The twelfth event from the series "Grounding and lightning protection: questions and problems arising in the design
Webinar text. Page 2
Quick navigation through slides:
1. Lightning and lightning protection at Krzhizhanovsky Power Engineering Institute
2. Statement of M.V.Lomonosov about lightning
3. Message of Franklin to count Shuvalov
4. The theory of J.Townsend
5. Air ionization threshold
6. Professor I.S. Stekolnikov’s work
7. Experiments of V.S. Komelkov
8. Laboratory of world records
9. Voltage pulse with a low angle front
10. What changed in the researches of lightning rods?
11. Dependence of the result on the voltage front pulse
12. Leader mechanism of spark and lightning
13. Why do long spark and lightning need a complex structure?
14. Role of streamer zone and spacial charge casing
15. Elementary theory of a leader
16. Theory extrapolation
17. Russian protection zones – where do they come from?
18. Pictures of researches
19. Lightning way
20. ENIN statistical theory
21. Methodical bases of calculation of a number of lightning strikes into overhead power lines
22. Possibilities of a statistical method
23. Influence of the working voltage
24. Influence of a forest area along the overhead power line route
25. David and Goliath (gas discharge version)
26. Corona and lightning
27. Streamer flash start
28. Gold’s hypothesis
29. Practical implementation
30. Catenary wire lightning rods for the protection of switchyard substations
31. Expected results
32. ESE lightning rods – myth not a reality
33. Danger of spak channels long the ground surface
34. Experiment in Sarov
35. United field tests by ENIN, OIV RAN, TINITI
36. Where else science is required
Why do long spark and lightning need a complex structure?
Для чего нужна сложная структура длинной искре и молнии – Why do long spark and lightning need a complex structure?
Перекрытие длинного промежутка всегда результат распространения волны ионизации – overlapping of a long gap is always a result of ionization wave distribution
Плазма в канале стримера холодная, потому что подъем напряжения не меняет удельной энергии= plasma in the streamer channel is cold, because voltage raise doesn’t change specific energy
Время жизни электрона при T=300K ~0,1 мкс – electron life time at T=300 K is ~0,1 ms
При скорости 10 (7) – 10 (9) см/с стример теряет проводимость на расстоянии 1-100 см за фронтом ионизации – at the speed of 10(7)- 10 (9) cm/s the streamer loses the inductivity at the distance of 1-100 cm behind the ionization front
Канал сохранит проводимость неограниченно долго, если нагревом до ~5000K включить реакцию N+O→ e + NO – the channel will keep the conductivity endlessly if to enable reaction N+O→ e + NO by heating up t ~5000 K
0,1 пкФ/см – 0,1 pF/cm
— If some object has electric capacity, then the energy it can store in this capacity is CU 2/2. It is a well-known formula, even schoolchildren know it. Not more than CU2/2 energy may dissipate in this channel and it is impossible to take more energy in the channel. Despite the fact that there is a lot of it everywhere. When this elementary idea came to the minds of people, it became clear, how the channel, which is built and the streamers, which fall out of the head of this channel correlate with each other. It turns out, that at the expense of filling space by streamers, the capacity of this system increases.
Role of streamer zone and spacial charge sheath
Роль стримерной зоны и чехла объемного заряда – role of streamer zone and special charge sheath
Стримерная зона направляет в головку лидера ток многочисленных стримеров, не потерявяших проводимости - Streamer zone directs the current of multiple streamers that did not lose their conductivity to the leader head.
Емкость единицы длины канала увеличивается вплоть до C1= ПЕ0 приблизительно втрое - The capacity of a unit of channel length increases up to C1= ПЕ0 – in approximately three times
Объемный заряд чехла, снижая поле на поверхности канала препятствует его ионизационному расширению и повышает удельное энерговыделения - The special charge of the sheath, reducing the field on the channel surface prevents its ionization widening and increases the energy production.
— And the energy which can be put in the channel increases proportionally to the capacity. But that's not all. This energy is not enough, it is necessary to increase voltage. And the increase of voltage is very effective, because energy increases into a proportional square of voltage. It turns out that it is spent to no purpose, because together with the increase of voltage, the radius of the channel increases at its ionization expansion. And the sheath of streamers which is formed in space prevents this expansion.
The elementary theory of leader
Элементарная теория лидера – the elementary theory of leader
Условия старта – start conditions
Нормальные условия – normal conditions
Условие жизнеспособности процесса- conditions of the process working life
Основные функции связи – main connection functions
Ток лидера – leader current
Внешнее поле атмосферы- external field of the atmosphere
Поле в канале – field in the channel
Скорость лидера – leader speed
— When these structures were created, a simple theory of long spark was made, which is applicable for lightning protection. We managed to check this theory experimentally in the intervals of up to 100 meters.
