Investigation of main and secondary transformers on mitigation of voltage sags, swells and interruptions in unbalanced medium voltage distribution systems

Abstract

Since voltage interruptions, sags and swells are Power Quality (PQ) disturbances with great economic impact, studies that seek alternatives to mitigate its effects have been conducted extensively. The PQ Brazilian standard names these disturbances as Short-Duration Voltage Variations (SDVVs), classified them in terms of magnitude, duration, and frequency of occurrence. These parameters are used to calculate the Impact Factor (IF) of SDVVs, a severity-characterization index of their incidence. In this context, this work assesses the influence of three-phase transformer winding connection and neutral grounding on the quantities of SDVVs and the IF observed by an industrial consumer in a distribution system. Fault simulations at ATPEMTP perform the study, considering two different winding connections for the secondary transformer and applying a grounding resistance to the neutral of the main transformer of the distribution system. The SDVVs are verified in two different ways: phase-to-ground and phase-to-phase voltages. It is observed that there are differences in these quantities and for the value of the IF due to the winding connection of the secondary transformer, the value of the neutral grounding resistance of the main transformer and the ways of voltage verification.