Operating instructions for lightning arresters and surge protectors
catalogue
I. Definition
Second, the comparison between lightning arrester and surge protector
Three. Application and explanation of line arrester
Four. Design principle, characteristics and application scope of surge protector
Verb (abbreviation of verb) reference basis and literature
I. Definition
1. arrester
Lightning arrester is a device to protect substation from lightning shock wave. When the lightning shock wave introduced into the substation along the line exceeds the protection level of the lightning arrester, the lightning arrester discharges first, and the lightning current is safely introduced into the earth through a good conductor, and the lightning voltage amplitude is limited below the lightning shock level of the protected equipment by using the grounding device, thus protecting the electrical equipment.
2. Surge protector
Also known as lightning arrester, it is a device that provides safety protection for all kinds of power equipment, instruments and communication lines. When the peak current or voltage suddenly appears in the electric line or communication line due to external interference, the surge protector can shunt in a very short time, thus avoiding the damage of surge to other equipment in the line.
As can be seen from the following data, surge protector is also a kind of lightning arrester, but there are great differences.
Second, the comparison between lightning arrester and surge protector
Lightning arrester refers to the building lightning arrester, which forms a faraday cage with lightning rod and grounding rod to prevent the building from being damaged. The basic principle of lightning arrester is to introduce the lightning electromagnetic pulse (LEMP) into the ground to eliminate it. But why are a large number of buildings and their equipment still damaged by lightning after lightning arrester installation?
First of all, the conductor of lightning arrester is copper-iron alloy, so the performance of conductor is limited, and the response speed is only 200 microseconds (uS). However, the half-peak speed (maximum energy) of LEMP is 20 microseconds (uS), which means LEMP is faster than lightning arrester, so that after the lightning arrester introduces the first direct lightning into the ground, it often does not respond to the second lightning and the third lightning, and directly leaks electricity on the equipment. In other words, the lightning arrester has little influence on the secondary lightning and the tertiary lightning.
Secondly, after LEMP is introduced into the earth, it will return from the earth to form induced lightning. Induction lightning will leak to equipment (network cable, power cable, signal cable, transmission line, etc. ) From all wires containing metal. Because the arrester is unidirectional, it has no effect on induction lightning, which will directly damage the equipment. What's more, lightning arresters are often not installed in conductor parts.
Thirdly, only 20% of the surge comes from the external environment such as lightning strike, and 80% comes from the internal operation of the system. Lightning arrester has no effect on this 80%.
Answer the difference between surge protector (SPD) and lightning arrester according to the analysis:
1, the application range (voltage) is different: lightning arresters have a wide range and many voltage levels, generally ranging from 0.4kV low voltage to 500kV ultra-high voltage (see the analysis upstairs for details), while SPD generally refers to overvoltage protectors used below 1kV;
2. Different protection objects: lightning arresters protect electrical equipment, while surge protectors generally protect the secondary signal loop or power loop of electronic instruments.
3. Different insulation level or withstand voltage level: the withstand voltage level of electrical equipment and electronic equipment is not an order of magnitude, and the residual voltage of overvoltage protection device should match the withstand voltage level of the protected object.
4. Different installation positions: lightning arresters are generally installed on the primary system to prevent the direct invasion of lightning waves and protect overhead lines and electrical equipment; SPD surge protectors are mostly installed in the secondary system, which is a supplementary measure for lightning arresters to eliminate the direct invasion of lightning waves or when lightning waves are not completely eliminated by lightning arresters. Therefore, lightning arresters are mostly installed at the incoming line; SPD is mostly installed at the terminal exit or signal loop.
5. Different current capacity: the relative current capacity of lightning arrester is large because its main function is to prevent lightning overvoltage; For electronic equipment, its insulation level is far less than that of ordinary electrical equipment, so SPD is needed to protect against lightning overvoltage and operating overvoltage, but its current capacity is generally small. (SPD is usually at the end and will not be directly connected to the overhead line. After the current limiting of the previous stage, the lightning current has been limited to a low value, so the SPD with small current capacity can completely play a protective role. Current value is not important, residual pressure is important. )
6. Other insulation levels and concerns about parameters are also quite different.
7. Surge protector is suitable for fine protection of low-voltage power supply system, and various corresponding specifications can be selected according to different AC and DC power beds. Power surge protector -I Because the terminal equipment is far away from the front surge protector, it is easy to generate oscillating overvoltage or induce other overvoltage on this line. It is suitable for fine power surge protection of terminal equipment, and the protection effect is better when it is used in conjunction with the previous surge protector.
