How to measure temperature of transformer winding

Fiber optic temperature sensor, Intelligent monitoring system, Distributed fiber optic manufacturer in China

Why do transformer windings need temperature measurement

The hottest temperature of transformer windings is the main determining factor for the safe, economical operation, and service life of transformers. The aging caused by overheating of the insulation structure at the hottest point of the winding may develop into damage to the entire transformer. So transformer manufacturers and operating departments urgently need to monitor the temperature of transformer hotspots. Therefore, IEEE standard C57.12.00-2000 requires the ability to determine the temperature and location of hotspots.

Power transformers are one of the most critical equipment in the power transmission network, and their performance is of great significance for the reliable operation of the entire power grid. In a power transformer, a portion of the electrical energy is converted into heat generated by the transformer. Although this heat is relatively small compared to the total energy converted by the entire transformer, it can cause a significant temperature rise in the transformer. This thermal effect not only leads to a decrease in the insulation capacity and lifespan of the transformer, but also is a limiting factor for the actual operation of the transformer. Therefore, studying the temperature field of transformers, especially the hot spot temperature, is of great significance. As is well known, the capacity of a transformer is directly proportional to its economic and technical indicators. Therefore, with the continuous progress of new processes and technologies, the voltage level and individual capacity of power transformers will continue to increase. As the single-phase capacity of transformers gradually increases, the thermal problems in transformers become increasingly urgent to be solved. The overheating of transformer windings not only causes accelerated aging of insulation and affects its service life, but also causes malignant accidents due to local overheating of windings both domestically and internationally. These accidents have caused huge economic losses to industrial production and have had a huge adverse impact on society. So the heating problem of transformers is increasingly attracting the close attention of transformer design and usage departments.

Fiber optic temperature measurement of transformer winding

The thermal design of large transformer windings has always been mainly to calculate the average temperature rise of the transformer winding to the oil. To obtain the hot spot temperature rise of the winding, empirical formulas can only be used to estimate it. With the increasing demand for safe operation of transformers from users, thermal design based on average coil temperature rise can no longer guarantee the reliability of transformers. Due to the aging caused by overheating of the local insulation structure in the hottest part of the winding, it is possible to develop into damage to the entire transformer. Therefore, the safety, economic operation, and service life of the transformer mainly depend on the hottest temperature of the transformer winding. Therefore, accurate monitoring of the hot spot temperature of transformer windings has become a guarantee for the safe and economical operation of transformers. The traditional temperature measurement methods for power transformer windings include thermal resistance temperature measurement, thermocouple temperature measurement, and infrared temperature measurement. However, the winding is exposed to harsh environments such as high voltage, high temperature, and extremely strong electromagnetic interference. Thermistors and thermocouples transmit signals through metal wires and are susceptible to electromagnetic interference. Moreover, metal wires are exposed to insulation oil for a long time and are prone to short circuits after aging. Infrared thermometers cannot be installed inside transformers. Currently, they can only be used to measure the surface of oil tanks and the outer surface of transformers such as bushings, and the measurement results are affected by environmental temperature. Therefore, there is an urgent need for a new measurement method. Nowadays, countries around the world are generally shifting their focus to using fiber optic probes to directly measure the temperature of hotspots. Installing a fiber optic thermometer on a transformer does not significantly increase the overall production cost of the transformer, so foreign transformer manufacturers and operating departments widely adopt this technology.