Evaluation of Lightning Current Distribution on Macro Base Station Telecom Sites

The exponential growth of mobile data traffic will continue furthermore in the course of the increasing distribution of smartphones, Tablet-PCs and the possibilities which 5G will bring along. Data services emerged in the 2G era, grew in the 3G era and diversified in the 4G era. 5G is not just a generational change, it will fundamentally change the impact which mobile technology has on society. An innovation for change, 5G will adopt the different needs of consumers, governments and vertical industries. Offering a massive leap in bandwidth speeds in comparison to previous mobile networks, it will also reduce latency and improve overall network efficiency and will allow offering ultra-reliable low-latency communication for machine-to-machine, public safety and other mission critical applications, like autonomous vehicle control and remote health services. Unlike today's mobile networks, a very high reliability and a global coverage is the key for such mission critical services. The new network will not only be built using large towers scattered every few kilometers, it will require a massive deployment of Small Cell technology to enable the network to handle the exponential growth of data transmission. Nevertheless, Macro Base Stations will play an important role in that game, because of the interconnections between Small Cells and this Macro sites. One import part of the future network will be the power supply for all the different components. The increased power demand of this network will drive the power supply demands to a different level compared to previous mobile networks. DC micro grids with a higher system voltage (e.g. 400 VDC) can help to fulfill this demand. To increase the reliability and the availability of this power supply architecture, Surge Protective Devices (SPDs) are not "nice to have", they are mandatory. In consideration of technical needs and economical assessment, the right choice of these SPDs can help to enlarge the efficiency of such sites. Measurements and simulations have shown that a reduction of the duration of the 10/350 μs current waveform of the partial lightning current injected into the DC cables via the DC SPDs is a characteristic of the lightning current distribution in such buildings. To be able to compare this energy content with the SPD parameters, the real values need to be converted into a standardized 10/350 μs lightning current impulse by calculating the equivalent impulse energy. That means for an effective SPD selection or testing, the peak amplitudes can be tested with the well-known normative 8/20 μs test setup, defined in IEC 61643 for CLASS II SPDs. And the converted real energy content can be tested with the normative 10/350 μs test setup, defined in IEC 61643 for CLASS I SPDs. For SPD selection both parameters are important. This paper provides information about effective selection of SPDs used in Macro Base Stations to protect the DC side. The knowledge of lightning current distribution in Macro Base Stations is important for a profitable selection and the most effective location of installation of such SPDs. With the help of examination and simulation tools the values of surge current sharing are determined and calculated for different structures like steel towers, reinforced concrete towers considering different tower heights.