Magnetizing Inrush Current Suppression for Capacitor-Equipped Circuit-Breakers
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Solution Overview
Problem
Existing methods struggle to suppress magnetizing inrush current when powering on a transformer with a circuit-breaker connected in parallel with a capacitor, as the residual magnetic flux is complicated by superposed AC and DC components, making it difficult to match prospective and residual magnetic fluxes for effective current suppression.
Innovation Solution
A magnetizing inrush current suppressing device that measures three-phase AC voltages, calculates DC components of residual magnetic fluxes, detects a notable phase, and controls the circuit-breaker to close phases in a staged manner, minimizing the difference between prospective and residual magnetic fluxes, thereby suppressing the inrush current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a circuit-breaker with inter-pole capacitor is used to shut down the transformer, then current interruption is facilitated, but the residual magnetic flux becomes complicated by superposed AC and DC components, making it difficult to suppress magnetizing inrush current
Solution Approach 1:
The patent segments the residual magnetic flux into two distinct components: DC component (representing the steady-state residual flux) and AC component (representing the oscillating flux due to inter-pole capacitor). By separately analyzing and controlling these components, the system can determine the optimal closing timing to minimize inrush current despite the complicated flux waveform.
Solution Approach 2:
The patent employs feedback by measuring the actual residual magnetic flux components (DC and AC) after shutdown, comparing them with the prospective magnetic flux, and using this information to determine the optimal closing timing. This closed-loop approach allows the system to adapt to the specific flux conditions created by the inter-pole capacitor and achieve effective inrush current suppression.
2Ease of operation
If the circuit-breaker closes all three phases simultaneously, then the operation is simple, but a large magnetizing inrush current flows when the transformer core has residual magnetic flux
Solution Approach 1:
The patent performs preliminary action by calculating the DC component of the residual magnetic flux before closing the circuit-breaker, determining the optimal closing timing in advance. This allows the system to close the phases at the most favorable moment when the prospective magnetic flux best matches the residual flux, thereby preventing large inrush current while maintaining simple simultaneous phase closing operation.
Solution Approach 2:
The patent changes the timing parameter of phase closing based on the measured residual flux components. By adjusting the closing timing to coincide with the optimal moment when prospective and residual fluxes match, the system eliminates inrush current while maintaining the simplicity of simultaneous phase closing, without requiring complex sequential switching.
3Reliability
If conventional inrush current suppression methods are applied, then magnetizing inrush current can be suppressed for standard circuit-breakers, but they become ineffective when inter-pole capacitors are connected between the poles
Solution Approach 1:
The patent introduces an intermediary measurement and calculation system that acts as a mediator between the inter-pole capacitor and the inrush current suppression control. By measuring the residual flux components and calculating the optimal closing timing, this intermediary system enables effective inrush current suppression to work with circuit-breakers equipped with inter-pole capacitors, bridging the gap between conventional suppression methods and modern capacitor-equipped breakers.
Solution Approach 2:
The patent modifies the control parameters by specifically targeting the DC component of residual flux and using it to determine optimal closing timing. This parameter change approach makes the suppression method adaptable to inter-pole capacitor configurations, as it directly addresses the fundamental flux condition rather than relying on methods that assume simpler flux waveforms without capacitor-induced AC components.
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 reduces the magnetizing inrush current to a few amperes, even with inter-pole capacitors connected, by determining the optimal phase closure times based on measured voltage and flux components, ensuring reliable current suppression during transformer power-on.
Implementation Method 1
When shutting down a transformer by the circuit-breaker in which a capacitor is connected between the poles, an AC voltage having a small amplitude appears at a transformer terminal after shutdown due to the inter-pole capacitor
Implementation Method 2
The magnitude of this magnetizing inrush current is several times as large as the rated load current of the transformer. When shutting down a transformer by the circuit-breaker in which a capacitor is connected between the poles, an AC voltage having a small amplitude appears at a transformer terminal after shutdown due to the inter-pole capacitor. In this state, the residual magnetic flux of the transformer is obtained by superposing a component of this small-amplitude AC voltage on a DC component.
Data Source
AI summary
According to one embodiment, a magnetizing inrush current suppressing device includes, a first closing unit closes the circuit-breaker at the notable phase by the first phase determined by the first-phase determination unit, a second-phase determination unit determines a second phase at which the notable phase detected by the notable phase detection unit from the three-phase AC voltage measured by the power-supply-side voltage measurement unit becomes a zero point after the first phase determined by the first-phase determination unit, and a second closing unit closes the circuit-breaker at two phases other than the notable phase by the second phase determined by the second-phase determination unit.