Transformer Inrush Current Suppression via Residual Flux Phase Control
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Solution Overview
Problem
Existing methods for suppressing magnetizing inrush currents in transformers, especially in non-solidly earthed systems, are ineffective as they require additional equipment like circuit breakers with resistors or single-phase circuit breakers, which cannot accurately calculate residual magnetic flux and fail to suppress currents in transformers with non-solidly earthed systems.
Innovation Solution
A magnetizing inrush current suppression device that calculates line-to-line steady-state and residual magnetic fluxes to control the phase-wise closure of circuit breakers, allowing for simultaneous three-phase power supply without additional equipment, using steady-state magnetic flux calculation, residual magnetic flux calculation, phase detection, and closing control mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a circuit breaker with a resistor is used to suppress magnetizing inrush current, then the magnetizing inrush current is suppressed, but the equipment size increases
Solution Approach 1:
The invention extracts and eliminates the need for additional resistive circuit breakers by using intelligent control of standard three-phase circuit breakers. The control device calculates residual magnetic flux and determines optimal closing phases to suppress inrush current without requiring physical resistor components or additional breaker units.
Solution Approach 2:
The invention replaces the mechanical/resistive approach (circuit breaker with resistor) with an electronic control approach. The control device uses voltage integration and phase detection algorithms to calculate residual magnetic flux and determine the optimal closing phase, substituting physical resistance with intelligent timing control.
2Ease of operation
If single-phase circuit breakers are used to supply power to a transformer, then one phase can be supplied in advance, but it is impossible to suppress magnetizing inrush current in non-solidly earthed systems
Solution Approach 1:
The invention uses feedback by continuously monitoring phase voltages, integrating them to calculate residual magnetic flux, and using this information to determine the optimal closing phase. The control device adjusts the closing sequence based on the calculated flux state, creating a closed-loop control system that adapts to the transformer's magnetic condition.
Solution Approach 2:
The invention changes the control parameter from simple phase sequencing to optimized phase timing based on residual magnetic flux calculation. By calculating the integral of phase voltages to determine flux magnitude and polarity, the system dynamically adjusts which phase should close first to ensure the transformer core is in a non-saturated state, making the method effective for non-solidly earthed systems.
3Object-generated harmful factors
If circuit breakers interrupt at the zero point of magnetizing current, then the interruption is clean, but a zero-phase voltage appears and DC voltage remains on the transformer, making accurate residual magnetic flux calculation impossible
Solution Approach 1:
Instead of integrating phase-to-ground voltages (which becomes problematic with DC offset), the invention inverts the approach by integrating phase-to-phase voltages. This mathematical inversion eliminates the DC voltage component issue because the neutral point voltage cancels out when calculating line-to-line voltages, allowing accurate residual flux calculation even after zero-point interruption.
4Speed
If three-phase simultaneous closing is performed, then the power supply is fast, but voltage fluctuations occur due to large magnetizing inrush current
Solution Approach 1:
The invention performs preliminary action by calculating the residual magnetic flux state before closing and determining the optimal closing phase in advance. The control device integrates phase voltages to assess the magnetic flux condition, then selects which phase should close first to ensure the transformer core is in a non-saturated state, preventing large inrush current while maintaining fast three-phase power supply.
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
Accurately suppresses magnetizing inrush currents by determining the correct phase for circuit breaker closure, reducing voltage fluctuations and eliminating the need for resistive circuit breakers, thereby enhancing system stability and efficiency.
Implementation Method 1
a magnetizing inrush current suppression device for transformer and control method of same, which accurately calculate the residual magnetic flux and enable suppression of the magnetizing inrush current
Data Source
AI summary
A first calculation part calculates the phase-to-phase steady-state magnetic flux of the three phases of the power supply. A second calculation part calculates the phase-to-phase residual magnetic flux of the three phases in the primary windings side of the transformer when the circuit breakers interrupt the transformer. A phase detection part detects a voltage phase at which polarity and magnitude of the calculated steady-state magnetic flux and residual magnetic flux coincide. Closing control part firstly causes only the circuit breakers of the two phases to close at the detected voltage phase, and then causes the circuit breaker of the remaining one phase to close.