Lighting industry lightning protection misunderstanding: LED lighting lightning protection = power lightning protection

LED semiconductor lighting network news I once heard in a very good Shenzhen company: "Whether wave soldering is relatively simple compared to reflow soldering, our company needs a full-time expertise to do this. What our company needs is: special personnel do special things." I only use this sentence as a starting point, special person to do special things, personal expertise! The same as the company.

In the LED lighting industry, I have published four articles, each of which is half of the explanation for what is reasonable lightning protection technology, and half is why the LED lighting industry is not doing well in the field of outdoor lighting. Today, let's take a look at how the lighting, lights, electrical equipment, platforms and garages of the former Ministry of Railways do "lightning protection".

In view of the fact that the entire LED lighting industry has to deal with lightning protection related matters to the power company, then let's see what happens to the lightning surge.

1 The cause of lightning surge

Just Baidu, everyone will find that the cause of the lightning surge is divided into two parts: external reasons and internal reasons.

External causes: direct lightning strikes or lightning between clouds, extremely unstable changes in electromagnetic fields, etc.;

Internal reasons: operation overvoltage, ground potential counterattack, space electromagnetic coupling and other reasons.

2 lightning strikes

Power line crosstalk, space electromagnetic coupling into sensitive devices, PE potential is too high or unstable, resulting in PE breakdown to N, antenna effect, etc.

3 lightning strikes the energy of the surge

The energy of a single direct lightning strike is about 55 kilojoules of energy, which is 55 degrees of electricity. The problem is that the 55-degree power passes through a fixed physical point in less than a nanosecond. Therefore, we say that the lightning surge is very energetic, but there is a way to solve this problem.

There is a joke in our lightning protection industry: the heroes of Marvel will always absorb the thunder and lightning energy, and then they will become very powerful and powerful. Then the question is coming. How long does it take for the hero of this sad reminder to be filled with the energy of Superman?

4 general solutions for lightning surges

Following the EMC theory, in the lightning protection industry, we also use the same method: partition multi-level protection, the specific method I have already detailed in the previously published article, this "partition multi-level protection" method on Baidu It can also be easily queried.

So, let's take a look at the LED lighting industry. Since my article has been seen by many people, I am saying whether I can participate in the outdoor high-power power solution. Then I can say very responsibly here: Thank you for your trust in me. But I don't think lightning protection is a main function of the power supply. I don't agree that the responsibility of lightning protection needs to be borne by the power company. I don't agree that the system protection project is just something that the power company can afford.

In the power industry, the standards to be followed are completely different from the lightning protection industry. The safety test requirements for power supplies are as follows:

1. There must be no leakage current;

2. The insulation withstand voltage is at least 3000V.

However, the core principle of SPD is bleed, it is impossible to have no leakage current when the surge invades, and the leakage current is the nominal discharge current In, up to 5000A or 10000A. In the power industry, some companies' SPD products use a single-pressure-sensitive, differential-sensitive startup voltage of 470V. The common-mode uses a varistor of the same specification in series with a 3000V10kA ceramic gas discharge tube.

In this circuit, there are several problems:

1. The circuit structure is asymmetrical, and the LN and L-PE paths are not equal;

2. The varistor will operate at 470V, but the starting voltage of the gas discharge tube is as high as 3000V, which seriously hinders the discharge of surge energy. When there is a surge below 3000V, the gas discharge tube will not Action, but the varistor will start to work. Excessive energy can only be absorbed by the varistor when it cannot be discharged. At this time, once it exceeds the tolerance limit of the varistor itself, the varistor will burn violently. The high temperature sputter is sprayed outward.

And this is the reason for the fire in several of my cases. Here I would like to remind everyone that 10A glass tube current fuse will not open circuit protection when subjected to In10kA under 8/20us waveform, so using current fuse in SPD is absolutely wrong, meaningless hoe! So what about thermistor RTH?

I personally experimented: RTH did the expected short-circuit current experiment at 600V10A, and would not disconnect the connection at all. The short-circuit fire still had to be short-circuited, so RTH was a gimmick.

Our lightning protection industry is very grateful to the power industry and the LED lighting industry. In the SPD black box's internal circuit, we have come up with many wonderful ideas, which greatly enriched our knowledge and frankly said: These ideas are useless and useless.

In the EMC industry, everyone says that EMC is a systems engineering. In our lightning protection industry, it is no exception. For example, the application standard IEC61000-4-5 solves the surge immunity problem of the constant current switching power supply itself. Can this power supply solve the lightning protection problem when it is used outdoors? The answer is obviously impossible! Because the lightning protection standard is GB18802.1-2011 and IEC61643.11-2011, UL1449 and so on. Lightning protection must be designed for the entire system in terms of the system perspective of the entire lamp. The better companies that are currently doing are only patching the entire lamp system from a system perspective. What are the components of LED outdoor lighting?

What kind of target tasks do you need to achieve separately? Lightning protection only needs to be protected at every interface. Therefore, we need to think of some methods to deal with the reliability of every two adjacent components of the whole lamp system.

As the owner, I walked on my way to my door every night. I personally only care about it: Is this light not bright? Doesn't flash? Bad or not? If a street light doesn't light up, I personally won't entangle it. What is the reason? It doesn't light up. I only think: I paid a tax of ¥100.00, how much light did I buy? Where have these lights died now? Is this time the equipment supplier has to find the power company to say: You are going to pay me! In this vicious circle, does China's LED industry still need to continue to do so?

I used to talk about Huawei's lightning protection technology as a cow. The communication industry understands the lightning protection industry. This time we changed, let's see how the Chinese Ministry of Railways did lightning protection.

