With the rapid advancement of modern high technology, the use of precision instruments, communication devices, and data networks has become increasingly widespread. As a result, lightning-induced accidents have also risen significantly. These incidents not only cause direct economic losses but also damage critical equipment and, in severe cases, lead to complete system paralysis. Video surveillance systems, as an essential part of low-voltage systems, are gradually gaining attention for their lightning protection measures. However, due to their non-critical nature, they are often overlooked by users and integrators due to factors like input costs and workload.
**Lightning Protection for the Monitoring Center:**
In a video surveillance system, protecting the monitoring room is the most crucial aspect. Economically, the equipment in the monitoring room is large, complex, and expensive. Functionally, the room serves as the central hub of the system and plays a vital role in overall operations. In terms of risk, its wiring is more complex and susceptible to lightning damage. Therefore, it must be prioritized in all lightning protection strategies, incorporating multiple measures such as direct lightning protection, surge protection, equipotential bonding, and lightning wave intrusion prevention.
**1. Surge Protection:**
Surge protection in the monitoring center involves safeguarding equipment by protecting power lines and signal cables that enter the room and connecting them to an equipotential bonding system. It can be divided into two main categories: power protection and signal protection. From a usage perspective, it includes both the power supply section and the back-end equipment.
Power supply systems typically come in three-phase or single-phase configurations. Power cables may be steel-sheathed, directly buried, or overhead. The power distribution box is usually installed on the wall of the monitoring room, with surge arresters (class 1 and 2) placed inside or outside the box. If the incoming line is buried, one level of protection may suffice. For direct-buried lines, one or two levels of protection should be applied based on the hazard level and equipment importance. Overhead lines require at least two levels of protection.
**2. Overhead Power Lines Entering the Monitoring Room:**
When power lines are overhead and enter the monitoring room, three-level surge protection is required. If using a limited-voltage type arrester for the first stage, the current capacity should be ≥80 kA (8/20). If a switch-type arrester is used, the capacity should be ≥15 kA (10/350). These arresters are installed on the three-phase power supply lines, with repeated grounding of the neutral line.
**3. Buried Steel Pipe Power Lines Entering the Monitoring Room:**
For power lines introduced via buried steel pipes, one or two levels of surge protection can be applied. A first-stage voltage-limiting arrester should have a current capacity of ≥40 kA (8/20). If the first stage is already installed, it can serve as the second stage of protection. The arrester is typically installed at the total incoming line of the power distribution boxes in the monitoring room.
**4. Final Stage Surge Protection for the Power System:**
For rooms where front-end surge arresters are already in place, terminal power equipment must be carefully protected to absorb residual surge energy from the inlet arrester. Modular power surge arresters or surge-protected sockets with a limiting voltage of less than ≤1.5 kV or even <1 kV are recommended. For devices with indoor circuit breakers, install the final-stage surge protection module in an open space. If the power comes from a wall outlet, use a surge-protected power strip at the equipment’s outlet.
**5. Lightning Protection for Front-End Equipment Power Supply:**
Surge arresters should be installed on the power outlets of front-end equipment in the monitoring room. The arrester should be selected based on the output voltage of the power cable, with a current capacity of 20 kA (8/20).
**6. Video Cables Entering and Leaving the Monitoring Room:**
The number of video arresters should match the number of video lines entering the monitoring room. However, if optical fibers are used, no video surge protection is needed. Before the video transmission line enters the hard disk recorder or other equipment, install a coaxial video signal arrester in each direction.
**7. Control Lines Entering and Leaving the Monitoring Room:**
Control signal lines, such as PTZ control lines or data communication lines, are generally 485 lines. Each signal line should be equipped with a surge arrester before connecting to the equipment. Install one additional control signal arrester in each direction to prevent damage from surges.
**Equipotential Bonding:**
An equipotential busbar should be installed in the monitoring room and connected to the PE wire, equipment ground, and other grounding points to eliminate dangerous potential differences. All arrester grounding wires should be connected to the busbar using the shortest and straightest path possible.
**Lightning Wave Intrusion Prevention:**
All cables entering the monitoring room should be buried. Metal conduits should be grounded before entering the room. If overhead lines are used, all metal hanging wires or objects must be grounded to prevent lightning waves from entering.
**Direct Lightning Protection:**
The building housing the monitoring room should be equipped with lightning rods, lightning belts, or mesh systems to protect against direct strikes. These measures must comply with GB50057-94 standards for direct lightning protection.
Good grounding is essential for effective lightning protection. The lower the grounding resistance, the better. When using a dedicated grounding device, the resistance should not exceed 4Ω. If using a combined grounding grid, the resistance should be less than 1Ω.
**Front-End Equipment Lightning Protection:**
There are two types of front-end equipment: outdoor and indoor. Indoor equipment is not exposed to direct lightning but still needs protection against overvoltage. Outdoor equipment requires protection against both direct strikes and induced surges. Surge arresters should be installed on power, video, signal, and control lines. Cameras powered by AC220V or DC12V should have a surge arrester connected to the DC transformer. If the power line is longer than 15 meters, a low-voltage DC arrester should also be installed at the camera end. Signal lines are vulnerable to induced surges, so fast-acting signal protectors should be used. Outdoor equipment should be within the protection range of a lightning rod, with a minimum distance of 3–4 meters. If not possible, the rod can be mounted on the camera support. Shielded metal pipes should be used for power and signal lines to reduce electromagnetic induction.
**Transmission Line Lightning Protection:**
CCTV systems mainly rely on signal and power lines. Outdoor cameras may draw power from nearby sources. Control and alarm signal lines are usually shielded and laid between the front end and the terminal. According to GB50198-1994, transmission lines in suburban areas can be directly buried. If not possible, they can be laid in conduits or overhead. Overhead lines are most vulnerable to lightning, so grounding should be done at regular intervals. Shielded cables or metal pipes are highly effective in reducing electromagnetic interference and induced currents.
**Grounding System Lightning Protection:**
The grounding system must consider the ground potential rise from each camera and the direct lightning strike. For distributed systems, natural grounding bodies can be used. For smaller systems, centralized grounding is feasible. Copper or galvanized flat steel can be used to connect the central control room to the front-end equipment. Transmission lines can also serve as grounding conductors. For cameras without proper grounding, SPDs can be added before the signal enters the area, with the line passing through metal pipes or armored cables for better protection.
According to national regulations, the grounding resistance for individual power supplies should be less than 4Ω, while the joint grounding resistance should be less than 1Ω.
In the early stages of video surveillance system design, countries like Australia and the United States have fully recognized the importance of lightning protection technology. They have implemented effective measures to reduce lightning-related damage and improve system safety, benefiting society. These nations emphasize people-centered approaches, quality products, and community service.
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