Bushing Tap Assembly Minimizing Inductance
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Solution Overview
Problem
High voltage bushings experience flashovers during fast transients due to increased impedance, leading to power outages and equipment damage, as very high currents pass through the tap and flow to ground via the bushing flange, causing voltage increases.
Innovation Solution
A bushing design with a tap assembly featuring a hollow electrically conductive sleeve portion, a conductor, a pin, an insulating body, and a conductive lid with an extension portion that minimizes inductance by providing a multi-contact connection between the sleeve and flange, ensuring the return current is close to the conductor and pin, reducing the risk of flashover.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional tap assembly is used with a simple conductor connection to the flange, then the device complexity is low and ease of manufacture is high, but the inductance during transients is high leading to flashover and power outage
Solution Approach 1:
The tap assembly is segmented into multiple functional components: a conductor for current carrying, an insulating body surrounding the conductor, a flange body mounted to the bushing, and a lid with a cap portion and extension portion. This segmentation allows each component to perform its specific function optimally, with the extension portion providing a low-inductance return path while the insulating body maintains electrical isolation.
Solution Approach 2:
The insulating body is nested within the hollow flange body, and the conductor is nested within the insulating body. The lid with its extension portion is assembled onto the flange body, with the extension portion nesting within the flange body's hollow space and surrounding the insulating body. This nested arrangement minimizes the loop area for current flow, reducing inductance while maintaining insulation.
2Reliability
If the tap assembly uses a multi-contact connection with extension portion surrounding the insulating body, then the inductance is minimized and flashover risk is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The extension portion of the lid and the flange body are both electrically conductive and connected to form an equipotential surface during normal operation. This equipotential connection provides a stable low-inductance return path for transient currents, ensuring that the voltage difference between these components remains minimal even during fast transients.
Solution Approach 2:
The tap assembly uses composite construction combining electrically conductive materials (conductor, flange body, lid, extension portion) with insulating material (insulating body). This composite structure allows the conductive parts to form low-inductance current paths while the insulating body maintains electrical isolation, achieving both low inductance and high reliability.
3Ease of operation
If a simple conductor connection is used without insulating body and extension portion, then the ease of operation is high and device complexity is low, but the impedance increases during fast transients causing voltage increase and flashover
Solution Approach 1:
The insulating body acts as an intermediary between the conductor and the flange body, providing electrical isolation while allowing the conductor to pass through. The extension portion of the lid acts as an intermediary return path, providing a low-inductance connection between the conductor and the flange body without requiring direct contact between dissimilar components.
Solution Approach 2:
The invention changes the electrical parameters of the tap assembly by introducing the extension portion that reduces inductance and the insulating body that controls impedance. These parameter changes ensure that during fast transients, the impedance remains low enough to prevent dangerous voltage increases while maintaining ease of operation through modular assembly.
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 design effectively reduces inductance during transients, minimizing the risk of flashover and maintaining the integrity of the bushing and connected electrical equipment by ensuring the return current follows the path with the lowest inductance, closest to the conductor and pin.
Implementation Method 1
At high frequencies inductance will dominate and the current choses the route with the lowest inductance. The route with the lowest inductance is the one which is closest to the current flowing from the electrode via the conductor and the pin.
Implementation Method 2
Since the electrically conductive extension portion surrounding the insulating body in the sleeve portion fills the space between the insulating body and the flange body/sleeve portion, the return current will be as close as practically possible to the current flowing through the conductor and the pin, and the inductance during transients will thus be minimised
Data Source
AI summary
A bushing including: a bushing comprising: a bushing body, an electrode contained in the bushing body, a flange body mounted to the bushing body, a tap assembly including: a hollow electrically conductive sleeve portion extending from the flange body, a conductor connected to the electrode and extending from the electrode into the sleeve portion, a pin connected to the conductor, an insulating body provided around the conductor in the sleeve portion, and an electrically conductive lid configured to be assembled with the sleeve portion, the lid having a cap portion and a hollow cylindrical extension portion, wherein the cap portion is configured to receive an end portion of the pin, wherein the extension portion extends axially from the cap portion and is configured to be received by the sleeve portion, and wherein the extension portion is configured to surround the insulating body in the sleeve portion when the lid is assembled with the sleeve portion.