No abstract

Microgrids active characteristics such as grid-connected or islanded operation mode, the distributed generators with an intermittent nature, and bidirectional power flow in active distribution lines lead to malfunction of traditional protection schemes. In this article, an impedance-based fault detection scheme is proposed as the main protection of microgrids by applying the proposed equivalent circuits for doubly-fed lines. In this scheme, relay location data and positive sequence voltage absolute value of the other end of the line are used. It can detect even high impedance faults in grid-connected and islanded modes. It is robust against load and generation uncertainties and network reconfigurations. Low sampling rate and minimum data exchange are among the advantages of the proposed scheme. Moreover, a backup protection scheme based on the conductance variations is suggested. No requirement for the communication link is a distinguished advantage of the proposed backup protection scheme. The proposed schemes have been simulated using PSCAD and MATLAB software and the results confirmed their validity.

Microgrid properties including bidirectional power flow in feeders, fault level decrease in the islanded mode, and intermittent nature of distributed generators (DGs) result in the malfunctioning of microgrid conventional protection schemes. In the present article, a protection scheme based on impedance is suggested for fault detection in LV and MV overhead and cable distribution lines in both grid-connected and islanded modes. To determine a fault detection index, new suggested equivalent circuits for doubly fed lines are applied. Relay location data and magnitude of positive sequence voltage of the other end of the line are used. It is simulated by PSCAD and MATLAB software in order to evaluate its performance and approve its validity. This scheme can detect even high-impedance faults in both grid connected and islanded modes in LV and MV overhead and cable distribution lines. In addition, it is robust against load and generation uncertainty and network reconfigurations. Low sampling rate and minimum data exchange are among the advantages of the proposed scheme.