1) The tank of a 1250 KVA natural oil cooled transformer has the dimensions of length, width and height as 1.55m x 0.65m x 1.85m respectively. The full load loss is 13.1 kw. Determine the and ampere conductors per metre as flux density 1wb/m2 number of tubes for this transformer assuming: W/m2°C due to radiation = 6 and due to convection = 6.5. Improvement in convection due to provision of tubes = 40% temperature rise = 40°C. Length of each tube = 1m and diameter of tubes. Neglect the top and bottom surfaces of the tank as regards cooling.
2) Approximate the stator core dimensions, number of stator slots and number of the stator conductors per slot for a 100 kw, 3300v, 50 Hz, 12 pole star connected slip ring induction motor. Assume average gap density = 0.4 wb/m2 efficiency = 0.9, power factor = 0.9 and winding factor = 0.96 choose main dimensions to give overall design.
3) A 3 phase, 6 pole, 50Hz, 10kw, 220v star connected Induction motor has 54 stator slots each containing 6 conductors. Determine the values of bar and end ring currents. The number of Rotor bars is 64. The machine has an efficiency of 0.86 and a power factor of 0.85. The rotor mmf may be assumed as 85% of stator e.m.f. Also determine the bar and end ring sections if the current density is 5A/mm2
4) a) Deduce the output equation of the salient pole synchronous machine.
b) describe the several factors affecting the choice of short circuit ratio.
5) The field coils of a salient pole alternator are wound with a single layer winding of bare copper strip 30mm deep with separating insulation 0.15mm thick. Determine a suitable winding length, number of turns and thickness of conductor to develop an mmf of 12,000 A with potential difference of 5v per coil and with a loss of 1200 w/m2 1.2m. The resistivity of copper is 0.021?/m and mm2; Conductors per metre = 25,000 A/m of total coil surface. The mean length of turn is.