Transformer Inrush Current Suppression via Phase Control
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Solution Overview
Problem
Existing transformer inrush current suppression apparatuses fail to consider mechanical variations and pre-arc influences when determining energizing phases, leading to excessive magnetizing inrush currents, and are not applicable to three-phase power supplies with simultaneous three-phase energizing and de-energizing.
Innovation Solution
A transformer inrush current suppression apparatus that calculates target closing phases to minimize energization flux errors by considering residual flux values, pre-arc characteristics, closing time variations, and connection conditions of the three-phase transformer, using a target closing phase determining means and three-phase circuit breaker controller to control the three-phase circuit breaker for simultaneous three-phase energizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional phase controlled energizing method is used without considering mechanical variation and pre-arc, then the control system is simple, but excessive magnetizing inrush current flows due to offset from optimum energizing phases
Solution Approach 1:
The system performs preliminary calculations of the optimum closing phase by considering residual flux values, pre-arc characteristics, and closing time variations before actual energization. This advance preparation ensures that the circuit breaker closes at the optimal moment to minimize inrush current, rather than using simple predetermined phase angles.
Solution Approach 2:
The system measures actual residual flux values in the transformer core and uses this feedback information to dynamically calculate the optimum closing phase. This closed-loop approach adjusts the energizing timing based on the actual magnetic state of the transformer, preventing excessive inrush current even when mechanical variations occur.
2Object-generated harmful factors
If individual phase energizing control is implemented to suppress inrush current, then magnetizing inrush current is reduced, but simultaneous three-phase energizing capability is lost
Solution Approach 1:
The system dynamically calculates individual closing phases for each phase based on real-time residual flux measurements and pre-arc characteristics, while still coordinating all three phases to close simultaneously. This dynamic adjustment allows the system to maintain simultaneous energizing capability while optimizing each phase's closing moment to minimize inrush current.
3Device complexity
If target closing phase is calculated without considering pre-arc characteristic and closing time variation, then calculation is simpler, but actual energization occurs at offset phase leading to excessive inrush current
Solution Approach 1:
The system performs preliminary calculations of the optimum closing phase by considering residual flux values, pre-arc characteristics, and closing time variations before actual energization. This advance preparation ensures that the circuit breaker closes at the optimal moment to minimize inrush current, rather than using simple predetermined phase angles.
Solution Approach 2:
The system replaces simple mechanical timing-based closing control with an electronic calculation system that computes the optimum closing phase based on measured electrical parameters (residual flux, pre-arc voltage) and stored characteristic data. This substitution of mechanical timing with electronic computation achieves high precision in energizing phase 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
Effectively suppresses magnetizing inrush currents by determining optimal target closing phases, reducing the likelihood of excessive inrush currents and ensuring stability during simultaneous three-phase energizing and de-energizing of the transformer.
Implementation Method 1
residual flux calculating means for obtaining residual flux values for the first to third phases by time-integrating voltage signals for the first to third phases
Data Source
Figure 1
Figure 2~4
Figure 5(a)~5(b)
AI summary
A target closing phase determining circuit (8) determines energization flux errors in respective phases and respective closing phases of a first phase, and determines a target closing phase of the first phase so as to substantially minimize an evaluated value related to determined energization flux errors in the first to third phases, where each of the energization flux errors is the maximum value of absolute values of center values of transformer fluxes generated in a static state after energization. The target closing phase determining circuit (8) determines the energization flux errors in the respective phases and the respective closing phases of the first phase based on, residual flux values for the first to third phases of a three-phase power supply (2), respectively, a pre-arc characteristic and a closing time variation characteristic of a three-phase circuit breaker (3), a connection condition of windings of a three-phase transformer (1), to which the three-phase circuit breaker (3) is connected, and voltage phase differences among the phases of the three-phase power supply (2). A three-phase circuit breaker controller (9) controls the three-phase circuit breaker (3) to be closed at a timing corresponding to the target closing phase of the first phase.