(Also called guard gap):
Generally, it consists of two metal bars exposed to the air and separated by a certain gap. One metal bar is connected to the power phase line L 1 or neutral line (N) of the protected equipment, and the other metal bar is connected to the grounding line (PE). When instantaneous overvoltage strikes, the gap is broken down, and a part of overvoltage charge is introduced into the earth, thus avoiding the voltage rise on the protected equipment. The distance between two metal rods in this discharge gap can be adjusted as required, and its structure is simple, but its disadvantage is poor arc extinguishing performance. The improved discharge gap is angular, and its arc extinguishing function is better than the former. It extinguishes the arc through the electromotive force f of the circuit and the rising action of the hot air flow.
gas discharge tube
It is composed of a pair of cold cathode plates separated from each other and encapsulated in a glass tube or ceramic tube filled with some inert gas (Ar). In order to improve the trigger probability of the discharge tube, there is also a trigger auxiliary in the discharge tube. There are two kinds and three kinds of gas-filled discharge tubes.
The main technical parameters of gas discharge tube are: DC discharge voltage Udc；; Impulse discharge voltage Up (generally up ≈ (2 ~ 3) UDC; Power frequency and current in; Impact and give the current IP; Insulation resistance r (> 109Ω); Interpolar capacitance (1 5PF)
The gas discharge tube can be used under dc and AC conditions, and the selected DC discharge voltage Udc is as follows: UDC ≥1.8u0 under DC conditions (U0 is the DC voltage for normal operation of the line).
Use under AC conditions: U dc≥ 1.44Un(Un is the effective value of AC voltage during normal operation of the line).
voltage dependent resistor
It is a metal oxide semiconductor nonlinear resistor with ZnO as the main component. When the voltage across the resistor reaches a certain value, the resistor is very sensitive to the voltage. Its working principle is equivalent to the series-parallel connection of multiple semiconductors P-N. The varistor is characterized by good nonlinear characteristics (I = the nonlinear coefficient α in Cu α), large current capacity (~ ~2KA/cm2), small normal leakage current (10-7 ~ 10-6a) and low residual voltage (depending on the varistor)
The technical parameters of varistor mainly include: varistor voltage (i.e. switching voltage) UN, reference voltage Ulma；; Residual pressure; ; Residual pressure ratio k (k = Ures/UN); Maximum flow Imax；; Leakage current; Response time.
The use conditions of varistor are: varistor voltage: UN≥[(√2× 1.2)/0.7]Uo(Uo is the rated voltage of power frequency power supply).
Minimum reference voltage: ulma ≥ (1.8 ~ 2) UAC (used under DC condition)
Ulma ≥ (2.2 ~ 2.5) Uac (used under AC conditions, Uac is AC working voltage)
The maximum reference voltage of the varistor should be determined by the withstand voltage of the protected electronic equipment, and the residual voltage of the varistor should be lower than the loss voltage level of the protected electronic equipment, that is, (Ulma)max≤Ub/K, where K is the residual voltage ratio and Ub is the loss voltage of the protected electronic equipment.
Suppression diode
The suppression diode has the functions of clamping and voltage limiting, and works in the reverse breakdown region. Because of its advantages of low clamping voltage and fast action response, it is especially suitable for the last few protection elements in multi-stage protection circuits. The volt-ampere characteristics of the suppression diode in the breakdown region can be expressed by the following formula: I=CUα, where α is the nonlinear coefficient, zener diode α = 7 ~ 9, avalanche diode α = 5 ~ 7.
The technical parameters of the suppression diode mainly include:
(1) Rated breakdown voltage refers to the breakdown voltage under the specified reverse breakdown current (usually lma). As for the rated breakdown voltage of Zener diode, it is generally in the range of 2.9V~4.7V, while the rated breakdown voltage of avalanche diode is often in the range of 5.6V~200V.
⑵ Maximum clamping voltage: refers to the highest voltage at both ends of the pipe when the pipe passes through a large current with a specified waveform.
⑶ Pulse power: refers to the product of the maximum clamping voltage at both ends of the tube and the equivalent current in the tube under a specified current waveform (such as 10/ 1000μs).
(4) Reverse displacement voltage: the maximum voltage that can be applied at both ends of the pipeline in the reverse leakage area, under which the pipeline should not be broken down. This reverse displacement voltage should be significantly higher than the peak value of the highest working voltage of the protected electronic system, that is, the system cannot be in a weak conduction state when it works normally.
5] Maximum leakage current: refers to the maximum reverse current flowing in the pipe under the action of reverse displacement voltage.
[6] Response time:10-11s.
choking coil
Choke is a * * * mode interference suppression device with ferrite as the core. It consists of two coils with the same size and the same number of turns wound symmetrically on the same ferrite ring core to form a four-terminal device, which can suppress the * * * mode signal and has little leakage inductance to the differential mode signal. Choke can effectively suppress the * * mode interference signal (such as lightning interference) in the balanced line, but it has no effect on the differential mode signal normally transmitted by the line.
