Transformer Energization Sequence Selection
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Solution Overview
Problem
Existing methods for minimizing inrush currents during the energization of power transformers are inefficient, as they either rely on costly and unreliable pre-insertion resistors or phase angle adjustments that are sensitive to uncertainties in remanent magnetic flux estimation, leading to suboptimal performance.
Innovation Solution
A method that automatically selects between two sequences of energization based on the de-energization type, using a first sequence for controlled openings and a second sequence for uncontrolled openings, where the first sequence generates a predetermined flux equal to the remanent flux and the second sequence generates a dynamic flux equal to the estimated remanent flux, thereby minimizing inrush currents robustly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pre-insertion resistors are used to damp inrush currents, then inrush current levels are reduced, but device complexity and cost increase significantly
Solution Approach 1:
The patent extracts the harmful remanent flux from the system by detecting its presence and compensating for it through controlled opening timing. Instead of adding complex damping components, the solution removes the root cause of inrush currents by managing the magnetic flux state, thereby reducing inrush currents without increasing device complexity.
Solution Approach 2:
The patent changes the timing parameter of circuit breaker opening to control the remanent flux level. By adjusting when the breaker opens relative to the voltage waveform, the system optimizes the residual flux to minimize inrush currents upon reclosing, achieving current reduction through parameter optimization rather than additional hardware.
2Object-affected harmful factors
If phase angles are adjusted based on estimated remanent flux, then inrush currents are reduced, but reliability decreases due to estimation uncertainty
Solution Approach 1:
The patent implements feedback by detecting whether the circuit breaker performed a controlled or uncontrolled opening and using this information to select the appropriate energization sequence. This feedback mechanism eliminates estimation uncertainty by relying on actual breaker operation history, thereby improving reliability while maintaining inrush current reduction.
Solution Approach 2:
The patent introduces dynamic selection between two different energization sequences based on the breaker's operational state. The system adapts its energization strategy in real-time based on whether the previous opening was controlled or uncontrolled, optimizing performance for each scenario and ensuring reliable operation across varying conditions.
3Object-affected harmful factors
If controlled opening is used to fix remanent flux, then inrush current reduction is optimized, but ease of operation decreases due to additional control requirements
Solution Approach 1:
The patent segments the energization process into two distinct sequences based on the breaker's operational history. By dividing the control strategy into controlled-opening-specific and uncontrolled-opening-specific paths, the system maintains operational simplicity for each case while optimizing overall performance, avoiding the need for complex continuous control.
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
This approach statistically guarantees the most optimal reduction of inrush currents in all circumstances, with the first sequence achieving less than 1 pu inrush current in 98% of cases following controlled openings and the second sequence achieving this in 90% of cases following uncontrolled openings.
Implementation Method 1
a circuit breaker adapted to apply a voltage in a first phase among the at least one phase
Implementation Method 2
They have their origin in the hysteresis behavior of the core included in the power transformer, and are associated with the existence and failure to take account of a remanent magnetic flux remaining in said core
Data Source
Figure 1~2a
Figure 2b~3
Figure 4
AI summary
The invention relates to a method for switching on a transformer (2), including a phase, by means of a circuit breaker (3) suitable for applying a voltage in a first phase. Said method includes a step for selecting between a first or second sequence, and a step for switching on the transformer (2), at a first moment, according to the previously selected sequence. The first sequence is suitable for generating a first flux, predetermined in the first phase at the first moment and equal to a residual flux. The second sequence is suitable for generating a dynamic flux, in the first phase at the first moment and equal to an estimate of the actual residual flux in the power transformer (2). The first sequence is selected when the actual residual flux is the result of a controlled shut-off. The second sequence is selected in the other cases.