ELEC 4302 – Power System Protection Tutorial submission week 12 Due 22/10/2021 4:00 pm a) Explain the advantage of neutral overcurrent relay scheme over differential protection scheme for identifying phase to earth faults of generators. [10 Marks] b) A three-phase transformer rated for 30 MVA, 33 kV/6.6 kV is connected for wye delta and protected by a differential relay. The CT ratio on the low voltage side is 2500:5. i. Identify suitable winding connection type for line-CT secondaries with the aid of circuit diagram. [10 marks] ii. Determine the CT ratio on high voltage side for the correct operation of the differential protection scheme. [10 Marks] iii. Select a suitable CT assuming that transformer never exceeds the full load capacity. Following CTs are available to select: 500:5, 600:5, 800:5, 900:5, 1000:5 and 1200:5. Provide reasons for your choice [10 Marks] iv. Find the operating current setting suitable for differential relays going to be used with the given CT in (iii) for faults drawing up to 200% of the rated current. [10 Marks] Marking criteria – To achieve full marks all calculation steps must be clearly presented and any assumptions you have used should be clearly stated.