Composite Hollow Insulators
In generation, transmission and distribution of electric energy, for technical reasons, it’s necessary to vary the voltage level of the electricity and to measure and monitor it. This is done by using specific electrical apparatus, static or rotating, to pass from medium voltage of the generation to the high voltage of transmission and back to the medium and low voltage for distribution but also for measuring, metering and for protection and interruption of electric networks.
Insulators are used in all these electrical apparatuses: their aim is to insulate two metal parts with different voltage levels (usually one is grounded) in order to avoid short-circuits which cause the breakdown of the network or damages and destruction of electrical apparatus.
TCI is able to supply hollow composite insulators as well as assembled bushings which use SF 6 as insulating media.
Bushings are used to carry conductors, at live voltage, inside all types of electrical apparatus such as transformer, switchgears or a bus-duct and through building walls.
Bushings are grouped into non condenser and condenser and among the latter are divided considering their application into air-to-air bushings, air-to-SF6, air-to-oil, through-wall (etc…) and their insulating media (gas insulated, RIP, OIP). For the composite insulator it’s important to know the insulating media and the specific application as well as the pollution level, altitude installation and so on.
In high and very high voltage applications, SF6 gas is often used as insulating media since it is non-ageing, non-poisonous, non-flammable, has good dielectric, arc-quenching and thermal capabilities and it’s possible to control the dielectric strength through its density (by a pressure compensated device).
Insulators are divided into porcelain or composite insulators, with silicon housing for outdoor applications or without housing for indoor applications or inside the apparatus (usually vacuum-impregnated).
Composite insulators manufacturing complexity is increasing exponentially as the rated voltage increases; for this reason, electrical and mechanical design must be very accurate. Also their manufacturing must be implemented with the highest accuracy and precision possible to avoid any minor problem or defect which could cause catastrophic effects (flashovers and/or apparatus fault)
Most insulators currently in use are porcelain ceramic insulators, but over the last decades composite insulators – that were developed 30 years ago - have increased their market share, which is constantly increasing for their important advantages:
· safety for workers and apparatus. Because of their design, materials and technology of manufacturing, hollow composite insulators can’t explode like porcelain insulators in case of fault. Porcelain is a very rigid and brittle material and in case of a manufacturing defect (not always possible to detect) or for a high thermal stress, can break. For gas insulated apparatus in normal service conditions (usually service pressure is 8-9 MPa) or under internal overpressures (above 1,2 MPa) , the fault of a porcelain could mean a real explosion with “porcelain bullets” thrown at high distances. Fault of composite insulators, if any, is a yielding of fibers which lead to the release of the internal pressure or overpressure. This is for sure one of the main advantages of hollow composite insulators in comparison with porcelain insulators, considering the usual presence of people working in the installations but also nearby private houses and offices;
· high hydrophobicity of the silicon which means no need to wash their housing from time to time (less maintenance costs);
· very short lead time of composite insulators manufactured in TCI HV Division in comparison to average lead time of high voltage porcelain insulator manufacturers;
· Lighter weight compared to porcelain insulators and this is a double advantage in terms of cheaper transportation costs and of possibility to design leaner (that means less expensive) electrical apparatus;
· composite insulators are less fragile compared to porcelain insulators and this make their handling much easier and faster during the assembly of apparatus or during their installation in service, moreover, in case of damage of the silicon shed, very often it can be repaired.
