Hybrid On-Load Tap Changer Control to Prevent Tap Short Circuits
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Solution Overview
Problem
Existing on-load tap-changers lack a monitoring function, leading to potential tap short circuits if semiconductor switching elements fail unnoticed, causing destructive consequences.
Innovation Solution
Implementing a hybrid tap changer with independent semiconductor and mechanical switching elements, controlled by separate control units, ensuring mechanical contacts are actuated only if semiconductor switches are functioning correctly, using sensors to monitor voltage and current for reliable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hybrid tap changer with semiconductor switching elements and mechanical contacts is used, then switching without interruption is achieved, but monitoring function is lacking leading to potential tap short circuits
Solution Approach 1:
The control system is segmented into two independent controllers: a first controller for mechanical switching elements and selector arms, and a second controller for semiconductor switching elements. This segmentation allows independent monitoring and control of each switching type, enabling the first controller to verify semiconductor functionality before actuating mechanical contacts, thereby preventing tap short circuits while maintaining manageable system complexity
Solution Approach 2:
The first controller receives feedback signals from the second controller regarding the operational status of semiconductor switching elements. This feedback mechanism enables the first controller to make informed decisions about whether to proceed with mechanical contact actuation, ensuring that mechanical switching only occurs when semiconductor elements are functioning correctly, thus preventing harmful short circuits
2Speed
If mechanical contacts are actuated without monitoring semiconductor functionality, then switching speed is maintained, but harmful tap short circuits occur
Solution Approach 1:
The system performs preliminary verification of semiconductor switching element functionality through the second controller before the first controller actuates mechanical contacts. This preliminary action ensures that semiconductor elements are operational and ready to handle the switching task, preventing tap short circuits while maintaining switching speed by only delaying mechanical actuation when necessary
3Reliability
If independent control units for semiconductor and mechanical switching elements are implemented, then operational safety is enhanced, but device complexity increases
Solution Approach 1:
The control system is divided into two specialized, independent controllers with distinct responsibilities: the second controller manages semiconductor switching elements while the first controller manages mechanical switching elements and selector arms. This segmentation enhances operational safety through independent verification while keeping each controller's complexity manageable by assigning specific, focused functions to each unit
Solution Approach 2:
The first controller acts as an intermediary between the semiconductor switching elements and the mechanical switching elements. It receives status information from the second controller and translates it into appropriate mechanical actuation commands, creating a safe interface that prevents direct harmful interactions while coordinating the overall switching operation
Data Source
AI summary
An on-load tap-changer for switching, without interruption, between winding taps of a tap-changing transformer, including a diverter switch for performing a switch-over from a first to a second fixed contact, a selector for preselecting, without power, the first and second fixed contact, and a first controller, wherein the diverter switch has a plurality of semiconductor and mechanical switching elements, the selector has a first and second selector arm, which are actuatable independently of one another and can contact each of the fixed contacts, and the first controller is configured to trigger a switch command and to actuate the first and second selector arm and the plurality of mechanical switching elements by a motor drive, wherein the on-load tap changer includes a second controller to actuate the plurality of semiconductor switching elements, and wherein during the switch-over the first controller actuates the motor drive depending on the second controller.