Conductor Temperature Rise Research Articles

Numerical study on temperature rise and structure optimization for a three-phase gas insulated switchgear busbar chamber

In order to improve the simulation accuracy of the temperature rise, reduce the operating temperature, and improve the insulation performance of the gas insulated switchgear (GIS) busbar, this paper numerically studied a 252 kV three-phase GIS busbar chamber based on multiphysics coupling method. Various factors affecting busbar electromagnetic loss are analyzed, and the busbar structure is optimized combined with the Taguchi method. Firstly, the loss computational results show that, both skin effect and proximity effect change the conductor current distribution, the skin effect increases the GIS loss by 18.59 W/m (12.2%), and the proximity effect has little effect on the loss. The additional heat loss caused by conductor temperature rise cannot be ignored (13.2%). Secondly, Taguchi performance statistics show that, the conductor thickness (δ) and center distance (d0) have the greatest impact on the maximum temperature and minimum gas breakdown margin of GIS busbar, respectively, with the contribution rate of 80.2% and 65.1%, respectively. Finally, the optimal design parameter combinations with lowest operating temperature and best insulation performance for GIS busbar chamber are obtained with Taguchi method, respectively.

Recent developments in engineering design for the quasi-axisymmetric stellarator CFQS

A quasi-axisymmetric stellarator, the CFQS, has been designed as a joint project of the National Institute for Fusion Science and Southwest Jiaotong University to prove intrinsic advantages of quasi-axisymmetry. Principal parameters of the CFQS are as follows: the major radius is 1 m, the magnetic field strength is 1 T, the aspect ratio is 4, and the toroidal periodic number is 2. The magnetic field configuration is designed based on that of the CHS-qa. Enhanced confinement properties within the context of neoclassical theory are achieved by its quasi-axisymmetric configuration. In the entire radial range, the magnetic well is retained to keep favourable stability features in the magnetohydrodynamic equilibrium. A magnetic field coil system was designed for the CFQS, which consists of 16 modular coils, 12 toroidal field coils, and 4 poloidal field coils. The supporting structure is designed to withstand strong electromagnetic force under 1 T operation, maintaining enough space for heating and diagnostic systems. The mock-up modular coil with the most complicated shape was constructed by Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd. to check manufacturability and the achieved accuracy. A heat-run test was performed to check the temperature rise of conductors, and the capability of 1 T operation was confirmed. After various tests for the mock-up coil, construction of actual modular coils and the vacuum vessel has begun.

LBM simulation of heat transfer processes inside GIS capsule filled with different insulation gas mixtures

Lattice Boltzmann method (LBM) scheme is adopted to simulate the heat transfer processes inside isolated phase and three-phase enclosure gas insulated switchgear (GIS) capsules. D2Q9 fluid flow and thermal Lattice Boltzmann equations (LBEs) are solved through streaming and collision processes. Buoyancy force driven by natural convection is considered by the Boussinesq model. Power losses and thermal boundary conditions are obtained from closed formulas. Numerical results by LBM simulations are compared with those from physical experiments and conventional CFD simulations. Results show that LBM scheme could provide a simple and efficient alternative tool in the flow-thermal simulation of GIS equipment with desirable accuracy. Thermal performances of GIS capsule filled with different insulation gas mixtures (SF6, N2, CF4, CO2, CF3I) are then analyzed. Results show that upper conductors of three-phase GIS has larger temperature rise than lower conductor due to the natural convection effect. Conductor temperature rise inside gas mixture increases with the increase of second gas (N2, CO2, CF4) fraction. The thermal performance of GIS capsule could be reduced with the presentation of insulation gas mixtures.

Solving the Overhead Transmission Conductor Heat Balance Equation Using the Newton Raphson Algorithm

This paper utilizes the Newton Raphson (NR) iterative algorithm to solve a detailed heat balance equation for overhead transmission conductors, for the purpose of calculating a Dynamic Line Rating or temperature-dependent impedance using real-time or forecasted weather data. Provided ambient weather conditions, conductor parameters and electrical current passing through the conductor, a starting guess is formed and the iterative solution method arrives upon a solution within a preset solution tolerance. A simple method to approximate the Rayleigh Number / Nusselt Number and Reynolds Number / Nusselt Number relationships is proposed to ensure successful convergence. The paper performs a thorough, numeric electrothermal conductor simulation to demonstrate proper solution convergence. This exercise identifies a minimum conductor temperature rise necessary for the solution method to converge successfully. Error related to the minimum starting conductor temperature rise, and error introduced by the approximated air property functions is illustrated. The temperature solution method is compared with several well-known thermal models.

