BACKGROUND

The present disclosure relates to voltage sensing in electrical distribution systems, and more particularly to capacitive voltage sensors, some embodiments of which are particularly well-suited for metering and/or protection as well as voltage presence indication in high-voltage (HV) and/or medium-voltage (MV) environments, such as in MV switchgear, controlgear, and power transformer.

Capacitive voltage sensors have been implemented in various components of electrical power transmission and distribution systems. For instance, in medium-voltage electrical power distribution systems, capacitive voltage sensors have been implemented as stand-alone capacitive voltage transformers (sometimes referred to as capacitive Low Power Voltage Transformers (LPVTs)) for voltage measurement for metering and/or protection (e.g., for protective relays). Capacitive sensors (e.g., configured as capacitive voltage dividers) have also been incorporated into some components such as bushings, insulators, and T-connectors, such as those used in MV switchgear, controlgear, and power transformer.

Designing capacitive sensors capable of providing desired and/or required reliable, accurate voltage measurement (e.g., magnitude and phase) over variations in monitored voltage (e.g., providing linearity) and sensor temperature (e.g., due to external environment and/or monitored-conductor current-induced temperature variations), as well as under stray high electric fields (e.g., due to neighboring phases) and possibly under additional electromagnetic noise sources, remains technically challenging. Some known approaches attempting to address such challenges include, for example, sensor designs employing electrically grounded shields (e.g., a Faraday cage) and/or external compensation (e.g., based on the sensor temperature-based and/or the apparent measured voltage).

Smart Grid development and deployment further increases the need for precise (e.g., such as IEC Accuracy Class 1 or, in some applications, possibly 0.5 or 0.2) capacitive voltage sensors for use throughout, e.g., the electrical power distribution network, such as in secondary substations. To facilitate Smart Grid deployment, such capacitive sensors should be compact (e.g., to fit within available space in existing switchgear, controlgear, or power transformer), and preferably capable of being implemented as standard-sized components (e.g., a bushing) that may readily replace existing components that do not incorporate a sensor. The multitude of smart sensors required by the Smart Grid also presents a particular need for accurate capacitive sensors that may be manufactured cost-effectively.

Accordingly, there remains a need for improved capacitive voltage sensors that are well-suited for providing accurate voltage measurements (e.g., possibly for protection or metering, such as smart metering sensors as may be required for implementing Smart Grid functionalities), preferably well-suited for use in existing distribution equipment such as switchgear, controlgear, power transformer and/or preferably well-suited for manufacturing cost-effectively.

SUMMARY OF SOME ILLUSTRATIVE EMBODIMENTS

The present disclosure describes various illustrative embodiments of a capacitive voltage sensor apparatus, including some embodiments comprising an electrically insulating body, an elongated conductor embedded at least partially in the insulating body, a first floating sensor electrode embedded in the insulating body and capacitively coupled to the elongated conductor and configured to provide a first output representing the voltage of the elongated conductor, and a second floating sensor electrode embedded in the insulating body and capacitively coupled to the elongated conductor and configured both to provide a second output representing the voltage of the elongated conductor and to shield the first floating sensor electrode from electric fields that may originate from sources external to the capacitive voltage sensor apparatus. A capacitor may be embedded in the insulating body and electrically connected with the first electrical sensor to form a capacitive voltage divider that provides the first output. In some embodiments, the first output provides a precision LPVT output and the second output provides a VPIS or VDIS output. Some such embodiments are not only well-suited for providing precise voltage measurement, but also for providing compact and cost-effective sensors, at least insofar as a separate grounded shield electrode embedded within the capacitive voltage sensor apparatus may be excluded therefrom.

