Electromagnetic Intensity Distribution Of Lightning Stroke On Indoor Substation Buildings

With the development of the automation in power system, more and more electronic and micro-electronic equipments are used in the substations especially after the micro-computerized of relay protection. These weak current equipments widely have weaknesses such as: low level of dielectric strength, poor over current and overvoltage tolerance ability, high sensitivity to electromagnetic interference and so on. Once a substation building is struck by lightning, the strong lightning current suddenly flows from the lightning strike point into all the distributed branches of the building's structural reinforcing steel and finally scatters from the grounding body into earth. In the transient process of lightning, the lightning current flowing in all the branches will cause transient magnetic field in the inner space of the substation building. The transient magnetic field can impose harms via induction and radiation onto electronic system in the building, which may easily make electronic and micro-electronic devices temporarily ineffective or even permanently damaged. The research report AD-722675 of USA indicates that unshielded computers will malfunction at magnetic induction B=0.07Gs and will be damaged at magnetic induction B=2.4Gs.In this paper, it has complete computer simulation and study of the electromagnetic environment of the substation in various lightning stroke based on the tool of CDEGS software, and tested in a laboratory environment. The research work mainly includes five aspects: computation of lightning current's distribution in the conductors, computation of magnetic field distribution in indoor space of ordinary architecture and of real substation buildings, computation of indoor circuits'induced voltage. The main results are as follows:(1) Based on the calculation of electrical parameters of buildings'reinforcing steel bar structure, the calculation of capacitance parameters via average potential method and of inductance parameters via Neumann's formula. Based on the calculated electrical parameters, the calculation method of transient currents in conductors of branches of buildings'reinforcing steel bar structure is pointed out and the transient current in classic structure of reinforcing steel bar is simulated via computer. This article compared the laboratory test results and the computed results, they are well agreed with each other. (2) This article calculates and simulates the building's structural reinforcing steel model's magnetic field intensity changing considering different grounding manners, which based on the model's currents'distribution obtained. And then found the law that the lowest magnetic field intensity point location will drift to the opposite direction to primary grounding network and secondary grounding network junction moving. The laboratory test results show that it is basic in conformity with the computed result. In addition, at the foundation of space magnetic field intensity distribution, this article calculated the induced voltage of conductor circuits is given.(3) This article calculated the magnetic field distribution in inner space of main control building and the induced voltage of conductor circuits, which referenced a real model of 110kV substation's parameters.