Online Measurement Of Transformer Winding DC Resistance

It is well known that the measurement of dc resistance in transformer winding is must to be conducted in manufacturing process、overhaul、acceptance trial、measuring the average temperature rise of windings and fault diagnosis, and it has the vital significance for finding the defects in transformer. At present, the various existing measuring methods are all limited to offline measurement which is bad for the realization of condition maintenance. A kind of online measurement methods of winding’s dc resistance is put forward. This method adopts power separation which can separate transformer’s core loss from winding’s copper loss, and then use copper loss and the current of winding to calculate the dc resistance. Through the field test, it proved the feasibility of the online measurement in transformer winding’s dc resistance. First of all, this paper sets up the simulation model of transformer. Through doing alternating voltage sampling and alternating current sampling in both primary side and secondary side of the transformer, the dc resistance of transformer winding can be calculated. This simulation model laid a theoretical foundation for the resistance’s analysis and calculation. Secondly,-takes three points method as an example, this paper revised the model of transformer winding which is used in dynamic measurement of dc resistance. Through the theoretical analysis and experimental verification, it confirmed the existence of incremental resistance in the model of transformer’s winding. The revised model can reflect the operating condition of transformer winding veritably. Thirdly, under the ac power supply excitation, the experiment of measuring winding’s dc resistance was conducted in both the two case of transformer’s unloaded state and loaded state, which laid the experimental basis for online measurement. Finally, it structured an online measurement system of transformer winding’s dc resistance by using Single Chip Microcomputer, and completed hardware design and software design in the system.In case the transformer is not off-stream, monitoring the dc resistance of winding in real time can omit the measuring content of winding’s dc resistance in preventive test, which will improve the work efficiency and the level of automation management greatly. What’s more, the realization of the on-line monitor will lay the foundation of the state overhaul of transformer in the future, and it also provide an important function for intelligent transformer.