ASSESMENT 1
1. A 50-Hz, 6-pole synchronous generator has 36 slots. It has two-layer winding with full-pitch coils
of 8 turns each. The flux per pole is 0.015 Wb (sinusoidally distributed). Determine the induced
emf (line-to-line) if the coils are connected to form (a) 2-phase winding (b) star-connected 3-
phase winding.
2. Find the number of series turns required for each phase of a 3-phses, 50-Hz, 10-pole alternator
with 90 slots. The winding is to be star-connected to give a line voltage of 11 kV. The flux/pole is
0.2 Wb.
3. The armature of a 3-phase machine with 16 poles and 180 slots is wound with fractional slot
windings. Construct the winding table for one basic unit of poles. Indicate the start of each phase.
For the basic unit determine the distribution of coil groups and the phase sequence.
4. A 3-phase, 10-pole machine has 72 slots. Construct the winding table for fractional slot winding.
Draw the winding diagram with a coil-span of seven slots.
5. A synchronous generator feeds power to a power system. The generator and power system data
are: Generator: 100 MVA, 11 kVUnsaturated synchronous reactance Xs = 1.3 pu Power System:
Thevenin’s equivalent as seen from the generator terminals is VTH = 1 pu, XTH = 0.24 pu (on
generator base) Generator open circuit voltage 11 kV at a field current of If = 256 A (a)
Generator internal emf Ef is adjusted to 1 pu. What is the maximum power that the generator
supplies to the power system? (b) The generator feeds power Pe = 1 pu to the power system at
generator terminal voltage Vt = 1 pu. Calculate the power angle d of the generator and the
corresponding field current If . (c) The generator is fitted with automatic voltage regulator, which
is set for Vt = 1 pu. Load is now varied. Plot If versus Pe.
6. A three phase 10 kVA, 400 V, 4-pole, 50 Hz star connected synchronous machine has
synchronous reactance of 16 W and negligible resistance. The machine is operating as generator
on 400 V bus-bars (assumed infinite). (a) Determine the excitation emf (phase) and torque angle
when the machine is delivering rated kVA at 0.8 pf lagging. (b) While supplying the same real
power as in part (a), the machine excitation is raised by 20%. Find the stator current, power factor
and torque angle. (c) With the field current held constant as in part (a), the power (real) load is
increased till the steadystate power limit is reached. Calculate the maximum power and kVAR
delivered and also the stator current and power factor. Draw the phasor diagram under these
conditions.
