There are two main transformer temperature measurement methods, one is the oil surface temperature and the other is the winding temperature.
There are also two temperature measurement methods for oil surface temperature, one is pressure type, and the other is platinum resistance temperature measurement.
There is a kind of liquid in the pressure probe. According to the temperature, the liquid expansion degree is different. At the end of the liquid conduit is a sensing device that measures the pressure value. According to the pressure, it is converted into a temperature signal and sent out. Common signal types are 0-5V voltage signal, 4-20mA current signal, pt100 platinum resistance signal, RS485 signal. This temperature measurement method is widely used.
Platinum resistance temperature measurement is directly used as a platinum resistance probe. At present, there are few manufacturers that can make this kind of thermometer, and the price is expensive, and there are not many practical applications.
There are also two methods for winding temperature measurement, one is the method of transformer conversion, and the other is optical fiber temperature measurement.
The transformer conversion is based on the pressure temperature measurement, first the oil surface temperature, and then according to the relationship between the secondary current of the casing CT and the temperature conversion, superimpose a copper oil temperature difference on the oil surface temperature, and simulate the winding temperature. This measurement method is not accurate, it is only a theoretical calculation value. But it is the most commonly used method.
Optical fiber temperature measurement is a new technology, which requires temperature measurement components to be preset in the transformer. However, due to insulation reasons, this method has inherent defects, especially in UHV transformers. It is quite difficult to apply.
Recently, manufacturers are also required to provide portable infrared thermometers. This can only be used for inspection purposes. It measures the temperature of external structural parts and cannot be considered as a temperature measurement method for the main transformer itself.