Lightning protection design of monitoring system

The rainy season is approaching, and monitoring of lightning protection is an important part of testing product performance. This article focuses on analyzing the lightning protection design of the monitoring system.

First, the front-end equipment direct lightning protection Security monitoring system has two kinds of outdoor and indoor front-end equipment, installed in indoor equipment generally will not be subject to direct lightning, and installed in outdoor equipment, most of them in a relatively open area, the risk of direct lightning , you must consider direct lightning protection.

The front-end equipment of the security monitoring system, such as the camera, should be placed within the effective protection range of the lightning arrester (lightning rod or other lightning conductor). For front-end equipment that is already within the protection scope of the original lightning protection systems of other air-termination or high-rise buildings, it is generally not necessary to consider lightning protection directly; for front-end equipment that is not within the protection scope of any lightning protection system, Should consider direct lightning protection. From a technical and economical point of view, front-end equipment with direct lightning strike protection and installation of independent lightning rods is not feasible. Generally, the lightning rods are installed on the support rods of the cameras, and the downleads can directly use the metal rods themselves (the Φ8 galvanized steel can also be used. Round steel or 30 × 3 galvanized flat steel), but in order to prevent electromagnetic induction, the power cable and signal cable led to the camera along the rod should be laid through the metal pipe, and the metal pipe should be reliably grounded.

Grounding and lightning protection monitoring front-end measures should follow the following rules:

1. Outdoor cameras should be equipped with lightning rods, and separate grounding lines should be used to isolate the power and image signals of the monitoring equipment so as to avoid interference with currents and damage to the lines. Lightning rods should be erected higher than the camera. It is within the range of the virtual three-dimensional vertebral body that is 45-60 degrees down from the tip of the lightning rod. It is the safety scope of the camera. When the lightning rod is installed, it should be insulated from the steel of the fixed camera.

2. The grounding of the front-end equipment of the camera must be concentrated on a grounding bus at the terminal part so that the grounding of the entire monitoring front-end equipment can reach the requirement of no ground potential difference, otherwise it may cause a potential difference to the ground loop and cause the equipment to be burned.

3. The indoor front-end camera should be connected to the grounding terminal of the shared terminal by a grounding wire, and a non-fuse breaker and a leakage breaker should be installed at the power supply end of the front-end device. At the same time, 3000KV can be installed under the permit. Avoid inductive or conductive lightning damaging equipment.

4. After the outdoor security surveillance camera is grounded, the test grounding resistance is less than 10Ω, and the grounding rod should be installed according to the standard three-point impedance test.

Second, the transmission line direct lightning protection In order to protect the transmission line from direct lightning damage, transmission lines should be avoided as much as possible overhead laying, it is best to wear buried metal pipe laying, the two ends of the metal pipe should be reliably grounded.

Third, the terminal equipment direct lightning protection terminal equipment room (generally known as the monitoring room) where the building should take measures to prevent direct lightning, can use φ10 round steel (brush silver paint) in the roof to build lightning protection zone, in addition to the use of φ10 round The steel is used as a lightning protection belt support with a support height of 15cm, a support is set every 1m, and a 40×4mm galvanized flat steel is used as the deflector to connect to the ground network (ground resistance should be less than 10Ω). The distance between the downlead should not be More than 25 meters. Lightning rods can also be used as a measure to prevent direct lightning strikes. A 40×4 mm galvanized flat steel is used as the deflector wire to connect to the ground net. The height and location of the lightning rod should be calculated according to the rolling ball method.

Fourth, lightning protection grounding system All lightning protection systems should have a reliable and effective grounding. Grounding system is also one of the necessary components of lightning protection. The front-end and terminal equipment of the security monitoring system should have good lightning protection grounding, and the corresponding grounding system should meet the requirements of the specification. The front-end equipment, which is generally independent of the building in which the monitoring equipment room is located, must be provided with an independent grounding. However, it needs to be specifically pointed out here: No matter the front end or the grounding system of the terminal equipment, if the distance is less than 20 meters, equipotential bonding should be done between the two grounding systems.