Choke coil shall meet the following requirements when manufacturing:
1) The wires wound on the core of the coil should be insulated from each other to ensure that the coil does not have turn-to-turn breakdown short circuit under the action of instantaneous overvoltage.
2) When the coil flows with instantaneous high current, the magnetic core should not be saturated.
3) The magnetic core in the coil should be insulated from the coil to prevent the breakdown between them under the action of instantaneous overvoltage.
4) The coil is wound in a single layer as far as possible, which can reduce the parasitic capacitance of the coil and enhance the tolerance of the coil to instantaneous overvoltage.
1/4 has a shorter wavelength.
1/4 wavelength short circuit breaker is a microwave signal surge protector based on lightning wave spectrum analysis and antenna feeder standing wave theory. The length of the metal short-circuit bar in the protector is determined according to the wavelength of 1/4 of the working signal frequency (such as 900MHZ or 1800MHZ). For the working signal frequency, the length of the parallel short-circuit bar has infinite impedance, which is equivalent to an open circuit and does not affect the signal transmission. However, for lightning wave, because the lightning energy is mainly distributed below n+KHZ, the impedance of short-circuit rod to lightning wave is very small, which is equivalent to short circuit, and the lightning level discharges underground.
Because the diameter of 1/4 wavelength short-circuiting rod is generally several millimeters, it has good surge current resistance, which can reach above 30KA(8/20μs) and the residual voltage is very small. This residual voltage is mainly caused by the inductance of the short-circuit bar. Its disadvantage is that the frequency band of power supply is narrow, and the bandwidth is about 2% ~ 20%. Another disadvantage is that it cannot add DC bias to the antenna feed. Classification protection of surge protector (also known as lightning arrester)
Because the energy of lightning stroke is very huge, it is necessary to gradually release the lightning stroke energy to the earth by means of graded discharge. The primary arrester can not only discharge the direct lightning current, but also discharge the huge energy transmitted when the transmission line is directly struck by lightning. For places where direct lightning may occur, first-class lightning protection must be carried out. The second stage arrester is a protective device against residual voltage of the previous stage arrester and induced lightning strike in the area. When the lightning energy of the previous stage is absorbed in a large amount, a considerable part of the energy for the equipment or the three-stage arrester will be transferred and needs to be further absorbed by the two-stage arrester. At the same time, the lightning electromagnetic pulse radiation LEMP will also be induced when the transmission line passes through the primary arrester. When the line is long enough, the energy of induced lightning will become large enough, and a secondary arrester is needed to further release the lightning energy. The third arrester protects LEMP and the residual lightning energy passing through the second arrester.
Primary protection device
The purpose is to prevent the surge voltage from directly conducting from LPZ0 area to LPZ 1 area, and limit the surge voltage from tens of thousands to hundreds of thousands of volts to 2500-3000 volts. ..
The lightning arrester installed on the low-voltage side of household power transformer should adopt three-phase voltage switching type lightning arrester as the first-level protection, and its lightning flux should not be less than 60KA. The lightning arrester of this level of power supply shall be a large-capacity lightning arrester connected between each phase of the entrance incoming line of the user power supply system and the earth. Generally, it is required that the lightning arrester of this level of power supply has a maximum impact capacity of more than 100KA per phase, and the required limiting voltage is less than 1500V, which is called a primary lightning arrester. These electromagnetic lightning protection devices are specially designed to withstand the heavy current of lightning and induced lightning stroke and attract high-energy surge, which can shunt a large amount of surge current to the earth. They only provide medium-level protection with limited voltage (the maximum voltage on the line when surge current flows through the arrester is called limit voltage), because Class I protectors mainly absorb large surge current, and they cannot completely protect sensitive electrical equipment in the power supply system.
The first-class power arrester can prevent lightning waves of 10/350μs and 100KA, reaching the highest protection standard stipulated by IEC. Its technical reference is that the lightning flux is greater than or equal to100ka (10/350μ s); The residual voltage value is not more than 2.5KV；; The response time is less than or equal to100ns.
Secondary protection
The purpose is to further limit the residual surge voltage through the primary arrester to 1500-2000 V, and to implement equipotential connection to LPZ 1-LPZ2.
When the power arrester output from the distribution cabinet line is used as the secondary protection, it should be a voltage-limited power arrester with a lightning current capacity of not less than 20KA, and should be installed in a shunt distribution place that supplies power to important or sensitive electrical equipment. These power surge arresters can more perfectly absorb the residual surge energy passing through the surge arresters at the user's power supply entrance, and have excellent suppression effect on transient overvoltage. The power arrester used here requires the maximum impulse capacity of each phase to be greater than 45kA and the limiting voltage to be less than 1200V, which is called Class II power arrester. The power supply system of general users can meet the requirements of electrical equipment operation by realizing secondary protection.
