Transfer Switch Gating for Low-Inrush Transformer Energization
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Solution Overview
Problem
Conventional methods for transformer energization suffer from high inrush currents that can exceed fault protection trip levels, risking damage to system components and requiring complex, slow, and error-prone control algorithms.
Innovation Solution
A method and system using a transfer switch with controlled gating signals to bi-directional solid-state switching devices (SSSDs) that manage transformer flux saturation by alternating gate signals to limit inrush currents, employing SiC MOSFETs, IGBTs, or SCRs with resonant circuits to enable rapid commutation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transformer energization methods are used, then the transformer can be energized, but high inrush currents are drawn that exceed fault protection trip levels and stress system components
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor bank before transformer energization. The capacitor is charged through a charging resistor prior to closure, which limits the inrush current when the capacitor connects to the transformer. This preliminary charging action prevents excessive current spikes that would otherwise occur during direct connection.
Solution Approach 2:
The patent uses a charging resistor as an intermediary element between the capacitor bank and the transformer during energization. This resistor mediates the energy transfer, limiting the rate of current flow and preventing direct high-inrush current connection. The resistor serves as a temporary intermediary that is bypassed after charging is complete.
2Reliability
If a bypass switch is used to withstand higher inrush currents, then the main thyristor switch is protected, but the transformer still draws high inrush current risking fault protection tripping and component damage
Solution Approach 1:
The charging resistor serves as an intermediary that limits inrush current during capacitor bank energization. Unlike a bypass switch that merely withstands high current, the resistor actively limits the current flow through ohmic resistance, protecting both the switching devices and the transformer from excessive inrush currents.
Solution Approach 2:
The patent changes the electrical parameters during energization by using a high-resistance path initially, then transitioning to a low-resistance path. The charging resistor provides high resistance during charging to limit current, and after charging is complete, the bypass switch closes to provide a low-resistance path for normal operation. This parameter change strategy controls inrush current while maintaining system efficiency.
3Object-affected harmful factors
If gradual phase angle increase is used to control inrush current, then some control is achieved, but the process is slow requiring multiple voltage cycles and complex control algorithms
Solution Approach 1:
The capacitor bank is pre-charged before connection to the transformer, which is a preliminary action that prepares the system for energization. This pre-charging phase, separated from the main energization event, allows the capacitor to be ready without causing inrush current issues during the actual transformer connection, achieving fast and controlled energization.
Solution Approach 2:
The energization process is segmented into distinct phases: capacitor charging phase (through resistor) and transformer energization phase (with bypass switch). This segmentation separates the functions of charging and energizing, allowing each to be optimized independently - the charging phase limits current through resistance while the energization phase achieves fast connection without complex 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
Prevents transformer failure and upstream device damage, reduces load drops, and extends component life by controlling inrush currents, allowing for higher inrush currents without system disruptions.
Implementation Method 1
a first switch connecting a first power source to the transformer and a second switch connecting a second power source to the transformer
Implementation Method 2
employing SiC MOSFETs, IGBTs, or SCRs with resonant circuits to enable rapid commutation
Data Source
AI summary
Systems and methods for reducing inrush current to energize a transformer from a first power source or second power source using a transfer switch device including monitoring input phase voltage at a first and second switching pair, sending a first set of gate signals to the first switching pair and second set of gate signals to the second switching pair to selectively couple the transformer to the first power source or second power source, and operating the first switching pair and second switching pair in a normal operating mode at a next cycle once transformer flux reaches a saturation point. The transfer switch device includes a first switch and second switch connected to the first power source and second power source, respectively, and each switch including the first switching pair and second switching pair connected in a reverse orientation to enable a bi-directional flow of current at each phase.