User login

You are here

Alain Cardou's blog

CABLE UNDER AXIAL LOADING: AN ANALYTICAL MODEL

The classical problem of a cable under axial load has been revisited by Weiguo Wu and Xin Cao: Mechanics model and its equation of wire rope based on elastic thin rod theory, International Journal of Solids and Structures, in press, 9 pages. On line 22 october 2016 at http://www.sciencedirect.com/science/article/pii/S0020768316303122 .

Model is applied to a multistrand ccable given in a book by Costello (1990). Axial stiffness results compare very well.   

OVERHEAD ELECTRICAL CONDUCTORS IN BENDING : A SEMI-CONTINUOUS MODEL

As indicated in the review by Cardou & Jolicoeur (1997), and depending on the application, a helically stranded system may be modelled using a semi-continuous approach whereby each layer is replaced by a continuous helical orthotropic material. For those able to read Russian, this approach is presented in a paper by Danilin & Al. specifically oriented towards Overhead Electrical Conductor mechanics: “Modelling of Deformation of Wire Spiral Structures” published in the PNRPU Mechanics Bulletin (2015, No 4, pp.

OVERHEAD ELECTRICAL CONDUCTORS IN BENDING : NEW TEST DATA

A paper by Kubelwa et al. (Statistical Modelling of Bending Stress in ACSR Overhead Transmission Line Conductors subjected to Aeolian Vibrations –I) reports data from vibration tests on 4 ACSR.  under  3 axial loads (20, 25 and 30% UTS). An 84.5 m conductor span is vibrated at various bending amplitudes and strain is measured near a clamped end (distance not given). Clamps are rigid square-faced bushings. Vibration amplitude is measured at 89 mm from bushing. Strain gages are glued on 3 adjacent top layer wires.

Overhead Electrical Conductor in bending: Papailiou's model revisited

 In a paper to appear and available online,( An analytical approach to model the hysteretic bending behavior of spiral strands, Applied Mathematical Modeling 2016, http://www.sciencedirect.com/science/article/pii/S0307904X16300592 )

Cable bending stiffness: new test data

A new paper by Chen et al.: Experimental research on bending performance of structural cable. In: Construction and Building Materials, 15 October 2015, Vol. 96, pp. 279-288. Equivalent bending stiffness has been obtained applying a force at midspan of simply supported, about one meter long, specimens. A number of tensile force levels have been applied (including zero). Non-linear force-deflection curves are shown.

Overhead Electrical Conductor fatigue testing: a new standard

The International Electrotechnical Commission (IEC) just released a new international standard titled: "Overhead lines - Method for fatigue testing of conductors". IEC 62568. Edition 1.0 2015-07. www.iec.ch . It closely follows previous CIGRE and EPRI publications on this topic:

CIGRE SC B2 WG11 TF7 "Fatigue Endurance Capability of Conductor/Clamp Systems - Update of Present Knowledge" CIGRE TB 332, 2007, Paris.

A cable bending stick-slip analytical model

Single strand cable bending, stick-slip, analytical models require that a choice be made between two contact modes between adjacent wires: either radial (between layers) or lateral (between same layer wires). In most recent models (e.g. Papailiou’s) radial contact is selected. A “lateral contact” model has been presented by Panetti in 1944 and can be found in the proceedings of the Turin Royal Academy of Science. A translated version from Italian is proposed in the attached file.

Helical Strand Mechanics Modelling

Some 2014 papers on the mechanics of helical strands: cables and electrical conductors

Cable FEA modelling

A 2014 paper on cable FEA modelling

Coupling in taut helical strand bending

Usually, taut helical strand bending is dealt with by decoupling axial load and bending analysis. In the attached report,  based on a purely geometrical approach, it is shown that there is indeed some coupling, albeit small.

An early stick-slip model for cable bending analysis

One approach to helical strand (cable or overhead electrical conductor) bending analysis puts the emphasis on friction rather than on elastic curved rod behavior. Based on Coulomb’s laws of friction, it leads to stick-slip models where strand  bending stiffness varies with imposed curvature (Papailiou, 1995). Such an approach can be traced back to a Ph.D. thesis by H. Ernst, in 1933. This work is in fact often referred to in cable analysis reports. An English translation (with a short presentation) of the dissertation analytical part is attached.

Helical Strand in Bending

Several approaches have been used to deal with the complex problem of helical strands in bending. One of them is based on Love’s curved rods theory. It has first been used by Costello in his classical monograph “Theory of Wire Rope”. It has been extended by Sathikh et al. in several papers. A new contribution from this group is a Ph.D. Thesis by D. Gopinath : “Some studies on bending response of the stranded cable under free bending and constrained bending”, Anna University, Chennai (India), October 2013, 121 pages.

