Optical Current Sensors for Standby Transformers
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Solution Overview
Problem
Current optical current sensors face challenges in accurately detecting low-level currents in standby power transformers, particularly in unloaded conditions, due to high noise interference and the need for multiple sensing fiber wraps, which is costly and impractical.
Innovation Solution
The use of a fiber optical current sensor system that incorporates a comb filter with a synchronous voltage reference to improve signal recovery from noise, allowing detection of currents below 10 mA without requiring extensive sensing fiber wraps, and includes logic for determining open-phase conditions based on current thresholds and zero sequence analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensing fiber wraps (e.g., 600 fiber turns) are used in the optical current sensor, then the current detection capability for low-level currents (below 10 mA) is improved, but the device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent changes the electrical parameters of the transformer (connecting auxiliary windings to create resonant circuits) to amplify the magnetization current signal, thereby improving current detection capability without increasing the number of fiber wraps. This transforms the problem from increasing sensor complexity to modifying system parameters for signal enhancement.
Solution Approach 2:
The patent introduces auxiliary windings and capacitors as intermediary elements that create resonant circuits to amplify the magnetization current. These intermediaries act as signal amplifiers, allowing the optical sensor to detect low currents without requiring excessive fiber wraps, thus resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If multiple sensing fiber wraps are used to detect low-level currents, then measurement precision improves, but ease of manufacture deteriorates due to installation difficulty and cost
Solution Approach 1:
By modifying the electrical configuration of the transformer (connecting auxiliary windings to ground or neutral through capacitors), the system creates resonant conditions that amplify the magnetization current. This parameter change approach allows standard fiber wrap counts to achieve detection capabilities that would otherwise require excessive wraps, significantly improving ease of manufacture and installation.
Solution Approach 2:
The patent segments the transformer system by utilizing auxiliary windings separately from the main power windings. These auxiliary windings are configured to create resonant circuits that amplify the signal, allowing the optical sensor to function effectively with fewer fiber wraps, thus reducing installation complexity and cost.
3Measurement precision
If the standby power transformer is kept unloaded, then the magnetization current remains low (50-800 mA) for detection purposes, but the ability to detect open-phase conditions deteriorates when capacitive current becomes the dominant signal
Solution Approach 1:
The patent creates resonant circuits using auxiliary windings and capacitors that periodically amplify the magnetization current at the power frequency. This periodic resonance action ensures that even when capacitive current is present, the magnetization current component can be reliably detected through its resonant amplification, improving open-phase detection accuracy without changing the transformer load state.
Solution Approach 2:
The auxiliary windings and capacitors act as intermediary resonant circuits that selectively amplify the magnetization current signal. These intermediaries filter and enhance the specific frequency components associated with magnetization current, allowing reliable detection even when capacitive current is present, thus resolving the reliability issue in open-phase detection.
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 enhances the ability to detect open-phase conditions in standby power transformers with improved noise rejection, reducing the need for multiple wraps of sensing fiber and providing reliable low-current measurements, thus addressing the limitations of existing systems.
Implementation Method 1
measuring a current flowing through a high voltage side of a standby power transformer using an optical current sensor
Implementation Method 2
filtering the measured current using a comb filter with a synchronous voltage reference
Data Source
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AI summary
Systems and methods according to these exemplary embodiments provide for methods and systems related to optical current sensors used to monitor standby power transformers, specifically fiber optical current and voltage sensors and, more particularly, to applications involving filters for use in such sensors, such as frequency tracking comb filters. According to one embodiment, a method for monitoring a connection condition of a stand by power transformer includes the steps of measuring a current flowing through a high voltage side of the standby power transformer using at least one optical current sensor disposed proximate to a current flow path of the high voltage side, using a comb filter to filter the measured current, determining whether the filtered, measured current is less than a predetermined threshold value; and generating an alarm indication that the high voltage side of the standby power transformer is unconnected.