Transformer Closing Angle Selection for Lower Inrush Current
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Solution Overview
Problem
Minimizing transformer inrush current in electrical three-phase systems is challenging due to the magnetic state of the transformer core affecting the optimal phase angle for circuit breaker closing, and existing methods require complex estimations or site-specific simulations with uncertainties and significant engineering efforts.
Innovation Solution
A method where the switching device is closed at different angles during start-up iterations, with the same opening angle, to determine a preferred closing angle based on inrush current analysis, eliminating the need for remanent flux estimation by monitoring voltage in one phase and selecting the angle resulting in reduced inrush currents for future operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensors are installed downstream of the circuit breaker to estimate remanent flux through voltage integration, then the optimal closing angle can be determined, but the device complexity and engineering effort increase significantly
Solution Approach 1:
The invention extracts and eliminates the complex remanent flux estimation step entirely. Instead of measuring voltage downstream and integrating it to estimate flux, the method directly tests different closing angles and selects the one that produces the lowest inrush current, bypassing the need for flux estimation completely.
Solution Approach 2:
The system performs self-testing by automatically trying different closing angles during startup and selecting the optimal one based on actual inrush current measurements. This self-service approach replaces the need for external flux estimation systems and their associated sensors and calculations.
2Measurement precision
If site-specific simulations are performed to find the optimal phase angle, then the optimal closing angle can be determined, but significant engineering efforts and time are required
Solution Approach 1:
The invention performs preliminary angle selection during the startup phase itself. By testing different closing angles in the initial iterations and selecting the optimal one based on actual performance, the system prepares the optimal setting in advance without requiring separate simulation studies.
Solution Approach 2:
Instead of performing complex site-specific simulations, the method uses actual measured inrush current data from a few test iterations to copy the successful approach. The optimal angle determined from these test iterations is then reused for all subsequent operations, eliminating the need for detailed simulations.
3Device complexity
If different closing angles are tested during start-up iterations, then the optimal angle can be determined without estimating remanent flux, but additional opening and closing operations are required
Solution Approach 1:
The system uses periodic testing during startup iterations, where the circuit breaker is opened and closed multiple times at different angles to determine the optimal setting. Once the optimal angle is found, it is then used periodically for all subsequent operations, making the initial periodic testing worthwhile.
Data Source
Figure 1~2B
Figure 2C~2F
Figure 3~4
AI summary
The present disclosure relates to a start-up method for reducing inrush current to a transformer (3) when closing a switching device (2). The method comprises monitoring a voltage (U) in one of the phases. The method also comprises, for each of a sequence of iterations: at a same opening angle relative to a reference angle of the monitored voltage, opening 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, closing the switching device; and obtaining a peak value of the overall inrush current resulting from the closing. The method also comprises selecting for future use with said same 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.