BASIC ELECTRICAL ENGINEERING JNTU previous years question papers




Time: 3hours Max.Marks:75

Answer any FIVE questions

All questions carry equal marks

1.a) Explain the basic circuit components.
b) Three resistances 2 ohms, 4 ohms and 6 ohms are connected in series across 24V supply. Find the voltages across three resistors. [7+8]

2.a) State and explain Superposition theorem.
b) Write short notes on star – delta transformation. If Rab, Rbc and Rca are connected in delta, derive the expressions for equivalent star connection. [7+8]

3.a) Show that power dissipated by a pure inductor exited by a sinusoidal voltage source
V = Vm Sin ωt is Zero.
b) An alternating current is expressed as I = 14.14 Sin 314t.
i) RMS current ii) Average current
iii) Form factor iv) Peak factor. [7+8]

4.a) Explain the constructional details of Transformer.
b) A 100 kVA, 1000/10000 V, 50 Hz, Single phase transformer has an iron loss of 1100 W. The copper loss with 5 A in the high voltage winding is 400 W. Calculate the efficiency
at 25 %, 0.8 Power factor. The out put terminal voltage being maintained at 10000 V.

5.a) Derive the emf equation of a DC generator.
b) A 4 – pole DC shunt generator with lap connected armature supplies a load of 100 A at 200 V. The armature resistance 0.1 ohms and the shunt field resistance is 80 ohms find the
i) Total armature current
ii) Current per armature path
iii) Emf generated. [7+8]

6.a) Explain the losses that occur in a DC machine.
b) A 200V DC shunt motor takes a total current of 100 A and runs at 750 rpm. The resistance of the armature winding and shunt field winding is 0.1 ohms and 40 ohms respectively. Find the total copper losses. [7+8]

7.a) Explain with the help of diagrams how a rotating magnetic field is produced in a 3 phase induction motor.
b) Three phase induction motor is wound for 4 – poles and is supplied from a 50 Hz supply.Calculate
i) The synchronous speed
ii) The speed of the motor when the slip is 3 %
iii) The rotor frequency. [9+6]

8. Explain the construction and operation of Moving iron repulsion type instruments with a neat diagram. [15]