What are the intelligent monitoring systems for substations? How to use fluorescent fiber optic monitoring for transformer temperature

Fibra optica temperatus sensorem, Magna ratio intelligentis, Distribuit fibra opticus opticus in Sinis

1、 Components of the intelligent monitoring system for substations
The intelligent monitoring system for substations is an important technical means to ensure the safe and stable operation of substations, covering multiple monitoring contents and components.

（1） Equipment operation status monitoring
Monitoring of electrical equipment parameters
Real time monitoring of operating parameters of various electrical equipment in the substation, such as voltage, current, potentia, etc. of transformers. By installing sensors on the device to obtain these parameters, the system can promptly alert if the parameters exceed the normal range. Exempli gratia, current overload may cause equipment to overheat or even damage. By accurately monitoring the current, potential problems can be detected in advance. This helps power workers to adjust the operation status of equipment in a timely manner, avoid faults, and improve the reliability of power supply in substations.
For devices such as circuit breakers and isolating switches, their opening and closing status can also be monitored. Intelligent analysis of the status of its opening and closing signs ensures the correctness of device operation and prevents safety risks caused by misoperation. This is particularly important in the daily switching operations of substations, which can effectively ensure the stable operation of the power system and the safety of operators.
Equipment temperature monitoring
The equipment in the substation generates heat during operation, especially large equipment like transformers. Excessive temperature can affect the performance and lifespan of equipment, and even cause malfunctions. ergo, monitoring device temperature is an important component of intelligent monitoring systems. In addition to transformer temperature monitoring (which will be described in detail later), it also includes temperature monitoring of equipment and busbars inside the switchgear. Exempli gratia, real-time monitoring of the surface or internal temperature of equipment can be achieved through infrared thermal imaging technology or fiber optic temperature sensors to promptly detect temperature anomalies such as local overheating.
Equipment insulation performance monitoring
The insulation performance of electrical equipment is directly related to the safe operation of the equipment. The intelligent monitoring system can evaluate the insulation status of equipment by monitoring parameters such as insulation resistance and partial discharge. Exempli gratia, partial discharge is an important indicator of insulation degradation, and by installing partial discharge sensors, partial discharge signals inside the equipment can be captured. Based on the characteristics of signal strength, frequentia, etc., determine the health status of insulation. If the insulation performance decreases, it may lead to serious faults such as equipment short circuit and grounding. Monitoring the insulation problem in advance and taking measures, such as replacing insulation components, can effectively extend the service life of the equipment and reduce maintenance costs.
（2） Environmental monitoring
Temperature and humidity monitoring
The temperature and humidity inside the substation have a certain impact on the operation of the equipment. Excessive humidity may cause equipment to become damp, leading to decreased insulation performance, corrosion, and other issues; Excessive or insufficient temperature can also affect the performance and lifespan of the equipment. By installing temperature and humidity sensors in the substation, real-time temperature and humidity data of the environment can be obtained. Exempli gratia, in some southern humid areas, humidity monitoring is particularly important. Once the humidity exceeds the set threshold, the system can activate dehumidification equipment such as dehumidifiers to keep the environment dry and protect the equipment from the hazards of humidity.
Water immersion monitoring
Flooding may be caused by factors such as rainfall or water pipe leaks. If there is flooding in the substation, it may cause serious damage to electrical equipment. Water immersion monitoring sensors are usually installed in low-lying areas of substations, cable fossas, and other places that are prone to water accumulation. Once water immersion is detected, the system will immediately sound an alarm so that staff can take timely drainage measures to prevent equipment from being damaged by water immersion.
Smoke detection monitoring
Smoke detection monitoring is to prevent the occurrence of fires. There are a large number of electrical equipment in the substation, and if faults such as short circuits and overloads occur, they may cause fires. Smoke detectors can detect smoke in a timely manner. Once smoke is detected, the system will trigger an alarm signal and can also be linked with the fire extinguishing system, such as activating fire extinguishers, fire water sprinklers, etc. (if equipped), to minimize the damage of fires to substations.
（3） Video surveillance and intelligent analysis
Video surveillance function
There are multiple cameras installed in the substation, which can provide comprehensive video monitoring of various areas of the substation. These cameras have multiple functions, such as the ability to capture clear images during both day and night, and some cameras also have infrared fill light function, which can work normally even at night or in low light environments. Video surveillance can real-time view the appearance status of equipment and personnel activities in the substation. Exempli gratia, staff can use video surveillance to check for any abnormalities in the appearance of transformers, such as oil leakage, smoke, or unauthorized personnel entering hazardous areas of substations.
Intelligent analysis function
In addition to basic video surveillance functions, the intelligent monitoring system also has intelligent analysis capabilities. Exempli gratia, facial recognition of personnel in the video allows only authorized personnel to enter specific areas of the substation, which helps improve the security of the substation. Simul, intelligent analysis of the operating status of the equipment can also be carried out, such as analyzing the color changes of the equipment appearance (which may indicate abnormal temperature), the displacement of equipment components (which may indicate looseness or malfunction), etc., to assist in determining the operating status of the equipment. This intelligent analysis function can reduce the workload of manual inspection and improve the efficiency and accuracy of monitoring.
（4） Communication Network and Data Processing
Communication Network
The various monitoring devices in the substation intelligent monitoring system need to transmit the collected data to the monitoring center through a communication network. The communication network can adopt a combination of wired communication (such as fiber optic communication) and wireless communication (such as ZigBee, Wi Fi, 4G/5G, etc.). Fiber optic communication has the advantages of fast transmission speed and strong anti-interference ability, making it suitable for transmitting large amounts of real-time monitoring data, such as equipment operating parameters, video images, etc; Wireless communication, on the other hand, has the characteristics of high flexibility and easy deployment, and is suitable for networking some sensor nodes, such as temperature and humidity sensors, water immersion sensors, etc. Through a reliable communication network, ensure that monitoring data can be accurately and timely transmitted to the monitoring center for subsequent analysis and processing.
data processing
At the monitoring center, a large amount of monitoring data received needs to be processed. Data processing includes operations such as storage, analysis, and mining of data. Data storage can use a database system to store different types of monitoring data according to certain rules for subsequent queries and analysis. Data analysis can use various algorithms, such as data filtering, trend analysis, etc., to extract useful information from massive data. Exempli gratia, by analyzing the long-term trend of transformer temperature data, the health status of the transformer can be predicted, and maintenance and repair work can be arranged in advance. Data mining techniques can also discover the correlation between different monitoring data, such as the relationship between temperature and equipment operating power, providing a basis for optimizing the operation of substations.

