411 research outputs found
Magnetic field shielding of underground cable duct banks
In this paper an in-depth parametric analysis of shielding effectiveness obtained when using ferromagnetic or conductive screens to mitigate the field generated by duct banks is presented. Due to the need of a case-by-case approach, all the simulations, performed by a finite element software (GetDp), are applied to a case study composed by 9 (3 × 3) ducts, with six of them including high voltage single-core
cables and the three left empty for eventual future expansion. Two shielding geometries are tested: horizontal and U-reverse, changing in each one the main parameters: width, thickness, clearance to conductors, etc. Moreover, the conductors are grouped in two balanced in-phase three-phase circuits arranged in three configurations: vertical, horizontal and triangular. The mutual phase ordering of both circuits is the one that minimizes the field, so no further field reduction can be obtained by simple methods. The power losses and cost of different shielding solutions are also presented, including the effect of adding a third circuit if required
Hybrid 2D/3D fully coupled electrothermal model for three-core submarine armored cables
The computation of the power losses in submarine three-core lead sheathed armored cables is overestimated by the IEC 60287 standard, and hence its size and cost. 3D finite element simulations in COMSOL Multiphysics have proved to provide accurate results in losses computation thanks to recent advances that help in reducing the model length by applying rotated periodicity boundary conditions [1,2]. However, for obtaining the ampacity of a particular cable a fully coupled 3D electrothermal model would require a highly detailed 3D geometry, something that can be difficult due to the special operations required to create and mesh the geometry for applying such boundary conditions [3]
Experimental validation of ultra-shortened 3D finite element electromagnetic modeling of three-core armored cables at power frequency
Due to recent advances, the numerical analysis of submarine three-core armored cables can nowadays be
developed through the finite element method (FEM) in a small slice of the cable. This strongly reduces the
computational burden and simulation time. However, the performance of this ultra-shortened 3D-FEM model is
still to be fully assessed with experimental measurements. This paper focuses on this validation for an extensive
variety of situations through the experimental measurements available in the specialized literature for up to 10
actual cables. In particular, it deals not only with relevant calculations at power frequency, like the series
resistance and inductive reactance or the induced sheath current, but also with other aspects never analyzed
before through 3D-FEM simulations, such as the zero sequence impedance, the magnetic field distribution around
the power cable, as well as side effects due to the nonlinear properties of the armor wires. All this considering
different armoring and sheath bonding configurations. Results show a very good agreement between measured
and computed values, presenting the ultra-shortened 3D-FEM model as a suitable tool for the analysis and design
of three-core armored cables, and opening the possibility to reduce the need of extensive experimental tests in
the design stage of new cables.FEDER / Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (Spain) project ENE2017-89669-RUniversidad de Sevilla (Spain) VI PPIT-US grant 2018/0000074
Experimental validation of ultra-shortened 3D finite element models for frequency-domain analyses of three-core armored cables
Recently, large offshore wind power plants have
been installed far from the shore, using long HVAC three-core
armored cables to export power. Its high capacitance may contribute
to the appearance of unwanted phenomena, such as overvoltages
or resonances at low frequencies. To adequately assess
these problems, detailed and reliable cable models are required to
develop time-domain/frequency-domain analyses on this type of
cables. This paper presents, for the first time in the literature, an
assessment on the performance of 3D finite element method-based
(3D-FEM) models for developing frequency-domain analyses on
three-core armored cables, confronting simulation results with
experimental measurements found in the literature for three
real cables. To this aim, a simplified ultra-shortened 3D-FEM
model is proposed to reduce the simulation time during frequency
sweeps, through which relevant aspects never analyzed before
with frequency-domain 3D-FEM simulations are addressed, such
as total losses, induced sheath current, magnetic field around the
power cable, positive and zero sequence harmonic impedances,
as well as resonant frequencies. Also, a time-domain example
derived from the frequency-domain analysis is provided. Remarkable
results are obtained when comparing computed values
and measurements, presenting the simplified ultra-shortened 3DFEM
model as a valuable tool for the frequency-domain analysis
of these cables
Impact of electromagnetic losses in closed two-component magnetic shields on the ampacity of underground power cables
In this paper two typical arrangements of underground
single-core high voltage three-phase power cables (flat and trefoil
protected by PVC pipes) inside a closed shield of three different
materials (low-carbon steel, non-oriented grain steel and aluminium)
are analysed. The shield has two components: a U-shaped base and
a flat plate (cover) located on top of the base. Whereas most of
previous papers on this subject only dealt with the degree of mitigation
obtained with each material, this paper, in addition to also addressing
this issue, mainly focusses on the effect that electromagnetic losses
induced in the shield have on the ampacity of the cable and the cost
involved (material and losses). To obtain the numerical results, a
high number of simulations by a well-known commercial finite element
method software (COMSOL Multiphysics) have been performed. The
results obtained in the numerous cases analysed are widely commented
and the solutions that enable an important mitigation with no current
derating and at a comparatively low cost are highlighted
Loss Allocation in Submarine Armored Three-core HVAC Power Cables
Loss allocation of the three different components (conductor, sheaths and armor) of solidly bonded three-core separated lead-sheathed armored cables, frequently employed in offshore wind farms, is challenging due to the lack of accurate enough analytical expressions in the IEC standard. Also, loss allocation through experimental tests leads to inaccurate results since it is based on questionable assumptions. This paper improves both the IEC formulae and experimental methods by means of different analytical corrections in the conductor and sheath loss expressions. To this aim, an ad hoc application interface (Virtual Lab) based on 3D numerical simulations (finite element method) has been developed. This tool virtualizes and automates different test setups to emulate, in few seconds, the most employed experimental procedures in this type of cable. The analytical corrections have been derived from an in-depth analysis of a first set of 368 cables, ranging from 30 to 275 kV. The new loss expressions were successfully applied to a second set of 645 armored cables of quite diverse features (voltages from 10 to 275 kV, sections and dimensional parameters), hence bringing a general framework for any kind of three-core armored cable
On Simplified 3D Finite Element Simulations of Three-Core Armored Power Cables
This paper analyzes different ways to electromagnetically simulate three-core armored
cables in 3D by means of the finite element method. Full periodic models, as lengthy as 36 m,
are developed to evaluate the accuracy when simulating only a small portion of the cable, as
commonly employed in the literature. The adequate length and boundary conditions for having the
same accuracy of full periodic models are also studied. To achieve this aim, five medium voltage
and high voltage armored cables are analyzed, obtaining the minimum length of the cable that
may be simulated for having accurate results in shorter time and with less computational burden.
