How to measure transformer temperature with optical fiber

חיישן טמפרטורה בסיב אופטי, מערכת ניטור חכמה, יצרנית סיבים אופטיים מבוזרת בסין

Fluorescent optical fibers measure transformer temperature by detecting the fluorescence decay time of fluorescent substances, as the fluorescence decay time is a function of temperature

1. Method for measuring transformer temperature using optical fiber

1.1 Measurement method based on fiber Bragg grating

Fiber Bragg Grating is a passive device in which the refractive index is modulated periodically within the fiber core. When the external temperature changes, it will affect the refractive index of the fiber Bragg grating and the refractive index of the fiber core, thereby causing changes in the reflection or transmission peak wavelength of the fiber Bragg grating. By accurately measuring the wavelength of the reflected signal, temperature detection can be achieved. This method typically requires installing fiber Bragg grating sensors near transformer windings or other critical locations to accurately sense temperature changes.

1.2 Fluorescence fiber optic temperature measurement method

Fluorescent fiber optic sensors can be used to measure the internal temperature of transformers. The principle is to utilize the characteristics of fluorescent materials. When a light pulse is emitted from a light source and transmitted through an optical fiber to a sensor, the fluorescent substance in the probe is illuminated by the spectrum. The molecules absorb light and are excited to an excited electronic state, then radiate fluorescence outward and return to the electronic ground state. The temperature of the surrounding environment and the decay time of fluorescence exhibit a functional relationship, and the temperature value can be obtained by detecting the decay time of fluorescence. Insert the probe of the fluorescent fiber thermometer into the position inside the transformer that needs to be measured, such as the transformer winding, to perform temperature measurement.

1.3 Fiber optic sensor measurement method based on semiconductor materials

There is a relationship between the temperature and light absorption of semiconductor materials. The bandgap width of most semiconductors shows a linear negative correlation with temperature, כלומר, as the temperature increases, the bandgap width decreases linearly and the wavelength of the light absorption band increases. This characteristic can be utilized to manufacture intensity modulated fiber optic sensors, such as using reflective or transmissive modulation, as well as refractive index and absorption coefficient intensity modulation methods. When measuring, if a light source corresponding to the radiation spectrum and absorption band is selected, an increase in temperature will cause a decrease in the light intensity of the semiconductor. ולאחר מכן, based on the functional relationship between light intensity and temperature, the temperature of the semiconductor material can be calculated by the value of the reflected light intensity. This type of fiber optic temperature sensor mainly consists of photoelectric conversion devices, light sources, and sensitive components (such as gallium arsenide semiconductors).

1.4 Measurement method based on all fiber optic technology

Design a temperature detection system using fiber Bragg gratings as sensing elements. During the measurement process, there may be external interference issues, which can be effectively addressed by using the difference method to improve the accuracy of the measurement results.

2. Application case of optical fiber in transformer temperature measurement

2.1 Temperature Monitoring of Transformer Winding in Substation

A transformer winding fiber optic temperature online monitoring system based on fiber optic technology was used in a substation of a certain power company. This system mainly consists of fiber optic temperature sensors, fiber optic temperature transmitters, fiber optic temperature measurement systems, וכו. Fiber optic temperature sensors are responsible for collecting temperature information of transformer windings, and then analyzing the optical signal through fiber optic temperature transmitters to obtain temperature change information. Finally, the fiber optic temperature measurement system processes and analyzes the obtained temperature data to achieve real-time monitoring of transformer winding temperature. By arranging fiber optic sensors at different positions of the transformer winding, real-time temperature data can be collected. Once abnormal conditions are detected, the system will issue an alarm and take corresponding measures in a timely manner to avoid transformer failures.

2.2 Temperature Monitoring of Oil Immersed Transformers

Application of Fiber Bragg Grating Temperature Measurement
In oil immersed transformers, fiber Bragg gratings are used for oil temperature monitoring. לדוגמה, by encapsulating the fiber optic grating inside an insulating shell, the external ambient temperature is transmitted through the shell to the fiber optic grating, causing a change in its wavelength. Due to the excellent linear relationship between the center wavelength of fiber Bragg gratings and temperature, oil temperature can be detected by measuring the wavelength of the reflected signal. And typically, multiple (כגון 18) fiber optic grating temperature sensors with different wavelengths can be connected to a single fiber optic cable. The reflected signals from the sensors are returned to the detector through a loopback device, and the data is read into the computer through a digital DIO card, thereby achieving effective monitoring of the oil temperature of oil immersed transformers.
In the transformer winding temperature detection system based on fiber Bragg grating sensing, the system adopts fiber Bragg grating sensors with strong anti-interference ability and extremely sensitive to temperature. The measurement and transmission of optical signals, followed by demodulation into temperature signals, can meet the high-precision temperature measurement requirements of transformer windings, accurately measure the winding temperature of oil immersed transformers, and ensure the safe operation of transformers.
Application of Fluorescent Fiber Optic Temperature Measurement
For large oil immersed transformers, fluorescence fiber optic temperature measurement method is adopted. לדוגמה, the fluorescent fiber optic temperature sensor from Fuzhou Yingnuo Technology can be used for temperature monitoring of large oil immersed transformers. It has the characteristic of essential insulation and can perform online temperature monitoring on components that withstand high voltage or strong current. Inserting the probe of the fluorescent material into the position inside the transformer that needs to be measured, and detecting temperature through the relationship between fluorescence lifetime and temperature, significantly reduces the impact of light source stability.

