Research of the distribution symmetrical components in an electrical system with a diesel generator at an unsymmetrical load

Abstract

Purpose. Investigation symmetrical components of current and voltage in microgrid elements with an autonomous synchronous generator of limited power, which works in parallel with a network transformer under the condition of non-metric load.

Methodology. During the research, visual programming methods were used in the Simulink/Matlab package, methods of electrical engineering theory in terms of determining symmetrical component currents and voltages in observation branches, methods of synthesizing schemes for replacing elements of electric power systems for symmetrical component currents, methods of data processing and construction diagrams using specialized software tools..

Findings. As a result the analysis known studies, it was established that under the condition of researching low-power generating systems in conditions of asymmetry, insufficient attention is paid to the nature of the asymmetric load. Using the well-known structure of a microgrid, which includes a synchronous generator, a machine load, and an external network transformer, its model was built, in which, by introducing asymmetric loads of various types, a series of experiments was implemented with the registration of voltages and currents of forward, reverse, and zero sequences in the branches of the network. The analysis of the results obtained during the research established that the positive sequence voltage in the case of a change in the active load does not change its level, under the same circumstances, in the case of an active-capacitive and active-inductive load, the voltage change has the opposite character. In the case of increasing asymmetry of an active-inductive nature, the positive sequence voltage decreases, and in the case of an active-capacitive one, it increases. The specified changes in some cases exceed 3%. Positive sequence currents in the case of active load imbalance differ slightly. In the case of a positive sequence current of the transformer, its continuous growth is observed, which in the case of active-capacitive and active-inductive loads exceeds the active one by an average of 1.5 times. Negative sequence currents in the studied model, which are formed by an asymmetrical load, are completely closed to the transformer, causing zero-sequence voltages, and the nature asymmetrical load significantly affects the value of these currents, a 61% increase was noted.

Originality. It was established that in a microgrid, which includes a synchronous generator, a machine load, a symmetrical active load of comparable power to the generator, an external network transformer, in addition to the fact of asymmetry caused by an asymmetrical load, the character of an asymmetrical load (active, active-inductive or active-capacitive).

Practical value. In the case of using in microgrids devices that provide an increase in the quality of electrical energy, for example, symmetrical devices, it is necessary, in addition to the asymmetry factor, to take into account the natural load that causes the latter.