This also results in the proposal of a new method comprising the advantages of short geometries
and the applicability of periodic boundary conditions. Its accuracy is compared with experimental
measurements and the International Electrotechnical Commission (IEC) standard for 145 kV and
245 kV cables. The results show a very good agreement between simulations and measurements
(errors below 4%), obtaining a reduction in the computation time of about 90%. This new method
brings a more effective tool for saving time and computational resources in cable design and the
development of new analytical expressions for improving the IEC standard.Agencia Estatal de Investigación (AEI) ENE2017-89669-RFondo Europeo de Desarrollo Regional ( FEDER, UE) ENE2017-89669-RUniversidad de Sevilla (VI PPIT-US) 2018/0000074
Bayesian network modeling of the consensus between experts: an application to neuron classification
Neuronal morphology is hugely variable across brain regions and species, and their classification strategies are a matter of intense debate in neuroscience. GABAergic cortical interneurons have been a challenge because it is difficult to find a set of morphological properties which clearly define neuronal types. A group of 48 neuroscience experts around the world were asked to classify a set of 320 cortical GABAergic interneurons according to the main features of their three-dimensional morphological reconstructions. A methodology for building a model which captures the opinions of all the experts was proposed. First, one Bayesian network was learned for each expert, and we proposed an algorithm for clustering Bayesian networks corresponding to experts with similar behaviors. Then, a Bayesian network which represents the opinions of each group of experts was induced. Finally, a consensus Bayesian multinet which models the opinions of the whole group of experts was built. A thorough analysis of the consensus model identified different behaviors between the experts when classifying the interneurons in the experiment. A set of characterizing morphological traits for the neuronal types was defined by performing inference in the Bayesian multinet. These findings were used to validate the model and to gain some insights into neuron morphology
Direct torque control of multiphase doubly converter-fed asynchronous machines incorporating the harmonic torques
Doubly fed asynchronous machines have an outstanding property: they can be operated up to twice rated speed delivering full rated torque. This paper presents, for the first time in the literature, a control system for multiphase asynchronous machines fed by Voltage Source Inverters (VSIs) both in stator and rotor that incorporates the harmonic torques. The system has three main and distinctive features: the independent control of the fundamental and harmonic torques, a very fast dynamic response for each one of these torques and a powerful method for selecting the best suited inverter state to achieve the evolution of the fundamental and harmonics flux linkage space phasors prescribed by the external control loops. The first feature is achieved through the decoupling of the multiphase machine provided by the Space Phasor Theory (SPhTh). The second one comes from the application of the General Approach for a very Fast TOrque Control (GAFTOC) principle. The third feature relies on using for multi-phase VSIs a simple but powerful switching-table based mode of operation that overcomes the limitations of the switching-table based modes of operation developed up to now, that only enable for the inverter to feed machines with no harmonic torques contribution
Loss Allocation in Submarine Armored Three-core HVAC Power Cables
Loss allocation of the three different components (conductor, sheaths and
armor) of solidly bonded three-core separated lead-sheathed armored cables,
frequently employed in offshore wind farms, is challenging due to the lack of
accurate enough analytical expressions in the IEC standard. Also, loss
allocation through experimental tests leads to inaccurate results since it is
based on questionable assumptions. This paper improves both the IEC formulae
and experimental methods by means of different analytical corrections in the
conductor and sheath loss expressions. To this aim, an ad hoc application
interface (Virtual Lab) based on 3D numerical simulations (finite element
method) has been developed. This tool virtualizes and automates different test
setups to emulate, in few seconds, the most employed experimental procedures in
this type of cable. The analytical corrections have been derived from an
in-depth analysis of a first set of 368 cables, ranging from 30 to 275 kV. The
new loss expressions were successfully applied to a second set of 645 armored
cables of quite diverse features (voltages from 10 to 275 kV, sections and
dimensional parameters), hence bringing a general framework for any kind of
three-core armored cable
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