Extrapolation of the theory
Пробивное напряжение, мВ – sparking voltage, mV
Эксперимент - experiment
Теория - theory
Длина промежутка, м – gap length, m
Разряд молнии- lightning discharge
— There was no doubt, that the theory could be extrapolated further and it was possible to show that to break an interval 1 km long, quite modest voltage is required. Not more than, say 15-20 MB. Scientific base was prepared so it would be possible to work on practical lightning protection. It became clear, that no laboratory experiments could get a reliable idea about the protective action of lightning rods, because it turned out, that the results of laboratory experiments do not only depend on the shape of pulse voltage, at which they are held, but on the scale too. And they depend on the scale strongly.
Russian protection zones - where do they come from?
Российские зоны защиты – откуда они? – Russian protection zones – where do they come from?
Результат неоднозначен – the result is ambiguous
— This dependence on scale was studied by the joint experiments of the Energy Institute to the name of Krzhizhanovsky and Leningrad Politechnical institute. We held researches in the intervals up to 12 meters long and saw that we get different results in different intervals. These different results do not allow understanding what result is correct. The tendency was such. The longer is the interval; the worse is the protective action at the laboratory. It is clear, that it is impossible to build a protection zone with such results.
Pictures of researches
— Not looking at the fact, that the experiments with the construction of protection zones have been continually done and are still done. The researches are held in intervals up to 30 meters long. Anyway, these results obtained in the laboratory are high-quality results. And it was not very clear how to transpose these results to lightning. It was necessary to make a calculation model, which on one side would be probable in physical relation. On the other side, this model could be tested, and thirdly, the model should be basing on some experimental facts. They made such a statistical model. They came out of the following.
Путь молнии – lightning way
Вероятность пробоя – breakthrough probability
Но - but
— If you put two intervals of different length parallely. Interval S1 and interval S2, it is not obligatory that the first, the short one will be broken down. With a certain probability, the longer interval will be broken down, because there exists a large scatter of breakdown voltages. Look, for example. The height of the tower is 34 meters. The charge should have left the tower and run to the ground along the shortest way, but it went another, ran for more than 100 meters, the channel stopped its development on the neighbouring support of power line 100 kV. Or the second result - Ostankino tower. Lightning should have hit its top, as Franklin and Lomonosov thought, but it missed 202 meters below the top and hit under the restaurant "Seventh heaven". This statistics should have been introduced into the calculation model. It was introduced, basing on two ideas. The first idea was as follows. Lightning starts from a cloud absolutely indifferent to the state of ground surface. And starts to distinguish this ground surface, coming down to some height, which is called the height of orientation. Here lightning chooses its way, either to the towering object, or to the ground surface. And the choise of this way is defined by simple statistical regularities, because one way and another way are far from each other and they do not affect each other.
Statistical theory of ENIN
Статистическая теория ЭНИН – statistical theory of ENIN
Два независимых события – two independent events
Ориентировка к заземленной системе – orientation to the grounded system
Выбор точки удара внутри системы – strike point choice inside the system
— When the choice is made, the second process starts. This second process chooses the strike point of an oriented lightning either on the surface of the lightning rod, or on the surface of the protected object. According to a well-known and well-checked hypothesis of Gold, it happens at the expense of development of counter channels, counter leaders from lightning rod to the object. They influence each other with their electric fields, because lightning rod and object, as a rule, stand near each other. And all that was taken into account in the statistical method, which was developed at ENIN for a simple situation first, and then for any number of lightning rods and protected objects. This calculation model required adjustable parameters only.
Methodical bases of calculation of the number of lightning strikes into overhead lines
Методические основы расчета числа ударов молнии в ВЛ – methodical bases of calculation of the number of lightning strikes into overhead lines
Статистическая методика расчета по усредненным параметрам разряда молнии - Statistical method of calculation by the average parameters of lightning discharge
Процесс ориентировки лидера молнии в направлении ВЛ - Process of lightning leader orientation towards overhead power lines
Выбор точки удара на элементах ВЛ - Choice of strike point on overhead power lines elements
Исходные параметры - Source parameters
- Габаритные размеры опоры - Dimensional sizes of the support
- Координаты подвеса тросов - Coordinates of wires hanging
- Провес троса в пролете - Wire sag in the span
- Координаты подвеса проводов - Coordinates of wires hanging
- Провес проводов в пролете - Sag of wires in the span
- Наличие и координаты лесных массивов по трассе ВЛ - Presence and coordinates of forest areas along the overhead power line route
- Профиль земной поверхности по трассе ВЛ - Profile of ground surface on overhead power line route
- Интенсивность грозовой деятельности по трассе ВЛ - Intensity of thunder activity along the overhead power line route
— The probability of a strike point choice, which should be determined by the experimental data, was acting as such adjustable parameter. There is a serious problem here. There were plenty of natural experiments, because damages of overhead power lines were registered. And it was registered with what probability lightning doesn't hit the ground wire, but hits overhead power lines. International organization CIGRE collected a great number of experimental material.
