2017-09-SMH-RPLF

Gas discharge tube (GDT) arresters provide protection to electrical systems from lightening induced voltage surges. They are designed to have a short circuit path when the voltage across it exceeds a certain threshold. The arrester is placed in series with the protected equipment, as it is sensitive to both lightning and electrical transient voltages. In the de-energized state, the GDT operates as an open circuit but at the moment when the voltage exceeds the threshold level (pre-defined by the manufacturer) the arrester discharges the excess voltage into the atmosphere. The current is then dissipated safely and the GDT returns to its open state.

The 2017-09-SMH-RPLF application field is placed in series with downstrean loads, such as telecommunications equipment, electrical or electronic components, cables, or even residential homes, providing effective protection in both lightning and electrical transient events.

Working principle behind GDTs can be described as: Two electrodes are placed within a sealed chamber filled with a rarefied gas such as Nitrogen. The electrodes are separated by a protective insulating material often referred to as a ‘gap’. Under normal operating conditions, the potential difference between both electrodes is so low that no current flows as no ionization of the gas can take place. This means the guard gap acts as an open circuit.

When the external voltage exceeds the breakdown voltage of the GDT, the guard gap suddenly reduces to very small dimensions becoming a highly conductive region. Electrical current is generated in the gap due to the emission of electrons and they accelerate into the gap to collide with the positive ions. These impacted ions and the electrons dispersed in the gas form a conductive path within the gap and allow the arrester to function as a short circuit. This process is known as the \'avalanche effect\' or \'streamer emission\'.

Once the peak of the transient surges has passed, the current through the GDT reduces and the avalanche subsides. This reduces the guard gap size and the arrester again returns to its open circuit. With a sufficiently high current, the electrodes of the GDT can suffer erosion. Therefore, it is important to choose the correct GDT for the specific application. Additionally, as GDTs are susceptible to operation in humid environments, it is critical to monitor the humidity within the system.

It is important to remember that GDTs are not designed to protect against direct lightning strikes and should be used in combination with a surge diverting device, such as a tower arrestor, to ensure adequate protection.

In summary, the 2017-09-SMH-RPLF application field provides effective protection to downstream loads from lightning and electrical transient events using the Gas Discharge Tube Arresters. These gas-filled tubes work on the principle of the \'avalanche effect\' and short circuit high voltage surges and quickly return to the original open state when the peak of the transient has passed.