Everyone should have a lot of companies and many people who have experienced the "Metro System Lighting" project. Is there any feeling of grievance? I have encountered the most amazing thing: in a normal situation in a subway station, a subway will be replaced by a deceleration according to the regulations, and all the subway stations will be tripped and powered off when entering the station.

Before analysing the reasons, please think about what I have said many times before: if the protected equipment application is near water source (river and river), cross-bridge, tunnel, open and dry area, mountain top and other areas, it must be added. Install the lightning protection device, and also do the engineering grounding. why? The reason is what we call "ground potential counterattack". The railroad of the subway is a good conductor. It can attract the remote lightning surge. After the long-distance transmission of the surge energy, the amplitude is superimposed or the attenuation is smaller. It is necessary to see the mood of God. At that time, it is definitely too late to pray. If it is getting bigger, then the electronic equipment at the adjacent station will be innocent.

The Ministry of Railways' Ministry: TB/T2311-2008, which clearly stipulates the electrical parameters of SPD and its testing methods and judgment basis. At present, in the LED lighting industry, for the practical guiding significance of SPD selection, I think only this one TB/T2311-2008. At present, many companies find my company, and we can't move it: we want a 15kV lightning arrester. Sorry, our lightning protection industry uses current values ​​to characterize energy values. All voltage values ​​are converted. You can only recommend 5kA SPD for 15kV. Internationally, North America requires not only the current value to characterize the SPD bleed capacity, but also the number of joules that the SPD can withstand. This way of characterizing SPD performance with Joules is available in the communications industry for the simple reason that Huawei requires it.

In TB/T2311-2008, there is a parameter preference table for SPD "nominal discharge current In". In this table, everyone can select the product with the corresponding parameters according to their actual use. The same parameter preference table also appears in the LED industry standard CSA027-2014 that I participated in drafting. Please note: In the case of AC mains input, the minimum specification should be In10kA.

In the railway system, the "signal indicator light", "lighting" and "wireless communication system" applied to the track also use AC mains, some are dedicated lines, some are TN-S systems, and the best place is the single item 220. .

After the Wenzhou accident, the entire Ministry of Railways did not allow lightning protection as an optional function to be solved by a supplier of a main functional component. The Ministry of Railways must personally conduct technical and quality control. Here, the Ministry of Railways' requirements for the failure trip warning of SPD are very strict. In my last article (How do lightning protection industry look at LED streetlights?), I showed a few photos of failed lightning arresters. In the Ministry of Railways requirements, SPD must be used after 600V breakdown of SPD. To be able to withstand the short-circuit experiment of continuous current in small, medium and high three:

Small current: 10mA, 20mA, 50mA, 80mA, 100mA;

Medium current: 1A, 2A, 5A, 8A, 10A;

High current: 50A/150A (optional one).

Everyone knows what is the circuit principle of SPD for LED outdoor lighting now? Differential mode single pressure sensitive, common mode pressure sensitive string gas discharge, also requires a product that does not have polarity! I believe that many companies have dismantled the SPD they purchased. Please believe me, it is caused by the "low cost requirements" of the LED industry. Some of you have told me directly: we do not require certification, nor do we need big companies. The request, anyway, you can do something for me to have this meaning! So can this circuit withstand such experiments? This kind of thing is a fake, but someone wants to buy it, and dare to use it! This experiment is a well-known TOV experiment in our lightning protection industry. At present, only a few companies in our industry dare to promise customers to pass this experiment!

Why is our lightning protection industry very entangled in this experiment? In fact, the reason is very simple: some things in the engineering interface can't be changed. We only hope that our SPD will have a protective effect when it encounters the first injury. When the SPD is unable to continue to bear it, it will scream: I can't, fast. Find the next one for me! Generally, this way of conveying the SPD screams to the owner, we will use LED indicators or remote signal output. We are afraid that after the SPD fails, it will cause a short circuit between the L/N lines and further cause a power line fire. One of the purposes of the TOV experiment in the lightning protection industry is to avoid "secondary damage." At present, I have two LED streetlight projects in China. Because of the SPD fraud, I have been involved in the case of street lamp fires. Unfortunately, I have been warned not to issue them.

Finally, let's talk about how SPD works with power supplies. Constant current switching power supply is the only choice for LED outdoor lighting. Regardless of isolation, non-isolation, high power, low power, there is always an EMC part of switching power supply? Some companies require me to make products. The residual voltage of SPD must be controlled within 900V, that is, Up≤0.9kV. Then I only have one requirement: I can do it, but I must develop it with your company!

why? If SPD wants to lower the residual voltage, it only increases the “multi-level protection” method, and doubles the cost per additional level. Moreover, in order to do the decoupling function between multiple stages, we will choose in the power frequency mains. The inductor acts as a decoupling device. This will also bring a lot of side effects. I have encountered this situation many times: after the SPD is added, the conduction radiation of the power supply cannot pass. We can't add a common mode inductor to the SPD. It is necessary to know that the temperature rise of the inductor is very fast. The requirement of our SPD product is that the temperature rise of the inductor must not exceed 45 Kelvin. The operating temperature of each device in the entire SPD must not exceed 85 °C. So there is a saying in our lightning protection industry: SPD's thermal design is more important than everything else!

I once predicted that the communications industry has suffered losses due to lightning surges in the global market. The LED lighting industry has to go back again to understand that it is very wrong to change. At present, it seems that it is not bad at all.

I have always thought that the Meteorological Administration's supervision of the lightning protection industry is a very wonderful thing. It has always been very opposed, but now I see the LED industry and the photovoltaic industry. I suddenly feel that it is a good thing for the Meteorological Bureau to supervise our lightning protection industry, at least we Most companies in the industry are doing their best to make products in the industry. We are definitely not a company that is well-dressed but swindled in the industry!