Why do we need lightning protection grounding?
The widespread application of microelectronic network equipment makes the issue of lightning protection increasingly important. Since microelectronic equipment has the characteristics of high density, high speed, low voltage, and low power consumption, it is very sensitive to various electromagnetic interferences such as lightning overvoltage, power system operating overvoltage, electrostatic discharge, electromagnetic radiation, etc. If protective measures are not adequate, you may suffer heavy losses anytime and anywhere.
The necessity of lightning protection in computer rooms
Lightning strikes can produce different forms of damage. The International Electrotechnical Commission has called lightning disasters "a major public hazard in the electronic age." Instantaneous overvoltages such as lightning strikes, induced lightning strikes, and power supply spikes have become the main culprits in destroying electronic equipment. From the analysis of a large number of lightning strike cases on communication equipment, experts believe that lightning electromagnetic pulse (LEMP) caused by lightning induction and lightning wave intrusion is the main cause of damage to equipment in the computer room. The prevention principles adopted for this purpose are "overall defense, comprehensive management, and multiple protections." Strive to reduce the harm caused by it to the lowest point.
Design of lightning protection grounding system for computer room
1. Lightning protection design
The lightning protection grounding system is an important subsystem for the protection of weak current precision equipment and computer rooms. It mainly ensures the high reliability of the equipment and prevents the harm of lightning. The central computer room is a place with very high equipment value. Once a lightning strike occurs, it will cause immeasurable economic losses and social impact. According to the relevant provisions of GB50057 "Lightning Protection Design Code for Buildings" and the IEC61024-1-1 standard, the lightning protection level of the central computer room should be designated as a Category II standard design.
2. Grounding system design
According to the national standard GB50174 "Computer Room Design Specification", the computer room should have the following four grounds: DC ground, AC working ground, AC protection ground and lightning protection ground for the computer system.
The resistance of each grounding system is as follows:
Ø The DC ground resistance of computer system equipment shall not be greater than 1Ω.
Ø The grounding resistance of the AC protective ground should not be greater than 4Ω;
Ø The grounding resistance of the lightning protection ground should not be greater than 10Ω;
Ø The grounding resistance of the AC working ground should not be greater than 4Ω;
1. Equipotential connection in the computer room
Set up a ring-shaped grounding bus in the computer room. The equipment and chassis in the computer room adopt an S-type equipotential connection form and are connected to the grounding bus. Use 50*0.5 copper-platinum strips to lay them under the movable floor bracket, forming a vertical and horizontal 120 0*1200 grid, 30*3 (40*4) copper strips are laid around the machine room. The copper strips are equipped with special grounding terminals. All metal materials in the machine room are grounded with braided soft copper wires and connected to the protective ground of the building.
All grounding wires (including equipment, SPD, wire troughs, etc.) and metal wire trough lap jumpers in the project should be short, flat, and straight, and the grounding resistance must be less than or equal to 1 ohm.
2. Computer room shielding design
The entire machine room is shielded using color steel plates for hexahedral shielding. The shielding plate is seamlessly welded in front of the shielding plate. Each side of the wall shielding body is grounded at no less than 2 places with the grounding busbar.
3. Design of grounding device in computer room
Due to the high grounding resistance requirements of the computer room, an additional artificial grounding device was added near the building. 15 galvanized angle steels were driven into the ground grid trough, welded with flat steel, and backfilled with resistance reducing agent. The electrostatic grounding of the computer room is introduced using 50mm² multi-stranded copper core wires through pipes.
The grounding resistance of the grounding device is required to be less than or equal to 1 ohm.
The lightning arrester manufacturer tells you how to do lightning protection and grounding in the computer room?
The so-called grounding refers to connecting a certain metal shell in the circuit to the earth to form an electrical circuit. The purpose is to allow current to flow easily into the earth and protect people and equipment.
Grounding method:
The DC ground suspension method means that the DC ground is not connected to the earth and is strictly insulated from the ground;
The DC grounding method connects the potential of digital circuits in computers and other equipment to the ground and the network.
No matter what form is used, there must be a grounding busbar and grounding rod. It is particularly emphasized that it is recommended to use a grounded buried grounding network board, which can better guide the earth. The following issues should be paid attention to when grounding:
Ø Try not to short-circuit or mix the DC ground and AC ground in the computer room;
Ø AC lines and DC ground wires are not allowed to be laid in parallel to prevent interference or short circuit;
Ø The DC ground wire network should be installed under the floor to facilitate side connection, which can reduce the grounding resistance and facilitate leakage.
1. Grounding copper bar
The grounding of the indoor computer room uses a 30*5 (width*thickness, unit mm) copper sheet, which is 10cm high from the ground around the wall of the computer room, and is connected to the outdoor grounding busbar. Drill small holes every 50 cm in the copper sheet to facilitate grounding of equipment distributed in various areas of the computer room.
2. Ground copper plate
The grounding copper plate is fixed to the floor using an L-shaped copper plate with a width of 60mm (thickness 10mm). This copper wall and iron wall plate serves as the general grounding for all facilities that should be grounded in the computer room.
3. Ground network
If the computer room has a raised floor, 2.5mm multi-core bare copper wires should be wrapped around the raised floor columns as a ground net.
Precautions for lightning protection and grounding in the computer room:
1. Considering the interference from lightning or other telecommunications equipment, the computer room should not be set up on the top floor of the building or near the outer wall. If limited by special circumstances, a shielding layer should be installed to prevent lightning interference. For particularly important computer systems, an independent shielded computer room should be considered. The grounding installation of equipment and pipelines in buildings (including computer rooms) should be carried out in accordance with relevant specifications, and equipotential bonding should be done well;
2. To prevent lightning hazards, electromagnetic pulses caused by lightning strikes should also be prevented. The distribution box in the computer room should be equipped with an SPD (electromagnetic surge protection) protection device to prevent the power supply of the computer room from being cut off due to electromagnetic pulses caused by lightning strikes. In addition, for important system hosts, their communication cables should also be equipped with SPD protection devices. Since the number of communication cables is generally relatively large, the protection settings of communication lines should be reasonably set according to the specific actual conditions;
3. The electrical grounding system should adopt the TN-S grounding system, the PE line and the phase line should be separated, and the power access point of the computer room should be repeatedly grounded;
4. The grounding of the computer room is generally divided into AC working grounding, DC working grounding, safety working grounding, and lightning protection grounding. According to the requirements of the "Building Lightning Protection Design Code", when the lightning protection design adopts a shared grounding system, each grounding system should share a set of grounding devices. All exposed conductive objects in the information system (metal components such as various boxes, shells, racks, etc.) should establish a first-grade potential bonding network.
Therefore, the electrical lightning protection design should set up a dedicated equipotential bonding row in the computer room and connect it to the main equipotential bonding row of the building through down conductors. According to the layer-by-layer equipotential principle of the shared grounding system, the main structural steel bars are used as down conductors, which is more suitable for the shared grounding system. It is also emphasized that the grounding resistance of the building's grounding system should not be greater than 1Ω.
