GAS DISCHARGE TUBES & GAS FILLED SPARK GAPS

As a manufacturer of gas arresters and gas-filled spark gaps, CITEL has a wide range of products that most configuration requirements and specifications to the market:

  • Gas tubes in 2- and 3-electrode configuration
  • flashover voltages from 75 to 3500 V
  • Dissipation capacities from 5 to 150 kA (8/20 μs)
  • Optional external short circuit element
  • Mounting on supports, printed circuit boards or surface mounted components possible.



Technology & Functionality

Gas discharge tubes and gas-filled spark gaps consist of two or three electrodes in a housing filled with a (non-radioactive) noble gas. A defined pressure prevails in this housing. The housing is a ceramic tube closed at the ends by metal caps which also serve as electrodes. They are mainly used to protect telecommunication lines, but are also suitable for other applications.





Hibernation:
This is characterized by a practically unlimited high insulation resistance.

Glow discharge:
At the response voltage the conductivity increases abruptly. If the current derived from the gas discharge tubes is less than about 0.5 A (this is an approximate value depending on the component), the glow voltage at the terminals is in the range of 80-100 V.

Arcing:
As the current rises, the arc voltage (approx. 20 V) is established across the gas discharge tubes instead of the glow voltage. The gas arrester is most effective in this operating state because the discharged current can reach several thousand amperes without the arc voltage applied to its terminals rising.

Extinguishing:
At a bias voltage approximately equal to the glow voltage, the gas arrester returns to its original insulating properties.




Electrical properties

A gas discharge tube is characterized by the following main electrical properties:

  • DC flashover voltage (V)
  • Pulse flashover voltage (V)
  • Leakage current strength (kA)
  • Insulation resistance (GΩ)
  • Capacity (pF)

DC-overvoltage:
This is the most important parameter that describes the operating behaviour of a gas discharge tube. It is the voltage at which a voltage flashover occurs between the electrodes when a slowly rising voltage (dV/dt = 100 V/s) is applied to the component. It depends on the distance between the electrodes, the pressure and the properties of the gas mixture and the emitting substance.

**Available DC surge voltages

  • Minimum voltage: 75 V
  • Medium voltage: 230 V
  • High voltage: 500 V
  • Very high voltage: 1000 to 3000 V

The tolerance range of the flashover voltage is generally ± 20%.





Leakage current:
This size depends on the gas properties, the volume and the electrode material and its treatment. The leakage current is an important parameter of a gas arrester and distinguishes it from other protective components such as varistors or Z-diodes. For standard components it is between 5 and 20 kA with an 8/20μs pulse. The component can withstand this current repeatedly (for typically ten pulses) without being destroyed or its basic specifications changed.

Pulse flashover voltage:
Flashover voltage in the presence of a steep rising edge (dV/dt = 1 kV/μs): The pulse flashover voltage increases with increasing dV/dt-value.

Insulation resistance and capacity:
These parameters make the gas arrester practically "invisible" in a power line that is in a steady state:
The insulation resistance is very high (>10 GΩ), the capacitance very low (<1 pF).

3-electrode configuration

If a two-core cable (e.g. a telephone line) is protected with two gas arresters in a 2-electrode configuration, each connected to one wire and earth, the following problem may occur:
A common mode overvoltage occurs on the line. Because of the scattering of the flashover voltages (± 20%), the flashover of one of the two gas arresters occurs very shortly (a few microseconds) before that of the other. Thus, the wire that caused the flashover is grounded (neglecting the arc voltages), which turns the common mode overvoltage into a differential overvoltage. This is very dangerous for the terminal equipment to be protected. This danger no longer exists only when the second gas arrester also causes the flashover (a few microseconds later). The 3-electrode configuration eliminates this disadvantage. The flashover of one pole triggers a "general" flashover of the component almost instantaneously (within a few nanoseconds), since all electrodes are in the same gas-filled housing.

End of service life

Gas discharge tubes are designed to withstand multiple pulses non-destructively or without loss of their initial characteristics (typical pulse tests use ten 5 kA pulses of each polarity). On the other hand, a sustained high current (e.g. with a RMS value of 10 A for 15 seconds, which corresponds to the case where a high-voltage overhead line falls on a telecommunications line) defi nitively destroy the component. If fail-safe behaviour at the end of the operating life is desired (where a short circuit signals a line malfunction to the user upon detection), gas arresters with this fail-safe function (external short circuit) should be selected.

Standards

The CITEL gas discharge tubes meet the specifications of the most important telecommunications operating companies (Deutsche Telekom, France Telecom, British Telecom, etc.) as well as the international recommendation ITU-T K12 and the IEC 61643-31x.
standards.

Mechanical properties

CITEL gas discharge tubes are available in different mechanical Configurations are available to adapt to the desired setting:

  • Blank version for mounting adapted support
  • Version "S" wire output (diameter 0.8 or 1 mm) for Mounting on printed circuit board
  • SMD "-version for surface mounting, with optional" SQ " (anti-roll rectangular electrode version).

Surface mounting
Most of the CITEL range of gas discharge tubes are available for surface mounting (SMD), with optional square electrode (SQ) anti-rolling" version. The welding profile with reflow must follow the recommended curve (opposite).
The 3-pin BMSQ CMS FL gas line is equipped with its Anti-Roll" electrode and exclusive external short circuit system, which is matched to this type of mounting, especially suitable for surface mounting technology.

PCB mounting
Most CITEL gas discharge tubes are equipped with wire output (diameter 0.8 or 1 mm) for mounting on a printed circuit board. Different output types possible depending on the range:
Axial, radial, straight, folded output.
Wave soldering must be done according to the recommended profile (opposite).

Radial taping
The CITEL gas discharge tubes with wire outlet are supplied in a radial strip in a package of 500 components corresponding to the areas (plan opposite) and in accordance with the IEC 286-1 specification.

tape and reel
The CITEL gas discharge tubes with SMT mounting are supplied in tape and Reel-Pack, reel with 500, 800 or 1000 components (facing plan) and supplied according to IEC 286-1 specification.


Download "Main Catalogue Gas Arresters and Gas-Filled Spark Gaps"


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