1.a. With the help of phasor diagram, explain the operation of practical transformer on load.

1.b. A 3 -phase $1000 \mathrm{KV} \mathrm{A}, 6600 / 1100 \mathrm{V}$ transformer is delta connected on primary and star connected on secondary. The primary resistance/ph is 1.8$\Omega$ and secondary resistance/ph is 0.025$\Omega$ . Find the efficiency when secondary is supplying full load at 0.8 $\mathrm{p}$ . $\mathrm{f}$ and the iron loss is 15 $\mathrm{kN}$ . Also determine efficiency on full load unity p.f.

2.a. Explain star zig- zag - star and open delta connection with the help of connection diagram and phasor diagram. Mention its advantages applications.

2.b. The parameters of $10 \mathrm{KVA}, 500 / 250 \mathrm{V}, 50 \mathrm{Hz}$ , single - phase transformer are as follows:

Primary resistance $=0.2 \Omega$ . Primary reactance

Secondary resistance $=0.5 \Omega$ Secondary reactance $=0.1 \Omega$

3.a. What is the need for parallel operation of transformer? Mention the conditions to be satisfied for parallel operation and explain.

3.b. An autotransformer is used to supply a resistive load of 5 $\mathrm{kW}$ at 400 $\mathrm{V}$ . Supply voltage is 440 $\mathrm{V}$ . Neglecting the losses calculate the currents in various parts of the winding. Find the percentage of copper saving effected due to use of the autotransformer instead of equivalent two winding transformer.

4.a. With a neat diagram, (explain the construction and operation of on load tap changer for transformer.

4.b. Two transformers gave the followings test results: with the LV side shorted, transformer A takes current of 10 $\mathrm{A}$ at 200 $\mathrm{V}$ , power input is 1000 $\mathrm{W}$ . Similarly transformer $\mathrm{B}$ takes 30 $\mathrm{A}$ at $200 \mathrm{V} ;$ the power input is 1500 $\mathrm{W}$ . On open circuit both transformers gave a secondary voltage of 2200 $\mathrm{V}$ when 11 $\mathrm{KV}$ is applied to the primary terminals. These terminals of the two transformers are connected in parallel. Calculate the load shared by each transformer.

5.a. Explain the current in rush phenomenon in transformer.

5.b. With neat diagram, explain the commutation process in DC machines.

5.c. A 4 - pole, $3-$ phase, 50 $\mathrm{Hz}$ star connected alternator has 60 slots, with 4 conductors per slot. The coils are short pitched by 3 slots. If the phase spread is $60^{\circ},$ find the line voltage induced for a flux per pole of 0.943 wb, sinusoidally distributed in space. All the turns per phase are in series.

6.a. With a neat diagram, explain how sumpnesis test is used to find efficiency and voltage regulation of a transformer?

6.b. A $4-$ pole, lap wound armature running at 1400 rpm delivers a current of 100 $\mathrm{A}$ and has 64 conductor segments. The brush width is equal to 1.4 commutator segments and inductance of each armature coil is 0.05 $\mathrm{mH}$ . Calculate the value of the reactance voltage assuming linear commutation.

6.c. What are the methods used to reduce the harmonics in alternator?

7.a. Explain the effect of variation of excitation of an alternator supplying constant load.

7.b. A synchronous generator has a direct axis synchronous reactance of 0.8 $\mathrm{pu}$ and a quadrature axis synchronous reactance of 05 $\mathrm{pu}$ . It is supplying full load at rated voltage at 0.8 $\mathrm{p} \cdot \mathrm{g}$ lag. Find the open circuit voltage.

8.a. Explain two reaction theory as applied to synchronous machines.

8.b. Two identical, three phase star connected alternators, operating in parallel share equally a total load of 1000 $\mathrm{kW}$ at 6600 $\mathrm{V}$ and 0.8 power factor lagging. The field of the first generator is excited so that the armature current is 50 $\mathrm{A}$ lagging. Find

i) Armature current of second machine

ii) The power factor of each machine.

9.a. Explain MMF method of determining voltage regulation of an alternator.

9.b. A $3-$ phase, $10 \mathrm{KVA}, 400 \mathrm{V}, 50 \mathrm{Hz}$ star connected alternator supplies the rated load at 0.8 power factor lagging. If the armature resistance is $0.5 \Omega,$ and synchronous reactance is $10 \Omega,$ find the voltage regulation.

10.a. With suitable graphs, explain the capacity curves for an alternator.

10.b. A $2300 \mathrm{V}, 50 \mathrm{Hz}, 3-$ phase star connected alternator has an effective armature resistance of 0.2$\Omega .$ A field current of 35 $\mathrm{A}$ produces a current of 150 $\mathrm{A}$ on short circuit and an open circuit emf 780 $\mathrm{V}$ (line) Calculate the voltage regulation at 0.8 $\mathrm{p} . \mathrm{g}$ , lagging and 0.8 leading for the full load current of 25 $\mathrm{A}$ .