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Surge protector

Time:2018/5/6Author:adminClick: 2674
Surge protector
(Surge Protection Devices, referred to as SPD), also known as surge protectors, over-voltage protectors, commonly known as lightning arresters, lightning protection devices.
 
In response to the emergence of various kinds of SPDs on the market, the quality is uneven, and some even do not ask (such as: do not have to ground the arrester, until now, do not understand how it works), therefore, By introducing the working principle and composition of the arrester, it is helpful for the customer to identify the true and false, and the advantages and disadvantages.
From the response characteristics of lightning arrester components, there are two kinds of soft and hard. Discharge elements with hard response characteristics include spark gaps (corner spark gaps and coaxial discharge spark gaps based on Xenon arc technology) and gas discharge tubes. Soft-response characteristic discharge elements include metal oxide varistors and transient suppression. diode. The difference between these components lies in the discharge capacity, response characteristics, and residual voltage. The lightning arresters use their different advantages and disadvantages, avoid weaknesses, and combine them into various lightning arresters to protect the circuit.
A. Arc chopping
1, discharge gap:
The principle is that two electrodes, such as horns, present a very short distance and are separated by an insulating material. When the electric field strength between the two electrodes reaches the breakdown strength, a current path is formed between the electrodes. When the lightning wave arrives, it first breaks down at the gap, so that the air in the gap is ionized to form a short circuit, and the lightning current flows into the earth through the gap. At this time, the voltage across the gap is very low, so as to achieve the purpose of protecting the line. When the electric field intensity is lower than the breakdown gap, the discharge gap type arrester resumes its insulation state. It is often used in lightning protection of high-voltage lines. In low pressure systems,
Commonly used for power protection. The advantages and disadvantages of spark gap arrester products lie in the electrode material, gap distance and insulation material.
advantage:
With strong discharge capacity and large flow rate, 10/350μs pulse waveform can ease the pulse current of 50KA for 8/20μs pulse current, can be greater than 100KA, high insulation resistance and very small parasitic capacitance, and low leakage current. There will not be any harmful effects on the equipment that works normally.
Disadvantages:
The residual voltage is high (2.5~3.5KV), the reaction time is long (≦100ns), the operating voltage accuracy is low, and the frequency is freewheeling. Therefore, a fuse should be connected in series in the protection circuit so that the freewheeling current is rapidly cut off.
Note: Since the two discharge tubes are respectively mounted on two wires of a loop, they sometimes discharge at the same time, causing a potential difference between the two wires. In order to make the discharge tubes on the two wires approach the same time, the discharge is reduced by two. Between the potential difference between the lines, a three-level discharge tube was developed. It can be seen as a combination of two secondary discharge tubes. The middle level of the three-level discharge tube serves as the common ground, and the other two stages are respectively connected to the two wires of the circuit.
2. Gas discharge tube (GDT): It is a ceramic or glass package. The tube is recharged with inert gas (such as argon gas) with certain pressure.
There are two electrodes and three electrodes. When the electric field strength reaches the breakdown inert gas strength, gap discharge is caused, thereby limiting the inter-electrode voltage. 8/20μs pulse current can ease 10KA. Discharge voltage is not stable, when the voltage is greater than 12V, current and voltage 100mA, it will generate follow-up current. It is commonly used in measurement, control, regulation technology circuits and electronic data processing transmission circuits.
 
Second, metal oxide varistor (Metal oxide varistor, MOV): Metal oxide semiconductor nonlinear resistors with zinc oxide as the main component, when the voltage across the resistor is less than the varistor voltage, the varistor is high resistance State, if connected in parallel on the circuit, the valve is in the open state; when the voltage across the varistor is greater than the varistor voltage, the varistor will break down, showing a low resistance value, and even close to the short circuit state. Varistors are hit
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