Fatigue of Overhead Electrical Conductors

A new paper on  the OEC fatigue problem: “Determination of Early Failure Sources and Mechanisms for Al 99.7% and Al-Mg-Si Alloy Bare Conductors Used in Aerial Transmission Lines”, by S. Karabay and E. Feyzullahoglu. Paper has been accepted for publication in March 2014 in the “Engineering Failure Analysis” journal. Abstract can be found on-line:  http://dx.doi.org/10.1016/j.engfailanal.2013.12.002

CABLE BENDING ANALYSIS THOUGH FEA

Single strand cable (spiral) bending and OEC (Overhead Electrical Conductor) bending are somewhat similar problems. This is the reason why the following new paper is noteworthy within the context of this blog. It emanates from a Slovak team: S. Kmet, E. Stanova, G. Fedorko, M. Fabian, J. Brodniansky. Title : “Experimental investigation and finite element analysis of a four-layered spiral strand bent over a curved support”. Published in “Engineering Structures”, Vol. 57, December 2013, pp. 475-483.

Overhead Electrical Conductors

I just discovered (thanks to Dr K.O. Papailiou) this interesting 2007 paper on helical strand mechanical modelling. It is an up-to-date (and apparently quite exhaustive, except for non-English language contributions) review on the subject by T. Manvel Raj and N.S. Parthasarathy, of India. Its title: “A Complete Review on Friction Models of Composite Cables”. It was published in a Russian Academy of Applied Mechanics and Sciences journal, the International Journal of Mechanics of Composite Materials and Constructions, Vol. 13, No 3, pp. 356-384. Here is the Abstract:

Overhead Electrical Conductors

Stick-slip model (based exclusively on Coulomb’s laws of friction) for conductor bending may be improved by taking into account actual inter-layer contact conditions: elliptical contact areas with tangential elasticity and micro-slip regions. Starting with Papailiou’s model, this has been done by Paradis and Légeron. Work was presented in 2011 at the 9th International Symposium on Cable Dynamics, held in Shanghai (China).  Model has been applied to variable curvature case using FEA (in a Matlab environment). Numerical results are compared with Papailiou’s experimental  results.

Bending of cables : a stick-slip model

Bending of cables and, for that matter, of any helical strand system (such as overhead electrical conductors) is a challenging solid mechanics problem, with geometry and multibody frictional contact aspects. As seen in several recent papers, one workable approach is based on Coulomb’s laws of friction.  An earlier contribution by Lehanneur (1949), published in French, has generally been  ignored. The attached report presents a translation into English (including a presentation) of this most interesting work.

Overhead Electrical Conductors and High Intensity Wind

Effect of tornadoes on electrical power lines has been discussed by Sébastien Langlois in his M.Eng. thesis : “Design of Overhead Transmission Lines subject to Localized High Intensity Wind”. McGill University, Montreal, QC, Canada, 2007 (available on-line on the “Theses Canada” portal). Work presents various national and international standards (ASCE, Cigré, IEC etc.), historical cases, as well as models for numerical simulation.

Aeolian vibrations and fatigue of Overhead Electrical Conductors

An interesting presentation of the state of the question by  Dr Louis Cloutier, in 2008.

Overhead Electrical Conductors

In the review paper by Spak & al. (January 2013) on cable bending mechanical models, one class of models was not specifically mentioned, in which authors attempt to take into account the tangential elasticity at points of contact between cable layers. There are at least two noteworthy contributions:

Cables and Overhead Electrical Conductors

Cable  and Overhead Electrical Conductor mechanical models are closely related. This can be seen from a recent review (January 2013) by Spak, K., Agnes, G. and Inman, D. : Cable Modeling and Internal Damping Developments, in the ASME journal Applied Mechanics Reviews, Vol. 65. The 18 pages paper, with its 86 references, has an interesting section on bending stiffness, with a rather (comparatively) extensive presentation of Papailiou’s stick-slip model. Use of the Coulomb spring-slider model for internal damping prediction is also presented.

Overhead Electrical Conductors

In elementary mechanics textbooks, power lines are generally given as a typical example of a so-called “flexible cable”. However, in the design of these critical elements of a power grid  it is often necessary to take into account the conductor bending stiffness, or flexural rigidity. While relatively low compared with a bar having an equivalent solid cross-section, it does have some influence on a conductor response to wind excitation, in particular from the fatigue strength point of view.

Overhead Electrical Conductors

As a follow-up, here is a photograph of a (rather extreme) case of conductor fatigue.

Overhead Electrical Conductors

Mechanics of overhead electrical conductors under wind excitation is a complex problem . It is described in detail in  the following book:

EPRI Transmission Line Reference Book: Wind-Induced Conductor Motion. Second Edition. EPRI. Palo Alto, CA. 2009. 1018554.

EPRI : Electric Power Research Institute.

Subscribe to RSS - Alain Cardou's blog

More comments

Syndicate

Subscribe to Syndicate