Classification and Application of Lightning Arrester
- Categories:Industry News
- Time of issue:2020-07-14 13:11
Classification and Application of Lightning Arrester
- Categories:Industry News
- Time of issue:2020-07-14 13:11
The surge arrester is an overvoltage protection device. When the grid voltage rises to the operating voltage specified by the surge arrester, the surge arrester acts to release the voltage load and limit the amplitude of the grid voltage rise below a certain level, thereby protecting the equipment insulation. Tolerable level, in addition to limiting lightning overvoltage, modern surge arresters can also limit part of the operating overvoltage, so it is called whether the overvoltage limiter is accurate.
Lightning arresters are installed in places where overvoltage is required, for example: high and low voltage sides of transformers, line inlet and outlet sides, busbars, cable ends, generator outlets, overhead lines and other places. Therefore, many power devices are widely used.
First, the role of lightning arrester
Lightning arrester is a device to protect the substation from lightning shock wave. When the lightning shock wave entering the substation along the line exceeds the protection level of the lightning arrester, the lightning arrester first discharges and the lightning current is safely introduced into the ground through a good conductor. The grounding device is used to limit the amplitude of the lightning voltage to below the lightning shock level of the protected equipment. Electrical equipment is protected.
Lightning arrester is essentially a discharger, connected in parallel near the equipment to be protected. The protection principle of the arrester is shown in the figure. The breakdown voltage of the arrester is lower than that of the protected equipment. When the overvoltage wave invades along the line and exceeds the discharge voltage of the surge arrester, the surge arrester first discharges the intrusion wave into the ground, limiting the value of the overvoltage acting on the equipment, thereby protecting the equipment insulation from breakdown damage. After the intrusion wave disappears, the surge arrester should be able to restore the insulation capacity by itself to avoid causing a power frequency ground short circuit accident.
2. Application of Lightning Arrester in Transformer
The damage to the transformer caused by overvoltage is very large. There are two types of transformer overvoltage: atmospheric overvoltage and operating overvoltage. The value of the operating overvoltage is generally 2 to 4.5 times the rated voltage, while the atmospheric overvoltage can reach 8 to 12 times the rated voltage. The dielectric strength of the transformer is generally considered to be able to withstand 2.5 times the overvoltage. Therefore, over-voltage of more than 2.5 times, no matter which kind of over-voltage may damage the transformer insulation. The voltage distribution inside the expander is greatly affected by the frequency of the voltage and the resistance, inductance, and capacitive reactance of the transformer. In the case of power frequency voltage, the capacitive reactance is very large, and the circuit formed by it is equivalent to an open circuit. Therefore, under normal circumstances, only the resistance and inductance of the transformer's internal voltage distribution are considered, and the distribution is basically uniform. The atmospheric overvoltage or operating overvoltage is basically a shock wave. Due to the high frequency of the shock wave and the steepness of the wave front, the frequency of the shock wave with a wave front time of 1.5 μs is equivalent to 160 kHz. Therefore, under the effect of the overvoltage shock wave, the transformer The capacitive reactance is very small, which has a great influence on the voltage distribution inside the transformer.
In order to prevent the overvoltage from damaging the transformer, first install a lightning arrester to prevent the voltage amplitude exceeding the winding insulation strength from acting on the winding. And when lightning strikes at high altitudes, the high discharge current will be led into the ground through its lightning arrester first, so as to protect the transformer and other equipment.
3. Classification of lightning arresters
Lightning arresters can be divided into:
Protection gap-is the simplest form of lightning arrester
Tube-type arrester-also a protective gap, but it can extinguish the arc after discharge.
Valve-type arrester-is to divide a single discharge gap into many short series gaps, while increasing the nonlinear resistance, improving the protection performance.
