Transformer temperature monitoring methods

There are several common ways to monitor transformer temperature:

Oil temperature monitoring

Oil surface thermometer: usually installed on the top of the transformer tank, used to measure the oil temperature of the upper layer of the tank, with on-site instructions and signal transmission function. Such as electric contact glass thermometer, through the temperature package temperature sensing displacement driven pointer to indicate the temperature, can also set the alarm temperature.
Buried thermometer: the temperature sensor is directly buried in the bottom of the transformer tank or winding, can more directly reflect the winding or the bottom of the oil temperature, but the installation and maintenance is relatively complex.
Thermistor thermometer: the use of thermistor resistance with temperature change characteristics to measure the oil temperature, high precision, commonly used in small transformers.

Winding temperature monitoring

Fiber optic temperature measurement: the use of fiber optic temperature sensors, such as fluorescent fiber optic sensors, will be buried directly in the transformer windings, can achieve real-time, accurate measurement of the hot spot temperature of the windings, with the advantages of anti-electromagnetic interference, electrical insulation, corrosion prevention, etc., suitable for high-voltage, high-current and other harsh environments, and can provide key data for the safe operation of the transformer.
Resistance method: The temperature is deduced by measuring the resistance change of the transformer windings, based on the characteristic that the resistance of a metal conductor increases with temperature. Need to accurately measure the winding resistance value and rated current resistance temperature coefficient and other parameters.
Infrared thermal imaging monitoring: the use of infrared thermal imaging camera to monitor the transformer winding, can visualize the temperature distribution on the surface of the winding, and quickly find overheating areas, but vulnerable to environmental factors, and can not directly measure the internal temperature.

mathematical modeling approach

Thermal modeling: Based on the design parameters of the transformer, such as loss, oil volume, heat dissipation method, etc., establish the heat balance equation and the calculation formula of oil temperature rise and winding temperature rise, and calculate the temperature of the top oil and winding hot spot. However, the accuracy of this method is affected by the accuracy of the parameters and the perfection of the model.
Finite element analysis model combined with rational fractional model: first obtain the specifications and design information of the transformer to construct a three-dimensional model, then carry out finite element analysis to obtain the electromagnetic field-temperature field coupling model, then use the rational fractional model to predict the inversion of the model, and finally establish a temperature detection model to process the operation data and obtain the hot spot temperature information.

Other monitoring modalities

Pressure thermometer: Measure the temperature through the principle of temperature-sensitive liquids or gases produce pressure changes when the temperature changes, with a wide range of temperature measurement, medium accuracy, simple structure, etc., but poor seismic resistance.
Temperature indication wax piece: using different melting point of the wax piece in the temperature rises to the melting point of the melting characteristics, intuitive indication of the transformer temperature is over a certain temperature value, low cost, simple to use, but can only provide the temperature over the limit of the warning, can not accurately measure the temperature.