Dimensiong of isolating mast
S – изоляционное расстояние - S – isolation gap
Диэлектрические держатели - Dielectric holders
Металлический токоотвод - Metal down conductor
Изолирующая стойка - Isolating mast
Защищаемая антенна - Protected antenna
Металлическая заземленная стойка антенны - Metal grounded antenna
Связь с системой уравнивания потенциалов - Connection with the potential equalization system

When discussing the dimensions of isolating mast in the isolated lightning protection systems, it is necessary to start with the flashover voltage of the lightning mast. Two fundamentally different options are available in the current situation. In the first option, a completely isolated lightning protection system is considered, when the lightning current is introduced into a ground terminal specially provided for this purpose that is isolated from the ground terminal of the protected structure at a distance that prevents a really significant conductive coupling through the soil. In the second option, the facility's own ground terminal is used for the current discharge. It is quite obvious that the isolation requirements for lightning mast are more stringent in the first option, when the lightning current passes the facility's ground terminal and therefore all its metal elements are exposed to almost a zero potential, while the lightning mast potential is determined by the sum of voltages on the individual ground terminal and the related down conductor.

If the mast is completely dielectric and does not have any metal reinforcement, its flashover voltage is not very different from the breakthrough voltage of an air gap of the same length with a sharply inhomogeneous electric field distribution.

Read more in our article "Feasibility of isolated lightning protection".

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