Surge protector selection often see 8/20μs or 10/350μs label, so what is the actual meaning?
Briefly speaking, the main role of the surge protector is to instantly release the lightning current when the lightning strike occurs. The generation of lightning current includes direct lightning and inductive lightning. The waveform of direct lightning and inductive lightning are not the same, and the energy is not the same. The current waveform is similar to 10/350μs (direct strike) and 8/20μs (inductive strike).
The 10/350μs (direct thunderbolt) waveform is shown as follows:
8/20μs (inductive lightning) waveform is shown as follows:
In the surge protector to do the form of the experiment, through the test equipment to produce two kinds of waveforms of current, simulated direct lightning and inductive lightning, the surge protector for destructive impact test, so as to get the parameters under the current waveform.
First, lightning waveform
The 8/20μs and 10/350μs waveforms represent the curves of time and current. The 10/350μs waveforms represent the curve of lightning current when typical lightning breaks down the ground, and the curve of lightning current when lightning directly hits the power line, lightning rod or other buildings. We call this a direct thunderwave.
Where 10 (microseconds) represents the time FOR the IMPULSE pulse to reach 90% of the current peak, while 350 represents the time from the current peak to the half-peak, and 8/20 is the same definition.
8/20μs is the electromagnetic pulse induced overvoltage caused by typical lightning breakdown of the ground (lightning rod or near the contact). This induced overvoltage breakdown and burn the current curve of equipment. We call these inductive thunderwaves.
Two, the difference between direct and inductive lightning wave shape
Differences between standards and regulations: The IEC International Electrotechnical Commission standard IEC1024 TAG_1 Lightning Protection Specification and IEC1312 Lightning Electromagnetic Pulse Protection implement 10/350μs and 8/20μs lightning waveform. The national standards GB11032-2000 "AC Lightning arresterand GB3482-3483-83" Lightning Test and Guidelines for Electronic Equipment "execute 8/20μs lightning waveform.
According to the theoretical calculation, under the same lightning current, the ratio of the lightning joule energy of 10/350μs and 8/20μs is 17.5:1(e.g. An 8/20μs lightning current of 10KA has a lightning joule of 1000J, then a 10/350μs lightning current of 10KA has a lightning joule of 17500J), 10/350US and 8/20μs lightning joule energy are essentially different.
According to IEC's "New requirements", the 10/350 waveform impulse pulse should be used when testing "surge protectors against direct lightning strikes", while the 8/20 waveform should be used when testing "surge protectors against indirect lightning strikes".
It can be seen that 10/350μs and 8/20μs have their own characteristics, so do lightning protection should be according to the protection level and protection site needs to match the corresponding surge protector.
