Two-Phase Liquid Dielectric
Lawrence Livermore National Laboratory researchers have developed a two-phase liquid dielectric composite with synergistic properties that boost the benefits of each separate form. Fluid dielectrics are versatile compounds that assist or govern numerous industrial processes such as precision cooling, high-voltage capacitance, and the electrical protection of high-voltage switchgear. Liquid dielectrics suppress or instantly quench corona discharge and arcing without forming permanent conductive tracks in the medium (a “self-healing” feature). Common dielectric liquids range from purified water to perfluoroalkanes. In the example of a capacitor, the dielectric (fluid or solid) resides in the spaces between the metal plates in the capacitor. An applied electric field polarizes the dielectric, increasing the surface charge on each plate.Description
Lawrence Livermore National Laboratory researchers have developed a two-phase liquid dielectric composite with synergistic properties that boost the benefits of each separate form. A dielectric fluid fills the interstices between macro-sized dielectric beads packed into a confined volume so that the beads inhibit electro-hydro dynamically-driven current flows in the liquid and increase the resistivity and breakdown strength of the two-phase composite over a liquid alone. The beads are arranged to increase the effective flashover distance and obstruct the flow of breakdown-initializing particles in the liquid insulator. The combined-phase medium provides superior performance and preserves the self-healing advantages of a purely liquid dielectric.
The dielectric beads are insoluble in the dielectric fluid, ensuring their structural integrity without interfering with the electrical properties of the fluid. The macro-size (greater than about 1mm in diameter) of the beads works to quell current flows between the conductive components. The composite dielectric affords a method of electrically insulating between conductive components of differing electrical potential. This mixture/composite dielectric medium retains the volume-filing, self-healing, and serviceability advantages of a liquid insulator, while achieving the higher resistivity and breakdown strength provided by the solid beads.
The LLNL research team validated this novel technology using silicone oil and polyethylene beads and they believe that the two-phase formulation can replace any conventional liquid dielectric. In particular, silicone oil is less flammable than hydrocarbons, less damaging to the atmosphere, and only slightly more expensive. Other combinations of dielectric fluids and solids are expected to afford similar enhanced performance.Benefits
- The composite is resistant to ionization, allowing capacitors to operate at higher voltages before the insulating dielectric ionizes and begins to permit undesirable current flows.
- The two-phase mixture dissipates electric and magnetic energy where none is wanted.
- Serviceability is preserved; high-voltage system performance can be improved in situ without expensive and time-consuming reconfiguration.
- The size of the beads is less than the distance between any two points of different electrical potential so that no bead simultaneously contacts any two points of different potential.
- Charge separation in a parallel-plate capacitor causes an internal electric field. This two-phase dielectric reduces that field and increases the capacitance. For example, electrical grade castor oil in high-voltage capacitors can help prevent corona discharge and increase capacitance.
- Dielectric oils are used extensively in electrical transformers as fluid dielectrics and to assist in cooling.
- Precision cooling is necessary in certain solid-state applications. This composite facilitates longer use intervals, and therefore fewer interruptions in cooling cycles.
- Compact accelerators benefit from the high-voltage insulation advantages of the two-phase form of this dielectric medium.
|Title and Abstract||
Two-phase mixed media dielectric with macro dielectric beads for enhancing resistivity and breakdown strength
A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.
|Lawrence Livermore National Laboratory||06/10/2014
|Technology ID||Development Stage||Availability||Published||Last Updated|