The amount of literature on partial discharge (PD) and partial discharge induced degradation is vast. In the past 10-20 years significant progress has been made on research within partial discharge induced aging of dielectrics. Researchers now agree on the main mechanisms pertaining to this topic. With the advent of a new generation of dielectrics of which many properties now can be affected by the introduction of small amounts of nano-sized particles it seems to be a good moment to review the progress on the understanding of PD induced aging. Focusing on internal partial discharge in solid polymeric insulation this paper tries to identify achievements and at the same time challenges still to be solved.

/pdf/degradation-of-solid-dielectrics-due-to-internal-partial-p7t3m31s2v.pdf

Degradation of solid dielectrics due to internal partial discharge: some thoughts on progress made and where to go now

Solid-state transformer (SST) is an emerging technology integrating with a transformer power electronics converters and control circuitry. This paper comprehensively reviews the SST topologies suitable for different voltage levels and with varied stages, their control operation, and different trends in applications. The paper discusses various SST configurations with their design and characteristics to convert the input to output under unipolar and bipolar operation. A comparison between the topologies, control operation and applications are included. Different control models and schemes are explained. Potential benefits of SST in many applications in terms of controllability and the synergy of AC and DC systems are highlighted to appreciate the importance of SST technologies. This review highlights many factors including existing issues and challenges and provides recommendations for the improvement of future SST configuration and development.

/pdf/state-of-the-art-of-solid-state-transformers-advanced-4j8kucud9h.pdf

State of the art of solid-state transformers: Advanced topologies, implementation issues, recent progress and improvements

Partial discharge (PD) taking place in a solid dielectric-bounded cavity involves physical processes such as free electron supply, discharge development and surface charge decaying, which bring about memory effects and become the main reasons for stochastic behavior of PDs. This paper reviews numerical modeling of cavity PD in the past 30 years. In the first place, physical processes relevant to PD activity are summarized, and modeling methods for discharge development are classified. Then some differences of PD modeling at AC and DC voltages are distinguished. Subsequently, reproducing methods from simulations to experiments are introduced, as well as their comparison under different conditions and with the emphasis on voltage frequency and PD aging. At last, some problems about current simulation models are discussed, and our suggestions for future work are proposed.

/pdf/numerical-modeling-of-partial-discharges-in-a-solid-2gq1cmwcrz.pdf

Numerical modeling of partial discharges in a solid dielectric-bounded cavity: A review

In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01-100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.

Partial discharges in a cavity at variable applied frequency part 1: measurements

The measurement of partial discharge (PD) activity has become an invaluable tool for monitoring the insulation condition of high-voltage components in service. In particular, it is important for factories and for the utilities to get an indication of the time to breakdown. In this paper, the authors describe a study on the use of a damped ac voltage (DAC) method and a very low frequency (VLF) method to stress insulation and to detect partial discharge activity. The main goal of this study was to find out whether the PD patterns obtained at 50 (60)-Hz voltage correspond to those obtained at either lower frequency voltage (VLF) or higher frequency voltage (DAC). For this purpose, a combined theoretical and experimental approach for dielectric bounded cavities was used. The effect of the frequency and the shape of the voltage (DAC) on the PD phase-resolved pattern were studied in the laboratory. Tests were performed on dielectric bounded cavities in polyester with the DAC method, the VLF method (0.1 Hz), and the 50 (60)-Hz method. Moreover, the PD phenomenon was theoretically analyzed at different stress frequencies, and a comparison was made between theory and measurement.

/pdf/pd-recurrence-in-cavities-at-different-energizing-methods-2kr8l6lscy.pdf

PD recurrence in cavities at different energizing methods

The knowledge of partial discharge (PD) as a physical phenomenon has made considerable progress in the last decade(s). These efforts have led to a validated statistical-mathematical model able to simulate the PD behavior in dielectric bounded spheroidal cavities. Recent studies demonstrated that an approach based on simulations can give both qualitative information on the PD process and a good estimation of the main PD quantities (PD magnitude, PD inception/extinction voltage, PD pattern). This theoretical operating procedure was until now restricted to discharges ignited at the power stress frequency of 50 (60) Hz. In this paper the authors describe the use of a procedure to simulate partial discharges in dielectric bounded spheroidal cavities at frequencies in the range of 0.1 Hz....1000 Hz. Information on the effect of voltage frequency on the PD process has been derived from the simulation results. The results were validated by measurements at a range of test frequencies on test specimens containing spherical cavities.

The effect of voltage frequency on partial discharge activity

The measurement of partial discharge (PD) activity is used for monitoring the insulation condition. In particular, it is of importance to obtain an indication of the time to breakdown for high voltage distribution power cables, both for cable factories and for the utilities. In this paper the authors investigate the use of the Oscillating Waves method (OWTS) and of the Very Low Frequency (VLF) method to stress the insulation of service aged components and to detect partial discharge activity.

F.J. Wester

Papers

PD recurrence in cavities at different energizing methods

The effect of voltage frequency on partial discharge activity

Partial discharge detection using oscillating voltage at different frequencies