Overvoltages and Transients Identification In On-line Bushing Monitoring

Abstract

Overvoltages and transients are sometimes recognized as the cause of bushings’ rapid failure. This fact is confirmed by the studies published at the 2018 CIGRE session. They can also initiate dangerous resonance phenomena in transformer windings. The identification of very fast overvoltages characterized by high dynamics of voltage changes, so-called "transients", is difficult due to the limited frequency response of station voltage transformers. However, the bushing monitoring systems, based on the so-called "voltage method" can be used for this purpose successfully. There are several running bushing monitoring systems based on this method in Poland. The transients’ events are registered together with their oscillographs in Transformer Monitoring Systems (TMS). The overvoltage statistics are also performed to support service procedures.The TMS are integrated with station systems, which greatly increases the possibility of overvoltages phenomena analyzing.

Calculation of Fast Front Overvoltages in Vicinity of a Power Transformer

“…The cumulative relative error of the mathematical description calculated using expression ( 5) is about 5%, which is consistent with the literature [12]. , (5) where: N = number of transformer terminals, f k = frequency at which admittance matrix elements where measured, N k = number of frequency points, Y ij = measured transformer admittance matrix coefficient, Y ij,fit = mathematical description of transformer admittance matrix coefficient.…”

“…, where: N = number of transformer terminals, f k = frequency at which admittance matrix elements where measured, N k = number of frequency points, Y ij = measured transformer admittance matrix coefficient, Y ij,fit = mathematical description of transformer admittance matrix coefficient. , (5) where:…”

“…Due to the significant share of high frequencies in such overvoltages, re phenomena may occur within the windings of the power transformer, which can endanger its di insultation. For this reason, on-line monitoring systems for measurement of overvoltages can be in and usually they are connected over measuring tap of transformer bushing [4], [5]. The electrom behaviour of the transformer at its terminals is a function of these resonant phenomena.…”