Estimation of the lightning current passing through the SDP

Estimation of the lightning current passing through the SDP

Кольцевой заземляющий электрод - Annular grounding electrode
Стенка - Wall
Металлическая водопроводная труба - Metal water pipeline
Заземляющие шины - Grounding buses
Фаза - Phase
Электрическая силовая шина - Electrical power bud
Сумма - Sum
Нейтраль - Neutral wire
100% попадание молнии в здание - 100% lightning strike to the building
Металлическая труба газопровода - Metal gas pipeline
Металлическая труба - Metal pipeline
Кабели связи или передачи информации - Communication or data transfer cable
Ввод электропитающей линии - Input power line
10/350 мкс - 10/350 mcs

The figure shows the schemes recommended for a priori estimation of a fraction of the lightning current loading the SDP. They have been taken from the regulatory documents: IEC or Russian. The schemes are obviously intended to reduce the current required to choose an SDP.

Only manufacturers are interested in them. A half of the current, for some reason, goes to the grounding electrode, while the remaining part is divided equally among the utilities. Utility parameters are not considered, and particular grounding resistance values are only considered when the current is divided among parallel grounding electrodes. The replacement schemes do not even provide for inductances. It seems like top managers do not even know this parameter of the electrical circuit. Here, we would have to place one more proposal of a French specialist. He recommends dividing the lightning current between the grounding electrode and the protected circuit always in half. It is so easy and you do not need any calculations!

The main mistake of the provided schemes is related to ignoring the wire inductance. This is the reason why the current pulses in all circuits are similar in their shape to the lightning current pulse, and the sum of their maximums is equal to the lightning current maximum. In practice, the times of these maximums can be different, and each of maximums is significantly more than the one obtained according to the estimate scheme.

We cannot understand what these proposed schemes are associated with. Modern specialists have long since mastered PC and surely know the typical calculating software to estimate the pulse current in circuits of any complexity level. MatLab is an example. All of these have been discussed in ZANDZ publications, and you hardly need to repeat it. An elementary estimation performed in the section is intended to prove the danger associated with possible errors which may be caused by the application of the recommended calculation schemes. Here, using the simplest situations, you can do that without the PC.

Read more details in the article by Prof. E. M. Bazelyan SDPs Unvarnished.

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