Research on secondary voltage distortion of three-phase three-element combined transformer basedon Yyn0 wiring mode

At the combined instrument transformer operation site, it was found that a three-phase three-element combined instrument transformer under Yyn0 connection had a surge in secondary side voltage harmonic content after years of operation. Aiming at the abnormal phenomenon of harmonic voltage on the secondary side of combined transformer, this paper analyzes the generation mechanism of harmonic voltage when the neutral point of the primary side is suspended, determines the key factors affecting the phenomenon, and verifies it through the simulation model of three-phase three-element combined transformer built by Maxwell. Tests simulating field conditions were carried out on a three-phase four-wire combined transformer test platform. The data error between the secondary side voltage test value and the simulation value did not exceed 5%, verifying the effectiveness of the simulation model.