2、 Principle of Transformer Temperature Fluorescence Fiber Optic Monitoring
Transformer temperature fluorescence fiber monitoring is an advanced temperature monitoring technology based on fluorescence characteristics.
（1） The characteristics of fluorescent substances and the relationship between fluorescence afterglow and temperature

Fluorescent optical fibers contain specific fluorescent substances that emit fluorescent signals when exposed to excitation light. Its important characteristic is the specific relationship between fluorescence afterglow (i.e. the time of fluorescence decay) and temperature. At lower temperatures, the fluorescence afterglow is longer; As the temperature increases, the molecular motion of fluorescent substances intensifies, energy transfer and conversion accelerate, resulting in a shortened fluorescence afterglow. Exempli gratia, some rare earth doped fluorescent materials experience a gradual decrease in fluorescence afterglow from a few milliseconds to several hundred microseconds as the temperature increases from 20 ° C to 100 ° C. The quantifiable relationship between fluorescence afterglow and temperature is the basis for fluorescence fiber optic temperature monitoring.

（2） The role of optical fiber in temperature monitoring
Optical signal transmission
Fiber optic cables play an important role in transmitting optical signals in this monitoring system. Fiber optics have excellent optical performance, which can efficiently transmit excitation light to the location of fluorescent substances, and also transmit the fluorescence signal emitted by fluorescent substances to detection equipment. The transmission loss of optical fiber is low, and even over long distances (such as inside large transformers, where optical fiber may need to transmit signals from the winding to external detection equipment), it can ensure effective signal transmission. Exempli gratia, in some large substations, optical fibers can extend from the depths of the windings to the monitoring host outside the transformer, with a transmission distance of up to tens of meters, and the signal attenuation is relatively small.

Electrical insulation and anti-interference
There is a strong electromagnetic field inside the transformer, and optical fibers are made of insulating materials such as glass or plastic, which have excellent electrical insulation performance. This enables optical fibers to operate normally in harsh electromagnetic environments inside transformers without being affected by electromagnetic interference. Compared with traditional electrical signal transmission methods, such as using thermocouples or resistance thermometers, optical fibers are not affected by noise interference caused by electromagnetic induction, thus providing more accurate temperature measurements. Exempli gratia, in the vicinity of transformer windings, the electromagnetic field strength may reach thousands of Gauss, and traditional electrical sensors may produce significant measurement errors, while fluorescent fiber optic sensors can accurately measure temperature.

（3） Overall monitoring principle
Conversion of temperature and fluorescence signals

In the transformer temperature fluorescent fiber monitoring system, fluorescent fiber sensors are arranged at key parts of the transformer, such as windings. When an external light source excites the fluorescent substance in the fluorescent fiber, the fluorescent substance emits a fluorescent signal, and the detection system measures the afterglow time of the fluorescent signal. Based on the pre calibrated relationship curve between fluorescence afterglow time and temperature (which was obtained through extensive experiments and calibration work, such as accurately measuring the afterglow time of fluorescent substances at different temperatures and establishing mathematical models), convert the measured fluorescence afterglow time into corresponding temperature values. This achieves the conversion from fluorescence signal to temperature, allowing for real-time monitoring of temperature changes in transformers.

