Microgrid Central Protection for Smart Cities Based on the Phase Angle Variations Between Voltage and Current Signals

Recently, smart city concept has gained a great interest attention, as it utilizes the advanced Information and Communication Technology in form Microgrids to improve the quality and ensure the continuity of load supplying. Microgrids can tackle the problem of growing load demand by integrating clean renewable energy resources (RES) into smart cities. The main challenges associated with the protection of Micro-grids are fast fault detection. During the internal faults in a microgrid containing different distributed generation units, the existing inverters suppress the increase in the short circuit currents. Therefore, simple, and effective central protection algorithm for a smart microgrid is proposed based on the phase angle alteration between current and voltage signals of the feeder measured at its terminal buses. The measured signals are transmitted to the protection and control center through the communication facilities in the smart grid. After recording of these signals, they are continuously sampled forming movable window patterns. The width of this window is selected as ¼ cycle to consider the grid transient and intermittent nature of the DG generations. For effective fault detection, trigonometry indexes for terminal bus angles are estimated and their variations are tracked for the subsequent movable windows. Fault detection depends on the indexes' magnitudes deviations, while its direction is determined based on the signs of these estimated indexes. The proposed technique's sensitivity and accuracy are tested under different types of transient faults and the tripping action for internal fault in the feeder is taken by the corresponding relay action while blocking the external ones. Also, it is justified during contingency conditions such as feeder disconnections, DG unit outages, sudden load changes, and grid-connected or isolated modes of operation.