See slide 19. During many years they had been registering lightning strikes into the tower. The charge I showed you is taken from their collection. In the result, another very important point on which it was possible to test the method appeared. Thanks to this and another experimental base, it was possible to test the static method and offer this method for practical use.
Possibilities of the statistical method
Возможности статистической методики – possibilities of the statistical method
Расчет надежности защиты объекта произвольной формы любой системой молниеотводов - calculation of reliability of protecting an object of arbitrary shape by any system of lightning rods;
Определение ожидаемого числа прорывов в любой конструктивный элемент защищаемого объекта - determination of the expected number of breakthroughs into any constructive element of the protected object;
Учет локальной неоднородности атмосферы над защищаемым объектом- consideration of local atmospheric inhomogeneity above the protected object;
Оценка влияния рабочего напряжения объекта на вероятность прорыва молнии- estimation of the influence of object’s working voltage on the probability of a lightning breakthrough;
Учет влияния окружающей застройки объекта или рельефа местности- consideration of the influence of surrounding structures of the object or local relief
— What did this method give? Firstly, it gave calculation of a number of lightning strikes, probabilities of a strike for absolutely any construction of lightning rods and protected objects and it was very important, because lightning rod protection zone in which they were bilt, in the best case they could build for double lightning rods. That's it. Secondly, they gave a possibility to consider local irregularities at te surface of the protected object or lightning rod. It was very important. Imagine a chimney of a heating station. Exhausing gases are emissioned through it. These gasses are flammable, their density is reduced. And in the result, the conditions of the counter charge development which will capture lightning on the chimney will be different, not like at an ordinary object.
Working voltage impact
Влияние рабочего напряжения – working voltage impact
Вероятность прорыва молнии – Lightning breakthrough probability
Эффект реально заметен при – the effect is really noticeable at
— Or take another thing - electric transmission line of ultra-high voltage, when voltages of phase cables are about a million volts. It is local change of atmospheric state and the method could take it into account too.
Influence of a forest area along the overhead power line route
Влияние лесного массива по трассе ВЛ - Influence of a forest area along the overhead power line route
Число прорывов молнии – number of lightning breakthroughs
Пролет длиной 400 м- span 400 m long
Опоры ПБ4 – supports of Industrial Safety 4
Высота повеса провода – 23 см – Height of wire sag – 23 cm
Провес провода – 6 м – wire sag – 6 m
Тросы демонтированы- the catenary wires are dismantled
Расстояние до леса 20 м – distance to the forest 20 m
Лес с одной стороны ВЛ – forest on one side of the overhead power line
ВЛ по лесной просеке – overhead power line along the forest firebreak
Высота леса, м – forest height, m
— Besides, the method could take surrounding reliefs into account. For example, the line goes along the narrow clearing. There is forest on the right and on the left. Forest areas also take part in the orientation of lightning. In the reult of that, it turned out that the probabilities of lightning strikes into overhead power line turned out to be independent on the fact on which side the forest was - the second curve - if you have working voltage. With the increase of working voltage, lightning rods work worse, worse and worse. And it should be considered too. On the base of this static method, the guiding recommendations on lightning protection which exist till the present day were created. It is AD 34-21-122-87, and IS 153, it is an authorizing document of many authorities, Gazprom, United Energy System, other branches of technical industry. This method is in all these things. And in the end, agreed by GosTekhNadzor and on the base of the technical memo 25-2009, this method was officially recommended for use on the whole territory of the Russian Federation. And it doesn't mean,
<< Previous Page
Slides from 1 to 12
Next Page >>
Slides 25 to 37
Useful materials for designers:
- Webinars with the leading industry experts
- Everything for the calculation of grounding and lightning protection
- Useful materials: articles, recommendations, examples
The full version of the article is available only to registered users!
Get access to all the materials on the site for free!