P250G - Low voltage limiter - 50804

P250G and P400G - new types of low-voltage surge arresters, Type 1 VLD-F, meeting the requirements of ČSN EN 50122-1 ed. 2:2011, designed to protect non-normally live metal parts of railway traction power supplies supplied with direct or alternating voltage. They are used to effectively protect persons who may come into contact with these parts during a lightning strike or in the event of a catenary failure. The arrester has high internal resistance when the voltage applied is less than its specified rated value UV DC, and conducts when this level is exceeded. In the event of a fault resulting from a connection between a live part of the catenary supply and a conductive part accidentally connected to the return line, the arrester protects against inadmissible touch voltage by conducting and disconnecting the power supply. According to ČSN EN 50122-1 ed. 2:2011, this type of arrester is primarily recommended for connection between the protected part and the return network of traction lines or in the area of ​​a current collector, which may be in contact with a conductor or a damaged current collector; also on supporting structures of a mast, which may be live following an insulation failure. When the applied voltage drops below a specified nominal level again, the arrester returns to a non-conductive state. The functional part of the P250G (P400G) is a special gas-filled lightning arrester with a shortened response time of 20 ns, rated for three consecutive lightning impulses of 50 kA (10/350). The working chamber of the built-in lightning arrester is equipped with a technically sophisticated hardware protection, the so-called A fail-safe module that automatically switches to short circuit mode (this condition is irreversible) in the event of a prolonged overload of more than 500 A DC (AC). The product is supplied with an integrated bracket, enabling direct mounting of the arrester on a protected metal structure (pole, wall, or flange). A vertical mounting position with the bracket facing upwards is recommended. The arrester can be activated by a surge current or by the current flowing as a result of contact between the protected metal structure and a broken traction wire. In such a case, a potential difference of more than 250 V (applies to the P250G) or 400 V (applies to the P400G) is created between these parts. The built-in lightning arrester will trip immediately (response time is typically 20 ns) and conductively connect both parts for a temporary period (typical internal resistance of a P250G (P400G) lightning arrester is 0.001÷0.002 Ω). This temporary phenomenon ends automatically through potential equalization between the protected structure and the return network, when the lightning arrester trips automatically as a result of gas exchange.