8. The main material of lightning arrester is mostly zinc oxide (a kind of metal oxide varistor), while the main material of surge protector varies according to the surge resistance grade and classification protection (IEC6 13 12), which is much more precise than ordinary lightning arrester in design.
9. Technically, lightning arrester can't reach the level of surge protector in response time, voltage limiting effect, comprehensive protection effect and anti-aging characteristics.
* * * Similarity: All can prevent lightning overvoltage.
Based on the above reasons, SPD came into being.
The principle of SPD is to convert LEMP into heat energy for digestion. Because it is not conductive, the reaction speed is very fast, which can be lower than nanosecond, and it can effectively prevent secondary lightning and tertiary lightning. Surge protectors are divided into power surge protectors, precision instrument surge protectors and digital line surge protectors, which also act in two directions, so they can effectively prevent induced lightning. Therefore, IEEE standard stipulates that SPD should be added when lightning arrester is installed, forming double insurance against lightning stroke.
In addition, SPD can effectively suppress 80% internal surge, which lightning arresters can't do.
Generally speaking, lightning arrester is a protective device specially designed to protect electrical equipment from lightning shock wave, and surge protector is a more advanced protective device than lightning arrester. In addition to the lightning shock wave, it can also greatly weaken other destructive surge impacts generated by the power system itself. In the case that lightning arresters have been installed in the high-voltage incoming line system (10KV and above) of power users, surge protectors with more accurate protection functions should be installed in the low-voltage system.
Three. Application and explanation of lightning arrester
1, the basic principle of lightning protection of line arrester
When a tower is struck by lightning, part of the lightning current flows to the adjacent tower through the lightning rod, and the other part flows into the earth through the tower. The grounding resistance of tower is transient resistance, and generally it is impulse grounding resistance.
When lightning strikes the tower, the potential at the top of the tower rises rapidly, and its potential value is
ut = iRd L.di/dt( 1)
Where I-lightning current;
Rd-impulse grounding resistance;
L.di/dt-transient component.
When the difference between the tower top potential Ut and the induced potential U 1 on the conductor exceeds the discharge voltage of the insulator string 50, flashover from the tower top to the conductor will occur. That is ut-u1> u50; If the influence of line power frequency voltage amplitude Um is considered, it is ut-u 1um > u50. Therefore, the lightning withstand level of the line is related to three important factors, namely, the 50 discharge voltage of the line insulator, the lightning current intensity and the impulse grounding resistance of the tower. Generally speaking, the 50 discharge voltage of transmission lines is constant, and the lightning current intensity is related to geographical location and atmospheric conditions. Without lightning arrester, the lightning withstand level of transmission lines is often improved by reducing the grounding resistance of towers. In mountainous areas, it is very difficult to reduce grounding resistance, which is also the reason why transmission lines are repeatedly struck by lightning.
After the lightning arrester is installed, the shunt of lightning current will change when the transmission line is struck by lightning. Part of the lightning current will pass from the lightning rod to the adjacent tower, and part of the lightning current will enter the ground through the tower. When the lightning current exceeds a certain value, the lightning arrester will act to join the shunt. Most lightning current flows into the conductor from the lightning arrester and propagates to the adjacent tower. When lightning current flows through the lightning rod and the conductor, coupling components will be generated on the conductor and the lightning rod respectively due to electromagnetic induction between the conductors. Because the shunt of lightning arrester is much larger than the lightning current shunted by lightning conductor, the coupling effect of this shunt will increase the potential of conductor, make the potential difference between conductor and tower top smaller than the flashover voltage of insulator string, and the insulator will not flashover. Therefore, the line arrester has a good potential clamping effect, which is also an obvious feature of the line arrester used for lightning protection.
