Transformer Tap Change Timing via Phase-Corrected Zero Crossing Control
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Solution Overview
Problem
Existing methods for controlling transformer tap changes in wind turbine transformers are inefficient in managing short circuit currents, often requiring large changeover impedances or oversizing thyristors, which increase costs and reduce transformer lifetime due to mechanical and thermal stress.
Innovation Solution
A method for generating a timing control signal that accurately determines the zero crossings of transformer taps by applying phase corrections to monitoring signals, allowing precise timing of switching elements to minimize short circuit currents without additional impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If changeover impedances are provided to lower the short circuit current peak value during tap change, then the short circuit current is reduced, but the volume and cost of the required impedances increase
Solution Approach 1:
The patent extracts and removes the changeover impedances from the system by implementing precise timing control of switching elements. The switching elements are controlled to switch at specific points in the voltage waveform cycle, which naturally limits the short circuit current without requiring additional impedance components. This eliminates the need for volume-consuming impedance elements while achieving the same current-limiting effect.
Solution Approach 2:
The patent replaces the mechanical/physical solution of adding impedance components with an electronic control solution. By using timing control signals to precisely coordinate the switching of switching elements, the system achieves current limitation through temporal coordination rather than through physical impedance elements. This substitutes a control-based approach for a component-based approach.
2Object-affected harmful factors
If changeover impedances are provided to lower the short circuit current peak value during tap change, then the short circuit current is reduced, but the cost of the required impedances increases
Solution Approach 1:
The patent removes the costly impedance components from the system by implementing precise timing control of switching elements. The switching elements are controlled to switch at specific points in the voltage waveform cycle, which naturally limits the short circuit current without requiring additional impedance components. This eliminates the need for expensive impedance elements while achieving the same current-limiting effect.
Solution Approach 2:
The patent replaces the costly physical impedance components with an electronic control solution. By using timing control signals to precisely coordinate the switching of switching elements, the system achieves current limitation through temporal coordination rather than through expensive physical impedance elements. This substitutes a low-cost control-based approach for a high-cost component-based approach.
3Productivity
If the transformer tap is changed using conventional switching control, then the tap change function is achieved, but the lifetime of the transformer and thyristors is reduced due to mechanical and thermal effects of short circuit currents
Solution Approach 1:
The patent applies preliminary action by generating timing control signals that coordinate the switching of elements before the actual tap change occurs. The control system determines the voltage waveform characteristics and pre-calculates the optimal switching moments, ensuring that switching elements are activated at the precise moment when current stress is minimized. This preliminary timing coordination prevents high short circuit currents from occurring during the tap change process.
Solution Approach 2:
The patent implements feedback by continuously monitoring the voltage waveform and using this information to dynamically adjust the switching timing. The control system measures the actual voltage characteristics and uses this feedback to optimize the switching moments, ensuring that the tap change always occurs at the most favorable point in the voltage cycle regardless of variations in operating conditions. This feedback mechanism protects the transformer and thyristors from excessive current stress.
Data Source
AI summary
A method of generating a timing control signal for controlling the timing of a change of a transformer tap of a transformer is provided. The transformer includes an on-load tap changer including plural respective transformer taps. The method includes monitoring a voltage on a primary side and/or on a secondary side of the transformer to obtain a monitoring signal and deriving, from the monitoring signal, an intermediate signal that is indicative of at least one zero crossing of a tap voltage at the transformer tap. Deriving the intermediate signal includes estimating, based on the monitoring signal, a phase of the monitored voltage to obtain a phase signal and applying to the phase signal a phase correction for a phase shift between the monitoring signal or a signal derived therefrom and the tap voltage at the transformer tap. The timing control signal is derived from the intermediate signal.