Analysis on the application of WLAN Ethernet power supply lightning protection technology

In recent years, VoIP, WLAN, network video surveillance and other services have developed rapidly. The number of IP phones, wireless APs, network cameras and other equipment terminals, the power data cable wiring is complex, power supply is difficult, and the cost is high. Ethernet power supply technology allows the power supply equipment to provide a certain power of DC power to the network powered equipment while transmitting data signals through Ethernet. It can ensure the safety of existing structured wiring while ensuring the normal operation of the existing network, minimizing costs. This technology is favored by many domestic and foreign telecom operators.

1. Overview of Power over Ethernet Technology

IEEE began standardizing POE in 1999, and the current general standard is IEEE 802.3af. POE mainly consists of two parts: the device that provides power, called power supply equipment (PSE), and the device that receives and uses power, called powered device (PD).
POE (Power Over Ethernet) refers to a technology that can provide AC and DC power supply to some IP-based terminals (such as IP phones, wireless LAN access points AP, network cameras, portable device chargers, card readers, etc.) while transmitting data signals without making any changes to the existing Ethernet Cat.5/Cat.6 wiring infrastructure.

2. The harm of lightning to WLAN system

POE technology has been developed for more than ten years and has been widely used in WLAN and other systems in China's communications field. The maximum reliable transmission distance can reach 100 meters. Both ends of the Ethernet connection are expensive, but the protection of the communication equipment is extremely fragile, especially the outdoor WLAN system. Once struck by lightning, it will cause equipment damage, signal interruption, permanent data loss, and even personal injury. Over the years, lightning protection has become a difficult point in the infrastructure construction of operators.

The WLAN system is mainly composed of antennas, wireless APs, switches, servers and other equipment. The hazards mainly come from direct lightning strikes and lightning electromagnetic pulses. Direct lightning strikes mainly cause damage to WLAN system equipment by directly hitting it, while lightning electromagnetic pulses mainly cause damage to equipment through feeder cables, network cables, power supplies and other lines.

3. Difficulties of POE lightning protection

In the WLAN system, outdoor wireless APs are located on rooftops or towers. Because it is difficult to obtain electricity and lay cables, POE power supply is used in most cases. The POE switch is often dozens of meters away from the AP. The network cable at this distance is prone to form lightning electromagnetic pulses in the event of a lightning strike. The lightning electromagnetic pulses invade the wireless AP or POE switch along the network cable, causing damage to the equipment.

According to the characteristics of POE itself, the maximum reliable transmission distance of POE is 100 meters. When a lightning arrester or other equipment is installed in the middle, problems such as signal attenuation and power loss are likely to occur. The power, communication effect and transmission distance cannot be guaranteed, which puts extremely high demands on the performance of the lightning arrester.

4. WLAN overall lightning protection solution

For WLAN system lightning protection, in addition to direct lightning protection, lightning electromagnetic pulses become the focus of lightning protection work.

Direct lightning protection, the direct lightning protection system consists of lightning arresters, down conductors, and grounding devices. First, lightning rods should be installed on outdoor antennas, and the down conductors should be connected to the ground grid to ensure that a discharge channel is provided for lightning current. The characteristic of direct lightning is that it is easy to cause damage to a certain point.

Lightning electromagnetic pulse protection. Lightning electromagnetic pulse is an electromagnetic field generated by lightning, which causes overvoltage in the WLAN system feeder, network cable, power supply and other lines, invading the equipment and causing damage. The characteristic of lightning electromagnetic pulse is that it can easily cause damage within a range of several kilometers, so it has become the focus of lightning protection. The WLAN system needs to install R25N70F feeder lightning arrester and POE series Ethernet power supply lightning arrester on the AP feeder port and network port respectively, and install M40B1+N single-phase power supply lightning arrester and POE series Ethernet power supply lightning arrester on the POE switch power supply and network port respectively.

5. Introduction to POE lightning protection solution

In response to the two major problems of POE power supply and lightning protection, Tiandun, a leading domestic lightning protection solution provider, took the lead in launching an integrated power supply, communication, and lightning protection solution:

First, when the switch has the POE function, the wireless AP is powered by Ethernet: the ordinary POE lightning arrester can achieve the lightning protection function, that is, when the signal line maintains normal communication and supplies power to the AP at the same time, the internal lightning protection module can effectively discharge the lightning component on the line. Install the POE lightning arrester on the switch side and the AP side respectively to ensure the safety of the device ports on both sides and avoid damage from lightning strikes.

Second, when the switch is an ordinary switch, Ethernet power supply is provided to the wireless AP: There are two ports on the input side of the POE combiner, one port is connected to an external AC/DC power supply to obtain power, the other port is connected to the switch to obtain signals, and the output port is connected to the wireless AP. Through the POE combiner, the wireless AP is integrated to realize power supply, communication, lightning protection and other functions at the same time.

Third, when the switch has the POE function, a separate power line is used to power the wireless AP: the input side of the POE splitter is connected to the POE switch to obtain power and signals, and the output side is divided into two ports, one port is connected to the AP power line to power the AP, and the other port is connected to the AP communication port to communicate with the AP.

With the widespread application of WLAN systems in China, POE technology has been developed and improved. In order to ensure the normal operation of WLAN systems in environments such as lightning, we not only need to improve our understanding of lightning protection, but also actively study modern lightning protection technology to avoid lightning disasters to the greatest extent.