A complete 5G mobile base station power lightning protection solution

preface
With the continuous promotion of the 5G industry by the country, 5G construction is constantly unfolding.
Because power lightning protection belongs to system engineering and must be considered as a whole. It generally includes the following four aspects: lightning protection of AC power cables, grounding connection between base station grounding network and station equipment, lightning protection of station combined power supply system, lightning protection of power lines and power ports, etc. Only by comprehensively protecting in these four aspects can the ideal lightning protection effect be achieved.
This article explores four aspects of lightning protection for 5G base station power supply and provides a complete solution for lightning protection of 5G mobile base station power supply.
1、 Lightning protection scheme for mobile base station power supply
Lightning protection of AC power cables
1. For the protection of AC power cables entering the station, for conditional base stations, the high-voltage and low-voltage cables of transformers should be buried and installed. According to the "YD 5098-2005 Design Specification for Lightning Protection and Grounding Engineering of Communication Bureaus (Stations)" (hereinafter referred to as the "Postal Standard"), "when using dedicated transformers, the burial length of high-voltage power cables should not be less than 200m, and when low-voltage cables enter the computer room, their burial length should not be less than 15m (when high-voltage power cables have been buried, this requirement is generally not applied to low-voltage side cables). For low-voltage buried cables, power cables with metal armor layers or buried through steel pipes should be used to introduce them into the computer room. The metal armor layer of the cable should be connected to the transformer grounding network and the computer room grounding network nearby at both ends.". However, for high-voltage cables, the investment and construction difficulty of buried installation are relatively high, which is difficult for general base stations to achieve. According to the same standard requirements above, lightning protection lines should be installed along the overhead line and high-voltage lightning arresters should be installed on the high-voltage side of the transformer.
2. Install a B-level lightning protection box at the entrance of the AC low-voltage power cable into the computer room. Special attention should be paid to the installation of B-level lightning protection boxes using the "Kevin" wiring method to reduce residual voltage on the leads and fully utilize the function of B-level lightning protection boxes. For base stations where AC low-voltage power cables are buried, the attenuation effect on lightning current after AC low-voltage power cables are buried is very obvious. B-level lightning protection boxes can use ordinary varistor lightning protection modules with an 8/20 μ s waveform. However, for non buried low-voltage power cables, the lightning current may be relatively large. Therefore, it is recommended to use active ignition gap type lightning protection modules with a high current capacity of 10/350 μ S waveform.
II The bottom line connection between the N base station ground network and the equipment inside the station
The grounding network of the base station should be designed in accordance with Chapter 7 "Lightning Protection and Grounding of Small Wireless Base Stations" of the postal standard, and the grounding resistance should also meet the standard of less than 10 Ω.
A good grounding network design and low grounding resistance play an important role in the lightning protection of base stations, but this is far from sufficient. The success of a lightning protection grounding system largely depends on the ground wire connection (installation) relationship between equipment within the station.
1. Common Unreasonable Ground Connection Relationship of Station Equipment This is the most common ground connection relationship of equipment in the computer room. Its drawbacks are very obvious: the ground wire lead of the B-level lightning protection box at the entrance of the computer room is too long, which cannot play its due role; In addition, the ground wire of the switch power supply is also too long, and the residual voltage on the ground wire will accumulate on the power port of the backend device. For this type of base station, no matter how well the grounding network design is or to what extent the grounding resistance is small, it cannot play a good lightning protection role.
2. The postal label recommends two types of equipotential ground wire connection schemes: circular equipotential connection and star shaped equipotential connection. According to the "Postal Code" regulations, "When using a circular equipotential connection, a circular grounding collector line should be set up along the cable rack and wall in the computer room. The circular grounding collector line should be connected to the grounding network at multiple points nearby, and the equipment in the station should be grounded by the circular collector line nearby."
According to the "Postal Code" regulations, "when using star shaped equipotential connection, the main grounding busbar of the base station should be located near the distribution box and the first level power supply SPD. The grounding busbar of the switch power supply and other equipment should be connected by the main grounding busbar. If the equipment rack is far away from the main busbar, a two-stage busbar can be used.". It is recommended to use the equipotential ground wire connection scheme specified in the "Postal Standard" for the connection between the base station grounding network and the equipment inside the station, so as to truly fully utilize the role of lightning arresters at all levels and achieve good lightning protection effects.
Lightning protection and grounding of mobile base stations
III Lightning protection of N station combined power supply system
For the lightning protection of the combined power supply system in the station, its lightning protection circuit is relatively simple and mature. According to the "Postal Standard", a "3+1" AC level lightning arrester with a current capacity of 40kA (8/20 μ S waveform) is used on the AC side of the combined power supply system, and a "1+1" DC lightning arrester with a current capacity of 15kA (8/20 μ S waveform) is used on the DC side of the combined power supply.
IV N power cord and power port lightning protection
The power line is led from the tower bottom machine room all the way to the tower top, with a large spatial span. The potential difference between the tower top and the tower bottom ground grid is also significant, and its lightning protection is very important and relatively difficult. The following lightning protection points should be paid attention to:
1. Use shielded cables, and both ends of the shielding layer should be reliably grounded. The upper end of the shielding layer should be connected to the outer shell (for systems with external lightning protection boxes, connect to the outer shell of the external lightning protection box), and the lower end of the shielding layer should be connected to the outdoor busbar at the feeder window, and should not be introduced indoors to avoid the power line shielding layer from introducing lightning current into the tower indoors.
2. The lightning protection circuit of the power port should be connected in series with a differential inductor to suppress the flow of lightning current to the backend circuit. Note: If there is no suitable DC lightning arrester configured inside the combined power supply, a first level DC lightning protection box should be installed at the point where the power line leads out of the machine room; Because the specific parameters of lightning protection devices vary from manufacturer to manufacturer, they should be selected based on the specific usage location.
Conclusion
At present, the construction of 5G base stations is mainly concentrated in cities and has not yet been widely promoted to rural and remote mountainous areas. The lightning strike environment in cities is relatively good because buildings are generally high and the iron towers (poles) of the base stations are often not the surrounding high points. Once 5G base stations are deployed on a large scale in rural and remote mountainous areas, they will face extremely harsh lightning strike environments.
In addition to taking the above measures for the power supply, 5G base stations should also comprehensively consider various aspects such as lightning protection for the feeder line, lightning protection design for internal circuits, and lightning protection for GPS in order to ensure the stable and reliable operation of 5G base stations.