FirstSemester B.E. Degree Examination, Jan 2019
18ELE 15/25BASIC ELECTRICAL ENGINEERING
Time: 3 hrs. MODEL PAPER Max. Marks: 100
Note: Answer FIVE full questions, choosing one full question from each module
Module 1
1 a
.
A resistance of 10Ω is connected in series with two resistances each of
15Ω arranged in parallel. What resistance must be shunted across this
parallel combination so that the total current taken shall be 1.5A with 20V
applied?
6 marks
b
.
For the given circuit calculate the value of the current in either branch and
the value of the unknown resistance R when the total current taken by the
network is 2.25 A.
6 marks
c
.
Define the following with respect to sinusoidal alternating quantity:
Average Value, RMS value, iii) Form factor and peak factor
8 marks
OR
2 a
.
Define RMS value of a sinusoidal alternating quantity and derive an
expression for it.
6 marks
b
.
Two resistors are connected in parallel and a voltage of 200V is applied to
the terminals. The total current taken is 25A and the power dissipated in
one of the resistors is 1500W. What is the resistance of each element?
6 marks
c
.
Find current in the battery, the current in each branch and p.d. across AB
in the network shown in fig.2(c)
8 marks
Module 2
3 a Show that in a pure inductor the current lag behind the voltage by
Also draw the voltage and current waveforms.
6marks
b A series RLC circuit is composed of 100 Ohms resistance,1.0 H inductance and8 marks
5μF capacitance. A voltage,V(t)=141.4 Cos377t volts is applied to the
circuit.Determine the current and vlotages VR VL and VC
c With the help of a phasor diagram show that in a three phase star
connected system the line to line voltage is √3 Emes the phase to neutral
voltage
6 marks
OR
4 a Derive an expression for power in a single phase R-L series circuit in terms
of voltage, current and power factor of the circuit.
6marks
b Given v=200 sin 377t volts and i=8 sin(377t-30°) amps for an a.c. circuit,
determine :a)Power factor b)True power c)Apparent power d)Reactive
power indicate the unit of power calculated
8 marks
c Three identical coils.each having a resistance of 10 and a reactanece of
10 are connected in delta,across 400 V,3-phase supply.Find the line
current and the reading on the two Wattmeters conneted to measure the
power.
6 marks
Module 3
5 a Derive the equation for the induced emf in a single phase transformer 6 marks
b With a neat connection diagram explain three way control of lamp. Also
develop the truth table indicating the state of the lamp for different
positions of the switches.
6 marks
c A transformer is rated at 100KVA. At full load its copper loss is 1200 W and
its iron loss is 960 W. Calculate the efficiency at full load, unity power
factor efficiency at half full load, 0.8 power factor the load KVA at
which maximum efficiency will occur and Maximum efficiency at 0.85
power factor
8 marks
OR
6 a Explain the principle of transformer and compare the core and shell type
transformer.
6 marks
b A single phase 50 Hz core type transformer has a square core of 20 cm
side. The permissible maximum density is 1 Wb m2. Calculate the
number of turns per limb on the high and low voltage sides for a 3000
220 V ratio
6 marks
c What is earthing? Why earthing is required? With the help of sketch
explain plate earthing.
8 marks
Module 4
7 a 8 marks
b 6 marks
c 6 marks
OR
8 a 6 marks
b 6 marks
c 8 marks
Module 5
9 a 8marks
b 6 marks
c 6 marks
OR
10 a 8 marks
b 4 marks
c 8 marks