Basic component Varistor gas discharge tube suppression diode choke coil 1/4 wavelength short circuit breaker discharge gap classification protection
Surge protector, also called lightning protector, is an electronic device that provides safety protection for various electronic equipment, instruments, and communication lines.When a spike current or voltage is suddenly generated in the electrical circuit or communication circuit due to external interference, the surge protector can conduct and shunt in a very short time, so as to prevent the surge from damaging other equipment in the circuit.Basic component discharge gap (also known as protection gap): It is generally composed of two metal rods exposed to the air with a certain gap between them, one of which is connected to the power phase line L1 or neutral line (N) of the required protection device Connected, another metal rod is connected to the grounding wire (PE). When the instantaneous overvoltage strikes, the gap is broken down, and a part of the overvoltage charge is introduced into the ground, avoiding the voltage increase on the protected equipment.The distance between the two metal rods in the discharge gap can be adjusted as required, and the structure is relatively simple, but the disadvantage is that the arc extinguishing performance is poor.The improved discharge gap is an angular gap. Its arc extinguishing function is better than the former. It relies on the electric power F of the circuit and the rising effect of the hot air flow to extinguish the arc.
The gas discharge tube is composed of a pair of cold cathode plates separated from each other and enclosed in a glass tube or ceramic tube filled with a certain inert gas (Ar).In order to improve the triggering probability of the discharge tube, there is an auxiliary triggering agent in the discharge tube.This gas-filled discharge tube has two-pole type and three-pole type. The technical parameters of the gas discharge tube mainly include: DC discharge voltage Udc; impulse discharge voltage Up (usually Up≈(2～3) Udc; power frequency The current In; the impact and the current Ip; the insulation resistance R (>109Ω); the inter-electrode capacitance (1-5PF). The gas discharge tube can be used under both DC and AC conditions. The selected DC discharge voltage Udc is as follows: Use under DC conditions: Udc≥1.8U0 (U0 is the DC voltage for normal line operation) Use under AC conditions: U dc≥1.44Un (Un is the effective value of the AC voltage for normal line operation) The varistor is based on ZnO As the main component of the metal oxide semiconductor non-linear resistance, when the voltage applied to its two ends reaches a certain value, the resistance is very sensitive to the voltage. Its working principle is equivalent to the series and parallel connection of multiple semiconductor PNs. The characteristics of varistors are non-linear Good linearity characteristics (I=non-linear coefficient α in CUα), large current capacity (~2KA/cm2), low normal leakage current (10-7～10-6A), low residual voltage (depending on the work of the varistor Voltage and current capacity), fast response time to transient overvoltage (~10-8s), no freewheeling. The technical parameters of varistor mainly include: varistor voltage (ie switching voltage) UN, reference voltage Ulma; residual voltage Ures; residual voltage ratio K (K=Ures/UN); maximum current capacity 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 the industrial frequency power supply) Minimum reference voltage: Ulma ≥ (1.8 ~ 2) Uac (used under DC conditions) Ulma ≥ (2.2 ~ 2.5) Uac (used under AC conditions, Uac is the AC working voltage) The maximum reference voltage of the varistor should be determined by the withstand voltage of the protected electronic device, and the residual voltage of the varistor should be lower than the loss voltage level of the protected electronic device, namely (Ulma)max≤Ub/K, the above formula K is the residual voltage ratio, Ub is the loss voltage of the protected equipment.
Suppressor diode Suppressor diode has the function of clamping and limiting voltage. It works in the reverse breakdown area. Because of its low clamping voltage and fast action response, it is especially suitable for the last few levels of protection in multi-level protection circuits. element.The volt-ampere characteristics of the suppression diode in the breakdown zone can be expressed by the following formula: I=CUα, where α is the nonlinear coefficient, for the Zener diode α=7～9, in the avalanche diode α=5～7. Suppression diode The main technical parameters are: ⑴ Rated breakdown voltage, which refers to the breakdown voltage under the specified reverse breakdown current (usually lma). As for the Zener diode, the rated breakdown voltage is generally in the range of 2.9V～4.7V , And the rated breakdown voltage of avalanche diodes is often in the range of 5.6V to 200V.⑵Maximum clamping voltage: It refers to the highest voltage that appears at both ends of the tube when the large current of the specified waveform is passed.⑶ Pulse power: It refers to the product of the maximum clamping voltage at both ends of the tube and the equivalent value of the current in the tube under the specified current waveform (such as 10/1000μs).⑷Reverse displacement voltage: It refers to the maximum voltage that can be applied to both ends of the tube in the reverse leakage zone, and the tube should not be broken down under this voltage.This reverse displacement voltage should be significantly higher than the peak operating voltage of the protected electronic system, that is, it cannot be in a weak conduction state when the system is operating normally.⑸Maximum leakage current: it refers to the maximum reverse current flowing in the tube under the action of reverse displacement voltage.