A review on pre-breakdown phenomena in ester fluids: Prepared by the international study group of IEEE DEIS liquid dielectrics technical committee

Abstract

In this article, a robust Lyapunov demodulator (LD) based on orthogonal signal generation (OSG) approach for single/three-phase application is proposed. Conventionally, LD is not capable of rejecting the DC-offset in the grid signal. Thus, an additional estimation loop is required which may affect the dynamic performance. Nevertheless, an application of harmonically polluted grid voltage signal to LD may severely affect the steady-state performance of the estimated parameters. To address these issues, an enhanced LD based-OSG is proposed, wherein a moving average filter is incorporated in the LD-OSG structure. Thus, rapid rejection of DC-offset and harmonics is easily achieved without any additional loop. The proposed structure may accurately estimate the fundamental in-phase and the quadrature components. However, these orthogonal components may suffer from amplitude imbalance and errors in the phase information under off-nominal frequency conditions. Additionally, the errors in the amplitude and the phase information are eliminated using an open-loop frequency deviation detector and a feed-forward curve fitting approach. The dynamic performance of the proposed scheme has been validated by numerical and hardware studies. It is reported that, with the less sensitivity toward phase angle jump and good immunity to fundamental negative sequence, the proposed scheme is a potential technique for synchronization of single/three-phase grid connected power electronic equipment.

Use Performance and Management of Biodegradable Fluids as Transformer Insulation

“…qualitatively similar, but the streamer propagation process is different for both cases [26], particularly for long gaps subjected to overvoltages of impulse nature ester liquids which are more susceptible to develop fast and high-energy discharges [24].…”

“…Regarding the dielectric design of transformers, two main differences between MO and ester fluids must be taken into account [22,24]:…”

“…Analyzing the streamer behavior is crucial because it allows us to understand the pre-breakdown phenomena in liquid dielectrics. The streamer behavior of esters and MO is qualitatively similar, but the streamer propagation process is different for both cases [26], particularly for long gaps subjected to overvoltages of impulse nature ester liquids which are more susceptible to develop fast and high-energy discharges [24].…”

“…Still, the dielectric design of the transformer might need some adjustments if esters are used as liquid insulation. Some authors have carried out experimental work to compare Energies 2021, 14, 6357 7 of 18 the breakdown voltages of esters and MO for homogeneous and inhomogeneous fields and with different voltage waveforms concluding that, although the pre-breakdown and breakdown behavior of the different liquids might differ, since these are dependent on the chemical composition of the insulation, the performance of esters is generally similar to that of MO under quasi-uniform fields [1,24]. On the other hand, it has been observed that streamer propagation is faster in esters, which might be a weakness in large oil gaps [24,27].…”

Alternative liquid dielectrics in power transformer insulation: a review

“…During the experiment, the DGA is used to explain gasses generated during streamer generation. Rao et al [5] also used streamer breakdown theory and concludes that the presence of cellulose promotes streamer initiation more in mineral oil-based dielectric than natural ester-based dielectric. This greatly reduce BDV of mineral oil.…”