Optimal replacement scheduling of obsolete substation equipment by branch & bound method

In this paper, the authors propose an algorithm using branch and bound method to search an optimal replacement scheduling of obsolete equipment in aged primary substations. The developed tool can efficiently find an optimal solution from huge combinations of replacement schedules. The objective function to be minimized is the net present value of the sum of operation and maintenance cost, replacement cost, and the reliability cost in case of CB failure for each substation during the specified time frame. To solve this problem under the constraints such as annual budget ceiling, number of replacement targets per annum, and replacement time frame for each substation, we apply the branch and bound method, which is well known as an efficient combinatorial optimization technique. The proposed algorithm is demonstrated using a small scale model (2 substations, 4-year time frame) to verify its effectiveness.