⑹Response time: 10-11s Choke coil The choke coil is a common mode interference suppression device with ferrite as the core. It consists of two coils of the same size and the same number of turns that are symmetrically wound on the same ferrite A four-terminal device is formed on the body toroidal core, which has a suppressive effect on the large inductance of the common-mode signal, but has little effect on the small leakage inductance for the differential-mode signal.The use of choke coils in balanced lines can effectively suppress common mode interference signals (such as lightning interference) without affecting the normal transmission of differential mode signals on the line.The choke coil should meet the following requirements during production: 1) The wires wound on the coil core should be insulated from each other to ensure that no short-circuit breakdown occurs between the turns of the coil under the action of instantaneous overvoltage.2) When a large instantaneous current flows through the coil, the magnetic core should not be saturated.3) The magnetic core in the coil should be insulated from the coil to prevent breakdown between the two under the action of transient overvoltage.4) The coil should be wound in a single layer as much as possible. This can reduce the parasitic capacitance of the coil and enhance the coil’s ability to withstand instantaneous overvoltage.1/4 wavelength short-circuit device 1/4-wavelength short-circuit device is a microwave signal surge protector made based on the spectrum analysis of lightning waves and the standing wave theory of antenna and feeder. The length of the metal short-circuit bar in this protector is based on the working signal The frequency (such as 900MHZ or 1800MHZ) is determined by the size of 1/4 wavelength.The length of the parallel shorting bar has infinite impedance for the frequency of the working signal, which is equivalent to an open circuit and does not affect the transmission of the signal. However, for lightning waves, because the lightning energy is mainly distributed below n+KHZ, this shorting bar The lightning wave impedance is very small, which is equivalent to a short circuit, and the lightning energy level is leaked into the ground.Since the diameter of the 1/4-wavelength short-circuit bar is generally a few millimeters, the impact current resistance performance is good, which can reach more than 30KA (8/20μs), and the residual voltage is very small. This residual voltage is mainly caused by the short-circuit bar’s own inductance. The disadvantage is that the power frequency band is relatively narrow, and the bandwidth is about 2% to 20%. Another shortcoming is that it is not possible to add a DC bias to the antenna feeder facility, which limits certain applications.
Hierarchical protection of surge protectors (also known as lightning protectors) hierarchical protection Because the energy of lightning strikes is very huge, it is necessary to gradually discharge the energy of lightning strikes to the earth through the method of hierarchical discharge.The first-level lightning protection device can discharge direct lightning current, or discharge the huge energy conducted when the power transmission line is directly struck by lightning. For places where direct lightning strikes may occur, CLASS-I lightning protection must be carried out.The second-level lightning protection device is a protection device for the residual voltage of the front-level lightning protection device and the induced lightning strike in the area. When the front-level lightning strike energy absorption occurs, there is still a part of the equipment or the third-level lightning protection device. It is quite a huge amount of energy that will be transmitted, and it needs to be further absorbed by the second-level lightning protection device.At the same time, the transmission line passing through the first-level lightning protection device will also induce lightning electromagnetic pulse radiation LEMP. When the line is long enough, the energy of the induced lightning becomes large enough, and the second-level lightning protection device is required to further discharge the lightning energy.The third-level lightning protection device protects LEMP and the residual lightning energy passing through the second-level lightning protection device.The purpose of the first level of protection is to prevent the surge voltage from being directly conducted from the LPZ0 zone into the LPZ1 zone, and to limit the surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V.The power surge protector installed on the low-voltage side of the home power transformer should be a three-phase voltage switch-type power surge protector as the first level of protection, and its lightning flow rate should not be less than 60KA.This level of power surge protector should be a large-capacity power surge protector connected between each phase of the incoming line of the user’s power supply system and the ground.It is generally required that this level of power surge protector has a maximum impact capacity of more than 100KA per phase, and the required limit voltage is less than 1500V, which is called CLASS I power surge protector.These electromagnetic lightning protection devices are specially designed to withstand the large currents of lightning and induced lightning and to attract high-energy surges, which can shunt large amounts of surge currents to the ground.They only provide medium-level protection (the maximum voltage that appears on the line when the impulse current flows through the power surge arrester is called the limit voltage), because CLASS I protectors mainly absorb large surge currents. They cannot completely protect the sensitive electrical equipment inside the power supply system.The first-level power lightning arrester can prevent 10/350μs, 100KA lightning wave, and reach the highest protection standard stipulated by IEC.The technical reference is: the lightning flow rate is greater than or equal to 100KA (10/350μs); the residual voltage value is not greater than 2.5KV; the response time is less than or equal to 100ns.The purpose of the second level of protection is to further limit the value of the residual surge voltage passing through the first level of lightning arrester to 1500-2000V, and implement equipotential connection for LPZ1-LPZ2.The power surge protector output from the distribution cabinet circuit should be a voltage-limiting power surge protector as the second level of protection, and its lightning current capacity should not be less than 20KA. It should be installed in the substation that supplies power to important or sensitive electrical equipment. Road distribution office.These power supply lightning arresters can better absorb the residual surge energy that has passed through the surge arrester at the user’s power supply entrance, and have a better suppression of transient overvoltage.The power surge protector used here requires a maximum impact capacity of 45kA or more per phase, and the required limit voltage should be less than 1200V. It is called a CLASS Ⅱ power surge protector.The general user power supply system can achieve the second-level protection to meet the requirements of the operation of the electrical equipment. The second-level power supply lightning arrester adopts the C-type protector for phase-center, phase-earth and middle-earth full mode protection, mainly The technical parameters are: the lightning current capacity is greater than or equal to 40KA (8/20μs); the residual voltage peak value is not greater than 1000V; the response time is not greater than 25ns.
