Webinar «Surge protection of low-current lines, part 1», page 1

The 4th webinar about Surge Protection

(took place on 6 April 2016 at 11:00 a.m. Moscow time)

Generally, characterized by a low level of electromagnetic resistance from the part of its signal interfaces. This is primarily due to the use in such systems of an increasing number of electronic circuits that are sensitive to electromagnetic interference. Overvoltages caused by lightning strikes or interference in the power supply network are especially dangerous for such devices. They may damage or even destroy electronic devices. The corresponding losses do not relate only to the material (the need for repair or replacement of equipment), but they usually include additional costs associated with the loss of system functionality that includes a failed module or an entire electronic device resulting in a loss of company reputation because of interruptions in its work.

To ensure high reliability of various types of low-current systems operating under conditions of a significant level of electromagnetic interference, it is necessary to use overvoltage protection circuits (SPDs) selected according to the standard of the protected interface, as well as with the expected level of interference (partial lightning currents or induced overvoltage currents). Such SPDs should limit overvoltage to safe levels maintained by the protected device without losing the nominal functional properties of the system.

The presentation will also consider examples of ways to protect existing low-voltage systems, taking into account the principles of zonal protection concept in accordance with the requirements of the IEC 62305 standard.

Webinar text. Page 1

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Approximate Reading Time: 1 hour 26 minutes.

— Hello, colleagues! Hello, Miroslaw! Welcome to our next online event. This is our fourth meeting of Surge protection series. You can watch the video of the previous webinars, as well as register for new ones, you may click the link that I send you every time in the chat. Let me remind you that at previous meetings we discussed in detail the zonal concept of lightning protection, since all protection schemes are build on it,as well as the differences in surge protection devices. And in previous webinars we talked about the protection of 230/400V, 50 Hz power supply lines. Today we have the first part of "Surge protection of low-current lines". The topic is interesting, popular and raises many questions about how to properly organize protection. Today we will talk about this, consider examples and measures necessary for protection devices layout.

— The lecturer of this webinar is still a recognized expert in the field of lightning protection, Miroslaw Zielenkiewicz. On the slide you can see some of his merits and awards, but believe me - these are not all of them. My name is Aleksei Korytko. I am the webinar administrator and I will answer your questions and comments which you can leave in the chat at the bottom left. We will try to answer the question at the end of the webinar that will last from 60 to 90 minutes. Also the presentation may have schemes with fine details, you can use a special magnifying glass tool to see them all. It is located down below the presentation window. I think that organizational part is over. I am pleased to hand over the word to Miroslaw. Miroslaw, good afternoon!

— In this case we cut off not only the power supply lines, but also the data lines, block them from interference into our object by using overvoltage protection elements.

— We should already know how to install elements of overvoltage protection, because if we use the zonal protection concept, and it, as can be verified in practice, is simply perfect for protection. We see that if the wires enter the object outside, on the border we install protection both for the power supply network on the right, and for the signal lines. If this is an outdoor shield, for example, automation cabinet on a railroad, then the same here, we must install overvoltage protection at the input of all the cores of our power supply and signal lines.

— Here on the left there is the wall that looks like a strange object. We install at the cable entry. Always the question is: outside the wall or inside? In practice it does not matter, if we divert this current to earth in a way that it does not interfere the electromagnetic energy to sensitive devices. If there is a danger of it happening, we should definitely do it outside observing all measures for protection from moisture. In this way the system price increases and the system is simplified. I am showing that the connection with grounding is the shortest, because then our limiter will get voltage restriction, and the voltage drop across this inductance on the way to the grounding conductor will be minimum. Please, take a look, there will be a voltage limit at our limiter plus a voltage drop across the inductance of this wire. If we see that these points fit our protected device, then this sum of voltages will give us the voltage after restriction through our device.

— How to choose a surge protection device for low-current systems then? First, we must understand that we have different standards of signals, therefore, when we start designing, our first principle is not to change the signal in any way. In any mode of operation of this system our signal must pass the way the designers of this system have designed it. In other words, while dealing with this system we should not change its properties. And then we have to think about how should this element be protected? So, we need to understand what kind of resistance of this system affects overvoltage from the side of low-current lines. And the question is: how to define it? It may be that the designer will each time determine the stability of this system. But at that moment you should apply the standard that I have said. Nothing needs to be invented, nothing needs to be sought, you just need to know. The knowledge in this area now has reached the level at which we can find stability in interference to any system.

— If we take a look at the following table, here we see the stability of the signalling wires ports and the data bus that are involved in the process control. Stability ports of processors and measuring and control wires, as well as ports of long buses and test conductors. And port stability, DC input. But if we look here, we will not see too much data. Basically, what we can take from here when selecting is the magnitude and voltage pulse with which our devices were tested when they were allowed to work in railway systems in this case. We see, that there are 2 and 1 kV. Question: who thought up the voltage and why exactly 2 or 1 kV?

— See slide 11. 2 kV - core-ground, and 1 kV - core-core. But here you just have to realize that we can't set too high requirements to the manufacturer, because devices will become very expensive. And in this case these standards, these tables do not consider cases when a lightning strikes an object. In these standards it is always written openly, mainly in the introduction to this standard. This means that this equipment must work inside the object in some second zone without interference, but it is stable against such interference for which we tested it here. This does not mean in any way that this equipment will work properly without failure, without interfering, when lightning strikes the object or close to it.

— See slide 12. But these tables, this data gives us important information that we have determined the minimum level of resistance. So, if you think about the table, let's return to it again, we should limit overvoltages in this case at least up to level of 1.2/50 µs pulse, our overvoltages should not be more than 2 or 1 kV. But in reality, if the rated voltage of low-current lines is about 12-48 V, we always try to limit the voltage close to these values in order to reduce the energy that leaks inside the object. Therefore, in this case, the voltage will be much lower if we design right, than the pulses indicated here for the stability of our object.

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