Do you know what common temperature measuring devices are used in oil-immersed transformers?

Commonly used temperature - measuring devices for oil - immersed transformers include thermal resistance thermometers, thermocouple thermometers, pressure - type thermometers, optical fiber thermometers, etc. The following is a detailed introduction:

Thermal Resistance Thermometer

• Working Principle: It utilizes the property that the resistance value of a thermal resistance changes with temperature. By measuring the resistance value, the temperature can be calculated. Thermal resistances are usually made of metal materials such as platinum and copper. Platinum resistance (Pt100) is widely used, and it has a good linear relationship between the resistance value and temperature.
• Characteristics: It features high accuracy, good stability, and a wide measurement range, generally from - 200℃ to 850℃, which can meet the temperature - measurement requirements of oil - immersed transformers. It has good linearity, which is convenient for signal processing and display. However, it is relatively sensitive to environmental electromagnetic interference and requires external measurement circuits and good shielding measures.
• Installation and Use: The thermal resistance is usually installed in the windings, oil, or other parts of the transformer where temperature needs to be measured. The signal is transmitted to the measuring instrument through wires for temperature display and recording.

Thermocouple Thermometer

• Working Principle: Based on the thermoelectric effect, two different types of conductors or semiconductors form a closed loop. When the temperatures at the two junctions are different, a thermoelectric potential is generated in the loop, and the temperature is determined by measuring this potential.
• Characteristics: It has an extremely wide measurement range, from - 270℃ to 2800℃, which is suitable for measuring the temperature of oil - immersed transformers under various operating conditions, especially in high - temperature environments. It has a fast response speed and can quickly sense temperature changes. The output signal is an electrical signal, which is convenient for remote transmission and control. However, its accuracy is slightly lower than that of thermal resistance thermometers, and cold - end compensation is required.
• Installation and Use: According to the measurement requirements, the measuring end of the thermocouple is installed at specific positions of the transformer, such as the hot spots of the windings and the tank wall, while the reference end is placed in an environment with a stable temperature to ensure the accuracy of the measurement.

Pressure - type Thermometer

• Working Principle: It consists of a temperature - sensing bulb, a capillary tube, and an indicating instrument to form a closed system. The temperature - sensing bulb is filled with a temperature - sensitive liquid. When the temperature changes, the volume of the temperature - sensitive liquid changes, and this change is transmitted to the indicating instrument through the capillary tube, causing the elastic element to displace and drive the pointer to indicate the temperature.
• Characteristics: It has a simple structure, low cost, good shock resistance, and does not require an external power supply, which makes it easy to install and use. However, its accuracy is relatively low, and the measurement distance is limited. Generally, the length of the capillary tube does not exceed 20m.
• Installation and Use: Generally, the temperature - sensing bulb is installed in the oil of the transformer tank, and the pressure change is transmitted to the indicating instrument installed outside the tank through the capillary tube to directly display the oil temperature.

Optical Fiber Thermometer

• Working Principle: It uses the fluorescence afterglow principle of optical fibers. By measuring the temperature difference at the temperature - sensing position of the optical fiber, the temperature change on the object surface is determined. After the temperature - sensing probe in the optical fiber sensor is heated, the fluorescent optical fiber changes, and the signal processing device obtains the temperature value based on this.
• Characteristics: It has the advantages of good electrical insulation, resistance to electromagnetic interference, resistance to chemical corrosion, small size, intrinsic safety, and stable performance. It can achieve multi - point distributed measurement and comprehensively monitor the internal temperature distribution of the transformer. It has high accuracy, high resolution, and good real - time performance. However, the cost is relatively high, and the technical requirements for installation and maintenance are high.
• Installation and Use: The optical fiber sensors are installed in the key parts of the transformer, such as the windings and oil ducts. The signals are transmitted through optical fibers to achieve accurate measurement and real - time monitoring of the internal temperature of the transformer.

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