Magnetic blowing lightning arrester——The use of magnetic blowing spark gap improves the ability of arc extinguishing, and also has the ability to limit internal overvoltage,
Zinc Oxide Arrester-Utilizes the ideal volt-ampere characteristics of zinc oxide valves (non-linear extremely high, that is, low resistance characteristics at high voltage, limiting the voltage on the arrester, showing high resistance characteristics at normal power frequency voltage) It has the advantages of no gap and no residual current and low residual voltage. It can also limit the internal overvoltage and is widely used.
In the above classification types, protective gaps and tube-type arresters are mainly used for the protection of power distribution systems, lines and power plants, substations, to limit the intrusive atmospheric overvoltage; valve-type arresters and zinc oxide arresters are used The protection of substations, power plants and transformers is mainly used to limit atmospheric overvoltage in systems of 220kV and below, and is also used to limit internal overvoltage or as backup protection for internal overvoltage in ultra-high voltage systems. The protection performance of valve-type arresters and zinc oxide arresters has a direct impact on the determination of the insulation level of transformers or other electrical equipment.
Arresters are divided into high-voltage and low-voltage arresters. There are many types of surge protectors in my country's market. There are more than one hundred kinds. How to classify different brands and different models of arresters may be before us. From the combined structure; there are several types of lightning arresters on the market now:
1. Gap class-open gap, closed gap
2. Discharge tube type-open discharge tube sealed discharge tube
3. Varistors-single-chip, multi-chip
4. Suppression diodes
5. Varistor/gas discharge tube combination-simple combination, complex combination
6. Silicon Carbide——According to its protective properties, it can be divided into: open circuit arrester, short circuit arrester or switch type, voltage limiting type.
Fourth, the structure and characteristics of the arrester
1. Open gap arrester: Working principle: Based on the arc discharge technology, when the voltage between the electrodes reaches a certain level, the breakdown air arc discharges on the electrodes. Advantages: Strong discharge capacity, large flow rate (can reach 100KA), small leakage current, good thermal stability. Disadvantages: high residual voltage, slow reflection time, and continuous current. Process characteristics: Since the metal electrode withstands a large current during discharge, it is easy to cause sublimation of the metal, and the metal coating formed in the discharge chamber affects the start and normal use of the arrester. The production of discharge electrodes is mainly concentrated in some arrester manufacturers abroad. The main component of the electrode is an alloy of tungsten metal. Engineering application: The arrester of this structure is mainly used in the power system as a B-level arrester. However, due to the cause of the arrester itself, it is easy to cause a fire. After the arrester is operated (flying out), it will break away from the switchboard and other accidents. According to different models, it is suitable for various power distribution systems. The installation distance must be considered during engineering installation to avoid unnecessary losses and accidents.
2. Closed gap arrester: Now there is a multi-layer graphite gap arrester in the domestic market. This type of arrester mainly uses multi-layer gap continuous discharge, and each discharge gap is insulated from each other. This stacking technology not only solves the problem of continuous current but also It is a layer-by-layer discharge, which virtually increases the flow capacity of the product itself. Advantages: large discharge current test, maximum 50KA (actual measured value), small leakage current, no continuous current, no arc diarrhea, good thermal stability. Disadvantages: high residual pressure, slow response time. Technological characteristics: Graphite is the main material. The all-copper coating is used in the product to solve the heat dissipation problem of the arrester during discharge. There is no subsequent current problem. The biggest feature is that no arc is generated, and the residual voltage is more important than the open gap arrester. Much lower. Engineering application: This type of arrester is used in various B and C occasions, and it does not need to consider the arc problem compared with the open gap. Depending on the model, this product is suitable for various power distribution systems.
3. Open discharge arrester: The product is essentially the same as the open gap arrester, and it belongs to the air discharger. But compared with the gap discharger, its flow capacity has dropped by one grade. Advantages: small volume, strong flow capacity (10-15KA), small leakage current, no arc discharge disadvantage: high residual voltage, continuous current, poor product consistency (starting voltage, residual voltage), slow response time.
