K-factor transformers are transformers used to deal with harmonic generation loads. They are designed to withstand harmonic currents without exceeding the rated temperature of the insulated system. The K factor design compensates the stress on the insulation of transformer winding and prevents insulation breakdown and premature failure, thus prolonging the service life of transformer.
The K factor mainly affects the eddy current loss and stray loss of the transformer. The eddy current loss is related to the size of the conductor orthogonal to the leakage magnetic field, and the stray loss is due to the stray magnetic field in the iron core, clamps, oil tanks and other steel parts. The stray loss will cause the temperature of the metal structure of the transformer to rise. In view of the reasons for the two kinds of losses, the following points will be mainly paid attention to in the design of the transformer:
Because the leakage magnetic field is bent at the end of the coil, in order to reduce the leakage magnetic field passing through the end of the coil, the primary and secondary windings can be designed with equal height, which can reduce the eddy current loss concentrated at the end of the coil. It is well known that the eddy current loss is also related to the size of the transformer conductor. The thicker the conductor, the greater the eddy current loss. Therefore, foil winding or multiple strands can be used to reduce the eddy current loss.
Due to the additional effect of harmonic currents on the neutral point, the neutral point current is twice the phase current, so when designing the transformer, the neutral point connection busbar is twice the size of the phase busbar.
Due to the existence of current harmonics in the load, a shielding layer can be set between the primary winding and the secondary winding to reduce the impact of load harmonic currents on one side.
Because harmonic currents have an impact on stray losses, the stray losses of the transformer can be reduced by using non-magnetic materials to make the metal parts of the transformer.
Because of the existence of harmonic voltage, harmonic voltage will improve the magnetic density of iron core, increase the loss of iron core, and increase the excitation current, noise and temperature rise of iron core. The influence of voltage on the core is reduced by reducing magnetic density.
