Tap Changer Pre-Selector Varying Speed Cam Mechanism
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Solution Overview
Problem
Existing tap changers in transformers face issues with arcing during contact movement, leading to increased wear and risk of damage due to high friction locking mechanisms and the limitations of tie-in-resistors, which are expensive and not always necessary.
Innovation Solution
A pre-selector arrangement with a contact carrier and drive mechanism that provides rotational movement with varying angular velocity, utilizing a cam structure and cam follower mechanism to facilitate fast and controlled separation of contacts, minimizing arcing and wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high friction locking mechanism is used to securely lock the pre-selector, then the locking reliability is improved, but the contact separation speed deteriorates leading to increased arcing
Solution Approach 1:
The locking mechanism is segmented into two independent systems: a friction-based locking mechanism that provides secure positioning, and a cam-based acceleration mechanism that provides rapid contact separation. This segmentation allows each mechanism to optimize its function without interfering with the other, resolving the contradiction between locking reliability and separation speed.
Solution Approach 2:
The cam mechanism is pre-positioned and spring-loaded to provide preliminary acceleration force before the contacts actually separate. This preliminary action ensures that the contacts are already moving at high speed before the arc forms, minimizing arcing duration and intensity while maintaining secure locking during the stationary phase.
2Reliability
If tie-in-resistors are installed to limit arcing, then the contact wear is reduced, but the device complexity and cost increase
Solution Approach 1:
The harmful arcing effect is extracted and eliminated by fundamentally changing the contact separation mechanism. Instead of using tie-in-resistors to suppress arcs, the invention extracts the root cause of prolonged arcing (slow contact separation) and eliminates it through cam-based acceleration, thereby removing the need for additional protective components like tie-in-resistors.
Solution Approach 2:
The spring force that naturally exists in the system is converted into a beneficial acceleration mechanism. The spring, which would normally just return the cam follower to its resting position, is instead used to provide the acceleration force needed for rapid contact separation, turning a passive element into an active protective feature that reduces arcing without additional components.
3Object-affected harmful factors
If the pre-selector contacts are separated quickly, then the arcing is reduced, but the locking stability during operation may be compromised
Solution Approach 1:
The system transitions from a static friction-based locking mechanism to a dynamic system where the cam mechanism provides controlled motion. The cam profile is specifically designed to provide acceleration only during the separation phase, while maintaining stability during the connected phase. This dynamic approach allows rapid separation to reduce arcing while preserving locking stability during normal operation.
Solution Approach 2:
The friction-based locking mechanism continuously maintains the pre-selector in the connected position, ensuring stability during operation. The cam-based acceleration mechanism then provides a brief, continuous acceleration action during separation to minimize arcing. This continuity of useful action in both phases resolves the contradiction between stability and rapid separation.
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 enables rapid and controlled separation of contacts, reducing arcing and wear, and ensuring secure locking without the need for expensive tie-in-resistors, thereby extending the operational life of transformer windings.
Implementation Method 1
The staggering mechanism includes a cam structure and a cam follower, which cam follower act on the cam structure during rotation
Implementation Method 2
Preferably, the cam follower is spring loaded against the cam structure
Data Source
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AI summary
A pre-selector of a tap changer is provided with an operating arrangement, which provide varying speed for the movable contact of the pre-selector. The arrangement is provided in a cylindrical tap changer (10) that includes a cylinder (24) provided with tap contacts and pre-selector contacts (25-27) extending inside the cylinder, the arrangement comprises a contact carrier (9) provided with at least one movable contact (8) for mating the pre-selector contacts of the cylinder (24), and a drive mechanism (21) for providing a rotational movement to the contact carrier (9), which contact carrier (9) during use is rotated by means of the drive mechanism (21) so that the movable contact (8) selectively mate with the pre-selector contacts (25-27) on the inside of the cylinder. The arrangement is characterised in that the drive mechanism (21) is operatively connected to the contact carrier (9) via a staggering mechanism (1) arranged to provide a rotation with varying angular velocity to the contact carrier (9).