RELAY COORDINATION IN GRID WITH DISTRIBUTED GENERATION

Abstract

Reliability of power in modern power system is endowed by presence of distributed generation in the system. A typical power system is composed of multiplicity of elements like generators, transformers and distribution circuits, the numerous elements lead to inevitable uncertainty in the system which is manifested as failure of portion of system. In event of failure of any part of the system, it must be immediately detected and disconnected from the rest of system. So far protective relays are most commonly employed for protecting power systems owing to economic reasons. Timely removal of the faulty section of power system depends on appropriate settings of these relays under various system conditions. The modern power system which will eventually be heavily penetrated by DG, coordination of overcurrent relays will be a big challenging task for protection engineers. Addition of DG causes distribution system to experience change in the short circuit level and thus the settings chosen earlier may result in mal operation of relays. The change in system because of addition or removal of DGs will require the protection engineers to have set of relay settings pertinent to all possible system conditions. To reduce the burden of deciding the settings for numerous cases, various programming optimization techniques are frequently used to find optimal settings of overcurrent relays. In the present study Particle Swarm Optimization (PSO) technique has been implemented for solution of non-linear equation describing operation of an overcurrent relay. The optimization has been done to reduce overall time of operation of relays as well as keep them in coordination with each other. A proper combination of primary and backup relay is selected to avoid mal operation of relays and unwanted outages in healthy part of system. The study is done in two parts. In first part the mentioned optimization technique is tested on an eight bus system fault data to check consistency of obtained settings with respect to that mentioned in journal. The optimization algorithm is implemented using MATLAB software. In second part of study a standard IEEE 14 Bus system is designed on PSCAD/EMTDC software. The fault data of simulation is used to obtain optimal settings of relays for a coordinated system.