How To Choose The Size Of The Surge Protector
How to choose the size of a surge protector? There are many types and parameter models of surge protective device on the market, with different sizes. Although there are detailed instructions in GB50057 and GB50343, it is still unclear how to choose the size of a surge protection device when encountering complex environments in actual projects. Below, Yizao will give you a detailed answer, hoping to provide you with a useful reference. When choosing the size of a surge protector, it is necessary to combine the lightning protection partition of the building and the installation location of the surge protector in the circuit system. First, let me introduce the concept of lightning protection partitions to facilitate your understanding later.
How to choose the size of a surge protector? The concept of lightning protection partitions described in the international standard IEC62305-4 has been proven to be reasonable and effective. The basic idea of this theory is to reduce the overvoltage to a harmless level step by step before it reaches the terminal equipment and causes damage. To achieve this goal, the entire protection space of the building is divided into several lightning protection zones (LPZs). Install a surge protector where the online route enters from one zone to another, and install lightning arresters of corresponding levels according to the specific requirements of different zones.
The main advantages of lightning protection zoning theory:
Harmful lightning currents containing high energy are directly diverted and discharged into the earth at the point where the wire enters the building, minimizing the overvoltage value entering other systems.
How to choose the size of the surge protector? Avoid interference due to the magnetic field. New, expanded and renovated buildings can be designed by a separate protection theory.
1. On the power lines that continuously cross the interface between LPZ0A and LPZ0B and LPZ1, such as the main power supply distribution box, the main distribution cabinet on the low-voltage side of the distribution transformer, and the distribution box of the power line that is led out to the protection range of the building's lightning protection device. T1-level (10/350us) surge protectors should be installed. If it cannot be calculated, Iimp ≥ 12.5KA is generally used, that is, 12.5KA is sufficient in most cases, but we recommend using Iimp=20KA or 25KA so that there will be a larger margin and a longer service life.
2. At the interface between LPZ1 and LPZ2, such as in distribution boxes in floor distribution boxes, computer centers, telecommunications rooms, elevator control rooms, etc. T2-level (8/20us) surge protectors should be installed in this level of distribution box. Here we recommend using Imax=40KA surge protectors, because in actual use, lightning strikes above 40KA (after LPZ1) are very rare.
3. For equipment that needs to limit transient overvoltage to a specific level (especially information system equipment), its location is located at the junction of LPZ2 and its subsequent lightning protection zone. For example: T2-level or T3-level surge protectors should be installed in front of or in the nearest socket box of computer equipment, information equipment, electronic equipment and control equipment. Here, Imax=20KA surge protectors are recommended based on the model of easy-to-make surge protectors.
