Jun 2026· Journal of Physics, Conference Series· Vol 3254, pp. 042060· 0 citations· 8 references
Physics
Abstract
This study designs a multi-parameter detection platform to investigate inter-turn discharge faults in transformer oil-paper insulation. Experiments on typical defect modelreveal distinct differences in breakdown characteristics and PRPD spectra. Statistical feature analysis shows that the EMA change rate of ultra-high frequency signals is effective for early warning.
Partial discharges (PD) in large electric machines are a critical phenomenon often misunderstood. Partial discharges are neither harmless nor extremely dangerous. They indicate a localized electrical breakdown within the insulation of high-voltage equipment. Over time, especially in the long term, PD can deteriorate the insulation, leading to significant damage and potential failure of the machine. This paper addresses common misconceptions about PD, elucidating their implications for high voltage rotating machines based on existing literature and own research.
T. Hildinger, T. E. Lamas, J. F. Cordeiro et al.· Electrical Insulation Confer...· 0 citations
To investigate the development characteristics of winding interturn insulation partial discharge in a full-scale converter transformer, an interturn insulation defect specimen was installed inside a ±400 kV full-scale converter transformer. A partial-discharge test was conducted under stepwise alternating-current (AC) voltage, while pulse-current, high-frequency, ultra-high-frequency, ultrasonic, sound-pressure, and vibration signals were acquired synchronously. To reduce the subjectivity of discharge-stage classification, a dimensionless discharge-development index was constructed by integrating the 95th-percentile apparent charge, discharge pulse count, and phase occupancy, and the stage-transition points were identified using piecewise-linear change-point analysis. Two change points at approximately 1.9 and 4.3 min divided the discharge process into the inception, development, and severe stages. The apparent charge increased from approximately 1.5 × 102 pC in the inception stage to the order of 103 pC in the development stage, and then rose sharply to approximately 1.6 × 105 pC in the severe stage. Meanwhile, the discharge activity changed from an intermittent low-intensity state to a continuous high-intensity state. After the test, insulation-paper ablation and carbonization, conductor exposure, and a continuous breakdown channel were observed in the defect region. These post-test observations confirm severe final damage to the interturn insulation, although the time sequence of the individual damage features could not be determined from the final morphology alone. Under the present sensor arrangement, the HF channel provided the earliest identifiable response at approximately 1.9 min, whereas the UHF and internal ultrasonic channels supplied complementary evidence during subsequent discharge development. The external ultrasonic, sound-pressure, and vibration responses were more strongly affected by propagation paths, structural coupling, sensor location, and background disturbance and were therefore treated as supplementary indicators. These findings support a staged multisensor interpretation strategy for interturn partial discharge in a full-scale converter transformer rather than a universal ranking of sensor performance.
Yunpeng Tang, Shu-Chen Ma, Hong Liu et al.· Energies· 0 citations
Power transformer windings can be damaged by internal faults, such as short-circuit currents and the forces they generate, which can lead to, e.g., internal shorts due to damaged insulation. If these faults are not detected early, they can lead to catastrophic failures. In general, distributed-parameter models can simulate the performance of a transformer in both time and frequency domains more accurately than conventional lumpedparameter models, especially at higher frequency range (> 1 MHz). In this work, a multiconductor transmission line (MTL) model is used to simulate transformer windings in the frequency domain. Two typical winding configurations, continuous disk and interleaved disk, are studied. Internal shorts and buckling faults are applied to both models, and their frequency responses are compared using the frequency response analysis (FRA). The results show that each fault causes a noticeable change in the resonant frequency and admittance curve, except in the case of buckling in the interleaved-disk winding. The results demonstrate that combining MTL simulations with FRA can effectively identify the type of internal faults in transformer windings, offering a more comprehensive diagnostic tool than conventional frequency-domain analyses using lumped-element models.
Amir Ali Kaabi Nejadian, Hamed Moradi Tavasani, Waldemar Ziomek et al.· Electrical Insulation Confer...· 0 citations
This paper investigates the aging behavior and lifetime performance of full-size stator and rotor bars subjected to realistic inverter voltage stress. A dedicated high-voltage test setup combining an AC transformer and a bipolar square-wave generator is used to simulate voltage waveforms representative of modern inverter topologies, including voltage source inverters (VSI) and modular multilevel converters (MMC). The results enable a comparative evaluation of insulation systems used in DFIM rotor bars and CFSM stator bars under different converter technologies.
C. Staubach, T. Hildinger· Electrical Insulation Confer...· 0 citations
In practical power systems, transformers are continuously involved in voltage conversion and electrical-energy transmission, so once abnormal operating conditions appear inside the equipment, the influence may gradually spread to the stability of the entire grid. Because early-stage transformer faults are usually weak and not easy to observe directly from conventional electrical quantities, this paper investigates a fault-monitoring method based on current-signal trajectories and discusses its application to transformer operating-state analysis. In the proposed approach, the primary-side and secondary-side current signals are taken as the basic data source, and the corresponding Lissajous trajectories are then constructed under different operating conditions. Instead of analyzing only waveform amplitude or phase separately, the method converts the current relationship into geometric trajectory characteristics, making the variation process easier to observe visually. To examine whether the method remains effective under different fault levels, a transformer equivalent-circuit model was built in Multisim, and several abnormal operating conditions were reproduced by changing equivalent impedance parameters and related electrical quantities. During the simulation analysis, several ellipse-related quantities were extracted from the generated trajectories, mainly including ellipse area together with the ratio between the major axis and minor axis. These geometric quantities were then compared under healthy and faulty operating conditions. The obtained results show that even under relatively weak parameter disturbances, such as ±3% variations, the trajectory shape had already changed slightly compared with the normal state, and the corresponding feature deviation approached about 5% in some simulation cases. After the disturbance level continued to increase, especially when the parameter variation reached around ±30%, the deformation of the ellipse became much more obvious, while part of the geometric feature variation exceeded 32%. From the overall simulation results, it can be seen that the trajectory characteristics still maintain visible differences under different transformer operating conditions, including relatively weak abnormal states appearing at an early stage. Compared with directly using conventional electrical signal quantities for analysis, the proposed method represents operating-state variation through geometric trajectories, so some small parameter changes can be reflected more intuitively. The study therefore suggests that current-signal trajectory analysis may provide another possible way for transformer online monitoring and operating-condition evaluation in practical engineering applications.
Rui Zhu· Applied and Computational En...· 0 citations
Without HV Bushings, large transformers are unthinkable and failure in any of the bushing results in transformer failure as well. Bushing failures are rarely analyzed separately from the transformer failure. The approach laid out in this paper is to expand bushing failure research so that besides terminal transformer failures, incipient failures (non-transformer-damaging) are also looked up to. Bushing failure mechanism in the presence of very fast transients (VFT) during AIS bus bar switching lead to certain failure scenario, that is been described and supported by a case study. Mitigation measures for such failure mechanism are also suggested.
S. Bhutada· ITEGAM- Journal of Engineeri...· 0 citations