Air Gap Transformer Passband Correction via Series Filter
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Solution Overview
Problem
Air gap transformers used for current measurements in electrical installations face challenges due to high pass filtering effects from the air gap, which attenuate low frequencies and shift phases, making it difficult to balance performance, design, and saturation, especially in medium and high voltage applications.
Innovation Solution
A filter device is connected in series with the air gap transformer to amplify low frequencies below the cut-off frequency, effectively increasing the passband and reducing low-frequency filtering, allowing for a smaller, lighter, and less expensive transformer design that maintains the benefits of the air gap while reducing sensitivity to electromagnetic disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If an air gap is introduced in the transformer to reduce saturation and decrease dimensions, then the transformer size and weight are reduced, but the low-frequency response deteriorates due to high-pass filtering effects
Solution Approach 1:
A correction device (filter or digital processing system) is introduced as an intermediary between the air gap transformer and the measurement system. This intermediary compensates for the high-pass filtering effects by amplifying low-frequency components and correcting phase shifts, thereby restoring accurate low-frequency measurements while allowing the transformer to maintain its reduced size and weight benefits from the air gap
Solution Approach 2:
The invention changes the electrical parameters (gain and phase) of the signal through a correction device. By applying frequency-dependent gain adjustment and phase correction, the system compensates for the air gap's high-pass filtering characteristics, enabling accurate low-frequency measurements without requiring a larger transformer core
2Reliability
If an air gap is increased to improve saturation resistance, then the transformer can handle higher transient currents, but the cut-off frequency increases causing greater low-frequency attenuation
Solution Approach 1:
The correction device serves as a mediator that restores the measurement bandwidth by compensating for the frequency-dependent attenuation introduced by the air gap. It amplifies attenuated low-frequency components and corrects phase shifts, thereby extending the effective measurement bandwidth while allowing the transformer to operate with a larger air gap for improved saturation resistance
Solution Approach 2:
The invention converts the harmful high-pass filtering effect of the air gap into a beneficial characteristic by using the correction device to selectively amplify low-frequency components. The air gap's frequency-selective attenuation is transformed into a controlled filtering function, where the correction device restores desired frequencies while maintaining the saturation resistance benefits
3Reliability
If a Rogowski coil is used to avoid saturation, then saturation phenomenon is eliminated, but electromagnetic disturbance sensitivity increases
Solution Approach 1:
The invention merges the advantages of both approaches by combining the air gap transformer's saturation resistance with a correction device that compensates for frequency response issues. This hybrid solution maintains the magnetic core's ability to reject electromagnetic disturbances while avoiding saturation through the air gap, and uses electronic correction to restore low-frequency response, thereby eliminating both the saturation problem and the sensitivity issue
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
The solution enhances the air gap transformer's performance by expanding its passband, reducing low-frequency filtering, and minimizing phase shifts, resulting in a more efficient and cost-effective design that is less sensitive to electromagnetic disturbances, similar to transformers without or with smaller air gaps.
Implementation Method 1
A transformer has an iron core and one of its characteristics is that it becomes saturated starting at a given current passing through it
Data Source
AI summary
Device for correction of the passband of an air gap transformer with a cut-off frequency, characterized in that it includes a filter adapted to be connected to the transformer in series, and in that the filter is adapted to amplify the signal that it receives from the transformer for frequencies below the cut-off frequency of the transformer, so that the passband of the transformer fitted with the correction device is increased and has a cut-off frequency lower than the cut-off frequency of the transformer.