In the last years, the power demand of Perú keeps rising and the power system expands the scale extraordinary, in order to transport more energy, the overhead lines and substations in 500 kV has been built, especially in the last decade. Currently, the international standards for the minimum safety distances in electrical substations have been designed considering the insulation co-ordination, however if some designer considers the equipment installed in the same phase, there are just a recommendation in some papers, without considers the effect of electric and magnetic field and contamination between assets. This research has analyzed a failure mode caused by electric field in 500 kV substations, the problem was focus on current transformers. Three current transformers have failed, exploiting near the circuit breakers in the same phase, the analysis and the root cause of this fault has been developed in a special condition, the coast of Peru, and the novel contribution is a recommendation for the physical layout in substations, insulation coordination and standards of electric field for the design of substations for 500kV.