In the past, the lightning protection of transmission lines mainly used the method of reducing the grounding resistance of towers, which was relatively easy in plain areas. For towers in mountainous areas, long radiation grounding wires or deep wells are often used at the four tower feet to increase the contact area between the grounding wire and the soil and reduce the resistivity, and the grounding resistance will be reduced under the power frequency state. However, when struck by lightning, because the grounding wire is too long, there will be a large additional inductance. The transient component of lightning overvoltage will be added to the tower potential by L.di/dt,, which will greatly increase the tower potential, which will more easily lead to flashover between the tower and insulator string, but will reduce the lightning withstand level of the line. Because the line arrester has the function of clamping potential, the requirement for grounding resistance is not strict, and it is easier to realize lightning protection for mountain lines.
2 the use and function of line arrester
The 1 10kV longbo 1 line and the 35kV south black line and Tan diagonal line under the jurisdiction of Zibo Electric Power Bureau are located in hilly and mountainous areas, and lightning trip failures often occur for many years. According to statistics, 1 10kV dragon wave 1 line is in 1989 ~ 1999. In 1997, seven groups of ***20 linear zinc oxide arresters were installed at No.62 ~ 64 of Longbo 1 Line, No.87, No.89 and No.90 of Nanhei Line and No.5 of Tanxie Line. The installation method is to hang three groups of nine lightning arresters on the Longbo 1 line and the south black line, respectively, at No.56540 Tanxie Line.
3 Selection, installation and maintenance of lightning arrester
There are two types of line arresters with series gap and without series gap, which are different from power station arresters in structural design due to different operation modes.
Attention should be paid to the installation of line arrester: (1) Choose transmission line towers that are vulnerable to lightning and have many minefields, and it is best to install them on adjacent towers at the same time; (2) The vertically arranged lines can only be matched with the lower phase; (3) When installing the lightning arrester, try not to use force, and keep a safe distance; (4) The lightning arrester shall be separately laid with grounding wire along the tower, and its cross section shall not be less than 25mm2, so as to reduce the influence of grounding resistance.
Necessary maintenance after commissioning: (1) Measure insulation resistance regularly in combination with power failure, and the results should not change obviously with time; (2) Check and record the action of the counter; (3) Tighten fasteners to prevent loosening; (4) Disassemble 4)5a, and measure the leakage current under the reference voltage of 1 times DC, 1mA, 75.
Four. Design principle, characteristics and application scope of surge protector
design principle
Among the most common surge protectors, there is a component called Metal Oxide Varistor (MOV) for transmitting overvoltage. As shown in the figure below, MOV connects live wire and ground wire together.
MOV consists of three parts: metal oxide material in the middle, and two semiconductors connected to power supply and ground wire.
These semiconductors have a variable resistance that varies with voltage. When the voltage is lower than a certain value, the movement of electrons in the semiconductor will produce extremely high resistance. On the contrary, when the voltage exceeds this specific value, the movement of electrons will change and the semiconductor resistance will be greatly reduced. If the voltage is normal, MOV will be idle. However, when the voltage is too high, MOV can conduct a lot of current and eliminate excess voltage. Because the excess current is transferred to the ground through MOV, the voltage of the live line will return to normal, which will lead to the rapid increase of the resistance of MOV again. In this way, MOV only transmits surge current, while allowing standard current to continue to supply power to equipment connected to surge protector. For example, MOV is like a pressure-sensitive valve, which only opens when the pressure is too high.
Another common surge protection device is gas discharge tube. These gas discharge tubes have the same function as MOV-they transfer excess current from live wire to ground wire, which is realized by using inert gas as conductor between two wires. When the voltage is within a certain range, the composition of the gas determines that it is a bad conductor. If the voltage surges and exceeds this range, the current will be strong enough to ionize the gas, thus making the gas discharge tube a very good conductor. It will conduct current to the ground until the voltage returns to normal level, and then it will become a poor conductor.
Both methods use parallel circuit design-excess voltage flows from the standard circuit to the other circuit. Several surge protector products use series circuit design to suppress surge. They will not shunt excessive current to another line, but reduce the amount of current flowing through the live wire. Basically, these suppressors store electric energy when a high voltage is detected, and then gradually release the electric energy. The company that makes this protector explains that this method can provide better protection because it has faster response speed and will not be shunted to the ground wire, but on the other hand, this shunt may interfere with the power system of the building.
