AC Stray Current and Environmental Effects on Concrete Power poles

Authors
A. Aghajani
M. Golozar
A. Saatchi
S. Shabani
Isfahan University of Technology
Abstract
The purpose of this article is study of effects of high voltage AC stray current (380 VAC) and environmental effects on durability of concrete power poles. In Iran, annually spend large costs for replacing them with new concrete poles. In this study, the degradation effects and mechanisms of 380 VAC stray current on water saturated concrete were investigated via field and laboratory tests. They included electrical and electrochemical tests and microscopic inspections. Based on the results of tests both environment and AC stray current reduce durability of the concrete power poles. Formation of galvanic macro cell, carbonation, vibration of concrete pole due to wind force and weight of cable, diffusion of corrosive ions from soil to concrete power pole and its accumulation in near ground level are some of environmental effects on degradation of concrete power poles. In addition pollution of air can form deposit layer on insulations of concrete power pole. In raining condition, the layer absorbs water and surface resistance of insulators reduces considerably. So high voltage AC current can creep in surface of the insulator and can exchange between two other phases and ground. Generally grounding system can't act immediately or have not suitable low electrical resistance. Meanwhile if concrete of power pole has low quality then it absorbs high content of rain and its resistivity decreases considerably. Thus some parts of fault current can pass through water saturated concrete power pole. In an special location around Isfahan with polluted air condition, in raining condition current creep through the surface of some insulators occur and immediately many cracks forms on concrete cover of power pole and in some cases concrete cover start to fall without any corrosion in rebar. Based on field study, AC stray current does not occur in concrete power poles which manufactured by centrifugal method and they have very low w/c ratio in their mix design. In this method excess water of concrete mix is removed before staring curing of concrete. Microscopic study of concrete of the molded pole and centrifugal pole showed that the later had much denser structure and for this reason depth of carbonation in the later was much lower than the first. In addition the centrifugal poles have pre-stress condition and it reduce their vibration against wind force and weight of cables. Vibration has destructive effect on concrete cover of concrete poles, special in their ground level because force of vibration concentrates in this location. For study mechanism of degradation of AC stray current, some concrete samples prepared and in water saturated condition subjected to 380 VAC stray current. Based on results of tests, high voltage AC stray current can reduce the concrete pole durability by thermal and shrinkage stress and also by creating vapor pressure within water saturated concrete and transport calcium hydroxide toward cement paste-aggregate interfaces. Application of new technology for reducing water to cement ratio and proper installation and maintenance of the concrete poles considerably increases durability of them against destructive effects of AC stray current.

Keywords

Colin Bayliss and Brain Hardy, Transmission and
Distribution Electrical Engineering, fourth ed., USA,
Elsevier Ltd, 2012, chapter 6.
[2] NACE International Publication 01110, Stray-Current-
Induced Corrosion in Reinforced and Prestressed Concrete
Structures, NACE International, USA, 2010, pp.1-34
[3] Aghajani1, A. Saatchi, M. A. Golozar, K. Raeissi,
“Electrochemical Impedance Spectroscopy Study of
the Effects of High Voltage AC Stray Current on
Concrete” Journal of transportation research, article
No. 1370-91, 2012, accepted.
[4] Aghajani1, A. Saatchi, M. A. Golozar, K. Raeissi,
“Effects of stray current on reinforcement concrete
structures in urban and industrial installations” Zang
Journal, acceptance letter No. 91-1578, 2013, accepted
[5] Aghajani1, A. Saatchi, M. A. Golozar, K. Raeissi,
“Application of Electrochemical Impedance
Spectroscopy in study concrete microstructure” Zang
Journal, acceptance letter No. 91-1555, 2013, accepted
1- Cross arm
A. Saatchi, A. Aghjani,“Interference Problems and nonuniform
potentials in CP of a complex Installation”
Materials Performance, Dec.2005, pp.22-25.
[6] Saatchi, A. aghajani, “Correcting Non-uniform
Potential distribution and Interference Problems in the
Cathodic Protection System of a Gas Compressor
Station” Corrosion 2013 Conference, Document
Number: C2013-0002108, 2013, accepted.
[7] TxDOT Designation: Tex-617-J, Test Procedure for
Determining Chloride in Concrete, Texas Department
of Transportation, 2005
[8] ASTM C876, Standard Test Method for Half-Cell
Potentials of Uncoated Reinforcing Steel in concrete,
Astm International, USA, 2012.
[9] John H. Bungey, Stephen G. Millard & Michael
G.Grantham, Testing of Concrete in Structures, forth
ed., USA, Taylor & Francis, 2006, pp. 185-190
[10] Luca Bertolini, Bernhard Elsener, PietroPedeferri,
Rob Polder, Corrosion of Steel in Concrete, first ed.,
Italy, Wiley-VchVerlag GmbH & Co. KGaA, 2004,
pp. 277-282, 291, 43, 82, 4, 23-26, 6-8
[11] Meilun Shi, Zhiyuan Chen, Jian Sun, “Determination
of chloride diffusivity in concrete by AC impedance
spectroscopy” Cement and Concrete Research, Vol.
29, 1999, pp. 1111–1115
[12] R. Vedalakshmi, V. Saraswathy, Ha-Won Song, N.
Palaniswamy, “Determination of diffusion coefficient
of chloride in concrete using Warburg diffusion
coefficient” Corrosion Science, Vol.51, 2009, pp.
1299–1307
[13] Roar Myrdal, Rescon AS, “Phenomena That Disturb
the Measurement of Potentials in Concrete” The
NACE International Annual Conference and
Exposition, paper No. 339, March 24 - 29, 1996
[14] Kyung-Man Moon, Sung-Yul Lee, Myung-Hoon
LEE, Yun-Hae Kim, “Effect of W/C ratio and cover
thickness on polarization characteristics of embedded
steel in mortar” Transactions of Nonferrous Metals
Society of China, Vol. 19, 2009, pp. 909-912
[15] P. Kumar Mehta Paulo J. M. Monteiro, Concrete
Microstructure, Properties, and Materials, third ed.,
USA, McGraw-Hill, 2006, pp. 24
[16] W. Bogajewski, F. Dawalibi, Y. Gervais, “Effects of
sustained ground fault current on concrete poles”
IEEE Transactions on Power Apparatus and
Systems, Vol. PAS-101, No. 8, August 1982.
[17] R. Vedalakshmi R. Renugha Devi Bosco Emmanuel
N. Palaniswamy “Determination of diffusion
coefficient of chloride in concrete: an
electrochemical impedance spectroscopic approach”
Materials and Structures, Vol. 41, pp. 1315–1326
Modares Civil Engineering journal
Volume 14, Issue 2
July and August 2014
Pages 1-12