Temperature safety analysis and backup protection scheme improvement for overhead transmission line in power oscillation condition

The oscillating block module is usually adopted to avoid false action of distance protection of overhead transmission lines during power oscillation. However, this scheme ignores the safe operation of conductor temperature during oscillating block. This paper focuses on the conductor overheating problem and safety protection issue during power oscillation. Firstly, through analysis the differences in conductor temperature calculations under oscillating current, short-circuit current and normal load, a numerical iterative method of conductor temperature rise (CTR) calculation under power oscillating current is proposed using the transient thermal balance equation. Then, the safe operation scheme of transmission line is proposed by setting temperature alarm and temperature off-limit trip out. An improved backup protection based on the combination of temperature and impedance is proposed to avoid false action of distance protection, also provide overheating protection for transmission line during power oscillation. Finally, a two-source power system and the modified 29-bus system are adopted to verify the CTR calculation and the improved backup protection. Results indicate that the proposed scheme can provide effective evidence of safe operation and relay setting for transmission lines through excavating the tolerance ability of overcurrent and oscillating current.

Quantification of temperature rise in unipolar organic conductors during short voltage-pulse excitation using electrical testing methods

To quantify the rise in device temperature caused by Joule heating during short voltage-pulse excitation at high current densities (>10 A/cm2), the device temperatures of unipolar organic conductors were measured using electrical testing methods. For a maximum voltage amplitude of 59 V at a current density of ∼300 A/cm2, temperature rose over 145 °C within a pulse duration of 5 μs in an N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (α-NPD)-based single-carrier organic conductor. This result is in reasonable agreement with numerically calculated values. These findings indicate that suppressing the effects of Joule heating by carefully adjusting pulse width, substrate and organic materials, and device configuration is important to achieve further carrier injection in the ultra-high current density region (>1 kA/cm2).

Influence of soil temperature characteristic on the grounding electrode temperature rise

The working current of DC grounding electrodes is constantly increasing with the rapid development of high-voltage direct current systems. Thus, the temperature rise of grounding electrode conductors is increasingly becoming an important safety factor. Therefore this study measured the soil temperature characteristics of water content and resistivity; established an electric heat coupling finite element model for DC grounding electrodes that is based on current field and temperature field theories to analyse the temperature changes in common DC grounding electrodes. In contrast to traditional models, the proposed model realises electric heat coupling field calculation by considering the mutual influence of temperature rise and soil parameters. The results show that the soil resistivity increases with increasing temperature and the soil resistivity change further influence the temperature changes of the grounding electrodes. The change in grounding electrode temperature rise is not steady and includes a sharp growth stage.

A proposed algorithm for an overhead transmission line conductor temperature rise calculation

SUMMARY The work carried out in this paper is to deal with a proposed conductor temperature rise computation algorithm. This simple algorithm gives more accurate calculation, making use of the load current and the weather data parameters, particularly the amount of solar incidental radiation upon the conductor and the conductor material properties. The calculation is based on the heat transfer mechanisms occurring in the stranded exposed overhead transmission lines (OHTL) conductors in a natural environment. In this paper, the mathematical models for the use of the natural and forced convections are presented by using Numbers of Grashof and Reynolds, respectively, in the determination of the temperature rise of the OHTLs. Skin effect and iron losses are also taken into account in order to determine the alternating current resistance of an Aluminium Conductor Steel Reinforced in the process of iteration's heat balance equation. The surface area factor of the stranded conductors that increases the loss by radiation from the conductor surface is also used to calculate the temperature rise of the stranded OHTL. Copyright © 2012 John Wiley & Sons, Ltd.

Ampacity Calculations for Deeply Installed Cables

In this paper, a new method is proposed for ampacity calculations of deeply installed cables. Two factors make these types of installations different from more common situations of cables located up to five meters underground. On the one hand, the time constant of the soil layer above the cable trench is very large, resulting in a very slow conductor temperature rise when the cable is first loaded, and, on the other hand, the weekly and yearly load-cycle variations can be taken into account to take the advantage of the greater laying depth. Both issues are explored in this paper. This paper introduces the concept of the equivalent laying depth which makes it possible to use the rating rules applicable to the steady-state conditions and avoid transient analysis.

