Transformer Switching Angle Selection for Low Inrush Current
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Solution Overview
Problem
Existing methods for minimizing transformer inrush current are complex and require significant engineering efforts due to uncertainties in estimating remanent flux and site-specific simulations, especially in medium voltage circuit breakers.
Innovation Solution
A method involving a single-pole operated switching device with three independently operable current interrupting means, which iteratively closes at different angles to determine a preferred closing angle based on inrush current analysis, eliminating the need for remanent flux estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensors are installed downstream of the circuit breaker to integrate voltage with respect to time for estimating remanent flux, then the optimal closing angle can be determined, but the device complexity and engineering efforts increase significantly
Solution Approach 1:
The patent extracts only the necessary measurement (voltage upstream of the breaker) and eliminates unnecessary components (downstream sensors and integration systems). By taking out only the essential elements needed to determine the optimal closing angle, the solution reduces device complexity while maintaining the ability to account for remanent flux effects through iterative testing.
Solution Approach 2:
The system performs self-characterization by automatically testing different closing angles during an iterative start-up procedure and selecting the angle that produces acceptable inrush current. This self-service approach eliminates the need for complex external estimation systems, as the breaker system determines its own optimal parameters through controlled experimentation.
2Loss of energy
If site-specific simulations are performed to find the optimal phase angle, then the transformer inrush current can be minimized, but significant engineering efforts and time are required for each installation
Solution Approach 1:
The patent performs preliminary testing during the start-up procedure by iteratively closing the breaker at different angles and measuring the resulting inrush current. This preliminary action characterizes the specific installation conditions and determines the optimal closing angle before normal operation begins, eliminating the need for time-consuming site-specific simulations while still achieving minimized inrush current.
Solution Approach 2:
The system uses periodic iterative testing during start-up to determine the optimal closing angle. By performing a sequence of controlled closing operations at different angles and selecting the best result, the system efficiently characterizes the installation without requiring extensive engineering time, converting a potentially time-consuming simulation process into a rapid empirical determination.
3Loss of energy
If the optimal closing angle is determined based on remanent flux estimation methods, then transformer inrush current can be reduced, but the reliability is affected by uncertainties in flux estimation
Solution Approach 1:
The patent implements feedback by measuring the actual inrush current resulting from each test closing operation and using this measurement to determine whether the closing angle was optimal. This feedback mechanism allows the system to verify the effectiveness of each angle selection and reliably identify the optimal angle based on actual system response rather than uncertain theoretical estimations.
Solution Approach 2:
The system determines its own optimal closing angle through self-testing and self-characterization during the iterative start-up procedure. By relying on its own measurements and responses rather than external estimation methods, the system improves reliability by basing its decisions on actual observed behavior rather than uncertain theoretical models.
Data Source
AI summary
A start-up method for reducing inrush current to a transformer when closing a switching device. The switching device includes three single-pole operated current interrupting means. The method includes monitoring a voltage. The method includes, for each of a sequence of iterations: at a same opening angle relative to a reference angle of the voltage, starting an opening sequence of the switching device; at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, starting a closing sequence of the switching device; and obtaining an indication of the overall inrush current resulting from the closing. The method includes selecting for future use with the opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence.