Base Station

Mobile base station lightning protection solution


Most of the mobile base stations are built on high grounds, such as mountains, suburbs, and buildings. The base station antennas are often higher than the existing lightning protection lightning receptors in the building, which is a high point of lightning strikes. Therefore, the lightning protection of the mobile base station should not only consider the protection of the direct lightning strike, but also the protection against lightning induction, the protection against lightning wave intrusion, the shielding of the communication line and the establishment of a good grounding system to reduce the grounding resistance. Equipotential bonding to avoid ground potential counterattack.

One direct lightning protection

      In order to avoid the lightning strike of the mobile base station smart antenna, a highly suitable lightning rod can be welded on the main pole of the mobile base station bracket, so that the lightning rod can adequately protect the smart antenna scattered at a 90 degree angle, and the lightning rod and the sky are welded with a 95 mm multi-strand twisted pair. Surface lightning protection belt. If conditions permit, an optimized lightning rod can be placed approximately 3 meters from the antenna bracket. The height of the lightning rod should be such that the base station antenna is placed within its protection range. The specific calculation method can be based on the height of the antenna and refer to the rolling ball method. In this way, the lightning rod and the antenna are separately arranged. Before the lightning is developed into a discharge, due to the strong electric field strength near the tip of the lightning rod, a continuous discharge path can be generated in advance to meet the descending pilot of the thundercloud, and the lightning current is attracted to the body and passed. The down-conductor and grounding devices safely vent lightning current into the earth, effectively protecting the base station antenna and the main equipment. The material selection and technical specifications for the lightning rod may depend on the surrounding environment of the mobile base station and the local climate.

2. Protection against indirect lightning and lightning wave intrusion

       Inductive lightning is caused by lightning when the lightning is discharged between the thundercloud and the thundercloud. The nearby outdoor power line, transmission signal line, and equipment connection line generate electromagnetic induction and invade the equipment, causing the serial connection in the middle of the line or the terminal equipment to be damaged. . Lightning wave intrusion refers to a lightning wave that invades along a transmission line by direct or electromagnetic induction and electrostatic induction. According to the wave transmission theory, the change of the wave impedance during the transmission of the lightning wave will cause reflection and refraction, which may cause the voltage at the sudden change of the wave impedance to rise, generate a surge, and increase the harm to the device. The harm of the mobile base station to the intrusion of the inductive lightning and the lightning wave is mainly to enter the induced overvoltage wave and the lightning electromagnetic pulse of the device through the electromagnetic coupling or the electromagnetic induction of the power line, the signal line and the antenna feeder connected to the base station main device. Therefore, it is necessary to install a corresponding lightning arrester on various interfaces of the power line, the signal line, and the antenna feeder of the base station equipment.

1, base station power supply lightning protection

       At present, the AC power supply of the mobile base station is mainly provided by the municipal power grid. Due to the instability of the power grid and the power outage, and the working environment of the mobile base station is harsh and the conditions are harsh, the surge of the equipment power grid and the possibility of lightning overvoltage damage are more likely. Big. Therefore, it is necessary to classify the power supply system in the base station. First, install the 80-120kA power lightning protection box at the base station mains inlet, and then install the 40-60kA power supply lightning protection module in the AC power distribution cabinet, so that the residual voltage is minimized and the communication is protected. The equipment power system is safe.

2. Base station antenna feeder lightning protection

       In order to prevent the inductive lightning current and lightning waves from invading the base station main equipment from the base station antenna feeder, the electronic board of the equipment is damaged. Therefore, the antenna feeder lightning arrester should be connected in series to the interface of the antenna feeder. The operating frequency and interface mode of the arrester should be compatible with the working requirements of the antenna feeder, and the high-pass filter design should be adopted to effectively reduce the insertion loss and not affect the receiving and transmitting of the signal by the base station. A typical mobile base station has six antenna feeders that transmit signals from different angles. Therefore, each line needs to be connected in series with a lightning arrester.

3, base station signal line lightning protection

       The signal line of the mobile base station is laid over a long distance before entering the base station main equipment, thereby increasing the probability of inductive lightning intrusion. In order to avoid the intrusion of the inductive lightning from the signal line, the signal lightning arrester can be installed in some base stations. The arrester should have a two-stage protection device that can avoid the induced overvoltage and instantaneous surge voltage damage caused by lightning, which can minimize the residual voltage and parasitic capacitance. And fast response capabilities. At the same time, the signal line should be shielded by a certain length of metal pipe in the sky surface.

Three mobile base station grounding system

1, joint grounding

       Grounding is the most important part of lightning protection technology. Whether it is anti-direct lightning, anti-side lightning or anti-inductive lightning, lightning current is safely introduced into the earth. Therefore, there is no reasonable, appropriate, and good grounding device that cannot be lightning-proof. The mobile base station connection system should adopt joint grounding, that is, the antenna lightning protection grounding, the base station equipment protection ground, the base station equipment working grounding, and various lightning arrester grounding and other grounding systems are combined into one grounding system, but the lightning rod grounding should be introduced separately from the other grounding into the joint grounding device. The grounding points of the two should be 5 meters apart. The grounding resistance of the joint grounding grid is required to be no more than 10Ω.

2. Lightning protection grounding treatment of mobile base station:

(1) Lightning protection rod lightning protection grounding can be made of -40×4 galvanized flat steel, which is led from the two directions to the lightning protection belt on the lightning protection rod base; and reliable lightning welding with lightning protection belt, lightning protection grounding down conductor It should also be welded to the lightning protection belt.

