Transformer Tap Change Timing via Phase-Corrected Zero Crossing
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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 and require large changeover impedances or thyristor over-sizing, leading to increased costs and reduced transformer lifetime.
Innovation Solution
A method for generating a timing control signal that accurately estimates zero crossings of transformer taps by applying phase corrections to monitoring signals, compensating for phase shifts and delays, 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 invention changes the timing parameter of the tap switch operation to occur at or near the zero-crossing point of the tap voltage. This parameter change allows the short circuit current to be naturally limited by the voltage waveform itself, eliminating the need for additional changeover impedances while still protecting the transformer and switching elements
2Reliability
If thyristors are over-sized or snubber circuits are installed to handle short circuit currents, then the transformer and thyristors lifetime is protected, but the costs increase
Solution Approach 1:
The invention performs preliminary action by detecting the zero-crossing point of the tap voltage in advance and timing the switch operation to occur at this predetermined moment. This preliminary timing action prevents high short circuit currents from occurring in the first place, thereby protecting the transformer and thyristors without requiring over-sized components or expensive snubber circuits
3Stability of the object's composition
If the closing of a switch associated with the new tap is delayed to avoid two tap connections being conductive at the same time, then discontinuity of current at the load side is avoided, but the timing precision requirements increase
Solution Approach 1:
The invention uses feedback by continuously monitoring the tap voltage and detecting its zero-crossing point in real-time. This feedback mechanism provides precise timing information that automatically adjusts the switch operation moment, ensuring both current continuity and accurate timing without requiring complex external synchronization systems
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).