Modeling the Operation of the Synchronous Generator of an Autonomous Electric Power System During the Test Input of Quasi-Direct Current

The authors developed a MATLAB model of an autonomous electric power system that accounts the saturation of a step-up power transformer magnetic system through the introduction of a piecewise-linear approximation of the magnetic flow dependency by a magnetizing current. The model was developed to study the synchronous generator operation during a high geomagnetic activity taking into account the operation of an automatic excitation regulator (AER). The modeling results show that, during a high geomagnetic activity, the stator current curve distorted due to the transformation of the reverse order harmonics occurring when the step-up transformer saturated. The second harmonic prevailing and reach up to 10% of the fundamental. During the power transformer saturation, the synchronous generator output active power reduced by 9.65%, and it minimum value corresponded with an achieving the maximum unilateral power transformer magnetic system saturation depth rather than the moment of achieving the maximum quasi-direct current. The AER operation results in a smaller reduction of the active generator power, approximately by 2%. As the synchronous generator active power decreases, the reactive power is increased. During the AER operation, reactive power generation increases by almost 14 times since the moment when the magnetic system of the power transformation begins to saturate. Without AER, the generator bus voltage is reduced (by 6%), while the AER operation leads to the voltage increase by 1.5%. After the quasi-direct current input is over, there is an trend for the recovery of the initial active and reactive power generation levels of the synchronous generator.