Lightning disasters belong to high-risk natural disasters, and whether it is construction projects, power systems, communication, or intelligent equipment, they all face safety threats brought by lightning strikes. A comprehensive lightning protection scheme design, selection of surge protectors, and on-site construction acceptance all rely on accurate understanding of professional terminology. Many engineers often confuse various lightning protection concepts with SPD parameter definitions. This article systematically summarizes the mechanism of lightning action and the definition of core terms in the field of surge protectors, providing reference and learning for industry technicians.

1、 Basic concepts related to lightning

Direct lightning strike

Refers to the phenomenon of lightning strikes directly hitting the building body, resulting in lightning strikes. Lightning strikes can generate electrical effects, thermal effects, and strong mechanical forces at the same time, which can easily damage building structures, cause fires, component damage, and other accidents. It is the highest risk form of lightning strikes.

lightning induction

When lightning discharges, it will generate static and electromagnetic induction phenomena on various metal conductors in the surrounding area. The induced overvoltage may cause discharge sparks between different metal components, which can easily ignite flammable and explosive materials, penetrate precision electronic components, and trigger various secondary safety accidents.

1. electrostatic inductionDuring the development stage of thundercloud precursor, charges of opposite polarity will be induced on the surface of surrounding conductors; When the thundercloud completes the main discharge, the charges in the leading channel quickly neutralize. If the induced charges accumulated on the conductor cannot be discharged to the ground in a timely manner, the potential of the conductor will rise sharply, forming a dangerous overvoltage.

   
   

2. electromagnetic inductionLightning current has the characteristic of fast change speed, which will form a fast alternating strong magnetic field in the surrounding space. Adjacent conductive circuits will be affected by the magnetic field and induce high electromotive force, thereby forming overvoltage, which poses a particularly prominent threat to weak current systems.

Lightning electromagnetic pulse (LEMP)

Lightning strikes the lightning protection facilities of buildings directly, or produces a comprehensive effect in the surrounding areas of buildings. Most lightning strike equipment failures in daily engineering are caused by electromagnetic pulses from lightning strikes. There are various forms of interference propagation, including conductor conducted lightning currents, equipment potential surges, and space electromagnetic radiation interference. Computer rooms, automation control systems, and communication equipment are easily affected by them.

Lightning wave intrusion

After lightning strikes linear structures such as overhead cables and metal pipelines, lightning overvoltage will continue to propagate along the pipelines indoors. This type of overvoltage not only damages electrical equipment, but also threatens the personal safety of indoor personnel, and is the most common cause of lightning strikes in industrial plants and civilian buildings.

2、 Interpretation of terms related to surge protectors (SPDs)

Surge Protective Device, abbreviated as SPD, is commonly referred to as lightning arrester, overvoltage protector, surge suppressor, and security device in the industry. It can limit transient overvoltage in the circuit, guide surge currents, and contain at least one nonlinear component inside the device. According to the working principle, it can be divided into three types: switch type, voltage limiting type, and combination type, which are indispensable protective devices in the internal lightning protection system.

1. Port category

• One port SPDThe device is used in parallel with the protected circuit, with independent input and output terminals, and there is no special series impedance between the input and output terminals.

• Two port SPDEquipped with two sets of independent input and output terminal blocks, with a dedicated series impedance structure set between the two sets of terminals.

2. Key parameters of current

Nominal discharge current In (nominal current carrying capacity/impulse current carrying capacity)Under the premise of no substantial damage to the SPD, it can withstand the peak value of the specified frequency and standard 8/20 μ s waveform impulse current, which is an important reference indicator for SPD grading selection.

Maximum discharge current Imax (maximum current carrying capacity/maximum impulse current carrying capacity)SPD can withstand a single 8/20 μ s waveform impulse without permanent damage to the maximum current peak; On the same model of product parameters, the Imax value is greater than In.

Impulse current IimpSpecifically referring to the test current wave with a waveform of 10/350 μ s; Within a duration of 10ms, the total charge Q conveyed by the current waveform is equivalent to 50% of the peak current Ipeak, and is commonly used for parameter calibration of Class I surge protectors.

3. Key voltage parameters

Maximum continuous operating voltage UcThe power frequency AC root mean square voltage or DC voltage that can be stably applied to both ends of the SPD for a long time is equivalent to the rated working voltage of the SPD. When selecting, it must be matched with the voltage of the on-site power supply system.

Voltage protection level UpWhen SPD starts voltage limiting operation, the highest limiting voltage appears at both ends of the device, which is the core indicator for measuring SPD protection performance. The value of Up should be higher than the maximum measured limit voltage, which intuitively reflects the ability of SPD to suppress overvoltage between terminals. When selecting, the value should not be lower than the withstand overvoltage level of the backend equipment.

4. Special parameters for signal channel SPD

insertion lossUnder a fixed testing frequency environment, measure the voltage ratio of the point before and after the channel type SPD is connected to the line, in decibels (dB). The insertion loss value directly determines the signal transmission quality and is a key indicator for selecting network and control signal lightning arresters.

Transmission rate (bit/s)After the channel type SPD is connected to the digital signal transmission line, the maximum data transmission rate that the system can stably carry under the condition that the insertion loss meets the specification limit. In the selection of scenarios such as security monitoring and industrial Ethernet, it is necessary to match the communication rate.

3、 Engineering application tips

A complete comprehensive lightning protection system is divided into two major sections: external lightning protection and internal lightning protection. External lightning protection devices are mainly used to intercept direct lightning strikes; Internal lightning protection focuses on preventing overvoltage damage caused by lightning electromagnetic pulses and lightning waves. In the implementation process of engineering projects, it is necessary to distinguish between the different design ideas of direct lightning protection and induced lightning protection; In the stage of SPD grading and procurement selection, it is necessary to accurately distinguish the meanings of various parameters such as In, Imax, Iimp, Uc, Up, and reasonably select lightning protection products based on power supply methods, electronic equipment voltage standards, and signal transmission types in order to build a safe and effective lightning protection system.

Haipengxin HPXIN is deeply involved in the field of lightning protection, continuously outputting standardized lightning protection knowledge, assisting in the implementation of industry standard engineering, and reducing equipment damage and economic losses caused by lightning disasters.