Research and Analysis on Unbalanced Current of Annular Power Supply System
Since the phase sequences of short-distance untransposed common-tower double-circuit lines are different,unbalanced current caused by asymmetric parameter varies seriously.Therefore,a recursive algorithm was put forward to reduce the unbalanced current when multi-circuit common-tower double-circuit lines are switched in the same substation to optimize the phase sequence arrangement.When one single line of the common-tower double-circuit lines switches in other substation to form a annular power-supply system with a single/double-power-source,the unbalanced current would be influenced by reactive power compensation due to varied impedance.After analysis,the approaches of adjusting phase sequence and reactive power compensation strategy were proposed to reduce unbalance current.Finally,combining with the schemes above,the situation of unbalanced current of 8 transmission lines around a 220 kV substation was studied and verified based on PSCAD electromagnetic transient simulation.
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