Webinar "Overvoltage protection. Zone concept of lightning protection." page 2

The first webinar of a series "Surge protection"

Webinar text. Page 2

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Zonal concept target

Target:
Create protection zones inside the construction facilities, which contain devices with a similar level of resistance to the impact of thunder electromagnet pulses (LEMP)
Result:
Provision of continuous work of single devices and complex distribution systems even in case of a direct lightning strike into the object

- That is why, I recommend you to get familiarized with these standards, they simplify the life of designers sigificantly. This zonal concept target is to create protective zones inside construction objects, which contain devices with a similar level of resistance to the impact of thunderstorm electromagnetic pulses. In the result, we provide flawless operation of single devices, and also complex distributional systems even in case of a direct lightning strike into this object. Question - is it true or word-play?  Example of my company's solutions shows that for a 20-year-experience something really happens at the objects where we workd. And we work at the unique objects I have to say. These are different stations and other industrial objects, these are high-rise objects, telecommunicational, where the towers are 326 meters high and they are hit by lightning 2-3 times a year and all the equipment remains untouched. It is real if to do what we are talking about today.

LEMP – lightning electromagnetic pulse

Zonal protection concept against electromagnet lightning pulse refers not only to external lightning protection, but it presents itself an effective method of general behaviour for the provision of electromagnet compatibility of devices and their electromagnet environment.
The aim of using zonal protection concept is limitation of values of surge currents and voltages caused by them (surge protection devices) and values of pulse fields strength by shielding.

- Zonal concept of lightning protection from electromagentic lightning pulse, it is called LEMP for short. We've started to use international abbreviations to make a common language for engineers. LEMP – lightning electromagnetic pulse. Zonal concept refers not only to external lightning protection, but it presents itself an effective way of common behavior for provision of electromagnetic compatibility of devices and their electromagentic environment. The aim of using zonal protection concept is restriction of surge currents' values and overvoltages caused by them (surge protection devices) and values of pulse field strength by shielding. It means that at the border of the zones, we put surge protection devices and shields.

Lightning protection zone (LPZ)

 Lightning protection zone:

- it is a zone, inside which, the electromagnet environment of the lightning discharge should be defined and constantly controlled

- protected space is divided into lightning protection zones for division of spaces with different intensity of LEMP and determination of location of connection points at the border of the zones

- separate zones characterize the solid change of electromagnetic conditions at their borders

- Lightning protection zone - LPZ - is a zone inside which the electromagnetic environment of lightning discharge can be determined and subject to constant control. On the right we see an image LPZ1, LPZ2 - zone one, zone two. The protected volume is divided into lightning protection zones to single out spaces with different intensity of LEMP lightning pulse and determination of places of connection points at the zone borders. That is, we define the space and define in what points it will get inside, cross the wire or it will be some metal structure, for example, ventilation system. Separate zones characterize the substational change of electromagnetic conditions at their borders. If it means that we put equipment which should stand such conditions in these zones.

Main and additional conditions

Main condition:
During picking of certain protection means it is necessary to know about real levels of expected disturbances in this zone and also about the levels of pulse resistance of the devices and systems located in the studied object

Additional condition:
Protection of particularly sensitive and strategically important electronic devices and systems should consider that beside the threat of galvanic impact of lightning current and voltage, there is the threat of affecting the protected systems of the pulse electromagnet field appearing from the lightning current.

- That is, we perform the main condition that during selection of certain protection means, it is necessary to know about real conditions of expected disturbances in this zone. We simply know what we can start calculating coming out of well-known values of lightning current - 200 kA, 100 kA, 150 kA for different lightning protection categories. And also about levels of pulse resistance of devices and systems in the studied object. All the manufacturers know this information. All equipment, if it was tested for electro-compatibility and their resistance is known, because it is determined during these tests.

