Integrated protection scheme for hybrid AC/DC transmission grids

• The transient characteristics of AC/DC intersystem faults are analyzed and summarized. • A whole set of protection scheme is designed to respond to AC/DC intersystem faults. • The protection can detect any intersystem failure within 10 ms. • Protection only uses the same side of the AC and DC electricity, communication delay is very small. Given the limited Right-of-Way (ROW) for transmission lines, AC and DC transmission lines are transferred in parallel and adjacent to each other, forming a hybrid AC/DC transmission overhead line system for the consumption of renewable energy. The system is affected by extreme weather or complex external environment, which is easy to induce AC/DC intersystem fault (ISF). As a new fault type, the unique phenomenon and characteristics of ISF challenge the conventional protection concepts. This paper analyzes the fault characteristics of hybrid AC/DC transmission overhead line system based on “Yang-Zhen” project in China. And the focus is on AC/DC intersystem faults, i.e. galvanic contact between DC and AC systems. On this basis, a new integrated protection scheme of hybrid AC/DC transmission overhead lines which can adapt to ISF is proposed in this paper. The findings of this paper are based on semi-physical simulation platform with detailed RTDS-models of the hybrid AC/DC overhead lines and the LCC-converters. The proposed protection scheme tests have been conducted and confirmed the results.