Temperature Compensated Bushing Draw Rod Arrangement
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Solution Overview
Problem
High voltage bushings face challenges in maintaining constant contact pressure between the bottom contact and conductor over operational temperature ranges due to thermal expansion differences between metal draw rods and copper or aluminum conductors, leading to increased losses and potential deformation, especially in longer bushings at higher voltages.
Innovation Solution
A draw rod arrangement with a support tube made from the same material as the draw rod, ensuring constant thermal expansion, and a clamping mechanism that applies force to maintain contact pressure, independent of temperature changes, without requiring special materials or complex designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a metal draw rod is used to apply contact pressure to the conductor, then sufficient contact pressure can be ensured during assembly, but thermal expansion differences between the metal draw rod and copper/aluminum conductor cause contact pressure to vary with temperature
Solution Approach 1:
The patent changes the material parameter of the draw rod from metal to composite material, specifically designing it with thermal expansion characteristics that match the conductor. This parameter change ensures that both the draw rod and conductor expand at the same rate with temperature, maintaining constant contact pressure throughout operational temperature ranges.
Solution Approach 2:
The patent employs composite materials for the draw rod, combining materials with different thermal expansion properties to create a composite structure whose overall thermal expansion matches that of the conductor. This allows the draw rod to maintain dimensional stability relative to the conductor across temperature variations, ensuring stable contact pressure.
2Ease of manufacture
If the contact pressure varies with temperature due to thermal expansion differences, then assembly is simplified, but losses increase and deformation may occur in longer bushings at higher voltages
Solution Approach 1:
By changing the draw rod material to a composite with matched thermal expansion properties, the patent eliminates contact pressure variation with temperature. This ensures consistent low losses throughout operation, particularly important for longer bushings at higher voltages where even small increases in contact resistance can lead to significant energy losses.
3Ease of operation
If conventional metal draw rods are used, then assembly is straightforward, but cold start at very low temperatures with full current can lead to loss of contact pressure
Solution Approach 1:
The patent changes the thermal expansion parameter of the draw rod by using composite materials designed to match the conductor's thermal expansion characteristics. This ensures that during cold start conditions, both the draw rod and conductor contract uniformly, preventing any loss of contact pressure that would otherwise occur with conventional metal draw rods.
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 solution maintains nearly constant contact pressure between the bottom contact and conductor, reducing losses and minimizing assembly errors, while allowing for accurate control of contact pressure during assembly and operation, thus optimizing heat dissipation and cooling efficiency.
Implementation Method 1
thermal expansion differences between metal draw rods and copper or aluminum conductors
Data Source
AI summary
A bushing including a bottom contact, and a tubular conductor, having a lower part having an end in electrical and mechanical contact with the bottom contact, and a draw rod arrangement, inside the conductor, arranged to exert sufficient contact pressure between the bottom contact and the conductor, and the draw rod arrangement includes a member in mechanical contact with the conductor and draw rod having a second end, fixedly connected to the bottom contact, and a first end in connection to the member and clamping means, the clamping means is adapted to apply a force, urging the member in the direction of the bottom contact to generate sufficient contact pressure between the bottom contact and the conductor. The member of the draw rod arrangement is arranged to apply the force to the lower part of the conductor.