|مجال التميز||تميز دراسي وبحثي|
|عنوان البحث:||Modeling Multi-Layer OHL Conductors Undergoing Wind-Induced Motion|
|رابط إلى البحث:||Click here|
|موجز عن البحث:||Utilities aim to improve asset management strategies and enhance the utilization of their assets through low-risk reliable practices. Overhead lines and conductor designs have been evolving to increase systems’ power capacity and mechanical integrity, which have also extended asset lifetimes. Nevertheless, it is still challenging to predict a conductor’s fatigue stresses due to wind-induced vibrations that can help to estimate its useful life. A finite element model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on multi-physics accounting for the conductor’s thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminum strands. The bigger the difference between the material properties of the core and aluminum, the lesser the conductor vibrations, especially when the aluminum becomes slack. In fact, a conductor equipped with carbon core (ACCC), has the best vibration resistance among other conductors with steel core (ACSR) and homogeneous (AAACs). Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Larger trapezoidal ACSRs exhibit better fatigue resistance compared to smaller and round stranded AAACs.|
|عنوان البحث:||EMF Analysis for a 380kV Transmission OHL in the Vicinity of Buried Pipelines|
|رابط إلى البحث:||Click here|
|موجز عن البحث:||The induction of Electromagnetic Fields that are generated through the interaction of highvoltage transmission lines with neighboring buried metallic pipelines produce uncontrolled hazardous potential voltages, which can infringe safety limits. The paper presents the findings of the electromagnetic interference effects on water buried pipelines constructed within the vicinity of an Extra High-Voltage 380 kV transmission overhead line (OHL) in Riyadh-Salboukh route within the Saudi national grid power network. The presented case study showed that some segments of the buried pipelines under this line have not experienced voltages that exceeded the standard limits for the steady-state condition. However, in the event of L-G fault currents (short circuits), the pipelines experienced a voltage level that is above the local electric utility safety limits. Therefore, the work produced implemented the mitigation method of gradient control wires to reduce the potential voltages experienced by the pipelines to enforce the safety limit. The variation of wire resistance has been proven to be a feasible solution to reduce the excessive induced voltages. The comparison has shown that a 0.1 Ω is sufficient to maintain the safe limit for at least this line. These findings may vary depending on the OHL design and site topology.|
|عنوان المؤتمر:||Mediterranean Conference on Power Generation, Transmission, Distribution and Energy Conversion (MEDPOWER 2018)|
|مكان الانعقاد:||Dubrovnik, Croatia.|
|طبيعة المشاركة:||Oral Presentation|
|عنوان المشاركة:||Finite element modelling of Aeolian vibrations on stranded high-voltage OHL conductors|
|ملخص المشاركة:||The problem of Aeolian vibrations has been studied in indoor test-spans for many years. Its relevant standard experimentations have resulted in introducing the Energy Balance Method (EBM) which is the most commonly implemented method in the industry. Besides conductor properties, aerodynamic forces (Lift and Drag forces) acting on the conductor are the main input data for the EBM. The existing models frequently use experimental data of Lift and Drag forces for a cylinder. To further investigate the capabilities of wind-conductor interaction numerical modelling, it is useful to take advantage of Finite Element Modelling techniques. This paper simulates the wind flow around single OHL conductors with different outer layer stranding shapes and sizes utilizing COMSOL Multiphysics software. The simulations are based on solving the Navier-Stokes equation to compute the aerodynamic forces by integration of the pressure and shear forces within the boundaries of the conductor geometry. The numerical model computes the aerodynamic forces for three conductor geometries including smooth-surface, round-stranded, and trapezoidal stranding shapes. The numerically obtained solutions show that less aerodynamic forces are experienced by rounds and trapezoids compared to the cylinder geometry. This observation is true for high Reynolds numbers.|
|عنوان المؤتمر:||2019 IEEE Power & Energy Society General Meeting (PESGM)|
|مكان الانعقاد:||Atlanta, GA, USA.|
|طبيعة المشاركة:||Poster presentation|
|عنوان المشاركة:||Finite Element Modelling Approach to Assess Fatigue of Composite OHL Conductors|
|ملخص المشاركة:||Electricity utilities are obliged to developing renewable energy strategies, and electrification of energy sectors to reduce fossil fuels footprint. To accommodate this trend, utilities try to avoid the expensive solution of building new overhead lines and reinforce existing networks through re-conductoring with bigger size conductors or making use of novel designs such as High-Temperature Low-Sag technologies. The effect of conductor structure and material properties on its vibrations and fatigue responses have not yet been captured thoroughly in literature. In this respect, a Finite Element Model has been established in COMSOL Multiphysics to examine the fatigue performance of the composite structure of OHL conductors. To validate the model, simulation results are compared against the standard Poffenberger-Swart theory. The presented work have shown that the vibration and fatigue of bi-metallic conductors is not a linear problem and the assumption of a homogeneous structure does not apply to all conductor sizes. The internal structure of the conductors must be considered rather than a simplified homogeneous assumption especially for multi-layered conductors. The results also showed that trapezoidal conductors experience less fatigue compared to round designs. The FEM analysis are limited to the efficiency and power of used computing resources.|
|عنوان المؤتمر:||2019 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe)|
|مكان الانعقاد:||Bucharest, Romania.|
|طبيعة المشاركة:||Oral presentation|
