A Logarithmic Function based Relay Characteristics for Optimal Protection Coordination in Distributed Generation Systems

Abstract

The main component of an effective protection strategy is its ability to quickly identify, categorise and isolate the fault while minimising the impact on the load that is not faulted. The existence of distributed generators (DGs) converts unidirectional power flow into bidirectional power flow and varies the magnitude of short circuit current (SCC) rendering protection solutions based on conventional inverse time- current characteristics (ITCC) as ineffective. As a result, a directional element and communication component are required for optimal coordination of protection system, which raises the price and complexity of the protection system. Distribution system (DS) with high penetration of power electronic resources, the converter’s SCC is not as high as in synchronous based DGs (SBDGs). Hence, conventional overcurrent relays (OCRs) may not detect the fault or require a longer time to isolate the fault. In this context, this paper presents a study of the voltage-based protection scheme for an efficient protection for the DS. Since the fault is associated with a voltage drop at the line ends, fault bus voltage-based relay characteristics are considered to determine relay operating time (ROT) expressed as nonlinear function of time multiplier setting (TMS) and parameter m. The above system contains graded relays that are independent of microgrid operating modes. The suggested strategy is simple and economical because it does not call for any special communication channel. The genetic algorithm (GA) and simulated annealing (SA) based optimization approaches are used to find the best solution to the protection coordination problem. Using the MATLAB/Simulink software, the suggested method is studied on a modified IEEE 15- bus radial DS.