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When partial discharge occurs within transformers， the pulse current signal propagates along the winding. Detecting this pulse current signal at both ends of the winding enables the identification of partial discharge within the transformer. To this end， a wideband equivalent circuit model for the transformer is established. In high-voltage windings where partial discharges are likely to occur， partial discharge pulses are applied between different wound disks and the ground to simulate the discharge to the ground at different locations of the high-voltage winding. Pulse current signals are then collected at the end screen of the high-voltage casing and at the neutral point to study the propagation rules of the partial discharge pulse current signal at different locations within the transformer windings. Through calculations， it is observed that the energy ratios of pulse current signals in two distinct frequency bands are linearly correlated with the distance ratio of pulse current propagation， and the maximum error observed in this context is 9.80 wound disks. This method facilitates localization of partial discharge within the transformer， and the results of field experiment subsequently validate the effectiveness of this localization technique.

Partial dampness is the initial stage in the bushing damp process,so the effective diagnosis of partial dampness can avoid the further development of the damp. The partial damp diagnosis method of bushing based on the frequency domain spectroscopy (FDS) is proposed in this paper. Firstly,oil-paper insulation samples with different moisture content are prepared,and partial damped samples are formed through combination. Then the FDS characteristics are obtained. The results show that partial distribution of moisture leads to oil-paper insulation interfaces with different moisture content,and the interface relaxation polarization loss peak is introduced in the FDS curves. The greater the degree of partial dampness in the radial direction,the greater the amplitude of the loss peak,and it moves to the high frequency direction. The effectiveness of the diagnosis of partial dampness of bushing based on the characteristics of the interface relaxation polarization loss peak is verified by the simulation model of the transformer bushing. It shows that a new method for early fault warning and diagnosis of the transformer bushing is provided.

SF6 gas insulated transformers (GITs) are extensively utilized in underground substations within densely populated areas of large- and medium-sized cities, praised for their excellent non-flammability and operational reliability. However, the aging characteristics of gas–solid composite insulation (SF6–PET) within GITs remain unclear, complicating the effective evaluation of their aging condition. In this study, we performed accelerated thermal aging experiments on type 6020 polyethylene terephthalate (PET) films under an SF6 gas environment at 150 °C. We investigated the aging characteristics of PET materials at various stages using differential scanning calorimetry, tensile tests, near-infrared spectroscopy (NIRS), and frequency domain dielectric spectroscopy. Our findings indicate that the crystallinity and fracture elongation of PET materials initially increased before decreasing as aging progressed, while tensile strength steadily declined. In addition, the absorption rate observed in NIRS diminished with aging. Utilizing linear discriminant analysis, we achieved dimension reduction of characteristic parameters across different wavelengths, facilitating the classification of PET materials at diverse aging times. The tan δ–f curves of PET films initially decreased and subsequently rose with aging. By applying the Havriliak–Negami (H–N) dielectric relaxation model across three distinct frequency bands of the dielectric spectrum, a significant correlation was discerned between the aging state of PET materials and the characteristic relaxation peaks, τ1 and τ2. Fitting the H–N relaxation model and Arrhenius equation allowed us to negate the impact of "temperature drift," yielding an interface polarization activation energy of Ea = 0.69 eV. This research on the aging performance of PET materials in an SF6 gas atmosphere provides a vital foundation for assessing the aging state of SF6-insulated GITs. [ABSTRACT FROM AUTHOR]