Maintenance requirementsQuarter-wave lightning/EMP protectors
Quarter-wave lightning/EMP protectors are basically maintenance-free. However, we recommend customers to check the condition of the grounding/bonding system connections and of the connector interfaces in the context of a routine system maintenance. Connector interfaces which are heavily damaged by lightning current overload (in excess of specification) will lead to increased reflections and will be detected by the return loss tracing circuit of the transmitter anyway. Field experience shows that lightning protectors are not the only components which can be affected in such cases of direct hits.
Gas discharge tube (GDT) lightning/EMP protectors
Gas discharge tube protectors use different technology but are still very reliable products. The MTBF value determined by the carefully selected HUBER+SUHNER GDT is about 10 fit (1 fit is defined as 10-9 h-1 ) – one failure within 108 hours. This is true as long as no events of critical surge current load occur.
A degradation of the GDT is possible due to surge current overload and multiple loads at the specification limit. A lot of previously performed tests reveal that there is a large safety margin built into HUBER+SUHNER GDTs. Even with excessive overload the capsules maintain at least their dynamic switching performance (dynamic spark-over voltage specification) which determines the residual pulse amplitude left by transient surges of lightning events.
Any destruction of the GDT caused by a heavy overload would lead to a short due to its unique and special design and therefore a shutdown of the the transmitter. This will be recognised immediately. But this is most probably not the only system damage in such cases, and a service will be necessary anyway. Our EMP protectors feature an easy access to the GDT and the exchange is quickly made.
Generally, inspection and maintenance schedules depend on the grade and frequency of surge loads. This is determined by the isokeraunic level (number of thunderstorm days, which decreases with latitude) of the operation area and several factors which determine the exposure of the equipment (e.g. altitude, country profile, nearby structures, water, etc., and even the existence of a lightning protection system). This is the reason why only the operator or his local consultant can judge the inspection requirements of their equipment (e.g. BTS), according to the actual exposure.
Recommendation
We recommend as a general rule to test the static spark-over voltage of the GDT in the course of a routine inspection every 5 years and to exchange the failing parts. A suitable test unit can be supplied by HUBER+SUHNER (type 9075.99.0053).
As an alternative, a general overall replacement without testing might be more cost-effective in certain situations.
After a direct hit, causing damages in the antenna system, the capsules of the GDT protectors involved should be exchanged during the service in any case.
