P400GI and P250GI are a new types of low voltage limiters (voltage limiter devices type 1 .... VLD-F) based on requirements of EN 50122-1, which are designed to protect the non-live parts of metallic structures in DC ev. AC traction power supply systems. They are used to effectively protect persons who may come into contact with these parts during lightning strikes or a defect of the tractive overhead line. The limiter has a high internal resistance when voltage on it is less than the nominal level its spark over voltage UVDC and becomes conductive when this level is exceeded.

In case of failure arising from a contact between live parts of the power system and traction conductive portion unintentionally associated with return path limiter protects illegal contact voltage that becomes conductive and causes the power is turned off. According to EN 50122-1, this type of limiter is recommended primarily for connection between the protected area and return circuit in overhead line areas (or pantograph areas) that may be in contact with live conductors or damaged current collector, then the support structures pylons which can become live due to a fault isolation. After re-applied voltage drops below of its nominal level spark over voltage UVDC the limiter returns to the non-conducting state again.  
Functional part P250GI (P400GI) is made using a special gas-filled gas discharge tube (GDT) with shortened response time 20 nsec, rated for up to 3 consecutive strikes of lightning current 50 kA (10/350). On the outer insulating cover is used a light blue silicone rubber. Working chamber of built GDT is equipped with technically sophisticated fail-save mode hardware that provides an automatically transition to short-circuit mode in the event of longtime overloads above 500 A DC (AC) (this state is non-reversible). On the outer insulating cover is used a blue silicone rubber, which is hydrophobic and has excellent resistance against weathering, pollution and UV rays. Mounting bracket, connecting bolts and nuts are made from stainless steel, suitable for connection of conductors with cross section 16-50 mm2 Fe (Cu).

The product is delivered with an integrated bracket, allowing direct mounting of P250GI (P400GI) to the protected metal structure (pillar, wall or flange). Recommended mounting position is vertical bracket up. Limiter is installed directly to a protected building construction (using two bolts M12), so that in the event of its activation was generated a conductive connection between this structure and the return path. The limiter can be activated either by lightning current or current resulting from contact protected metallic structure with a fallen overhead line. In such case there will be a potential difference between these parts, which amounts to more than 250 V (valid for P250GI), or 400 V (valid for 400GI). The in-built GDT ignites instantly (response time is typically 20 ns) and forms a temporary electrical connection between both parts (typical internal resistance of the ignited P250GI (P400GI) is 0.001 ÷ 0.002 Ω). The duration of this transient process is automatically broken up by potential equalization between the protected structures and a return path, when it comes to an automatic switching off GDT due to recombination its gas filling.


1) Products P400GI (P250GI) are maintenance-free, have very little reaction time (20nsec), high insulation resistance (> 1GΩ) and high protective ability. Next is this product resistant against to harsh treatment, acid rain and mechanical damage.

2) To perform diagnostics it is recommended to use measuring instrument G-TESTER (supplier ACER VOLTAGE s. r. o.). This device allows to control the one hand, the DC spark over voltage of the built GDT, then the value of the insulation resistance Riso (from 25VDC up to 1000VDC).