Transformer Pre-magnetization to Suppress Inrush Current
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Solution Overview
Problem
Electrical systems that utilize transformers experience significant transient inrush currents when first energized, leading to potential fuse opening, breaker tripping, and protection relay false trips, which increases system costs and reduces reliability.
Innovation Solution
A system and method that involves a transformer with primary and secondary windings, and a charging module generating a magnetizing AC voltage to pre-magnetize the transformer windings in phase with the main AC voltage before full energization, reducing or eliminating inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transformer is first energized from the main AC source, then the electrical system can operate normally, but a transient inrush current up to 10 to 15 times larger than the rated transformer current flows for several cycles
Solution Approach 1:
The patent applies preliminary action by magnetizing the transformer core with a controlled magnetizing voltage before connecting to the main AC source. The charging module generates a magnetizing AC voltage that is applied to the transformer windings in advance, establishing the magnetic flux in phase with the upcoming main AC voltage, thereby preventing inrush current when full power is applied
Solution Approach 2:
The patent uses an intermediary approach by introducing a charging module as a mediator between the transformer and the main AC source. This charging module generates a controlled magnetizing AC voltage that serves as an intermediate step, preparing the transformer core before full energization from the main source, thus avoiding direct inrush current exposure
2Object-affected harmful factors
If the transformer is magnetized before energization, then inrush current is reduced or eliminated, but additional charging module and control circuitry are required
Solution Approach 1:
The charging module is designed with multi-functionality, serving both as a magnetizing source for the transformer and as a means to charge the DC link capacitors. This universal approach eliminates the need for separate pre-charge circuits and magnetizing devices, reducing overall system complexity despite the addition of the charging module
3Reliability
If the capacitors are charged during initial energization, then damage to rectifier, fuses and associated circuitry is prevented, but the energization process becomes more complex
Solution Approach 1:
The patent merges the capacitor charging function with the transformer magnetizing function. The charging module simultaneously performs both tasks: magnetizing the transformer core and charging the DC link capacitors through the rectifier bridge. This combination eliminates the need for separate pre-charge circuits and simplifies the overall energization process while providing component protection
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
This approach effectively reduces or eliminates inrush currents, enhances system reliability, and reduces costs by preventing unnecessary stress on fuses and protection relays, while also charging capacitors to prevent damage.
Implementation Method 1
a charging module structured to generate a magnetizing AC voltage... one or more of the number of sets of primary windings will be magnetized in a manner wherein a flux of the one or more of the number of primary windings is in phase with the main AC voltage
Data Source
AI summary
An electrical system (2) includes a transformer (16) coupled to an AC source (6) that provides a main AC voltage, the transformer having a number of sets of primary windings (18) and secondary windings (20), and a charging module (32) structured to generate a magnetizing AC voltage. The charging module is structured to selectively provide the magnetizing AC voltage to: (i) one of the number of sets primary windings, or (ii) one of the number of sets secondary windings. The magnetizing AC voltage is such that responsive to the magnetizing AC voltage being provided to one of the sets of primary windings or one of the sets of secondary windings, one or more of the sets of primary windings will be magnetized in a manner wherein a flux of the one or more of the number of primary windings is in phase with the main AC voltage provided from the AC source.