Transformer Tap Change Timing via Phase-Corrected Zero Crossing
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Solution Overview
Problem
Existing solutions for on-load tap changers in wind turbine transformers are inefficient in managing short circuit currents during tap changes, leading to increased costs and reduced transformer and thyristor lifespan due to high short circuit current peak values, which current methods attempt to mitigate with large changeover impedances or over-sizing of components.
Innovation Solution
A method for generating a timing control signal that accurately determines the zero crossing of the tap voltage by monitoring voltage on the primary and secondary sides, applying phase corrections to improve precision, and deriving the timing control signal to minimize short circuit currents by switching the switching elements before the zero crossing, thus avoiding the need for large changeover impedances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large changeover impedances are used to limit short circuit currents during tap changes, then short circuit current peak values are reduced, but device complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by determining the zero crossing point of the tap voltage in advance and generating a timing control signal that triggers switching elements to conduct exactly at this predetermined moment. This advance planning of the switching timing eliminates the need for large changeover impedances, as the switching is synchronized to occur when the voltage is naturally zero, thereby limiting short circuit currents without adding complex impedance components to the circuit.
2Productivity
If switching elements are switched without precise timing control, then tap changes can be made, but high short circuit currents occur reducing transformer and thyristor lifespan
Solution Approach 1:
The patent employs feedback by continuously monitoring the tap voltage and using this feedback information to determine the exact zero crossing point. The control system uses the monitored voltage signal to generate a timing control signal that triggers the switching elements at the precise moment when the voltage crosses zero. This closed-loop feedback mechanism ensures that tap changes are performed with accurate timing control, preventing high short circuit currents and thereby extending the lifespan of the transformer and thyristors while maintaining productive tap change capability.
3Measurement precision
If phase correction is not applied to the monitoring signal, then the system is simpler, but the timing precision of zero crossing detection is reduced
Solution Approach 1:
The patent applies parameter changes by introducing a phase correction value that compensates for the phase shift between the monitored voltage signal and the actual tap voltage. The control system determines this phase correction parameter and applies it to the timing control signal generation process. By adjusting this temporal parameter, the system achieves precise zero crossing detection accuracy without requiring complex hardware modifications, thereby improving measurement precision through parameter optimization rather than structural complexity.
Data Source
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AI summary
A method of generating a timing control signal (80) for controlling the timing of a change of a transformer tap of a transformer (20) is provided. The transformer (20) comprises an on-load tap changer (30) comprising plural respective transformer taps (25-27). The method comprises monitoring a voltage on a primary side and/or on a secondary side of the transformer (20) to obtain a monitoring signal (91) and deriving, from the monitoring signal (91), an intermediate signal (95) that is indicative of at least one zero crossing of a tap voltage at the transformer tap (25-27). Deriving the intermediate signal (95) comprises estimating, based on the monitoring signal (91), a phase of the monitored voltage to obtain a phase signal (94) and applying to the phase signal a phase correction for a phase shift between the monitoring signal (91) or a signal derived therefrom and the tap voltage at the transformer tap (25-27). The timing control signal (80) is derived from the intermediate signal (95).