The arrester of the secondary power supply adopts class C protector to protect phase-neutral, phase-ground and neutral-ground in full mode. The main technical parameters are: the lightning current capacity is greater than or equal to 40 kA (8/20 μ s); The peak value of residual pressure shall not exceed1000 v; The response time shall not exceed 25ns.
Three-level protection
The purpose is to finally protect the equipment and reduce the residual surge voltage to below 1000V, so that the surge energy will not damage the equipment.
The power arrester installed at the incoming terminal of the AC power supply of electronic information equipment should be a series voltage-limiting power arrester as the third-level protection, and its lightning current capacity should not be less than 10KA.
The last line of defense can use the built-in power arrester in the power supply part of the electrical equipment to completely eliminate the tiny transient overvoltage. The maximum impulse capacity of the power arrester used here is 20KA or less per phase, and the required limiting voltage should be less than 1000V. There should be three-level protection for some particularly important or sensitive electronic equipment, and at the same time, it can also protect electrical equipment from transient overvoltage generated inside the system.
For the rectifier power supply used in microwave communication equipment, mobile communication equipment and radar equipment, DC power arrester with suitable working voltage should be selected as the final protection according to the protection needs of its working voltage.
Level 4 and above protection
According to the withstand voltage level of the protected equipment, if two-level lightning protection can limit the voltage lower than the withstand voltage level of the equipment, only two-level protection is needed, and if the withstand voltage level of the equipment is low, four or more levels of protection may be needed. The lightning current capacity of the four-level protection is not less than 5KA. Main points of working principle
1. switch type: its working principle is that it presents high impedance when there is no instantaneous overvoltage, but once it responds to lightning instantaneous overvoltage, its impedance suddenly becomes low, allowing lightning current to pass. When used as such devices, the devices include: discharge gap, gas discharge tube, thyratron and so on.
2. Voltage-limited type: Its working principle is that it has high impedance when there is no instantaneous overvoltage, but with the increase of surge current and voltage, the impedance will decrease, and its volt-ampere characteristics are strongly nonlinear. Devices used as such devices include zinc oxide, varistor, suppression diode, avalanche diode, etc.
3. Shunt type or choke type.
Parallel connection type: it is connected in parallel with the protected equipment, showing low impedance to lightning pulse and high impedance to normal working frequency.
Choke type: connected in series with the protected equipment, showing high impedance to lightning pulse and low impedance to normal working frequency.
Devices used as such devices include choke, high-pass filter, low-pass filter, 1/4 wavelength short circuit device, etc.
Divide by purpose
⑴ Power protectors: AC power protectors, DC power protectors and switching power protectors.
The lightning protection module of AC power supply is suitable for power protection of power distribution room, power distribution cabinet, switch cabinet, AC /DC power distribution panel and other systems; There are outdoor input distribution boxes and building floor distribution boxes in the building; Power surge protector is used in low-voltage (220/380VAC) industrial power grid and civil power grid; In power system, it is mainly used as the input or output end of three-phase power supply in the power panel of automation machine room and substation master control room. Suitable for various DC power supply systems, such as: DC distribution panel; DC power supply equipment; DC distribution box; Electronic information system cabinet; Output end of secondary power supply equipment.
⑵ Signal protectors: low-frequency signal protectors, high-frequency signal protectors, antenna feeder protectors, etc.
The application scope of network signal arrester is used to protect network equipment such as 10/ 100Mbps switches, hubs and routers from lightning stroke and induced overvoltage caused by lightning electromagnetic pulse. Protection of network switch in network computer room: server protection in network computer room; Protection of other equipment with network interface in the network room; The 24-port integrated lightning protection box is mainly used for centralized protection of multi-signal surge protectors in integrated network cabinets and sub-exchange cabinets. The application scope of video signal lightning protection device is mainly used for point-to-point cooperative lightning protection of video signal equipment, which can protect various video transmission equipment from the harm caused by induced lightning and surge voltage of signal transmission line, and is also suitable for RF transmission under the same working voltage. The integrated multi-port video lightning protection box is mainly used for centralized protection of control equipment such as hard disk video recorder and video cutting machine in the integrated control cabinet. Well-known surge protector brand
Common surge protectors in the market include: Bull Electrical Anti-surge Socket, Chinese mainland Ruikexing LKX Surge Protector, American ECS Surge Protector, French Soule Surge Protector, British ESP furse Surge Protector, German OBO Surge Protector, DEHN Surge Protector, American PANAMAX Surge Protector, INNOVATⅳEⅳE Ⅳ E Ⅳ E Surge Protector, and American POLYPHASER Surge Protector.