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Technological developments in protective devices have established the basis for appearance of numerical overcurrent relays (OCRs), which enable the users to apply their desired time-current characteristics (TCCs). This study propounds novel stepwise and combined stepwise–piece-wise linear TCCs and presents clear procedure to utilise them for coordinating OCRs in large meshed power systems. The TCCs keep constant time interval between the main/backup relay pairs within entire fault current range. They are examined first by coordinating the OCRs in a 4-bus power system and by coordinating the ground fault OCRs in a practical 60 kV looped power system. Then, the OCRs of the IEEE 14-bus test system, which is a rather large meshed power system with 39 OCRs and 102 main/backup pairs, are coordinated by using the novel TCCs. The same relays in the aforesaid power systems are coordinated using some non-standard TCCs recently introduced in the literature. The comparison verifies that the lowest operating times are achieved by using the novel TCCs. The devised TCCs are simply formed as look-up tables to be exactly set on the existing industrial relays. This fact is verified by setting them on an industrial OCR, and then, by testing the relay through the current injection method. [ABSTRACT FROM AUTHOR]

This study proposes a new application of micro‐phasor measurement units (µPMUs) for adaptive coordination of overcurrent relays in microgrids. Mis‐coordination of overcurrent relays usually arising from the variation of relays fault current and it can cause damage to equipment of network and raise operating costs. Fault current injection and direction to microgrid are highly dependent on network uncertainties; therefore, fault current is affected by line and power plant outages. This study proposes an algorithm to detect these uncertainties in online operation. Then, microgrid overcurrent relays coordination is optimised again. Uncertainties are line and power plant outages in transmission network and microgrid side and two distinct methods are used for each. For online detection of uncertainties in the transmission side, it is assumed that a µPMU is installed between transmission network and microgrid point of common coupling; so, the topology changes such as line outage is detected by monitoring of Thevenin impedance estimation that is obtained by µPMU measurements. Uncertainties detection in a microgrid is done by signals that are sent by µPMUs and installed all over the microgrid. All data are gathered and analysed in phasor data concentrators and then overcurrent relays coordination is updated with such changes. [ABSTRACT FROM AUTHOR]