High-Voltage Bushing Current-Collecting Member for Surge Management
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Solution Overview
Problem
High-voltage bushings with field-grading layers of increased resistivity face challenges in managing high-frequency surge currents, leading to potential insulation damage due to high surface current densities at connection points, as conventional connections are inadequate for distributing large currents effectively.
Innovation Solution
A current-collecting member with a lower surface resistivity is strategically placed on the surface of the field-grading layer, covering a larger area than the connection point, to direct a substantial part of the surge current along the layer's surface, thereby damping high-frequency oscillations while limiting surface current density to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If field-grading layers of increased surface resistivity are used, then high-frequency oscillations are damped and insulation damage risk is reduced, but the ability to conduct large surge currents is diminished
Solution Approach 1:
The field-grading layer is designed with non-uniform electrical properties: the peripheral region has higher surface resistivity to damp oscillations, while the central region has lower surface resistivity to conduct surge currents effectively. This spatial variation in resistivity allows simultaneous achievement of both oscillation damping and surge current conduction.
Solution Approach 2:
The field-grading layer is functionally segmented into different zones with distinct resistivity characteristics. The layer is divided into a peripheral zone for oscillation damping and a central zone for current conduction, allowing each zone to perform its specific function optimally without compromising the other.
2Device complexity
If conventional small connection points are used for field-grading layers, then the connection structure is simple, but the surface current density becomes excessively high during surge conditions
Solution Approach 1:
The connection approach transitions from a point-like (0D) or small area (2D) connection to a distributed annular connection. By spreading the connection over a larger peripheral area of the field-grading layer, the current density is reduced while maintaining structural simplicity.
3Power
If field-grading layers with metal foil are used, then surface current conduction is excellent, but resonant high-frequency oscillations of large quality factor occur
Solution Approach 1:
The surface resistivity parameter of the field-grading layer is increased from the very low values characteristic of metal foils to higher values that provide adequate damping of high-frequency oscillations. This parameter change trades some current conduction capability for oscillation damping, improving reliability.
Solution Approach 2:
The field-grading layer uses composite material structures such as conductive paint on fabric or nonwoven cloth, or paper/fabric with suspended conducting particles. These composite materials provide moderate surface resistivity that dampens oscillations while maintaining sufficient current conduction capability.
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
The solution effectively damps high-frequency oscillations and manages surge currents, preventing insulation damage by distributing the current through a larger surface area, ensuring the bushing's reliability during surge conditions.
Implementation Method 1
a condenser core with a number of concentric electrically conducting field-grading layers of cylindrical shape arranged around the central conductor so as to form a capacitive divider uniformly distributing the voltage among the field-grading layers
Implementation Method 2
Field-grading layers of the condenser core are usually made of metal foil. Bushings using such field-grading layers are known... Field-grading layers made of metal foil are characterized by very low surface resistivity... The geometrical arrangement of the field-grading layers of such low resistivity in the condenser core constitutes a number of interconnected capacitance and inductance elements prone to resonant high-frequency oscillations of large quality factor... One of the methods to avoid such oscillations is application of field-grading layers of increased surface resistivity. Increased resistivity of the field-grading layers leads to reducing the quality factor of the oscillation circuits.
Implementation Method 3
A current-collecting member with a lower surface resistivity is strategically placed on the surface of the field-grading layer, covering a larger area than the connection point, to direct a substantial part of the surge current along the layer's surface
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
The subject of the invention is a high-voltage bushing applicable in electric power engineering. The high-voltage bushing comprises a condenser core (1) and electrically conducting field-grading layers (3) which are arranged coaxially around the central conductor (2) and are embedded in insulating material (4) of the condenser core (1). An electric connection (6) is provided to at least one layer (3a) of the field-grading layers (3) by means of a current-collecting member (5). The layer (3a) is made in form of thin metal film deposited on an electrically insulating substrate layer or in form of a percolating network of conductive particles suspended in a layer of electrically insulating material, and the current-collecting member (5) is positioned on the surface of the layer (3a) and it covers a part of the surface area of the layer (3a) and has the surface resistivity many times smaller than the surface resistivity of the layer (3a). The current-collecting member (5) is shaped so that the length of the contour line of its circumference (L) is greater than the length of the shorter side of the layer (3a).