A matrix method for the study of interferences in transformers neutrals due to HVDC ground current injection

Abstract

This paper discusses the occurrences caused during the commissioning of the ground electrode of the Porto Velho Converter Station, located at the North region of Brazil, and the methodology used to analyze and mitigate the problem.The converter station is composed of a group of agents and linked with two major power plants – Santo Antonio and Jirau, several 500 kV and 230 kV transmission lines and nearby substations. The main issue caused by an electrode at long distances is the DC current at transformers neutrals caused by ground potential difference between locations.The predicted current at the transformers neutrals are unacceptable, which main effect is the core saturation, resulting in audible noise, vibrations and excessive heating in the equipment. Due to the multi-agent nature of the station, the use of current blocking devices at third party assets are not an option.The paper will describe the investigation of alternatives, resulting in a site selection for a new electrode. We will emphasize the importance of a proper geologic survey and soil model, not only for the site selection but also for predict the ground potential rise, an effect which could extend for several kilometers.