Leakage current measurements in complex-geometry EHT systems

Properly insulated EHT systems with capacitive energy storage lose energy by the leakage of electrical current through the insulation (an example is seen in the flow of insulating oil). In many cases the energy lost is simply replaced from the charging power supply. In situations where the energy of the system can't be 'topped up' the stored energy will leak away and the system performance will fall. In order to estimate the timescale between charging and useful operation of such a system an understanding of the magnitude of the leakage current is needed. To this end an ammeter has been developed which can measure currents in the range of a few tens of nanoamperes and operate within a system charged to high voltage. Results are presented for the three different types of insulation.