System composition and collaborative work

The entire monitoring system mainly consists of a light source, fluorescent fiber optic sensors, detection system, and data processing system. The light source provides excitation light, and the fluorescence fiber sensor senses temperature and generates corresponding fluorescence signals. The detection system measures the relevant parameters of the fluorescence signal (such as afterglow time), and the data processing system processes, analyzes, and stores the detected data. Exempli gratia, the data processing system can display the collected temperature data in real time, determine the alarm threshold (if the temperature exceeds the set safety threshold, the system will issue an alarm), and perform long-term trend analysis on the temperature data to evaluate the health status of the transformer.
3、 Steps for Fluorescent Fiber Optic Monitoring Transformer Temperature
（1） Sensor layout
Determine the monitoring location
Before conducting fluorescence fiber optic monitoring of transformer temperature, the first step is to determine the placement of sensors. The temperature distribution of different parts inside the transformer is uneven, for example, the hot spot temperature of the winding is often the most important concern. Hotspot refers to the area where heat is accumulated in certain local positions of the winding during the operation of a transformer due to the heat generated by the current passing through the winding, resulting in a relatively high temperature. According to the structure and thermal characteristics of transformers, fluorescent fiber optic sensors are usually arranged at key parts of the winding, such as the upper or lower layer near the winding, as well as the middle part of the winding. Insuper, sensors may need to be installed at locations such as the iron core and oil passages to comprehensively monitor the temperature inside the transformer. This requires a deep understanding of the heat transfer mechanisms such as conduction, convection, and radiation in transformers to ensure that sensors can accurately monitor temperature changes inside the transformer.

Exempli gratia, for oil immersed transformers, the flow of oil has a certain impact on temperature distribution. In areas with slower oil flow rates, heat may accumulate more easily, so placing sensors in these areas can better monitor potential temperature anomalies. Simul, the installation method of the sensor also needs to be considered to ensure that the sensor is in close contact with the internal components of the transformer, so as to accurately sense temperature changes. For windings, sensors can be installed by winding or embedding, while for the surface of the iron core, sensors can be installed by pasting or fixing fixtures.

Sensor installation

After determining the placement of the sensor, proceed with the installation of the sensor. For fluorescent fiber optic sensors, the installation process needs to follow strict operating procedures. Uno modo, it is necessary to ensure that the fiber optic part of the sensor is not damaged, as the integrity of the fiber optic is crucial for the transmission of optical signals. During the installation process, special tools and equipment may be required, such as fiber fusion splicers (if fiber segments need to be connected). For sensors embedded in windings, it is important to avoid affecting the insulation performance of the windings. Exempli gratia, the insulation paper or insulation paint layer of the winding cannot be damaged during installation. Simul, the sensor should be fixed after installation to prevent displacement or damage to the sensor due to vibration or other reasons during the operation of the transformer. For the case of connecting internal and external optical fibers through flanges, it is necessary to ensure good sealing of the flanges to prevent oil leakage to the fiber optic connection and affect the transmission of optical signals.

（2） Signal excitation and acquisition

Selection and setting of excitation light source

Choosing the appropriate excitation light source is an important step in fluorescence fiber monitoring. The wavelength of the excitation light source needs to match the excitation wavelength of the fluorescent substance in the fluorescent fiber. Generally speaking, commonly used excitation light sources include laser diodes, etc. Exempli gratia, for some rare earth doped fluorescent fibers, the excitation wavelength may be between 400-500nm, and a laser diode of the corresponding wavelength needs to be selected as the excitation light source. When setting up the excitation light source, factors such as the power and stability of the light source should be considered. The power of the light source should not be too high to avoid causing light damage to the fluorescent substance, affecting its service life and fluorescence characteristics; interea, the stability of the light source should be good to ensure the reproducibility of the fluorescence signal generated by each excitation. Exempli gratia, if the power fluctuation of the light source is large, it may cause the measured fluorescence afterglow time to be unstable, thereby affecting the accuracy of temperature measurement.

Collection of fluorescence signals

When the excitation light source is irradiated onto the fluorescent fiber sensor, the fluorescent substance emits fluorescent signals, which need to be collected by a detection system. The detection system usually includes components such as photodetectors. Photodetectors can convert received fluorescent light signals into electrical signals for subsequent processing. When collecting fluorescence signals, attention should be paid to factors such as the angle and distance of collection. Because the intensity of fluorescence signals varies at different angles and distances, in order to ensure accurate collection of fluorescence signals, it is necessary to determine the optimal collection angle and distance based on the characteristics of the sensor and detection system. Exempli gratia, for some fiber optic sensors, collecting fluorescence signals at a 45 degree angle to the photodetector may achieve better results. Simul, in order to reduce the interference of external stray light, the detection system may be equipped with devices such as light shields.

