Analysis of electrical tree inception in silicone gels

Abstract

This work assesses the initial and crucial part of electrical treeing degradation, the inception stage, focusing on its dependence on applied voltage waveform and frequency. Tests have been performed on needle-plane configuration samples in solids and gels. A physical model has been formulated through an adaptation of an established theory for solids in which electrical tree inception is related to damage-producing injection currents. The voltage rise time appeared to be the most important parameter influencing the tree inception in the gel, while in the solid material the frequency is more relevant. The analysis leads to the conclusion that tree inception in gels is due to a single highenergy event, in contrast to what is commonly known for solids where damage accumulation takes place. A tree inception model is proposed for the gel, in which initiation is driven by a pressure wave generated by the electric field and the space charge injected into the sample. The model fits the experimental data and may be used to predict the tree initiation for different waveforms and voltage values.

Insulation Materials and Systems for Power Electronics Modules: A Review Identifying Challenges and Future Research Needs

“…Due to the flexible polymer network chains as explained above, silicone gel possesses a unique two-phase liquid-solid nature, which makes the tree morphologies in silicone gel very different from solid materials. It was shown that under AC voltage, there is a filamentary branched component of trees in silicone gel that is retained after the electrical field is removed, like in solids, as well as bubble-like cavities that expand, become isolated, and collapse during growth, like streamers in liquid [8,15].…”

“…Electrical tree initiation in silicone gel for sinusoidal and square voltages as a function of the frequency applied was studied in [15]. It was found that a square waveform exhibits a much lower tree inception voltage (TIV) than a sinusoidal waveform at the low frequency of 1 Hz.…”

“…Here, the technical gaps are: 1) Both frequency and slew rate of square wave voltages tested to date (1 kHz and 12.5 kV/μs) are much lower than present and targeted values (up to MHz and hundreds of kV/μs) for WBG power modules; 2) All justifications, for example those mentioned above, are qualitative. Even models developed in [15] for electrical treeing inception are based on simple assumptions and hypotheses, not on fundamental (first principle) physics. Hypotheses were considered so that simulation results from the model were in good agreement with the test results for a specific test condition and setup.…”

Ageing of DC conduction in thermally aged oil‐impregnated pressboard

“…Step 4: Step 1 to Step 3 were repeated, incrementing the value of r by 0.1 nm, until calculated conductivity matches well with measured conductivity. The range of β was chosen from 10 −9 to 10 −7 according to [29]. Figure 5 shows a comparison of observed conductivity and calculated conductivity for x 10 oil-pressboard specimens having different ageing status.…”

Partial Discharge Analysis under High-Frequency, Fast-Rise Square Wave Voltages in Silicone Gel: A Modeling Approach

“…However, from the insulation side, frequency and slew rate are two of the most critical factors of a voltage pulse, which influences the level of degradation of the insulation systems that are exposed to such voltage pulses [4]. Solid dielectrics are found to be vulnerable to frequency, while the dominant factor for PD inception in liquid dielectrics is rising [5,6]. In this regard, the study of the insulation degradation of silicone gel, which has the properties of both liquids and solids can be challenging.…”