Protection zones design stage

Stage of protection zones design at the object:

- division of zones inside the construction object, in which appearing of disturbances of the estimated level is expected
- output of required protection means for the room at the borders of the zones
Shields – weakening of electromagnet field caused by a lightning discharge
Elements/ surge protection circuits

- choice of devices foreseen for working at this object considering the need of their choice by the principle of their resistivity level correlation to the expected overvoltage parameters, declared by the manufacturer on the base of the documents delivered.

Помехоустоймость- resistance to disturbances to the lightning strike impact
Гальванич.эффекты – galvanic effects
Эффект сопряжения – conjugation effects with electromagnetic field

- In this case, the designer should consider several important things, that is, he singles out zones inside a construction object, and where appearing of disturbances of a prte-estimated level is expected. The designer, knowing these levels, chooses the required protection means for the premises at the border of the zones. He places shields to weaken the electromagnetic field, caused by the lightning discharge and surge protection methods. And the only thing which is not written here - equalization of potentials of conductive utilities system at the zone border. The choice of devices foreseen to work at this object. It is also designer's challenge. Those who work at an object, considering the need of their choice according to the principle of correspondence of their level of resistance to the expected overvoltage parameters, declared by the manufacturer on the base of the documents delivered. It means, we estimate the resistance of such devices out of data which the manufacturer gives to us. If we look at the standards, beside the lightning strike impact, we define the galvanic effect,it will be Polish, because I call it so. I mean conductive effect according to IEC 6100-4-5 and the effect of coupling with elecctromagnetic field - it is IEC 61000-4-9 standard, for instance.

Zones construction method 

Экраны - shields
Стены здания – walls of the building
Магнитное поле согласно – magnet field according to IEC 62305-4
Зона - zone
Излучаемые помехи- radiated disturbances
Помехи проводимые – conducted disturbances
Например: диспетчерская или серверная 
Частичный ток молнии – partial lightning current
Наружные линии электропитания и слаботочные – external power supply lines or low-current lines

- Everything comes down to a more scientific picture. In practice. It is simply very practical. If we look at the method of zones construction, we see zone LPZ 0 on top - the external zone is defined this way. The zone in which lightning can hit any object or this object must stand this lightning current. Conventionally, all objects which stand such a lightning current. And on the right, we see the current, flowing along the conductors - it's 10/350 ms, which flows to LPZ 1. Electromagnetic field of lightning current also gets into this zone. On the left we see, that we drew shields on the walls of the building and of the premises of the second zone. On the cable input into these zones I wrote SPD, surge protection device. This is how these devices are called. At the building entry, there is an SPD which stands partial lightning currents. That means, there are surge restriction elements, which are characterized by the resistance 10/350. Very often there is a problem in Poland; in Russia it is even stronger to my mind, when the manufacturers try to convince you that you can put weaker protection elements, cheap ones at the cable entry of the object. But you know, nothing cheap can be good. And these elements are described by 8/20 ms pulse, which you see. They are characteristic for surge protection devices at the zones border inside the object between the first and the second zone inside the object. And for simplification of these solutions' understanding, it is necessary to take into account, that all external effects, when lightning current flows - are 10/350 ms pulse. And the second pulse 8/20, 8 is front time, 20 - time for a hemi-downturn that is half of maximal value in this recessing part. This pulse is much weaker the energy, about 35 times less, than lightning current pulse at the same maximal current. These are pulses which we study inside the object. Simplification can accept that galvanical external conductive, effect is 10/350 and inside the object there is pulse 8/20 ms. Some pulse should be accepted, it will be simply in the standards and this pulse describes internal effects, when the current part soaks through the first surge protection device at the border of LPZ 0 and LPZ 1.

Design of lightning protection zones at a construction site

Zonal protection concept

- In the result, we get some picture, where under the lightning protection system, which is shown in red here, external zones appear. Outside, sorry, on the top right zone 0A - external zone. Under lightning protection system, there appears building protection zone 0B. Zone 0B may appear where there is an elevator, we can characterize it so.

- Miroslav Zelenkevich, allow me to interrupt you. I'd like to offer you to use a pointer for your convenience. It is located on the bottom left, under the presentation, a red arrow. You can click on it.

