How to measure temperature in transformers? The advantages of using fluorescent optical fibers to measure windings

Száloptikai hőmérséklet-érzékelő, Intelligens felügyeleti rendszer, Elosztott száloptikai gyártó Kínában

Transformer temperature measurement method
There are three types of online measurement methods for transformer winding temperature, namely direct measurement method, indirect calculation method, and thermal simulation measurement method.

Direct measurement method

The direct measurement method usually involves embedding temperature measuring elements during manufacturing, and the number of embedding points is directly proportional to the accuracy of the measurement. For example, placing fiber optic temperature sensors near the winding or in the winding wire cake can directly obtain the hot spot temperature of the transformer winding. This is because the signal received by the fiber optic temperature sensor is not easily affected by the electromagnetic field inside the transformer, and the measured results are more accurate. But this method also has its drawbacks, on the one hand, it is difficult to maintain and has extremely high costs; On the other hand, embedding sensors inside the winding requires high insulation structure design requirements, which can easily affect the normal operation of the transformer. Moreover, due to the uncertainty of the location of the winding hotspot, the location where the sensor is buried may not necessarily be the hottest spot, and the measurement result may not be the hotspot temperature of the winding.
For dry-type transformers and oil immersed transformers, the testing voltage is usually 500V to 5kV (the specific voltage should be selected according to the rated voltage level of the transformer). The testing method is the same, but the testing environment should be different. Dry type transformer testing should be conducted in a dry environment. The temperature rise testing methods include direct load method, mutual load method, cyclic current method, zero sequence current method, short circuit method, stb. Ezek közé tartozik, the short circuit method requires the lowest test voltage and the smallest power capacity. For oil immersed transformers, the national standard stipulates that the short circuit method is the standard method for temperature rise testing.

Indirect calculation method

The indirect calculation method is based on setting a thermal model for the insulation structure of transformers, combined with manufacturing experience and standards IEC345/GB1564, to derive a formula for calculating the temperature rise of hotspots. Its advantages are economy, simplicity, and strong practicality; The disadvantage is that the calculations are complex, many of which are based on experience and have weak universality. They are usually not applicable on transformer sites, and different insulation structures can lead to certain deviations in the results.
Thermal simulation measurement method
Thermal simulation method is to install thermal simulation temperature measuring instruments (such as winding temperature indicators, stb.) in transformers to convert the winding temperature. The advantage of this method is that it is economical and can directly start the cooling system; The disadvantage is poor accuracy and there is a certain time difference in measuring temperature.

The principle of measuring winding temperature with fluorescent optical fiber

The fluorescence fiber optic temperature measurement system is a technology that utilizes the excitation of fluorescent substances inside the optical fiber to achieve temperature measurement. When the excitation light source is incident on an optical fiber containing a fluorescent substance, the fluorescent substance will be excited and emit a specific wavelength of fluorescent signal, and its afterglow is proportional to temperature. By detecting the changes in the afterglow of this fluorescent signal, the temperature at the location of the optical fiber can be calculated. Kifejezetten, by coating the end of the optical fiber with a fluorescent substance and measuring the decay time of fluorescence energy, the temperature value of the measured point can be obtained by utilizing the intrinsic afterglow time temperature correlation of the fluorescent substance. The temperature of the winding can also be calculated by monitoring the fluorescence lifetime time. Real time, long-distance, and high-precision temperature monitoring can be achieved through appropriate fiber optic transmission, excitation light sources, and data processing.

The advantages of using fluorescent optical fibers to measure winding temperature

high-precision
Fluorescent fiber optic temperature sensors have high temperature measurement accuracy and can achieve precise monitoring of transformer winding temperature. The fiber optic temperature sensor using fluorescence effect is suitable for a temperature range of -50 to 200 °C, with an accuracy of about ± 1 °C. It can monitor the temperature changes of transformer windings in real time and provide accurate measurement results, so as to timely grasp the subtle changes in winding temperature and help to accurately judge the operation status of transformers.

Strong anti-interference ability
Due to the excellent electrical insulation of optical fibers, the fluorescent fiber temperature measurement system is not affected by the internal electromagnetic field of transformers and can operate stably in high-voltage and strong magnetic field transformer operating environments. This feature makes the measurement results more reliable, reduces measurement errors caused by interference, and ensures the accuracy and effectiveness of temperature monitoring data. It is particularly important for equipment such as transformers, which have complex internal structures and generate a large amount of microwave and electromagnetic interference during operation.

quick response

Fiber optic sensors have a fast response speed and can promptly detect abnormal conditions in transformer winding temperature. Once there is an abnormal increase or fluctuation in the winding temperature, the fluorescent fiber optic temperature sensor can quickly capture the temperature change signal and provide timely feedback to the monitoring system, so that the operation and maintenance personnel can take timely measures to deal with it, avoid equipment failures, and ensure the safe and stable operation of the transformer.