3. Principle of Fiber Optic Technology for Transformer Temperature Measurement

3.1 Principle of Fiber Bragg Grating Technology

Basic principles
Fiber Bragg grating is a reflective fiber filter device. It is achieved by irradiating a bare optical fiber with ultraviolet interference fringes, and the core absorbs ultraviolet radiation to generate permanent periodic changes in refractive index. When the wavelength entering the optical fiber satisfies the Bragg condition (λ B=2n ∧, where λ B is the center wavelength of the Bragg reflected light wave of the fiber grating, n is the refractive index of the fiber core, and ∧ is the grating period), the forward guided mode propagating in the optical waveguide will couple to the backward reflected mode, forming Bragg reflection.
The central wavelength of a fiber Bragg grating is related to stress and temperature changes, and its relationship formula is Δ λ B=λ B (1- ρ) Δ ε+λ B (1+ξ) Δ T, where Δ λ B is the change in the central wavelength of reflected light caused by stress and temperature changes; Δ ε is the change in stress; Δ T is the change in temperature; ρ is the optical elastic coefficient of the optical fiber; ξ is the thermal optical coefficient of the optical fiber. When the fiber optic grating is encapsulated inside an insulating shell, it is mainly affected by temperature. The external environmental temperature changes the n and ∧ of the fiber optic grating, resulting in a change in the wavelength of the reflected light. By accurately measuring the wavelength of the reflected signal, temperature detection can be achieved, and the center wavelength of the fiber optic grating has a very good linear relationship with temperature.
Sensing process
The broadband light source is input into the optical fiber, and after passing through the fiber Bragg grating, the narrowband spectrum at the Bragg wavelength is reflected to the input end of the fiber, while the remaining wavelengths are transmitted through. When the temperature changes, the refractive index and other parameters of the fiber Bragg grating change, causing the Bragg wavelength to change, and the wavelength of the reflected light also changes accordingly. By detecting the change in reflected light wavelength and based on a predetermined wavelength temperature relationship, the corresponding temperature value can be obtained.

3.2 Principle of Fluorescent Fiber Technology

Principle of Fluorescence Generation
The fluorescent substance in the fluorescent fiber thermometer has a special energy level structure. When the light pulse is emitted by the light source and transmitted through the optical fiber to the fluorescent substance in the sensor probe, the molecules of the fluorescent substance absorb photon energy and transition from the ground state to the excited state. Due to the instability of the excited state, molecules will release energy through radiative fluorescence and return to the ground state.
The relationship between temperature and fluorescence characteristics
The temperature of the surrounding environment and the decay time of fluorescence exhibit a functional relationship. At different temperatures, the fluorescence decay time of a fluorescent substance changes as it returns from the excited state to the ground state. באופן כללי, the higher the temperature, the shorter the fluorescence decay time. By detecting the fluorescence decay time and utilizing the predetermined fluorescence decay time temperature function relationship, the temperature value of the measurement point can be obtained.

4. Comparison of Temperature Measurement of Transformers Using Different Optical Fibers

4.1 חיישן גרינג Fiber Bragg

advantage
High precision: The center wavelength of fiber Bragg grating has a very good linear relationship with temperature, and high-precision temperature measurement can be achieved by accurately measuring the change in reflected wavelength. לדוגמה, in some experiments and practical applications, it can meet the high-precision temperature measurement requirements of transformer windings with relatively small measurement errors.
Good stability: Fiber Bragg grating sensors themselves have good stability and can adapt to the temperature monitoring needs during long-term operation of transformers. During long-term temperature monitoring, its performance will not experience significant fluctuations and can continuously and accurately reflect temperature changes.
Anti electromagnetic interference: In the strong electromagnetic environment of transformers, fiber Bragg grating sensors, based on the principle of optical signal transmission and detection, are not affected by electromagnetic interference and can ensure the accuracy of measurement data. This feature makes it highly advantageous in measuring transformer temperature in power systems.
Reusability: Multiple fiber Bragg grating temperature sensors with different wavelengths can usually be connected to a single optical fiber, facilitating multi-point temperature measurement in different parts of the transformer, constructing a sensing network, and monitoring the overall temperature distribution of the transformer.
shortcoming
Relatively high cost: The production process of fiber Bragg grating sensors is relatively complex, requiring special equipment and technology to prepare fiber Bragg gratings, and the related demodulation equipment is also relatively expensive, which makes the cost of the entire fiber Bragg grating temperature measurement system high.
High installation requirements: When installing fiber Bragg grating sensors, it is necessary to ensure the accuracy of their packaging and installation position to accurately sense temperature changes and avoid unnecessary interference factors such as stress. If installed improperly, it may affect measurement accuracy.

