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Q 8

a) Explain the working of Improved Series Inverter. What are its

advantages over Basic Series Inverter? 7

b) Explain the operation of 3- phase bridge inverter in 180

conduction mode. Draw output phase and line voltage waveforms.

6

Q 9.

a) Explain the motoring and regenerative braking of a separately

excited DC motor using two quadrant chopper? 7

b) A full wave converter is connected to RLE load. The source

voltage is 230 V, 50 Hz. The average load current is 10 A is

assumed to be continuous over the working ranges. For R= 0.4 and

L= 2 mH. Compute:

i) Firing angle delay for E= 120 V

ii) Firing angle delay for E= -120 V 6

Q 10. Write short note (ANY THREE) 14

i) AC Voltage regulators and their application :

ii) SMPS

iii) Jones Chopper

iv) Current Source Inverter

SET-1

PCE/EN/W/EVEN-13/5ET4

Department of Electronics Engineering

IV Semester Sessional Examination

BASICS ELECTRICAL MACHINES

Time -THREE Hours Max. Marks-80

___________________________________________________________

INSTRUCTION TO CANDIDATES

(1) Answer Three questions from Section A and Three questions

from Section B.

(2) Illustrate your answers whenever necessary with the help of neat

sketches.

(3) Diagram and equations should be given wherever necessary.

SECTION A

Q 1.

a) Derive the EMF Equation for transformer. 5

b) A 5 kVA 200/1000 V 50 Hz, single phase transformer gave following

test result:

O.C. Test (LV Side) : 200 v, 1.2 A, 90 WS.C. Test (H.V. Side): 50 V, 5A, 110 W.

(i) Calculate the parameters of the equivalent circuit referred to the LV

side.

(ii) Calculate the output secondary voltage when delivering 3 kW at 0.8

p.f. lagging, the input primary voltage being 200 V. Find the percentage

regulation also. 8

Q 2.

a) Derive the equivalent circuit of transformer referred to primary

side in Detail 7

b) A 5 kVA distribution transformer has a full load efficiency at

unity p.f. of 95%, the copper and iron losses then being equal

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Calculate its all-day efficiency if it is loaded throughout the 24

hours as follows:

No Load for 10 Hours Quarter load for 7Hours

Half load for 5 Hours Full load for 2Hours 7

Q 3.

a) What is mean by Armature Reaction. Explain in Detail. 7

b) An 8 pole dc shunt generator with 778 wave-connected armature

conductors and running at 500 rpm supplies a load of 12.5

resistance at terminal voltage of 50 V. the armature resistance is

0.24 and field resistance is 250 . Find the armature current, the

induced emf and the flux per pole. 6

Q 4.

a) Draw and explain different characteristics for DC Shunt motor

6

b) A 220 V d.c. shunt motor takes 4 A at no-load when running

at 700 r.p.m. The field resistance is 100 . The resistance of

armature at standstill gives a drop of 6 volts across armature

terminals when 10 A were passed through it.

Calculate: 1. Speed on load. 2. Torque in N-m. 3. Efficiency.

The normal input of the motor is 8 kW. 7

Q 5.

a) Write notes on (any THREE)

i) Programmable Unijunction Transistor. 5

ii) Digital Methods for Turning ON SCRs 4

iii) Asymmetrical SCR 4

iv) Heat Sinks. 4

.SECTION BQ 6.

a) Explain the operation of dual converter. Why they are used in

motors? 6

b) Draw and explain the circuit of 1- phase full wave fully controlled

bridge rectifier considering heavy inductive load and = 45 with

neat waveform. Also derive expression for Vdc.

7

Q 7.

a) What are the different control techniques used in Choppers?

Explain. 7

b) A single quadrant chopper is operated with following specification

i) Ideal battery of 220 V

ii) On time ton= 1m sec

iii) Off time toff=1.5 m sec

Find:

i) Average and RMS output voltage

ii) Ripple factor and form factor. 6