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Two hydro generators were chosen to renew the stator winding. The motivation of this investment was an expertise about the condition of the generators. Beside technical diagnosis the operational dates and maintenance history was taken into account as well as the age of these generators. The stator windings were replaced with an insulation system that had the benefit of a 10 % power increase. The aged...
Recently, considerable efforts were deployed at Hydro-Quebec to retrieve all partial discharge (PD) files recorded with the PDA-H instrument over the last 25 years and which were scattered all over in plant computers. These initial raw data files have been centralized on a corporate computer, where all new measurements are now systematically saved. The statistical analysis of the first 10000 files...
Partial discharge (PD) is one of key factors which lead to premature failure of inverter-fed motors. It is proved that characteristic parameters of PD can be used to evaluate life of insulation material effectively under alternating current (AC). In this paper, some parameters of PD are statistically based on measurement results. Influence of impulse frequency on inception voltage of PD (PDIV), mean...
The important properties of ZnO nonlinear ceramic include its nonlinear coefficient, alpha, which is the derivative of the log of the current density with respect to the log of the field, the threshold voltage, energy absorption capability, etc. However the shape of alpha is also important. One would prefer that the ZnO "turn on" (become substantially conductive) very rapidly, while how...
Some evidence in the literature suggests that nano fillers in a polymer matrix can provide beneficial dielectric properties. The obvious question is "What is `nano'?" Where and based on what criteria is a system nanofilled or microfilled? A statistical approach is applied to this problem to develop criteria based on worst case field conditions over critical distances. The criteria are based...
It is well known that thermal and electrical stresses have a strong influence on the degradation of insulation, but the effect of the stress duration is not yet well analysed. On this account thermal, electrical, and a combination of thermo-electrical stresses were applied to a number of cast-resin samples, and their effects were evaluated via partial discharge measurements. Stress duration as well...
A new algorithm for the separation of partial discharge (PD) signals due to multiple sources is presented in this paper. It evaluates the similarity of the signals shape by comparing their auto-correlation functions (ACFs), on the assumption that the same PD source can exhibit signals having similar ACFs. The new classification algorithm is based on a modified K-mean clustering (KMC) method. A laboratory...
The effect of UV treatment on dielectric breakdown strength of metallized biaxially-oriented polypropylene (BOPP) capacitor film was studied. Results from Weibull statistical analysis indicate that an optimal UV exposure level of ~3.4 J/cm2 (200-400 nm) increases the breakdown strength at 1% probability by ~20%. UV spectroscopic analysis indicates that the antioxidant in BOPP was consumed almost entirely...
This paper has been prepared to illustrate the value of partial discharge (PD) testing in assessing the condition of stator windings on operating generators and motors. Because of the magnitude of the data base accumulated by one particular PD system vendor during the last 15-20 years, this data base was chosen for study. It was felt that sufficient data had been accumulated to allow useful statistical...
PD-source localization in a complicated multi-material insulating system like that of a power transformer is still a challenge for all testing engineers. Additionally to the measurement of apparent charge with a conventional PD-system (according to the Standards), detection of acoustical PD-signals can be used to localize the PD-source. In many cases however, especially for PD-sources hidden in the...
AC breakdowns are commonly used as a performance indicator for power cables, and yet the data generated can be misinterpreted if the test section of cable is found to have a manufacturing defect. As an example, in a recent publication, dielectric a breakdown value on a 17-year field aged cable was treated as a "suspension" by the authors after the discovery of a conductor shield skip at...
This paper describes the first results from experimental investigations which have been carried out to study the partial discharge phenomena in power transformer insulation. Using different types of modeled insulation defects and ageing tests it is aimed to organize a database of known defects, which will be used for recognition of discharges of unknown sources of defects. Moreover, the first results...
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