During the operation of dry-type transformers, a large amount of thermal energy is emitted. High temperatures exceeding the insulation tolerance can cause insulation damage and accidents in dry-type transformers. Therefore, the long-term safe and reliable operation of dry-type transformers cannot be separated from real-time monitoring and protection by temperature controllers. As the input terminal of temperature controllers, temperature sensors are crucial for sensing the actual temperature value of dry-type transformers. Based on the temperature input, temperature controllers make logical judgments to determine how to protect the transformer and send corresponding signals to the outside world. This is intelligent protection for the safe operation of dry-type transformers
The key link.
There are many types of fiber optic temperature sensors, including fluorescent and distributed fiber optic temperature sensors. Fluorescent sensors are used on dry-type transformers. The physical essence of fiber optic temperature sensors is to use the characteristic parameters of light waves transmitted in the fiber optic, such as amplitude, phase, polarization state, wavelength, and mode, which are sensitive to external environmental factors such as temperature, pressure, radiation, etc. It belongs to contact temperature measurement. This type of sensor is mainly used for temperature measurement in high-voltage equipment such as high-voltage switchgear.
Thermistor temperature sensors mainly include PT100 linear platinum resistance and PTC nonlinear thermistor. These two types of thermistors are mainly used for temperature measurement in dry-type transformers. The principle of PT100 linear platinum resistance is that when the platinum resistance is between 0 and 200 ℃, the resistance value increases linearly. As the temperature increases, the resistance value will increase linearly, showing a linear relationship; The principle of PTC nonlinear thermistors is to use the jump characteristics of resistance values at different temperatures to determine whether the temperature value has reached. For example, PTC150, when the temperature is below about 150 ℃, the resistance is small, but when the temperature change exceeds about 150 ℃, the resistance value sharply increases, thus determining whether the temperature value has been reached; These two types of sensors are installed on the transformer coil and serve as backup for each other. The PT100 linear platinum resistor is used to measure and display temperature values, and together with the PTC nonlinear thermistor, it participates in logical judgment to determine the high temperature alarm and over temperature trip signals of the temperature controller. This type of sensor is mainly used for temperature measurement in low-voltage equipment.
Due to the characteristics of the structure of dry-type transformers, voltage tap plates are installed on the high-voltage coils. Therefore, the high-voltage coils are placed on the outer side of the transformer, the low-voltage coils are placed on the inner side, and the innermost part is the iron core. Both the high and low voltage coils and the iron core will heat up during the operation of the transformer, resulting in poor heat dissipation conditions for the low-voltage coils. Therefore, the hottest temperature is usually on the low-voltage coils. Therefore, the temperature measurement point for overheating protection of dry-type transformers is set on the low-voltage coils.
Comparison of fiber optic temperature measurement and platinum resistance temperature measurement methods for dry-type transformers
Fiber optic temperature measurement transmits temperature signals, which are not affected by electromagnetic interference, have good electrical insulation performance, and can be carried out under strong electromagnetic interference. In addition, the transmission of optical wave signals does not generate electrical sparks, and will not cause combustion or explosion of the measured medium. It is resistant to high voltage, safe and reliable; But optical fibers are prone to damage under external forces and have relatively high costs.
Thermistors use cables and wires to transmit signals, which may be subject to electromagnetic interference. However, through corresponding design, they can pass anti-interference tests. In addition, the wiring of cables and wires is flexible and convenient, limited by location and environment, and has relatively low manufacturing costs.
Fiber optic temperature sensors are prone to damage and breakage, requiring users to handle the sensors and fibers with care and take certain measures to protect the temperature sensors and fibers from being cut by sharp tools. The optical fiber cannot be pulled too tightly, leaving a certain margin. When bending optical fibers, the turning radius should be 20 times larger than the diameter of the fiber itself. Fiber optic does not have load-bearing performance, so be careful not to hang any items on the fiber optic during use. Avoid excessive distortion of the fiber optic, otherwise its optical properties will deteriorate. Avoid contact between optical fibers and plasticizers or polymer materials containing plasticizers, otherwise it may cause damage to the optical fibers. Avoid friction between the fiber optic connector end face and any surface to prevent damage.
The thermistor temperature sensor is connected to the temperature controller through a cable, so there are no special requirements during installation or maintenance. It has strong adaptability to the environment and is relatively less prone to damage compared to fiber optic temperature sensors and optical fibers.
Based on the above, the two types of temperature sensors have different temperature measurement principles and different actual temperature sensing effects on transformers. However, both sensors can meet the needs of temperature controller temperature input. However, due to their different materials, the connection lines to the temperature controller are different. Therefore, whether during on-site installation and maintenance or later maintenance, thermistor temperature sensors are more suitable for complex on-site situations than fiber optic temperature sensors. Later maintenance is also simpler and more convenient. Therefore, thermistor temperature sensors will be applied in related fields for a long time. In the short term, fiber optic temperature sensors cannot completely replace thermistor temperature sensors. However, looking forward to the future, due to the advantages of fiber optic temperature sensors in harsh environments such as high temperature, strong chemical corrosion, and severe electromagnetic interference, etc, If the cost of fiber optic temperature sensors can be reduced to a level that is not much different from that of thermistor sensors, and the wire materials for transmitting signals can adapt to the needs of the on-site environment, that is, the durability can be greatly improved, fiber optic temperature sensors still have a relatively broad application prospect.