In the lightning protection project, there are many controversies about the installation position and selection of the power supply arrester. The author combines the work experience of these years with the lightning protection theory to explain some of his own views:
Class B arrester (installed in LPZ0A area)
1. Installation principle Theoretically, the first-level arrester (Class B) should be installed in the front end of the main inlet line as much as possible. If it is not convenient to install, it can also be installed in the open rear end. However, if there is a dual power switching device at the front end of the incoming line, it must be installed at the front end of the dual power switching device to protect the switching device (the current dual power switching device is mostly mechanical and electronically controlled, and some have 232 And 485 control device and 24 volt fire power supply, once the lightning current passes, it is easy to damage). The reason is that the operating time of the open circuit breaker is far greater than the operating time of the arrester. Once the lightning current (overvoltage) passes, the lightning arrester will act in advance before the circuit breaker operates, and the overcurrent will be discharged, thereby protecting the circuit. And the electrical equipment at the back end.
2, selection principle B-class arrester try to choose the voltage switch type arrester, the flow capacity is large, the protection voltage UP should be as small as possible. Generally, the front end of the arrester should be connected in series with the circuit breaker of the corresponding capacity. The function of the circuit breaker: when the arrester is damaged, it is convenient to replace; the second is to avoid the current-to-ground fault when the arrester is aging.
Class C arrester (installed in LPZ1 area)
1. The installation principle adopts a voltage-limiting arrester, which can be installed in parallel on the front end or the rear end of the secondary power supply. The front end of the arrester is connected in series with the circuit breaker of the corresponding capacity. The role is the same as above.
2. Selection principle The Class C arrester adopts a voltage limiting type, and the residual voltage generated after the B-level arrester is turned on is controlled below the impact insulation level of the equipment. Since the corresponding time of the voltage limiting component is fast, generally about 25 ns, and the corresponding time of the discharge gap is relatively slow, about 100 ns, so the B-level arrester should be turned on before ensuring that the Class C arrester is turned on. This must be guaranteed to have a certain installation distance between the B and C levels. Theoretical Analysis (Calculation of Inter-SPD Levels - Application of Traveling Wave Theory for Overvoltage Analysis)
Class D arrester
Ibid.
The role of the Class B arrester is mainly to discharge the amplified current. The role of the Class C and Class D arresters is mainly to limit the residual pressure of the Class B arrester below the withstand voltage of the back end equipment. To protect the device.
C and D class arresters should be installed as close as possible to the protected object.
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