Class B surge arrester (installed in LPZOA area)
1. Installation principle: Theoretically, the first-level arrester (Class B) should be installed at the front end of the main incoming line circuit breaker. If the installation is inconvenient, it can also be installed at the back end of the circuit breaker. 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 (most of the current dual power switching devices are mechanical and electronically controlled, and some also have 232 and 485 control devices and 24-volt fire power supply. Once the lightning current passes through, it is easily damaged). The reason is that the operating time of the circuit breaker (circuit breaker) is much longer than the operating time of the arrester. Once lightning current (overvoltage) passes through, the arrester will act in advance before the circuit breaker operates to discharge the overcurrent, thereby protecting the circuit and its back-end electrical equipment.
2. Selection principle: For Class B arresters, try to choose voltage switching arresters, which have large current capacity and the protection voltage UP should be as small as possible. Generally, the front end of the arrester must be connected in series with a circuit breaker of corresponding capacity. The function of the circuit breaker is to facilitate replacement when the arrester is damaged. Secondly, to avoid current to ground faults when the arrester ages.
Class C arrester (installed in LPZ1 zone)
1. Installation principle: Use a voltage-limiting arrester, which can be installed in parallel at the front or rear end of the secondary power circuit breaker. The front end of the arrester is connected in series with a circuit breaker of corresponding capacity. The function is the same as above.
2. Selection principle: Class C arresters are of the voltage-limiting type, and the residual voltage generated after the Class B arrester is turned on is controlled below the impact insulation level of the equipment. Since the response time of the voltage-limiting component is fast, generally about 25ns, while the response time of the discharge gap is relatively slow, about 100ns, the Class B arrester should be turned on before ensuring that the Class C arrester is turned on. This must ensure a certain installation distance between Class B and Class C.
The main function of Class B arresters is to discharge large currents. The main function of Class C and Class D arresters is to limit the residual voltage of Class B arresters below the withstand voltage level of the back-end equipment. to protect the equipment.
Class C and D arresters should be installed as close as possible to the end of the protected object.
