What winding configuration in a hydro-generator is most resistant to the effects of third-harmonic currents?

A delta-connected winding configuration in a hydro-generator is the most resistant to the effects of third-harmonic currents. Third-harmonic currents are multiples of the fundamental frequency (e.g., 180 Hz in a 60 Hz system) that can arise due to non-linearities in the generator's magnetic circuit. These harmonics, if not properly addressed, can cause overheating, increased losses, and voltage distortion. In a wye (star)-connected generator with a grounded neutral, third-harmonic currents can flow freely in the neutral connection, leading to the problems mentioned above. However, in a delta-connected winding, the third-harmonic currents circulate within the closed delta loop. Because the sum of the third-harmonic voltages around the delta loop is ideally zero, these currents are largely confined within the winding itself. This circulating current does cause some additional heating in the windings, but it prevents the third-harmonic currents from propagating into the external power system, which mitigates the risk of voltage distortion and interference with sensitive equipment. While a delta connection doesn't eliminate third harmonics, it effectively contains them, making it a preferred configuration for generators where harmonic mitigation is a priority.