The purpose of the third level of protection is the ultimate means of protecting the equipment, reducing the value of the residual surge voltage to less than 1000V, so that the surge energy will not damage the equipment.The power surge protector installed at the incoming end of the AC power supply of electronic information equipment should be a series voltage-limiting power surge protector as the third level of protection, and its lightning current capacity should not be less than 10KA.The last line of defense can use a built-in power lightning arrester in the internal power supply of the electrical equipment to achieve the purpose of completely eliminating the tiny transient overvoltage.The power surge protector used here requires a maximum impact capacity of 20KA or less per phase, and the required limit voltage should be less than 1000V.For some particularly important or particularly sensitive electronic equipment, it is necessary to have the third level of protection, and it can also protect the electrical equipment from the transient overvoltage generated inside the system.For the rectifier power supply used in microwave communication equipment, mobile station communication equipment and radar equipment, it is advisable to select a DC power supply lightning protector adapted to the working voltage as the final protection according to the protection needs of its working voltage.The fourth level and above protection is based on the withstand voltage level of the protected equipment. If the two levels of lightning protection can limit the voltage to be lower than the withstand voltage level of the equipment, only two levels of protection are required. If the equipment has a lower withstand voltage level , May require four or more levels of protection.The lightning current capacity of the fourth level protection should not be less than 5KA. The working principle of the classification of surge protectors is divided into ⒈ switch type: its working principle is that when there is no instantaneous overvoltage, it presents a high impedance, but once it responds to the lightning transient overvoltage, its impedance suddenly changes to a low value, allowing lightning The current passes.When used as such devices, the devices include: discharge gap, gas discharge tube, thyristor, etc.⒉Voltage-limiting type: Its working principle is high resistance when there is no instantaneous overvoltage, but with the increase of surge current and voltage, its impedance will continue to decrease, and its current-voltage characteristics are strongly nonlinear.The devices used for such devices are: zinc oxide, varistors, suppressor diodes, avalanche diodes, etc.⒊ Shunt type or choke type shunt type: connected in parallel with the protected equipment, it presents a low impedance to the lightning pulse, and presents a high impedance to the normal operating frequency.Choke type: In series with the protected equipment, it presents high impedance to lightning pulses, and presents low impedance to normal operating frequencies.The devices used for such devices are: choke coils, high-pass filters, low-pass filters, 1/4 wavelength short-circuit devices, etc.
According to the purpose (1) Power protector: AC power protector, DC power protector, switching power protector, etc.The AC power lightning protection module is suitable for the power protection of power distribution rooms, power distribution cabinets, switch cabinets, AC and DC power distribution panels, etc.; There are outdoor input power distribution boxes in the building, and building floor power distribution boxes; power wave Surge protectors are used for low-voltage (220/380VAC) industrial power grids and civil power grids; in power systems, they are mainly used for three-phase power input or output in the power supply panel of the main control room of the automation room and substation.It is suitable for various DC power supply systems, such as: DC power distribution panel; DC power supply equipment; DC power distribution box; electronic information system cabinet; output terminal of secondary power supply equipment.⑵Signal protector: low-frequency signal protector, high-frequency signal protector, antenna feeder protector, etc.The scope of application of the network signal lightning protection device is used for 10/100Mbps SWITCH, HUB, ROUTER and other network equipment lightning strikes and lightning electromagnetic pulse induced overvoltage protection; ·Network room network switch protection; ·Network room server protection; ·Network room other Protection of equipment with network interface; ·24-port integrated lightning protection box is mainly used for centralized protection of multi-signal channels in integrated network cabinets and branch switch cabinets. Signal surge protectors. Video signal lightning protection devices are mainly used for point-to-point video signal equipment. The synergy protection can protect all kinds of video transmission equipment from the hazards caused by the induced lightning strike and surge voltage from the signal transmission line, and it is also applicable to 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 recorders and video cutters in the integrated control cabinet.
Post time: Nov-25-2021