Calculation of Transformer Capacity Suitable for Induction Generator Operation

Abstract

The proportion of using induction generators instead of synchronous generators in small-scale power plants where power generation output is not large is gradually increasing. Induction generators, like induction motors, are the biggest problem in that a voltage drop occurs due to a large inrush current when the grid is connected. Since the terminal voltage of an induction generator is usually low voltage, a voltage drop can greatly affect other equipment on the same branch line. In order to reduce the inrush current of the induction generator, a lot of research has been conducted through improvement of the starting method. Since inrush current is related to impedance, it is necessary to review the capacity of the transformer on the power side of the generator connected to the grid. In order to analyze the effect of voltage drop due to inrush current, the transformer capacity was calculated using the formula for calculating the capacity of the emergency generator capable of responding to the start of an induction motor. In this study, voltage drops at the primary and secondary sides of the transformer were calculated using a simplified equivalent circuit and an electromagnetic transient analysis program, respectively, for the transformer capacity obtained according to the inrush current ratio. As a result of the analysis, when connecting the induction generator to the grid, the magnitude of the inrush current did not differ in the transformer capacity. However, there is little difference in the voltage drop on the primary side of the transformer, but on the secondary side of the transformer, it was confirmed that the voltage drop was significantly different depending on the transformer capacity.