A design methodology for installing reactive compensation equipment in ultra high voltage AC transmission system based on a modified particle swarm optimisation method

Ultra high voltage (UHV) AC system operates at 1000kV or above and is characterised with having a large transmission capacity (5000MW or above per single circuit) and long transmission distances. It is capable of producing over 4 times more reactive power gains than a conventional 500kV transmission line, and also absorbing a significant amount of reactive power when power flow across the line is high. Managing UHV AC voltage profile across a range of operating conditions is a major design challenge, especially in the early stage of development in UHV AC transmission systems. It requires an appropriate amount of inductive and capacitive compensation equipments with different characteristics installed at appropriate locations. This paper presents a practical method for designing, installing and operating reactive power compensation schemes for UHV AC systems. The method takes into account the cost of different types of reactive power compensation equipment, such as mechanically switched capacitors, static var compensators, fixed shunt reactors, controllable shunt reactors, etc, and minimises the overall cost of reactive compensations such that the system operates satisfactorily across a range of operational conditions whilst satisfying system constraints, including voltage and thermal constraints. The optimisation problem is solved by a modified particle swarm optimisation algorithm. The design framework is applied to a real UHV system design as case study, and is compared with conventional design method.