On the nature of surface discharges in silicone-gel: Prebreakdown discharges in cavities

Ghassemi

IEEE Trans. Dielect. Electr. Insul.

2021

This manuscript critically reviews recent research on electrical insulation materials and systems used in power electronics devices and focuses on electrical treeing in silicone gel, PD modeling, and mitigation methods. For mitigation methods, electric field grading techniques, such as 1) various geometrical techniques, and 2) applying nonlinear dielectrics are discussed. Alternatives for silicone gel, such as liquid dielectrics, are also highlighted. The drawbacks of reported research and technical gaps are identified. In particular, we show that the investigations carried out to date are in their infancy regarding the working conditions targeted for next-generation WBG power devices. This review will provide a useful framework and point of reference for future research.

Section: Dynamics Of Electrical Treeing In Silicone Gelmentioning

confidence: 99%

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

Ghassemi

IEEE Trans. Dielect. Electr. Insul.

2021

2022 IEEE 4th International Conference on Dielectrics (ICD)

“…Local high field can induce PDs, and ultimately breakdown. PDs in silicone gel quickly reduce its insulation capabilities due to formation of permanent cavities [1][2][3]. PD measurements carried out with liquids instead of gel [4] evidenced the fact that embedding substrates in a high temperature liquid such as JarythermDBT provides good PD properties at high temperatures, up to 350°C with Alumina substrates, i.e., far higher than the maximum temperature limit of silicone gels.…”

Section: Introductionmentioning

confidence: 99%

Breakdown Properties of Epoxy and Ceramic Substrates Embedded in Liquids at High Temperature

Muslim

Lesaint

Hanna

et al. 2022

Surface breakdown is investigated with substrates made either from standard glass/epoxy PCB board or Alumina ceramic, and embedded in silicone gel or dibenzyltoluene (DBT) high temperature liquid. Depending on the substrate nature and gap distance, breakdown may occur either above the surface within the encapsulant material, or below within the solid substrate. In the case of ceramic substrate with liquid encapsulation, which could be tentatively used at high temperatures above 200°C, the weakest material is the ceramic, which shows irreversible degradation (cracks) after a single breakdown. Therefore, such insulating structure does not benefit from the self-healing character of liquids. Breakdown voltages also show a marked decrease at high temperature.

“…This causes irreversible degradation of the gel. 7 The presence of moisture in the module can lead to processes such as electrical treeing that can cause failure of the device. 8,9 Changing the encapsulation of the power electronic module to an insulating material with self-healing properties is considered to be more desirable.…”

Section: Introductionmentioning

confidence: 99%

“…These will also serve as a good heat transport medium and prevent electrical discharges in the module. 7 There is also high electric field stress at metallisation along the trench of the IGBT baseplate. These resulted from unipolar switching.…”

Section: Introductionmentioning

confidence: 99%

Electric field enhancement control in active junction of IGBT power module

Abdelmalik¹,

Liland²

2020

JPS

Dielectric liquids are incompressible, able to fill voids and have selfhealing effect and hence are being considered as alternative encapsulation materials to establish power electronics at ambient high pressure at subsea conditions. In a long-term endurance test, insulated-gate bipolar transistor (IGBT) chips subjected to 6.5 kV DC stress in dielectric oil environment was reported to have failed after less than one week in operation. A critical look at the failed objects revealed contamination fibres at the surface and around the high field regions. This paper presents the numerical simulation of field distribution around a conducting fibre at the surface of the IGBT chip. It also evaluates the influence of the nature of the encapsulation material on the integrity of power electronic modules using a long-term experiment at a medium elevated temperature for high and low relative humidity operated close to service load using IGBT relevant chips. Finite element method (FEM) calculations show how the high field region can be shielded from impurities that can easily trigger partial discharge (PD) and breakdown. The simulation suggests that coating the surface of the module with a thin polymer layer with a thickness of 20 μm or more could be sufficient to improve the reliability of the encapsulation system. Additional polymer coat with thickness 27 μm on the chip made the system survive without failure for 67 weeks under test and dry operating condition. Meanwhile, thick coating such as silicone gel protected the object longer under higher relative humidity.