Generator winding I2R losses and harmonic interference under variable frequency operation of an HVDC unit-connection scheme

Variable frequency operation of an HVDC unit-connection scheme may affect the generator winding I²R losses, and may cause harmonic interferences on both the AC and DC system. The purpose of this research is to determine the magnitudes of generator winding I² R losses under a certain frequency range so as to improve the efficiency of the hydro unit operation at nonrated head and output power. The generator winding additional I²R losses and harmonic interference, are investigated by using the EMTDC program and other subordinate programs. The overall study shows that the generator winding power losses will be increased as the operating frequency decreases under the condition of a fixed generator output. The magnitude of increased losses, though, will not exceed 8-10% of generator total winding I²R losses under normal system operating conditions. Harmonic interference, on the other hand, will become more severe in both the AC and DC systems, as compared to fixed frequency operation. Active or on line tuning harmonic filters may be considered for a particular variable frequency operation scheme being implemented