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 ATP-EMTP 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.

Keywords:

• neutral grounding
• transformer winding connection
• voltage sags
• voltage swells
• interruptions
• mitigation
• short-duration voltage variation
• power quality
• load connection
• distribution system

Acknowledgment

The authors are gratefully Younes Mohammadi for the comments on the paper.

Additional information

Funding

This paper was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

Notes on contributors

Lucas Araujo da Costa

Lucas Araujo da Costa was born in Porto Alegre, Rio Grande do Sul, Brazil, September 25, 1991. He received the B.Eng. degree in electrical and M.Sc. degree in electrical engineering from Universidade Federal do Rio Grande do Sul (UFRGS), Brazil, in 2015 and 2018, respectively. He is currently a Ph.D. student at UFRGS. In 2019 and 2020, he was a visiting student at the University of Nottingham, United Kingdom. His research interests are power quality, power system grounding, fault location, and numerical transients simulation.

Daniel da Silva Gazzana

Daniel da Silva Gazzana was born in Veranópolis, Rio Grande do Sul, Brazil, December 6, 1977. He received the B.Eng. degree in mechatronics and the M.Sc. degree in electrical engineering from Pontifical Catholic University of Rio Grande do Sul (PUCRS) and the Ph.D. degree in electrical engineering from the Federal University of Rio Grande do Sul (UFRGS), Brazil, in 2002, 2004, and 2012, respectively. Currently, he is an Assistant Professor at UFRGS. His main research fields are grounding systems, lightning, power systems, and numerical methods.

Roberto Chouhy Leborgne

Roberto Chouhy Leborgne received the B.Sc. and M.Sc. degrees from Universidade Federal de Itajubá, Brazil in 1998 and 2003, and the Ph.D. degree from Chalmers University of Technology, Sweden in 2007. He is currently Associate Professor at Universidade Federal do Rio Grande do Sul, Brazil. His research interests are power quality, power systems analysis and fault location.