| Installation of shunt capacitors in radial distribution system can efficiently reduce the real power losses and improve voltage level, so that the yearly running charge will be reduced and the quality of power energy can be increased. The limitation of traditional experience based capacitor configuration reveals the lack or excess of configured capacitors, more seriously, when part of capacitors should be put into operation, they cannot be switched on because of the restriction of local voltage.Based on the summarization of previous work in this field, taking account of power flow, voltage and capacitor capability restraint, a corresponding mathematical model is established ,whose objective function is that the total cost, including the cost for network real power losses, the purchasing cost, the installation cost and the maintenance cost of capacitors, should be minimum. Due to the discrete nature of the problem, discrete particle swarm optimization algorithm which can deal with discrete variable convenient is adopted to solve it. To avoid the premature and lose diversity, simulated annealing algorithm is presented to intensify local search ability; and a diversity retaining strategy based on antibody concentration is proposed to save the excellent antibody, restrain the antibody with high concentration. It adopted information entropy to calculate the affinity antibody and antibody. A threshold based on fitness was adopted to control the number of particle that for local search, and network loss sensitivity is designed to shorten the calculating time, increase the convergence speed. In the maximal load condition, voltage is often violating the constraints, and the penalty factor is not efficient, so a constraint handing strategy suit for discrete particle swarm optimization algorithm is proposed.Based on the data of IEEE 33-node distribution system, a computer program is developed. The results show that the presented algorithm is feasible and effective.
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