Accurate Calculation of Electromagnetic Torque and Harmonic Characteristics of Hydro Generator Based on Positive and Negative Sequence Decoupling

Aiming at the technical problems of electromagnetic parameter analysis of large hydro generators, this paper innovatively proposes an electromagnetic torque analysis method based on the characteristics of fundamental electric quantity, with the core idea of positive and negative sequence decoupling. Under the condition of ungrounded neutral point, the method eliminates the interference of zero-sequence magnetic field and realises the decoupling of positive-sequence and negative-sequence components in the system. It models the generator as an independent positive-sequence network and negative-sequence network, decomposes the three-phase voltage and current into positive-sequence and negative-sequence components through symmetrical component transformation and establishes separate mathematical models for each sequence component to achieve independent analysis of their electromagnetic characteristics. By accurately modelling the actual connection relationship of each phase branch of the stator winding, the accurate mathematical model of the three-phase fundamental voltage, current and electromagnetic power of the stator side under the stable operation of the generator is constructed. The test results of the finite element simulation experiment platform based on 280 MVA large hydro generator show that the proposed method can effectively identify the fundamental electromagnetic torque and second harmonic electromagnetic torque under stable operating conditions, and the measured relative error range is 0.01%–9.41%, which has high engineering application accuracy.