Webinar «Lightning and Lightning Protection at Krzhizhanovsky Power Engineering Institute», page 2

The twelfth event from the series "Grounding and lightning protection: questions and problems arising in the design

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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.

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.

— 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.

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.

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.

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,

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