Numerical Sheet On Unit-IV
Q:-1
An electromagnet has
a gap of 4 mm and flux density in the gap is 1.3 Wb/m2. Determine the
ampere-turns for the gap.
Q:-2
The total core loss
(hysteresis plus eddy-current) for a specimen of magnetic sheet steel is found
to be 1800 W at 60 Hz. If the flux density is kept constant and the frequency
of the supply increased 50%, the total core loss is found to be 3000 W. Compute
the separate hysteresis and eddy-current losses at both frequencies
Q:-3
A coil of 1000 turns
is wound on a laminated core of steel having a cross section of 5 cm2.
The core has an air gap of 2 mm cut at right angle. What value of current is
required to have an air gap flux density of 0.5 T ? Permeability of steel may
be taken as infinity. Determine the coil inductance.
Q:-4
The core of a
magnetic circuit is of mean length 40 cm and uniform cross-sectional area 4 cm2.
The relative permeability of the core material is 1000. An air gap of 1 mm is
cut in the core, and 1000 turns are wound on the core. Determine the inductance
of the coil if fringing is negligible
Q:-5
A coil of 200 turns
is wound uniformly on an iron ring of mean circumference 10 cm and a cross
sectional area 5 cm2. Current 10 Amp is flowing through coil. Relative
permeability of the material is 3000. Find : (i) MMF (ii) Magnetizing force
(iii)Total flux (iv) Reluctance
Q:-6
A circular ring of
mean length 4π cm and of cross-sectional area 10 cm2 has an air gap 0.4 π mm
long. The relative permeability of iron is 1000. The ring is wound with a coil
of 2000 turns. Determine the flux in the air gap, if the coil carries a current
of 2 mA. Also find the inductance of the coil.
Q:-6
A ring of
ferromagnetic material has a rectangular cross section. The inner diameter is
7.4 inches, the outer diameter is 9 inches and the thickness is 0.8 inches.
There is a coil of 600 turns wound on the ring. When the coil carries a current
of 2.5 A, the flux produced in the ring is 1.2 × 10– 3 Wb. Find :
(i) Magnetic field intensity (ii) Reluctance (iii) Permeability
Q:-7 Explain
relative permeability. Calculate the MMF required to produce a flux of 0.015 Wb
across an air gap 2.5 mm long having an effective area of 200 cm2.
Q:-8 A
transformer has a primary winding of 600 turns and a secondary winding of 150
turns. When the load current on the secondary is 60 A at 0.8 power factor
lagging. Determine the no-load current of the transformer and its phase with
respect to the voltage.
Q:-9
Derive emf equation
for a single phase transformer. A 25 kVA, 2200/220 V, 50 Hz. 1-phase
transformer has following parameters R1 = 1.75 Ω, R2 = 0.0045 Ω, X1 = 2.6 Ω, X2
= 0.0075 Ω. Calculate: Equivalent resistance referred to primary and secondary.
Q:-10
A 100 kVA, 1100/220
V, 60 Hz transformer has a high-voltage winding resistance of 0.1 Ω and a
leakage reactance of 0.3 Ω. The low-voltage winding resistance is 0.004 Ω and
the leakage reactance is 0.012 Ω. The source is applied to high-voltage side.
(i) Find the equivalent winding resistance and reactance referred to the
high-voltage side and low-voltage side. (ii) Compute the equivalent resistance
and equivalent reactance drops in Volts and in per cent of the rated winding
voltages expressed in terms of the primary quantities. (iii) Calculate equivalent
leakage impedances of the transformer referred to the primary and secondary
sides.
Q:-11
A 20 kVA, 2000 V/200
V, single phase 50 Hz transformer has a primary resistance of 1.5 Ohm and a
reactance of 2 Ohm. The secondary resistance and reactance are 0.015 Ohm and
0.02 Ohm respectively. The no load current of transformer is 1 A at 0.2 power
factor. Determine: (i) Equivalent resistance, reactance and impedance referred
to primary (ii) Total copper loss. (iii) Draw approximate equivalent circuit.
Q:-12
A voltage v = 200
sin 314 t is applied to the transformer winding in a no-load test. The
resultant current is found to be i = 3 sin (314 t – 60°). Determine the
core-loss and the parameters of no-load approximate equivalent circuit.
Q:-13
What is the
significance of turn ratio in transformer? The maximum efficiency of a 100 kVA
transformer is 98.40% and operates at 90% full load unity power factor.
Calculate the efficiency of transformer at unity power factor at full load.
Q:-13
Explain the
operation of single phase transformer at load. A single phase 10 kVA, 11000 /
220 V transformer has core loss 300 W at rated voltage and copper loss 400 W at
full load. Find the efficiency of transformer feeding to a load 8 kVA at 0.8
p.f. lagging. What will be the maximum efficiency of the transformer?
Q:-14
A single phase 100
kVA, 6.6 kV/230 V, 50 Hz transformer has 90% efficiency at 0.8 lagging power
factor both at full load and also at half load. Determine iron and copper loss
at full load for transformer.
