Inside high voltage substations, the protective and control equipment are placed in the switchyard and control room as well as the main elements. Proper design for these equipment should include precise clarifications of the immunity levels to typical exposure of transient electromagnetic fields produced inside high voltage substations. Consequently, accurate calculation of very fast transient electromagnetic fields inside high voltage substations is essentially demanded early in the design stage. This paper presents full simulation of a typical high voltage substation of 500/220 kV to calculate the transient electromagnetic field during switching conditions based on Finite Difference Time Domain (FDTD). Very fast transient electromagnetic fields are calculated taking the effects of the complete configuration including all current carrying conductors inside high voltage substations. The effects of switching different lines are monitored at different accessible points and inside the control room. The obtained results show a good agreement with the previous studies and electromagnetic compatibility standards.