Semiconducting Condenser Core Bushing for VFT Overvoltage Damping
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Solution Overview
Problem
High voltage bushings are vulnerable to transient overvoltages due to resonances at high frequencies, which can lead to failure, and existing solutions either do not effectively address these issues or are impractical due to robustness concerns.
Innovation Solution
A bushing design featuring a condenser core with disjoint regions of semiconducting material wound around a conductor, where the overlap length of these regions is optimized to resonate within the very fast transient (VFT) frequency spectrum, providing built-in damping and filtering capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the overlap length of conducting material regions is increased to reduce capacitance and shift resonance frequency, then resonance frequency increases beyond VFT spectrum, but the bushing cannot effectively dampen VFT transients
Solution Approach 1:
The patent optimizes the overlap length parameter of the conducting material regions to achieve a specific capacitance value that resonates within the VFT frequency spectrum (typically 0.5-10 MHz). By precisely controlling this geometric parameter, the resonance frequency is tuned to match VFT frequencies, enabling effective energy absorption and damping of transient overvoltages without requiring extreme values that would compromise other performance aspects.
2Loss of energy
If semiconducting material with very thin conducting layers is used to provide resistive damping, then VFT attenuation is improved, but mechanical robustness deteriorates making the concept difficult to realize
Solution Approach 1:
The patent employs composite material structures where semiconducting material with controlled conductivity is integrated into the condenser core assembly with dielectric sheets and conducting material regions. This composite approach provides the necessary resistive damping for VFT attenuation while the overall structural design ensures mechanical robustness, avoiding the use of extremely thin fragile layers alone.
Solution Approach 2:
The semiconducting material is applied in specific localized regions rather than uniformly throughout the entire structure. The conducting material regions are positioned at specific locations where they provide the necessary electrical properties for damping while maintaining mechanical strength in other critical areas of the bushing.
3Reliability
If manual short-circuiting of overlap positions is performed during winding, then resonance prevention is achieved, but manufacturing complexity increases and VFT propagation is not affected
Solution Approach 1:
The patent extracts and addresses only the specific frequency range problematic for VFTs by designing resonance circuits that target the 0.5-10 MHz spectrum. Rather than implementing complex manual short-circuiting procedures at multiple positions, the design uses the natural resonance properties of the condenser core structure with optimized overlap lengths to achieve frequency-selective damping, simplifying the manufacturing process while maintaining effectiveness.
4Object-affected harmful factors
If the overlap length is reduced to decrease capacitance, then resonance frequency shifts higher than VFT spectrum, but the bushing becomes vulnerable to transient overvoltages
Solution Approach 1:
The patent carefully selects and optimizes the overlap length parameter to achieve a capacitance value that places the resonance frequency within the VFT spectrum range (0.5-10 MHz). This optimized parameter selection ensures that the bushing resonates at frequencies where VFT energy is concentrated, maximizing the damping effect and protecting against transient overvoltages, while avoiding both extremely small and extremely large overlap lengths that would compromise performance.
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 bushing effectively dampens transient overvoltages and acts as a high-frequency band-stop filter, protecting the system from VFTs while being robust enough to withstand manufacturing processes.
Implementation Method 1
the dielectric sheet extends between the overlapping edges whereby a capacitance is formed between the overlapping edges
Implementation Method 2
the overlap length is such that the resonance circuit has a resonance frequency contained in a very fast transient, VFT, spectrum
Implementation Method 3
Since resonance occurs at a VFT frequency the ohmic heating and thus the absorption capability is increased
Implementation Method 4
Due to the resistive damping, attenuation of the VFT should be expected
Data Source
AI summary
A bushing for a power system, comprising: a conductor, and a condenser core, wherein the condenser core comprises a dielectric sheet and a plurality of disjoint regions of electrically conducting material provided on the dielectric sheet, wherein the dielectric sheet and the electrically conducting material form a wound structure around the conductor, wherein in at least one region the electrically conducting material is a semiconducting material, wherein the semiconducting material extends more than one turn around the conductor, whereby the at least one region has overlapping edges in the radial direction, and wherein the dielectric sheet extends between the overlapping edges whereby a capacitance is formed between the overlapping edges, which capacitance is partly defined by an overlap length of the overlapping edges and which capacitance forms part of a resonance circuit of the at least one region, wherein the overlap length is such that the resonance circuit has a resonance frequency contained in a very fast transient, VFT, spectrum.