Switching Impulse air distances withstand voltages during pin type insulators replacement operations. Claudio Valagussa*, Giorgio De Donà**, Silvano Bena***, Roberto Emma*** ICOLIM 2008-9th International Conference on Live Maintenance Torun, Polonia 4-6 Giugno 2008 * CESI RICERCA ** TERNA SpA ***ENEL DISTRIBUZIONE Medium Voltage systems are characterized by reduced insulation distances toward earth and between phases. Live Line Works on MV lines often introduce critical situation in the respect of the minimum approaching distances imposed by the standards or by the in force national legislations. The present paper describes the work carried out by CESI RICERCA, in collaboration with ENEL DISTRIBUZIONE and TERNA, with the purpose to verify the dielectric characteristics of isolation configurations determined during maintenance operations on pin type insulators installed on MV pole crossarms. An experimental investigation on representative configurations of Live Line Maintenance was performed. The reference air configuration (rod- plane) was also considered for comparison purpose. The relevant results have been analyzed and compared with standard and national law prescriptions. Since the international standards prescribe indications for the calculation of the electric component of minimum approaching distances only for voltages higher than 72,5 kV, the present work may be utilized for the verification of the applicability of such criterion to MV systems. PUBBLICATO 07005235 (PAD – 785134)