Strings for Transmission Lines

Insulator strings for high-voltage overhead transmission lines provide the mechanical insulator system between the live conductors and the pole.

The biggest share of the string is taken by the insulators, which are made of porcelain, glass or composite materials.

The connecting elements, which are also called fittings in technical jargon, guarantee mechanical connection of all the components.

Depending on their positioning within the string, the fittings of insulator strings will be classified differently. Thus they will be called pole connection fittings, connecting fittings, protective fittings or conductor fittings. The pole connection fittings establish the mechanical transition to the extension arm of the pole.

Protective fittings has the tasks to minimize the electric field and thus prevent annoyance due to noise caused by the corona phenomenon and to control the electric light arc in case of spark-over in order to prevent thermal overload on the insulator. Conductor fittings are defined as being all the fittings that are in direct contact with the conductor. The remaining fittings are regarded as being connecting fittings.

In order to guarantee the best possible operating safety, all the components of an insulator string will have to be dimensioned according to the mechanical and electric requirements of the respective line parameters.

A factor decisive for mechanical design is formed by the line specific load cases, which are country specific as well as project specific. Strings in a level desert area will have other static constant loads than, for example, strings in high mountain regions.

Insulator strings are not only exposed to static loads but also to dynamic loads, which are, for example, caused by many kinds of vibrations and oscillations or short-term dynamic load peaks due to ice dropping.

Still another aspect is thermal load, which will lead to heating of the components in case of short circuit and can be avoided in order to prevent a complete rupture if the string is designed adequately.

In the field of insulator strings, Mosdorfer offers complete systems that will be optimized on the basis of the provided line parameters and pole patterns in order to guarantee a long product life cycle.

As the influencing factors, such as insulator type, connecting dimensions, loads, conductor type and arrangement or short-circuit currents are so different, it is hardly possible to standardize insulator strings. Therefore, each insulator string will have to be designed specifically to the customers’ needs and requirements.

Due to a changed environment, new requirements are placed on insulator chains in terms of mechanical carrying capacity, the mechanical behavior at low temperatures and resistance to short circuits.