Valoarea parametrilor curentului trăsnetului în raport cu nivelul de protecţie

When a spark gap (PZH I I/50-50) or a gas discharge tube (PZH I G110) are chosen as class I surge protection, in case of a surge, the current is conducted through the arrester or shorted to the ground. After the conduction begins, the voltage collapses and the arrester should stop conducting, but this does not occur. A so called continuing current starts flowing through the arrester and flows until the current changes the value or passes through zero value. Whether or not the current will be blocked when passing through zero value depends on the capacity for blocking the arc in the arrester. The size of the current depends primarily on the distance between the arrester and the transformer and the type of the connection to the building (overground wires, underground wires, combined wires). For effective protection, the surge arrester has to have an appropriately high capacity of blocking the continuing current. In case of an insufficient capacity, the arrester has to have an appropriate fuse that interrupts the operations of the arrester.

Diagram of dependency of the continuing current on the distance from the transformer

When a varistor is chosen as the class I surge protection, the continuing current does not occur.

The correct choice of class II surge protection depends primarily on the charging system. This also holds true for class I surge protection.

When both class I and class II surge protections are used, an adequate physical distance (at least 10 m of conductor) has to be established between the two. In case this distance is not achieved, induction elements (connecting tubes) have to be installed between the two levels. In case the distance is inadequate or the induction elements have not been installed, class II surge protection may be destroyed in a lightning stroke.