- You did not tell me that. Yes, I can see.

- You can press the red arrow which appeared on the slide, hold it and move around the slide to demonstrate.

- Frankly speaking, I don't see it. Thank you, Alexey. It doesn't work.

- You need to click on it and drag. Yes.

- Yes, I can see. Thank you. Better late than never. It will help me a bit, thank you, Alexey. I always need it. We see in thius case, it is not necessarily a lightning protection system, but if you are a bit familiarized with the standard 62305. Then you see that one method is applied there. It's a rolling sphere method, which we apply on the object. And everything that is under this sphere is protected. The radius of this sphere is from 20 to 60 meters. For the first category - it is 20 meters. It strains requirements to lightning protection in comparison to the old standards and we usually use this method that means, the sphere will touch this place from the building structure, and there will be the start of the protective zone 0B, where direct lightning must not strike. The same under the lightning protection system on the building roof. Inside the object, the designer builds the first zone, as a rule, the borders of this zone are the object walls. Shields are set at this border. Or zone 2 is where there is a special device, for instance, we've made recently for a medical suite, sorry I don't know in Russian, where a patient is connected to the device by electrodes from his heart. We made a special shielding system for such rooms, because people are now afraid to be responsible for such a patient. It's not a joke- it happens every day.

Lightning protection zones

Zonal protection concept
Lightning protection zones
Zone 0a – a direct lightning strike is possible. Lightning current impact with the maximal value. No shielding from LEMP
Zona 0b – a direct lightning strike is impossible. Current and voltage pulses impact induced from the conjugation with the electromagnet field of the lightning current. No shielding from LEMP
Zone LPZ 1 – undetermined states with high level of energy, caused by : impact of EM field from LEMP, flowing of partial lightning currents, commutation overvoltage. LEMP field is weakened by the shield at the border of zones 0a/1 or 0b/1
Zone LPZ 2 – undetermined states with the high level of energy, caused by: impact of EM field from zone 1, commutation overvoltages, electrostatic discharges. EM field is weakened by the shield at the border of zones ½
Zone LPZ 3 –Room “free” of the dangerous level of EM field

- If we look at the description of these zones, it is a conventional description for sure.  The designer decides how they are going to be called, but in order to summarize; it is good to study it the way, that outside there is zone 0A, where a direct lightning strike is possible. We also deal with the impact of lightning current with maximal values. There is no shieding from lightning electromagnetic pulse. In zone 0B, under lightning protection system a direct lightning strike is impossible, because the system is created in order not to allow a lightning strike. It will capture this current, but then we deal with the impact of current and voltage pulses, induced due to the tracking with the lightning current electromagnetic field. There is no shielding of this field, because there is usually none outside. In the first zone, that is inside the object, behind the wall, the shield, which is on this wall, behind the protective elements which are set on all wire strands and other conductive utilities. We deal with an underfined state with a high level of energy, which is caused by the impact of electromagnetic field from LEMP, flowing of partial lightning currents, commutational overvoltages.

Example of utilities at an object

Кабель электроэнергетический – electricity cable
Антенна - antenna
Отверстие, например окно, двери – hole, for example window or door
Границы зон – borders of zones
Металлические коммуникации, например водопровод, канализация – metal utilities, for example water pipeline, sewerage
Мачта, ограждение, металлические конструктивные элементы – mast, railing, metal construction elements
Место входа проводок в объект, а также монтажа защитных устройств – place of input of harnessing into the object and also installation of protective features
Элемент- схема защиты – element of protection circuit
Непосредственное выравнивание потенциалов – direct potential equalization
Защищенные устройства – protected devices
Кабель сигнальный, например телефонный, компьютерный, RTV, автоматика и управления – signal cable, for example , telephone, computer, RTV, automation and control

