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Descripción
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| The condition assessment of the insulation of large power transformers by means of on-line partial discharge measurements has been traditionally a significant challenge for Utilities, especially for power transformers installed in urban substations. The identification of an internal PD source in a power transformer, the determination of PD amplitude and rate level and the insulation medium affected are critical to make a decision on repairing it. The main difficulty of on-line PD testing is to remove the background noise existing in the substation. Distinguishing the PD pulses from other external PD signals coming from other equipment, or even PD pulses coming from the bushing or from the cable termination is an important challenge. A new on-line PD system has been used for monitoring of power transformer applying power signal processing numerical tools for filtering and PD clustering and using non-invasive sensors (HF and UHF) placed in each input phase of the power transformer and an additional HFCT sensor at the tank earth connection. The signal acquisition of each sensor is synchronized to discriminate where an eventual PD source found is placed, inside or outside the transformer. This paper presents the selection and the testing setup of the PD sensors used when the power transformer is connected to the grid by oil-air bushing or by cable terminal. Different alternatives of sensors are taking into account for this approach: coupling capacitor with measuring impedance, high frequency current transformers clamped to the grounding cable sheath, high frequency current transformers clamped to earth connection of the transformer tank and UHF sensors placed on the cable sheaths or close to the transformer bushing when used. The signal processing tools used for noise suppression, PD clustering, PD location and PD phase resolved pattern recognition are also presented to get an appropriate diagnosis. The signal processing analysis permits to identify whether the PD source is in the power transformer, in the bushing, in the cable termination or along the cable system. Measurements of load current, voltage and ambient temperature are also complementary parameters used to correlate PD activity behavior. A histogram of the hourly distribution of the PD activity along with a monitoring period of several weeks allows a better understanding of correlation between the insulation defect and these parameters, in order to have a better insulation diagnostic. | |
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Internacional
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Si |
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Nombre congreso
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CIGRE 2018 |
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Tipo de participación
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960 |
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Lugar del congreso
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París |
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Revisores
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Si |
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ISBN o ISSN
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DOI
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Fecha inicio congreso
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21/08/2016 |
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Fecha fin congreso
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26/08/2016 |
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Desde la página
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2017 |
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Hasta la página
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2107 |
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Título de las actas
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CIGRE 2016 Session Proceedings |