TEN350 The waveform that hijacked the IEC lightning standards
IEC 62305 Series: Basic Problems
The 10/350 waveform causes IEC standards a number of undesirable problems: some insidious and all unnecessary.
The hard fact to face is that standards that enforce the 10/350 waveform test and impose spark gap protectors on the world are not just innocent bystanders. They are actually CAUSING damage to equipment and electronic systems.
Faulty Logic brought us to this unfortunate situation:
The above sequence would be logical except for the fact that the first premise is a falsehood. CIGRE's 2013 Technical Brochure 549 shows that the10/350 waveform does not now and never has represented any mathematically significant percentage of any type of lightning.
Because the first premise is false, it follows, as thunder follows lightning, that the conclusion is also false.
The above “logic” allows one to forgive all the weaknesses of spark gap protectors since “they can pass the 10/350 waveform test.” The above “logic” allows one to forgive all damage to electronic equipment protected according to 10/350-based standards. The above "logic" makes incidents like the one on the right (which destroyed an entire telecommunications site) “acceptable” in the world of lightning protection.
This is more broadly recognized than you might think. One TC 81 member (who asked to remain anonymous) recently told us: "Everybody knows that the 10/350 waveform is nonsense. The Germans derived the 350 by formula. There was never any evidence it represented actual lightning. But people are afraid to say it out loud."
CIGRE's 2013 Technical Brochure 549 puts the 2000 pound gorilla in TC 81's conference room beating its chest and firing lightning bolts out of both arms.
The Lightning Protection Zone (LPZ) System.
The diagram to the left (from IEC 62305-4) shows just how deeply the above "logic" has insinuated the 10/350 waveform into the IEC 62305 series. The yellow/orange color indicates "Zone Zero" -- any location where lightning can possibly strike. The grey zones depict the inside of a building.
IEC 62305 theory holds that the wave shape of lightning currents that hit Zone Zero can only be represented by a 10/350 waveform. It further holds that only SPDs tested with that waveform can be installed at the borders between Zone 0 and Zone 1. Those borders include all service entrances, generally the most important SPD locations.
So here we have international standards requiring that the most inefficient SPDs (the spark gaps) be installed at the most critical locations. Very bad for the customer’s equipment, but that is not the end of the story. Read more about this here.
Coordinated SPD protection
"SPD" is a term that has gone out of fashion in the IEC 62305 lightning protection standard. The politically correct way of expressing that concept has now become "Coordinated SPDs," a term used hundreds of times in the 62305 series. But what does it mean? It is well documented and even admitted by spark gap manufacturers, that a spark gap is incapable of affording a low enough protection level to alone protect electronic equipment. Consequently spark gaps must be used in coordination with the more effective MOV-based SPDs. Problem is the two technologies don't mix very well. One reason is that MOVs respond hundreds of times faster than spark gaps. (nanoseconds compared to microseconds). When the two are installed together, great efforts are made to get the Class 1 spark gap protector to fire before the Class 2 MOV protector responds. (MOV based protectors used in conjunction with spark gaps are usually rated only 20-40kA. These so-called "Class II MOV protectors" are too small and inefficient to conduct the full lightning current.) The major spark gap players each have their own patented “solutions” to deal with this problem but TC 81 nevertheless felt compelled to devote 1/3 of the pages of IEC 62305-4 to “standardize” this coordination. All to little effect. The stock solutions depend on introducing series inductances that will hopefully get the spark gap to fire quicker. The inductance sometimes relies on the building's wiring and other times is directly added by auxiliary components sold by the spark gap manufacturers. Results will always be inconsistent because they are dependent on peak currents and rise times and the CIGRE 2013 report shows that rise times vary between 10 and 400 kA/μs and peak currents vary from 2kA to 300k.. (Every year or two we hear how new spark gap breakthroughs have solved the coordination problems that weren't admitted to exist the previous year.)
There is more to the 10/350 waveform than the 10 and the 350.
In the original 1982 Hasse 10/350 waveform Chart you can see the two parameters of the 10/350 signature highlighted in pink: T1 = 10μs and T2 = 350μs. But the "10/350 waveform" has always been something of a misnomer. Look again at Hasse's Chart and you will see it includes three other parameters (highlighted in yellow): Peak current = 200 kA; Charge (Q) = 100 coulombs; and W/R = 10MJ / Ω. For over 30 years the "10/350 waveform" has always been a package deal. It always includes those 5 parameters. And the value of peak current (kA) is always twice the value of the charge (coulombs). Why? Maybe because all 5 of those parameters were needed to lock-in the use of the spark gap surge protectors.
Which came first?
The IEC 62305 series claims the 10/350 waveform values were computed based on Ipeak and charge transfer values. It might just as easily have been the other way around. But since the CIGRE 2013 report lends no credibility to any of those parameters (with the possible exception of peak current) or to any dependency between parameters, one can only conclude they have no basis in reality or in science and for that reason alone should be stricken from all lightning protection standards.