Effects of the HVDC system on converter transformers

HVDC is a recognized economical and technical advantageous solution for long distance transmission, asynchronous interconnections and long submarine cables crossing. The number of projects already in operation or under consideration has increased in the last years, reflecting the global interest on this technology. The new converter designs have permitted HVDC to be used in a wide system application options, such as underground interconnections and offshore renewable energy generation. HVDC technology presents an economical solution for power transmission, with fewer losses when compared to equivalent high-voltage AC systems. The converters nonlinearity operation produces some effects in the transformers, such as, additional losses, vibration and noise level increase. In many cases, the design solution to deal with those effects is to increase margins, what may affect not only the transformer manufacturing cost, but also its operating life. This article discusses the most relevant effects produced by the line-commutated converters (LCC) technology listed on IEC/IEEE 60076-57-129 technical standard, analyzing the consequences into the converter transformer operation and design considerations.