4.2 Fluorescent Fiber Optic Sensor
advantage

Reduced requirement for light source stability: Compared with fluorescence intensity type temperature sensors, detecting temperature through the relationship between fluorescence lifetime and temperature significantly reduces the impact of light source stability. This allows fluorescent fiber optic sensors to still accurately measure temperature in some application scenarios where the stability of the light source may be poor.

Intrinsic insulation properties: Fluorescent fiber optic sensors have inherent insulation properties, making them highly suitable for temperature measurement in high-voltage equipment such as transformers. It can directly perform online temperature monitoring on components that withstand high voltage or strong current, without worrying about safety hazards caused by insulation issues.
Fluorescent materials with high temperature resistance and stable performance: Fluorescent materials themselves have the characteristics of high temperature resistance and stable performance, which can adapt to the high temperature environment inside transformers and ensure the reliability of temperature measurement during transformer operation.
shortcoming
System debugging: In practical applications, the installation and debugging of fluorescent fiber optic temperature measurement systems require precise adjustments to the position of sensors, fiber optic connections, וכו., to ensure accurate temperature measurement.

4.3 Fiber optic sensors based on semiconductor materials

advantage
Low cost: This fiber optic temperature sensor mainly consists of photoelectric conversion devices, inexpensive light-emitting diodes as light sources, and commonly used gallium arsenide semiconductors as sensitive components. The structure is simple and easy to manufacture, so the cost is relatively low.
Simple principle and structure: It is based on the relationship between temperature and light absorption of semiconductor materials, and measures temperature through intensity modulation (such as reflective or transmissive modulation, as well as refractive index and absorption coefficient intensity modulation methods). The principle and structure are relatively simple.

shortcoming
The performance of sensors is greatly affected by light intensity, which is their main drawback. The variation of light intensity will directly affect the accuracy of measurement results.
Calibration work is required: Before measurement, temperature and light intensity need to be calibrated. Moreover, in addition to the influence of temperature on light intensity, factors such as photodetectors for measuring light intensity, unstable light source illumination, coupling losses, and random fluctuations caused by fiber bending may also have an impact. לכן, relying solely on the pre calibrated temperature light intensity function relationship cannot effectively improve its temperature measurement performance.

5. Accuracy of Fiber Optic Temperature Measurement for Transformers

5.1. Accuracy of Fiber Bragg Grating Sensor

Fiber Bragg grating sensors have high accuracy. Due to the excellent linear relationship between the center wavelength of fiber Bragg gratings and temperature, as long as the change in reflected light wavelength can be accurately measured, the temperature value can be accurately obtained. In practical applications, such as in a transformer winding temperature detection system based on fiber Bragg grating sensing, it can meet the high-precision temperature measurement requirements of transformer windings, achieve accurate monitoring of transformer winding temperature, and provide guarantees for the safe operation of transformers.

5.2 Accuracy of Fluorescent Fiber Optic Sensor

Fluorescent fiber optic sensors determine temperature by detecting fluorescence decay time, and their accuracy depends on the characteristics of the fluorescent material and the accuracy of the detection equipment. Under normal circumstances, if the fluorescent material has stable performance and the detection equipment has high accuracy, it can achieve more accurate temperature measurement. לדוגמה, some fluorescent fiber optic sensors can measure the temperature of transformer windings once per second within their normal monitoring temperature range, and the temperature resolution can reach a certain standard, meeting the accuracy requirements of transformer temperature monitoring.

5.3 Accuracy of Fiber Optic Sensors Based on Semiconductor Materials

The accuracy of this sensor is affected by various factors. Due to its measurement of temperature based on the functional relationship between light intensity and temperature, the light intensity itself is easily affected by various factors such as unstable light source illumination and fiber bending. In an ideal situation, if these factors affecting light intensity can be well controlled and the temperature light intensity function relationship can be accurately calibrated, temperature measurement with certain accuracy can also be achieved. עם זאת, the overall accuracy may be relatively low compared to fiber Bragg grating sensors and fluorescent fiber sensors.