High security
The fiber optic sensor in the fluorescent fiber optic temperature measurement system itself does not generate dangerous factors such as electric sparks, and has inherent safety characteristics. Using in the environment of high-voltage equipment such as transformers can avoid safety accidents caused by sensor factors and improve the safety and reliability of equipment operation. Ugyanakkor, its high temperature resistance also adapts to the high temperature environment during transformer operation, ensuring that it can still work normally and accurately measure temperature under high temperature conditions.

Flexible and easy to install

Fiber optics have the characteristics of flexibility and small size, which can be conveniently arranged on transformer windings. It does not take up too much space, is easy to install, and can flexibly adjust the position of sensors according to needs to better monitor the temperature at different positions of the winding. Internal optical fibers can be arranged on winding coils, iron cores, oil surfaces, and other parts according to design requirements. They are connected to external optical fibers through penetrators on flanges, and the optical signal is transmitted to the temperature measurement host through the optical fiber to analyze the temperature at the measurement point.

Low maintenance cost

Compared to some traditional temperature measurement methods, the maintenance cost of fluorescent fiber optic temperature measurement systems is lower. Due to its strong anti-interference ability and high stability, it reduces the maintenance workload and cost caused by fault repair and frequent calibration. And the components in the system, such as fiber optic sensors, have a longer service life, further reducing the maintenance costs of long-term operation and helping to improve the economic efficiency of transformer operation.

Comparative Analysis of Transformer Temperature Measurement Technologies

Comparison between direct measurement method and indirect calculation method

Direct measurement method
Advantages: If temperature measuring components (such as fiber optic temperature sensors) can be accurately embedded, the winding temperature can be directly obtained, and the measurement results are relatively accurate and intuitive. For example, placing fiber optic temperature sensors near the winding or in the winding coil of a transformer can directly obtain the hot spot temperature of the transformer winding. Due to the anti-interference property of fibers, the measured results are more accurate.
Disadvantages: Temperature measuring elements need to be embedded during manufacturing, and the number of embedding points affects accuracy. The embedding process is complex and requires high insulation structure design, which can easily affect the normal operation of transformers. And the location of the winding hotspot is uncertain, which may result in measurement results that are not the true hotspot temperature, and maintenance is difficult and costly. For example, when burying sensors in transformer windings, various factors such as the installation position of the sensors and the insulation coordination with the windings need to be considered. Once problems arise, maintenance is difficult and costly.

Indirect calculation method
Advantages: No need to embed complex temperature measuring components inside the transformer, relatively simple and economical. By setting a thermal model and combining manufacturing experience and relevant standards to derive a formula for calculating the temperature rise of hot spots, it has certain practicality for some preliminary estimates and simple evaluations of transformer operating conditions. For example, in some small transformers or situations where temperature accuracy is not extremely high, the approximate range of winding temperature can be quickly obtained through indirect calculation methods.
Disadvantages: Complex calculations, many calculations rely on experience, weak universality, and different insulation structures can cause deviations in the results. Moreover, in the actual application of transformers on site, they may be affected by various factors, making it difficult to guarantee accuracy and usually unable to accurately reflect real-time changes in winding temperature.

Comparison between direct measurement method and thermal simulation measurement method

Direct measurement method

Advantages: The direct measurement method theoretically allows for a closer approximation of the actual winding temperature, especially when using advanced temperature measuring components such as optical fibers, resulting in higher measurement accuracy. For example, fiber optic temperature sensors can directly sense the temperature around the winding, avoiding the accumulation of errors caused by indirect measurements.

Disadvantages: In addition to the difficulties in burial and high maintenance costs mentioned above, the measurement points of the direct measurement method are limited, making it difficult to fully reflect the temperature distribution of the entire winding. Due to the complex structure of transformer windings, it is difficult to embed sensors at all possible hotspots.

Thermal simulation measurement method

Advantages: The installation of temperature measuring instruments using thermal simulation method is relatively simple, and the economic cost is relatively low. And it can be directly associated with the cooling system. When the temperature reaches a certain value, the cooling system can be directly started to provide certain protection for the transformer. For example, in some conventional oil immersed transformers, thermal simulation temperature measuring instruments can convert the winding temperature based on oil temperature and other conditions, and then control the start-up of the cooling system.
Disadvantages: Poor accuracy, there is a certain time difference in the measured temperature, and it cannot accurately reflect the true temperature changes of the winding in real time. Due to the fact that the temperature is obtained through simulation conversion, there may be significant deviations from the actual winding temperature, especially in situations where the transformer load changes frequently or the operating conditions are complex.
Comparison between fluorescence fiber optic temperature measurement and other direct measurement methods