(2) Install a joint grounding busbar on the metal component of the antenna base. The metal shielding layer of the signal line and the power line, the metal casing of the base station equipment, the grounding of the antenna feeder, the power supply, the signal lightning arrester, and the grounding of the metal components of the antenna frame are all connected to the joint grounding copper by an insulated multi-strand copper core wire with a cross-sectional area of 10 mm 2 . Row up.

(3) Welding from the joint grounding copper busbar with a 35mm2 insulated copper core wire (or with -40×4 galvanized flat steel) to the grounding point of the joint grounding grid. This 35mm2 copper core wire (or -40x4 galvanized flat steel) is called a base station equipment grounding lead-in.

(4) In some rented residential buildings, if there is no grounding, a qualified joint grounding grid should be built. The grounding resistance of the grounding grid should be less than 4Ω.

3. Use a grounding resistance reducing module.

       If the grounding resistance does not meet the requirements, the grounding resistance module can be used; in areas with high soil resistivity, the use of a resistance-reducing module can effectively reduce the grounding resistance and at the same time effectively reduce engineering costs.

The resistance-reducing module is mainly composed of a non-metallic material with good electrical conductivity and stable chemical properties and a conductive electrolytic medium. When the galvanized metal rod is built and connected to the protected ground wire, the effective contact area between the metal grounding body and the earth is It will be greatly increased, and since the resistance-reduction module is connected to the metal ground wire, the contact resistance of the metal grounding body and the earth will be greatly reduced, thereby fully exerting the resistance reduction effect of the grounding module, so that the lightning current can be quickly discharged into the earth.

Fourth, mobile base station lightning protection installation construction

       Due to the diverse construction environment of mobile base stations, the environment in which a base station is located is different, and the number of mobile base stations is large, the lightning protection installation of the base station should be implemented according to the principle of efficient, scientific, safe and local conditions, ensuring that the customer's needs are met.

1. Mobile station base station lightning protection installation construction process

Before the lightning protection installation, check whether the mobile base station works normally. If it is normal, follow the steps below to install and construct. Otherwise, the installation of the base station equipment must be eliminated before installation.

(1) Test the grounding resistance of the building where the base station is located, and make a test record (the grounding resistance should be less than 4Ω).

(2) Install the lightning rod.

(3) Determine the specific location of the lightning rod according to the base station antenna.

(4) The lightning rod base and the roof slab are fastened with expansion screws, and the lightning rod bracket and the lightning rod body are installed at the same time.

(5) Use a -40 × 4 flat steel welded lightning rod base lightning protection lead down to the building lightning protection belt or welded to the joint grounding grid.

(6) Install the grounding busbar copper to the appropriate position on the antenna base, or connect the grounding wire directly to the bracket grounding hole without using the busbar.

(7) Disconnect the power of the base station (unplug the base station power switch), and disconnect the power protection ground wire connected to the chassis in the base station.

(8) Shield the power cable and the signal cable sleeve from the metal tube, and the shield tube is grounded at least two points, which can be soldered to the lightning protection belt.

(9) Disconnect the 220V power cable. After installing the UPS power supply, combine the power signal with the lightning arrester. Connect the power supply and signal cable to the end of the device.

(10) Connect each antenna feeder arrester string to the end of the antenna feeder line.

(11) Connect the antenna feeder, power supply, signal lightning arrester ground wire and equipment protection ground wire to the grounding busbar.

(12) Seal the antenna feeder lightning arrester with waterproof tape, and seal the power supply signal combination arrester into and out of the cable and the external interface.

(13) Finish the protective grounding wire with cable ties or plastic sleeves.

(14) Apply each solder joint with a rust preventive material.

(15) Turn on the power of the base station, wait for the base station to resume work, and test the caller and the called party. If the work is normal, clean the installation site and clean up the installation tools to complete the installation of the arrester device.

(16) If the base station equipment is working abnormally, check the grounding sequence of the arrester and the corresponding relationship of the line and contact the relevant technical personnel of the telecommunications company.

2. Mobile station base station lightning protection installation construction instructions

(1) The position of the optimized lightning rod should be about 3 meters away from the base station antenna, and the base station antenna should be within the protection range of the lightning rod.

(2) All solder joints should be treated for rust prevention.

(3) The power supply, signal, antenna feeder grounding wire and equipment working grounding wire must be connected reliably. When the multiple ground wires are connected together, they are crimped together with cold copper lugs and soldered, and then bolted to the grounded busbars by bolts.

(4) It is strictly forbidden to use the roof water supply pipe, outdoor air conditioning unit, solar water heater, metal cooling tower and other metals as the grounding of the base station. For mobile base stations that do not have a ground or ground network failure, the ground network should be newly built or rectified to be qualified.

(5) For the interface of the antenna feeder lightning arrester, each interface should be waterproofed. The method is the same as the waterproof processing method of the base station equipment. The input and output terminals of the power supply and signal lightning arrester should also be waterproof.

(6) The power supply line and the signal line should be separated.

(7) The power supply arrester and the signal lightning arrester should be assembled together in a sealed iron box with waterproof sunscreen.

V. Summary of lightning protection scheme for mobile base stations

       Lightning protection is a systematic project, so effective protection cannot be based on a single protection. If only the protection against direct lightning strikes is considered, and the other inductive lightning parts are not protected or the protective measures are insufficient, the lightning induced overvoltage and lightning electromagnetic pulses will invade the base station equipment from various lines, and if the grounding system is not processed, The entire lightning protection system did not play a safety role. Therefore, we should carry out comprehensive lightning protection design for the lightning protection design principle of mobile base stations, and adhere to measures such as “flashing, shielding, equipotential bonding, voltage equalization, shunting, grounding, and reasonable wiring” for comprehensive lightning protection.

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