Porcelain Electrical Insulators
Porcelain is a conventional insulating ceramic that has been widely used for many years. It provides good quality electrical insulation at an economical price compared to other engineering ceramics.
Porcelain electrical insulators are commonly used in insulating environments where high mechanical strength and chemical corrosion resistance are not required and it is usually supplied in a glazed (glass coated) form.
Function of Electrical Insulators
The primary function of porcelain electrical insulators is to provide insulation in electrical circuits by physically separating the conductors as well as preventing current flow between them. It can also provide some level of mechanical support, heat dissipation and environmental protection for the conductors.
Porcelain insulators can also be used at elevated temperatures without degradation to their chemical, mechanical and dielectric properties.
Porcelain insulators are characterised by:
- Moderate mechanical strength
- Good creep resistance
- High corrosion resistance
- Excellent electrical insulation
- Good dimensional stability even under loads
- Good abrasion resistance
Porcelain insulators are commonly used in industries such as:
- High voltage
- Refractory plants
The ceramic structure of a porcelain body is a polycrystalline material usually containing more than about 10% of a vitreous (glassy) secondary phase. It is this second phase that controls the strength, density and porosity of the porcelain body, effectively holding all of the particles in the composition together.
The main categories of porcelains are described below:
- Triaxial porcelains – these are largely used as a standard insulator in industry. They have moderate mechanical strength, fair thermal shock resistance and because of their poor high-frequency characteristics they are generally only used for low-frequency applications. The raw material compositions are typically 60% clays, 20-35% feldspar and 20-30% flint. Each contributes different characteristics to the fired porcelain body. The clay provides the main body for the ceramic, controls the firing range and distortion during sintering and provides the first liquid phase in the system. The feldspar provides the main flux phase, lowering the maturing temperature.
- Nonfeldspathic Porcelains – these include steatite, forsterite, spinel, mullite and cordierite. They are all in the system MgO/SiO2 or MgO/Al2O3/SiO2. The raw materials for these are usually kaolin clays and fluxes and these porcelains are typically higher purity than triaxial porcelains having superior dielectric properties. However they are more difficult to produce due to a shorter sintering (maturing) range.