From 2002, we have set up a new line of composite insulators. We manufacture our composite insulators with HTV (High Temprature Vulcanized) silicone rubber housing and sheds in collaboration with NRI (Niroo research institute), a sub organization of ministry of energy.
Composite insulators were introduced in the late sixties. The basic idea consists of the combination of different materials, which perform different duties in the insulator function corresponding to their particular strength and properties (Fig. 1).
Fig. 1: Parts of a composite insulator
The end fittings are typically made of metal, such as forged steel or aluminum. For line insulators, a high degree of standardization has been achieved for the end fittings, which enables the easy replacement of existing conventional insulators by composite solutions.
The fiberglass reinforced resin rod is responsible for bearing the mechanical loads, which can be tension, bending or compression, or a combination of all three, depending on the application and load scenario.
Materials for the housing are as manifold as the corresponding methods of manufacturing. However, there are performance trends as a result of the existing service experience, details of which are provided later.
Today these composite insulators made of high-grade synthetic materials have exhibited outstanding mechanical and electrical characteristics, and have exceeded all overhead line and switch gear engineering applications in more than 50 countries worldwide.
– Excellent for High contamination applications
– Reduced weight in comparison with porcelain or glass insulators
– High flexibility and shock resistance
– High tracks and power arcs resistance
– High safety where vandalism is a problem
– High creepage on a short length
– Excellent behavior in polluted areas
– Resistant against atmospheric variations
– Self extinguishable with low toxicity index and smoke emission.
– Compact line applications
The modular principle was invented in the early sixties and has been continuously perfected since then. It combines the advantages of the HTV-Silicone Rubber technology with the high flexibility of easy adaptation to specific insulator dimensions (especially the ratio between creepage and striking distance – Fig. 2). As a result of having several pre-processes for the “modules”, this process cannot directly compete with injection molding in terms of cost, despite a high degree of production automation for the individual processes.
Fig. 2 : The advantage of “Modular”
Clamping moulds or machines are used to apply the sheds to a rod with extruded silicone rubber housing. It has proven beneficial for the inner diameter of the sheds to be smaller than the outer diameter of the extruded silicone rubber housing. The resulting press fit stabilises the shed position until the silicone rubber used to achieve an adhesive bond between the sheds and shanks has been fully vulcanised (often known as ‘‘silicone adhesive’’). To secure the interface between two vulcanised silicone elastomers, the specific property of silicone rubber is used to achieve chemical vulcanisation of three physically independent components through the use of an additional silicone elastomer. Figure. 3 shows the ‘‘chemistry’’ for an acetate system (RTV-1) that reacts when acetic acid is released. The fine-particle silica (HDK) in silicone rubber plays an important role here: Since not all hydroxyl groups of HDK react during vulcanisation of the sheds and the shank material, they are available for subsequent reactions. The silicone adhesive (RTV-1 or RTV-2 system) applied where the shed is positioned or applied liberally over the shank reacts with the HDK and produces an adhesive composite. Bonds are also created without the direct presence of water. To document the interface strength, a colourant was added to the RTV-1 used in this case before it was applied. It shows that an interface fracture occurs in the extrudate when sheds are mechanically separated and detached. No colourant is visible at the positions where sheds have been detached.
Fig. 3 Chemistry for the vulcanisation of pre-fabricated HTV semi-finished parts with an acetate-vulcanising RTV-1
Nowadays, the modular principle is considered as an excellent method for the production of standard insulators, with great deal of technical advantages compare to other methods and serves as a suitable, proven alternative method for DC applications requiring high creepage distance.
Sassani’s composite insulators up to 63 KV have been tested at CESI laboratories Italy according to IEC 61109 standard. 132 KV composite insulators tested by Abbaspour university and Niroo Research Institute in Iran.