Model of a highly saturated three‐phase autotransformer with tertiary winding and five‐limb core and analysis of a time‐varying short‐circuit transient

The paper deals with the model of a highly saturated three‐phase autotransformer and the analysis of a power system short circuit with topological configuration changing during the transient (time‐varying configuration fault). The power system includes two power networks interconnected by a five‐limb core autotransformer rated 400 MVA, 400 kV/230 kV, with an internal tertiary delta‐connected winding. The short circuit considered here occurs on the 230 kV side and changes in sequence during the transient from line‐to‐earth short circuit to a line‐to‐line‐to‐earth short circuit to a three‐phase short circuit. This complex fault is intended to reproduce a real short circuit due to the failure of a current transformer in a transformer station which involves the two current transformers of the adjacent phases. It gives peak currents much higher than those obtained with conventional time‐invariant configuration short circuits. The proposed non‐linear circuit model of the autotransformer takes into account the actual configuration of both the core and the windings in highly saturated operations. The simulation of the transient is carried out by the ATP program.