the second part of this work, sent for publication at the same time. The model is applicable to the study of buried cables in both the steady state and transient states for short-circuit and overload situations.     

Retrofitting-new high voltage XLPE cables substitutingpaper-insulated power cables in steel pipes

Many utilities still have paper-insulated pipe type cables in service. In the near future they may have to replace some of these systems due to local increases in electric power demand or aged cable insulation. In many cases the steel pipes are well protected against corrosion and thus suitable for further use. For retrofitting in such installations, XLPE-insulated cables offer several advantages. Felten & Guilleaume Energietechnik AG has developed a new three-core XLPE-insulated 64/110 kV cable with reduced insulation thickness (10 mm), that can be pulled into a pipe. In co-operation with VEW ENERGIE AG, the cable performance is being investigated in a field test, that started in October 1996. This long-term loading cycle test will last for three years. The test voltage, applied between conductor and earth, amounts to 127 kV. The temperature is measured with the help of an optical-fiber measurement system. This device is computer controlled and works as a remote monitoring system     

Transient tolerance analysis of power cables thermal dynamic by interval mathematic

The safeguard of power equipments is assuming a major role in the deregulated electricity market, where a malfunctioning power system could be responsible for serious damages to a large number of system operators having access to the shared energy resource.In this context thermal monitoring of power cables represents a key issue in evaluating the risks associated with a given load management policy especially during emergency conditions. In particular this demands for reliable assessment models that should be able to predict the transient thermal behaviour when the load exceeds the nameplate value.In this connection the application of both simplified and detailed power cable thermal models is often complicated by the presence of uncertainties affecting the tolerances of the input data. The effect of these uncertainties could influence the final solution to a considerable extent.A comprehensive tolerance analysis is therefore required in order to incorporate the effect of data uncertainties into the thermal modelling process.To address this problem, in the paper the employment of interval mathematic is proposed. Several numerical results are presented and discussed in order to assess the effectiveness of the proposed methodology which offer a rough qualitative insight of the solution in a very short time, comparable to the time required for a deterministic numerical simulation.     

Multiconductor analysis of underground power transmission systems: EHV AC cables

It is widely ascertained that the multiconductor analysis is a powerful tool which can solve any structurally complex circuit (e.g., high-speed railway supply system, gas insulated lines, etc.). Moreover, this method can be also used as an in-depth analysis of the electric networks after the power-flow studies when they introduce simplifying hypotheses especially in the presence of asymmetry. In this paper, the multiconductor cell analysis has been applied to AC underground cable lines (UGC). This multiconductor procedure based on the use of admittance matrices, which account for the line cells (with earth return currents), different types of sheath bonding, possible multiple circuits, allows predicting the steady-state (and faulty) regime of any cable system. The method calculates the proportion and behavior of the phase currents carried by each parallel conductor, the circulating current in the sheath of each cable and the stray current in the earth. Moreover, some comparisons have been made with traditional programs showing the great accuracy of multiconductor cell model.     

Technological progress in high-voltage XLPE power cables in Japan.II

For pt.I see ibid., vol.4, no.5, p.9-16 (1988). Cables designed for particular applications and improved performance are described. The products discussed are: (1) water-impervious cable; (2) composite XLPE/optical fiber cable; (3) 66-kV submarine cable; (4) commercial long-distance 275-kV line; and (5) 500-kV short-distance line. The discussion is confined to the Japanese cable industry     

Insulation coordination of MV power cables

In medium voltage power cables, the concept of cost/reliability has been current since the end of the 1980s when the Brazilian Standards introduced ethylene-propylene-rubber (EPR) insulated cables, with different thicknesses of insulation for conventional cables and for those with blocked conductors or with water tightness constructions. However, despite the benefits obtainable by use of such cables, they have had limited use by electrical power utilities; perhaps because the concept has not become widely recognized. This paper intends to clarify and submit a new approach for design of the dielectric system of medium voltage cables, for use in underground and insulated overhead distribution feeders. Theoretical aspects of sizing the dielectric system, by means of coordinating the insulation, and also using reliability parameters, is dealt with in the paper. Results of practical applications are also presented and discussed     

Rating power cables in wrapped cable trays

Conductor temperatures for a given ampacity loading is a function of ambient temperature inside the tray. In other words, the ampacity of cables included in these tray systems has to be rated at the ambient temperature inside the tray. Cable overheating and eventual failure can result if cables are overloaded or not derated for operation. IPCEA Pub. No. 54-440/WC lists cable ampacities in air ambient temperature of 40°C. Cables operating at temperatures above this have to be derated accordingly. An algorithm is presented for determining ambient temperatures in the cable tray for conditions of natural air convection with different cable loading. Hence, derated cable ampacities can be derived from those at 40°C. Although at present, there is no industry standard for wrapped cable trays, the method used here can be used to develop such a standard