Fluoreszcencia száloptikai hőmérséklet mérés

Advantages: In addition to the direct measurement method that can directly obtain temperature, fluorescence fiber optic temperature measurement also has the characteristics of high accuracy and sensitivity, which can achieve precise monitoring of temperature. Ugyanakkor, it has the advantages of strong anti-interference ability and low maintenance cost. For example, its measurement accuracy is about ± 1 °C, and it can still accurately measure in complex electromagnetic environments. Due to the characteristics of optical fibers, its maintenance is relatively simple and the long-term operating cost is low.
Disadvantages: Although optical fibers are small and flexible, they still require certain techniques and processes for embedding in transformer windings. Improper embedding may affect measurement results. And the equipment cost of the fluorescent fiber temperature measurement system may be relatively high, including the procurement and installation costs of components such as fluorescent fiber and demodulation host.
Other direct measurement methods (such as traditional thermocouples, stb.)
Advantages: Traditional direct measurement methods such as thermocouples are relatively mature and have certain applications in some simple transformer temperature measurements that do not require particularly high accuracy. For example, in some small industrial transformers, thermocouples can be simply installed on the winding surface for temperature measurement.
Disadvantages: Thermocouples and other sensors are susceptible to electromagnetic interference, resulting in significant measurement errors in high electromagnetic environments such as transformers. Moreover, its accuracy is relatively low, and the response speed may be slow, which cannot meet the measurement requirements for high-precision and fast response of transformer winding temperature.

Application examples of different temperature measurement methods in transformers

Application examples of direct measurement method

In some large power transformers, in order to accurately monitor the winding temperature, the direct measurement method of placing száloptikai hőmérséklet-érzékelők in the winding wire cake is adopted. For example, in oil immersed power transformers of 110kV and above, due to the importance of the transformer and the high requirements for operational reliability, it is necessary to accurately grasp the temperature situation of the winding. By accurately embedding the fiber optic temperature sensor in the winding coil during manufacturing, real-time temperature information of the winding can be obtained. Operations personnel can adjust the load of the transformer in a timely manner based on these temperature data to avoid problems such as insulation aging caused by winding overheating. Meanwhile, these temperature data can also be connected to the monitoring system for remote monitoring and control. Once the temperature exceeds the set threshold (such as the alarm limit for winding temperature usually between 90 ℃ and 95 °C), an alarm signal can be issued in a timely manner to notify the operation and maintenance personnel to take corresponding measures, such as increasing the operating power of the cooling equipment or reducing the load on the transformer.

Application examples of indirect calculation method

In some small distribution transformers, due to their small size, relatively simple operating conditions, and low precision requirements for temperature measurement, indirect calculation methods are sometimes used to estimate winding temperature. For example, in some 10kV distribution transformers in rural areas, the hot spot temperature rise of the winding is calculated using empirical formulas based on parameters such as the rated capacity, load current, ambient temperature, and insulation structure of the transformer. This method can provide a rough assessment of the operating temperature of transformers without the need for complex temperature measurement equipment. Azonban, this method has certain limitations. For example, under special working conditions such as high temperatures in summer and sudden increases in transformer load, the calculated results may have significant deviations from the actual temperature. Következésképpen, operation and maintenance personnel need to combine experience and other monitoring methods (such as oil surface temperature monitoring) to comprehensively judge the operating status of the transformer.

Application examples of thermal simulation measurement method

In some ordinary oil immersed transformers, thermal simulation temperature measuring instruments (such as winding temperature indicators) are used to convert the winding temperature. For example, in some small and medium-sized factories’ power transformers, thermal simulation temperature measuring instruments calculate the winding temperature based on parameters such as oil surface temperature and transformer load current according to a certain conversion relationship. This method is economical and practical, and can be linked with the cooling system. When the calculated winding temperature reaches a certain value (such as around 70 °C, which may vary among different transformers), cooling equipment such as cooling fans or oil pumps can be started to cool the transformers. Azonban, due to its relatively poor accuracy, it may not be suitable in some situations where high temperature accuracy is required. It is necessary for maintenance personnel to regularly inspect and maintain the transformer to ensure its safe operation.

Application examples of fluorescence fiber optic temperature measurement

In some places where the reliability of transformer operation is extremely high, such as power transformers in large data centers or important substation transformers, fluorescent fiber optic temperature measurement systems have been widely used. Taking the 10000kVA oil immersed transformer in a large data center as an example, internal optical fibers are arranged in the winding, iron core, oil surface and other parts to measure temperature using the afterglow principle of fluorescent optical fibers. The internal optical fiber is connected to the external optical fiber through a connector on the flange, and the optical signal is transmitted to the temperature measurement host to analyze the temperature at the measuring point. The fluorescence fiber optic temperature measurement system can monitor the temperature of various parts of the transformer in real time and with high accuracy, with an accuracy of ± 1 °C. When the winding temperature shows an abnormal upward trend (such as a rapid rise from the normal operating temperature of 80 °C), the monitoring system can quickly detect and issue an alarm signal. Meanwhile, due to the strong anti-interference ability of the fluorescent fiber optic temperature measurement system, it can operate stably in the complex electromagnetic environment of transformers, reducing false alarms caused by electromagnetic interference. Ráadásul, its low maintenance cost also enables it to reduce operation and maintenance costs, improve the economy and safety of transformer operation during long-term operation.