The Vivitron is a large electrostatic accelerator in operation under high voltage since December 1990. Since then, the machine sustained more than 750 sparks and operated more than 17&hthinsp;000 hours at voltages up to 20 MV. The paper presents a review of the electric stresses applied on the insulators of that particular HV generator following the operational experience of the last years. It discusses some of the most recent results related to the electrical stress characterization i.e. calculations and data from bench, factory and field tests. ©1999 American Institute of Physics.