The temperature of transformer windings has a significant impact on the characteristics of the insulation material. Excessive winding temperatures can accelerate the rate of insulation material脆ification and reduce dielectric strength, posing a threat to the reliable operation of transformers. Therefore, accurate measurement and real-time monitoring of transformer winding temperatures are particularly important. Since transformer windings are located at high potentials, immediate and accurate temperature measurement must overcome challenges such as insulation and interference signals. Although existing research suggests the use of photoelectric sensors for accurate winding temperature measurement, due to their high cost and complexity, indirect measurement of winding temperature is still widely used.
Basic Principle of Transformer Winding Temperature Measurement:
The temperature measurement of the winding in oil-type power transformer engineering typically employs an indirect measurement method based on the "thermal simulation" approach. The winding temperature Tw of an oil-type transformer can be equivalently represented as:
Tw=T0+k*△Two
In the formula, T0 represents the transformer's upper oil temperature, △Two denotes the copper oil temperature difference, obtained through thermal simulation methods, and k is the thermal index, related to the transformer's volume and winding structure.
The detection system is primarily composed of a temperature sensor module, a temperature measurement compensation circuit, and a controller. Both the temperature measurement compensation circuit and the temperature controller are housed within the temperature sensor module, which is immersed in the high-voltage transformer oil. This module is used for magnetic induction high-voltage oil temperature measurement. The controller consists of two parts: a temperature controller connected to the on-site winding temperature watch, whose temperature readings are displayed on the temperature indicator; and a Pt100 thermistor, whose resistance value changes with temperature, with the collected temperature values used for the computer background management and video monitoring system.
The transformer winding temperature measurement compensation circuit is composed of a variable circuit and a heating circuit in series, leading to the secondary side of the current voltage transformer. The secondary side current I of the current voltage transformer is directly proportional to the winding load current. Part of current I is separated through the variable circuit, while the rest flows through the heating circuit, with the current flowing through the heating circuit denoted as Ih. When the winding passes through the load current, the heating resistor in the heating circuit generates an additional temperature under the effect of current Ih. The winding temperature detection system must be calibrated before application, which involves adjusting the resistance in the variable circuit to modify the size of Ih, thereby allowing the temperature generated by the heating circuit to simulate the copper oil temperature difference △Two. This enables the winding temperature to be indirectly measured in an accumulated manner.
