Particularly in the case of mobile phones, the constant availablility of the transmitter and receiver stations is subject to high requirements. Lightning strokes must not impair the operation of the network. The causes of down-times are of little interest to the mobile phone customer; he can expect a connection whenever he picks up the receiver. A safety package made up of surge voltage protection and uninterruptible power supply can be put together, with which maximum availability can be achieved, thereby fulfilling the requirement for optimum customer satisfaction. Down-times, regardless of the reason for them, cause the customer to be dissatisfied and mean a direct loss of turnover and a long-term loss of image.

E-Plus mobile phone network has a hierarchical structure.
The Base Transceiver Stations (BTS) with radio contact to the mobile telephone are at the base. Due to the ideal transmitting and receiving properties, such a BTS is located in an exposed area, which, by its very nature, is at high risk of being struck by lightning. The Mobile Switching Service Center (MSC), the switching point, is at the top end of the network hierarchy. Here, up to 150 000 subscribers can log in, whereas a standard BTS with three sectors can handle a maximum of 42 conversations simultaneously. The figures clearly show that EMC protection measures are less a matter of protecting the material element than the non-physical, i.e. system failure.

Almost one hundred percent safety
The E-Plus network operator protects the power supply of his MSC sites, for example in the "Alte Post" buildings in Dortmund, against 99.9% of all lightning currents with the Flashtrab lightning current arrester. The arc chopping spark gap (ArC) of Flashtrab has the advantage that the short circuit current of the power supply network up to 4kA, ignited by the lightning current, extinguishes itself within 10 ms. Line follow currents of a longer duration would trigger the back-up fuses. But it can do even more: it does not only protect from damage, but also enables continued operation in the interests of system availability.

Dipl.-Ing. Stephan J. Michalowski