| Popis: |
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 detection system functions in real time and non-invasively, using the common 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 which monitor the same sample respectively at an 'active' (treeing) region, and a 'reference' (no treeing) region. The currents in the sample are observed by their image currents in the electrodes. Noise that appears identically in both channels (e.g. corona) can be ignored by a fast logic circuit that selects data to be recorded. Noise components that are different in the two channels and their effects also are studied; they are small enough to be defeated primarily by a fast discriminator. An averaging mode is sometimes used to characterize signals and further 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 system is studied carefully in this paper for confidence in the ultimate conclusions. The use of the system to study events during water treeing is described in the following paper. |