- In practice we see an object here. These are its walls. Different utilities enter it - water pipeline, sewage pipes. But, all these utilities are plastic now; I am not sure about all Russian regions, because the temperatures are different. In our country - water pipeline, sewage and gas pipe are made of plastic, so we don't have a chance for the lightning to flow along the insulators. But if they are metal elements of the structure, they are grounded in the grounding system at the entry to the object. The mast, fencing, metal structural elements at the object entry on the border of zone 0A and zone 1 are grounded. All cables which enter the object - signal cable, phone, computer cable, television, automation and control, etc. Electric energy, antenna cable are protected with the help of surge protection elements. All the cables enter another zone, all utilities at this border too or are connected to the system of potential equalization directly or via surge protection elements, like in case of a signal cable and power supply cable. Then we consider that all devices, working in zone 1 and 2 are protected and won't be damaged during a lightning strike.

Approximate parameters of strikes in certain zones

Zonal protection concept 
Zone LPZ 0a
Zone LPZ 1
Zone LPZ 2
Zone LPZ 0b
Surge protection  - защита от перенапряжений

- Let me give you an example here. You see different values. If we look on the left, we will see LPZ 0A zone. And the designer defines, that I am setting devices here, which stand 100 kA, because the system of the third, fourth category of lightning protection - 10/350, its constant component 200 A for 0,5 seconds, and the second component 200 kA with the pulse 0,25/100 ms. Have a look, it is indicated here that not one pulse, not one current flows in one lightning channel. And if it ionized the channel, then, as a rule, lightning energies flow over it several times and the second strike is much quicker. Please, see, the growth speed is 40 times faster here. This pulse is responsible for inductive effects, which appear when lightning current flows along the conductors. In that case, we place a device in zone 0B under lightning protection system, which will stand 50 kV pulse 1,2/50 ms and 30 kA 8/20, because we have only induced lightning currents there, not partial ones. In order to restrict the energy soaking into the object, I called SPDs ZOP. ZOP at the border 0-1, which restricts all pulses to the level not more than 4 kV in voltage and 10 kA in current. And further the designer builds the following parameters, considering the resistance of devices, which are installed in this zone.

Example of substation building

Zonal protection concept 
Zoning into protection zones
110/35/10 kV Substation building

- Let's have a look at the example. Substation building, here is such an example. Let's switch to an enlarged picture.

Protection zones division

Zonal protection concept 
Zoning into protection zones
110/35/10 kV Substation building
УЗИП - SPD
Пульт управления – control box
Релейная защита и автоматика – relay protection and automation
Распределительное устройство - distribution device
Радио связь – radio connection
Автоматика - automation

- And what do we see here? Since it is an old object, there are many entries. Entry 1, 2, 3, 4, and 5. Five - are high-voltage cables, we do not work with them, because we think, that energy engineers are very very clever people and they deal well with high-voltage surges. And in fact what we are doing are low-voltage systems up to 1000 V, because such voltages are characteristic for power supply cables and low-current cables of all signal systems which are present at such an object. And see what can appear such an object where we can't move equipment. There are radio location premises on the right. The second premises - automation of static works, very responsible premises, very valuable equipment. This equipment is connected with other premises via cable track. What are we doing at the object? For example, we install relay protection and automation into zone 1. Why zone 1?

Magnetic field shielding 

Shielding of the magnet field following the atmospheric discharge

- How do we shield? We need to see it in part 4. I will only briefly show you the image from this standard, which shows that we shield all premises.

Lightning current frequency spectrum

Lightning current frequency spectrum
 Zonal protection concept
Соединения в точках пересечений – connections in intersection points
Металлическая оконная коробка – metal window frame
Соединения- connections
Металлическая коробка дверей – metal door frame

- This shield, meaning the frequency and frequency spectrum of lightning current, the largest energy of which loses, somewhere up to 100 kHz for civial, non-military solutions. It is a very low frequency, that is why such a shield is not very thick - it is not a very expensive mesh and the solution price is affordable, but without them, our protection won't be complete, there may appear unexpected effects of various types.

Useful materials for designers:

• Webinars with the leading industry experts
• Everything for the calculation of grounding and lightning protection
• Useful materials: articles, recommendations, examples