Lightning protection - HUBER+SUHNER - #19

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Introduction ........................ .................. .................. ........................ HUBER+SUHNER 15 The voltage across the gas discharge tube then rises very rapidly. When the dynamic spark-over voltage has been reached (typ. 675 V at 1 kV/ìs for 230 V GDT), the gas discharge tube will ignite and become conductive. At this moment, the voltage across the GDT (called the glow-arc voltage) is between 72 and 90 V. This collapses to 10 – 20 V (called the arc voltage), as the current rises. The dynamic spark-over voltage of the GDT is a function of the pulse rise time. The gas discharge tube, once it sparks over, creates a potential equalization between the inner and the outer conductor (ground) of the coaxial transmission line. The current flows along the path of least resistance through the GDT to the ground. Only a very small portion of the energy, the so-called residual pulse, reaches the equipment. Its magnitude is determined by the GDT characteristics, the interference pulse rise time, and the ground conductor impedance (determined by the quality of the lightning protection system). After the interference has subsided, the gas discharge tube is extinguished, reverting to its original high-ohmic condition. Gas discharge tube protectors can generally be used in wideband applications from DC to over 2.5 GHz, latest designs up to 6.0 GHz. The upper limit for the operating frequency range is determined by the capacitive characteristics of the GDT. GDT protectors allow DC to be carried and thus towermounted electronic equipment to be fed power via the coax line. Lightning EMP protectors with quarter-wave (ë/4) shorting stub This technology is based on a quarter-wave transformation line. The coaxial shorting stub applied for this purpose is short-circuited at its end, and its length is matched to the mid-band frequency of the operation band. It thereby forms a bandpass filter. Its bandwidth can be adjusted up to ± 50% of the centre frequency. Operating principle of quarter-wave lightning EMP protectors