Three-position load isolating switch with segmented current paths
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Solution Overview
Problem
Existing three-position load-break switches for medium-voltage switchgear are costly and lack a compact structure, as they require high material properties for the main current path and involve complex electrical processes, especially when using vacuum interrupters.
Innovation Solution
A compact and cost-effective design is achieved by using a cam disc to actuate a rocker connected to the vacuum interrupter's moving contact bolt, along with a folding mechanism that allows the clearing contact system to be interrupted in the auxiliary current path, reducing material requirements and eliminating the need for vacuum interrupter involvement during switching, utilizing inexpensive materials like steel or aluminum for the sliding contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a vacuum interrupter is used for arc extinguishing in the main current path, then reliable current interruption is achieved, but the device becomes costly and complex
Solution Approach 1:
The patent divides the current path into two separate paths: a main current path for normal operation and a secondary current path for switching operations. The vacuum interrupter is exclusively assigned to the secondary current path, handling only switching currents. This segmentation allows the vacuum interrupter to operate under less demanding conditions, reducing its complexity requirements while maintaining reliable current interruption capability.
Solution Approach 2:
The patent introduces sliding contacts as intermediary elements that enable current commutation from the main current path to the secondary current path. These sliding contacts serve as a mechanical mediator that transfers the current load, allowing the vacuum interrupter to be bypassed during normal operation and only engaged when switching is required, thereby reducing overall device complexity.
2Power
If high-grade materials are used for the main current path, then high current carrying capacity is achieved, but manufacturing costs increase
Solution Approach 1:
The patent applies different material qualities to different parts of the system. The main current path uses high-grade materials optimized for continuous high current carrying capacity, while the secondary current path and sliding contacts use cost-effective materials since they only handle brief switching currents. This local differentiation of material quality reduces overall manufacturing costs while maintaining the required power capacity where it is most needed.
Solution Approach 2:
The patent design allows the secondary current path components to handle only partial current loads during brief switching intervals rather than continuous full load. This partial action approach enables the use of less expensive materials for the secondary path and sliding contacts, as they do not need to sustain the full current carrying capacity requirements of the main current path throughout continuous operation.
3Reliability
If the clearing contact system is designed for high spring force, then reliable contact pressure is achieved, but the mechanical structure becomes complex and costly
Solution Approach 1:
The patent segments the contact systems into a main contact system for continuous current carrying and a clearing contact system for arc extinguishing. The clearing contact system is designed with lower spring force requirements because it only needs to maintain contact pressure during brief switching operations, not continuous operation. This segmentation allows simplification of the mechanical structure while maintaining reliable contact pressure when needed.
Solution Approach 2:
The clearing contact system is designed to operate only during brief switching intervals rather than continuously. This partial action approach reduces the cumulative mechanical stress and allows for lower spring force design, simplifying the mechanical structure while still achieving reliable contact pressure during the limited periods when the clearing contacts are engaged for arc extinguishing.
4Volume of moving object
If a compact structure is achieved through diametrical arrangement of contacts, then space is reduced, but the switching mechanism becomes more complex
Solution Approach 1:
The patent merges multiple functions into the rotating moving contact: it serves as both a main contact for current carrying and a switching element for path commutation. By combining these functions into a single rotating component, the patent achieves compact spatial arrangement through diametrical positioning while avoiding the need for separate complex switching mechanisms, thus reducing overall device complexity despite the compact geometry.
Solution Approach 2:
The patent employs dynamic rotation of the moving contact to achieve switching between different current paths. Instead of using complex mechanical linkages or multiple static contact arrangements, the rotating contact dynamically transitions between positions, enabling compact diametrical arrangement of contacts while simplifying the switching mechanism through motion-based path selection rather than complex mechanical switching structures.
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 results in a mechanically simple, compact, and inexpensive switching device that can handle alternating current commutation from the main to the secondary current path without electrical influence, reducing the need for high spring force and minimizing vacuum interrupter requirements, enabling efficient switching with reduced material costs and simplified arc extinguishing.
Implementation Method 1
the means also have a folding mechanism such that when the three-position load-break switch is switched on from the third or second position of the rotatable moving contact is interrupted in its first position, the clearing contact system. The structure with the cam disk is mechanically simple and therefore compact and inexpensive, since with this structure only work has to be done against the low spring force of the contact pressure spring of the clear contact system
Data Source
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AI summary
In order to design a three-position load isolating switch for medium-voltage switchgear assemblies, which three-position load isolating switch can be produced in a cost-effective manner with a compact construction, a three-position load isolating switch (1), for medium-voltage switchgear assemblies having a main contact system, is formed from a first fixed contact (2) and from a second fixed contact (3), said fixed contacts being situated diametrically opposite one another, and from a moving contact (4) which can be rotated by means of a rotary support (7) which is arranged centrally between the first fixed contact (2) and the second fixed contact (3), so as to form a main current path in a first position of the rotatable moving contact (4), so as to form an isolating section in a second position of the rotatable moving contact (4) and so as to form an earthing position with an earthing contact system in a third position of the rotatable moving contact, and also from a secondary current path which is formed from the first fixed contact (2), from the second fixed contact (3), from an arc-quenching contact system (9) and also from a first sliding contact (15) and a second sliding contact (16) for forming a conductive connection to the rotatable moving contact (4) in a rotation angle region of the rotatable moving contact (4), which rotation angle region is located between the first position and the second position, in such a way that, when a rotary movement is initiated in the rotatable moving contact (4), commutation of an alternating current which flows across the switchgear from the main current path to the secondary current path is possible, wherein the rotatable moving contact (4) has means (18, 19, 25) for interrupting the arc-quenching contact system (9), and, when the arc is quenched and a further rotary movement is initiated, the isolating section can be formed.