1) a) Write down the comparisons of the electric circuits and magnetic circuits.
b) Also explain the factors that are need to be considered for selecting the specific electric loading and specific magnetic loading?
2) A 15 kW, 230 volt, 4 pole dc machine has the following data:
Armature diameter = 0.25 m, armature core length = 0.125 m, length of the air gap at the pole centre=2.5mm, flux per pole=11.7 mWb, ratio of pole arc to pole pitch=0.66. Determine the e.m.f needed for the air gap.
a) If armature surface is considered as smooth and
b) If armature is slotted.
3) Determine the chief dimensions of the 200 kW, 250 volt, 6 pole, 1000 rpm generator. The maximum value of flux density within the air gap is 0.87 Wb/m2 periphery are 31000. The ratio of the pole arc to pole pitch is 0.67 and the efficiency is 91 percent. Suppose the ratio of length of core to pole pitch = 0.75.
4) A 4 pole,25 HP,500 Volt,600 rpm series motor has the efficiency of 82%. The pole faces are square and the ratio of pole arc to pole pitch is 0.67. Consider Bav=0.55 Wb/m2. Find the major dimensions of the core and particulars of a appropriate armature winding.
5) a) Deduce the expression for the output equation of a 3 phase transformer?
b) Calculate the dimensions of the core and window for a 5 kVA, 50 Hz,1 phase, core type transformer. A rectangular core is used with the long side twice as long as short side. The window height is 3 times the width. Voltage per turn=1.8 Volt, Space factor=0.2, current density=1.8 A/mm2 and the ampere conductors per metre of the armature, Bm=1 Wb/m2.