Transformer Inrush Current Reduction via DC Premagnetization
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Solution Overview
Problem
Existing solutions for reducing inrush current during transformer connection are not suitable for high voltage applications due to the use of power electronics components that cannot withstand high voltages, leading to incomplete suppression of inrush current peaks.
Innovation Solution
A control system that applies a direct current to the transformer primary winding for core saturation, followed by AC voltage application at specific phase angles to maintain flux continuity, effectively reducing and potentially eliminating inrush current, utilizing only electromechanical switches capable of withstanding high voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If power electronics components are used to control phase angle and premagnetize the magnetic core, then inrush current can be limited, but the solution becomes inapplicable to high voltage due to component voltage limitations
Solution Approach 1:
The patent replaces power electronics components (semiconductor switches) with electromechanical switches that can withstand high voltages. The control method is substituted from electronic phase angle control to a sequence control system that uses timing circuits and electromechanical switching. This substitution maintains the inrush current limitation capability while enabling high voltage applicability.
Solution Approach 2:
The patent introduces a control system with timing circuits and sequence control logic as intermediaries between the power supply and the electromechanical switches. This intermediary control mechanism coordinates the switching sequence to achieve proper phase angle control and premagnetization without requiring high-voltage-rated power electronics components.
2Object-generated harmful factors
If capacitor discharge is used for premagnetization, then inrush current is limited to charge current value, but the method does not completely suppress inrush current peaks
Solution Approach 1:
The patent applies preliminary DC current to the transformer primary winding before AC voltage application to saturate the magnetic core and establish desired residual flux. This preliminary magnetization action ensures that when AC voltage is applied at the correct phase angle, the flux continuity is maintained and inrush current peaks are completely suppressed, not just limited.
Solution Approach 2:
The patent maintains flux continuity by applying AC voltage at a specific phase angle that matches the residual flux condition established by preliminary DC magnetization. This continuity of magnetic flux action prevents abrupt flux changes that would generate inrush current peaks, achieving complete suppression rather than mere limitation.
3Object-generated harmful factors
If transformer is permanently connected to mains to avoid repeated energization stress, then inrush current problems are avoided, but energy consumption increases and flexibility is reduced
Solution Approach 1:
The patent replaces power electronics-based phase angle control with electromechanical switches and sequence control, enabling safe repeated energization. This allows the transformer to be disconnected and reconnected as needed without inrush current damage, reducing energy consumption compared to permanent connection while maintaining reliability through controlled switching.
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
Significantly reduces or completely suppresses inrush current during transformer connection, ensuring transformer safety and reliability even at high voltage levels without the limitations of power electronics.
Implementation Method 1
applies a direct current to the transformer primary winding for core saturation
Implementation Method 2
the current in the primary winding required to produce that flux value
Implementation Method 3
control of the phase angle of the mains voltage... AC voltage application at specific phase angles to maintain flux continuity
Implementation Method 4
the knee of the magnetization hysteresis loop of the transformer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
Method for reducing the inrush current of an inductive load, particularly a transformer, comprising the following steps: a) Connecting a DC power source (4) to the transformer for a time tc, to magnetize its magnetic core until saturation is reached, and connecting the transformer to the AC mains by means of an electromechanical switch (6), in an initially open position. b) Disconnecting the transformer from the DC power source (4), the magnetic flux being reduced to its residual value. c) Closing the electromechanical switch (6) to complete the connection, this connection point being determined by the phase angle selected from the sinusoidal signal of the voltage mains, in such a way that magnetic flux corresponding to the steady state voltage equals the residual magnetic flux that remains when the transformer is disconnected from the DC power source (4).