Suppression diode: Suppression diode has the function of clamping and limiting voltage. It works in the reverse breakdown region. Because of its advantages of low clamping voltage and fast action response, it is especially suitable to be used as the last protection element 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:
Rated breakdown voltage (1) refers to the breakdown voltage under the specified reverse breakdown current (usually lma), that is to say, the rated breakdown voltage of Zener diode is generally in the range of 2.9V~4.7V, while that of avalanche diode is generally in the range of 5.6V~200V.
(2) Maximum clamping voltage: refers to the highest voltage at both ends of the tube when a large current with a specified waveform passes.
(3) 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 as101000μ s).
(4) Reverse displacement voltage: refers to 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- 1 1us.
As an auxiliary component, some surge protectors are also equipped with built-in fuses. A fuse is a resistor. When the current is below a certain standard, its conductivity is very good. Conversely, when the current exceeds the acceptable standard, the heat generated by the resistor will blow the fuse, thus cutting off the circuit. If MOV can't suppress surge, too high current will blow the fuse and protect the connected equipment. The fuse can only be used once and needs to be replaced once it is blown.
SPD front-end fuse shall be installed according to the parameters of arrester manufacturer.
If not specified by the manufacturer, the general selection principle is:
According to (maximum fuse strength A of surge protector) and (maximum power supply current B of connected distribution line), determine (breaking current C of switch or fuse).
Determination method:
When: b > When a, c is less than or equal to a.
When: B = A, c is less than a or c is not installed.
When: B < When a and c are less than b or c is not installed.
Some surge protectors have line regulation systems to filter "line noise" and reduce current fluctuation. The system structure of this basic surge protector is very simple. The live wire is connected to the power board socket through the ring choke. The choke coil is just a ring made of magnetic material, surrounded by wires-a basic electromagnet. The fluctuation of the current flowing through the live wire will charge the electromagnet and make it emit electromagnetic energy, thus eliminating the tiny fluctuation of the current. This "regulated" current is more stable, which can make the power supply current of the computer (or other electronic equipment) more gentle.
In electronic design, surge mainly refers to the strong pulse generated at the moment when the power supply is just turned on. Because of the nonlinearity of the circuit itself, there may be pulses higher than the power supply itself; Or surge, because the power supply or other parts of the circuit are interfered by their own or external sharp pulses. It is very likely that the circuit will burn out at the moment of surge, such as the breakdown of PN junction capacitance and the burning of resistance. Surge protection is a protection circuit designed by using the sensitivity of nonlinear components to high frequency (surge). Simple and commonly used are parallel capacitors and series inductors.
Classification of surge protectors
According to the 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 high impedance when there is no instantaneous overvoltage, but its impedance will decrease with the increase of surge current and voltage, and its volt-ampere characteristics are strongly nonlinear. Devices used as such devices include zinc oxide, varistor, suppression diode, avalanche diode, etc.
(3) Split flow or choke flow
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.
According to the purpose:
(1) Power protectors: AC power protectors, DC power protectors and switching power protectors.
(2) Signal protectors: low-frequency signal protectors, high-frequency signal protectors, antenna feeder protectors, etc.
Surge protector and its application
1, surge voltage
When the circuit is struck by lightning, inductive load or heavy load is turned on or off, it often produces high operating overvoltage. This instantaneous overvoltage (or overcurrent) is called surge voltage (or surge current), which is a kind of transient interference: for example, when the coil of DC 6V relay is turned off, a surge voltage of 300 V ~ 600 V will appear; When the incandescent lamp is turned on, there will be surge current of 8 ~ 10 times the rated current; When a large capacitive load such as compensation capacitor bank is connected, there will often be a large surge current impact, which will suddenly reduce the power supply voltage; When the no-load transformer is cut off, there will be operating overvoltage as high as 8 ~ 10 times the rated voltage. Surge voltage is increasingly endangering the safe operation of automation equipment. Eliminating surge noise interference and preventing surge damage have always been the core issues related to the safe and reliable operation of automation equipment. The integration of modern electronic equipment is constantly improving, but their ability to resist surge voltage is declining. In most cases, the surge voltage will damage the circuit and its components, and the degree of damage is closely related to the withstand voltage strength of the components and the convertible energy in the circuit.
