Boundary element estimation of current density distribution and eddy current loss in bundled multi-wire cables

A numerical approach to the estimation of the current density distribution and the eddy current loss in bundled multi-wire cables using the boundary element method is proposed. Under the assumption of the gradual twist of the bundled wires, the cables are modelled to be two-dimensional with respect to their cross-sections. Three-phase transmission lines of cyclic symmetrical configuration are considered for which a reduction method is utilized to provide efficient computation. Some numerical demonstrations are made for three types of three-phase transmission-line models, consisting of a single wire and three and seven bundled wires. Two cases are considered: one in which the bundled wires are electrically contacted one to another on their surfaces and one in which they are independently insulated. The equivalent resistance is also calculated to examine the skin effect. The skin effect and the effectiveness of the multi-wire configuration to reduce the skin effect are well demonstrated.     

Accurate modeling of interelectrode resistance and powerdissipation in electric glass melters

An accurate technique for modeling the interelectrode resistances as well as the potential and power density distributions in electric glass melters is presented. The model also provides necessary data for sizing the supply transformers associated with such melters. The solution technique involves only algebraic equations, and therefore can be implemented by simple computer software. An example melter with a two-phase supply and eight electrodes was simulated using the proposed three-dimensional modeling technique. Because of the general nature of the proposed model, this technique provides a valuable as well as reliable and easily implemented design tool for melters with multiphase power supplies and general electrode configurations     

Algorithm to predict dry-band arcing in fiber-optic cables

Utilities frequently use ADSS (all dielectric self-supporting) fiber-optic cables installed on transmission lines 3-6 m below the high voltage conductors. Dry-band arcing occurs on the fiber-optic cables when the cables are polluted and wet. This has been assumed to cause cable failures. An equivalent circuit has been developed to represent the polluted fiber-optic cable in the high voltage environment. The objective of this paper is to present a novel numerical method that can be used to predict dry-band arcing in fiber-optic cables. KCL (Kirchoff's current law) is used to derive node point equations for the equivalent circuit. Forward elimination and backward substitution of node voltage is used to solve the equations. The effect of pollution, tower arrangement, and conductor sag is analyzed. The numerical method has speed advantages over circuit simulation methods. This method includes conductor sag, nonuniform pollution, and variable capacitance. This algorithm can be used to predict dry band arcing in fiber-optic cables     

Modelling of maximum temperatures in aerial bundled cables feeding domestic loads using the beta probability distribution function

A method for the thermal sizing of aerial bundled cables (ABCs) feeding stochastic domestic electrical loads is presented in this paper. This method is based on an algorithm from an International Electrotechnical Commission (IEC) publication, but uses an adapted form of Morgan's method for calculating the external thermal resistance. The beta distribution of grouped loads is incorporated in the thermal sizing algorithm. A beta thermal model is calculated, from which size selections of ABCs can be made. The resulting approach is an improvement on previous methods which use the after-diversity maximum demand for describing the load.     

Proximity effect and eddy current losses in insulated cables

Insulated cables are generally designed according to thermal criteria: the current rating depends on the permissible temperature inside the insulation. As the heating of a cable mainly results from Joule losses, it is worthy to determine the current distribution in its metallic components (the core and the metallic screen for single core cables). The current distribution in tables is affected by the skin effect and the proximity effect due to neighbouring cables of the circuit itself or from parallel links. A general method is developed to calculate the current distribution in the core and the screen of a single-core cable, starting from Maxwell equations. The stress is set upon skin and proximity effects, taking into account the influence of the frequency. Joule losses are calculated in some practical cases of three-phase links     

A model to predict accommodations needed by disabled persons.

In this paper, several approaches to assist employers in the accommodation process for disabled employees are discussed and a mathematical model is proposed to assist employers in predicting the accommodation level needed by an individual with a mobility-related disability. This study investigates the validity and reliability of this model in assessing the accommodation level needed by individuals utilizing data collected from twelve individuals with mobility-related disabilities. Based on the results of the statistical analyses, this proposed model produces a feasible preliminary measure for assessing the accommodation level needed for persons with mobility-related disabilities. Suggestions for practical application of this model in an industrial setting are addressed.     

Refinements to the Neher-McGrath model for calculating the ampacityof underground cables

The Neher-McGrath method has been widely accepted as an accurate and relatively simple way to calculate the ampacity of underground cables. It is based on a number of assumptions that simplify the mathematics, but at the same time limit the accuracy and scope of the model. Furthermore, the model relies upon correlations that are now dated, because more up-to-date and accurate heat transfer correlations are now available. This paper examines improvements to the Neher-McGrath model in three different areas: a more accurate expression for the mutual heating parameter that accounts for unequal heating among the cables; improved correlations for the thermal resistance of a fluid layer that exists in pipe-type cables and cables installed in ducts; and a more accurate model for the thermal resistance of concrete duct banks with nonsquare cross-sections. Example installations are then considered to illustrate how the incorporation of these changes will affect the ampacity of the installation. The refinements suggested result in a more complex mathematical algorithm and require more computational time, but the changes can result in significantly different ampacity values than the ones provided by the Neher-McGrath model     

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.     

