A 3-phase. 10-pole alternator has 90 slots, each containing 12 conductors. If the speed is 600 r.p.m. and the flux per pole is 0.1 Wb, calculate the line e.m.f. when the phases are (1) star connected (ii) delta connected. Assume the winding factor to be 0.96 and the flux sinusoidally distributed.

A single-phase, 120V(rms),60Hz source supplies power to a series R-L circuit consisting of R=10 and L=40mH. (a) Determine the power factor of the circuit and state whether it is lagging or leading. (b) Determine the real and reactive power absorbed by the load. (c) Calculate the peak magnetic energy Wint stored in the inductor by using the expression Wint=L(Irms)2 and check whether the reactive power Q=Wint is satisfied. (Note: The instantaneous magnetic energy storage fluctuates between zero and the peak energy. This energy must be sent twice each cycle to the load from the source by means of reactive power flows.)

What conditions must be met before two alternators can be paralleled together?

Consider the three single-phase two-winding transformers shown in Figure 3.37. The high-voltage windings are connected in Y. (a) For the low-voltage side, connect the windings in , place the polarity marks, and label the terminals a, b, and c in accordance with the American standard. (b) Relabel the terminals a, b, and c such that VAN is 90 out of phase with Va for positive sequence.

A single phase 60 Hz transformer has its core volume of 1.5x10-3 cu m. The maximum flux density is 1.0 tesla and the hysteresis constant of the core is 6000. find the hysteresis loss.

Compare the emfs at 50Hz of the following 20 pole alternator windings wound in identical stators having 180 slots: a) A single winding with adjacent 5 poles per slot per pole wound, the remaining being unwound b) A single phase winding with all slots wound c) A 3 phase star connected winding with all slots wound All the coils in each phase are connected in series and each slot accommodates 6 conductors. The total flux per pole is 0.025Wb

4. A 3-phase 50 Hz star connected alternator has 180 conductors per phase and flux per pole is 0.0543 Wb. Find i) e.m.f generated per phase and ii) e.m.f between line terminals. Assume the winding to be full pitched and distribution factor to be 0.96.

i. A 2300 V, With 2500 kVA three phase delta-connected alternator has a resistance of 0.1ohm/phase and a synchronous reactance of 1.5 ohms/phase. The alternator is adjustedto rated voltage at no load. Calculate its terminal voltage when carrying ratedcurrent at no load power factor of 0.6 lagging.

Question three: A single phase, 4600/460 V, 60 Hz, transformer is connected to a 60 Hz, 4600V power supply. The maximum flux density in the core is 0.85 T. If the induced voltage per turn in 10V, determine (a) The primary turns (N1) and the secondary turns (N). (b) The cross-sectional area (A) of the core.

10. In a transformer, the leakage flux of each wind- ing is proportional to the current in that winding because (a) Ohm's law applies to magnetic circuits (b) leakage paths do not saturate (c) the two windings are electrically isolated (d) mutual flux is confined to the core. 11. In a two-winding transformer, the e.m.f.per turn in secondary winding is always.........the induced e.m.f. power turn in primary. (a) equal to K times (b) equal to 1/K times (c) equal to (d) greater than. 12. In relation to a transformer, the ratio 20: 1 indi- cates that (a) there are 20 turns on primary one turn on secondary (b) secondary voltage is 1/20th of primary voltage (c) primary current is 20 times greater than the secondary current. (d) for every 20 turns on primary, there is one turn on secondary.