IEC 62073 pdf download.Guidance on the measurement of hydrophobicity of insulator surfaces
1 Scope
The methods described in this technical specification can be used for the measurement of the hydrophobicity of the shed and housing material of composite insulators for overhead lines, substations and equipment or ceramic insulators covered or not covered by a coating. The obtained value represents the hydrophobicity at the time of the measurement. The object of this technical specification is to describe three methods that can be used to determine the hydrophobicity of insulators. The determination of the ability of water to wet the surface of insulators may be useful to evaluate the condition of the surface of insulators in service, or as part of the insulator testing in the laboratory.
2 Terms and definitions
For the purposes of this document, the following definitions apply. 2.1 hydrophobicity state of a surface with a low surface tension and thus is water-repellent 2.2 hydrophilicity state of a surface with a high surface tension and thus is wetted by water (in the form of a film) 2.3 surface tension region of finite thickness (usually less than 0,1 µm) in which the composition and energy vary continuously from one bulk phase to the other Note 1 to entry: The pressure (force field) in the interfacial zone has a gradient perpendicular to the interfacial boundary. A net energy is required to create an interface (surface) by transporting the matter from the bulk phase to the interfacial (surface) zone. The reversible work required to create a unit interfacial (surface) area is the surface tension and is defined thermodynamically as follows:The right side of the above equation (the difference between the surface tensions of the gas-solid and the solid- liquid interfaces) is defined as the surface tension of the solid surface. It is not a fundamental property of the surface but depends on the interaction between the solid and a particular environment. When the gas is air saturated with vapour of the liquid, γ GL will be the surface tension of the liquid. If the contact angle is 0°, the liquid is said to just wet the surface of the solid, and in this particular case (since cos θ s = 1 ), the surface tension of the solid will be equal to the surface tension of the liquid. 2.5 advancing and receding contact angle (dynamic contact angles) angles of a droplet on an inclined solid surface that exhibits two different angles Note 1 to entry: The advancing contact angle ( θ a ) is the angle inside the water droplet between the solid surface and the droplet surface at the lower part of the droplet on the inclined surface (see Figure 2). The receding contact angle ( θ r ) of a droplet on an inclined surface is the angle inside the droplet between the solid surface and the droplet surface at the droplet rear (highest part on the inclined surface). If the receding contact angle is zero, a completely wetted trace of water is formed as the drop moves along the solid inclined surface (see Figure 2). The general physical relation between the advancing and receding contact angle and the static contact angle defined
3 Methods for measurement of hydrophobic properties
3.1 General Three methods for measurement of the hydrophobicity, differing in accuracy, simplicity, size of measured surface area and applicability, are described in this technical specification and are as follows: a) the contact angle method; b) the surface tension method; c) the spray method. Guidance relative to the specific use of the three methods is found in Annex A. 3.2 Method A – Contact angle method 3.2.1 General The contact angle method is a measurement that involves the evaluation of the contact angle formed between the edge of a single droplet of water and the surface of a solid material. If done on a horizontal surface, the advancing and receding contact angles can be measured by adding water to or withdrawing water from the droplet. The contact angles depend strongly on the surface roughness and contact angles measured on polluted surfaces may differ significantly from contact angles measured on smooth, clean and planar surfaces.
IEC 62073 pdf download