In order to prevent the surge voltage from damaging sensitive automation equipment, the conductor with this surge voltage must be short-circuited with the potential equalization system (introduced into the earth) in a very short time. During its discharge, the discharge current can be as high as several thousand amps. At the same time, when the discharge current is large, people often expect the protection unit to limit the output voltage to as low a value as possible. Therefore, air spark gap, inflatable overvoltage arrester, varistor, avalanche diode, TVS(Transientvoltagesuppressor), FLASHTRAB, VALETRAB, SOCKETTRAB, MAINTRAB and other components are applied to the protected circuit alone or in the form of combined circuits, because each component has its own different characteristics and different performances: discharge ability; Response characteristics; Arc extinguishing performance; Pressure limiting accuracy. According to the requirements of different applications and equipment for surge voltage protection, overvoltage protection systems that meet the application requirements can be combined according to the characteristics of various products.
2. Surge voltage absorber
Surge noise is usually suppressed by surge absorbers, which are as follows:
(1) zinc oxide varistor
Zinc oxide varistor is a varistor made of zinc oxide as the main material, which has the advantages of high voltage nonlinear coefficient, large capacity, low residual voltage, small leakage current, no aftercurrent, symmetrical volt-ampere characteristics, wide voltage range, fast response, small voltage-temperature coefficient, simple process and low cost. It is a widely used surge voltage protection device at present. It is suitable for surge absorption of AC power supply voltage, surge voltage absorption and arc extinguishing between various coils and contacts, and surge voltage protection of power electronic devices such as triodes and thyristors.
(2)R, C and D combined surge absorber
R, C and D combined surge absorber is more suitable for DC circuit, and devices can be combined differently according to the characteristics of the circuit. As shown in figure 1(a), it is suitable for high-level DC control system, while in figure 1(b), zener diode or bidirectional diode is used, which is suitable for circuits that need protection in both forward and reverse directions.
Figure 1R, c and d surge protectors (a) unidirectional protection (b) bidirectional protection
Figure 2TVS voltage (current) time characteristics
(3) Transient Voltage Suppressor (TVS)
When the two poles of TVS are impacted by reverse high energy, it can make the impedance between the two poles change from high to low at the speed of 10- 12s, absorb the surge power as high as several kilowatts, clamp the potential of the two poles at a predetermined value, and effectively protect the components in automation equipment from the damage of surge pulses. TVS has the advantages of fast response time, large transient power, low leakage current, small breakdown voltage deviation, easy control of clamping voltage and small size, and is widely used in electronic equipment and other fields.
① Characteristics of TV
Its forward characteristics are the same as those of ordinary diodes, and its reverse characteristics are typical PN junction avalanche devices. Fig. 2 is the current-time and voltage-time curves of TVS. Under the action of surge voltage, the bipolar voltage of TVS rises from rated reverse turn-off voltage VWM to breakdown voltage Vbr and is broken down. With the appearance of breakdown current, the current flowing through TVS will reach the peak pulse current IPP, and the voltage at both ends will be clamped below the predetermined maximum clamping voltage VC. Then, as the pulse current decays exponentially, the voltage between the two poles of TVS also drops continuously, and finally returns to the initial state. This is the process that TVS suppresses the possible surge pulse power and protects electronic components.
② comparison between ②TVS and varistor
At present, varistors are widely used in many household devices that need surge protection. The performance comparison between TVS and rheostat is shown in Table 1:
Comparison between table 1 TVS and rheostat
Parametric TVs varistor
The reaction rate is10-12s50x10-9s.
Is it aging? No, it is.
The maximum service temperature is 175℃ 1 15℃
Device polar monopole bipolar monopole
Reverse leakage current 5 μ a 200 μ a
The clamping factor VC/VBR is not greater than 1? 5 Maximum 7 ~ 8
Sealing property, sealing property and air permeability
The price is more expensive and cheaper.
3. Integrated surge protection system combination
3. 1 tertiary protection
In the system design, the surge protection required by the automatic control system should be considered comprehensively. According to the characteristics of automatic control devices, surge protectors used in the system can be basically divided into three levels. For the power supply equipment of automatic control system, lightning arrester, overvoltage arrester and terminal equipment protector are needed. The interface circuit of data communication and measurement and control technology is obviously much more sensitive than the power supply system circuit of each terminal, so the data interface circuit must be carefully protected.
