Distribution Operations - Relay Protection Re-coordination (RPR) Function

Narrative

Narrative

This application adjusts the relay protection settings to real-time conditions based on the preset rules. This is accomplished through analysis of relay protection settings and operational mode of switching devices (i.e., whether the switching device is in a switch or in a recloser mode), while considering the real-time connectivity, tagging, and weather conditions. The application is called to perform after feeder reconfiguration, and, in case, when conditions are changed and fuse saving is required. No fault calculations are needed in this application, if the distribution system is radial without significant DER.

With DERs in distribution, the situation is much more complex, especially when supporting the fuse-saving protection policy. There are a variety of relationships between fault currents through the protective devices and through fuses. The room for adjustment of the settings of the protective devices is limited. Hence, it is possible, that under some conditions, the coordination for the fuse saving protection cannot be provided. Therefore, the relay protection coordination application should include a fault calculation routine determining probable fault currents through the protective devices and through the fuses. The range of these fault currents should be compared with the corresponding settings, and a decision about the coordination should be made. If the coordination with existing settings cannot be provided, and changes of settings of the protective devices are possible, then the recommended changes should be implemented. The assumption here is that the future protective devices will be available for remote change of their settings.

Another consideration in regards to fuse saving protection is the disconnection of the DER before the reclosing to avoid asynchronous connections. If the interruption of DER services for fuse saving purposes is unacceptable (contractual agreement between DER owner and DISCO), then the fuse saving protection cannot be implemented. The input data for the application should include the DER characteristics needed for calculations of the fault currents (different types of DER will have different characteristics) and the relevant contractual conditions, if any.

The situation is different when the coordination of several protective devices along the feeder should be coordinated, and there are DERs connected to the circuits between the protective devices. In this case, the fault current through the protective device downstream from the DER will be greater than the fault current upstream from the DER, and it is easier to provide coordination. But, if the DER disconnects before the fault is cleared due to low voltage, then the margin for coordination becomes smaller. This relationship between the residual voltage at the DER PCC, timing of the relay protection, and relay protection setting should be taken into account in the relay protection coordination application.

Distribution Operations - Relay Protection Re-coordination (RPR) Function

Contents

Narrative