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Extremely low frequency field safety
Published in Riadh Habash, BioElectroMagnetics, 2020
Passive shielding includes shields made of materials that are either conducting or ferromagnetic, as well as both, so that both passive shielding mechanisms are involved. Examples of conducting shields are enclosures or barriers made of typical non-ferromagnetic metals, such as copper or aluminum. Metals are the most conductive materials where metallic surfaces and/or grids insulate electromagnetically by reflecting backwards upcoming EM waves due to their free electrons. As discussed in Chapter 1, if the charges exist in a medium that permits the charges to move, the medium is considered conductive and the field can be adjusted in magnitude and direction with the movement of the charges. At ELF fields, air has a conductivity of less than 10−9 Siemens (S), while metals have conductivity greater than 107 S. The human body has a conductivity that ranges from 0.01 to 1.5 S [6]. Owing to the huge difference in conductivity, placing any grounded metallic surface between the electric field source and user will eliminate the electric field. The metal surface can be an inexpensive mesh chicken wire screen.
Insulation Strength Characteristics
Published in Andrew R. Hileman, Insulation Coordination for Power Systems, 2018
To determine the SI strength of a tower, a full-scale simulated tower is created in a high-voltage laboratory. This simulated tower shown in Fig. 1 is constructed of 1 inch angle iron covered with 1 inch hexagon wire mesh (chicken wire) to simulate the center phase of a transmission tower [17]. A two-conductor bundle is hung at the bottom of a 90-degree V-string insulator assembly. Switching impulses are then applied to the conductor with the tower frame grounded. First note the parameters of the test: (1) the strike distance, that is the clearance from the conductor to the tower side and the clearance from the yoke plate to the upper truss, (2) the insulator string length (or the number of insulators), (3) the SI waveshape (or actually the wavefront), and (4) wet or dry conditions.
Regulatory Activities and Safety Trends
Published in Riadh W. Y. Habash, Electromagnetic Fields and Radiation, 2018
As discussed in Chapter 1, if the charges exist in a medium that permits the charges to move, the medium is considered conductive and the field can be adjusted in magnitude and direction with the movement of the charges. At ELF fields, air has a conductivity of less than 10−9 siemens, while metals have conductivity of greater than 107 siemens. The human body has a conductivity that ranges from 0.01 to 1.5 siemens [25]. Due to the huge difference in conductivity, placing any grounded metallic surface between the electric field source and user will eliminate the electric field. The metal surface can be any inexpensive mesh chicken wire screen.
Parametric investigation on the post-fire flexural behaviour of novel ferrocement panels with geopolymer mortar
Published in European Journal of Environmental and Civil Engineering, 2023
[—Volume fraction of reinforcement, —Number of layers of mesh, —3.14, —diameter of mesh wire, —Thickness of ferrocement element, —Distance center to center between longitudinal wires, —Distance center to center between transverse wires.] For other type of mesh (hexagonal or chicken wire, expandable metal, fibre reinforced plastic—FRP or irregular meshes) Equation (2) is adopted (ACI, 1997; IFS, 10).
Effects of the wire mesh on pulsed eddy current detection of corrosion under insulation
Published in Nondestructive Testing and Evaluation, 2023
Zhiyuan Xu, Zhen Zhou, Hanqing Chen, Zhongyi Qu, Jixiong Liu
The wire mesh is typically welded or woven by wire strands made of mild steel, stainless steel or aluminium. For now, whether it impacts the CUI detection remains ambiguous. It was reported in [22] that embedding chicken wire in the insulation typically increases the footprint size by about 40%, while in [23] it was pointed out that the wire mesh is not a limitation and does not create any issue for the PEC results. This ambiguity motivates us to investigate whether and how the wire mesh affects the PEC probe’s performance in CUI detection. Numerical simulations were conducted to provide visualised eddy current distribution which helps examine the effects of the wire mesh on the probe footprint size and the probe detection capability to CUI. Subsequent experimental verification was carried out to support the simulation results.