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Surge generation, surge protection principle, surge protector (SPD) protection mode life

With the rapid development of microelectronics technology, the integration of half-body devices has continued to increase, the spacing of components has been reduced, and the thickness of semiconductors has become thinner.The possibility of electronic equipment being damaged by transient overvoltage is increasing.External surges and internal surges and overvoltages have become the main factors for damage to electronic equipment and interruption of work.In order to ensure that the precision electronic design system can work normally, it is required that the surge protection design should be more reasonable, and a qualified surge protector should be selected at the same time Overvoltage fluctuations usually last only one millionth of a second in the circuit.Surge is an abnormally large current pulse on the order of microseconds. The wave head time is generally 025~20us, and the unit energy is generally 25~10MJ/Ω.There are two types of surge sources: external surges and internal surges.External surges mainly come from lightning, and internal surges are overvoltages on power lines generated by switch operations in the power supply network.Lightning is the most obvious factor that causes surges. Lightning strikes the transmission line and causes huge overvoltage. An ordinary lightning voltage can reach 3~200 million V, and the current is 2000~3000A.The vast majority (88%) of internal surges on low-voltage power lines are caused by the opening of internal electrical equipment.The high voltage generated by surges far exceeds the voltage level that computers and other microelectronic devices can withstand, causing damage to the chips of computers and other electrical equipment, aging of components, and damage to electronic devices, which are extremely harmful to production and life. Protection principle (1) The most common method of surge protection The most common method of surge protection is to use a surge protector (Surge protection Device), also known as “surge protector, “surge protector” or overvoltage protector”. English abbreviated as SPD.The function of the surge protector is to limit the instantaneous overvoltage of the power line and the signal transmission line to the voltage range that the equipment or system can handle, and to leak the powerful current into the ground to protect the equipment or system from high voltage shocks. damage.The type and structure of surge protectors are different for different purposes, but they include at least one non-linear voltage limiting element.Commonly used surge protectors include Mov (Metal Oxide varistor) and gas discharge tubes, etc.

Surge contains powerful energy and cannot be stopped.For this reason, the strategy to protect sensitive electrical equipment from surge damage is to divert the surge from the equipment to the ground.(2) The surge protector MOV is composed of three parts, in the middle is a metal oxide material, and two semiconductors are connected to the power supply and the ground.When a surge occurs, MO will act immediately, and the response time is 1~3 nanoseconds. The v in MO∨ is a varistor. At the moment of response, the resistance of MOV drops from the maximum value to near zero ohms, and the overcurrent flows through the MoV. Flow into the earth.Protected electrical equipment continues to operate under normal operating voltage, and its semiconductor components have the property of changing resistance with voltage changes.When the voltage is lower than a certain value, the movement of electrons in the semiconductor produces high resistance.Conversely, when the voltage exceeds this specific value, the electron movement will change, and the semiconductor resistance will decrease close to zero ohms.If the voltage is normal, the surge protector MOV is used aside, and it does not affect the power line.(3) Indicators for evaluating the pros and cons of the surge protector MOV 1. Clamping voltage: indicates the voltage value that will cause MO∨ to connect to the ground wire.The lower the clamping voltage, the better the protection performance 2. Energy absorption and dissipation capacity: This nominal value indicates how much energy the surge protector can absorb before it burns out, the unit is joules, the higher the effective value, the better the protection performance. .Response time: Surge protectors will not be disconnected immediately, and they will have a slight delay in responding to surges. (4) Gas discharge tube Another common surge protection device is a gas discharge tube.The effect of these gas discharge lightning is the same as MO∨. They have to move the excess current from the fire system to the ground wire. This function is achieved by using an emotional gas as a conductor between the two wires.When the voltage is in a certain range, the composition of the gas determines that it is a poor conductor.If the voltage surges and exceeds this range, the intensity of the current will be so as to ionize the gas, so that the gas discharge tube becomes a very good conductor.It will be energized and conducted to the ground wire until the voltage returns to a normal level, and then it will become a bad conductor.

Third, the surge protector (SPD) protection mode sPD can be connected between L, N, and PE. These connection methods are called protection modes. They are related to the grounding method of the power supply system. The “Low Voltage Power Distribution Design Code” stipulates that the power supply system is grounded. Divided into: NS system (three-phase five-wire), TNC system (three-phase four-wire), TNCS system (from three-phase four-wire to three-phase five-wire), “system (three-phase three-wire) and TT system (three-phase four-wire) Line) The mode protector is a combination of 4 single chips, it does not protect all possible lines through which the surge current passes, such as between the live line and the live line, and the neutral line of the live line. 4 horizontal surge protectors It is possible to distort the sPD voltage protection level, and the protection level is poor, which will cause three situations: Voltage suppression level mismatch: Response time mismatch: Freewheeling problem has a safety hazard. Full mode protection. The three live lines are connected to the protection lines through surge suppression components, the neutral line is connected to the protection lines through surge suppression components, and the three live lines are connected through surge suppression components. In full mode, the surge current passes through. All lines are protected, and its advantages are that the full-mode surge protection device protects all possible lines through which the surge current passes; it is beneficial to the protection of the power grid and the surge protector itself; no voltage will appear. The problem of protection level distortion and component response time mismatch 4. Conclusion Through the generation of surges, the role of surge protectors and the wiring of surge protectors, we can avoid the hazards of surges in our daily work and study, and improve power consumption. Equipment service life