Step algorithms for wave processes calculation in problems of lightning protection at electric power substations

When lightning strikes into an overhead transmission line, a voltage surge occurs that can be dangerous for electrical equipment at electric power substations. Wave processes modeling is usually carried out in the EMTP program which is based on circuit models. The problem is the voltage oscillations caused by short front impulse current due to the use of trapezoid formula for differential equations integration. The combination of trapezoid and implicit Euler formulas, suggested in EMTP, does not solve the problem. The idea of this paper is adaptation and application of well-developed hybrid (EM field-circuit) models, methods and programs of the grounding theory for lightning protection problems. This way, wave processes are simulated together with current spreading processes in grounding conductors. The evident advantages of Vlach's and Singhal's high-order integration formulas compared to the trapezoid formula are shown. As a practical example, we have calculated voltage surges at power and measuring transformers of a substation caused by a lightning strike into a transmission line tower with insulator flashover. The effect of mounting surge arresters is shown.