Vacuum Interrupters (VI's) which are the product of choice at medium voltages for interruption of fault currents are being actively considered and applied at transmission levels also. As the voltage levels increases, so do the stresses. Hence, the high voltage withstand performance of the vacuum interrupter becomes extremely significant and demands greater attention. The withstand and breakdown voltage behaviour of a vacuum gap is a strong function of the electrode's shapes and surface conditions. The shape of electrodes and other metallic objects in the vacuum gap determines the geometric enhancement factor, β g . Appropriate design of the electrode results in the lowering of β g and hence enhancement of withstand and breakdown voltages. The micro-protrusions present on the surface of the electrodes results in increase of the stress and this is accounted for by a factor called microscopic enhancement factor, β m . This influence can be reduced by removing or levelling-off these micro-protrusions. The process to remove these micro-protrusions is called seasoning or conditioning and is a standard process in the manufacturing cycle of a vacuum interrupter. Two types of seasoning are employed: current seasoning and voltage seasoning. This paper concentrates on the voltage seasoning and specifically, on the impulse voltage seasoning or conditioning. The paper first presents a theoretical treatment of the process of impulse conditioning. Next the paper present a case study of conditioning process performed on a VI with a relatively longer gap and multiple floating shields. These results are significant in the light of the fact the high voltage vacuum interrupter would be having large inter-electrode gaps, also multiple floating shields. The paper concludes with recommendations for the conditioning of contacts and shield using impulse voltages.