Inrush-Current Suppression via Phase-Aligned Closing Control
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Solution Overview
Problem
Existing methods for suppressing excitation inrush current in three-phase transformers often result in asynchronous waveforms and magnetic flux saturation, leading to excessive inrush currents due to deviations in closing phases and time variations, causing higher-than-expected inrush currents when the actual input point deviates from the target.
Innovation Solution
An inrush-current suppressing device that calculates residual magnetic flux and input magnetic-flux errors for each phase, determining a closing order and setting target closing times to minimize errors, and using a predetermined delay time to avoid magnetic flux saturation, ensuring the three-phase breaker closes at optimal times to prevent excitation inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the closing phase is calculated to minimize input magnetic-flux error, then the magnetic flux error is reduced, but the actual input point deviates from the target input point due to closing-time variation characteristics, causing magnetic flux saturation and excitation inrush current
Solution Approach 1:
The patent applies preliminary action by pre-calculating the input magnetic-flux error based on residual magnetic flux and closing-time variation characteristics before the actual closing operation. This allows the system to predict and compensate for potential deviations, adjusting the closing phase in advance to ensure the actual input point aligns with the target input point, thereby preventing magnetic flux saturation and excitation inrush current.
2Reliability
If the closing phase is advanced to compensate for closing-time variation, then the actual input point alignment is improved, but the gap voltage of remaining phases increases, causing higher excitation inrush current
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the closing phase based on calculated input magnetic-flux error and closing-time variation characteristics. The system modifies the closing phase parameter to minimize magnetic flux error while simultaneously considering the impact on gap voltage of remaining phases. This balanced parameter adjustment ensures proper input point alignment without causing excessive gap voltage that would lead to higher excitation inrush current.
3Object-generated harmful factors
If the closing order is optimized to minimize inrush current, then the excitation inrush current is reduced, but the complexity of control increases due to multiple calculation and coordination requirements
Solution Approach 1:
The patent applies segmentation by dividing the three-phase closing control into distinct stages: first calculating residual magnetic flux for each phase, then determining input magnetic-flux error based on closing-time variation characteristics, and finally optimizing the closing order and phases sequentially. This segmented approach breaks down the complex control problem into manageable calculation steps, reducing overall system complexity while still achieving effective inrush current suppression.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively suppresses the maximum value of excitation inrush current, preventing excessive inrush currents by aligning closing phases and times to minimize magnetic flux errors and saturation, thus stabilizing gap voltages and reducing unintended inrush currents.
Implementation Method 1
a residual magnetic flux calculation means for calculating a residual magnetic flux in each phase generated within the three-phase transformer based on a voltage of each phase generated in the three-phase transformer before and after closing the three-phase breaker
Implementation Method 2
a closing-phase input magnetic-flux error for every phase based on the residual magnetic flux in each phase and in consideration of pre-arc characteristics and closing-time variation characteristics of the three-phase breaker
Data Source
AI summary
An inrush-current suppressing device includes a residual-magnetic-flux calculation unit that obtains a residual magnetic flux generated within a three-phase transformer, an input magnetic-flux-error calculation unit that obtains a closing-phase input magnetic-flux error, a closing-order determination unit that determines a closing order of phases of a three-phase breaker, a target-closing-phase/time setting unit that sets a time from a reference point to a target closing phase of a first closing phase as a first target closing time, and sets a time obtained by adding up a time from the reference point to a target closing phase of a second closing phase and a delay time set to exclude a period in which a magnetic flux in the first closing phase possibly saturates as a second target closing time, and a closing control unit that generates and outputs a closing control signal to close each phase at the target closing time.