On-load tap-changer with varistor auxiliary branch
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Solution Overview
Problem
Existing on-load tap changers require complex resistor design and varying resistor configurations based on specific circuit topologies, operating conditions, and load currents, making them difficult to adapt to different applications and complicating the structural design.
Innovation Solution
Integration of a varistor as a current-limiting element in an auxiliary branch of the on-load tap changer, which adjusts resistance based on applied voltage, eliminating circulating currents and simplifying the design by making the selection of varistors independent of load current, depending only on step voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ohmic resistors are used to limit circulating current during switching, then uninterrupted switching between winding taps is achieved, but the resistor configuration becomes complex and impacts overall design adaptability
Solution Approach 1:
The patent changes the fundamental parameter of current limiting from ohmic resistance (constant) to varistor resistance (voltage-dependent). This allows the same component to adapt to different operating conditions automatically, eliminating the need for complex resistor configurations tailored to specific applications.
Solution Approach 2:
The varistor serves multiple functions: it limits circulating current during switching, protects against voltage spikes, and maintains adaptability across different applications with a single component type, replacing the need for application-specific resistor designs.
2Reliability
If application-specific resistor configurations are used, then optimal performance for specific operating conditions is achieved, but device complexity and design difficulty increase
Solution Approach 1:
By using voltage-dependent resistance instead of constant resistance, the system automatically adapts to different operating conditions without requiring complex configurations. The varistor's resistance changes with voltage, providing optimal performance across varying load currents and tap positions.
3Reliability
If larger resistors are used to handle higher load currents, then current limiting capability is improved, but space requirements and design flexibility are reduced
Solution Approach 1:
The varistor's voltage-dependent resistance allows it to provide adequate current limiting for high load currents without requiring large physical size. At high voltages during switching, the varistor presents high resistance to limit current, while during normal operation with lower voltage drops, it presents low resistance and requires minimal space.
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 approach reduces voltage dips in the transformer output, simplifies the tap changer design, and allows for prefabrication as a stock item for specific step voltages, independent of actual load currents, thereby enhancing adaptability and reducing design complexity.
Implementation Method 1
Varistors are resistive components whose resistance depends on the applied voltage. The varistor is preferably dimensioned such that it is in a blocking state when a voltage drop across it is less than or equal to the step voltage.
Implementation Method 2
The main branch can connect the first movable contact to the load connection via the switching element
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
The invention relates to an on-load tap-changer, comprising – a first fixed contact, – a second fixed contact, – a first movable contact, which can contact each of the fixed contacts, – a second movable contact, which can contact each of the fixed contacts, – a main branch having a switch element, which can connect the first movable contact to a load discharge, – an auxiliary branch having a varistor, wherein the auxiliary branch connects the second movable contact to the load discharge, wherein the on-load tap-changer is designed such that, on a changeover from the first fixed contact to the second fixed contact, the first movable contact is not actuated until the second movable contact has reached the second fixed contact.