Estimation of the temperature rise in cylindrical conductors subjected to heavy 10/350 μs lightning current impulses

Lightning is a very high-energy phenomenon, which can pose serious dangers for human beings and the environment. Although much progress has been made in the area of lightning protection, there are still many cases of fires caused by lightning and power and telecommunication system outages. We have carried out an experimental and mathematical investigation into the temperature rise in cylindrical conductors subjected to heavy 10/350 μs lightning current impulses. The temperature rise measurements took place in one of the most reliable laboratories in Europe (BET, Menden, in Germany). The proposed mathematical models used to estimate the temperature rise in cylindrical conductors assumed both a uniform and non-uniform current density distribution by taking into account the transient skin effect. In addition, verification of the mathematical results were studied. Suggestions for further investigations are also provided. The experimental results are consistent with the results from the mathematical models. It is convincingly shown that copper conductors can be influenced by the transient skin effect. The additional temperature rise however, caused by the transient skin effect, is minimal, and can be neglected.

Simulation of quench for the cable-in-conduit-conductor in HT-7U superconducting Tokamak magnets using porous medium model

A cable-in-conduit-conductor (CICC) consists of superconducting cable, copper, supercritical helium and conduit. To keep the operating temperature of superconducting cable lower than its current sharing temperature, the supercritical helium is forced flow through the CICC. The supercritical helium through the cable bundle has the complex directional changes due to the interaction between the supercritical helium and strands. The structure of CICC is characterized with the porous medium. The quench characteristics of CICC are analyzed by the model which the temperature difference between the strands and helium is assumed to be very small due to the heating induced flow to generate high heat transfer coefficient of supercritical helium. A moving mesh method is developed for the numerical solution of the problem with the steep drop for temperature and density of supercritical helium in the short front region of the normal zone. The computational mesh is obtained by equidistribution of a monitor function tailored for the functional variation of the arguments for density, temperature and velocity of supercritical helium. Existence and uniqueness of the discretised equations using a moving mesh are also established. The coupled equation for porous medium is solved using the finite element method with the artificial viscosity term. The validation of the code is tested by comparing it with the other codes with good accuracy. The converged properties of numerical solution due to quench in CICC are studied. We present preliminary estimates of the maximum conductor temperature rise and helium pressure during a quench in the inner layer of toroidal field (TF) magnet for HT-7U. The quench scenarios with different dump time constants of 6.25, 12, and 21.1 s are considered. The goal of such work is to guide the protection scheme and a detailed prediction of the quench evolution of magnet.

A fundamental study on electrical insulation of N2/SF6 gas‐insulated electric power apparatus

AbstractIn this paper, we carried out a case study on fundamental insulation design for the application of N2/SF6 gas mixtures to a 275‐kV gas‐insulated busbar. First, we investigated the impulse ratio in N2/SF6 gas mixtures and point out that the insulation design might be based on the negative switching impulse voltage in the case of lower SF6 content. Second, we estimated the tank diameter and SF6 gas amount with consideration of the electric field strength on conductor surface and temperature rise in gas mixtures. We clarified that the tank diameter at the lower SF6 content is mainly determined by the electric field strength on the conductor surface and quantified the optimum gas pressure and SF6 content for a target reduction of SF6 gas amount. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 9–16, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.1163

AC losses and heat removal in three-dimensional winding pack of Samsung superconducting test facility under pulsed magnetic field operation

The Samsung superconducting test facility (SSTF) will be operated under the highly pulsed field to simulate the operating conditions of KSTAR. An analysis has been performed to study the transient heat removal characteristics and temperature margin for the main, blip and compensating coils in the SSTF. This method is based on a quasi-three-dimensional model, which the thermal coupling of turn-to-turn, pancake-to-pancake and channel-to-channel is taken into account, to simulate the conductor temperature rise and the thermal expansion of supercritical helium due to the high AC losses under the pulsed field. The local AC losses, which include coupling loss, eddy current loss and hysteresis loss in the cable-in-conduit conductor, are estimated. The temperature margin, mass flow rate, distribution of AC losses are studied under the given operating scenario. The mass flow reduction and peak temperature rise depending on the inlet pressure and inlet position of CICC are studied. It is shown that the initial mass flow rate remarkably influences on the peak temperature of superconducting strands. The large mass flow rate can reduce the temperature rise when the inlet of helium is located at the high field region. By contrast, because of heat induced flow to improve the cooling condition of the superconducting strands, the small initial mass flow rate results in the low peak temperature in strands when the inlet of helium is located at the low field region.

Analysis of electric arc short-circuit consequences in ITER toroidal field coils

Abstract Based on the results of the ITER magnet system structure analysis the thermal analysis of a toroidal field coil in the case of short-circuit has been performed in view of the normal zone propagation (quench), as well as the conductor temperature and coil resistance rise. The electric arc behaviour within the magnet system is considered. The main results of calculations and theoretical study of the electrical arc under conditions typical for short-circuits in the magnet system coils are outlined. Theoretical physical models for an arc discharge burning within the insulation and conductor bulk are developed and described. Energy release in the arc is a matter of concern. Dangerous consequences of the arc discharge burning in the magnet system are estimated.