The primary protection of the power supply equipment of the automation device adopts lightning exile appliances, which are installed at the entrance of the building or in the main distribution box. In order to ensure that the follow-up equipment does not bear excessive residual voltage, it is necessary to install overvoltage arresters in lower-level distribution facilities as secondary protection measures according to the nature of protection scope. The third level of protection is to protect instruments and equipment. The method adopted is to install the overvoltage arrester directly at the front end of the instrument. The three-level protection configuration of the automatic control system is shown in Figure 3. Between different levels of dischargers, the minimum length of conductor must be observed. In the power supply system, the distance between lightning arrester and overvoltage arrester should not be less than 10m, and the distance between overvoltage arrester and instrument protection device should not be less than 5m (that is, the distance between primary surge protector and secondary surge protector should be at least 10m, and the distance between secondary surge protector and tertiary surge protector should be at least 5m).
3.2 tertiary protection device
(1) inert gas-filled overvoltage arrester is a first-class surge protector widely used in automatic control system. Overvoltage discharger filled with inert gas can discharge transient current in 20kA(8/20μs) or 2.5kA( 10/350μs). The response time of gas discharger is in the order of nanosecond, which is widely used in the field of remote communication. One disadvantage of the device is that its trigger characteristic is related to time, and the instantaneous variable of its rise time intersects with the trigger characteristic curve in a range almost parallel to the time axis. Therefore, the protection level will be close to the rated voltage of the gas discharger. In particular, the fast transient variable will intersect the trigger curve at the working point of ten times the rated voltage of the gas discharger, that is, if the minimum rated voltage of the gas discharger is 90V, the residual voltage in the line can be as high as 900 V. Another disadvantage is that it may generate subsequent current. When the gas discharger is triggered, especially in the circuit with low impedance and voltage exceeding 24V, the following situation will occur: it was originally hoped to maintain the short-circuit state for several ms, but the gas discharger will continue to maintain, and the resulting consequence may be that the discharger will burst within a fraction of a second. Therefore, a fuse should be connected in series in the overvoltage protection circuit using the gas discharger to quickly interrupt the current in the circuit.
Fig. 3 Distribution Diagram of Discharge Devices
(2) Varistor is widely used as a secondary protection device in the system, because it has a faster response time in ns time range and will not cause the problem of subsequent current. In the protection circuit of measurement and control equipment, varistor can be used for intermediate protection devices with discharge current of 2.5 kA ~ 5 kA (8/20 μ s). The disadvantages of varistor are aging and large capacitance. Aging refers to p? N part, in the case of normal overload, P? N junction will cause short circuit, so its leakage current will increase, and its value depends on the frequency of load. Its application in sensitive measurement circuits will cause measurement distortion, and the device is prone to heat. Because of the large capacitance of varistor, it can not be used in high frequency information transmission line in many occasions. These capacitors will form a low-pass link with the inductance of the conductor, which will seriously suppress the signal. But in the frequency range below 30kHz, this damping effect can be ignored.
(3) Suppression diodes are generally used in high-sensitivity electronic circuits, and their response time can reach ps level, while the voltage limit of devices can reach 1.8 times the rated voltage. Its main disadvantages are weak current load capacity and high capacitance. The capacitance of the device varies with the rated voltage of the device, that is, the lower the rated voltage of the device, the greater the capacitance. This capacitor will also form a low-pass link with the inductance in the connecting wire, thus damping data transmission, and the damping degree is related to the signal frequency in the circuit.
Verb (abbreviation of verb) reference basis and literature
1c 61643-12: 2002surge protector (SPD) Part120: surge protector connected to low-voltage power system-selection and application principles;
2.IDT C 61643-1:1998: Surge Protector for Low Voltage Distribution System Part I: Performance Requirements and Test Methods.
3. Announcement No.24 of Code for Lightning Protection Design of Buildings (GB50057-94) on Partial Revision of Engineering Construction Standards
4. Administrative Measures for Lightning Protection and Disaster Reduction issued by China Meteorological Bureau No.3.
Cao Yuan, Chief Engineer of Beijing Demani Electromechanical Technology Co., Ltd.