Online coordination of directional overcurrent relays using binary integer programming

• The time dial and pickup current settings are determined in the discrete form, as available in electromechanical and digital relays with non-continuous settings.
• A binary integer programming model is used, solved by a mixed integer programming solver running on its default configuration.
• A pre-processing step is performed to reduce the simulation time. This step also ensures that the operation time curve of each relay is below the melting curve of the cables.
• The coordination is performed online and optimal settings are determined for each change in topology of the network, increasing the speed of the protection system.
• A single simulation is required to achieve the optimal settings for each power system.

This work presents a binary programming model for online coordination of directional overcurrent relay problems in interconnected power distribution and subtransmission systems. The proposed model considers discrete time dial and pickup current settings as in microprocessor-based relays. The coordination problem is solved for every topological change in the network and whose optimized settings are remotely adjusted on each relay through a SCADA system, enhancing the speed and sensitivity of the protection system. A pre-processing step is performed to ensure that the operation time of each relay be below the melting curve of the protected cable. Computational results for the binary programming model solved by CPLEX optimization package are compared to heuristic-based techniques. The simulation results indicates that our approach is suitable for online applications, since an optimal solution can be found in reduced times.