Optimum location of master agents in an agent based zone 3 protection scheme designed for robustness against hidden failure induced trips

The post-mortem analysis of few blackouts in US and Europe concluded that the hidden failure induced tripping of distance relays is one of the primary causes of blackouts. In order to provide the distance relays with situational awareness and improve their robustness to hidden failures, a non-intrusive agent based relay supervised distance protection scheme is proposed in [1] and their results seemed promising. Each relay is associated with an agent who has the ability to sense and communicate. The communication between hierarchically distinguished master and slave agents aid relays to differentiate a fault as a true fault or a hidden failure induced fault and respectively to trip or not to trip. The methodology presented in [1] is limited to single master agent and multiple slave agents communication therefore it can only be applied to smaller power system networks. In order to adapt the relay supervision scheme to a geographically widely distributed larger bus system, more than one master agent is required because the use of a single master agent may result in slave agent to master agent round trip communication delays greater than the relay fault clearing times which defeats the purpose of the relay supervision scheme. Therefore for a larger power grid that needs multiple master agents, finding the number of master agents required and the location of the master agents is an issue that has to be addressed. In this paper we modelled the problem of minimizing the number of master agents required to serve the slave agent queries and finding an optimum location for the master agents as a multiple facility location problem. Networking simulations are performed using OPNET and optimization models are developed and simulated using IBM ILOG CPLEX.