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(d) Design the feeder protection using the guideline below. (70 marks) The current setting of each relay should be set to a value that is well above the maximum load current in the feeder segment (such as larger than 120%) that it protects and well below the value of the minimum fault level (such as smaller than 60%) at the location of the relay. Select the EI characteristic, when fuses exist downstream, to ensure grading. The current setting should be also at least three times the largest fuse rating (located at the downstream of the relay). There should be at least 10% difference in the current settings of consecutive relays. Relay-relay grading margin: 0.3s and relay-fuse grading margin: t=0.4 tfuse + 0.15s (tfuse : fuse operating time) The overcurrent relay has the following current settings: 4, 5, 6, 7, 8, 10 and 12 A. At busbar E, fuse operating time (tfuse) = 0.025s for the maximum fault current.