Over the past 20 years the use of metalclad switchgear has spread steadily throughout electrical networks and its reliability continues to improve. To optimise the dimensions it is necessary to calculate exactly the transient overvoltages due to various causes (switching operations, short-circuits, lightning surges, etc.). The necessary models of the main components can be created using the Electromagnetic Transients Program so that an event can be simulated and the response of the electrical equipment of a metalclad substation to one or other event can be calculated