（3） Temperature Calculation and Data Processing

Calculate temperature based on fluorescence afterglow

After collecting the fluorescence signal, the detection system will measure the afterglow time of the fluorescence signal. Calculate the corresponding temperature value based on the pre established relationship model between fluorescence afterglow time and temperature. This relationship model was obtained through extensive experimentation and calibration. Exempli gratia, in the laboratory, fluorescent fiber optic sensors are placed in constant temperature environments at different temperatures to measure their fluorescence afterglow time. deinde, mathematical expressions for fluorescence afterglow time and temperature are obtained through data fitting and other methods, such as quadratic or exponential functions. In usu, by substituting the measured fluorescence afterglow time into this mathematical expression, the temperature value inside the transformer can be calculated.

Data Processing and Analysis

The calculated temperature data requires further processing and analysis. Data processing includes operations such as filtering and smoothing of data to remove noise and errors during the measurement process. Exempli gratia, digital filtering algorithms such as mean filtering, median filtering, etc. can be used to process temperature data, making the data smoother and more accurate. In terms of analysis, temperature data can be displayed in real time so that staff can intuitively understand the temperature condition of the transformer. Simul, an alarm threshold can be set, and the system will issue an alarm when the temperature exceeds the set safety threshold. Insuper, through long-term trend analysis of temperature data, the health status of transformers can be evaluated. Exempli gratia, if a gradual increase in temperature is found, it may indicate potential faults in the transformer, such as aging of winding insulation, which require further inspection and maintenance.

4、 Example of Fluorescence Fiber Optic Monitoring for Transformer Temperature

1. Installation and configuration of oil immersed transformer system
In the temperature monitoring project of oil immersed transformers in a large substation, the installation of a fluorescent fiber optic monitoring system was first carried out. According to the structural characteristics of the transformer, fluorescent fiber optic sensors are arranged at multiple key positions of the winding, including the top, middle, and bottom of the winding, as well as near the iron core. The sensor is installed on the winding through a special fixing device to ensure close contact with the winding without affecting the insulation performance of the winding. The internal optical fiber is connected to the external optical fiber through a flange, and the external optical fiber transmits the optical signal to the temperature measurement host located near the transformer. The temperature measurement host is equipped with a stable excitation light source, high-precision photoelectric detector, and powerful data processing system. The excitation light source selected a laser diode with a wavelength of 450nm, and its power was precisely adjusted to meet the excitation requirements of the fluorescent substance without causing damage to it.

In terms of data processing system, an appropriate data collection frequency has been set, such as collecting temperature data every 5 minutes. Simul, alarm thresholds were set based on the operating parameters and historical data of the transformer. For this oil immersed transformer, when the winding temperature exceeds 120 ° C, the system will issue a high temperature alarm signal. In order to ensure the reliability of the system, a comprehensive test was conducted on the entire system after installation, including optical transmission performance testing of optical fibers, temperature response testing of sensors, etc.

Operation monitoring and fault warning
During the daily operation of the transformer, the fluorescent fiber optic monitoring system continues to work. By collecting and analyzing temperature data in real-time, staff can understand the temperature distribution inside the transformer at any time. Exempli gratia, during the high temperature period in summer, due to the large load on the transformer, the winding temperature rises slightly. The monitoring system accurately captured temperature changes and promptly issued warning information when the temperature approached the alarm threshold. This enables the staff to take measures in advance, such as adjusting the load of the transformer, strengthening ventilation and heat dissipation, etc., to avoid faults that may be caused by further temperature rise. During a single operation, the monitoring system discovered an abnormal increase in temperature at a certain location of the winding. Upon further inspection, it was found that the blockage in the oil passage at that location was causing poor heat dissipation. By promptly cleaning the oil passage, the issue of abnormal temperature was resolved, avoiding potential transformer failures and ensuring the normal operation of the substation.

2. Example of temperature monitoring for dry-type transformers

Sensor layout and installation characteristics

For the dry-type transformer in the distribution room of a certain factory, the layout of sensors is different when using fluorescent optical fiber to monitor temperature. Due to the fact that the heat dissipation method of dry-type transformers is mainly air convection, the heat distribution is relatively uniform, but the end of the winding is still an area where the temperature is prone to rise. ergo, in terms of sensor layout, fluorescent fiber optic sensors are mainly arranged at the ends and middle parts of the winding. When installing sensors, considering the compact structure of dry-type transformers, miniaturized sensors were used and fixed on the winding surface using special fixtures. This installation method not only ensures good contact between the sensor and the winding, but also facilitates installation and maintenance.