Patent Application
20080057215
In a typical field installation, as shown in
In one embodiment of the invention, the polymer insulator (1) is a pin-type high-density polyethylene (HDPE) coated with a semi-conducting layer (3) consisting of a SiO2 (silicon dioxide) and carbon black paint in the neck (6) and saddle regions (5) of the polymer insulator (1). During manufacturing of the insulator, the semi-conducting layer is activated in a plasma chemical reactor to bond the SiO2-carbon black to the ends of the HDPE molecular chains. The plasma chemical reactor consists of an Ar/O2 plasma chamber and an electron beam of sufficient energy to activate the surface refractory semi-conducting paint coating. Insulators are thus processed in the chemical reactor as one step in the manufacturing process of the polymer insulator.
The refractory semi-conducting coating strategically placed on the neck (6) and saddle area (5) of the pin-type polymer insulator (1) prevents localized high intensity electric field areas by charge spreading the voltage over a wide area on the insulator (i.e. the SiO2:carbon black painted area). The mechanical contact of the electrical utility high voltage conductor (2) and semi-conducting painted area (3) on the polymer insulator (1) completes the electrical connection to the utility supply voltage. The semi-conducting region of the polymer insulator provides an area of equal voltage potential and constant voltage gradient on the semi-conducting painted surface (3) to prevent corona inception. The reduction of corona at typical voltages reduces or eliminates corona erosion (corona cutting) of the polymer material.
The insulator thus coated performs electrically as a parallel plate capacitor having a dielectric material separating the two conducting plates. As such, the insulator thus coated may be modeled as a further confirmation of the insulator electrical performance of the preferred embodiment. This mathematical model allows using Finite Element Analysis tools to optimize the placement of the surface paint materials for optimal insulator electrical performance. The total capacitance, and hence the amount of charge stored may be calculated and verified by actual measurement.
The mathematical model of the polymer insulator and semi-conducting coating is a parallel plate capacitor formed by the semi-conducting layer (3) top plate on the polymer insulator, the polymer insulator (un-coated areas) (1) dielectric area and the metal mounting insulator pin (4) bottom plate. The charge stored is given by well-recognized equations outside the scope of this application.
The difference in the capacitance formed by semi-conducting coated (4) area and a non-coated insulator represents the change in capacitance and hence the charge storage of the insulator. The increased charge storage of the semi-conducting coated polymer insulator allows for increased puncture strength of the coated insulator. The exact charge difference depends on the actual geometry and voltage class rating of the polymer insulator.
While a particular embodiment of the present invention has been shown and described, modifications may be made. For example, for those skilled in the art, other materials such as fluorinated ethylene propylene (Teflon FEP), polyimide (Kapton HN200) cross linked bimodal high density polyethylene and linear low density polyethylene HDPE:LLDPE (XLHDPE) and polyethylene terephthalate (Mylar) are suitable insulating materials and will bond with other refractory materials such as Al2O3 (aluminum oxide). Carbon black or another semi-conducting material is held in matrix with the refractory coating material to form the semi-conducting paint material. The refractive coating material used determines the exact percentage of carbon black or other semi-conductive material.
Additionally, the insulator is not limited to pin-type insulators. Those familiar with insulator types will recognize direct application of the method and process to polymer vise-top insulators, polymer line post insulators, and other polymer insulator types.
As stated above, and re-stated here, the coated polymer insulator may be mathematically modeled. The mathematical model of which is a capacitor the upper plate or electrode being formed by the semi-conducting layer on the surface of the polymer insulator, the dielectric material being made up of the polymer insulator (un-coated areas) and the bottom plate or electrode being the metal mounting insulator pin. The charge stored by the insulator is given by well-recognized equations to those skilled in the art.
It is the difference in capacitance of an insulator with no semi-conducting coated area and an insulator with a semi-conducting area that represents the change in capacitance and hence the charge storage of the insulator. The increased charge storage due to this difference in electrode area allows for increased puncture strength by use of the refractory semi-conducting coated insulator.
The foregoing describes an improved medium voltage polymer insulator by use of a semi-conducting refractory paint and process to bond the paint to the polymer and has been provided by way of introduction. In addition to the structures, sequences, and uses immediately described above, it will be apparent to those skilled in the art that other modifications and variations can be made the method of the instant invention without diverging from the scope, spirit, or teaching of the invention. Therefore, it is the intention of the inventor that the description of instant invention should be considered illustrative and the invention is to be limited only as specified in the claims and equivalents thereto.