Fifth, the choice of security AC lightning protection device for the security monitoring system, all AC power supply line for effective lightning protection. And make sure that the building where the equipment is located has a good lightning protection and grounding system, and further confirm whether the lightning protection device of the building is used properly.

The corresponding power surge protector should be installed at the incoming AC power supply of the front-end equipment. Considering that the power supply system of the security monitoring system is generally not very standardized, there will usually be several volts and more than ten volts between zero and ground, and sometimes even several tens of volts. In addition, single-phase power supply is installed for lightning protection. When installing the device, the installer generally does not pay attention to distinguish between zero and FireWire. In view of this situation, we recommend that when using a single-phase power supply lightning protector, try to avoid using a product with NPE protection mode, because if the NPE module has AC voltage Existence, when the NPE module operates, it will generate freewheeling, making it difficult for the NPE module to extinguish the arc, causing the NPE module to burn out.

The power line entering the monitoring room should be considered in level 3 protection. A primary power surge protector can be installed at the incoming line of the power distribution room of the building, and the power supply line of the distribution box on the floor where the monitoring equipment room is located should be installed. The power surge protector is installed with a three-level power surge protector at the incoming line of the important equipment in the monitoring room. In the case where the zero and ground voltages are relatively high, it is not recommended to use a 3 NPE or 1 NPE protection mode for the power surge protector. .

6. The "lightning protection" of the monitoring room is equally important. The lightning protection in the monitoring room is the most easily overlooked place for people. In fact, the lightning protection in the control room is the last step in the monitoring system's lightning protection. The monitoring system transmits the signal to the terminal receiver through the line transmission. The signal will be transmitted from the outside to the room or will pose a certain threat. Therefore, the building where the monitoring room is located should have lightning rods, lightning protection strips or lightning protection nets for direct lightning protection. In order to avoid the damage caused by lightning. The building shall be provided with a pressure equalizing ring, and all the downleads, metal structures and metal objects in the building shall be connected to the pressure equalizing ring.

For direct lightning strikes with too much power, only protective measures to reduce damage are currently available. This also requires the joint efforts of mine-prevention and security circles to develop and manufacture lightning protection equipment and measures that are more advanced and more capable of combating attacks. There are more and more types of security surveillance cameras, and lightning protection cameras are also rising stars in the market. We have reason to believe that with the expansion of surveillance applications, lightning protection cameras will surely burst out.

Monitoring room equipment Lightning monitoring room main equipment includes monitoring center computer, video matrix, hard disk video recorder, intercom system, and monitoring room power supply.

The location of the equipment room of the monitoring system equipment should be selected in the LPZ most advanced area and avoided in the top three floors of the building; when the size of the lightning protection grid on the building surface part does not meet the requirements of the system anti-jamming, it should be installed on the sky surface. Shield. Use unshielded cables. Before entering the home, wear a metal tube and bury it in the ground at a horizontal distance of 10 meters or more. If it is impossible to wear a metal pipe buried in a house due to conditions, the length of the access shield pipe or the trestle shall be extended. Equipotential bonding and grounding shall be performed at both ends of the metal pipe or trestle bridge and at the junction of the lightning protection zone. When the monitoring system equipment is a metal shell, the shortest wire is used to connect it to the equipotential bonding tape. If it is a non-metallic shell, when the shielding of the building where the equipment is located does not meet the equipment's electromagnetic compatibility requirements, metal screens or other shields shall be installed to shield the equipment. The metal mesh shall be connected to the equipotential bonding tape for equipotential bonding. Computers, communications,

The equipment in the monitoring room should be about 1 meter away from the external wall of the building. In order to prevent the building from being hit by direct lightning, strong electromagnetic fields are generated around the down conductors that leak into the ground along the outer wall and damage the microelectronic equipment.