Surge protection should be implemented in a hierarchical manner to achieve the ultimate goal of perfect protection of power distribution systems and electronic equipment. Graded implementation of the first step of surge protection is to classify the surge environment.
The classification of the surge environment is based on the strength and frequency of the surge. Internationally, the surge environment is generally divided into three categories (as shown in the figure):
(1) Category C: refers to the outdoor as well as the incoming main switch, these parts are prone to stronger lightning surges, the specific location of the meter and the distribution panel of the connection between the wire, the overhead line between the building, connecting to the underground cables of the underground;
(2) Category B: refers to the environment of the C category and the connection between the line of the short position, and lighting in large buildings. location, as well as lighting systems in large buildings, the surge in these locations can be generated both by lightning and internal electrical switching, the surge generated by lightning through the distribution line attenuation, has been attenuated a little more than the surge in the environment of class C;
(3) Class A: refers to the room of the power outlet and the terminals of the longer distribution line; the longer meaning is away from the location of the B class provisions of 10 meters power sockets that are more than 10 meters away from the location specified in Class B, or 20 meters away from the location specified in Class C. The surge in these locations is mainly the surge voltage generated by the internal electrical switches.
In accordance with the recommendations of the Institute of Electrical and Electronics Engineers (IEEE), surge protection should be implemented in a graded manner, the grading method corresponds to the classification of surge environments:
The first level: in the entry of the distribution cabinet, to eliminate the surge generated by outdoor lightning, to prevent the huge surge energy from entering the house;
The second level: in the distribution system of the switchboard at the distribution system, which serves two purposes, one is to further attenuate the residual voltage of the first level. One is to further attenuate the residual surge energy of the first level, and the other is to eliminate the surge generated by the internal electrical switch;
Third level: installed in the sensitive electronic equipment at the power supply into the line, to provide complete protection for electronic equipment.
The purpose of the graded protection is twofold, one is to attenuate the lightning surge step by step, and the other is to eliminate the surge generated when internal loads are switched on and off.
The first level of protection focuses on the surge voltage induced by lightning on the power line, the lightning surge will be moderate attenuation. This level of protection should be used to withstand the current energy surge protector. Some foreign manufacturers recommend the use of withstand current capacity of 200kA or more products. In fact, according to a large number of statistics, most of the amplitude of the surge current in the 10kA or so, the reason for retaining such a large margin, mainly in view of extending the life of the protector. Surge protector life is limited, after each surge impact, the on-state voltage will be reduced some, when reduced to the supply voltage, the surge protector declared the end of life. Surge protector each time the magnitude of the voltage reduction is related to its rated current capacity. The larger the rated current, the longer the life of the surge protector. Some manufacturers in Europe and the United States dare to promise a warranty of 20 years, is based on such a large margin. The first level of surge protector is characterized by large capacity, do not need sine wave tracking function.
The main function of the second level of protection is to further attenuate the residual lightning surge, and attenuate the surge voltage generated by internal electrical loads. This level of protection can utilize a surge protector that withstands less current. Depending on whether there is a third level of protection behind it, the decision to use a protector with sine wave tracking is made. If there is a third level of protection, there is no need for sine wave tracking; if there is no
Third level of protection, and the load is electronic equipment, it is necessary to have a sine wave tracking function.
The main function of the third level of protection is to provide surge-free voltages for electrical equipment, and it should have a sine wave tracking function. The third level of protection is necessary when encountering the following occasions:
(1) electronic equipment with microprocessor-based equipment;
(2) expensive electronic equipment or electronic equipment with a long maintenance cycle:
(3) lightning-prone areas;
(4) high-power electrical loads in the area;
(5) factories, mines, and in the automated control equipment;
(6) automated office equipment, computers, photocopiers, etc.;
(7) critical medical equipment, especially life monitoring equipment.