CURRENT PULSES DURING WATER TREEING - DETECTION SYSTEM

A detection system has been developed to seek signals associated with water treeing. In this paper, Part 1 of two parts, the test system is found able to detect fast pulses generated by charges as small as 1.2 fC and slow pulses with current amplitudes as small as 66 nA, with 27 MHz bandwidth. Such pulses are studied in the following paper. The det ection system functions in real time and non-invasively, using the com mon configuration of a dielectric between electrodes. Very low noise, wide bandwidth transimpedance (current in, voltage out) preamplifiers detect very small and fast current pulses in two ground electrodes whi ch monitor the same sample respectively at an 'active' (treeing) regio n, and a 'reference' (no treeing) region. The currents in the sample a re observed by their image currents in the electrodes. Noise that appe ars identically in both channels (e.g. corona) can be ignored by a fas t logic circuit that selects data to be recorded. Noise components tha t are different in the two channels and their effects also are studied ; they are small enough to be defeated primarily by a fast discriminat or. An averaging mode is sometimes used to characterize signals and fu rther reduce noise when one signal type is recurrent; noise artifacts in those averages are identified. A means is developed to observe the phase of the 60 Hz HV when short events are recorded. The detection sy stem is studied carefully in this paper for confidence in the ultimate conclusions. The use of the system to study events during water treei ng is described in the following paper.