Problems #1
1.
Calculate the number
of turns of each winding of a single-phase, 2400/240, 50 Hz transformer, if the
flux in the core is not to exceed 0.05 Wb.
2.
The emf per turn of a
single phase 2200/220 V, 50 Hz transformer is approximately 11.5 V. Calculate
(i) the number of primary and secondary number of turns, (ii) the net
cross-sectional area of the core, if the maximum flux density is 1.5 T.
3.
A single-phase 600/200
V, 25 kVA, 50 Hz, transformer is supplying full load on secondary side at 0.707
pf lagging. What is the load impedance? Assuming the transformer to be ideal,
what impedance is seen from the primary side? Calculate the primary current.
4.
A 100 kVA, 1100/230 V,
50 Hz transformer has an HV winding resistance of 0.1 ohm and a leakage
reactance of 0.4 ohm. The LV winding has a resistance of 0.006 ohm and a
leakage reactance of 0.01 ohm. Find the equivalent winding resistance,
reactance and impedance referred to HV and LV sides. Convert these to per unit
values.
5.
A single-phase 100
kVA, 6600/330 V, transformer has the effective impedance of 4.1+j10 ohm
referred to high voltage side. Calculate the voltage regulation at (i) full
load 0.707 lag and (ii) half load 0.9 lag.
6.
The maximum efficiency
of a 4400/440 V single-phase transformer is 98% and occurs at 75% of the full
load at unity power factor. If the impedance is 8%, calculate the regulation at
full-load 0.8 power factor lagging.
7.
The efficiency of a
single-phase, 6600/440 V, 250 kVA transformer is 98% both at full-load and
half-load at unity power factor. The power factor on no load is 0.22 and the
full-load regulation at 0.8 power factor lag is 4.5%. Draw the equivalent
circuit referred to the Low Voltage side.
8.
A single-phase, 5 kVA,
220/110 V, transformer has the maximum efficiency of 97% at 0.8 power factor
lagging. The core loss is 45 W and full-load regulation at 0.8 power factor
lagging is 5%. Find the efficiency and regulation at 75% of the full-load at
0.9 power factor lagging. At what power factor at full-load the regulation will
be zero? Find also the maximum regulation.
9.
A 200 kVA transformer
has its maximum efficiency of 98% at full load at unity power factor. The
transformer is loaded during the day as follows:
12 hours :
40 kW at power factor 0.5
6 hours
: 90 kW at power factor 0.8
6 hours
: 160 kW at power factor 0.9
Calculate all-day-efficiency of the transformer.