Dl. Dorris et al., CURRENT PULSES DURING WATER TREEING - DETECTION SYSTEM, IEEE transactions on dielectrics and electrical insulation, 3(4), 1996, pp. 515-522
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.