电力电缆载流量计算视窗化

相对于电压而言电缆载流量是电缆运行中重要的动态参数。在正常情况下它决定着电缆使用寿命。我国电缆载流量计算的行业标准 JB/T10 181- 2 0 0 0等同于 IEC6 0 2 87标准。电缆载流量计算软件化是发展的必然趋势。它将以现场为条件的动态视窗参数取代静态的载流量表 ,从而在使用方面更接近现场环境条件并从繁琐的数字计算解放出来。采用 VB编程是电力电缆载流量计算视窗化最理想的计算手段之一。我们将以XL PE电缆为契机向电力电缆载流量计算视窗化进军。     

Transient current measurement for the detection of water treegrowth in polymeric power cables

In this paper, the relationship between the frequency and time domain windows is discussed. From this study an appropriate time window for transient current measurements may be chosen so that reliable low frequency dielectric data can be obtained. The suitability of applying either Fourier transform or the Hamon approximation for the derivation of low frequency responses is discussed for transient currents with different shapes. With water-treed LDPE samples aged in the laboratory, measurements of transient currents, with subsequent transformation into the frequency domain, show a loss peak at ~10^-4 to 10^-3 Hz when moisture is retained in the samples. Even with free water removed, a higher dielectric loss is observed in water treed samples compared to virgin samples. The relaxation behavior may serve as an indicator of water treeing in polymeric cable insulation. The results of both transient measurements and TSDC results can be affected significantly by the treatment conditions of the samples. The application of vacuum to a water treed sample can alter the activation energy of the conduction process and the TSDC spectra     

A drain current model for Schottky-barrier CNT-FETs

We present here a physics-based drain current model for Schottky-barrier carbon nanotube field-effect transistors. The model captures a number of features exhibited by these transistors such as thermionic and tunnel emission, ambipolar conduction, ballistic transport, multimode propagation and electrostatics dominated by the nanotube capacitance     

Finite element computation of eddy current losses in nonlinearferromagnetic sheaths of three-phase power cables

A novel method for the finite element computation of the losses in a three-phase power cable is presented. The phase conductors carry sinusoidal, steady-state, and balanced currents, and the sheath is made of a nonlinear ferromagnetic material. A concept for an effective equivalent magnetic permeability is introduced that allows calculations in the complex domain. Sheath losses are presented and discussed for a symmetrical configuration     

Corona power loss, electric field, and current density profiles in bundled horizontal and vertical bipolar conductors

In this paper, computation of the corona current and, hence, the corona power loss associated with bipolar high-voltage direct current (HVDC) conductors is presented using the finite-element method (FEM) and the method of characteristics (MOC). The former method is used to solve Poisson's equation while the latter is used to satisfy the current continuity condition. The ground-plane current density and electric field profiles associated with the HVDC conductors are also calculated as a prerequisite for the computation of the corona current. The effectiveness of the present method is demonstrated using HVDC full-scale and laboratory-model transmission lines. Horizontal and vertical bipolar configurations are tested with 2 and 4 bundles. Comparison between previously measured and computed profiles and present calculations shows satisfactory agreement with previous measured and calculated values.     

A current sensor using the Faraday effect in optical fiber manufactured from flint glass

For application to current monitoring in electric power facilities, the authors have been developing a current sensor utilizing the Faraday effect of an optical fiber manufactured from flint glass having a very small stress-optic coefficient. This paper describes the result of study on constructing the sensing system, which is composed of a sensor head, a light source, fibers for light transmission and a signal processing circuit. First, results from investigation are reported with respect to causes affecting performance and durability of the sensor, and examinations of countermeasures also are described. As a result of the research, it was confirmed experimentally that several means are effective to improve characteristics of the sensor. Then, design and test results of a sensor model constructed with application of the means are described. From the test results it was proved that the model shows excellent characteristics satisfying basic requirements of the standard for conventional current transformers. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (3): 22–38, 1997     

Life model based on space-charge quantities for HVDC polymeric cables subjected to voltage-polarity inversions

This paper illustrates a new model that enables the estimation of life of polymeric insulation subjected to DC stress, both in the presence and in the absence of voltage polarity inversions. The derivation of the model parameters is based on the results of space charge measurements and accelerated life tests realized at constant DC stress, which allows the characterization of the performance of insulating materials under DC electrical stress to be carried out in short times. The expected life of a cable in service can be evaluated by means of this model, provided that the rate of voltage inversions expected during its life is known or estimated. The model is applied here to results of tests carried out on polyethylene-based materials for cable insulation, and model parameters are calculated resorting to two different approaches. A satisfactory fitting of life test results is achieved, thus confirming the validity of the proposed model.     

基于灰色模型企业电能预测系统的研究

能源预测在企业管理中起着重要的作用。为了解决电力能源预测系统存在的问题,先使用一个经典的灰色预测模型GM（1,1）进行建模,通过MATLAB仿真软件,然后根据企业前九个月的电能消耗数据预测后3个月的电能消耗数据,画出仿真曲线。最后利用改进的灰色模型PGM （1,1）再进行仿真,比较仿真结果曲线发现改进的预测算法模型具有更小的平均相对误差,PGM （1,1）算法克服了GM （1,1）灰色模型中数据可能存在短时间内出现波动的情况,使预测模型的结果更加接近企业实际的电能消耗数据。     

A contribution to the study of aging of XLPE insulated cables

The electrical, thermal, and multiple-stress (thermal and electrical) aging of cross-linked polyethylene (XLPE) cable models has been investigated in order to get information on aging effects and mechanisms. After endurance tests, XLPE cable models have been subjected to chemical, physical, electrical, and microstructural characterization. Thermal aging results reveal that bulk degradation occurs in the cables at temperatures higher than the melting point. Multiple-stress aging data emphasize a synergistic effect of electric field and temperature. Significant microstructural changes detected in the cables aged under multiple stress are evidence of this effect and can partly explain the time behavior of the electric strength