Research On Practical Algorithms Of Optimal Reactive Power Planning For MV Feeders

Optimal reactive power planning in a power system can efficiently reduce the electric power loss; improve voltage quality and cut the operation and investment cost. Reasonable reactive power distribution is the necessary condition of making sure that the operation of a power system is safe and economic. On the one hand, shortage of reactive power can lead to the low voltage; on the other hand, too much reactive power will not only bring additional investment, but also increase the loss. Therefore, the research on how to compensate the reactive power and reduce the loss of reactive power transmission is very important.Firstly, in this thesis, an algorithm is proposed for the optimal placement of capacitors in MV feeders under multi-load levels. In a distribution network, the loading will be divided into there levels: high, medium and low. Under the high loading level, the initial solutions of reactive power compensation, including the compensation locations and capacity, are determined based on the upper limits of compensation capacity for nodes, which takes the benefits by the reactive compensation and voltage constraint into account, and the voltage quality and real power loss are improved by using the way of transformer's on-load regulation; under medium and low loading levels, based on the initial solutions, the capacitor banks to be switched off, which makes the network loss minimal, are solved by an analytical method and experts'experience.Then, two estimation approaches of energy loss (i.e., the approach of maximum load loss hours and the approach of power flow analysis under multi-load levels) are compared, when they are applied to optimal reactive power planning for MV feeders. It is found that the compensation result will have a great deviation with the maximum load loss hours being few , and the method of maximum load loss hours will result in a big error of reactive power compensation. Therefore, researching on the approaches to real power loss computation under multi-load levels is important to reactive power planning for MV feeders.Next, when the future power factors for loads are directly known, an estimation method of reactive power compensation for the MV distribution network under planning is proposed, which solves the problem of ignoring the load power factor. In this thesis, according to planning guidelines, we can firstly obtain a reasonable degree of reactive power compensation based on the active and reactive watt-hour meter readings, and then estimate the capacity of reactive power compensation for MV feeders under planning based on the obtained degree of compensation, which wisely and effectively avoids the problem that the load power factor is difficult to be obtained directly.Finally, the proposed algorithms have been applied to some typical examples and the results show that the algorithms are effective and practical.