4. Closed gas discharge tube: also called inert gas discharge tube, which is mainly filled with inert gas, and the discharge method is gas discharge, which aims to discharge current at once by breakdown gas. Generally, there are two structures of 2 poles and 3 poles. . Advantages: small volume (the gas tube can be very small), large flow and no arc. Disadvantages: Poor product consistency (starting voltage, residual voltage) has a high continuous current and residual pressure Process characteristics: The air discharge tube is still an open product, and there is no guarantee that there is absolutely no sparking from the pressure discharge hole during operation, and the gas discharge tube It is a sealed structure, generally has 2 poles and 3 poles of excellent structural forms, generally 3 poles have thermal protection device (short circuit device), when the temperature of the discharge tube during operation exceeds a certain range, the short circuit device is activated to make the entire discharge tube conduct. To prevent the excessively high temperature from causing the air pressure generating device in the discharge tube to burst. Engineering applications: General air discharge tubes are now rarely used, and gas discharge tubes are now widely used in signal lightning arresters. Different models are also used in power supply surge arresters
5. Monolithic varistor arrester: It was first invented by Japan in the 1980s. Until now, the usage rate of single-chip varistors is also the highest among surge arresters. The working principle of the varistor arrester is to use the nonlinear characteristics of the varistor. When the voltage does not fluctuate, zinc oxide assumes a high resistance state, and when the voltage fluctuates to reach the starting voltage of the varistor, the varistor quickly assumes a low resistance state, limiting the voltage to a certain range.
6. Multi-chip varistor arrester: Because the flow rate of single-chip varistor has not been ideal (generally the maximum discharge current of single-chip varistor is 20KA\8/20uS), under this premise, multi-chip combined varistor The surge arrester is produced, and the multi-piece varistor combined surge arrester mainly solves the problem that the single piece varistor has a small flow rate and cannot meet the requirements of class B occasions. The generation of multi-chip varistor fundamentally solves the problem of varistor flow rate. Advantages: large flow capacity, low residual voltage, fast reaction time (≤25ns), no follow current (freewheeling). Disadvantages: large leakage current and fast aging speed. Thermally stable one. Process characteristics: Most of them use building block structure. Engineering application: Depending on the structure, varistor arresters are widely used in B, C, D and signal arresters. However, the problem that should be solved is that there are individual products in the project that are burning. Therefore, when selecting the product, pay attention to the shell material used by the manufacturer.
7. Suppression diode lightning protection devices: Suppression diode lightning protection products are mainly used in a large number of signal lightning protection products such as networks. The main devices used are P*KE (avalanche tube) and other products. The working principle is based on PN junction reverse breakdown protection. Advantages: low residual pressure, high action accuracy, fast response time, no free flow, small volume, shortcomings: small flow rate.
8. Combined arrester: The typical structure is N-PE structure. Compared with the single structure arrester, this arrester combines the advantages of two different products and reduces the disadvantages of a single device. Advantages: large flow rate and fast response time. Disadvantages: The residual pressure is relatively high. Engineering application: Lightning arrester used only in N-PE format, suitable for areas with large voltage fluctuation rate.
9. Complex combined arrester: This type of arrester makes full use of the advantages of various components. Generally, a large number of varistors and gas discharge tubes are used in the structure. The arrester of this structure generally has a higher flow capacity and a lower residual pressure. The industry also calls this type of arrester as an integrated arrester. Advantages: large flow rate, quick response time, low residual pressure, no continuous flow, good thermal stability. Disadvantages: no sound alarm, no counter. Process characteristics: The integrated surge arrester has a compact circuit structure, which fully utilizes the characteristics of the zinc oxide resistance reflecting time quickly, and has the advantage of combining a gas discharge tube with a high flow capacity. In the circuit, the surge arrester uses more zinc oxide resistance to improve the flow capacity of the overall surge arrester, and the gas discharge tube is used as the backup discharge channel. Based on this perfect circuit structure, the service life of the arrester is greatly improved. Engineering application: The integrated arrester is widely used in various installation environments of B, C and D according to different models. Because it is an integrated design, it is more suitable for use where there is no installation distance. (IEC stipulates that the shortest distance between the three stages of B, C, and D modular arresters should be above 10M).
