Directional Comparison scheme blocking signals

Contexts in source publication

Context 1

... protection for busbar faults in the Distribution Station is provided by the IDMT stage of the directional overcurrent relays at the remote ends of the Distribution Station -BSP and Distribution Station -Power Station feeders. An extra measure is required to ensure selectivity for faults on the "Loop Type" 66kV feeder (as shown in Figure 5) in the event of that feeder's unit protection failing to clear the fault. As this is a "Loop Type" feeder, there is no instantaneous overcurrent stage enabled on the directional overcurrent relay. ...

Context 2

... the case of the "City Tee" 66kV feeders, it is not possible to coordinate the directional overcurrent relays on circuits 1, 2 and 3 with the "City Tee" directional overcurrent relays for downstream 11kV faults, so a blocking signal is also required from each of these relays in the event that they pick up in the forward direction. A simplified schematic of these blocking signals is shown in Figure 5. The existing overcurrent relays on the two 66kV transformer feeders at the Distribution Station have no instantaneous element, so it is not possible to coordinate the directional overcurrent relays on the Distribution Station outlets at the BSP and the Power Station with those relays. ...