Switch Contact with Asymmetric Cam for Tap Changer Reliability
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Solution Overview
Problem
Existing mechanical switch contacts for tap changers require oscillating movements and are not reliable in maintaining secure contact-making between two end positions regardless of the rotational direction of the actuating shaft, leading to inconsistent switching performance.
Innovation Solution
A mechanical switch contact with pivotable contact finger blocks and multi-lever linkages actuated by a rotatable switching shaft with annular cams, allowing independent pivotation and secure contact-making regardless of the rotational direction, ensuring precise and reliable switching over high loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oscillating movements are used for switching contacts, then contact sequence control is achieved, but switching reliability deteriorates when rotational direction of actuating shaft changes
Solution Approach 1:
The cam profile is designed with asymmetric geometry that converts rotational movement in either direction into a unidirectional oscillating motion of the contact shaft. The cam's asymmetric shape ensures that regardless of whether the actuating shaft rotates clockwise or counter-clockwise, the follower experiences the same camber-induced oscillation pattern, thereby achieving direction-independent switching reliability.
Solution Approach 2:
The cam acts as an intermediary element between the actuating shaft and the contact shaft. It mediates the rotational input and transforms it into the required oscillating motion for contact making and breaking. This intermediary mechanism isolates the contact shaft from the rotational direction of the actuating shaft, ensuring consistent performance regardless of rotation direction.
2Reliability
If simultaneous contact-making and contact-separation is prevented, then electrical security is improved, but switching mechanism complexity increases
Solution Approach 1:
The cam profile is designed to initiate contact-making action before contact-separation is completed, and vice versa. By carefully shaping the camber, the mechanism ensures that one contact is already made before the other contact breaks, preventing any period of simultaneous connection or disconnection. This preliminary action is built into the cam geometry itself, avoiding the need for additional control mechanisms.
Solution Approach 2:
The switching mechanism uses dynamic timing control through the cam's varying radius profile to orchestrate the sequence of contact-making and contact-separation. The cam's dynamic geometry automatically adjusts the timing and duration of each contact's engagement, ensuring proper sequencing without requiring complex external control systems or additional actuators.
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 reliable and precise mechanical and electrical switching over, allowing contact-making and separation without simultaneous connection, with the ability to switch multiple times in one direction, and can be designed for various switching angles and ramps, enhancing the reliability and efficiency of tap changer operations.
Implementation Method 1
the cam disk moves in an oscillating motion between two end positions
Implementation Method 2
the contact rollers impinge on the spherical surface of respective oppositely arranged fixed contacts and in this manner produce respective electrical contact connections
Implementation Method 3
the switch lever is, in the case of action of force on the actuating profile, abruptly pivotable from one of its two stationary states into the respective other stationary state
Data Source
AI summary
The invention relates to a mechanical switch contact (10) for releasing, disconnecting, or switching over, in particular for an on-load tap changer of a step transformer, comprising at least two contact fingers or contact finger blocks (12, 14), which can each be pivoted between two end positions and which are connected to each other in an electrically conductive manner and which are each operatively connected to a rotatable switching shaft (18) by means of multi-arm joints (16), said switching shaft having all-around guide slots (24) for actuating the multi-arm joints (16) and for thereby deflecting the contact fingers or contact finger blocks (12, 14).