The picture above is a valve-type arrester, which is composed of spark gap and valve chip resistance. The material of the valve chip resistance is special silicon carbide. Using silicon carbide to make hair piece resistors can effectively prevent lightning and high voltage and protect the equipment. When there is a high lightning voltage, the spark gap is broken, the resistance value of the valve blade resistance drops, and the lightning current is introduced into the ground, which protects the electrical equipment from the lightning current. Under normal circumstances, the spark gap will not be broken down, and the resistance value of the valve disc resistance rises, preventing the normal AC current from passing. The valve type arrester is a lightning arrester made of special materials, which can protect electrical equipment and direct current to the ground.
Fifth, arrester model specifications
To understand the use of a lightning arrester, it is also necessary to understand its model description. The following figure introduces the model specifications of metal oxide surge arresters.
Generally speaking, there are several basic requirements for lightning arresters: firstly, it must have strong insulation self-recovery ability, secondly, it has a flat volt-second characteristic curve, and finally it has a certain flow capacity. Therefore, we need to pay attention to several indicators involved in the manufacture of electric lightning arresters
(1) Volt-second characteristic: refers to the corresponding relationship between voltage and time.
(2) Power frequency continuous current: refers to the end of the lightning voltage or overvoltage discharge, but the power frequency voltage still acts on the lightning arrester, making it flow through the power frequency short circuit ground current.
(3) Insulation strength self-recovery ability: the relationship between the insulation strength of electrical equipment and time, that is, the speed of recovery to the original insulation strength.
(4) Rated voltage of the arrester: After the power frequency freewheel is zero-crossed for the first time, the maximum power frequency voltage that the gap can withstand without causing reignition of the arc is also called the arc voltage.
When installing a lightning arrester for power equipment, it is necessary to pay attention to its normal operating conditions: ① suitable for indoor and outdoor operation; ② the ambient temperature is +40 ℃ ~ -40 ℃; ③ can withstand the radiation of sunlight; ④ the altitude does not exceed its design height ; ⑤ The frequency of the power supply is not less than 48Hz, not more than 62Hz; ⑥ The power frequency voltage applied to the arrester for a long time does not exceed the allowable value of the continuous operating voltage of the arrester; ⑦ Earthquake intensity of 7 degrees and below. When these conditions are noticed, the arrester can be installed in the right place so that it can exert the protection effect we need.
Accidents may also occur during the operation of the arrester. For example, explosions that occur during the operation of the arrester often occur. The cause of the explosion may be caused by the system or the cause of the arrester itself:
Due to the single-phase grounding in the neutral point ungrounded system, the non-fault relative ground voltage is increased to the line voltage, even if the voltage carried by the arrester is less than its power frequency discharge voltage, and under the effect of a long-term overvoltage, May cause an explosion;
Due to the ferromagnetic resonance overvoltage in the power system, the arrester is discharged, which burns out its internal components and causes an explosion;
When the line is struck by lightning, the surge arrester operates normally. Due to the poor arc extinguishing performance of the spark gap itself, when the gap cannot withstand the recovery voltage and breakdown, the arc is reignited, the power frequency freewheel will reappear, and the reignition valve burns out the resistance, causing the explosion of the arrester;
Or due to the failure of the arrester valve resistance, although the residual pressure is reduced, but the continuous flow is increased, the gap cannot be extinguished and cause an explosion;
Due to the loose or cracked joint between the arrester sealing gasket and the cement, the seal is not good and causes an explosion,
Sixth, precautions for the operation of lightning arrester
1. During thunderstorms, personnel are strictly prohibited from approaching the lightning protection device to prevent lightning strikes from releasing lightning
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