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High-voltage measurement using the quadrature method and permittivity-shielding Chavez, Patrick Pablo

Abstract

Using extensive finite element modeling, the quadrature method and permittivityshielding for measuring high voltage using electric field sensors were developed. The quadrature method is a technique that determines the necessary number of sensors that make point-like measurements of the field and the best positioning and weighting of those sensors for any chosen electrode geometry, for a given worst-case field perturbation due to external changes in the field (stray field effects), and for a particular minimum accuracy requirement. As a result, electrodes can be positioned much farther apart for a given number of sensors than was previously known to be possible, which results in lower field stresses in and around the electrodes requiring less insulation than was otherwise possible. Permittivity-shielding is a technique that offers an alternative to metallic shielding for the purpose of isolating electric field measurements from stray field effects. Materials with high dielectric constants, high-enough conductivities, or both supply the shielding by filling a space spanning from one electrode to the other and shield the field inside and nearby that space. With permittivity-shielding, electrodes are not required to be in close proximity with one another, avoiding the need for any special insulation. This kind of shielding also has the added benefit of moderating the field between the electrodes. 138 kV, 230 kV, and 345 kV optical voltage transducers (OVTs) each using three optical field sensors according to the quadrature method were constructed and tested. They meet the highest IEC and ANSI/IEEE accuracy requirements for instrument transformers even in the presence of substation-like changes in local geometry, such as the movement or installation of neighboring equipment. The 138 kV and 345 kV OVTs also use off-the-shelf resistors to supply resistive permittivity-shielding, and they maintain accuracy in the presence of severe stray field effects, typically caused by the mixture of moisture and pollution on an OVT's surface. These OVTs offer all the inherent advantages of optical sensor technologies but are simpler and safer in design than other OVTs. Their basic structure consists of an off-the-shelf insulator, three small optical field sensors, and possibly resistors (for resistive shielding).

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