Increasing Reactive Load of a Generator–Transformer Unit under the Influence of Quasi-Direct Currents

The parameters of the magnetization current of a block transformer are determined when the magnetic system is saturated under the influence of a quasi-direct current, taking into account the equipment of a synchronous generator with an automatic excitation controller and the parameters of an adjacent electric-supply system. It is shown that the main harmonic of the magnetization current, which is proportional to the value of the quasi-direct current, is responsible for the multiple increase in magnetization power of the block transformer and is additive with respect to the reactive component of the synchronous-generator stator current. It is noted that the increase in the reactive load of the synchronous generator is the result of the action of the automatic excitation controller to maintain a constant voltage on the generator buses, since the magnetization power of the block transformer is compensated by the increase in reactive power generation of the synchronous generator by increasing the excitation current. The ranges of safe values of the quasi-direct current causing a slight increase in the magnetizing power of the block transformer, which can be compensated by an increase in the excitation current without reducing the active load of the synchronous generator, are established, as are as the critical values of the quasi-direct currents causing an increase in the magnetizing power. To compensate for such power, it is necessary to reduce the setting of the automatic excitation controller by voltage and/or the synchronous-generator active load.