|عنوان المشاركة:||Electric Network Power Transfer Flexibility — Focusing on Power Conductors Electro-Mechanical Behavior|
|ملخص المشاركة:||Power and energy utilities are obliged to tackle the inevitable results of the transformation strategies involving integrating high-shares of clean energy sources. The traditional solution of building new OHLs has been substituted by re-conductoring through bigger size or high-temperature conductor technologies to maintain the OHL system clearances. Existing literature models conductor vibration and fatigue based on a homogenized conductor structure. This paper establishes a Finite Element Model (FEM) in COMSOL© to enable examining vibration and fatigue of the different sizes and types of the OHL conductor’s complex geometries. The simulations of the free vibration and tension-strain of the modelled geometry are corroborated with the experimental data. The FEM simulations for the single and multi-layered composite conductors show that conductor vibration and fatigue responses are not always linear with the change in vibration amplitudes. Hence, re-assessing the flexibility of the network capacity by re-tensioning conductors depends on the conductor type and operating conditions.|
|عنوان المؤتمر:||Cambridge COMSOL Conference 2019|
|مكان الانعقاد:||Cambridge UK.|
|طبيعة المشاركة:||Poster presentation|
|عنوان المشاركة:||Modelling the Structural-Dynamics of Electrical Overhead Line Power Conductors|
As a general definition, the presence of any repeated motion after a regular interval of time is known as vibrations. The basic theory of vibrations is described by the system of forces acting on a moveable and deformable body. The natural phenomena existing in the universe such as earthquakes, water waves (i.e., tidal), sound or noise (i.e., Aeolian tone), and light are the result of transmitted waves that are described by propagating vibrations in space. The characteristics of vibrations are usually quantified by measuring the resultant vibration wave amplitude, frequency, velocity, and wavelength. Moreover, the medium of vibration has a significant impact on the mechanism of the structural vibration motion, which depends on the fluid properties and impacted structure geometry.
One of the main assets in electrical power systems is Overhead Lines (OHLs), which are placed outdoors and exposed to various environmental conditions. The most common OHLs wind-induced structural motion is Aeolian conductor vibrations. The solid beam theory is merely implemented to model OHL conductors to predict their vibration response, based on the assumption of homogenized properties. Therefore, two models are considered in this paper:
Computing wind-conductor interaction.
Evaluating the Free Vibration of the conductor’s real design.
Computational Fluid Dynamics (CFD) and Structural Mechanics associated with existing COMSOL Multiphysics® numerical capabilities are a power tool to solve fluid-structure interactions (FSI) and bending response of complex structures. The physical phenomenon considered in this paper is Aeolian Conductor Vibration which implicates the flow of air across high-voltage OHL conductors, which induces Aerodynamic Forces through the vortex-shedding on the conductor’s wake. To model this phenomenon, the structural dynamics of FSI are reviewed in the case of OHLs, to compute the Aerodynamic Forces acting on the OHL conductor. The best application found to assist in building this model is the Fluid-Structure Interaction example found in COMSOL® built-in application library.
On a different study, the free vibrations analysis of the homogeneous and real conductor design is performed to determine the importance of considering the layer-to-layer interaction (using identity/Contact Pairs) and Material Properties as it is the case for OHL conductors. This is achieved by performing free vibration analysis using Structural Mechanics physics of the 3-D model by making use of the vibration Analysis of a Deep Beam example which is found in the application library. The same model is used to analyse the vibration of the real design of OHL conductor geometries and compares the use of Beam and Solid Mechanics interfaces.
The simulation results of the Aerodynamic Forces and Free Vibration Analysis showed good corroboration with the reported experimental data. The complex structure model greatly captured the interaction of conductor layers, which is evidence of the necessity of considering the complex structure of OHL conductors when evaluating their electro-mechanical response. The simulations time and accuracy are highly dependent on the computation capabilities of the utilized computing resources.
|عنوان المؤتمر:||2020 IEEE/PES Transmission and Distribution Conference and Exposition (T&D)|
|مكان الانعقاد:||Chicago, IL, USA.|
|طبيعة المشاركة:||Poster presentation|
|عنوان المشاركة:||Predicting the End-of-Life for OHL Conductors|
|ملخص المشاركة:||The electricity generation and demand have increased rapidly in recent years due to the improved quality of life, developed renewable energy strategies (RES), and electrification of traditional heat and transport energy sectors to replace traditional fossil fuels. To accommodate this trend, electric utilities try to avoid the expensive traditional solution of building new overhead lines (OHLs) and reinforce existing networks through re-tensioning old conductors or reconductoring with High-Temperature Low-Sag (HTLS) conductor technologies. The effect of conductor size, structure, and material properties of its individual components (conductive wires and core) on the vibrations’ response have not yet been captured thoroughly in the literature. The main aim of this study is to perform Finite Element Analysis (FEA) to investigate the effectiveness of modelling the real conductor design and studying its vibration fatigue taking into account the inner-interlayer interaction to predict the end-of-life cycles for different types of OHL conductor designs. The FEA showed that homogenizing the conductor geometry would produce underestimated end-of-life predictions, particularly for bi-metallic conductors. This might significantly affect the asset management strategies in the industry and current-uprating methods for OHL designs constrained to conductor vibrations.|