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Increasing need of cost effective identical sensors for partial discharge (PD) location prompted us to take up this research study. Four high-frequency current transformers (HFCT) were assembled and its performances with a used commercial sensor were compared with the known type of PD signals. In this paper, the responses due to surface, oil corona and air corona are analyzed. PD occurrence in 20 ms period and the shape of single PD with more sampled data points are characterized using seven techniques. The study indicates that HFCT with biflar winding is more sensitive in identifying different types of known PD. The number of turns and gauge of the used wire in HFCT play a role in increasing the sensitivity of PD detection. Index Terms--Cluster analysis, condition monitoring, HFCT, partial discharge, phase distribution, signal processing, time-frequency transformation, wave shape of single PD, weibull distribution.

We propose an objective formulation of the impulse analysis problem from a signal analysis viewpoint. The winding response is quintessentially that of a deterministic network to a finite energy signal, with breakdown and partial discharge being inherently nonlinear events. A significant improvement to the acquisition of waveforms is demonstrated by a virtual instrument approach. It retains the advantages of the time- and frequency-domain methods. The drawbacks of the transfer function method are highlighted and a new piecewise linear approach is proposed for analysis. Experiments on a discrete lumped parameter model of the winding are used to validate the PXI based instrument. Index Terms--Breakdown, extrapolation, impulse test, partial discharge, virtual instrument.

Switching impulse discharge performance of air gaps at high altitudes, which is a fundamental in the extremely high voltage external insulation design, remains an unsolved key technology across the world. Due to the limited applicable range of 'g' parameter method recommended by IEC Publication 60-1(1989), this paper aims to explore the relationship between positive switching impulse 50% discharge voltage [U.sub.50] of rod-plane air gaps and atmospheric parameters, and proposes two new voltage correction methods based on the parameter 'g' and the atmospheric pressure ratio, respectively. The two methods have been proved by the experimental investigations carried out on 1-m rod-plane air gap both in the artificial climate chamber and at three spots of different high altitudes in this study. The results show that, if the additional influence of absolute humidity is considered, the positive switching impulse 50% discharge voltage [U.sub.50] of rod-plane air gaps is a power function of relative pressure and relative air density; the 'g' parameter method in IEC Publication 60-1(1989) is not applicable to the regions with an altitude above 2000 m or the condition of h/[delta] > 15 g/ [m.sup.3]; compared with the correction method based on the 'g' parameter method, the correction method based on relative atmospheric pressure has a wider applicable range and less error; when the absolute humidity increases 1 g/[m.sup.3], [U.sub.50] varies within the range of 1.0%-1.15%. Index Terms--Air gap, atmospheric parameters, correction, high altitude, humidity, impulse discharge.

It is more important to obtain the sensitivity line, which is defined as a correlation between the ultra-high-frequency (UHF) signal (mV) and apparent charge (pC), for onsite calibration regarding partial discharge (PD). Synchronous measurement of the UHF method and IEC 60270 enables us to obtain the sensitivity line and to estimate the apparent charge in on-site substations. The sensitivity line of 3-phase gas-insulated switchgear (GIS) is compared to that of single-phase GIS, and differences in defects are also discussed. The fundamental data in this paper contribute to on-site insulation diagnosis of GIS. Index Terms--Calibration, gas-insulated switchgear (GIS), IEC 60270, insulation diagnosis, partial discharge, ultra-high-frequency (UHF) method.

This paper presents the measured and analyzed responses of the partial discharge (PD) when it propagates in a power network from its origin to the measuring nodes. On and offline measurements are done in a power network consisting of a 16.5-kV/250-MVA-rated power generator, busbar, and step-up transformer. The simultaneously measured PD at two ends of the busbar indicated that the intensity of PD decreased as it traveled a longer distance and the time interval of its occurrence had a finite delay indicating the dominant mode of PD propagation as a transmission line. Frequency-domain analysis indicated the presence of characteristic resonance frequencies and the number increased as the measuring node moved away from the PD origin. The offline measurement by injecting an exponential PD signal at the neutral indicated that the signal will be absorbed in the generator, and the signal at the measuring node will be attenuated by 50 times and will be distorted. Pspice simulation is used to develop the network model for the propagation path. The Pspice analysis indicated that the distributed models of generator, busbar, and lumped parameter models of a transformer can be used to match the offline measurement. The model showed that each model can have the characteristic resonant peaks depending on the selected parameters and it can distort the simultaneously observed PD at two different nodes. Index Terms--Busbar, generator, partial discharge (PD), propagation, simulation, transfer function, transformer.

Partial discharge (PD) is one of the factors that could lead to failure of power transformers, leading to power outage and expensive repairs. The acoustic wave induced by PD can be measured and used for monitoring, diagnosing, and locating potential failures in the transformers. Fiber optic sensors have been shown to be attractive devices for PD detection because of a number of inherent advantages including small size, high sensitivity, electrical nonconductivity, and immunity to electromagnetic interference. A fiber optic sensor based on a Fabry-Perot interferometry is constructed by a simple micromachining process compatible with microelectromechanical system technology. The sensors are used in a transformer to measure PD acoustic waves. The experimental results show the sensor not only has an inherent high signal to noise capability, but is able to accurately localize the PD sources inside the transformer. Index Terms--Acoustic sensor, partial discharge, transformer.