Fiber Optic Grating Sensor for Direct Transformer Moisture Measurement
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Solution Overview
Problem
Current methods for measuring moisture in the insulation system of oil-filled electrical transformers are indirect and inaccurate, particularly in determining the moisture content at the hottest spot within the winding, as they rely on equilibrium assumptions that are often not met in operational conditions.
Innovation Solution
A fiber optic-based sensing system with gratings is placed adjacent to the insulator or within the oil-filled transformer, using light transmission and reflection to directly measure moisture content by analyzing changes in spectral responses, allowing for precise moisture parameter determination at specific locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If indirect equilibrium-based methodologies are used to estimate moisture in insulation, then the measurement process is simplified, but the measurement precision deteriorates because the equilibrium assumption is often not met in operational conditions
Solution Approach 1:
The patent replaces indirect equilibrium-based estimation methodologies with direct optical sensing using fiber optic gratings. The fiber optic sensor system substitutes the theoretical equilibrium assumption approach with physical direct measurement, where light reflection from grating structures provides actual moisture content data without relying on equilibrium conditions between oil and insulation materials.
Solution Approach 2:
The patent introduces fiber optic grating sensors as intermediary elements that directly interact with moisture in the insulation system. These grating structures serve as mediators that convert moisture presence into optical signal changes, enabling direct measurement without requiring equilibrium between different materials or complex sampling procedures.
2Measurement precision
If paper samples are taken from the interior of the transformer for direct moisture measurement, then the measurement precision improves, but the ease of operation deteriorates due to de-energization requirements and sampling difficulty
Solution Approach 1:
The patent applies preliminary action by installing fiber optic grating sensors within the transformer during the manufacturing or maintenance phase, before operational use. This allows the sensors to be pre-positioned in strategic locations where moisture measurement is most critical, eliminating the need for future sampling operations that would require de-energization and complex access procedures.
Solution Approach 2:
The fiber optic sensor system enables self-service continuous monitoring of moisture content within the transformer. The sensors automatically measure moisture levels without requiring external intervention, sampling operations, or transformer shutdowns, providing ongoing data that serves the monitoring function independently.
3Measurement precision
If fiber optic-based sensing elements are installed for direct moisture measurement, then the measurement precision improves, but the device complexity increases due to the need for light transmission and optical signal sensing systems
Solution Approach 1:
The fiber optic grating sensor system serves multiple functions simultaneously: it measures moisture content, can be positioned at multiple locations including hot spots, provides continuous monitoring, and requires no external power or complex electronics within the transformer. This multi-functionality offsets the initial complexity by consolidating multiple measurement capabilities into a single sensor type.
Solution Approach 2:
The fiber optic grating sensors are relatively simple, inexpensive components compared to the overall transformer value. While the sensing system adds complexity, the individual sensor elements are simple optical gratings that can be replaced if needed, and their low individual cost makes the complexity investment worthwhile for the precision gained.
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 provides accurate and direct measurement of moisture content in the insulation paper and oil, bypassing the limitations of equilibrium-based methodologies, offering reliable data for transformer management and maintenance.
Implementation Method 1
senses optical signals based on light reflected by a grating sensor defined along a length of the fiber optic-based sensing element
Implementation Method 2
transmits light through the fiber optic-based sensing element and senses optical signals
Implementation Method 3
The fiber optic-based sensing element has a light- transmitting core and a hygroscopic material at least partially surrounding the light-transmitting core
Data Source
AI summary
A method of directly measuring moisture content in an oil-filled transformer includes using an optical fiber that having a grating sensor, such as a Fiber Bragg grating, defined in the optical fiber. The various conductors (windings) in the transformer are insulated using an insulator such as paper and insulating oil is filled inside the transformer. Moisture in the transformer is absorbed by the paper that surrounds the windings. A moisture content at a specific location can be measured by placing the optical fiber with the grating sensor directly at the specific location to be measured. A physical parameter of the paper that absorbed moisture changes over time, causing a change in the grating sensor of the optical fiber which changes the spectral response of optical signals that are reflected by the grating sensor. The method provides an accurate method of measuring the moisture inside the transformer at the specific location.