Security monitoring system lightning protection design

The lightning protection design of the security monitoring system is rarely used in practical applications, but this is an important aspect. In particular, the outdoor monitoring system and the places where thunder and lightning often appear should be designed for lightning protection.

Overview

We should first accurately understand the system configuration of the security monitoring system, and then accurately analyze the main reasons for damage caused by lightning strikes to the security monitoring system and the possible intrusion routes of lightning overvoltage. Based on this, choose suitable lightning protection devices, study and discuss the reasonable deployment of signals, power lines, clear shielding and grounding methods, can provide accurate and systematic lightning protection solutions. Effectively improve the anti-lightning over-voltage interference capability of the security monitoring system, and optimize the overall lightning protection level of the system.

Second, security monitoring system composition, classification and lightning protection overview

1. The composition of the security monitoring system

Security monitoring system generally consists of the following three parts:

Front-end part: mainly composed of black and white (color) cameras, heads, shields, brackets, etc.

Transmission part: using coaxial cables, wires, twisted pairs, overhead, ground or wall-mounted transmission of audio, video, control signals and feed AC and DC power supplies.

Terminal part: It mainly consists of control equipment, picture dividers, monitors, video storage devices, etc.

Security monitoring system lightning protection classification

According to the classification of transmission modes, security monitoring systems are mainly divided into the following categories:

A. Coaxial cable transmission monitoring system: The lightning protection focuses on the protection of the line interface at both ends of the transmission cable and the transmission cable itself;

B. Twisted-pair Transmission Monitoring System: The lightning protection focuses on the front-end and terminal power protection and twisted pair interface protection;

C. Optical fiber transmission monitoring system: The lightning protection focuses on the power protection of the front end and the terminal and the protection of the optical cable itself to shield the enamel layer and the ribs;

D. Microwave transmission monitoring system: The protection focuses on the self-direct lightning protection of the two stations before and after.

2. The main reason for damage caused by lightning strikes to the security monitoring system

2.1 direct thunder

A. Lightning strikes the open camera directly and damages the equipment directly;

B. The lightning strikes the cable directly, causing the cable to blow and damage.

2.2 Lightning Invasion Waves

When the power line, signal transmission line of the security monitoring system, or other metal cables entering the monitoring room are struck by lightning or induced by lightning, lightning waves invade the device along these metal lines/conductors, resulting in high potential difference and equipment damage.

2.3 Lightning induction

Electromagnetic induction: When there is a lightning flash in the nearby area, a strong transient electromagnetic field will be generated around the strike channel. The monitoring equipment and transmission lines in the electromagnetic field will induce a large electromotive force, which will damage and damage the equipment.

Electrostatic induction: When a charged lightning cloud appears, a confining charge opposite to that of a thundercloud will be induced on the buildings and transmission lines below the thundercloud. This induced charge can reach a static potential of 100 kV on a low-voltage overhead line and a static potential of 40-60 kV on the signal line. Once the thundercloud discharges, the bound charge rapidly spreads, causing an induced lightning strike.

The lightning strike caused by electromagnetic induction and electrostatic induction is called induction lightning, also known as secondary lightning. Its damage to the equipment is not a direct hit, but it is much more likely than straight strikes. Statistics show that induced lightning accounts for more than 80% of modern lightning strikes.

2.4 Ground Potential Counterattack

The direct lightning protection device (lightning rod) generates a very high instantaneous voltage on its down conductor, grounding body and the metal conductors connected to them when guiding powerful lightning currents into the earth. There is a huge potential difference between metal objects, equipment, lines, and the human body that are not connected to them. The electric shock caused by this potential difference is the ground potential counterattack. This counterattack is not only enough to damage electrical appliances and equipment, but also cause personal injury or fire and explosion.

Third, the design basis

3.1 GB50057-94 "Lightning Protection Design Specification for Buildings"

3.2 GB50174-93 <Code for design of computer room lightning protection>

3.3 GB2887-89 "Technical Documents for Computing Station Sites"

3.4 GB9361-88 "Safety Requirements for Computing Station Sites"

3.5 JGJ/T16-92 <Code for the Implementation of Electrical Codes for Civil Buildings>

3.6 GA173-1998 <Lightning Protection Device for Computer Information System>

3.7 IEC1312 <Protection of Lightning Electromagnetic Pulses>

3.8 IEC 61643 <SPD Power Supply SPD>

3.9 IEC 61644 <SPD Communication Network Lightning Protection Device>

3.10 VDE0675 <Overvoltage Protector>

3.11 GB50343-2004 Technical Specifications for Lightning Protection of Building Electronic Information System

IV. Lightning protection design

According to the analysis of the second article, with reference to the actual situation, with reference to the national lightning protection regulations, this design proposal is formulated.

1 outdoor equipment protection

Direct lightning protection: In the upper end of the outdoor camera support rod, install a small lightning rod, the height is higher than the camera, the lightning conductor off the lead, you can directly use the metal rod itself, you can also lay down artificial deduction, cited The line is connected to the lower ground network. The ground network resistance is less than 10 ohms.

Induction thunder protection of the camera: Lightning protectors are installed on the camera's power supply, control lines, and video lines. A three-in-one centralized lightning arrester can be used.

2 Monitoring room lightning protection:

The first stage power source lightning protection device is installed on the total power distribution of the building as the first level of power supply lightning protection for the entire building.

A second-level power surge protector is installed in the power distribution room of the equipment room as a secondary power source lightning protection for the equipment room.

At the front end of the UPS power supply, a third-level lightning arrester is installed to protect the UPS and its subsequent equipment.

3 grounding system

In the vicinity of the outdoor camera should be done near a set of grounding net, if the distance between the two ground nets is less than 20 meters, two ground nets to be connected together. The grounding resistance of the camera and lightning rod is less than 10 ohm.

Monitor the floor of the equipment room to less than 4 ohms. Taking into account the grounding space constraints, high-tech grounding modules can be used.