VIVITRON-1995 - TRANSIENT VOLTAGE SIMULATION, HIGH-VOLTAGE INSULATOR TESTS, ELECTRIC-FIELD CALCULATION

Preliminary investigations showed clearly that, because of the discret e electrode structure of the Vivitron, important overvoltage leading t o insulator damage can appear in case of a spark. The first high volta ge tests showed damage connected with such events. This fact leads to a severe voltage limitation. This work describes, at first, studies ma de to understand the effects of transients and the associated over-vol tage appearing in the Vivitron. Then we present the high voltage tests made with full size Vivitron components using the CN 6 MV machine as a pilot machine. Extensive field calculations were made. These involve simulations of static stresses and transient overvoltages, on insulat ing boards and electrodes. This work gave us the solutions for arrange ments and modifications in the machine. After application, the Vivitro n runs now without any sparks and damage at 20 MV. In the same manner, we tested column insulators of a new design and so we will find out h ow to get to higher voltages. Electric field calculation around the ti e bars connecting the discrete electrodes together showed field enhanc ements when the voltages applied on the discrete electrodes are not eq ually distributed. This fact is one of the sources of discharges and v oltage limitations. A scenario of a spark event is described and indic ations are given how to proceed towards higher voltages, in the 30 MV range.