Analysis of the QUELL experiment and comparisons with numerical simulations (QUENCHER)

This paper presents a detailed analysis of the Quench Long Length (QUELL) experiment. A number of different quench scenarios are compared with numerical simulations using the QUENCHER model. It is shown that in all cases the maximum helium pressure rise, the conductor temperature rise, the quench propagation velocity, and the quench voltage obtained from the numerical studies are in very good agreement with the experiment. Based on the experimental results during the heat pulse propagation, together with a more detailed analysis of the heat transfer mechanism between the helium in the central hole and the cable space a new heat diffusion term is proposed in QUENCHER. This diffusion mechanism is a direct consequence of the finite heat transfer coefficient between the cable and the central hole, and the fact that helium velocity in the hole is much larger than the cable space. Results are presented with and without the new diffusion term in the model.

Expert system application for the loading capability assessment of transmission lines

This paper describes the application of an expert system for the evaluation of the short-term thermal rating and temperature rise of overhead conductors. The expert system has been developed using a database and Leonardo expert system shell which is gaining popularity among commercial tools for developing expert system applications. The expert system has been found to compare well when evaluated against site tests. A practical application is given to demonstrate the usefulness of the expert system developed.

Coilgun technology at the Center for Electromechanics, the University of Texas at Austin

The engineering trade-offs performed on a coilgun design are described. The concept used was that of a collapsing field accelerator. This concept was chosen because of its passive operation, and because it lent itself to existing power supplies. The trade-offs described concern stress, maximum temperature rise in conductors, efficiency, time constants of the energy storage element, and weight. An example of such a trade-off concerns the mass of coilgun armatures. The more massive an armature, the greater its ability to absorb resistive losses and the higher its time constant. However, larger armature lower payload efficiency. Another trade-off concerns the fraction of armature weight that is devoted to structure. More highly stressed armatures have more attractive electrical performance at the expense of parasitic weight.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Statistical distribution of the temperature rise of an overhead-line conductor carrying constant current

The statistical distribution of the temperature, or temperature rise, of an overhead-line conductor carrying a constant current depends on the stochastic variation of the atmospheric parameters, particularly the wind speed and direction, the air temperature and the intensity of solar radiation. The paper presents probability density functions for the temperature, temperature rise, radial temperature difference, and thermal inertia of the 54/7/3.5 mm ACSR conductors in three spans of an outdoor test line erected in the form of a horizontal equilateral triangle at a height of 10 m. The experiment was conducted for a period of 32 months, with a constant current of 1500 A and a constant tension of 30 kN. An unenergized similar conductor was also studied. The results are classified by day and night, and by seasons. Bimodal probability density functions were found for conductor temperature, temperature rise and radial temperature difference.

交流用Ｎｂ３Ｓｎコイルに関する研究

We developed Nb3Sn superconductors for AC use and fabricated a coil. The Nb3Sn superconductors were manufactured using the internal tin diffusion process. To reduce AC losses, the spacing between Nb filaments was designed to be 0.5μm, sequentially, the space factor of Nb filaments was 6%. The diameter of a strand is 0.2mm, and the diameter of a Nb filament is 0.4μm. AC losses in the strand were 180kW/m3 at 0.5T, and were 18kW/m3 at 0.1T (60Hz, peak value). A coil was made by the Wind and React method using conductors composed of 7×7 strands. Specifications of the coil are as follows. The inner diameter is 156mm, outer diameter is 188mm, height is 34mm, and the number of turns is 17 turns×4 layers. To reduce wire motions, the coil is impregnated with epoxy resin. The first quench current for DC operation was 1, 130A. The third quench current was 1, 280A, and the maximum magnetic field of conductors was 1.6T. The magnet was tested under AC 60Hz operation. The quench current was 340A (rms). The cause of quenching is supposed to be the temperature rise of conductors due to coupling losses among the strands.

Computerized method for evaluating the suitability of trailing cables

A program to develop models for the enable computer calculation of conductor temperature rise versus time in trailing cables has been initiated. To date, a common model equation has been developed and parameters determined for two round trailing cables typically used on continuous miners, type G-GC, sizes 2/0 AWG and 4/0 AWG, rated 90 degrees C. The resulting cable models have been tentatively confirmed in laboratory trials using repetitive four-level constant-current cycles and triangular currents in which the peak current varied on succeeding cycles. Model refinement and additional laboratory trials are projected using randomly varying current, simulating actual current conditions in mine trailing cables. >