Capacitive Voltage Sensor With Hidden Electrode
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Solution Overview
Problem
Capacitive voltage sensors in switchgear face challenges with dielectric breakdown due to high electric fields in the low voltage capacitor layer, particularly when molding defects occur in the small gaps between the sensing and grounded electrodes, which are difficult to avoid during manufacturing.
Innovation Solution
The capacitive voltage sensor design incorporates an annular electrode assembly with a grounded electrode surrounding a hidden sensing electrode, where the electrode assembly is molded within a solid insulation body, and features such as multiple ring electrodes or strategically placed openings in the grounded rings to reduce the electric field in the low voltage insulating layer, ensuring capacitive coupling and minimizing the risk of breakdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensing electrode is positioned close to the grounded electrode to achieve accurate voltage measurement, then the measurement precision is improved, but the electric field intensity in the low voltage capacitor layer increases causing dielectric breakdown
Solution Approach 1:
The patent introduces an intermediate insulating structure (molded insulating body with embedded electrode assembly) between the sensing electrode and grounded electrode. This intermediary structure provides controlled insulation and field distribution, allowing the electrodes to be positioned close together for accurate measurement while preventing dielectric breakdown through proper insulation design.
Solution Approach 2:
The patent embeds the electrode assembly (including sensing electrode, grounded electrode, and insulating structure) within the molded insulating body of the switchgear. This nesting approach integrates the voltage sensing function into the existing switchgear structure, allowing close electrode positioning for accurate measurement while the outer insulating body provides additional protection against dielectric breakdown.
2Manufacturing precision
If the electrode assembly is molded within the solid insulation body to improve manufacturing precision, then the manufacturing precision is improved, but molding defects occur in the small gaps between electrodes
Solution Approach 1:
The patent segments the electrode assembly into separate components (sensing electrode, grounded electrode, and insulating structure) that are pre-positioned and then molded together as an integrated unit. This segmentation allows for precise positioning of each component before molding, ensuring accurate electrode spacing while the molding process creates strong, defect-free bonds between components.
Solution Approach 2:
The patent employs preliminary positioning of the electrode components within the mold cavity before the actual molding process. This preliminary action ensures that electrodes are correctly positioned and spaced to achieve accurate voltage measurement, while also allowing for proper mold design that prevents trapping air or creating voids during the molding process.
3Measurement precision
If the same insulation material is used for both high and low voltage capacitor layers to achieve good accuracy over temperature range, then the measurement precision is improved, but the high dielectric field causes increased breakdown probability
Solution Approach 1:
The patent applies different insulation strategies to different regions: the low voltage capacitor layer uses the same insulation material as the high voltage layer for temperature stability, but the critical gap region between sensing and grounded electrodes is designed with increased insulation thickness and optimized geometry. This local quality approach maintains temperature stability while reducing electric field intensity in the vulnerable region to prevent breakdown.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces the electric field in the low voltage insulating layer, making the sensor immune to defects and breakdowns, even under high voltage conditions, by adjusting the capacitance ratios and maintaining the dielectric strength of the high voltage insulating layer, thus enhancing the reliability and accuracy of the voltage measurement.
Implementation Method 1
Capacitive coupling is provided between the sensing electrode and the center conductor by one or more openings in the inner grounded ring
Implementation Method 2
These types of voltage sensors operate as a capacitive voltage divider
Implementation Method 3
where the same insulation material is used for both the high and low voltage capacitor layers
Data Source
AI summary
A capacitive voltage sensor that has particular application to be molded into an insulating body of a switch. The voltage sensor includes an annular electrode assembly having a grounded electrode including an inner ring and an outer ring defining a space therebetween, and a sensing electrode positioned in the space and being substantially surrounded by the inner and outer rings. The body is formed around the electrode assembly and a cylindrical center conductor extends through the electrode assembly. Capacitive coupling is provided between the sensing electrode and the center conductor by one or more openings in the inner ring, such as a single round hole, a slot or a plurality of symmetrically disposed round holes or slots. The inner and outer rings can be attached at one end so that the grounded electrode is a single piece or the rings can be separate rings electrically coupled together by conductive screws.