Finally curing agents are added for vulcanization (cross linking). Moreover pigments for obtaining a desired colour as well as silicone oils for processability, are added. Most of the commonly used fillers tend to reduce the price of the silicone. For improving tracking resistance, alumina trihydrate (ATH) is often added. The most common reinforcing filler used is different types of silica. It should be noted that filler treatments as well as filler particle sizes are what tend to distinguish different silicone rubber formulations. These fillers are usually surface-treated to become more chemically compatible with the silicone polymer. Thus it is necessary to reinforce the polymer by adding very fine, high surface area fillers. The silicone polymer, polydimethyl siloxane (PDMS), by itself is relatively weak when cross-linked, forming a brittle transparent rubber. Silicone rubbers used as housing materials usually consist of a number of different additives for obtaining desired properties. For high voltages (HV) silicone rubber is the only non-ceramic solution.ĪBB has today supplied over 1500 high voltage live tank breakers (LTB), over 6500 dead tank breakers (DTB) and over 40000 high voltage surge arresters with very good service experience to totally over 100 countries around the world. For MV surge arresters and MV cable terminations silicone rubber is the dominating insulating material. Today this has been further developed using the hydrophobic epoxies.

For the majority of medium voltage (MV) apparatuses such as instrument transformers, fuses, switches etc epoxy is the main insulating material. Usually the process of producing the insulators sets the requirement on which type of rubber to use.ĭifferent insulation concepts are today used within ABB. Other names used are abbreviations such as LSR (Liquid Silicone Rubber), RTV (Room Temperature Vulcanising silicone rubber) and HTV (High Temperature Vulcanising silicone rubber). Silicone rubber is a generic name commonly used to explain the type of housing material used. The work on part 3 (composite insulators) has just started and is expected to be finished within a few years. Part 1 (general definitions) and part 2 (ceramic insulators) are well on their way. IEC 60815 is under revision and will, when revised, consist of 5 parts. What is not specified is testing the performance under pollution. IEC 61462 specifies both electrical and mechanical tests as well as some aging tests. Test requirements of hollow composite insulators are specified in IEC 61462. There is some work remaining on certain properties such as corona and hydrophobicity. Testing and minimum requirements of the material itself is specified in for the most important properties. Another critical parameter is the design and testing of the insulator and its material. Due to this different additives are added to the formulation in order to protect the polymer. However, silicone rubber is, as most polymers, sensitive to electrical discharges. Silicone rubber as housing material for high voltage transmission lines has proven to have excellent performance under different conditions such as coastal, desert and industrial environments. An example from a substation in South Africa where all the electrical apparatuses are composite can be seen in figure 1 It is not unusual today that utilities choose to buy all the apparatuses with composite insulators when renovating or building new substations. A 132 kV substation in South Africa with composite insulators on all apparatuses. There is however very little information in the literature on aging of composite insulators used on high voltage apparatuses, in particularly on voltages equal to or higher than 145 kV.

As the acceptance for composite insulators in applications for HV apparatuses is increasing, the volume is also increasing. In other applications like dead tank breakers, composite insulators have been used for about 15 years. Composite hollow insulators for high voltage apparatuses such as high voltage live tank breakers are comparatively new. Lightweight, superior pollution performance and increased safety are some advantages of composite insulators. As well for surge arresters were the majority sold today is with non-ceramic solutions. Composite insulators for transmission line applications are today well accepted and are winning an increasing share of the market. The use of composite insulators is increasing as the market accepts the technology.

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