Circuit lightning protection knowledge (reposted)

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Circuit lightning protection knowledge (reposted) [Copy link]

Concept of protection zone
　　From the perspective of EMC (electromagnetic compatibility), an area to be protected can be divided into several levels of protection zones from the outside to the inside. The outermost layer is level 0, which is the direct lightning strike area with the highest risk. The further in, the lower the risk. The overvoltage is mainly in series along the line. The interface of the protection zone is formed by the shielding layer composed of the external lightning protection system, reinforced concrete and metal pipes, and the electrical channels and metal pipes pass through these interfaces.
　　From the level 0 protection zone to the innermost protection zone, graded protection must be implemented. For the power supply system, it is divided into I, II, III, and IV poles, so as to reduce the overvoltage to the level that the equipment can withstand. For the information system, it is divided into coarse protection and fine protection. The coarse protection level depends on the level of the protection zone, while the fine protection should be selected according to the sensitivity of the electronic equipment. In theory, about 50% of the lightning current flows directly into the earth, and the other 50% will flow evenly into each electrical pipeline (such as power lines, signal lines and metal pipes).
　　　　
Lightning strike is a kind of surge voltage
　　What is surge? Surge is also called surge, which means instantaneous overvoltage exceeding the normal working voltage. The English name of lightning arrester we often say is SPD - SURGE PROTECTION DEVICE, that is, [surge protector]. Therefore, lightning protection is actually a function of surge protector. Since the surge voltage and energy of lightning strikes are much higher than other types of surge voltages, we usually call SPD lightning arrester.
　　　　
General introduction and concept explanation
　　　　
　　Voltage limiting components
　　The main voltage limiting components are gas overvoltage arresters, surface arresters, varistors, diodes and decoupling resistors. All components have special advantages. In order to play the best role, one or a combination of several of the above components should be used to form a corresponding protection circuit according to the specific application.
　　The gas overvoltage arrester consists of an electrode structure installed in a ceramic or glass tube. Between the electrodes is an inert gas, such as argon or neon. When the ignition voltage is reached, the discharge element has a low resistance. The ignition voltage is related to the steepness of the overvoltage.
　　After ignition, there is an arc voltage of 10 to 30 volts on the overvoltage arrester. When the arrester is in the low-resistance state, a grid follow-up current is generated, the magnitude of which depends on the grid impedance. In order to interrupt the grid follow-up current, a fuse must be connected in series if necessary.
　　The ArC spark gap in the FLASHTRAB lightning arrester is based on the ArC arc extinguishing technology. The two opposing spark horns are kept at a certain distance by insulation. There is an arc extinguishing plate above the electrodes in the direction of the opening. In the event of an overvoltage, a surface discharge occurs in the upper half of the insulating block. The remaining arc is emitted outward and breaks up on the arc extinguishing plate. The resulting segmented arc will be safely eliminated in the range of several kiloamperes, depending on the magnitude of the grid follow-up current. The
　　surface discharge gap is a discharge gap with insulating material between the electrodes, sometimes also called a surface arrester. Based on the use of special plastics, the surface arrester can independently cut off the grid follow-up current within its operating range.
　　Block varistors with temperature rise release
　　Varistors are voltage-dependent resistors. According to their voltage/current characteristic curve, these resistors have a high discharge capacity at very low residual voltages.
　　　　
Disc varistors
　　Suppression diodes are characterized by short response times (microsecond range) and low limiting voltages.
　　The cut-off voltage UR is the highest voltage value at which the diode can still be reliably cut off. When the on-voltage UB is reached, the current flowing through the suppression diode is 1 mA. The suppression diode starts to limit overvoltages from this moment on. The maximum clamping voltage UC is the maximum voltage that can be applied to the suppression diode at the maximum operating current Ipp.
　　　　
Overvoltage protection devices
　　Many different applications require a variety of overvoltage protection devices with special performance. They mainly differ in the type of circuit, overvoltage limiting performance and construction. The TRABTECH series of PHOENIX CONTACT has many similar variants, such as conversion head arresters, connection sockets or modular arresters for rail mounting, which can provide system solutions that meet practical needs for all applications.
　　Overvoltage protection devices are designed for high-load electrical applications according to their use. However, it is still inevitable that overloads caused by excessively high or very frequent overvoltages occur. The possible result is that the protection function is restricted or even disappears, so that the relevant protection equipment and devices must be replaced. Therefore, overvoltage protection equipment and devices should be designed to be pluggable and detectable as much as possible.
　　The TRABTECH product series of PHOENIX takes this requirement into consideration when designing, and provides a variety of pluggable and two-part module-structured overvoltage protection equipment within the scope of current technical possibilities. In terms of plug-in and detection performance, the protection equipment of the PLUGTRAB product series is particularly worth mentioning. They have various protection circuit forms and rated voltages and are developed to protect power grids, measurement and control equipment and data interfaces.
　　According to the required protection circuit, different protection components can be used, such as gas overvoltage arresters, low-sensitivity resistors and suppression diodes. By adjusting and coordinating these components, their respective characteristics are best utilized.
　　　　
Concept explanation
　　　　
Arrester
　 Electrical equipment, whose main components are voltage-related resistors and spark gaps. These two components can be connected in series or in parallel, or used alone. The arrester is used to protect other electrical equipment and devices from damage by high voltage outside the allowable range.
The set voltage Ur of the arrester
　　The set voltage refers to the maximum allowable effective value of the voltage when the arrester works under its power frequency AC voltage.
　　Note: For the arrester involved here, the set voltage is equal to the continuous working voltage Uc of
　　　　
the arrester The continuous working voltage Uc
　　of the arrester refers to the voltage value continuously applied to the terminal when the arrester works under its power frequency AC voltage.
　　　　
Discharge impulse current iUs The
　　discharge impulse current refers to the current flowing through the arrester after the response is turned on. This current is the peak current.
　　　　
Discharge current
　　If a non-charged part (such as the equipment housing) is conductively connected to the midpoint of the circuit system or the direct grounding point or ground in the power grid, when the system is energized, a current will flow from the charged parts of the electrical equipment through the insulating parts to the non-charged parts. This current is called the discharge current. If a de-interference capacitor is used in the circuit, the discharge current may contain a capacitive component. Discharge
　　　　
capacity
　　: The discharge capacity of the overvoltage arrester is expressed by the discharge alternating current and the discharge current value.
　　　　
　　The discharge alternating current Iw is
　　a power frequency quasi-sinusoidal alternating current flowing through the overvoltage arrester, and its effective value is called the discharge alternating current.
　　　　
Separation device:
　　A device that disconnects the arrester from the power grid. If the discharge fails, the device can avoid causing a fire when separating the arrester, and send a signal to indicate the damaged arrester.
Note: The separation device is not used for "indirect contact protection".
　　　　
Live parts :
　　Live parts refer to the live wires and conductive parts in the electrical equipment under normal working conditions.

HWL0541

Understood

qmxn

xie le a

zf_zxsk

OK

stylet

konglongshi

Oh, that's why! Thank you! Where are you from?

hn_czg

It’s so difficult to achieve in practice!

chuchuda

Thanks, I understand.