In accordance with some embodiments, a capacitive voltage sensor apparatus comprises an electrically insulating body (e.g., comprising an epoxy resin) having an outer surface; an electrical conductor at least partially embedded in the insulating body; a first terminal configured to electrically connect the electrical conductor to an external conductor to be sensed; a first electrically conductive sensor electrode disposed in the electrically insulating body between the electrical conductor and the outer surface of the electrically insulating body, wherein the first electrically conductive sensor electrode is electrically floated and capacitively coupled to the elongated electrical conductor; a second electrically conductive sensor electrode disposed in the electrically insulating body between the first electrically conductive sensor electrode and the outer surface of the electrically insulating body, wherein the second electrically conductive sensor electrode is electrically floated and capacitively coupled separately to the electrical conductor and the first electrically conductive sensor electrode; a first output terminal on the electrically insulating body and electrically coupled to the first electrically conductive sensor electrode to provide a first output signal representing the voltage of the electrical conductor; a second output terminal on the electrically insulating body and electrically coupled to the second electrically conductive sensor electrode to provide a second output signal representing the voltage of the electrical conductor; and a third terminal on the electrically insulating body configured to be electrically connected to a reference potential.

In some embodiments, the capacitive voltage sensor may preferably further comprise a capacitor disposed within said electrically insulating body and configured to electrically couple said first electrically conductive sensor electrode to said third terminal, thereby forming a capacitive voltage divider. The capacitor may be disposed on or in a printed circuit board that is mounted on the second electrically conductive sensor.

The second output terminal and the third terminal may be configured as an inner conductor and an outer shield conductor, respectively, of an electrical connector that is coupled to said printed circuit board.

In some embodiments, the electrical conductor is elongated and extends lengthwise within the insulating body, wherein said first terminal is integral to a first longitudinal end of the electrical conductor that is exposed through the insulating body.

In some embodiments, the second electrically conductive electrode may be configured as a cylindrical shell disposed coaxially with the elongated electrical conductor and extending longitudinally over a second length, thereby defining an interior volume between the electrical conductor and the second electrically conductive electrode, wherein the first sensor electrode is disposed completely within the interior volume and has a longitudinal extent that is less than the second length. In addition, the first electrically conductive electrode may be configured as a cylindrical shell disposed coaxially with and radially surrounded by the first electrically conductive electrode. A respective cylindrical segment of each longitudinal end of the second electrically conductive electrode may be separated from the electrical conductor by a respective portion of the insulating body that does not include a portion of the first electrically conductive electrode, wherein the respective cylindrical segments are separated by an intervening segment of the second electrically conductive electrode having the second length and radially surrounding the first electrically conductive electrode.

In some embodiments, the capacitive voltage sensor apparatus is configured as a bushing, wherein the first terminal is integral to a first longitudinal end of the electrical conductor that is exposed through the insulating body, and wherein a second longitudinal end of the electrical conductor opposite to the first longitudinal end is exposed through the insulating body and includes a second terminal configured to electrically connect the electrical conductor to a second external conductor to provide for current conduction between the first and second external conductor via the electrical conductor.

In some embodiments, the first terminal is configured to be coupled to a bulbar, and the capacitive voltage sensor is configured as a low-power voltage transformer, a post insulator, or a bus support.

In some embodiments, the second sensor electrode has a capacitance configured for coupling to a voltage presence indicating system (e.g., VPIS or VDIS).

Some embodiments may further comprise a temperature sensor embedded in the electrically insulating body, and a second connector disposed on the electrically insulating body and electrically connected to the temperature sensor. The temperature sensor may be mounted on a second printed circuit board.

It will be appreciated by those skilled in the art that the foregoing brief description and the following description with respect to the drawings are illustrative and explanatory of some embodiments of the present invention, and are neither representative nor inclusive of all subject matter and embodiments within the scope of the present invention, nor intended to be restrictive or characterizing of the present invention or limiting of the advantages which can be achieved by embodiments of the present invention, nor intended to require that the present invention necessarily provide one or more of the advantages described herein with respect to some embodiments. Thus, the accompanying drawings, referred to herein and constituting a part hereof, illustrate some embodiments of the invention, and, together with the detailed description, serve to explain principles of some embodiments of the invention.

