Integrated protection scheme for both operation modes of microgrid using S-Transform

Abstract

An agent-based protection scheme for a low voltage microgrid (MG) is presented in this paper. This scheme can work accurately in all operating conditions and topologies of the network, such as grid-connected, autonomous mode, radial and mesh structures. In contrast with the conventional overcurrent protection methods used in the normal radial distribution systems, the proposed method does not depend on the short circuit level or the amplitude of the fault current. Instead, each relay uses the S-Transform (ST) of the transients generated in the branch currents due to the fault occurrence. The represented method can recognize the faulted zone in a quite acceptable time interval and send the trip signals to the relevant circuit breakers. The principals of the proposed algorithm are presented based on the IEC 61850 protocols for better performance during and after the short circuit faults. In this scheme, the Intelligent Electronic Devices (IEDs) that are playing the relay agent role for protection application,can perform several other functions sequentially, as well. The applicability of the proposed method is demonstrated in different modes of operation and topologies of the MG, different shunt faults with resistances and Fault Inception Angles (FIA) and High Impedance arc-assisted Faults (HIF). Moreover, the inherent nature of the MG as a distribution system such as different loading levels and switching of the distributed generation units is investigated, also. It is shown that the proposed method is very efficient for MGs because of its simplicity and speed of performance.