Electrode composition and partial discharges and their role in the breakdown of dielectric elastomer films

Abstract

The dielectric breakdown strength of the elastomer films used in dielectric elastomer actuators and generators (DEA & DEG) limits the peak actuation strains and maximum efficiency that can be achieved by these electromechanical transducers. In order to reduce the likelihood of failure during their operation, the factors that lead to breakdown should be well understood. Recent efforts in this area have focused on electromechanical and thermal effects that lead to breakdown, however degradation and ultimately breakdown caused by partial discharge activity represent another key way an insulating material can fail. This work presents partial discharge data collected from the VHB4910 (3M) acrylic elastomer, tested using solid stainless steel electrodes, solid graphite electrodes, and powdered carbon electrodes. It is found that degradation due to partial discharge activity does play a role in the breakdown of the samples tested using solid electrodes, and that their detection could provide an indication of the degradation that leads to breakdown. However when powdered carbon electrodes are used, significantly more partial discharge activity occurs between the carbon particles of the electrode on the surface of the dielectric. This obscures the detection of the partial discharges occurring due to internal defects that cause damage to the dielectric.

Inhibiting electro-thermal breakdown of acrylic dielectric elastomer actuators by dielectric gel coating

“…Acrylic dielectric elastomer (3M VHB, a trademark for 3M high-strength bonding tape), which is commonly used to make DEAs, can sustain very high electric fields when prestretched. 1 This enhanced dielectric strength of pre-stretched VHB membrane is attributed to suppression of air voids from partial discharges 5,6 and avoidance of electromechanical instability 7,8 up to a higher electric field. Ultimate breakdown of the pre-stretched acrylic DEAs is mainly due to local thermal runaway 9,10 and electronic avalanche 11 at a defective spot.…”

“…16 Such premature breakdown could be initiated by gas discharges. 5,6,17 A pinhole or puncture is usually formed at the defective spot 11,18 as a result of electro-mechanical instability, local burning by thermal runaway, and electronic avalanche (see Figures 1(a) and 1(b)).…”

Effects of Thinner Compliant Electrodes on Self-Clearability of Dielectric Elastomer Actuators

“…The purplish spark does not increase in size with growing puncture. This suggests the dielectric burn being fueled by limited power supply following Equation (5). In comparison, the actuator with thinner charcoal-powder electrodes did not show as much growth of dielectric puncture due to higher electrode resistance that further limited the current surge during dielectric breakdown.…”

“…Dielectric elastomer actuators can act as artificial muscles for driving bio-inspired robots [1,2], yet their performance still pales as compared to natural muscles; it is limited by dielectric breakdown which depends on properties and designs of both dielectric systems and electrodes. Causes of dielectric breakdown [3,4] include: (1) partial discharge [3,5] of air void in dielectrics; (2) electromechanical breakdown [3,4,[6][7][8], which happens at a weak spot where the dielectric elastomer membrane locally collapses under critical electrostatic pressure; and (3) electrothermal breakdown [3,[9][10][11][12], which happens at a hot weak spot where local resistive heating burns through and punctures the dielectric elastomer membrane. Among the causes that fail acrylic dielectric elastomer actuators [4,13], partial discharge of the air void happens in relatively weak electric fields of around 34 MV/m [13] while electromechanical and electrothermal breakdowns happen in stronger electric fields in the order of 100 to 500 MV/m [13].…”

Prognostication of Failures Using Signal-to-Noise Ratio to Determine Partial Discharges Activities in Power Transformers

“…Since the electric field in transformers is far less than the intrinsic strength of the cellulose paper insulation used as winding insula-tion, the catastrophic breakdown of insulation cannot be ruled out [11]. It has been known that air-filled cavities and voids exist in insulation due to its anisotropic nature [12]. Fur-thermore, the processes involved in forming and crafting the insulation may result in mechanical defects on a microscopic scale.…”